bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐T‐171: Use of Optically Stimulated Luminescence Dosimeters, OSLDs, for an Independent Verification of Dose Delivered by IMRT Treatments
Authors: Sharma R , Jursinic P
Published: August 2010

Purpose: To demonstrate how OSLDs can be used to independently verify the (absolute) dose delivered in IMRT treatments. Methods and Materials: OSLDs are discs infused with aluminum oxide doped with carbon (Al2O3:C). Crystals of Al2O3:C when exposed to ionizing radiation store energy that is released as luminescence (420nm) when the OSLD is illuminated with stimulation light(520 nm). The amplitude of the luminescence depends on the dose absorbed by the OSLD and the intensity of stimulation light. The OSLDs were calibrated against a 6X photon beam that was adjusted according to TG51. IMRT treatment plans were created for the RPC‐Tomotherapy‐Calibration Phantom and a 30‐cm diameter, cylindrical, solid‐water phantom, the TomoTherapy Cheese Phantom. IMRT plans were generated for both phantoms with the dose prescribed to the centrally located target‐volume, using the Tomotherapy Hi‐Art and CMS XiO treatment‐planning systems. The OSLD's were positioned in the center of the target volume. The treatments were delivered on a Tomotherapy Unit and a Varian Trilogy. Results: The calculated dose for the Tomo Therapy plans was 3.05 Gy, the measured dose to the RPC phantom was 3.06±0.03, the measured dose to the cheese phantom was 310 ±1.4. The calculated dose for the Xio plans was 3.12Gy and the dose delivered to the RPC phantom was 3.14 ±4.5. Conclusions: This method provides an independent verification of dose delivered for step and shoot as well as rotational therapy and should be implemented as part of the annual QA process. These measurements would be beneficial additions to the present RPC TLD irradiation checks and should be performed following software upgrades to treatment planning and R&V systems also.
SU‐GG‐T‐176: Influence of the Multileaf Collimator Step Size in Step&Shoot IMRT Prostate Treatments
Authors: Descamps C , Garrigo E , Venencia C
Published: August 2010

Introduction Reducing the beamlet size during step&shoot IMRT planning may lead to improve dose conformity. The beamlet length can be adjusted in the treatment planning system (TPS) with the leaf step‐size along the MLC travel direction. The aim of this paper was to analyse the step‐size influence during prostate treatments. Materials and methods Ten patients treated for prostate cancer with 6MV‐IMRT fields were selected. Each treatment was calculated with the Konrad v2.2, Siemens, TPS using leaves step sizes of 3, 5 and 10mm, and delivered with a Primus, Siemens, linac associated to an Optifocus MLC (10mm leaf width). For each step‐size, the plans were calculated so as to equal the dose received by 95% of the PTV. Plans were compared in terms of PTV dose uniformity, organ‐at‐risk doses, treatment time and MU number. For each plan, the beams were imported in a water‐equivalent phantom and the doses calculated were compared with Farmer (0.6cc) and Pinpoint (0.015cc) ion chambers measurements. Results Reducing the step‐size from 10 to 5 or 3mm leads to a better PTV dose uniformity (31.2% and 35.8% dose standard deviation increase) and higher prostate minimum dose (+0.2% and +0.6%). Rectum V40 (V65) decreased of 3.2% (3.6%) and 6.9% (12%) for 5mm and 3mm. Bladder V65 and femoral heads V50 decreased of 9.5% and 26% for 5mm and 18% and 42% for 3mm. The treatment time and MU number increased of about 10% and 27% for 5mm and 20% and 48% for 3mm. The dose measurement verification showed that both chambers can be used for all step‐sizes with errors less than 1.3%. However, the PinPoint chamber use for 3mm beamlet sizes decreases the error from 1.3% to 0.3%. Conclusion Using 5mm step‐size seems to be a good compromise by improving the IMRT plan quality without treatment time increase.
SU‐GG‐T‐177: Intensity‐Modulated Radiotherapy Planning Characteristics of Celiac Deep‐Seated Tumor
Authors: Zhu J , Liu M , Yin Y , Bai T
Published: August 2010

