Multi-planner validation of RapidPlan knowledge-based model for volumetric modulated arc therapy in prostate cancer.

PURPOSE: To investigate the performance of a model-based optimization process for volumetric modulated arc therapy (VMAT) applied to prostate cancer patients with the multi-planner. METHODS AND MATERIALS: The 120 prostate plans for VMAT treatment were entered into the database system of the RapidPlan (RP) knowledge-based treatment planning. The treatment planning data for each plan was used to create and train the RP model. Twelve prostate cancer cases were selected and were used for planning by a manual of 12 planners based on the clinical protocol for dose constraints. Then, the treatment plans for each patient were compared with the RP model plans and analyzed with Wilcoxon tests. RESULTS: On average, the RP models can estimate comparable doses among all planner plans and clinical plans for the PTV, which Dmax , D95% , D98% , HI, and CI were used to evaluate. For the normal organ doses of the bladder, rectum, penile bulb, and femoral head, all RP model plans showed comparable or better dose sparing than all planner plans and clinical plans. Moreover, the average planning time of the RP model was faster than manual plans by about two times. The RP model can significantly reduce the variation dose of the normal organs compared with the manual plans among the planners. CONCLUSION: The automated plans of the RP model might benefit from further fine-tuning of the dose constraints of the normal organs, although both procedure plans are acceptable and fulfill the clinical protocol goals so that the RP model can enhance the efficacy and quality of plans.

Dosimetric Comparison between Single-energy Computed Tomography and Dual-energy Computed Tomography Relative to Stopping Power Estimation in Proton Therapy.

Purpose: The focus of this work was given on the relative stopping power (RSP) using the water equivalent thickness (WET) validation on tissue substitutes and real pig organs, as well as a dosimetric comparison of proton treatment plans between single-energy computed tomography (SECT) and dual-energy computed tomography (DECT)-based dose calculations. Materials and Methods: The CT calibration curve of SECT and DECT data was generated using the stoichiometric calibration method. WET measurement was performed for RSP validation using a Giraffe dosimeter (IBA dosimetry) in various substitute tissues (Gammex) and real pig tissues. The thorax (008A, CIRS) and head (731-HN, CIRS) phantoms were used to generate proton plans. The dosimetric evaluations of SECT and DECT-based plans were performed using the gamma analysis with 1%/1 mm and the dose-volume histograms (DVHs) comparison. Results: For RSP validation of substitute tissues, the largest percent WET difference between measurement and calculation was observed up to 17.9% (4 mm) in lung tissue, using SECT based. In real pig tissues, the average WET difference was 2.3% ± 2.1% and 2.5% ± 2.3% for SECT and DECT, respectively. The average gamma passed of about 92.1% for the lung and 96.8% for the head regions was reported. For the lung region, the DVH of the target dose was observed with a higher predicted dose in SECT than in DECT, while results in the head region were in good agreement for both SECT and DECT. Conclusion: The performed dosimetric comparison indicates the dose differences between SECT and DECT. The impact of the CT calibration curve is more pronounced for the thorax region.

Measurement of Ambient Dose Equivalent in Compact Proton Therapy using In-house Neutron Moderator-based Poly Allyl Diglycol Carbonate.

Purpose: The high-energy proton produces the unwanted dose contribution from the secondary neutron. The main purpose of this study is to report the validation results of in-house neutron moderator based on poly allyl diglycol carbonate (CR-39) detector, Chulalongkorn University Neutron Moderator (CUMOD) through the ambient dose equivalent, H*(10) measurement. Materials and Methods: The Particle and Heavy Ion Transport code System (PHITS) Monte Carlo code was used to simulate the neutron response function. The CUMOD was calibrated with 241AmBe source calibrator in the range of 100-1000 µSv. The variation of neutron fields was generated employing different proton treatment plans covering most of the clinical scenarios. The ambient dose equivalents, H*(10), evaluated employing CUMOD were compared to those obtained with WENDI-II dosimeter. Results: The linear relationship between CUMOD and WENDI-II responses showed an R2 value close to 1. The H*(10) per Gy delivered dose was in the range of 22-105 µSv for a 10 cm × 10 cm field. Conclusion: The in-house CUMOD neutron moderator can expand the neutron detection dose range of CR-39 detector for ambient dose equivalent. The advantage of CUMODs is its capability to evaluate H*(10) in various positions simultaneously.

