Low-dose 2.5 MV cone-beam computed tomography with thick CsI flat-panel imager.

Most of the treatment units, both new and old models, are equipped with a megavoltage portal imager but its use for volumetric imaging is limited. This is mainly due to the poor image quality produced by the high-energy treatment beam (> 6MV). A linac at our center is equipped with a prototype 2.5 MV imaging beam. This study evaluates the feasibility of low-dose megavoltage cone-beam imaging with the 2.5MV beam and a thick cesium iodide detector, which is a high-efficiency imager. Basic imaging properties such as spatial resolution and modulation transfer function were assessed for the 2.5 MV prototype imaging system. For image quality and imaging dose, a series of megavoltage cone-beam scans were acquired for the head, thorax, and pelvis of an anthropomorphic phantom and were compared to kilovoltage cone-beam and 6X megavoltage cone-beam images. To demonstrate the advantage of MV imaging, a phantom with metallic inserts was scanned and the image quality was compared to CT and kilovoltage cone-beam scans. With a lower energy beam and higher detector efficiency, the 2.5 MV imaging system generally yields better image quality than does the 6 MV imaging system with the conventional MV imager. In particular, with the anthropomorphic phantom studies, the contrast to noise of bone to tissue is generally improved in the 2.5 MV images compared to 6 MV. With an image quality sufficient for bony alignment, the imaging dose for 2.5 MV cone-beam images is 2.4-3.4 MU compared to 26 MU in 6 MV cone-beam scans for the head, thorax, and pelvis regions of the phantom. Unlike kilovoltage cone-beam, the 2.5 MV imaging system does not suffer from high-Z image artifacts. This can be very useful for treatment planning in cases where high-Z prostheses are present.

Analysis of patient specific dosimetry quality assurance measurements in intensity modulated radiotherapy: a multi centre study.

AIM OF THE STUDY: Statistical analysis of pre-treatment dose verification of intensity-modulated radiotherapy (IMRT) fields to assess the quality of the IMRT practice at different radiotherapy centers. MATERIALS AND METHODS: The dose verification data acquired by the institutional physicist of 10 different hospitals for various types of patients were collected and analyzed for mean, median, standard deviation (SD), range, minimum and maximum % deviation. The percentage of cases having positive and negative dose differences as well dose differences within ± 3% were also determined. RESULTS: The mean values of percentage variation in difference between treatment planning systems calculated dose and difference between measured dose (D(TPS) and D(Meas)) are found to be from -1.79 to 1.48 and median from -1.79 to 1.51. The SDs are found to be from 0.76 to 3.70. The range of variation at these centers varies from 3.99 to 16.45 while minimum and maximum values of percentage variation in difference between D(TPS) and D(Meas) ranges from -10.33 to 13.38. The percentage of cases having positive dose difference ranges from 8 to 94 and cases having negative dose difference ranges from 6 to 92. The percentage of cases having dose difference within ± 3% varies from 57 to 100. CONCLUSION: IMRT centers are having random and biased (skewed towards over or under dose) distribution of the percentage variation in difference between measured and planned doses. The analysis of results of the IMRT pre-treatment dose verification reveals that there are systematic errors in the chain of IMRT treatment process at a few centers. The dosimetry quality audit prior to commissioning of IMRT may play an important role in avoiding such discrepancies.

Migration from full-head mask to "open-face" mask for immobilization of patients with head and neck cancer.