Objective: To examine the influence of energy and number of beams for intensity‐modulated radiation therapy on celiac deep‐seated tumor. Methods and Materials: 26 patients with cancer of pancreas were studied. Their IMRT plans were created for 6MV and 15MV photons using 5, 7, 9 and 11 coplanar non‐opposed fields. Plans were normalized to cover no less than 95% of the target volume at the 100% prescribed dose and were analyzed using two factor ANOVA with repetition and broken line graph for (a) dose distribution on PTV, (b) conformity index at prescribed dose for PTV, (c) dose on the organs at risk(OAR), (d) dose distribution on the region around the target which were divided into “near region”(NR: 1‐cm thick shell surrounding target), “surface region”(SR: 1cm thick shell under the surface) and “middle region”(MR: the region except NR and SR). Result: Dose distribution on PTV and OAR were the same for all the eight different plans; CI for all the other six plans had no significant deviations except the two 5‐beams plans which had less CI; Plans with the same number of beams but lower beam energy would enlarge the MR and SR volume significantly; Plans with 7 or 9 beams showed the better characteristics with the same energy. Conclusion: With IMRT for the celiac deep‐seated tumor, plans with 6MV and 15MV photons had no significant deviations on target and OAR, although the lower energy would enlarge the dose volume on MR and SR. The clinical significance of this increased dose, in terms of complications, remains to be detected. Considering the disadvantages of using the higher energy including higher secondary radiation dose to the patient and staff, increased non‐equilibrium effects and larger penumbra, the plan with 6MV photon and 7 beams should be considered first.
SU‐GG‐T‐178: Intensity‐Modulated Radiation Therapy (IMRT) in the Treatment of Oropharyngeal Carcinoma: Clinical Outcomes and Relation of Parotid Gland Volume with Xerostomia
Authors: Turaka A , Weinberg B , Li T , Nicos N , Burtness B , Lango M , Ridge J , Feigenberg S
Published: August 2010

Purpose: To determine the pattern of failures and relation of the parotid gland (PG) volume with xerostomia in patients treated with IMRT for squamous cell cancers of the oropharynx. Method and Materials: Between January 2001‐ December 2006, 49 patients with oropharyngeal cancer received IMRT with curative intent at Fox Chase Cancer Center. Among these, 48 were squamous cell and 1 adenocarcinoma. The median age was 58 years (range: 41–85), 82% smokers, and 90% with stage III or IV. 85% received definitive RT (63% concurrent chemoradiotherapy, 22% RT alone) to a median dose of 70 Gy in 35 fractions and 39% (19) had neck dissection. Wilcoxon test was used to determine the correlation between PG volumes (Vmean) and Xerostomia in 28 patients and Pearson's correlation coefficient to see relation between the percentage weight loss with PG volume. The mean dose to PG was 26 Gy. RTOG acute toxicity scoring was used to grade Xerostomia. Patient tumor and treatment related factors, including age, T, N stage, location of primary tumor, addition of chemotherapy, and RT doses were analyzed for outcomes and toxicities. Results: The median follow up was 16 months (range: 1 – 84). The 2‐year local, locoregional, distant metastases free and overall survival rates were 90%, 90%, 91% and 71% respectively with a median time to failure of 15 months. Median values for PG's were: Vmean 14 cc (5–48), 25 cc (12–77) and RT doses were 52 Gy (26–65), 25 Gy (17–32) for ipsilateral and contralateral PG's respectively. Median percent weight loss was 10% at 7th week of treatment. Only 4% patients had grade 3 xerostomia. There was no significant correlation seen for Xerostomia with percent weight loss and/or ipsilateral (p= 0.2) or contralateral PG volumes (p= 0.3). Conclusion: Use of IMRT resulted in acceptable xerostomia rates with promising locoregional control rates.
SU‐GG‐T‐180: Intensity‐Modulated Radiation Therapy (IMRT) for the Para‐Nasal Sinus (PNS) Malignancies: Outcomes from Fox Chase Cancer Center (FCCC)
Authors: Turaka A , Cattaneo R , Nicos N , Lango M , Burtness B , Ridge J , Feigenberg S
Published: August 2010

