GATE Monte Carlo approach to heterogeneity dose distribution in small fields used in radiation therapy.

The Accurate dosage prediction in Radiation Therapy is challenging, prompting a need for precision beyond conventional clinical Treatment Planning Systems (TPS). Monte Carlo-based methods are sought for their superior accuracy. The aim of this study is to compare dose distributions between the ACUROS algorithm and the GATE platform in various tissue densities and field sizes, focusing on smaller fields. This study was initiated with a homogeneous validation of the TrueBeam STX system, using measurements obtained from the Centre Hospitalier Interregional Edith Cavell (CHIREC) in Brussels. The validation compared dosimetric functions (Percentage Depth Dose (PDD), Dose profile (DP) and Collimator scatter fraction (CSF)) employing the GAMMA index with a 2% / 2 mm criterion tolerance. Following this, heterogeneous studies examined dose distributions between the ACUROS algorithm and the GATE platform in various tissue densities and field sizes, with a specific focus on smaller fields. Simulations were conducted using both platforms on chest phantoms with heterogeneous slabs representing bone, lung, and heart, each housing a central tumor. The impact of electronic equilibrium on tumors for different small field sizes was evaluated. Results showed a remarkable 99% agreement between measurements and GATE calculations in the homogeneous validation of the TrueBeam STX system. However, in heterogeneous studies, ACUROS consistently overestimated lung doses by up to 8% compared to GATE simulation, especially evident with a flattening filter and smaller beam sizes at density interfaces. This highlights significant dose estimation discrepancies between ACUROS and GATE, emphasizing the need for precise calculations. The findings support exploring Monte Carlo-based methods for enhanced accuracy in Radiation Therapy treatment planning.

Concomitant chemotherapy and radiation for the treatment of advanced-stage endometrial cancer.

INTRODUCTION: Ccombination chemotherapy and radiation therapy is used for adjuvant treatment of stage III-IV endometrial cancer. The goal of this study was to review the treatment duration, toxicity, and survival for patients treated with concomitant chemotherapy and radiation. METHODS: Women with stage III-IV endometrial cancer treated with concurrent chemotherapy and radiation between 2006 and 2013 were included. Toxicities were classified per CTCAE v3.0 and RTOG/EORTC late radiation morbidity scoring. Descriptive statistics were used to quantify treatment and toxicities. Kaplan-Meier method was used to estimate survival. RESULTS: Fifty-one patients met our inclusion criteria. Median age was 60 (range 33-85). Thirty-six patients (70.6%) had endometrioid histology, 13 patients (25.5%) had serous, clear cell, or mixed histology, and 2 women (3.9%) had carcinosarcoma. Forty-eight patients had stage III disease and three patients were stage IVB. Mean treatment duration was 107 ± 19 days. Forty-two patients received all planned chemotherapy, and 16 patients required a dose reduction. Thirty-four patients (66.7%) experienced grade 3-4 toxicities, the majority of which were hematologic. There were no deaths related to therapy. Eighty-six percent of patients received leukocyte growth factors, and 25% of patients received a blood transfusion. Seven late grade 3-4 complications occurred: four gastrointestinal and two genitourinary, and one patient had ongoing neuropathy. Median progression-free survival was 42.8 months (range 4.4-81.5 months) and median overall survival was 44.9 months (range 5.1-82.6 months). Three-year overall survival was 80%. CONCLUSION: Concomitant chemotherapy and radiation is an adequately tolerated treatment modality that allows for shorter treatment duration.

SU-E-T-393: Using TG119 to Assess RapidArc at Hamad Medical Corporation.

PURPOSE: To provide a confidence level within our clinic relating to the implementation and administration of RapidArc, the AAPM TG1 19 has been implemented. This task group provides a sound and relatively simple methodology for determining the accuracy of the overall IMRT process administered in the day-to-day clinicMethods: Six different test plans, of varying complexity, were created on mock structure sets, downloaded from AAPM, and delivered. The treatment planning system results were then compared with the delivered results. Plans were created and delivered on a solid water phantom, using 25×25cm water equivalent slabs of varying thicknesses. Delivered point and planar dose measurements were obtained using an ionization chamber and film, respectively. RESULTS: The confidence limit (CL), averaged for all test plans, was calculated for the high dose point in the PTV and for the low dose point in the avoidance structure. This was used as an indicator of the uncertainty of the average difference between measured and planned dose. Where the precision of the delivery is based on how small the CL value is.For both the high and low dose points, the local CL's were determined to be 0.036 and 0.011, respectively. The range of results for the CL presented in TG1 19 varies from 0.015 to 0.098 for the high dose point, and from 0.014 to 0.086 for the low dose point. CONCLUSIONS: Our results indicate the accurate implementation of RapidArc within our clinic, especially when compared to the results of other institutions, published in TG1 19. Furthermore, the CL value for the low dose measurements is lower than any of the results published in TG119. We recommend that any clinic conducting IMRT should implement this task group. This will not only provide a greater understanding of the delivery and its limitations, but will also give the overall accuracy and consistency of the technique as it applies to the various treatment sites.