Impact of Dosimetric Parameters on Interplay Effects in 6 MV Flattening Filter-Free Photon Beams to Treat Lung Cancer.

Context: Interplay effects have become the significant problem in lung cancer radiotherapy. Since these effects yield dose variation within the target and surrounding tissues. Aim: The aim of this study is to investigate the effect of the dosimetric parameters of interplay effects in 6 MV flattening filter-free (FFF) photon beams for lung cancer. Settings and Design: This study performed planning, measurement, and data analysis sections for examining different breathing amplitudes and phases, doses, dose rates, field sizes, and fractionations. Subjects and Methods: Standard and clinical plans were created on the eclipse treatment planning system. The static and dynamic measurements were performed using a robotic platform and two-dimensional (2D) diode array. The gamma passing rates were defined as the percent of dose variation caused by the interplay effects. Statistical Analysis Used: Unpaired t-test. Results: The outcomes showed three trends between gamma passing rates (γ) and dosimetric parameters. First, a decreasing trend was breathing amplitudes. The lowest γ of maximum amplitudes (2 cm) in both one dimensional and 2D were <25%. Second, an increasing trend was field sizes. The lowest γ of minimum field size (4 cm × 4 cm2) was <55%. Third, constant outcomes were breathing phases, doses, dose rates, and a number of fractions. The γ values of these factors were 53.1%, 55.1%, 34.7%, and 36.7%, respectively. Conclusions: Lung tumor motion-induced interplay effects in 6 MV FFF photon beams are more pronounced for higher breathing amplitudes and smaller field sizes.

Development and dosimetric verification of 3D customized bolus in head and neck radiotherapy.

The commercial flat bolus cannot form perfect contact with the irregular surface of the patient's skin, resulting in an air gap. The purpose of this study was to evaluate the feasibility of using a 3D customized bolus from silicone rubber. The silicone rubber boluses were studied in basic characteristics. The 3D customized bolus was fabricated at the nose, cheek and neck regions. The point dose and planar dose differences were evaluated by comparing with virtual bolus. The hardness, thickness, density, Hounsfield unit (HU) and dose attenuation of the customized bolus were quite similar to a commercial bolus. When a 3D customized bolus was placed on the RANDO phantom, it can significantly increase buildup region doses and perfectly fit against the irregular surface shape. The average point dose differences of 3D customized bolus were -1.1%, while the commercial bolus plans showed -1.7%. The average gamma results for planar dose differences comparison of 3D customized bolus were 93.9%, while the commercial bolus plans were reduced to 91.9%. Overall, A silicone rubber bolus produced the feasible dosimetric properties and could save cost compared to a commercial bolus. The 3D printed customized bolus is a good buildup material and could potentially replace and improve treatment efficiency.

Validation of RapidPlan Knowledge-Based Model for Volumetric-Modulated Arc Therapy in Prostate Cancer.

Aims and Objectives: This study aims to investigate the viability of using RapidPlan (RP) knowledge-based (KB) treatment plans to initiate the new prostate volumetric-modulated arc therapy (VMAT) plans. Materials and Methods: The planning data for 120 prostate VMAT treatment plans were entered into the RP system's database. The database of previous VMAT plans was divided into four model groups for training in the RP system. The models were based on the numbers of 20, 60, and 120 prostate VMAT plans. The model of 120 plans used automated priority and manual priority for the optimization process. The models of 20 and 60 plans used only manual priority for optimization. Each model was validated on 15 cases of new prostate cancer patients by comparing RP model plans against manual clinical plans optimized according to the clinical dose constraints. Results: The RP models can estimate the dose comparable target volume to the manual clinical plan, which evaluated values of Dmax, D95%, D98%, HI, and CI and showed comparable results. For the normal organ doses of the bladder, rectum, penile bulb, and femoral head, all RP models exhibited a comparable or better dose than the manual clinical plan, except for the RP models using the automated priority for the optimization process, which cannot control the rectum dose below the dose constraints. Conclusions: The Varian RP KB planning can produce comparable doses or better doses with the clinical manual in a single optimization, although the RP model uses a minimum requirement of the planning number for the model training. The RP models can enhance the efficacy and quality of plans, which depend on the number of VMAT plans used in RP model training for prostate cancer.

Determination of field output correction factors of radiophotoluminescence glass dosimeter and CC01 ionization chamber and validation against IAEA-AAPM TRS-483 code of practice.

