Dynamic Wedge Research Articles

SU‐GG‐T‐332: Dose to Contralateral Breast: A Comparison of Traditional Linac and Tomotherapy Techniques

Purpose: To characterize the dose and its distribution to the contralateral breast in patients undergoing whole‐breast radiotherapy using helical tomotherapy, and traditional linac with enhanced dynamic wedges or field‐in‐field techniques. Method and Materials: At the start of this IRB approved study, patients were selected and offered consent and enrollment. Dosimetry was performed using thermoluminescent dosimeters (TLDs) which were individually calibrated and tracked to generate a linear dose response curve for each. Positions for measurement were marked on the patient for reproducibility. The measurement positions were 5 cm superior, inferior, medial, and lateral to the breast center of the contralateral breast and 2 cm from center of sternum toward the contralateral breast. TLDs were placed in buildup caps to ensure buildup to electronic equilibrium. TLDs were placed daily for five consecutive treatments and then read 10 days after the last treatment. Calibration curves were applied to the TLD readings. Results: To date, three patients have been treated on Tomotherapy and five patients with traditional tangents. The contralateral breast doses, presented as a percentage of the prescription dose ± 1 standard deviation, are as follows: Tomotherapy; two cm from sternum 36 ± 8%, five cm medial 17 ± 6%, five cm superior 6 ± 1%, five cm lateral 6 ± 1%, five cm inferior 6 ± 1%. Traditional tangents; two cm from sternum 12 ± 5%, five cm medial 5 ± 2%, five cm superior 2 ± 1%, five cm lateral 2 ± 1%, five cm inferior 2 ± 1%. The average breast dose, calculated as the arithmetic mean of the doses five cm from the breast center, were 9 ± 6% for Tomotherapy and 3 ± 2% for traditional tangents. Conclusion: At our institution, helical tomotherapy produces doses in the contralateral breast that are approximately three times that of traditional tangents.

Linear array measurements of enhanced dynamic wedge and treatment planning system (TPS) calculation for 15 MV photon beam and comparison with electronic portal imaging device (EPID) measurements

Introduction.Enhanced dynamic wedges (EDW) are known to increase drastically the radiation therapy treatment efficiency. This paper has the aim to compare linear array measurements of EDW with the calculations of treatment planning system (TPS) and the electronic portal imaging device (EPID) for 15 MV photon energy.Materials and methods.The range of different field sizes and wedge angles (for 15 MV photon beam) were measured by the linear chamber array CA 24 in Blue water phantom. The measurement conditions were applied to the calculations of the commercial treatment planning system XIO CMS v.4.2.0 using convolution algorithm. EPID measurements were done on EPID-focus distance of 100 cm, and beam parameters being the same as for CA24 measurements.ResultsBoth depth doses and profiles were measured. EDW linear array measurements of profiles to XIO CMS TPS calculation differ around 0.5%. Profiles in non-wedged direction and open field profiles practically do not differ. Percentage depth doses (PDDs) for all EDW measurements show the difference of not more than 0.2%, while the open field PDD is almost the same as EDW PDD. Wedge factors for 60 deg wedge angle were also examined, and the difference is up to 4%. EPID to linear array differs up to 5%.ConclusionsThe implementation of EDW in radiation therapy treatments provides clinicians with an effective tool for the conformal radiotherapy treatment planning. If modelling of EDW beam in TPS is done correctly, a very good agreement between measurements and calculation is obtained, but EPID cannot be used for reference measurements.

Studying wedge factors and beam profiles for physical and enhanced dynamic wedges

This study was designed to investigate variation in Varian's Physical and Enhanced Dynamic Wedge Factors (WF) as a function of depth and field size. The profiles for physical wedges (PWs) and enhanced dynamic wedges (EDWs) were also measured using LDA-99 array and compared for confirmation of EDW angles at different depths and field sizes. WF measurements were performed in water phantom using cylindrical 0.66 cc ionization chamber. WF was measured by taking the ratio of wedge and open field ionization data. A normalized wedge factor (NWF) was introduced to circumvent large differences between wedge factors for different wedge angles. A strong linear dependence of PW Factor (PWF) with depth was observed. Maximum variation of 8.9% and 4.1% was observed for 60° PW with depth at 6 and 15 MV beams respectively. The variation in EDW Factor (EDWF) with depth was almost negligible and less than two per cent. The highest variation in PWF as a function of field size was 4.1% and 3.4% for thicker wedge (60°) at 6 and 15 MV beams respectively and decreases with decreasing wedge angle. EDWF shows strong field size dependence and significant variation was observed for all wedges at both photon energies. Differences in profiles between PW and EDW were observed on toe and heel sides. These differences were dominant for larger fields, shallow depths, thicker wedges and low energy beam. The study indicated that ignoring depth and field size dependence of WF may result in under/over dose to the patient especially doing manual point dose calculation.

