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1.
J Theor Biol ; 512: 110565, 2021 03 07.
Article in English | MEDLINE | ID: mdl-33346019

ABSTRACT

We developed a tumor control probability (TCP) model that incorporates variable time intervals between fractions and a kick-off time (Tk) for radiation-induced accelerated tumor proliferation. The resulting Lee-Rosen model, TCPLR, was used to compute TCPs for treatment courses with and without weekend treatment for tumors with different proliferation rates - slow (prostate), moderate (breast), and rapid (head and neck). TCPs were computed using ideal uniform dose distributions and actual patient plans. The doses for the uniform plans were the mean doses for the prostate and breast cases and the minimum tumor dose for the head and neck case. The TCPLR model predictions agreed with expectations that TCP increases with increasing Tk in all cases. For standard fractionation, as Tk increased from 0 to 4 weeks, TCP increased for the patient distributions by 74.7% for the head and neck cancer, by 6.2% for the breast cancer, and by 2.4% for the prostate cancers. For the uniform dose distributions, the increases were 79.2%, 5.7%, and 2.3%, respectively. TCP increased as the number of weekend breaks decreased. The effect of weekend breaks decreased as the tumor proliferation rate decreased. For the head and neck tumor, notable decreases in TCP of 6.0% (uniform dose distribution) and 6.8% (actual plan dose distribution) were observed with Friday starts compared to Monday starts for the standard 5 fx/wk schedule (Tk = 4 wk). The 7 fx/wk schedule produced increases in TCP of 17.0% and 20.5% for the uniform and patient dose distributions, respectively, compared to the standard schedule. For the breast cancer, starting the 5 fx/wk schedule on Friday decreased the TCP by 0.2% (Tk = 4 wk) compared to a Monday start. The 7 fx/wk schedule produced increases of 0.3% and 0.4% in TCP compared to the standard schedule for the uniform and patient dose distributions, respectively (Tk = 4 wk). For the prostate cancer, the change in TCP for 5 fx/wk schedules starting on different days was 0.1%. The 7 fx/wk schedule increased TCP by 0.8% compared to the standard schedule (Tk = 4 wk). TCP values for the uniform dose distributions for the standard schedule (Tk = 4 wk) agreed with the TCP values for the actual dose distributions within 4.5% for the head and neck tumor and within 0.2% for the breast and prostate tumors. This good agreement suggests that the doses chosen for the uniform dose distributions were good approximations to the clinical doses. The results for head and neck tumors support, in part, the current practice of hyperfractionated/accelerated radiotherapy. They also suggest that shortening the overall treatment time for conventional fractions by eliminating weekend breaks might be beneficial. The predicted effect on TCP of the various schedules studied was insignificant for prostate and breast tumors, suggesting that a weekend treatment might not be necessary for patients starting radiotherapy on a Friday. There is significant uncertainty in the values of the model parameters chosen for these calculations, and no consideration was given to the potential effects of these various schedules on normal tissues.


Subject(s)
Head and Neck Neoplasms , Prostatic Neoplasms , Dose Fractionation, Radiation , Head and Neck Neoplasms/radiotherapy , Humans , Male , Models, Theoretical , Probability , Prostatic Neoplasms/radiotherapy
2.
J Appl Clin Med Phys ; 12(2): 3296, 2011 Mar 08.
Article in English | MEDLINE | ID: mdl-21587171

ABSTRACT

This study evaluated the accuracy of measuring the motion of an internal target using four-dimensional computed tomography (4DCT) scanning and the BrainLAB ExacTrac X-ray imaging system. Displacements of a metal coil implanted in a commercial respiratory phantom were measured in each system and compared to the known motion. A commercial respiratory motion phantom containing a metal coil as a surrogate target was used. Phantom longitudinal motions were sinusoidal with a 4.0 second period and amplitudes ranging from 5-25 mm. We acquired 4DCT and ExacTrac images of the coil at specified respiratory phases and recorded the coordinates of the coil ends. Coil displacement relative to the 0% phase (full-inhale) position were computed for the ExacTrac and 4DCT imaging systems. Coil displacements were compared to known displacements based on the phantom's sinusoidal motion. Coil length distortion due to 4DCT phase binning was compared to the known physical length of the coil (31 mm). The maximum localization error for both coil endpoints for all motion settings was 3.5 mm for the 4DCT and 0.8 mm for the ExacTrac gating system. Coil length errors measured on the 4DCT were less than 0.8 mm at end inhale/exhale phases, but up to 8.3 mm at mid-inhalation phases at the largest motion amplitude (25 mm). Due to the fast image acquisition time (100 ms), no coil distortion was observable in the ExacTrac system. 4DCT showed problems imaging the coil during mid-respiratory phases of higher velocity (phases 20%-30% and 70%-80%) due to distortion caused by residual motion within the 4DCT phase bin. The ExacTrac imaging system was able to accurately localize the coil in the respiratory phantom over all phases of respiration. For our clinic, where end-respiration phases from 4DCT may be used for treatment planning calculations, the ExacTrac system is used to measure internal target motion. With the ExacTrac system, planning target size and motion uncertainties are minimized, potentially reducing internal target volume margins in gated radiotherapy.