Purpose: Due to the difficulties of air tissue interface interactions as well as the close proximity to the optical apparatus, tumors in the PNS region treated with IMRT may have increased local failure and higher complications. The clinical outcome of patients treated with IMRT for PNS malignancies are reported. Method and Materials: Between May 2001 and June 2008, 31 patients with PNS malignancies were treated at FCCC with IMRT to a median dose of 60 Gy in 30 fractions. There were 13 males and 18 females, with median age 68 years. Seventeen (59%) patients had AJCC stage III/IV disease at presentation. Twenty one of 31 patients presented with clinical stage NO neck disease. Histology was: 14 squamous cell, 3 adenocarcinoma, 3 adenoid cystic, 6 mucosal melanoma, 5 others. The base of skull was treated in 3 patients with perineural invasion. Median RT values to optic apparatus: Optic chiasm Dmax 22 Gy (range: 1–48); right and left optic nerve Dmax were 39, 37 Gy (range: 2–62; 2–65) and right, left parotids were 17; 25 Gy (range: 7–30; 5–53) respectively. Outcomes and toxicities were measured. Results: There were no grade 3 or 4 ocular or salivary function related toxicities. With a median follow up of 27 months (range: 4–98), the 2‐ and 5‐year local control and overall survival rates were 89%, 82% and 75%, 66%, respectively. The 2‐year locoregional control rates were 89% for stage I/II and 79%III/IV, 89% NO, 50% for N1/2, 71% squamous cell and 100% for other histologies, 100% negative margins, 78% for positive margins. Four patients had local recurrence, 2 residual disease, 2 regional (treated prior) and 4 distant metastases (1 squamous cell, 1 adenoidcystic ca, 2 melanomas). No marginal failures were seen. Conclusion: IMRT appears to be a safe and effective treatment for paranasal sinus tumors.
SU‐GG‐T‐185: Eliminating Errors in Setup and Positioning for Patient‐Specific IMRT QA
Authors: Kamath S , Palta J
Published: August 2010

Purpose: In patient‐specific IMRT quality assurance (QA), measured planar dose distributions are usually compared to calculated planar dose distributions. Any discrepancies between the two distributions can be due to: 1. Uncertainties in the linac delivery system. 2. Uncertainties in beam modeling in the treatment planning system. 3. Uncertainties in positioning the QA device/dosimeter. The purpose of this study is to develop and implement a method to eliminate all positioning uncertainties that affect the QA results, including the dosimeter or device positioning and MLC positioning errors, and thereby determine residual errors that are attributed to beam modeling and non‐positioning delivery system uncertainties. Method and Materials: Measured and calculated dose distributions are usually compared using a similarity measure such as gamma test or DTA/dose difference (composite) test based on which a pass percentage is determined. We have developed an efficient algorithm that eliminates the affect of setup and positioning errors on the gamma or composite pass percentages. The algorithm is designed to be optimal and fast so as to operate on high resolution (1 mm) dose distributions for misalignments (typically up to 10 mm). Results: An algorithm to align high resolution dose distributions using translation has been implemented in C++ and executes within a few seconds on a PC. The algorithm has been rigorously tested on randomly generated matrices for known misalignments and it is able to predict the shifts very accurately. Conclusion: We have developed a method that eliminates the impact of setup and positioning uncertainties on pass rates for IMRT QA. Any residual discrepancies between measured and calculated planar dose distributions can then be truly attributed to beam modeling and machine output variations.
SU‐GG‐T‐186: Fast and Generalized Dose Reconstruction Method Using Virtual Beamlet Dose Responses
Authors: Yeo I , Jung J , Kim J
Published: August 2010

Purpose: We have previously developed an accurate dose‐reconstruction algorithm that is based on non‐iterative inverse solution of deposited dose using Monte Carlo‐generated responses for known multi‐leaf collimator (MLC) positions. The method was time‐consuming in generating the responses. The objective of this study is to develop a faster algorithm that does not require MLC positions by using pre‐calculated virtual beamlet‐specific dose responses for an open beam, and thus can be used at the end of radiation delivery on‐the‐spot. Methods: The success of the method is based on the hypothesis that the ratio of dose responses in phantom and electronic portal imaging device (EPID) of delivered beam intensities is approximated by the ratio of virtual beam intensities. The possibility is mathematically shown by convolving reconstructed intensities from EPID to both numerator and denominator of the latter ratio. The inversion algorithm for the reconstruction is unchanged. To test the hypothesis, we have calculated virtual beamlet dose responses in Rando phantom and EPID for intensity modulated beams determined for prostate treatment. We have measured in EPID under the phantom and performed dose reconstruction for the two cases. A 6MV photon beam from a Varian 2100EX accelerator and aS500 EPID (integrated acquisition) was used. Results: When compared with a forwardly calculated dose in an isocentric plane within the phantom for an IMRT beam, the reconstructed doses of the two showed similar pass rates of >94.7%, given 3% dose difference or 3mm distance‐to‐agreement. The calculation used 5 minutes per beam using four 2.8GHz Intel XEON CPUs. Automation and the use of a higher data processor can potentially reduce the calculation time to less than a minute. Conclusion: A fast method of dose reconstruction was developed and more results will be presented. This method is applicable to detect delivery error. In part supported by Varian Medical Systems.
SU‐GG‐T‐188: A Field Size Specific Backscatter Correction Algorithm for Accurate EPID Dosimetry
Authors: Berry S , Polvorosa C , Wuu C
Published: August 2010