Analytical correction of an extension of the "MU Fraction Approximation" for Varian enhanced dynamic wedges

The most common method to determine enhanced dynamic wedge factors begins with the use of segmented treatment tables. These segmental dose delivery values set as a function of upper jaw position are the backbone of a calculation process coined the “MU Fraction Approximation.” Analytical and theoretical attempts have been made to extend and alter the mathematics for this approximation for greater accuracy. A set of linear equations in the form of a matrix are introduced here which correct one published extension of the MU Fraction Approximation as it applies to both symmetric and asymmetric photon fields. The matrix results are compared to data collected from a commissioned Varian Eclipse Treatment Planning System and previously published research for Varian linear accelerators. A total enhanced dynamic wedge factor with excellent accuracy was achieved in comparison to the most accurate previous research found. The deviation seen here is only 0.4% and 1.0% for symmetric and asymmetric fields respectively, for both 6MV and 18MV photon beams.

Études et contrôle de qualité des filtres dynamiques à l’aide de l’imageur portal aS500-II (Varian)

Purpose The work presented herein rests on the study of the Varian EPID aS500-II and the Image Acquisition system IAS3. We assessed the dosimetric performance of this EPID for measurements and quality assurance of enhanced dynamic wedge profiles and wedge factors. Materials and methods We evaluated the dosimeter properties using the integrated asynchronous mode of acquisition in treatments with enhanced dynamic wedges (EDW). We studied the performance, stability and the reproducibility in measurements of the transmission factors and profiles of the fields with dynamic wedges. EPID profiles were compared to the “Profiler Sun Nuclear” diode array and PTW ion chamber. Analytical functions were developed in order to correct EDW profiles. The dependence of EPID measurements on wedge direction, beam dimensions and source to EPID distance was assessed. Results The backscatter produced by the “exact arm” was evaluated; EPID profiles depended on the EDW direction and on the detector source distance. Wedge factors were determined using this detector and compared to the ion chamber response, differences were all within 1 %. Two empirical correction functions were developed to produce EPID wedge profiles that correspond to diode for all wedge angles and energies depending on the wedge direction. Conclusion The EPID is highly suited to regular measurement of EDW due to the reproducibility of the EPID-measured wedge factors and profiles.

Phantom Development for Constancy and Acceptance Test for Digital Radiographic Equipment

The development of specific phantoms to study the image obtained by computerized and direct digital radiographic equipment is the objective of this work to characterize the physical properties of the image chain. We have developed a specific phantom, named RACON, that is applied to an acceptance and constancy test to assess the image quality of digital radiographic equipment. This phantom has been designed with different test objects recommended by international and national associations (IEC-61223-2-9, RD 1976-1999) as low-contrast objects varying in diameter and size for threshold contrast resolution, a high-resolution test for the limiting spatial resolution, a dynamic step wedge for the dynamic range of the system, and a homogeneity zone and alignment marks for the position and size of the radiation field. Furthermore, we have developed specific software to analyze automatically and objectively the phantom images. The algorithms are based on digital image processing techniques, and they have been specifically designed for each test object in the phantom. The developed phantom is sensitive enough to the operating conditions of the radiographic digital system, and the automatic image evaluation allows the objective study of the global state of the image system.