SU-E-T-649: Evaluation of RapidArc- Based Stereotactic Cranial Radiotherapy Plans with MU Objective Using Multiple Non Coplanar Arcs in Comparison with Conventional Dynamic Conformal Arc Technique.

PURPOSE: Previous researches reported that RapidArc plans for stereotactic cranial radiotherapy have two to three times more MUs as compared to Conventional Dynamic Conformal Arc (DCA) Technique. This study aims to evaluate RapidArc plans using multiple non- coplanar arcs, developed with MU objective constraint in the optimization stage. METHODS: Five single brain metastasis and three multiple metastases cases previously planned using DCA techniques in BrainLab iPlan Version 4.1 were investigated in this study. For each case, the target was defined on CT-MR fused images in iPlan. The CT images and contours of these patients were exported from iPlan to Varian Eclipse TPS Version 8.6. For each case, a DCA plan and a RapidArc plan with multiple non-coplanar arcs with and without using MU objective in the optimization stage were generated using Varian Trilogy machine with Millennium 120 MLC keeping the same prescription and critical structure dose limits. All plans were evaluated according to Conformity Index (CI-modified Paddick) Homogeneity Index (HI), and the normal tissue volume receiving various dose levels (V80%, V50%, V25% and V10%). RESULTS: In all the plans, the target objectives were met and dose to OARs was within tolerance dose constraints. RapidArc plans with and without MU objective showed better CI and HI as supposed to DCA plans. V80%, V50%, V25% and V10% of normal tissue for RapidArc plans are equal or lesser than DCA plans. Single isocentre RapidArc plan for closely spaced multiple metastases cases showed better dose fall off between the lesions as supposed to DCA plans. RapidArc plans with MU objective resulted in comparable MUs as that of DCA plans. CONCLUSIONS: Our study showed RapidArc plans done with and without MU objective have no significant dosimetric difference in plan objectives. Therefore, multiple non-coplanar RapidArc plans with MU objective is clinically feasible and can provide better treatment plans than conventional DCA plans, especially for complicated cases.

SU-E-T-169: Initial Investigation into the Use of Optically Stimulated Luminescent Dosimeters (OSLDs) for In-Vivo Dosimetry of TBI Patients.

PURPOSE: To report on an initial investigation into the use of optically stimulated luminescent dosimeters (OSLDs) for in-vivo dosimetry for total body irradiation (TBI) treatments. Specifically, we report on the determination of angular dependence, sensitivity correction factors and the dose calibration factors. METHODS: The OSLD investigated in our work was InLight/OSL nanoDot dosimeters (Landauer Inc.). Nanodots are 5 mm diameter, 0.2 mm thick disk-shaped Carbon-doped Al2O3, and were read using a Landauer InLight microstar reader and associated software.OSLDs were irradiated under two setup conditions: a) typical clinical reference conditions (95cm SSD, 5cm depth in solid water, 10×10 cm field size), and b) TBI conditions (520cm SSD, 5cm depth in solid water, 40×40 cm field size,). The angular dependence was checked for angles ranging ±60 degree from normal incidence. In order to directly compare the sensitivity correction factors, a common dose was delivered to the OSLDs for the two setups. Pre- and post-irradiation readings were acquired. OSLDs were optically annealed under various techniques (1) by keeping over a film view box, (2) Using multiple scan on a flat bed optical scanner and (3) Using natural room light. RESULTS: Under reference conditions, the calculated sensitivity correction factors of the OSLDs had a SD of 2.2% and a range of 5%. Under TBI conditions, the SD increased to 3.4% and the range to 6.0%. The variation in sensitivity correction factors between individual OSLDs across the two measurement conditions was up to 10.3%. Angular dependence of less than 1% is observed. The best bleaching method we found is to keep OSLDs for more than 3 hours on a film viewer which will reduce normalized response to less than 1%. CONCLUSIONS: In order to obtain the most accurate results when using OSLDs for in-vivo dosimetry for TBI treatments, sensitivity correction factors and dose calibration factors should all be determined under clinical TBI conditions.

Significant differences between Yemenite and Egyptian STR profiles and the influence on frequency estimations in Arabs.

A population genetic study was performed on Yemenites using the set of nine short tandem repeat loci (STRs) D3S1358, VWA, FGA, D8S1179, D21S11, D18S51, D5S818, D13S317 and D7S820. Analysis of the data revealed that all loci were in Hardy-Weinberg equilibrium and evidence of linkage equilibrium was found for only 1 out of 36 locus pairs. At seven loci the allelic distributions found in the Yemenite sample were significantly different from those found for an Arab population sample from Egypt. Nevertheless, we assume that the Yemenite database can be used for Arabs of unknown or foreign (non-Yemenite) origin in the absence of population-specific databases without exerting a significant bias on the biostatistical interpretation. In an experimental set-up (ethnic profile frequency ratio test), the impact of calculating multi-locus profile frequencies for foreign Arab individuals (Egyptians) using the Yemenite database instead of a region-specific one was negligible.