To provide an alternative device for immobilization of the head while easing claustrophobia and improving comfort, an "open-face" thermoplastic mask was evaluated using video-based optical surface imaging (OSI) and kilovoltage (kV) X-ray radiography. A three-point thermoplastic head mask with a precut opening and reinforced strips was developed. After molding, it provided sufficient visible facial area as the region of interest for OSI. Using real-time OSI, the head motion of ten volunteers in the new mask was evaluated during mask locking and 15minutes lying on the treatment couch. Using a nose mark with reference to room lasers, forced head movement in open-face and full-head masks (with a nose hole) was compared. Five patients with claustrophobia were immobilized with open-face masks, set up using OSI and kV, and treated in 121 fractions, in which 61 fractions were monitored during treatment using real-time OSI. With the open-face mask, head motion was found to be 1.0 ± 0.6 mm and 0.4° ± 0.2° in volunteers during the experiment, and 0.8 ± 0.3 mm and 0.4° ± 0.2° in patients during treatment. These agree with patient motion calculated from pre-/post-treatment OSI and kV data using different anatomical landmarks. In volunteers, the head shift induced by mask-locking was 2.3 ± 1.7 mm and 1.8° ± 0.6°, and the range of forced movements in the open-face and full-head masks were found to be similar. Most (80%) of the volunteers preferred the open-face mask to the full-head mask, while claustrophobic patients could only tolerate the open-face mask. The open-face mask is characterized for its immobilization capability and can immobilize patients sufficiently (< 2 mm) during radiotherapy. It provides a clinical solution to the immobilization of patients with head and neck (HN) cancer undergoing radiotherapy, and is particularly beneficial for claustrophobic patients. This new open-face mask is readily adopted in radiotherapy clinic as a superior alternative to the standard full-head mask.

The impact of new technologies on radiation oncology events and trends in the past decade: an institutional experience.

PURPOSE: To review the type and frequency of patient events from external-beam radiotherapy over a time period sufficiently long to encompass significant technology changes. METHODS AND MATERIALS: Ten years of quality assurance records from January 2001 through December 2010 were retrospectively reviewed to determine the frequency of events affecting patient treatment from four radiation oncology process steps: simulation, treatment planning, data entry/transfer, and treatment delivery. Patient events were obtained from manual records and, from May 2007 onward, from an institution-wide database and reporting system. Events were classified according to process step of origination and segregated according to the most frequently observed event types. Events from the institution-wide database were evaluated to determine time trends. RESULTS: The overall event rate was 0.93% per course of treatment, with a downward trend over time led by a decrease in treatment delivery events. The frequency of certain event types, particularly in planning and treatment delivery, changed significantly over the course of the study, reflecting technologic and process changes. Treatments involving some form of manual intervention carried an event risk four times higher than those relying heavily on computer-aided design and delivery. CONCLUSIONS: Although the overall event rate was low, areas for improvement were identified, including manual calculations and data entry, late-day treatments, and staff overreliance on computer systems. Reducing the incidence of pretreatment events is of particular importance because these were more likely to occur several times before detection and were associated with larger dosimetric impact. Further improvements in quality assurance systems and reporting are imperative, given the advent of electronic charting, increasing reliance on computer systems, and the potentially severe consequences that can arise from mistakes involving complex intensity-modulated or image-guided treatments.

Correction of image artifacts from treatment couch in cone-beam CT from kV on-board imaging.

PURPOSE: To investigate image artifacts caused by a standard treatment couch on cone-beam CT (CBCT) images from a kV on-board imager and to develop an algorithm based on spatial domain filtering to remove image artifacts in CBCT induced by the treatment couch. METHODS: Image artifacts in CBCT induced by the treatment couch were quantified by scanning a phantom used to quantify CT image performance. This was performed by scanning the phantom setup on a regular treatment couch and in air with the kV on-board imager. An algorithm was developed to filter image artifacts from the treatment couch by processing of cone-beam radiographic projections using two scans: one scan of the phantom and treatment couch and a second scan of the treatment couch only. This algorithm is based on a pixel-by-pixel removal of beam attenuation due to the treatment couch from each projection of the phantom and couch scan. The net couch-filtered projections were then used to reconstruct CBCT. RESULTS: We found that the treatment couch causes considerable image artifacts: CT number uniformity is degraded and varies as much as 15%, and noise in CBCT scans with phantom plus couch (3.5%) is higher than for the phantom in air (1.5%). The spatial domain filtering technique reduces noise by more than 1.5%, improves uniformity by a factor of 2, and removes ringing and streaking artifacts related to the standard treatment couch in CBCT reconstructed from couch-filtered projections. This filtering technique was tested successfully to filter other hardware objects such as a patient immobilization body-fix frame. CONCLUSIONS: The standard treatment couch causes image artifact in CBCT from kV on-board imaging systems. The spatial domain filtering technique developed in this work improves image quality of CBCT by preprocessing the projections prior to CBCT reconstruction. This technique might be useful to filter other hardware objects from CBCT which may contribute to the degradation of image quality.