Purpose: Portal dose images acquired with an amorphous silicon electronic portal imaging device (EPID) suffer from artifacts related to backscattered radiation. The backscatter signal varies as a function of field size (FS) and location on the EPID. Most current portal dosimetry algorithms fail to account for the FS dependence. The ramifications of this omission are investigated and solutions for correcting the measured dose images for FS specific backscatter are proposed. Method and Materials: A series of open field dose images were obtained for field sizes ranging from 2×2 to 30×40 cm2 and analyzed to determine the amount of backscatter present. Two methods to account for the relationship between FS and backscatter are offered: discrete FS specific correction matrices and a single generalized equation. Each approach was tested on the clinical dosimetric images for 10 patients, 49 treatment fields to see whether there was an improvement in the dosimetric result over the vendor's algorithm. Results: Backscatter manifests itself as an asymmetry in the measured signal primarily in the inplane direction. The maximum error is 3.6% for 10×10 and 12.5×12.5 cm2 field sizes. The asymmetry decreased with increasing FS to 0.6% for fields larger than 30×30 cm2. The dosimetric comparison between the measured and predicted dose images was significantly improved (p ≪ .001) with the FS specific backscatter correction. The average percentage of points passing a 2%, 2mm gamma criteria increased from 90.6% to between 96.7% and 97.2%. Conclusion: The error observed in a measured portal dose image depends on how much its FS differs from the 30×40 cm2 calibration conditions. The proposed methods for correcting for FS specific backscatter effectively improved the ability of the EPID to perform dosimetric measurements. Correcting for FS specific backscatter is important for accurate EPID dosimetry and can be carried out using the described methods.
SU‐GG‐T‐194: Commissioning, Validation, and Implementation of the COMPASS System into a Clinical Intensity Modulated Radiotherapy Quality Assurance Program
Authors: Crass J , Morales‐Paliza M , Coffey C
Published: August 2010

Purpose: The purpose of this work was to commission, validate, and implement the COMPASS (IBA, Inc) system into a clinical intensity‐modulated‐radiotherapy (IMRT) quality‐assurance (QA) program. Method and Materials: The COMPASS system is comprised of an array of ionization detectors (MatriXX) mounted to the gantry using a custom holder and a software package for the analysis and visualization of quality assurance results. Commissioning of the COMPASS required reformatting 6‐MV photon data from a Varian‐Novalis‐TX linac into a software acceptable beam model. Validating COMPASS was a multi‐step process including the qualification of our Varian‐Eclipse‐treatment‐planning system (TPS) and the COMPASS computation, prediction, and reconstruction algorithms. Prior validation of our TPS included comparisons of measured dose in a pelvic phantom to calculated dose and correlation of predicted IMRT fluence with measured fluence using the MatriXX and OmniPro software. Validation of the computation algorithm involved direct comparison of TPS calculated dose to COMPASS calculated dose. The prediction algorithm was validated by comparing the predicted response to measured response on the MatriXX. Finally, the validation of the reconstruction algorithm included fluence measurements taken using COMPASS for actual patients undergoing IMRT treatment at our facility and comparing the reconstructed dose to the TPS calculated dose. Results: Validation of our TPS using point dose measurements was found to be within less than 1% from our TPS calculated dose. The COMPASS fluence prediction algorithm was evaluated using difference histograms; analyses indicated that ∼96% of the pixels were within ±1.5% difference. Conclusion: This work shows clinical potential for a new visualization display of IMRT QA; 2D fluence measurements in conjunction with a valid beam model and patient CT information can be utilized to reconstruct measured dose onto a patient 3D data set. Conflict of Interest: This study was sponsored by IBA, Inc., Bartlett, Tennessee.
SU‐GG‐T‐196: Effect of Small Field Output Factors on Pinnacle IMRT Dose
Authors: Azimi R , Alaei P , Higgins P
Published: August 2010