Population genetic studies on the tetrameric short tandem repeat loci D3S1358, VWA, FGA, D8S1179, D21S11, D18S51, D5S818, D13S317 and D7S820 in Egypt.

The short tandem repeat loci (STRs) D3S1358, VWA, FGA, D8S1179, D21S11, D18S51, D5S818, D13S317, D7S820 and a locus allowing for sex-discrimination (amelogenin) can be co-amplified by the polymerase chain reaction using a commercially available kit (AmpFlSTR Profiler plus, Perkin-Elmer Biosystems, San Jose, CA) and subsequently typed using capillary electrophoresis (ABI Prism 310 Genetic analyzer, Perkin Elmer Applied Biosystems, San Jose CA). To establish databases for these loci for an Arab population sample from Egypt, 140 unrelated persons were typed. Analysis of these data revealed that all loci except for VWA were in Hardy-Weinberg equilibrium, that the combined mean paternity exclusion chance (MEC) was 0.999875 and that the combined discriminating power (DP) was 2.635 x 10(-11). The allelic distributions found in the Egyptian sample were significantly different at four loci from those found for an Austrian Caucasian population, at all nine loci from an African-American sample and at six of six loci from a Chinese sample. No evidence of linkage equilibrium between any of the co-amplified loci was found. Our results support that the combination of multiplex PCR and capillary electrophoresis can both save time and yield excellent results for paternity testing and stain analysis.

Genetic variation at the STR loci D12S391 and CSF1PO in four populations from Austria, Italy, Egypt and Yemen.

The short tandem repeat systems (STRs) D12S391 and CSF1P0 were amplified by the polymerase chain reaction (PCR) on blood samples from 100 to 158 unrelated Austrians, Italians, Yemenians and Egyptians. The samples were analyzed by both native and denaturing electrophoresis and two primer pairs were tested for the CSF1PO locus. Except for the CSF1PO data on the Egyptians, no deviations from the Hardy-Weinberg equilibrium were detected. For D12S391, no significant differences were found between the two Arab populations and between the two European populations, but the differences between both Arab populations and the Italians were significant. For CSF1PO, differences were only observed between the Yemenians and all three other populations. No evidence of linkage disequilibrium between the two STRs was found. The observation of a D12S391 allele consisting of only 14 repeats was confirmed by sequencing.

Genetic variation at the short tandem repeat loci HumvWA, HumFXIIIB, and HumFES/FPS in the Egyptian and Yemenian populations.

The short tandem repeat systems (STRs) HumvWA, HumFXIIIB, and HumFES/FPS were amplified in a triplex polymerase chain reaction (PCR) on blood samples from 100 unrelated Yemenians and 100 unrelated Egyptians. The samples were analyzed by native horizontal discontinual electrophoresis. No deviations from Hardy-Weinberg equilibrium were detected. The mean exclusion chances for Egyptians and Yemenians were 0.634 and 0.591 (vWA), 0.530 and 0.531 (FXIIIB), and 0.573 and 0.583 (FES); the discriminating powers were 0.937 and 0.924 (vWA), 0.900 and 0.899 (FXIIIB), and 0.918 and 0.921 (FES); and the observed heterozygosity rates were 0.84 and 0.72 (vWA), 0.73 and 0.83 (FXIIIB), and 0.81 and 0.80 (FES). No significant differences were found between the two Arab populations, but the differences between both Arab populations and a European population for HumFES and FXIIIB and between the Yemenian sample and a European sample for vWA were significant. No evidence of linkage disequilibrium between any of the three STRs tested was found.

A study on the short tandem repeat systems HumCD4, HumTH01 and HumFIBRA in population samples from Yemen and Egypt.

The short tandem repeat systems (STRs) HumCD4 (CD4), HumTH01 (TH01) and HumFIBRA (FGA) were amplified by the polymerase chain reaction (PCR) on blood samples from 100 unrelated Yemenians and 100 unrelated Egyptians. PCR products were separated on native horizontal discontinuous gel electrophoresis followed by silver staining. The distribution of observed phenotypes did not deviate from Hardy-Weinberg equilibrium. While significant differences between both Arab populations and an European population from Austria were found at all loci, differences between the Egyptian and the Yemenian samples were found only for CD4. In a number of verified Austrian families (TH01: 426 meioses, CD4: 275 meioses, FGA: 144 meioses) no mutations were found. The observation of a TH01 allele consisting of 4 repeats was confirmed by sequencing. Moreover we report the structure of a TH01 allele 6.3 observed in a Hungarian Caucasian population.