PURPOSE: To determine the field output correction factors of the radiophotoluminescence glass dosimeter (RPLGD) in parallel and perpendicular orientations with reference to CC01, the ionization chamber. METHODS: The dose to a small water volume and the sensitive volume of the RPLGD and the IBA-CC01 were determined for 6-MV, 100-cm SAD, 10-cm depth using egs_chamber user-code. The RPLGD in perpendicular and parallel orientations to the beam axis were studied. The field output correction factors of each detector for 0.5 × 0.5 to 10 × 10 cm2 field sizes were determined. These field output correction factors were validated by comparing field output factors against data determined from IAEA-AAPM TRS-483 code of practice. RESULTS: The field output correction factors of all detectors were within 5% for field sizes down to 0.8 × 0.8 cm2. For 0.5 × 0.5 cm2, the field output correction factors of CC01, RPLGD in perpendicular and parallel orientations differed from unity by 14%, 19%, and 5%, respectively. The percentage difference between field output factors determined using RPLGD and CC01 data, corrected using the field output correction factors determined in this work and measurements with CC01 data corrected using TRS-483, was less than 3% for all field sizes, except for the smallest field size of RPLGD in perpendicular orientation and the CC01. CONCLUSIONS: The field output correction factors of RPLGD and CC01 are reported. The validation proves that RPLGD in parallel orientation combined with the field output correction factors is the most suitable for determining the field output factors for the smallest field used in this study.

The impact of corrected field output factors based on IAEA/AAPM code of practice on small-field dosimetry to the calculated monitor unit in eclipse™ treatment planning system.

The objective of this study was to investigate the effect of field output factors (FOFs) according to the current protocol for small-field dosimetry in conjunction to treatment planning system (TPS) commissioning. The calculated monitor unit (MU) for intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans in Eclipse™ TPS were observed. Micro ion chamber (0.01 CC) (CC01), photon field diode (shielded diode) (PFD), and electron field diode (unshielded diode) (EFD) were used to measure percentage depth doses, beam profiles, and FOFs from 1 × 1 cm2 to 10 × 10 cm2 field sizes of 6 MV photon beams. CC01 illustrated the highest percentage depth doses at 10 cm depth while EFD exhibited the lowest with the difference of 1.6% at 1 × 1 cm2 . CC01 also produced slightly broader penumbra, the difference with other detectors was within 1 mm. For uncorrected FOF of three detectors, the maximum percent standard deviation (%SD) was 5.4% at 1 × 1 cm2 field size. When the correction factors were applied, this value dropped to 2.7%. For the calculated MU in symmetric field sizes, beam commissioning group from uncorrected FOF demonstrated maximum %SD of 6.0% at 1 × 1 cm2 field size. This value decreased to 2.2% when the corrected FOF was integrated. For the calculated MU in IMRT-SRS plans, the impact of corrected FOF reduced the maximum %SD from 6.0% to 2.5% in planning target volume (PTV) less than 0.5 cm3 . Beam commissioning using corrected FOF also decreased %SD for VMAT-SRS plans, although it was less pronounced in comparison to other treatment planning techniques, since the %SD remained less than 2%. The use of FOFs based on IAEA/AAPM TRS 483 has been proven in this research to reduce the discrepancy of calculated MU among three beam commissioning datasets in Eclipse™ TPS. The dose measurement of both symmetric field and clinical cases comparing to the calculation illustrated the dependence of the types of detector commissioning and the algorithm of the treatment planning for small field size.

Multi-institutional evaluation using the end-to-end test for implementation of dynamic techniques of radiation therapy in Thailand.

AIM: In this study, an accuracy survey of intensity-modulated radiation therapy (IMRT) and volumetric arc radiation therapy (VMAT) implementation in radiotherapy centers in Thailand was conducted. BACKGROUND: It is well recognized that there is a need for radiotherapy centers to evaluate the accuracy levels of their current practices, and use the related information to identify opportunities for future development. MATERIALS AND METHODS: An end-to-end test using a CIRS thorax phantom was carried out at 8 participating centers. Based on each center's protocol for simulation and planning, linac-based IMRT or VMAT plans were generated following the IAEA (CRP E24017) guidelines. Point doses in the region of PTVs and OARs were obtained from 5 ionization chamber readings and the dose distribution from the radiochromic films. The global gamma indices of the measurement doses and the treatment planning system calculation doses were compared. RESULTS: The large majority of the RT centers (6/8) fulfilled the dosimetric goals, with the measured and calculated doses at the specification points agreeing within ±3% for PTV and ±5% for OARS. At 2 centers, TPS underestimated the lung doses by about 6% and spinal cord doses by 8%. The mean percentage gamma pass rates for the 8 centers were 98.29 ± 0.67% (for the 3%/3 mm criterion) and 96.72 ± 0.84% (for the 2%/2 mm criterion). CONCLUSIONS: The 8 participating RT centers achieved a satisfactory quality level of IMRT/VMAT clinical implementation.