Subject(s)
Four-Dimensional Computed Tomography/methods , Radiographic Image Interpretation, Computer-Assisted/methods , Radiotherapy Planning, Computer-Assisted/methods , Respiration , Tomography, X-Ray Computed/methods , Equipment Design , Humans , Motion , Phantoms, Imaging , Reproducibility of Results
3.
Med Dosim ; 36(4): 397-403, 2011.
Article in English | MEDLINE | ID: mdl-21377865

ABSTRACT

Helical tomotherapy plans using a combination of pitch and jaw width settings were developed for 3 patients previously treated for head and neck cancer. Three jaw widths (5, 2.5, and 1 cm) and 4 pitches (0.86, 0.43, 0.287, and 0.215) were used with a (maximum) modulation factor setting of 4. Twelve plans were generated for each patient using an identical optimization procedure (e.g., number of iterations, objective weights, and penalties, etc.), based on recommendations from TomoTherapy (Madison, WI). The plans were compared using isodose plots, dose volume histograms, dose homogeneity indexes, conformity indexes, radiobiological models, and treatment times. Smaller pitches and jaw widths showed better target dose homogeneity and sparing of normal tissue, as expected. However, the treatment time increased inversely proportional to the jaw width, resulting in delivery times of 24 ± 1.9 min for the 1-cm jaw width. Although treatment plans produced with the 2.5-cm jaw were dosimetrically superior to plans produced with the 5-cm jaw, subsequent calculations of tumor control probabilities and normal tissue complication probabilities suggest that these differences may not be radiobiologically meaningful. Because treatment plans produced with the 5-cm jaw can be delivered in approximately half the time of plans produced with the 2.5-cm jaw (5.1 ± 0.6 min vs. 9.5 ± 1.1 min), use of the 5-cm jaw in routine treatment planning may be a viable approach to decreasing treatment delivery times from helical tomotherapy units.


Subject(s)
Head and Neck Neoplasms/radiotherapy , Jaw/anatomy & histology , Radiotherapy Planning, Computer-Assisted/methods , Radiotherapy, Intensity-Modulated/methods , Head and Neck Neoplasms/diagnostic imaging , Humans , Radiometry , Radiotherapy Dosage , Time Factors , Tomography, Spiral Computed/methods
4.
J Appl Clin Med Phys ; 11(2): 3165, 2010 Apr 19.
Article in English | MEDLINE | ID: mdl-20592699

ABSTRACT

The purpose of this study was to quantify the performance and assess the utility of two different types of scanners for radiochromic EBT film dosimetry: a commercial flatbed document scanner and a widely used radiographic film scanner. We evaluated the Epson Perfection V700 Photo flatbed scanner and the Vidar VXR Dosimetry Pro Advantage scanner as measurement devices for radiochromic EBT film. Measurements were made of scan orientation effects, response uniformity, and scanner noise. Scanners were tested using films irradiated with eight separate 3x3cm2 fields to doses ranging from 0.115-5.119 Gy. ImageJ and RIT software was used for analyzing the Epson and Vidar scans, respectively. For repeated scans of a single film, the measurements in each dose region were reproducible to within +/- 0.3% standard deviation (SD) with both scanners. Film-to-film variations for corresponding doses were measured to be within +/- 0.4% SD for both Epson scanner and Vidar scanners. Overall, the Epson scanner showed a 10% smaller range of pixel value compared to the Vidar scanner. Scanner noise was small: +/- 0.3% SD for the Epson and +/- 0.2% for the Vidar. Overall measurement uniformity for blank film in both systems was better than +/- 2%, provided that the leading and trailing 2 cm film edges were neglected in the Vidar system. In this region artifacts are attributed to the film rollers. Neither system demonstrated a clear measurement advantage. The Epson scanner is a relatively inexpensive method for analyzing radiochromic film, but there is a lack of commercially available software. For a clinic already using a Vidar scanner, applying it to radiochromic film is attractive because commercial software is available. However, care must be taken to avoid using the leading and trailing film edges.


Subject(s)
Film Dosimetry/instrumentation , Film Dosimetry/methods , Radiotherapy Planning, Computer-Assisted/instrumentation , X-Ray Film , Calibration , Equipment Design , Humans , Radiotherapy Dosage , Radiotherapy Planning, Computer-Assisted/methods , Software
5.
Int J Radiat Oncol Biol Phys ; 77(3): 836-42, 2010 Jul 01.
Article in English | MEDLINE | ID: mdl-19879697

ABSTRACT

PURPOSE: To investigate the potential of helical tomotherapy for postmastectomy radiation therapy. METHODS AND MATERIALS: By use of the TomoTherapy Hi-Art II treatment-planning system (TomoTherapy Inc., Madison, WI), helical tomotherapy dose plans were developed for 5 patients and compared with the mixed-beam (electron-photon) plans with which they had been treated. The TomoTherapy plans were evaluated by use of dose-volume quantities, tumor control probability, normal tissue complication probability (NTCP), and secondary cancer complication probability (SCCP). RESULTS: The TomoTherapy plans showed better dose homogeneity in the planning treatment volume containing the chest wall and internal mammary nodes (p = 0.001) and eliminated the need for abutting fields. For the normal tissues, the TomoTherapy plans showed a smaller fractional volume receiving 20 Gy or greater for the ipsilateral lung (p = 0.05), no change in NTCP for postradiation pneumonitis, increased SCCP for each lung and both lungs together (p < 0.02), no change in the volume of the heart receiving more than 15 Gy, no change in NTCP for excess cardiac mortality, and a larger mean dose and SCCP in the contralateral breast (p < 0.001). For nonspecific tissues, the volume receiving between 5 Gy and 25 Gy and SCCP were both larger for the TomoTherapy plans (p < 0.01). Total SCCP was larger for the TomoTherapy plans (p = 0.001). CONCLUSIONS: Overall, the TomoTherapy plans had comparable tumor control probability and NTCP to the mixed-beam plans and increased SCCP. The TomoTherapy plans showed significantly greater dose homogeneity in the chest wall, which offers the potential for improved cosmesis after treatment. These factors have resulted in TomoTherapy often being the treatment of choice for postmastectomy radiation therapy in our clinic.