Purpose: To evaluate how changes in the measured small field size output factors affect the computed and measured doses in Pinnacle IMRT treatment planning. Method and Materials: A simple five‐field IMRT plan was created using Pinnacle treatment planning system. The plan was optimized to a cylindrical target of 2 cm diameter and 2 cm length. Measured output factors in the planning system were decreased or increased in 5, 10, and 20% increments for field sizes of 2×2 and 3×3 cm2 for both an Elekta and a Varian linear accelerator. The treatment unit was re‐commissioned in the planning system after each modification of the output factors and treatment plan was re‐optimized. All plans were delivered to a solid water phantom and dose measurements were made using an ionization chamber. The percentage differences between the measured and computed doses were calculated. Results: For the Elekta unit, decreasing output factor values resulted in higher measured than computed doses of 3.0% for the 10% and 7.6% for the 20% decrease. Increasing output factors resulted in lower doses by 6.1% for 10% and 9.1% for the 20% increase. For the Varian machine we observed no systematic trends as in Elekta between measured and computed doses as the output factors were changed from −20 to +20%. Conclusion: The measurement accuracy of the small field output factors are of importance especially when the treatment plan consists of small segments as in IMRT. This method could be used to verify the accuracy of the measured small field output factors for certain linear accelerators. Differences in optimization methods between fixed jaw IMRT delivery (Varian) and conformai jaw IMRT delivery (Elekta) when Pinnacle treatment planning is employed may be significant.
SU‐GG‐T‐197: Dosimetric Investigation of Patient Specific IMRT QA Using MatriXX
Authors: Lin T , Hossain M , Price R , Jin L , Ma C
Published: August 2010

Purpose: This study is to investigate the dosimetric differences between two methods of IMRT plan delivery with the IBA‐rmRT MatriXX measurements: gantry‐straight‐down and patient‐specific‐angle deliveries for three treatment sites. Methods and Materials: Varian‐Eclipse and CMS‐XiO TPSs are used for 6 IMRT patient plans including 2 each of Head‐and‐Neck(HN), prostate and breast. The MatriXX has a total of 1020 ion chambers distributed within a 24.4×24.4 cm2 area. Each chamber is 4.5mm diameter, having an active volume of 0.08cm3. Ion chambers are separated by a center‐to‐center distance of 7.62mm. IBA Dosimetry‐OmniPro I'mRT software is used to analyze 2D dose distributions. Comparisons between planning calculations and QA delivery measurements are made. Gamma analysis with different dose thresholds(10∼30%) and a fixed dose‐gradient‐threshold are applied to compare two dose distributions. Gantry angle dependence is explored by comparing dose planes between measurements and exported plans from the TPS in gantry‐straight‐down and patient‐specific‐angle scenarios. Results: The MatriXX total‐pixel‐passing‐percentage differences between gantry‐straight‐down and patient‐specific‐angle deliveries on MatriXX are small, 0.8% for prostate, 1.1% for breast, 2.7% for HN sites. Due to larger dose‐gradient angular dependence effects for complicated dose distribution(HN cases), slightly lower IMRT QA passing rates for HN cases can be expected and this could suggest lower QA passing criteria for HN cases. However, these large differences observed for HN cases between straight‐down and patient‐specific‐angle deliveries could also reflect dosimetric differences due to the machine gantry or MLC sag and other issues related to the detector array. Therefore, treatment plans with very low passing rates should be examined individually. Conclusion: Slightly lower passing rates for IMRT QA using MatriXX are expected for complex dose distributions and treatment geometries with MatriXX measurements. To reproduce the actual treatment situation for QA, patient‐specific‐angle deliveries are desired as it can detect real gantry and MLC delivery problems at different gantry angles.
SU‐GG‐T‐199: Quality Assurace for Large Field IMRT Using EPID Images
Authors: Rice R , Kim G , Kinsey E , Whitaker M , Pawlicki T
Published: August 2010