Accuracy of eight deformable image registration (DIR) methods for tomotherapy megavoltage computed tomography (MVCT) images.

INTRODUCTION: The application of deformable image registration (DIR) to megavoltage computed tomography (MVCT) images benefits adaptive radiotherapy. This study aims to quantify the accuracy of DIR for MVCT images when using different deformation methods assessed in a cubic phantom and nasopharyngeal carcinoma (NPC) patients. METHODS: In the control studies, the DIR accuracy in air-tissue and tissue-tissue interface areas was observed using twelve shapes of acrylic and tissue-equivalent material inserted in the phantom. In the clinical studies, the 1st and 20th fraction MVCT images of seven NPC patients were used to evaluate application of DIR. The eight DIR methods used in the DIRART software varied in (i) transformation framework (asymmetric or symmetric), (ii) DIR registration algorithm (Demons or Optical Flow) and (iii) mapping direction (forward or backward). The accuracy of the methods was compared using an intensity-based criterion (correlation coefficient, CC) and volume-based criterion (Dice's similarity coefficient, DSC). RESULTS: The asymmetric transformation with Optical Flow showed the best performance for air-tissue interface areas, with a mean CC and DSC of 0.97 ± 0.03 and 0.79 ± 0.11 respectively. The symmetric transformation with Optical Flow showed good agreement for tissue-tissue interface areas with a CC of (0.99 ± 0.01) and DSC of (0.89 ± 0.03). The sequences of target domains were significantly different in tissue-tissue interface areas. CONCLUSIONS: The deformation method and interface area affected the accuracy of DIR. The validation techniques showed satisfactory volume matching of greater than 0.7 with DSC analysis. The methods can yield acceptable results for clinical applications.

Evaluation of Deformable Image Registration (DIR) Methods for Dose Accumulation in Nasopharyngeal Cancer Patients during Radiotherapy.

INTRODUCTION: Deformable image registration (DIR) is used to modify structures according to anatomical changes for observing the dosimetric effect. In this study, megavoltage computed tomography (MVCT) images were used to generate cumulative doses for nasopharyngeal cancer (NPC) patients by various DIR methods. The performance of the multiple DIR methods was analysed, and the impact of dose accumulation was assessed. PATIENTS AND METHODS: The study consisted of five NPC patients treated with a helical tomotherapy unit. The weekly MVCT images at the 1st, 6th, 11th, 16th, 21st, 26th, and 31st fractions were used to assess the dose accumulation by the four DIR methods. The cumulative dose deviations from the initial treatment plan were analysed, and correlations of these variations with the anatomic changes and DIR methods were explored. RESULTS: The target dose received a slightly different result from the initial plan at the end of the treatment. The organ dose differences increased as the treatment progressed to 6.8% (range: 2.2 to 10.9%), 15.2% (range: -1.7 to 36.3%), and 6.4% (range: -1.6 to 13.2%) for the right parotid, the left parotid, and the spinal cord, respectively. The mean uncertainty values to estimate the accumulated doses for all the DIR methods were 0.21 ± 0.11 Gy (target dose), 1.99 ± 0.76 Gy (right parotid), 1.19 ± 0.24 Gy (left parotid), and 0.41 ± 0.04 Gy (spinal cord). CONCLUSIONS: Accuracy of the DIR methods affects the estimation of dose accumulation on both the target dose and the organ dose. The DIR methods provide an adequate dose estimation technique for observation as a result of inter-fractional anatomic changes and are beneficial for adaptive treatment strategies.

A method of setting limits for the purpose of quality assurance.