Subject(s)
Breast Neoplasms/radiotherapy , Breast Neoplasms/surgery , Radiotherapy Planning, Computer-Assisted/methods , Radiotherapy, Intensity-Modulated/methods , Adult , Aged , Breast/radiation effects , Breast Neoplasms/diagnostic imaging , Feasibility Studies , Female , Heart/diagnostic imaging , Heart/radiation effects , Humans , Lung/diagnostic imaging , Lung/radiation effects , Lymph Nodes/diagnostic imaging , Mastectomy , Middle Aged , Postoperative Period , Radiation Injuries/prevention & control , Radiography , Thoracic Wall/diagnostic imaging , Thoracic Wall/radiation effects
6.
Med Phys ; 35(8): 3565-73, 2008 Aug.
Article in English | MEDLINE | ID: mdl-18777917

ABSTRACT

Helical tomotherapy is a technique for delivering intensity modulated radiation therapy treatments using a continuously rotating linac. In this approach, fan beams exiting the linac are dynamically modulated in synchrony with the motion of the gantry and couch. Helical IMRT deliveries have been applied to treating surface lesions, and the purpose of this study was to evaluate the accuracy of dose calculated by the TomoTherapy HiArt treatment planning system for superficial planning target volumes (PTVs). TomoTherapy treatment plans were developed for three superficial PTVs (2-, 4-, and 6-cm deep radially by 90 degrees azimuthally by 4-cm longitudinally) contoured on a 27-cm diameter cylindrical white opaque, high-impact polystyrene phantom. The phantom included removable transverse and sagittal film cassettes that contained bare Kodak EDR2 films cut such that their edges matched the phantom surface (+/-0.05 cm). The phantom was aligned to the machine's isocenter (+/-0.05 cm) and was irradiated according to the treatment plans. Films were scanned with a Vidar film digitizer, and optical densities were converted to dose using a calibration determined from a 6 MV perpendicular film exposure. This perpendicular calibration required that axial film doses (parallel irradiation) be scaled by 1.02 so that mid-arc depth doses matched those measured in the sagittal plane (perpendicular irradiation). All film readings were scaled by 0.935 to correct for over-response due to phantom Cerenkov light. Measured dose distributions were registered to calculated ones and compared. Calculated doses overpredicted measured doses by as much as 9.5% of the prescribed dose at depths less than 1 cm. At depths greater than 1 cm, calculated dose distributions showed agreement to measurement within 5% in the high-dose region and within 0.2 cm distance-to-agreement in the dose falloff regions. In the low-dose region posterior to the PTVs (<10% of the prescribed dose), the dose algorithm underpredicted the dose by 1%-2% of the prescribed dose. Clinically, it is recommended that 1 cm of bolus be used on the surface to ensure that cancerous tissues less than 1 cm depth are not underdosed.


Subject(s)
Phantoms, Imaging , Radiation Injuries , Radiotherapy, Computer-Assisted/methods , Algorithms , Calibration , Humans , Polystyrenes , Radiation Injuries/prevention & control , Radiation Injuries/radiotherapy , Radiometry/instrumentation , Radiotherapy Dosage , Radiotherapy, Computer-Assisted/instrumentation , Radiotherapy, Computer-Assisted/standards , Sensitivity and Specificity
7.
J Appl Clin Med Phys ; 9(3): 43-57, 2008 Jun 23.
Article in English | MEDLINE | ID: mdl-18716591

ABSTRACT

This study assessed the potential of using megavoltage CT (MVCT) images taken with high density skin collimation in place for electron beam treatment planning. MVCT images were taken using the TomoTherapy Hi-Art system (TomoTherapy Inc., Madison, WI), and the CT numbers were converted to density by calibrating the Hi-Art system using an electron density phantom. Doses were computed using MVCT images and kVCT images and compared by calculating dose differences in the uniform dose region ( > 90%, excluding buildup region) and calculating distance-to-agreement (DTA) in high dose-gradient regions (penumbra and distal falloff, 90%-10%). For 9 and 16 MeV electron beams of 10 x 10 cm calculated on a homogeneous CIRS Plastic Water (Computerized Imaging Research Systems Inc., Norfolk, VA) phantom without skin collimation, the maximum dose differences were 2.3% and the maximum DTAs were 2.0 mm for both beams. The same phantom was then MVCT scanned nine times with square skin collimators of Cerrobend on its surface - field sizes of 3 x 3, 6 x 6, and 10 x 10 cm and thicknesses of 6, 8, and 10 mm. Using the Philips Pinnacle 3 treatment planning system (Philips Medical Systems, N.A., Bothwell, WA), a treatment plan was created for combinations of electron energies of 6, 9, 12, and 16 MeV and each field size. The same treatment plans were calculated using kVCT images of the phantom with regions-of-interest (ROI) manually drawn to duplicate the sizes, shapes, and density of the skin collimators. With few exceptions, the maximum dose differences exceeded +/-5% and the DTAs exceeded 2 mm. We determined that the dose differences were due to small distortions in the MVCT images created by the high density material and manifested as errors in the phantom CT numbers and in the shape of the skin collimator edges. These results suggest that MVCT images without skin collimation have potential for use in patient electron beam treatment planning. However, the small distortion in images with skin collimation makes them unsuitable for clinical use.