Commissioning Varian enhanced dynamic wedge in the PINNACLE treatment planning system using Gafchromic™ EBT film

In external photon beam therapies, the technique of dynamic wedge is a well established method for dose inhomogeneity compensation. The introduction of the enhanced dynamic wedge (EDW) on Varian LINACs considerably improved the pre-existing techniques. In the process of commissioning a Varian LINAC into a PINNACLE3 treatment planning system (TPS), the user is required to import quite a few measurements of EDW profiles and percentage depth doses (PDDs). Standard measurement devices like ionization chambers in a water phantom are not the most indicated ones for this situation where each measurement point is obtained by integrating during the entire exposure: Measurements would result to be a very laborious and time consuming operation, most of the times not practically possible. The goal of the present work is to introduce an alternative and hands-on procedure to perform the measurements using a combination of GafchromicTM EBT films, irradiated sideways in one single shot for both profiles and PDDs, and a single standard ionization chamber. The scanned profiles obtained at different depths have easily been imported in the TPS; for the PDD measurements, a correction was proven necessary to account for a "self-shielding" effect introduced by the presence of the films themselves, when irradiated sideways, resulting in an underestimation of the dose at deeper depths. A correction curve was derived comparing TPS open field validated measurements with the curves extracted from GafchromicTM EBT films. Finally, the curve was applied to all the wedged fields PDD measurements and could minimize the errors. The comparison for the 15 MV photon beam between the measured and the calculated 48 profiles and 12 PDDs (field sizes from 5 x 5 to 20 x 20 cm2, wedge angles ranging from 15 degrees to 60 degrees) was acceptable. The confidence limit (CL) was used as fit indicator, as suggested by the ESTRO Booklet No. 7: For the investigated PDDs the maximum value was 6.40 in the build up region and 2.83 beyond the maximum dose point; regarding cross beam profiles, the CLs were below 3 for 85% of the points within the field and for 96% of the points outside the field; in the penumbra region, a more appropriate parameter to evaluate the agreement between calculated and measured doses is the distance to agreement; only 73% of the profiles had CLs below 15, but for the remaining ones, distance-to-agreement values were within 3 mm. A hundred ionization chamber point dose measurements (for square and elongated fields at different depth and for points in field and out of field) were performed in a water phantom and 98 of them confirmed the TPS calculations with differences lower than 3% and considerably lower in most of the cases. This article gives valuable guidance and insight to other physicists attempting to approach EDW commissioning in the PINNACLE TPS software using Gafchromic EBT films.

THE QUALITY ASSURANCE OF ENHANCED DYNAMIC WEDGES USING DAILY QA CHECK 2

SUMMARY Background: Clinical implementation of enhanced dynamic wedges (EDW) requires, as any other dynamic treatment, very serious quality assurance (QA) program. In this work, we presented the results of six-month evaluation of Varian enhanced dynamic wedges and detailed QA program for those wedges. Methods: The Sun Nuclear Daily QA Check 2 was used for QA purpose. The QA program included daily and monthly checks. The daily QA program included central axis dose and wedge angle measurements. Within the monthly QA program wedge factors and delivered STTs from the Dynalog files were checked. Results: Our daily QA measurements of dose and wedge angle showed the reproducibility error less than ±1.5%. On the other hand, monthly QA measurements of wedge factor the reproducibility error was less than ±0.5%. The monthly QA check of delivered STTs showed excellent agreement. Conclusion: During the six-month quality control we observed a good reproducibility in the delivery of EDW treatment. Also, the Sun Nuclear Daily QA Check 2 showed to be very satisfying in QA of the EDW treatment.

SU-FF-T-642: Evaluation of 3-D Treatment Plans Using Physical and Motorised Enhanced Dynamic Wedges

Purpose: To analyze the treatment plans generated using physical and enhanced dynamic wedges for head and neck patients from Eclipse treatment planning system. Materials and Methods: The physical wedge filters of angles of 15°, 30°, 45° and 60° are used. In Enhanced Dynamic Wedge technique no external beam modifier is used to create wedge dose profiles, instead wedged isodose profiles is created by the sweeping action of the jaw from open to closed position while the beam is on. The dose rate and jaw speed are also varied during the treatment, which is the function of selected energy, field size and wedge angle. The single STT called Golden STT (GSTT) is used for 60° wedge angle and other wedge effects are obtained by mixing open and wedge field intensities. The conformal treatment plans of 20 head and neck patients were used in this study. Plans are generated using both physical and enhanced dynamic wedges. The dose was normalized to 100% at isocenter. The plans were compared using Dose-Volume histogram (DVH) tool. Results and Discussion: The treatment plans generated shows that the enhanced dynamic wedge plans were comparable with that of the physical wedge plan and the DVH analysis showed that the critical organ sparing is slightly better with enhanced dynamic wedge. The maximum dose within the target volume is higher in physical wedge plan. The number of monitor units to deliver a particular dose with EDW field is less than that of PW field due to change in wedge factor, which could probably reduce the scatter dose to structures off the field. Enhanced dynamic wedges eliminate the beam hardening effect, and also it is possible to obtain an asymmetric wedge fields with EDW. The dose and jaw position control accuracy statistics are displayed and saved to dynalog files after treatment.