The result from any assurance measurement needs to be checked against some limits for acceptability. There are two types of limits; those that define clinical acceptability (action limits) and those that are meant to serve as a warning that the measurement is close to the action limits (tolerance limits). Currently, there is no standard procedure to set these limits. In this work, we propose an operational procedure to set tolerance limits and action limits. The approach to establish the limits is based on techniques of quality engineering using control charts and a process capability index. The method is different for tolerance limits and action limits with action limits being categorized into those that are specified and unspecified. The procedure is to first ensure process control using the I-MR control charts. Then, the tolerance limits are set equal to the control chart limits on the I chart. Action limits are determined using the Cpm process capability index with the requirements that the process must be in-control. The limits from the proposed procedure are compared to an existing or conventional method. Four examples are investigated: two of volumetric modulated arc therapy (VMAT) point dose quality assurance (QA) and two of routine linear accelerator output QA. The tolerance limits range from about 6% larger to 9% smaller than conventional action limits for VMAT QA cases. For the linac output QA, tolerance limits are about 60% smaller than conventional action limits. The operational procedure describe in this work is based on established quality management tools and will provide a systematic guide to set up tolerance and action limits for different equipment and processes.

Retrospective analysis of linear accelerator output constancy checks using process control techniques.

Shewhart control charts have previously been suggested as a process control tool for use in routine linear accelerator (linac) output verifications. However, a comprehensive approach to process control has not been investigated for linac output verifications. The purpose of this work is to investigate a comprehensive process control approach to linac output constancy quality assurance (QA). The RBA-3 dose constancy check was used to verify outputs of photon beams and electron beams delivered by a Varian Clinac 21EX linac. The data were collected during 2009 to 2010. Shewhart-type control charts, exponentially weighted moving average (EWMA) charts, and capability indices were applied to these processes. The Shewhart-type individuals chart (X-chart) was used and the number of data points used to calculate the control limits was varied. The parameters tested for the EWMA charts (smoothing parameter (λ) and the control limit width (L)) were λ = 0.05, L = 2.492; λ = 0.10, L = 2.703; and λ = 0.20, L = 2.860, as well as the number of points used to estimate the initial process mean and variation. Lastly, the number of in-control data points used to determine process capability (C(p)) and acceptability (C(pk)) were investigated, comparing the first in-control run to the longest in-control run of the process data. C(p) and C(pk) values greater than 1.0 were considered acceptable. The 95% confidence intervals were reported. The X-charts detected systematic errors (e.g., device setup errors). In-control run lengths on the X-charts varied from 5 to 30 output measurements (about one to seven months). EWMA charts showed in-control runs ranging from 9 to 33 output measurements (about two to eight months). The C(p) and C(pk) ratios are higher than 1.0 for all energies, except 12 and 20 MeV. However, 10 MV and 6, 9, and 16 MeV were in question when considering the 95% confidence limits. The X-chart should be calculated using 8-12 data points. For EWMA chart, using 4 data points is sufficient to calculate the initial mean and variance of the process. The EWMA limits should be calculated with λ = 0.10, L = 2.703. At least 25-30 in-control data points should be used to calculate the C(p) and C(pk) indices.

Statistical process control analysis for patient-specific IMRT and VMAT QA.

This work applied statistical process control to establish the control limits of the % gamma pass of patient-specific intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) quality assurance (QA), and to evaluate the efficiency of the QA process by using the process capability index (Cpml). A total of 278 IMRT QA plans in nasopharyngeal carcinoma were measured with MapCHECK, while 159 VMAT QA plans were undertaken with ArcCHECK. Six megavolts with nine fields were used for the IMRT plan and 2.5 arcs were used to generate the VMAT plans. The gamma (3%/3 mm) criteria were used to evaluate the QA plans. The % gamma passes were plotted on a control chart. The first 50 data points were employed to calculate the control limits. The Cpml was calculated to evaluate the capability of the IMRT/VMAT QA process. The results showed higher systematic errors in IMRT QA than VMAT QA due to the more complicated setup used in IMRT QA. The variation of random errors was also larger in IMRT QA than VMAT QA because the VMAT plan has more continuity of dose distribution. The average % gamma pass was 93.7% ± 3.7% for IMRT and 96.7% ± 2.2% for VMAT. The Cpml value of IMRT QA was 1.60 and VMAT QA was 1.99, which implied that the VMAT QA process was more accurate than the IMRT QA process. Our lower control limit for % gamma pass of IMRT is 85.0%, while the limit for VMAT is 90%. Both the IMRT and VMAT QA processes are good quality because Cpml values are higher than 1.0.