Subject(s)
Electrons/therapeutic use , Phantoms, Imaging , Radiotherapy Planning, Computer-Assisted/methods , Head/anatomy & histology , Humans , Tomography Scanners, X-Ray Computed
8.
Int J Radiat Oncol Biol Phys ; 70(3): 883-91, 2008 Mar 01.
Article in English | MEDLINE | ID: mdl-18164857

ABSTRACT

PURPOSE: To investigate helical tomotherapy (HT) intensity-modulated radiotherapy (IMRT) as a postoperative treatment for parotid gland tumors. METHODS AND MATERIALS: Helical tomotherapy plans were developed for 4 patients previously treated with segmental multileaf collimator (SMLC) IMRT. A primary planning target volume (PTV64) and two secondary PTVs (PTV60, PTV54) were defined. The clinical goals from the SMLC plans were applied as closely as possible to the HT planning. The SMLC plans included bolus, whereas HT plans did not. RESULTS: In general, the HT plans showed better target coverage and target dose homogeneity. The minimum doses to the desired coverage volume were greater, on average, in the HT plans for all the targets. Minimum PTV doses were larger, on average, in the HT plans by 4.6 Gy (p = 0.03), 4.8 Gy (p = 0.06), and 4.9 Gy (p = 0.06) for PTV64, PTV60, and PTV54, respectively. Maximum PTV doses were smaller, on average, by 2.9 Gy (p = 0.23), 3.2 Gy (p = 0.02), and 3.6 Gy (p = 0.03) for PTV64, PTV60, and PTV54, respectively. Average dose homogeneity index was statistically smaller in the HT plans, and conformity index was larger for PTV64 in 3 patients. Tumor control probabilities were higher for 3 of the 4 patients. Sparing of normal structures was comparable for the two techniques. There were no significant differences between the normal tissue complication probabilities for the HT and SMLC plans. CONCLUSIONS: Helical tomotherapy treatment plans were comparable to or slightly better than SMLC plans. Helical tomotherapy is an effective alternative to SMLC IMRT for treatment of parotid tumors.


Subject(s)
Adenocarcinoma/radiotherapy , Parotid Neoplasms/radiotherapy , Radiotherapy, Intensity-Modulated/methods , Adenocarcinoma/diagnostic imaging , Adenocarcinoma/pathology , Carcinoma, Adenoid Cystic/diagnostic imaging , Carcinoma, Adenoid Cystic/pathology , Carcinoma, Adenoid Cystic/radiotherapy , Humans , Parotid Neoplasms/diagnostic imaging , Parotid Neoplasms/pathology , Radiotherapy Dosage , Radiotherapy Planning, Computer-Assisted/methods , Tomography, Spiral Computed , Tumor Burden
9.
Int J Radiat Oncol Biol Phys ; 62(4): 1195-203, 2005 Jul 15.
Article in English | MEDLINE | ID: mdl-15990025

ABSTRACT

PURPOSE: Out-of-field radiation doses to normal tissues may be associated with an increased risk of secondary malignancies, particularly in long-term survivors. Step-and-shoot intensity-modulated radiation therapy (IMRT), an increasingly popular treatment modality, yields higher out-of-field doses than do conventional treatments, because of an increase in required monitor units (beam-on time). METHODS: We used published risk coefficients (NRCP Report 116) and out-of-field dose equivalents to multiple organ sites to estimate a conservative maximal risk of fatal secondary malignancy associated with 6 IMRT approaches and 1 conventional external-beam approach for prostate cancer. RESULTS: Depending on treatment energy, the IMRT treatments required 3.5-4.9 times as many monitor units to deliver as did the conventional treatment. The conservative maximum risk of fatal second malignancy was 1.7% for conventional radiation, 2.1% for IMRT using 10-MV X-rays, and 5.1% for IMRT using 18-MV X-rays. Intermediate risks were associated with IMRT using 6-MV X-rays: 2.9% for treatment with the Varian accelerator and 3.7% for treatment with the Siemens accelerator, as well as using 15-MV X-rays: 3.4% (Varian) and 4.0% (Siemens). CONCLUSION: The risk of fatal secondary malignancy differed substantially between IMRT and conventional radiation therapy for prostate cancer, as well as between different IMRT approaches. Perhaps this risk should be considered when choosing the optimal treatment technique and delivery system for patients who will undergo prostate radiation.


Subject(s)
Neoplasms, Radiation-Induced/etiology , Neoplasms, Second Primary/etiology , Radiotherapy, Conformal/adverse effects , Dose-Response Relationship, Radiation , Humans , Organ Specificity , Radiotherapy, Conformal/methods , Risk Assessment/methods
10.
Int J Radiat Oncol Biol Phys ; 62(4): 1204-16, 2005 Jul 15.
Article in English | MEDLINE | ID: mdl-15990026

ABSTRACT

PURPOSE: To measure the photon and neutron out-of-treatment-field dose equivalents to various organs from different treatment strategies (conventional vs. intensity-modulated radiation therapy [IMRT]) at different treatment energies and delivered by different accelerators. METHODS AND MATERIALS: Independent measurements were made of the photon and neutron out-of-field dose equivalents resulting from one conventional and six IMRT treatments for prostate cancer. The conventional treatment used an 18-MV beam from a Clinac 2100; the IMRT treatments used 6-MV, 10-MV, 15-MV, and 18-MV beams from a Varian Clinac 2100 accelerator and 6-MV and 15-MV beams from a Siemens Primus accelerator. Photon doses were measured with thermoluminescent dosimeters in a Rando phantom, and neutron fluence was measured with gold foils. Dose equivalents to the colon, liver, stomach, lung, esophagus, thyroid, and active bone marrow were determined for each treatment approach. RESULTS: For each treatment approach, the relationship between dose equivalent per MU, distance from the treatment field, and depth in the patient was examined. Photon dose equivalents decreased approximately exponentially with distance from the treatment field. Neutron dose equivalents were independent of distance from the treatment field and decreased with increasing tissue depth. Neutrons were a significant contributor to the out-of field dose equivalent for beam energies > or =15 MV. CONCLUSIONS: Out-of-field photon and neutron dose equivalents can be estimated to any point in a patient undergoing a similar treatment approach from the distance of that point to the central axis and from the tissue depth. This information is useful in determining the dose to critical structures and in evaluating the risk of associated carcinogenesis.