Motion monitoring for cranial frameless stereotactic radiosurgery using video-based three-dimensional optical surface imaging.

PURPOSE: To establish a new clinical procedure in frameless stereotactic radiosurgery (SRS) for patient setup verification at treatment couch angles as well as for head-motion monitoring during treatment using video-based optical surface imaging (OSI). METHODS: A video-based three-dimensional (3D) OSI system with three ceiling-mounted camera pods was employed to verify setup at treatment couch angles as well as to monitor head motion during treatment. A noninvasive head immobilization device was utilized, which includes an alpha head mold and a dental mouthpiece with vacuum suction; both were locked to the treatment couch. Cone beam computed tomography (CBCT) was used as the standard for image-guided setup. Orthogonal 2D-kV imaging was applied for setup verification before treatment, between couch rotations, and after treatment at zero couch angle. At various treatment couch angles, OSI setup verification was performed, relative to initial OSI setup verification at zero couch angle after CBCT setup through a coordinate transformation. For motion monitoring, the setup uncertainty was decoupled by taking an on-site surface image as new reference to detect motion-induced misalignment in near real-time (1-2 frames per second). Initial thermal instability baseline of the real-time monitoring was corrected. An anthropomorphous head phantom and a 1D positioning platform were used to assess the OSI accuracy in motion detection in longitudinal and lateral directions. Two hypofractionated (9 Gy x 3 and 6 Gy x 5) frameless stereotactic radiotherapy (SRT) patients as well as two single-fraction (21 and 18 Gy) frameless SRS patients were treated using this frameless procedure. For comparison, 11 conventional frame-based SRS patients were monitored using the OSI to serve as clinical standards. Multiple noncoplanar conformal beams were used for planning both frameless and frame-based SRS with a micromultileaf collimator. RESULTS: The accuracy of the OSI in 1D motion detection was found to be 0.1 mm with uncertainty of +/- 0.1 mm using the head phantom. The OSI registration against simulation computed tomography (CT) external contour was found to be dependent on the CT skin definition with -0.4 mm variation. For frame-based SRS patients, head-motion magnitude was detected to be <1.0 mm (0.3 +/- 0.2 mm) and <1.0 degree (0.2 degrees +/- 0.2 degrees) for 98% of treatment time, with exception of one patient with head rotation <1.5 degrees for 98% of the time. For frameless SRT/SRS patients, similar motion magnitudes were observed with an average of 0.3 +/- 0.2 mm and 0.2 degrees +/- 0.1 degree in ten treatments. For 98% of the time, the motion magnitude was <1.1 mm and 1.0 degree. Complex head-motion patterns within 1.0 mm were observed for frameless SRT/SRS patients. The OSI setup verification at treatment couch angles was found to be within 1.0 mm. CONCLUSIONS: The OSI system is capable of detecting 0.1 +/- 0.1 mm 1D spatial displacement of a phantom in near real time and useful in head-motion monitoring. This new frameless SRS procedure using the mask-less head-fixation system provides immobilization similar to that of conventional frame-based SRS. Head-motion monitoring using near-real-time surface imaging provides adequate accuracy and is necessary for frameless SRS in case of unexpected head motion that exceeds a set tolerance.

Evaluation of tumor motion effects on dose distribution for hypofractionated intensity-modulated radiotherapy of non-small-cell lung cancer.

Respiration-induced tumor motion during intensity-modulated radiotherapy (IMRT) of non-small-cell lung cancer (NSCLC) could cause substantial differences between planned and delivered doses. While it has been shown that, for conventionally fractionated IMRT, motion effects average out over the course of many treatments, this might not be true for hypofractionated IMRT (IMHFRT). Numerical simulations were performed for nine NSCLC patients (11 tumors) to evaluate this problem. Dose distributions to the Clinical Target Volume (CTV) and Internal Target Volume (ITV) were retrospectively calculated using the previously-calculated leaf motion files but with the addition of typical periodic motion (i.e. amplitude 0.36-1.26cm, 3-8sec period). A typical IMHFRT prescription of 20Gy x 3 fractions was assumed. For the largest amplitude (1.26 cm), the average +/- standard deviation of the ratio of simulated to planned mean dose, minimum dose, D95 and V95 were 0.98+/-0.01, 0.88 +/- 0.09, 0.94 +/- 0.05 and 0.94 +/- 0.07 for the CTV, and 0.99 +/-0.01, 0.99 +/- 0.03, 0.98 +/- 0.02 and 1.00 +/- 0.01 for the ITV, respectively. There was minimal dependence on period or initial phase. For typical tumor geometries and respiratory amplitudes, changes in target coverage are minimal but can be significant for larger amplitudes, faster beam delivery, more highly-modulated fields, and smaller field margins.