Purpose: Quality assurance of Large Field IMRT (LFIMRT) treatments present a unique problem for users of portal dosimetry because LFIMRT calculations are not currently supported in the portal dosimetry calculation module. However, EPID images of LFIMRT delivery can be acquired in the normal manner used for portal dosimetry. This study reports a technique for the dosimetric analysis of LFIMRT delivery using integrated EPID images and IMRT analysis software. Method and Materials: LFIMRT plans are calculated using the ECLIPSE treatment planning system from Varian Medical Systems. Treatments are delivered and images are acquired using a Varian Trilogy linear accelerator and an as 1000 imager. For comparison with the acquired EPID images we use the AAA algorithm in Eclipse to calculate dose in a plane at dmax in a water phantom simulating the imager geometry. A single scaling factor is applied to the Dicom image to allow conversion to absolute dose. The calculated and measured images are then analyzed using the RIT113 IMRT analysis software. Results: Analysis of a 7 field Head and Neck plan was performed utilizing the gamma analysis with 3%/3mm criteria and a dose threshold of 10%. Gamma passing rates ranged from 98.6% to 99.7% with an average passing rate of 99.3% .Conclusion: Quality assurance of LFIMRT delivery can be performed with integrated EPID images and standard IMRT analysis software utilizing dose calculations at dmax in a water phantom with excellent results.
SU‐GG‐T‐202: Automation of Patient Specific IMRT QA Plan Generation
Authors: Yaddanapudi S , Yang D , Moore K , Goddu S , Mutic S , Rangaraj D
Published: August 2010

Purpose: An effort to automate the planning process for measurement based patient specific intensity modulated radiation therapy (IMRT) quality assurance (QA). Method: In our clinic before an IMRT plan is delivered, we perform measurement based QA using ionization chambers, MapCheck diode array and MatriXX chamber array. The patient plan is copied onto the phantom, dose is computed and ionization chamber points are picked or the planar dose planes are exported. This process is resource intensive and would require a physicist to spend time on generating the QA plan. To automate this process of QA plan generation we have implemented a set of software tools on the Pinnacle treatment planning system (TPS). The tools are implemented using Pinnacle scripting combined with other programming languages including Perl and C/C++. The scripts automatically operate the Pinnacle TPS to create the QA plans, export phantom dose data and generate all necessary documents and reports. Results and Conclusion: The developed scripts for QA plan generation have been used in clinic for months. They have aided in speeding up the plan generation process and reducing measurement failure/repetition rate. Overall, these tools are useful to make the daily QA plan generation on Pinnacle automatic, efficient and less repetitive.
SU‐GG‐T‐205: Limitations of Delta4 IMRT QA for Large Field Sizes
Authors: Lawrence M , Chang S
Published: August 2010

Purpose: Pre‐treatment QA of IMRT plans are critical to uphold patient safety. Given that IMRT plans are becoming more prevalent in radiation oncology it is important to exam the limitations of current IMRT QA devices. Current IMRT QA devices use a 2D array of detectors to examine IMRT QA plans, and 3D analysis is lacking. The Delta4 is a relatively new IMRT QA device, that can perform 3D plan analysis, however the field size limitations of the device are unknown. We herein examine the abilities of the Delta4 to perform IMRT QA on 80 IMRT plans on various treatment sites. Methods and Materials: Clinical IMRT plans from an in‐house TPS, PlanUNC, were retrospectively examined to determine the field size limitation on the Delta4. 20 IMRT plans for each of the following sites were examined: head and neck (H&N), prostate, breast, and pelvis. We determined if the entire intensity map could be measured using the Delta4 based upon the treatment field size using the suggested isocentric set‐up. We also determined which treatment field intensity maps with large field sizes could be completely measured using isocenter shifts for the Delta4. Results: Using the Delta4, 6 H&N, 20 prostate, and 3 pelvis IMRT QA plans were deliverable. Due to large field sizes 14 H&N, and 17 Pelvis plans required a shift to complete measure the dose fluence. All 20 breast IMRT QA plans were deliverable on the Delta4, however all fields were prescribed a table kick out, which greatly increased the time required to measure the plans. Conclusions: The 20cm × 20cm field size of the Delta4 limits its ability to measure large treatment fields using the isocentric set‐up. However shifting the device can increase the detector size, but also decreases IMRT QA efficiency.
SU‐GG‐T‐208: 3‐D Dosimetric Comparison of IMRT with 2.5 Mm HD120 MLC Using Optical CT Based Polymer Gel and PRESAGE Dosimeters
Authors: Wuu C , Maryanski M , Adamovics J , Xu Y
Published: August 2010