Dosimetric study of inverse-planed intensity modulated, forward-planned intensity modulated and conventional tangential techniques in breast conserving radiotherapy.

OBJECTIVE: The authors present the result of a dosimetric comparison of inverse-planed intensity modulated, forward-planned intensity modulated, and conventional tangential technique in breast conserving radiotherapy. METHOD AND MATERIAL: The breasts (Right side: Left side = 1:1), heart, and lungs of 28 patients were contoured on all the computed tomography (CT)-slice. Three different treatment plans were created: (1) inverse IMRT (iIMRT), (2) forward IMRT (fIMRT), and (3) conventional tangential technique (CVT). The total prescribed dose for all plans was 50 Gy/25 fractions. All treatment plans were normalized at 95% of the prescribed dose covered the entire PTV and used inhomogeneity corrections. RESULTS: For the entire group, the mean breast volume was 517 cc. The V105% for iIMRT, fIMRT and conventional plans was 1.12%, 2.36% and 16.81%, which iIMRT better than fIMRT and CVT (p < 0.001) and fIMRT better than CVT (p < 0.05). The Dmax for the iIMRT plan received 105.03%, which was significantly less than those from the fIMRT(106.6%, p < 0.001) and the conventional (110.68%, p < 0.001) plan. The PTV coverage (V95-105%) for the iIMRT, fIMRTand conventional was 96%, 91% and 87%, which iIMRT better than fIMRT and CVT (p < 0.05) and fIMRT better than CVT (p < 0.05). The PTV CI for the iIMRT technique was 0.704, which was significantly more conformity than those from the fIMRT (0.639, p < 0.001) and the conventional (0.539, p < 0.001) techniques. The PTV CI of fIMRT is significantly better than CVT (p < 0.005). Mean ipsilateral lung dose was 642.7 cGy, 747.6 cGy and 882.25 cGy for iIMRT fIMRT and CVT respectively (p < 0.05) The V20Gy reduced from 14.87% for conventional plan to 12.82% for the fIMRT plan, while 0.88% was obtained for the iIMRT plan (P<0.05). The heart V30 Gy value was 3.124%, 4.65%, and 5.84% for iIMRT, fIMRT and conventional plans, respectively (p < 0.05). The mean dose of contralateral breast was 55.86 cGy, 60.33 cGy, 68.57 cGy for iIMRT, fIMRT and conventional plans, respectively (p < 0.05 both). The mean contralateral lung dose was 57.8 cGy, 43.87 cGy, and 32.28 cGy for iIMRT, fIMRT and conventional plans, respectively (p < 0.005 both). CONCLUSION: The iIMRT technique provides significantly improved PTV Dmax, PTV V105%, PTV V110%, target volume coverage, dose homogeneity and dose conformity throughout the target volume of breast and reduced doses to all critical structures, compared to the fIMRT and conventional techniques. In view of fIMRT technique, it significantly improved the dose distribution and reduced dose to OARs compared to conventional technique, although not better than iIMRT technique.

LINE-1 methylation status of endogenous DNA double-strand breaks.

DNA methylation and the repair of DNA double-strand breaks (DSBs) are important processes for maintaining genomic integrity. Although DSBs can be produced by numerous agents, they also occur spontaneously as endogenous DSBs (EDSBs). In this study, we evaluated the methylation status of EDSBs to determine if there is a connection between DNA methylation and EDSBs. We utilized interspersed repetitive sequence polymerase chain reaction (PCR), ligation-mediated PCR and combined bisulfite restriction analysis to examine the extent of EDSBs and methylation at long interspersed nuclear element-1 (LINE-1) sequences nearby EDSBs. We tested normal white blood cells and several cell lines derived from epithelial cancers and leukemias. Significant levels of EDSBs were detectable in all cell types. EDSBs were also found in both replicating and non-replicating cells. We found that EDSBs contain higher levels of methylation than the cellular genome. This hypermethylation is replication independent and the methylation was present in the genome at the location prior to the DNA DSB. The differences in methylation levels between EDSBs and the rest of the genome suggests that EDSBs are differentially processed, by production, end-modification, or repair, depending on the DNA methylation status.

A two-year experience of implementing 3 dimensional radiation therapy and intensity-modulated radiation therapy for 925 patients in King Chulalongkorn Memorial Hospital.