SU‐FF‐T‐281: Variation of Beam Characteristics for Physical and Enhanced Dynamic Wedge From a Dual Energy Accelerator

Purpose: The aim of this study was to compare few of the dosimetric characteristics of a physical and enhanced dynamic wedge from a dual energy (6 and 18 MV) linear accelerator. Materials and Methods: This study used the Varian Clinac‐DHX (S.No.3172) linear accelerator which is equipped with three different type of wedges. To compare the change in beam quality with physical and enhanced dynamic wedge half value layer (HVL) was measured using a 0.14 cc ion chamber covered with brass build up cap positioned at 2 meter distance from the source and the distance from the target to absorber distance was maintained as 1 meter. Transmission measurements were made for varying thickness of white polystyrene phantom placed on the couch. The surface dose with physical and enhanced dynamic wedges were measured using a parallel plate chamber at 85 and 100 cm source to surface distance (SSD), for 6 and 18 MV photons. Results: The HVL was estimated for 6 and 18 MV photons along the central axis and at off‐axis points for the field size of 20 × 20 cm2 with 45° upper physical wedge and compared with that of the enhanced dynamic wedge (EDW). For physical wedged field, at heel edge side HVL value was high compared with the measured that of EDW. It was noticed that, the HVL variation across the beam was significantly high for 6 MV X‐rays than for 18 MV X‐rays. The measured surface dose was found to be more at 85 cm FSD for all the fields. The lower energy photons (6 MV) were found to result in higher surface dose than the higher energy photons (18 MV). Conclusion: The three wedge systems produce significantly different surface doses that should be considered in properly choosing a wedge system for clinical use.

SU-FF-T-627: Off-Axis Correction Factors for the Enhanced Dynamic Wedge

Purpose: To quantify the dependence of the dosimetric wedge factor for the Varian™ Enhanced Dynamic Wedge (EDW) upon the field size, angle, energy and distance from the machine isocenter. Method and Materials: Point dose measurements in solid water and a multi‐detector ion chamber array measurements in water were used to measure the x‐ray energy deposition from two Varian™ medical accelerators over a wide range of field sizes and distances off the machine isocenter. Measurements at two energies were compared to predictions from two treatment planning programs. Results: The variance between the dose predicted by the treatment planning software and that measured for EDW rectangular fields was found to be a smooth function of the distance from the center of the wedged axis. The amplitude of the variance increases with the EDW angle and decreases with increasing energy. The variance was not observed to have any dependence on the distance along the non‐wedged axis. A correction factor algorithm was developed which reduced the variance to <1% in all cases. Conclusion: The EDW factor is nominally dependent upon the position of the stationary jaw. This work demonstrates an additional correlation between the dose variance and the beam energy, EDW angle, and length of the field along the wedged field axis. The variance increases with increasing EDW angle and decreases with increasing beam energy, becoming as large as ∼6% in extreme cases. The width of the field in the unwedged dimension did not have an effect on the variance. A correction factors procedure was able to limit the variance to <1% under all circumstances. For fields centered on the central axis or with one edge on the central axis the variance was already <1% making any additional correction clinically unnecessary.