Purpose: To evaluate and compare the 3‐D dose distributions for IMRT with 2.5 mm HD120 MLC using optical CT based polymer gel and PRESAGE dosimeters. Method and Materials: In this study, a polymer BANG gel dosimeter and a PRESAGE phantom, together with an optical CT scanner, were employed to implement 3‐D dose distribution measurements. Both dosimeters, with 15 cm diameter and 14 cm height, were modified to optimal and linear dose‐response characteristics. A slice thickness of 2.5 mm without spacing was used for CT simulation on both the patient and cylindrical phantoms. The Varian Eclipse treatment planning system was used to design the IMRT radiosurgery plan for a patient with a 2.5 cc small brain tumor treated with 6 MV photon beams. To correlate the optical density response with radiation dose, the same batch of gel and PRESAGE phantoms were irradiated with a 16 MeV electron beam to a known dose at the depth of dmax. The optical density at a specific depth and the PDD table of the electron beam can be used to obtain the optical density dose response of the dosimeters. Both phantoms were scanned with 1 mm pixel resolution using a commercial optical CT scanner, OCTOPUS™ (MGS Research Inc., Madison, CT). Results: Both measured dose distributions from gel and PRESAGE and calculated results are in reasonable agreement. However, the isodose lines from the measurements show more variation than those from the calculation, and this trend is more significant for the 2.5 mm MLC. These discrepancies may be partly attributed to the fact that the calculation grid for the planning system is 2.5 mm yet the resolution of gel measurements is 1 mm, as well as the Trilogy TX having a smaller leaf width. Issues and difficulties on 3‐D dosimetric comparison will be presented.
SU‐GG‐T‐210: An Examination of the Usefulness of Films in Addition to Electronic Methods in Pre‐Treatment IMRT QA
Authors: Bailey D W , de Boer S F , Podgorsak M B
Published: August 2010

Purpose: Using radiographs for IMRT QA carries many disadvantages. Electronic QA methods, e.g. diode arrays, have become standard for efficiently and accurately verifying dose distributions. Because diode arrays have relatively low resolution, radiographs might be used in addition to array measurements to qualitatively verify geometric accuracy of fluence delivery. However, the finite ability of the human eye to compare films and TPS printouts is unreliable: diode arrays may detect geometric inaccuracies before the errors are recognizable on film. Does qualitative use of films contribute significantly to the pretreatment verification process? Methods and Materials: Four IMRT fluences (varying modulation) were delivered both on film and MapCHECK1 (Sun Nuclear Corporation). Errors were systematically introduced by omitting portions of the fluence, simulating a communication error between planning and delivery systems. Diode array measurements were compared to the TPS verification plan using DTA (3%, 3mm). Films were compared to TPS printouts by light‐box overlay. Increasingly larger portions of the fluence were omitted until the QA failed, either by errors observed on the film or MapCHECK DTA with <85% passing points. Results: For every modified fluence that failed QA, errors were apparent in MapCHECK before being observed on film. With up to 20% control points omitted, all radiographs appear virtually unchanged to the naked eye. On average, MapCHECK analysis of the same fluences failed due to omission of approximately 7% control points from the center of the fluences and 17% from the outer portions of the fluences. Conclusions: If an IMRT fluence is changed due to data transfer errors, qualitative analysis of radiographs does not improve upon the effectiveness of MapCHECK at detecting the error. Because such errors may not be detected if ≤20% control points are lost/corrupted, DTA analysis should always be accompanied by examination of isodose distributions and dose line profiles.
SU‐GG‐T‐212: Verification of IMRT Plans for SRT with 2D Detector Array
Authors: Ivanova T , Kassaee A
Published: August 2010