BACKGROUND AND OBJECTIVE: Three dimensional conformal radiation therapy (3D CRT) and intensity-modulated radiation therapy (IMRT) have been implemented at Department of Therapeutic Radiation and Oncology, King Chulalongkorn Memorial Hospital (KCMH) since July 2005. This is the first study in Thailand to evaluate the pattern of care and utilization of 3D CRT and IMRT for treatment in each individual cancer. MATERIAL AND METHOD: Between July 2005 and July 2007, 925 newly diagnosed cancer patients underwent IMRT or 3D CRT at KCMH. The authors retrospectively reviewed the experience and utilization of 3D CRT and IMRT for each disease site and region. RESULTS: There were 471 males and 454 females. There were 332 patients (35.9%) treated with IMRT. Among the 332 IMRT patients, there were 100, 32 and 27 nasopharyngeal, lung and prostate cancers, respectively. On the contrary, 593 patients (64.1%) were treated with 3D CRT. Among these, breast, cervix and lung cancers were the most common diseases. Except for head and neck as well as genitourinary cancer 3D CRT was still the main technique used in more than 60% of the patients at KCMH. CONCLUSION: 3D CRT and IMRT have been successfully implemented at KCMH for 2 years. Three dimensional conformal radiation therapy was still the main technique used in more than 60% of the patients at KCMH. Prospective studies evaluating tumor control and treatment sequelae are expected.

Radiation dose to medical staff in interventional radiology.

OBJECTIVE: The purposes of the present study were to determine the dose to medical staff in interventional radiology at different locations on the body measured by thermoluminescent dosimeter (TLD) and to relate the medical staff dose to patient dose measured by the dose-area product (DAP) meter. MATERIAL AND METHOD: The present study covered 42 patients in three interventional radiology procedures with three x-ray machines. Thermoluminescent dosimeters were stuck at eight positions on the radiologist's skin during the procedure. In addition, direct reading from the DAP meter placed in front of the collimator of the x-ray tube, was recorded to estimate the patient radiation dose. RESULTS: The surface dose to the primary radiologist showed maximum value at the left forearm of 407 microGy. The ratios between the maximum interventional radiologist surface dose and patient dose are 12.88 microGy per 10 Gycm2 for transarterial oily chemoembolization TOCE (Siemens Polystar), 22.58 microGy per 10 Gycm2 for transarterial oily chemoembolization TOCE (Siemens Neurostar), 148.29 microGy per 10 Gycm2 for percutaneous transhepatic biliary drainage PTBD (Siemens Polystar) and 100.46 microGy per 10 Gycm2for endoscopic retrograde cholangiopancreatography ERCP (GE Advantx). CONCLUSION: The interventional radiologist surface dose can be estimated from the mentioned ratio if the patient dose is measured. This will help the radiologists to avoid receiving an excess dose during their work.

Intensity-modulated radiation therapy in head-and-neck cancer, first report in Thailand.

OBJECTIVE: This is the first report in Thailand to evaluate the efficacy of using intensity-modulated radiotherapy (IMRT) in the primary treatment of head-and-neck cancer. MATERIAL AND METHOD: From July 2005 to March 2006, eighteen patients with head and neck cancer were treated with IMRT, fourteen of which were nasopharyngeal cancer. The median age at diagnosis was 52 years (range 23-58 years). The treatment plan composed of two sequential plans for PTV-low risk (50Gy in 25 fractions) and PTV-high risk (20Gy in 10 fractions). Chemotherapy was given to 13 patients with locoregionally advanced disease (stage T3/T4 and N2/3) using cisplatin (n = 3) or carboplatin (n = 10) every 3 weeks during the course of radiation therapy. RESULTS: The median overall treatment time was 49 days (range, 43-57 days), and 77.8 percent of the patients completed 35 fractions within 50 days. The clinical complete response and partial response rates at 3 months after complete radiation were 71.4% and 28.6%, respectively. However at the median follow-up of 5.6 months, the complete response rate increased to 89%. Treatment break during RT range from 3 to 7 days, was observed in three patients. All of them received concurrent chemoradiation. No distant metastasis was noted. CONCLUSION: The authors' experience of using concurrent chemotherapy with IMRT for a cohort of patients with head and neck carcinoma showed a very high rate response rate at early follow-up. Long-term clinical outcome is expected.