Subject(s)
Neutrons , Photons , Prostatic Neoplasms/radiotherapy , Radiation Dosage , Radiotherapy, Conformal/methods , Algorithms , Bone Marrow , Colon , Esophagus , Humans , Liver , Lung , Male , Particle Accelerators , Phantoms, Imaging , Radiotherapy, Conformal/instrumentation , Scattering, Radiation , Stomach , Thermoluminescent Dosimetry/methods , Thyroid Gland
11.
Med Phys ; 32(4): 838-50, 2005 Apr.
Article in English | MEDLINE | ID: mdl-15895566

ABSTRACT

We performed 858 two-dimensional (2D) patient-specific intensity modulated radiotherapy verifications over a period of 18 months. Multifield, composite treatment plans were measured in phantom using calibrated Kodak EDR2 film and compared with the calculated dose extracted from two treatment planning systems. This research summarizes our findings using the normalized agreement test (NAT) index and the percent of pixels failing the gamma index as metrics to represent the agreement between measured and computed dose distributions. An in-house dose comparison software package was used to register and compare all verifications. We found it was important to use an automatic positioning algorithm to achieve maximum registration accuracy, and that our automatic algorithm agreed well with anticipated results from known phantom geometries. We also measured absolute dose for each case using an ion chamber. Because the computed distributions agreed with ion chamber measurements better than the EDR2 film doses, we normalized EDR2 data to the computed distributions. The distributions of both the NAT indices and the percentage of pixels failing the gamma index were found to be exponential distributions. We continue to use both the NAT index and percent of pixels failing gamma with 5%/3 mm criteria to evaluate future verifications, as these two metrics were found to be complementary. Our data showed that using 2%/2 mm or 3%/3 mm criteria produces results similar to those using 5%/3 mm criteria. Normalized comparisons that have a NAT index greater than 45 and/or more than 20% of the pixels failing gamma for 5%/3 mm criteria represent outliers from our clinical data set and require further analysis. Because our QA verification results were exponentially distributed, rather than a tight grouping of similar results, we continue to perform patient-specific QA in order to identify and correct outliers in our verifications. The data from this work could be useful as a reference for other clinics to indicate anticipated trends in 2D verifications under various conditions.


Subject(s)
Film Dosimetry/methods , Radiotherapy, Conformal/methods , Algorithms , Analysis of Variance , Calibration , Humans , Ions , Phantoms, Imaging , Polystyrenes/chemistry , Quality Control , Radiometry/methods , Radiotherapy Planning, Computer-Assisted , Reproducibility of Results , Retrospective Studies , Software , Time Factors , Water , X-Ray Film
12.
Med Phys ; 32(2): 539-48, 2005 Feb.
Article in English | MEDLINE | ID: mdl-15789600

ABSTRACT

Patient-specific intensity-modulated radiotherapy (IMRT) verifications require an accurate two-dimensional dosimeter that is not labor-intensive. We assessed the precision and reproducibility of film calibrations over time, measured the elemental composition of the film, measured the intermittency effect, and measured the dosimetric accuracy and reproducibility of calibrated Kodak EDR2 film for single-beam verifications in a solid water phantom and for full-plan verifications in a Rexolite phantom. Repeated measurements of the film sensitometric curve in a single experiment yielded overall uncertainties in dose of 2.1% local and 0.8% relative to 300 cGy. 547 film calibrations over an 18-month period, exposed to a range of doses from 0 to a maximum of 240 MU or 360 MU and using 6 MV or 18 MV energies, had optical density (OD) standard deviations that were 7%-15% of their average values. This indicates that daily film calibrations are essential when EDR2 film is used to obtain absolute dose results. An elemental analysis of EDR2 film revealed that it contains 60% as much silver and 20% as much bromine as Kodak XV2 film. EDR2 film also has an unusual 1.69:1 silver:halide molar ratio, compared with the XV2 film's 1.02:1 ratio, which may affect its chemical reactions. To test EDR2's intermittency effect, the OD generated by a single 300 MU exposure was compared to the ODs generated by exposing the film 1 MU, 2 MU, and 4 MU at a time to a total of 300 MU. An ion chamber recorded the relative dose of all intermittency measurements to account for machine output variations. Using small MU bursts to expose the film resulted in delivery times of 4 to 14 minutes and lowered the film's OD by approximately 2% for both 6 and 18 MV beams. This effect may result in EDR2 film underestimating absolute doses for patient verifications that require long delivery times. After using a calibration to convert EDR2 film's OD to dose values, film measurements agreed within 2% relative difference and 2 mm criteria to ion chamber measurements for both sliding window and step-and-shoot fluence map verifications. Calibrated film results agreed with ion chamber measurements to within 5 % /2 mm criteria for transverse-plane full-plan verifications, but were consistently low. When properly calibrated, EDR2 film can be an adequate two-dimensional dosimeter for IMRT verifications, although it may underestimate doses in regions with long exposure times.


Subject(s)
Film Dosimetry/instrumentation , Quality Assurance, Health Care/methods , Radiotherapy Planning, Computer-Assisted/instrumentation , Radiotherapy, Conformal/methods , Dose-Response Relationship, Radiation , Equipment Failure Analysis , Film Dosimetry/methods , Radiotherapy Dosage , Radiotherapy Planning, Computer-Assisted/methods , Reproducibility of Results , Sensitivity and Specificity
13.
Med Phys ; 32(1): 153-62, 2005 Jan.
Article in English | MEDLINE | ID: mdl-15719966