SU-FF-T-630: Characterizing the Enhance Dynamic Wedge Parameters in the Eclipse Treatment Planning System and Assessing Its Accuracy in Beam Modeling

Purpose: The purpose of this study is to assess the accuracy of Eclipse treatment planning system in modeling Clinac EDW beams and to evaluate the effect of the three EDW parameters on its outcome. Method and Materials: The wedge factors(WFs) were measured in symmetric fields from 4×4 cm2 to 20×20cm2 and asymmetric fields to the maximum of 30×(20,10). Point of measurement was in solid phantom at 10cm depth and 100cm SSD setup using a PR06 ion chamber. Measured and calculated data for the standard set of wedge angles with 6, 10 and 23 MV photon beams by comparing the WFs. Effects of the three parameters were monitored by the MU changes. Results: The calculated WFs have more discrepancies on large wedge angles and field sizes and tend to be lower than the measured value. All parameters had minimal to no effect on 4×4cm2 fields. For field size ⩾10×10cm2, the deviations were less than 2% after the adjustment. Increasing the secondary source size will increase the MU and is more sensitive on the medium field sizes. It will take a minimum of 2mm change before any effect can be observed. Increasing the relative intensity will decrease the MU and the effect is more sensitive on 60° wedges. Increasing the mean energy increases the MU and the effect is greater for larger field size and wedge angle. Conclusions: There are limitations in utilizing the EDW parameters for modeling all field sizes and wedge angles to within 2% deviation from measured value. User has to compromise between the smallest field size and largest wedge angle. Best is to start with relative intensity to minimize deviation among wedge angles and field sizes before adjusting the second source size parameter to fine‐tune the MU between wedge angles.

Study of 2D ion chamber array for angular response and QA of dynamic MLC and pretreatment IMRT plans

Aim To study of 2 Dimensional ion chamber array for angular response and its utility for quality assurance of dynamic multileaf collimator and pretreatment intensity modulated radiotherapy plans. Materials and Methods The MLC QA test patterns and IMRT plans were executed on 2D ion chamber array having 1020 vented pixel ionization chambers. The dynamic MLC QA test patterns were chair test, x–wedge, pyramid, open swipe field, garden fence and picket fence. Performance of Dynamic wedges was compared with physical wedges. For IMRT verification, five patients with localized prostate carcinoma were planned using dynamic IMRT technique. Angular response of MatriXX was measured by exposing the system from different gantry angles. Results Dynamic MLC QA tests such as chair, x-wedge, pyramid, and open swipe field were successfully verified. MatriXX was not able to recognize the bar pattern of picket test and garden fence test. The response of MatriXX gradually decreases from 0° to 180° angles and it was 7.7% less at 180° angle. The dynamic wedge profiles were matching with corresponding physical wedge profiles. For pretreatment IMRT QA, the average dose difference between planned and measured dose was 1.26% with standard deviation of 1.06. Conclusion I'mRT MatriXX can be used for routine dynamic MLC and IMRT pretreatment QA but care should be taken while taking measurements in penumbra region because of its limited spatial resolution.

Verification of Varian enhanced dynamic wedge implementation in MasterPlan treatment planning system

This paper investigates the accuracy of the two available calculation algorithms of the Oncentra MasterPlan three‐dimensional treatment planning system (TPS) – the pencil beam method and collapsed‐cone convolution – in modeling the Varian enhanced dynamic wedge (EDW). Measurements were carried out for a dual high energy (6–15 MV) Varian DHX‐S linear accelerator using ionization chambers for beam axis measurements (wedge factors and depth doses), film dosimetry for off‐axis dose profiles measurements, and a diode matrix detector for two dimensional absolute dose distributions. Using both calculation algorithms, different configuration of symmetric and asymmetric fields varying the wedge's angle were tested. Accuracy of the treatment planning system was evaluated in terms of percentage differences between measured and calculated values for wedge factors, depth doses, and profiles. As far as the absolute dose distribution was concerned, the gamma index method (Low et al. (13) ) was used with 3% and 3 mm as acceptance criteria for dose difference and distance‐to‐agreement, respectively. Wedge factors and percentage depth doses were within 1% deviation between calculated and measured values. The comparison of measured and calculated dose profiles shows that the Van Dyk's acceptance criteria (Van Dyk et al. (14) ) are generally met; a disagreement can be noted for large wedge angles and field size limited to the low dose‐low gradient region only. The 2D absolute dose distribution analysis confirms the good accuracy of the two calculation algorithms in modeling the enhanced dynamic wedge.PACS number: 87.53.Bn, 87.55.kn, 87.56.ng