Evaluation of respiration-correlated digital tomosynthesis in lung.

Digital tomosynthesis (DTS) with a linear accelerator-mounted imaging system provides a means of reconstructing tomographic images from radiographic projections over a limited gantry arc, thus requiring only a few seconds to acquire. Its application in the thorax, however, often results in blurred images from respiration-induced motion. This work evaluates the feasibility of respiration-correlated (RC) DTS for soft-tissue visualization and patient positioning. Image data acquired with a gantry-mounted kilovoltage imaging system while recording respiration were retrospectively analyzed from patients receiving radiotherapy for non-small-cell lung carcinoma. Projection images spanning an approximately 30 degrees gantry arc were sorted into four respiration phase bins prior to DTS reconstruction, which uses a backprojection, followed by a procedure to suppress structures above and below the reconstruction plane of interest. The DTS images were reconstructed in planes at different depths through the patient and normal to a user-selected angle close to the center of the arc. The localization accuracy of RC-DTS was assessed via a comparison with CBCT. Evaluation of RC-DTS in eight tumors shows visible reduction in image blur caused by the respiratory motion. It also allows the visualization of tumor motion extent. The best image quality is achieved at the end-exhalation phase of the respiratory motion. Comparison of RC-DTS with respiration-correlated cone-beam CT in determining tumor position, motion extent and displacement between treatment sessions shows agreement in most cases within 2-3 mm, comparable in magnitude to the intraobserver repeatability of the measurement. These results suggest the method's applicability for soft-tissue image guidance in lung, but must be confirmed with further studies in larger numbers of patients.

Accurate positioning for head and neck cancer patients using 2D and 3D image guidance.

Our goal is to determine an optimized image-guided setup by comparing setup errors determined by two-dimensional (2D) and three-dimensional (3D) image guidance for head and neck cancer (HNC) patients immobilized by customized thermoplastic masks. Nine patients received weekly imaging sessions, for a total of 54, throughout treatment. Patients were first set up by matching lasers to surface marks (initial) and then translationally corrected using manual registration of orthogonal kilovoltage (kV) radiographs with DRRs (2D-2D) on bony anatomy. A kV cone beam CT (kVCBCT) was acquired and manually registered to the simulation CT using only translations (3D-3D) on the same bony anatomy to determine further translational corrections. After treatment, a second set of kVCBCT was acquired to assess intrafractional motion. Averaged over all sessions, 2D-2D registration led to translational corrections from initial setup of 3.5 ± 2.2 (range 0-8) mm. The addition of 3D-3D registration resulted in only small incremental adjustment (0.8 ± 1.5 mm). We retrospectively calculated patient setup rotation errors using an automatic rigid-body algorithm with 6 degrees of freedom (DoF) on regions of interest (ROI) of in-field bony anatomy (mainly the C2 vertebral body). Small rotations were determined for most of the imaging sessions; however, occasionally rotations > 3° were observed. The calculated intrafractional motion with automatic registration was < 3.5 mm for eight patients, and < 2° for all patients. We conclude that daily manual 2D-2D registration on radiographs reduces positioning errors for mask-immobilized HNC patients in most cases, and is easily implemented. 3D-3D registration adds little improvement over 2D-2D registration without correcting rotational errors. We also conclude that thermoplastic masks are effective for patient immobilization.

The effect of significant tumor reduction on the dose distribution in intensity modulated radiation therapy for head-and-neck cancer: a case study.