ABSTRACT

We investigated the feasibility of detecting intensity modulated radiotherapy delivery errors automatically using a scalar evaluation of two-dimensional (2D) transverse dose measurement of the complete treatment delivery. Techniques using the gamma index and the normalized agreement test (NAT) index were used to parametrize the agreement between measured and computed dose distributions to seven different scalar metrics. Simulated verifications with delivery errors calculated using a commercially available treatment planning system for 9 prostate and 7 paranasal sinus cases were compared to 433 clinical verifications. The NAT index with 5% and 3 mm criteria that included cold areas outside the planning target volume detected the largest percent of delivery errors. Assuming a false positive rate of 5%, it was able to detect 88% of beam energy changes, 94% of a different patient's plan being delivered, 25% of plans with one beam's collimator rotated by 90 degrees, 81% of rotating one beam's gantry angle by 10 degrees, and 100% of omitting the delivery of one beam. However, no instances of changing one beam's monitor unit setting by 10% or shifting the isocenter by 5 mm were detected. Although the phantom shift could not be detected by the small change it made in the dose distribution, our autopositioning algorithm clearly identified the spatial anomaly. Using tighter 3 %/2 mm criteria or combining dose and distance disagreements in an either/or fashion resulted in poorer delivery error detection. The mean value of the 2D gamma index distribution was less sensitive to delivery errors than the other scalar metrics studied. Although we found that scalar metrics do not have sufficient delivery error detection rates to be used as the sole clinical analysis technique, manually examining 2D dose comparison images would result in a near 100% detection rate while performing an ion chamber measurement alone would only detect 54% of these errors.


Subject(s)
Radiometry/methods , Radiotherapy Planning, Computer-Assisted/methods , Radiotherapy, Conformal/methods , Algorithms , False Positive Reactions , Film Dosimetry , Gamma Rays , Humans , Ions , Male , Paranasal Sinus Neoplasms/radiotherapy , Phantoms, Imaging , Prostatic Neoplasms/radiotherapy , Radiotherapy Dosage , Radiotherapy, Computer-Assisted , Software
14.
Med Phys ; 31(8): 2284-8, 2004 Aug.
Article in English | MEDLINE | ID: mdl-15377095

ABSTRACT

Kodak EDR2 film is a widely used two-dimensional dosimeter for intensity modulated radiotherapy (IMRT) measurements. Our clinical use of EDR2 film for IMRT verifications revealed variations and uncertainties in dose response that were larger than expected, given that we perform film calibrations for every experimental measurement. We found that the length of time between film exposure and processing can affect the absolute dose response of EDR2 film by as much as 4%-6%. EDR2 films were exposed to 300 cGy using 6 and 18 MV 10 x 10 cm2 fields and then processed after time delays ranging from 2 min to 24 h. An ion chamber measured the relative dose for these film exposures. The ratio of optical density (OD) to dose stabilized after 3 h. Compared to its stable value, the film response was 4%-6% lower at 2 min and 1% lower at 1 h. The results of the 4 min and 1 h processing time delays were verified with a total of four different EDR2 film batches. The OD/dose response for XV2 films was consistent for time periods of 4 min and 1 h between exposure and processing. To investigate possible interactions of the processing time delay effect with dose, single EDR2 films were irradiated to eight different dose levels between 45 and 330 cGy using smaller 3 x 3 cm2 areas. These films were processed after time delays of 1, 3, and 6 h, using 6 and 18 MV photon qualities. The results at all dose levels were consistent, indicating that there is no change in the processing time delay effect for different doses. The difference in the time delay effect between the 6 and 18 MV measurements was negligible for all experiments. To rule out bias in selecting film regions for OD measurement, we compared the use of a specialized algorithm that systematically determines regions of interest inside the 10 x 10 cm2 exposure areas to manually selected regions of interest. There was a maximum difference of only 0.07% between the manually and automatically selected regions, indicating that the use of a systematic algorithm to determine regions of interest in large and fairly uniform areas is not necessary. Based on these results, we recommend a minimum time of 1 h between exposure and processing for all EDR2 film measurements.


Subject(s)
Film Dosimetry/instrumentation , Image Processing, Computer-Assisted , Photons , X-Ray Film , Radiometry
15.
Int J Radiat Oncol Biol Phys ; 59(4): 1039-46, 2004 Jul 15.
Article in English | MEDLINE | ID: mdl-15234037

ABSTRACT

PURPOSE: To evaluate the relationship between the dose and volume of radiation to proximal penile structures and the development of erectile dysfunction after external beam radiotherapy (RT) for localized prostate adenocarcinoma. METHODS AND MATERIALS: The study cohort comprised 28 patients who were enrolled our in-house three-dimensional conformal RT dose escalation protocol. The patients were treated to 78 Gy between 1995 and 1998. This protocol included a planned quality-of-life questionnaire to assess sexual function 2 years after completing RT. All the study patients were potent before RT. The median follow-up was 66 months (range 39-95). Penile base contents were outlined retrospectively in restored treatment plans. The dose-volume histograms (DVHs) for the corpus spongiosum (penile bulb), corpora cavernosum and crura, and total penile structure (corpus spongiosum plus corpora cavernosum and crura) were calculated. Statistical significance was defined as p < 0.05. The Bonferroni correction was used to adjust for multiple comparisons. Power calculations showed that our study sample would detect radiation- induced impotence with a very high power. We also estimated that a relatively small difference of 10-15% in the DVHs between the potent and impotent patients could be detected. RESULTS: At 2 years after RT, 10 patients (35.7%) reported new-onset erectile dysfunction and were unable to attain firm enough erections to have intercourse. Only hypertension was observed to affect erectile dysfunction after external beam RT. We found no statistically significant correlation among age, diabetes, or heavy alcohol consumption and post-RT potency. The mean radiation dose +/- standard deviation delivered to the corpus spongiosum, corpora cavernosa and crura, and total penile structure was, respectively, 42.2 +/- 8.4 Gy, 36.3 +/- 8.0 Gy, and 38.2 +/- 7.5 Gy. t test comparisons were performed between DVHs of post-RT potent and impotent patients on multiple cutpoints. No dose-volume effect was found. Analysis of the DVHs when the patients were subdivided into normotensive and hypertensive groups also showed no dose-volume response. CONCLUSION: Our analysis did not show statistically significant correlations between potency preservation and radiation dose to the proximal penis. The entire etiology of radiation- induced erectile dysfunction remains unclear and further research is needed.