Impact dosimétrique du mouvement 2D d’une plateforme simulant la respiration lors d’un traitement en mode dynamique

Breathing-adapted techniques in external radiotherapy lead to the improvement of the taken into account of the tumour motion during the patient treatment. Indeed, this motion involves dosimetric uncertainties, in particular during a dynamic treatment (intensity-modulated radiation therapy, dynamic wedge…). As tumoral movement is complex and is carried out in various directions of space, a dynamic platform moving in one or two plans was conceived. This article approaches the technical aspects of design and functioning of this prototype. A study of the dosimetric effects of the respiratory movement on one and two plans during a dynamic treatment without gating will be presented. Films were irradiated while varying the rates with wedged fields at various speeds. The penumbra of beams were compared with the static case and appeared twice broader in the majority of the cases. The results highlighted the contributions of the longitudinal and the axial components of the motion on the form of the dose distribution. These results were completed with γ index measurements to determine an internal margin. Moreover, this platform proves to be a promising tool for breathing-adapted treatment, in particularly to test the synchronisation of RPM system in fluoroscopic mode in board imaging system.

Clinical implementation of enhanced dynamic wedges into the Pinnacle treatment planning system: Monte Carlo validation and patient-specific QA

The goal of this work is to present a systematic Monte Carlo validation study on the clinical implementation of the enhanced dynamic wedges (EDWs) into the Pinnacle3 (Philips Medical Systems, Fitchburg, WI) treatment planning system (TPS) and QA procedures for patient plan verification treated with EDWs. Modeling of EDW beams in the Pinnacle3 TPS, which employs a collapsed-cone convolution superposition (CCCS) dose model, was based on a combination of measured open-beam data and the ‘Golden Segmented Treatment Table’ (GSTT) provided by Varian for each photon beam energy. To validate EDW models, dose profiles of 6 and 10 MV photon beams from a Clinac 2100 C/D were measured in virtual water at depths from near-surface to 30 cm for a wide range of field sizes and wedge angles using the Profiler 2 (Sun Nuclear Corporation, Melbourne, FL) diode array system. The EDW output factors (EDWOFs) for square fields from 4 to 20 cm wide were measured in virtual water using a small-volume Farmer-type ionization chamber placed at a depth of 10 cm on the central axis. Furthermore, the 6 and 10 MV photon beams emerging from the treatment head of Clinac 2100 C/D were fully modeled and the central-axis depth doses, the off-axis dose profiles and the output factors in water for open and dynamically wedged fields were calculated using the Monte Carlo (MC) package EGS4. Our results have shown that (1) both the central-axis depth doses and the off-axis dose profiles of various EDWs computed with the CCCS dose model and MC simulations showed good agreement with the measurements to within 2%/2 mm; (2) measured EDWOFs used for monitor-unit calculation in Pinnacle3 TPS agreed well with the CCCS and MC predictions within 2%; (3) all the EDW fields satisfied our validation criteria of 1% relative dose difference and 2 mm distance-to-agreement (DTA) with 99–100% passing rate in routine patient treatment plan verification using MapCheck 2D diode array.

The accuracy of MU calculations for dynamic wedge with the Varian's Anisotropic Analytical Algorithm

In November 2007 Varian Medical Systems released a new version of ECLIPSE (version 8.1.17), which includes a correction to its Anisotropic Analytical Algorithm affecting monitor unit calculations for Enhanced Dynamic Wedge. The purpose of this study is to evaluate and compare the accuracy of the MU calculations for version 8.1.17 with that from the previous version (8.0.05).