We present a unique case in which a patient with significant tissue loss was monitored for dosimetric changes using weekly cone beam computed tomography (CBCT) scans. A previously treated nasopharynx patient presented with a large, exophytic, recurrent left neck mass. The patient underwent re-irradiation to 70 Gy using intensity modulated radiation therapy (IMRT) with shielding blocks over the spinal cord and brain stem. Weekly CBCT scans were acquired during treatment. Target contours and treatment fields were then transferred from the original treatment planning computed tomography (CT) to the CBCT scans and dose calculations were performed on all CBCT scans and compared to the planning doses. In addition, a "research" treatment plan was created that assumed the patient had not been previously treated, and the above analysis was repeated. Finally, to remove the effects of setup error, the outer contours of 2 CBCT scans with significant tumor reductions were transferred to the planning scan and dose in the planning scan was recalculated. Planning treatment volume (PTV) decreased 45% during treatment. Spinal cord D05 differed from the planned value by 3.5 +/- 9.8% (average + standard deviation). Mean dose to the oral cavity and D05 of the mandible differed from the planned value by 0.9 +/- 2.1% and 0.6 +/- 1.5%, respectively. Results for the research plan were comparable. Target coverage did not change appreciably (-0.2 +/- 2.5%). When the planning scan was recalculated with the reduced outer contour from the CBCT, spinal cord D05 decreased slightly due to the reduction in scattered dose. Weekly imaging provided us the unique opportunity to use different methods to examine the dosimetric effects of an unusually large loss of tissue. We did not see that tissue loss alone resulted in a significant effect on the dose delivered to the spinal cord for this case, as most fluctuation was due to setup error. In the IGRT era, delivered dose distributions can be more readily determined during treatment, and this information can be useful in deciding whether replanning is necessary.

Implanted cardiac defibrillator care in radiation oncology patient population.

PURPOSE: To review the experience of a large cancer center with radiotherapy (RT) patients bearing implantable cardiac defibrillators (ICDs) to propose some preliminary care guidelines as we learn more about the devices and their interaction with the therapeutic radiation environment. METHODS AND MATERIALS: We collected data on patients with implanted ICDs treated with RT during a 2.5-year period at any of the five Memorial Sloan-Kettering clinical campuses. Information regarding the model, location, and dose detected from the device, as well as the treatment fields, fraction size, and treatment energy was collected. During this time, a new management policy for these patients had been implemented requiring treatment with low-energy beams (6 MV) and close surveillance of the patients in partnership with their electrophysiologist, as they received RT. RESULTS: During the study period, 33 patients were treated with an ICD in place. One patient experienced a default of the device to its initial factory setting that was detected by the patient hearing an auditory signal from the device. This patient had initially been treated with a 15-MV beam. After this episode, his treatment was replanned to be completed with 6-MV photons, and he experienced no further events. CONCLUSION: Patients with ICDs and other implanted computer-controlled devices will be encountered more frequently in the RT department, and proper management is important. We present a policy for the safe treatment of these patients in the radiation oncology environment.

New technologies in radiation therapy: ensuring patient safety, radiation safety and regulatory issues in radiation oncology.

New technologies such as intensity modulated and image guided radiation therapy, computer controlled linear accelerators, record and verify systems, electronic charts, and digital imaging have revolutionized radiation therapy over the past 10-15 y. Quality assurance (QA) as historically practiced and as recommended in reports such as American Association of Physicists in Medicine Task Groups 40 and 53 needs to be updated to address the increasing complexity and computerization of radiotherapy equipment, and the increased quantity of data defining a treatment plan and treatment delivery. While new technology has reduced the probability of many types of medical events, seeing new types of errors caused by improper use of new technology, communication failures between computers, corrupted or erroneous computer data files, and "software bugs" are now being seen. The increased use of computed tomography, magnetic resonance, and positron emission tomography imaging has become routine for many types of radiotherapy treatment planning, and QA for imaging modalities is beyond the expertise of most radiotherapy physicists. Errors in radiotherapy rarely result solely from hardware failures. More commonly they are a combination of computer and human errors. The increased use of radiosurgery, hypofractionation, more complex intensity modulated treatment plans, image guided radiation therapy, and increasing financial pressures to treat more patients in less time will continue to fuel this reliance on high technology and complex computer software. Clinical practitioners and regulatory agencies are beginning to realize that QA for new technologies is a major challenge and poses dangers different in nature than what are historically familiar.