Subject(s)
Adenocarcinoma/radiotherapy , Erectile Dysfunction/etiology , Penis/radiation effects , Prostatic Neoplasms/radiotherapy , Radiotherapy, Conformal/adverse effects , Aged , Dose-Response Relationship, Radiation , Follow-Up Studies , Humans , Male , Middle Aged , Penile Erection , Quality of Life , Retrospective Studies
16.
Med Phys ; 30(8): 2065-71, 2003 Aug.
Article in English | MEDLINE | ID: mdl-12945972

ABSTRACT

Treatment planning involves selecting delivery parameters that distribute the dose to nontumor tissue in such a way as to minimize the risk of complications. This work studied the relationship between nontumor integral dose (NTID), the fractional energy deposited in nontumor tissue, and a variety of delivery parameters for three clinical cases: nasopharynx, pancreas, and prostate. Integral dose for an organ of uniform density is simply the product of the organ density, volume, and mean dose. For each case, conventional plans were generated with 2, 4, 8, 12 and 36 equally spaced beams. All plans were normalized to the same tumor mean dose (< 3%), which is equivalent to the same tumor integral dose. For the pancreas and prostate cases, the patients were assumed to be uniform density. For the nasopharynx case, bones and air cavities were outlined and each assigned a uniform non-unit density. With four or more beams and clinical margin values, the variation in NTID was < 1% as a function of number of beams. With eight or more beams, the variation was < 0.2%. Reducing the beam margin decreased the NTID because less normal tissue was irradiated. However, the effect of the number of beams on NTID was independent of margin size. Higher energy beams reduced the NTID, as expected, and the effect was independent of the number of beams. With four or more beams, variation in beam direction changed NTID by less than 1.5%. Changing beam weights changed NTID by < 2% for plans with four to eight beams. For the body sites studied, the majority of energy was deposited in nontumor tissue, ranging from 72% in the nasopharynx case to 97% for the prostate case. The NTID decreased with increasing tumor size for similar anatomic sizes and increased with increasing size of anatomical region for similar tumor size. Finally, the effect of heterogeneity-corrected doses on the NTID was found to be < 3% for the nasopharynx case. These data support the hypothesis that the NTID is approximately independent of beam orientation or relative weighting when many beams are used. Optimization, therefore, can only find the best distribution of dose; it cannot reduce the energy imparted. NTID may be useful in establishing an upper bound on the quality of plan that can be achieved by optimization.


Subject(s)
Neoplasms/radiotherapy , Radiotherapy Planning, Computer-Assisted/methods , Radiotherapy/methods , Dose-Response Relationship, Radiation , Female , Humans , Male , Models, Statistical , Radiometry , Radiotherapy Dosage
17.
Int J Radiat Oncol Biol Phys ; 56(5): 1464-79, 2003 Aug 01.
Article in English | MEDLINE | ID: mdl-12873692

ABSTRACT

PURPOSE: New multidimensional dose comparison parameters, normalized agreement test (NAT) values and the NAT index, are introduced and compared with an ideal dose comparison parameter. In this article, we analyze a clinically based two-dimensional (2D) quantitative dose comparison case using a wide range of new and old comparison tools. In doing so, we address the benefits and limitations of many common dose comparison tools. METHODS AND MATERIALS: An in-house software program was developed using the MATLAB 6.5 programming language. Using this software, several 2D quantitative dose comparison parameters were calculated for the computed and measured dose distributions in an intensity-modulated radiotherapy (IMRT) prostate cancer treatment. The experiences gained in the design and testing of this software program form the basis of the dose comparison tool analysis. RESULTS: Each dose comparison tool has unique strengths and weaknesses. The underlying assumptions of the NAT values and NAT index lead to acceptable generalized behavior, but are not always valid. CONCLUSION: A thorough 2D quantitative dose comparison analysis can only be accomplished through the use of many dose comparison tools. The introduction of the NAT index allows a 2D dose comparison to be reduced to a single value, and is thus ideal for setting clinical acceptance criteria for IMRT verifications.


Subject(s)
Prostatic Neoplasms/radiotherapy , Radiotherapy Dosage , Humans , Male , Radiotherapy Planning, Computer-Assisted , Research Design
18.
Med Phys ; 29(10): 2384-90, 2002 Oct.
Article in English | MEDLINE | ID: mdl-12408313

ABSTRACT

A method for measuring a film sensitometric curve using a single sheet of film exposed with a two field step-and-shoot MLC treatment was developed and tested with Kodak XV2 and EDR2 films. With this technique a film sensitometric curve can be completed in only 10 minutes, making it practical to generate new film calibrations daily. This method is applicable to film calibrations for all purposes, but is particularly useful in IMRT treatment verification due to the method's use of small fields. This method agrees with the traditional large-field multifilm calibration within 0.5% and will produce sensitometric curves with errors less than 1% throughout the dose range, including uncertainties in dose delivery, film response, and optical density measurements. OD values for XV2 and EDR2 films were consistent in the middle of exposure areas at high depths, but the XV2 film penumbra regions showed large amounts of over-response as the calibration depth increased. If XV2 film is used for IMRT treatment verification, it is necessary to reduce the fluence of low energy photons in areas around the film by using thin lead shields. EDR2 film was shown to have minimal energy dependence, as it accurately represented penumbra areas and yielded identical sensitometric curves generated with 6 and 18 MV photons. However, its darker tint may make it more sensitive to scanning laser film digitizers' horizontal nonuniformities. This single film method proved to be superior to the traditional calibration method and allows fast daily calibrations of films for highly accurate IMRT delivery verifications.