Poster - Thurs Eve-10: The accuracy of MU calculations for enhanced dynamic wedge with the Varian's anisotropic analytical algorithm

The Anisotropic Analytical Algorithm (AAA) of the Varian Eclipse treatment planning system calculates absolute dose for a variety of beam settings including those with an enhanced dynamic wedge (EDW). This algorithm has gone through a number of version updates since it was first released in July 2005. Previous versions of AAA have come with instructions on how to manually modify the several parameters that affect the EDW output factors. The current version of AAA (8.1.17) has had the EDW module modified so that problems associated with the second-source parameter calculation are resolved. The purpose of this paper is to report on the observed discrepancies between measured and calculated EDW output factors for the current version (8.1.17) and the most recent version (8.0.05) of the AAA algorithm. EDW output factors were measured in a water-equivalent phantom on a Varian 2100iX LINAC running 6MV and 15MV photon beams. A similar geometry was modelled in the treatment planning system to calculate the number of monitor units required to deliver a specified dose at a depth with or without an EDW. Measurements and calculations were performed for a wide range of EDW wedge angles, field sizes and depths. The best EDW output factor results possible with version 8.0.05 yielded discrepancies up to 7% despite considerable parameter adjustment. The new version (8.1.17) gave results within 1% of measured without any parameter adjustment. Care should be taken when using any Eclipse AAA algorithm earlier than version 8.1.17 to calculate MUs for Varian enhanced dynamic wedge.

SU‐GG‐T‐315: McGill Monte Carlo Research Platform (MMCTP) for Dose Comparison Studies

Purpose: To demonstrate recent improvements in the functionality of MMCTP, a radiotherapy research platform GUI, with integrated Monte Carlo (MC) dose calculation submission and dose analysis tools. MMCTP allows for quick MC dose calculations from standard radiotherapy formats. Clinical and MC dose distributions are analyzed under the same platform, which eliminates inherent planning system tool dependent effects. History: MMCTP has been internally distributed within the last year. External distribution, which has so far been limited to close contacts, will be open to the public. DICOM‐RT plans, which include: images, structures, dose distributions and beam information, have been successfully imported from TPS such as: Eclipse, Corvus and Tomotherapy. MC calculations use the images structures, and beam information to generate a beam and patient model. The GUI is capable of handling the following beam parameters: dynamic wedge, static/dynamic MLC, and static wedge. MC dose distributions are normalized to absolute dose with the beam monitor units and directly compared to the imported clinical dose distributions. The GUI includes a set of built in comparison tools: isodose lines and colour‐wash displays in transverse/sagittal/coronal view, DVH calculations, dose difference maps and dose profile graphs. Validation has been extensive and includes profile comparisons between MC and measured data. Results: Patient recalculations include a set of: conformal lung and breast patients, gated high dose lung patients, IMRT head and neck patients. Recalculations times vary depending on the number and complexity of beams, size and resolution of patient model. Heterogeneous recalculations reveal differences between planned and delivered dose distributions. Conclusion: MMCTP is a flexible research platform for the development of patient specific MC treatment planning for photon and electron external beam radiation therapy. The visualization, dose analysis tools offer extensive possibility for plan analysis and comparison to plans imported from commercial TPS through well‐documented protocols such as DICOM‐RT.

SU‐GG‐J‐143: Performance Optimization of the Integrated Acquisition Mode of the Varian AS500‐II EPID and Investigation for Measurement of Enhanced Dynamic Wedge

Purpose: To better understand the image acquisition operation of an EPID and to evaluate the dosimeter properties in treatments with enhanced dynamic wedges. Method and Materials: The Work presented rests on the study of the Varian EPID: aS500‐II and the Image Acquisition system IAS3. We are interested in integrated image acquisition mode not synchronized to the accelerator beam pulses. We investigated the influence of the Frame Cycle Time “FCT” parameter on the gray level, the speed of acquisition and the noise in the image, according to the energy of the X‐ray beams (6 and 15 MV) and the Clinac 2100 C/D dose rate. We also studied the performances, stability and the reproducibility of the EPID aS500‐II in measurements of the wedge factors of the fields with enhanced dynamic wedges. Results: In this mode, only one parameter the “FCT” influences the pixel value. The pixel value is directly proportional to this parameter. When the FCT ⩾ 55ms, the speed of acquisition is inversely proportional to this parameter. The noise lies between 0.2% and 0.5%. We determined a rule to avoid saturation. EPID measurements were found to exhibit a dependence on the wedge direction and EPID position. An empirical correction function was developed to correct the wedge profiles. Due the reproducibility of the EPID measured EDW factors the device is highly suited in this mode of acquisition to regular measurement of EDW. Conclusion: The choice of the acquisition parameters is essential for the complete detection of radiations and especially to use this detector as a dosimeter.