Comparison of kilovoltage cone-beam computed tomography with megavoltage projection pairs for paraspinal radiosurgery patient alignment and position verification.

PURPOSE: Implanted gold markers and megavoltage (MV) portal imaging are commonly used for setup verification of paraspinal tumors treated with high-dose, single-fraction radiotherapy. We investigated whether the use of kilovoltage cone-beam computed tomography (CBCT) imaging eliminates the need for marker implantation. METHODS AND MATERIALS: Patients with paraspinal disease who were eligible for single-fraction stereotactic body radiotherapy were accrued to an institutional review board-approved protocol. Each of 16 patients underwent implantation of fiducial markers near the target. The markers were visible on the MV images. Three MV image pairs were acquired for each patient (initial, verification, and final) and were registered to the reference images. Every MV pair was complemented by a CBCT scan. CBCT image registration was performed automatically by maximizing the mutual information using a region of interest that excluded the markers. The corrections, as determined from the MV images, were compared with these from CBCT and were used for actual patient setup. RESULTS: The mean and standard deviation of the absolute values of the differences between the CBCT and MV corrections were 1.0 +/- 0.7, 1.0 +/- 0.6, and 1.0 +/- 0.8 mm for the left-right, anteroposterior, and superoinferior directions, respectively. The absolute differences between the corresponding pre- and post-treatment kilovoltage CBCT image registration were 0.6 +/- 0.5, 0.6 +/- 0.5, and 1.0 +/- 0.8 mm. CONCLUSION: The setup corrections found using CBCT without the use of implanted markers were consistent with the marker registration on MV projections. CBCT has additional advantages, including better positioning precision and robust automatic three-dimensional registration, as well as eliminating the need for invasive marker implantation. We have adopted CBCT for the setup of all single-fraction paraspinal patients. Our data have also demonstrated that target displacements during treatment are insignificant.

Intensity-modulated radiation therapy (IMRT) for inoperable non-small cell lung cancer: the Memorial Sloan-Kettering Cancer Center (MSKCC) experience.

INTRODUCTION: Intensity-modulated radiation therapy (IMRT) is an advanced treatment delivery technique that can improve the therapeutic dose ratio. Its use in the treatment of inoperable non-small cell lung cancer (NSCLC) has not been well studied. This report reviews our experience with IMRT for patients with inoperable NSCLC. METHODS AND MATERIALS: We performed a retrospective review of 55 patients with stage I-IIIB inoperable NSCLC treated with IMRT at our institution between 2001 and 2005. The study endpoints were toxicity, local control, and overall survival. RESULTS: With a median follow-up of 26 months, the 2-year local control and overall survival rates for stage I/II patients were 50% and 55%, respectively. For the stage III patients, 2-year local control and overall survival rates were 58% and 58%, respectively, with a median survival time of 25 months. Six patients (11%) experienced grade 3 acute pulmonary toxicity. There were no acute treatment-related deaths. Two patients (4%) had grade 3 or worse late treatment-related pulmonary toxicity. CONCLUSIONS: IMRT treatment resulted in promising outcomes for inoperable NSCLC patients.

Incidence of late rectal and urinary toxicities after three-dimensional conformal radiotherapy and intensity-modulated radiotherapy for localized prostate cancer.

PURPOSE: To report the incidence and predictors of treatment-related toxicity at 10 years after three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT) for localized prostate cancer. METHODS AND MATERIALS: Between 1988 and 2000, 1571 patients with stages T1-T3 prostate cancer were treated with 3D-CRT/IMRT with doses ranging from 66 to 81 Gy. The median follow-up was 10 years. Posttreatment toxicities were all graded according to the National Cancer Institute's Common Terminology Criteria for Adverse Events. RESULTS: The actuarial likelihood at 10 years for the development of Grade>or=2 GI toxicities was 9%. The use of IMRT significantly reduced the risk of gastrointestinal (GI) toxicities compared with patients treated with conventional 3D-CRT (13% to 5%; p<0.001). Among patients who experienced acute symptoms the 10-year incidence of late toxicity was 42%, compared with 9% for those who did not experience acute symptoms (p<0.0001). The 10-year incidence of late Grade>or=2 genitourinary (GU) toxicity was 15%. Patients treated with 81 Gy (IMRT) had a 20% incidence of GU symptoms at 10 years, compared with a 12% for patient treated to lower doses (p=0.01). Among patients who had developed acute symptoms during treatment, the incidence of late toxicity at 10 years was 35%, compared with 12% (p<0.001). The incidence of Grade 3 GI and GU toxicities was 1% and 3%, respectively. CONCLUSIONS: Serious late toxicity was unusual despite the delivery of high radiation dose levels in these patients. Higher doses were associated with increased GI and GU Grade 2 toxicities, but the risk of proctitis was significantly reduced with IMRT. Acute symptoms were a precursor of late toxicities in these patients.