Subject(s)
Film Dosimetry/methods , Radiotherapy, Conformal/instrumentation , Radiotherapy, Conformal/methods , X-Ray Film , Calibration , Dose-Response Relationship, Radiation , Humans , Photons , Radiometry/methods , Radiotherapy Dosage , Radiotherapy Planning, Computer-Assisted/methods , Time Factors
19.
Int J Radiat Oncol Biol Phys ; 54(3): 677-85, 2002 Nov 01.
Article in English | MEDLINE | ID: mdl-12377318

ABSTRACT

PURPOSE: A positive biopsy after external beam radiotherapy in patients free of any evidence of treatment failure is not synonymous with eventual recurrence. Although biopsy positivity is a predictor of outcome, the utility of biopsy status as a surrogate end point, the effect of radiation dose on biopsy status, and the interrelationships of these associations to prostate-specific antigen (PSA) nadir level are not well-defined. These issues were investigated in a cohort of men with Stage T1-T3 prostate cancer who were randomized to receive between 70 Gy and 78 Gy and were prospectively biopsied at about 2 years after the completion of radiotherapy (RT). METHODS AND MATERIALS: Of the 301 assessable patients in the trial, 168 underwent planned sextant or greater prostate post-RT biopsies in the absence of biochemical or clinical failure; this group constituted the study cohort. Of the 168 patients, 87 were in the 70-Gy arm and 81 in the 78-Gy arm. Biopsies were classified into four groups: negative (no tumor), atypical/suspicious cells (not diagnostic of carcinoma), carcinoma with treatment effect (CaTxEffect), and carcinoma without treatment effect (CaNoTxEffect). Any diagnosis of carcinoma in the specimen was classified as biopsy positive. Freedom from failure (FFF) included biochemical failure and/or clinical failure. Kaplan-Meier curves were calculated from the completion of RT. For those alive in the study cohort, the median follow-up was 65 months. RESULTS: The rate of biopsy without tumor was 42%; with atypical cells, it was 28%, with CaTxEffect 21%, and with CaNoTxEffect 9%. The overall biopsy positivity rate (CaTxEffect + CaNoTxEffect) was 30%; 28% in the 70-Gy group and 32% in the 78-Gy group (p = 0.52). The distribution of PSA nadir levels was 73% 0.5-1.0, 5% >1.0-2.0, and 1% >2.0 ng/mL. Significantly more patients randomized to 78 Gy had a PSA nadir of 2.0 ng/mL. CONCLUSION: For patients free of treatment failure at the time of prostate biopsy 2 years after RT, the prognosis of no tumor cells was the same as that of atypical/suspicious cells and CaTxEffect was the same as CaNoTxEffect. The biopsy positivity rate was not altered by dose, suggesting that most of the outcome differences between the 70-Gy and 78-Gy groups were due to events occurring before prostate biopsy at 2 years and/or were not entirely dependent on biopsy status. Biopsy status is a strong prognostic factor, but, as an early end point, it may be misleading. PSA nadir appears to have little clinical value in patients treated to doses of >/=70 Gy who are failure free 2 years after RT.


Subject(s)
Prostate-Specific Antigen/blood , Prostate/pathology , Prostatic Neoplasms/pathology , Prostatic Neoplasms/radiotherapy , Aged , Biopsy , Chi-Square Distribution , Cohort Studies , Dose-Response Relationship, Radiation , Humans , Male , Prognosis , Proportional Hazards Models , Prospective Studies , Prostatic Neoplasms/blood , Radiotherapy Dosage , Survival Analysis , Time Factors , Treatment Failure
20.
Int J Radiat Oncol Biol Phys ; 53(2): 261-8, 2002 Jun 01.
Article in English | MEDLINE | ID: mdl-12023128

ABSTRACT

PURPOSE: Although the interfraction motion of the prostate has been previously studied through the use of fiducial markers, CT scans, and ultrasound-based systems, intrafraction motion is not well documented. In this report, the B-mode, Acquisition, and Targeting (BAT) ultrasound system was used to measure intrafraction prostate motion during 200 intensity-modulated radiotherapy (IMRT) sessions for prostate cancer. METHODS AND MATERIALS: Twenty men receiving treatment with IMRT for clinically localized prostate cancer were selected for the study. Pre- and posttreatment BAT ultrasound alignment images were collected immediately before and after IMRT on 10 treatment days for a total of 400 BAT alignment procedures. Any ultrasound shifts of the prostate borders in relation to the planning CT scan were recorded in 3 dimensions: right-left (RL), anteroposterior (AP), and superior-inferior (SI). Every ultrasound procedure was evaluated for image quality and alignment according to a 3-point grading scale. RESULTS: All the BAT images were judged to be of acceptable quality and alignment. The dominant directions of intrafraction prostate motion were anteriorly and superiorly. The mean magnitude of shifts (+/-SD) was 0.01 +/- 0.4 mm, 0.2 +/- 1.3 mm, and 0.1 +/- 1.0 mm in the left, anterior, and superior directions, respectively. The maximal range of motion occurred in the AP dimension, from 6.8 mm anteriorly to 4.6 mm posteriorly. The percentage of treatments during which prostate motion was judged to be 5 mm. The extent of intrafraction motion was much smaller than that of interfraction motion. Linear regression analysis showed very little correlation between the two types of motion (r = 0.014, 0.029, and 0.191, respectively) in the RL, AP, and SI directions. CONCLUSION: Using an ultrasound-based system, intrafraction prostate motion occurred predominantly in the anterior and superior directions, but was clinically insignificant. Intrafraction motion was much smaller than interfraction motion, and the two types of movement did not correlate.


Subject(s)
Movement , Prostate/diagnostic imaging , Prostatic Neoplasms/diagnostic imaging , Prostatic Neoplasms/radiotherapy , Radiotherapy, Conformal/methods , Humans , Linear Models , Male , Ultrasonography
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