Ultra-high dose (86.4 Gy) IMRT for localized prostate cancer: toxicity and biochemical outcomes.

PURPOSE: To report toxicity and preliminary biochemical outcomes with high-dose intensity-modulated radiation therapy (IMRT) to a dose of 86.4 Gy for localized prostate cancer. METHODS AND MATERIALS: Between August 1997 and March 2004, 478 patients were treated with 86.4 Gy using a 5- to 7-field IMRT technique. To adhere to normal tissue constraints, the mean D95 and V100 for the planning target volume were 83 Gy and 87%, respectively. Toxicity data were scored according to the Common Terminology Criteria for Adverse Events Version 3.0. Freedom from biochemical relapse was calculated. The median follow-up was 53 months. RESULTS: Thirty-seven patients (8%) experienced acute Grade 2 gastrointestinal (GI) toxicity. There was no acute Grade 3 or 4 GI toxicity. One hundred and five patients (22%) experienced acute Grade 2 genitourinary (GU) toxicity and three patients (0.6%) had Grade 3 GU toxicity. There was no acute Grade 4 GU toxicity. Sixteen patients (3%) developed late Grade 2 GI toxicity and two patients (<1%) developed late Grade 3 GI toxicity. Sixty patients (13%) had late Grade 2 GU toxicity and 12 (<3%) experienced late Grade 3 GU toxicity. The 5-year actuarial PSA relapse-free survival according to the nadir plus 2 ng/mL definition was 98%, 85% and 70% for the low, intermediate, and high risk NCCN prognostic groups. CONCLUSION: This report represents the largest data set of patients treated to ultra-high radiation dose levels of 86.4 Gy using IMRT for localized prostate cancer. Our findings indicate that this treatment is well tolerated and the early excellent biochemical control rates are encouraging.

Radiation therapy of large intact breasts using a beam spoiler or photons with mixed energies.

Radiation treatment of large intact breasts with separations of more than 24 cm is typically performed using x-rays with energies of 10 MV and higher, to eliminate high-dose regions in tissue. The disadvantage of the higher energy beams is the reduced dose to superficial tissue in the buildup region. We evaluated 2 methods of avoiding this underdosage: (1) a beam spoiler: 1.7-cm-thick Lucite plate positioned in the blocking tray 35 cm from the isocenter, with 15-MV x-rays; and (2) combining 6- and 15-MV x-rays through the same portal. For the beam with the spoiler, we measured the dose distribution for normal and oblique incidence using a film and ion chamber in polystyrene, as well as a scanning diode in a water tank. In the mixed-energy approach, we calculated the dose distributions in the buildup region for different proportions of 6- and 15-MV beams. The dose enhancement due to the beam spoiler exhibited significant dependence upon the source-to-skin distance (SSD), field size, and the angle of incidence. In the center of a 20 x 20-cm(2) field at 90-cm SSD, the beam spoiler raises the dose at 5-mm depth from 77% to 87% of the prescription, while maintaining the skin dose below 57%. Comparison of calculated dose with measurements suggested a practical way of treatment planning with the spoiler--usage of 2-mm "beam" bolus--a special option offered by in-house treatment planning system. A second method of increasing buildup doses is to mix 6- and 15-MV beams. For example, in the case of a parallel-opposed irradiation of a 27-cm-thick phantom, dose to D(max) for each energy, with respect to midplane, is 114% for pure 6-, 107% for 15-MV beam with the spoiler, and 108% for a 3:1 mixture of 15- and 6-MV beams. Both methods are practical for radiation therapy of large intact breasts.