Purpose: To evaluate the use of 2D detector array for verification of intensity modulated radiotherapy (IMRT) fields for stereotactic radiotherapy (SRT) treatments. Method and Materials: We evaluated ten SRT plans with field sizes ranging from 3 cm to 6 cm with MapCHECK device that is routinely used for IMRT plan verification. We calculated the percent of passing points (PPP) for the distance to agreement (DTA) for absolute dose between measured and planned isodose lines above 10% using the MapCHECK software. We selected a value of 3 mm for DTA and 3% dose difference criteria for comparison. Dose sampling by MapCHECK detector array is limited for small field sizes due to detector geometry with 0.7 cm spatial resolution diagonally. To increase the number of points for more accurate evaluation, we repeated the measurement four times by shifting the array 0.5 cm in orthogonal directions. We then compare the combined measurement for each plan. We also measured the relative dose fluence using Kodak EDR2 films. We performed the γ analysis both for 3%, 3 mm and 2%, 2 mm criteria. The OmniPro‐I'mRT software was used for film comparison with treatment plans. There was no direct comparison between film results and MapCHECK measurements. Results: The average PPP for merged shifted fields is 98.7%, while for single plan delivery is 98.5%. Slightly lower PPP was shown for a 3 cm field size plan with high dose gradient. For each individual plan, the variation between shifted measurements could rise as high as 8% for smaller fields. The average PPPs for film and MapCHECK compared to planned dose are 98.7% vs. 100% for γ analysis with 3%, 3 mm criteria and 92.2% vs. 97.7% for γ with 2%, 2 mm, correspondingly. Conclusion: MapCHECK is an appropriate clinical tool for verification of IMRT plans for SRT.
SU‐GG‐T‐213: Portal Dosimetry for Pre‐Treatment Verification of IMRT Plan: A Comparison with 2D Ion Chamber Array
Authors: Sharma D , Mhatre V , Heigrujam M , Talapatra K , Mallik S
Published: August 2010

Purpose: To compare portal dosimetry (PD) and 2D pixel ion chamber (MatriXX) for pre‐treatment verification of photon fluence. Method and Materials: PD was performed for 181 fields from 14 IMRT plans of various clinical sites using aSi1000 electronic portal imaging device (EPID) and portal dose prediction (PDP) algorithm implemented in Eclipse Treatment planning system (TPS). Agreement of PDP predicted and EPID measured photon fluence were evaluated using gamma (γ) index set at 3% at 3 mm. Three γ scaling parameters, maximum γ (γmax), average γ (γavg) and percentage of points with γ≤1 (γ%≤1) were estimated for each field. An independent measurement was carried out using MatriXX with detector plane at 100 cm and γmax, γavg and γ%≤1 were estimated using Omnipro IMRT analyzing software. Effect of extended source to detector distance (SDD) and gantry rotation on PD outcome was also investigated for another 45 IMRT fields. Results: PDP predicted and EPID measured photon fluence agrees well with overall mean values of γmax, γavg and γ%≤1 at 2.02, 0.24 and 99.43% respectively. γmax value was lower in 15 MV compared to 6 MV IMRT plan. Independent verification using MatriXX showed comparable overall mean values of γavg and γ%≤1 at 0.25 and 99.80%. However, in all plans, MatriXX showed significantly lower γmax (p<0.05) with an overall mean value of 1.35. In PD, compare to γ values at 100 cm SDD, γmax, γavg and γ%≤1 values improve from a mean of 0.16, 0.03 and 0.25 at 110 cm SDD to 0.34, 0.05 and 0.29 at 140 cm SDD. PD outcome was independent of gantry rotation. Conclusion: Both PD and MatriXX showed comparable result and can be use as an alternative to each other for relative photon fluence verification. While portal dosimetry reduces measurement time, absolute dose measurement needs further investigation.
SU‐GG‐T‐216: Practical Considerations and Clinical Implementation of Patient Specific QA for Volumetric Modulated Arc Therapy
Authors: Song Y , Obcemea C , Mueller B , Burman C , Mychalczak B
Published: August 2010

Objectives: We developed the first no‐commercial treatment planning system for volumetric modulated radiation therapy (VMAT) in the United States. Because VMAT involves multi‐parameter modulations, it is imperative to develop a comprehensive, rigorous and yet, practical procedure for routine patient‐specific QA. Here, we present our own approach as currently practiced at our institution. Materials and Methods: Our patient‐specific QA procedure involves multi‐levels: pre‐treatment QA, on‐treatment QA, and post‐treatment QA. The pre‐treatment QA focuses on dosimetry verification. It is done with the commercial MapCHECK in MapPHAN, mounted on an isocentric mounting fixture (IMF). This approach is also called the fixed‐gantry technique, i.e., the beams are always perpendicular to the detector plane. The on‐treatment QA involves in‐vivo optically stimulated luminescent dosimetry (OSLD). Prior to the treatment, two nanoDot™ OSLD dosimeters are placed on the patient abdomen under 1 cm bolus at the isocenter location. The irradiated dosimeters are read by a nanoDot™ reader and the average reading of the two is calculated. The post‐treatment QA involves analyzing the DynaLog and DLog files. The DynaLog is a treatment log file that contains the planned and actual leaf positions for a given gantry angle. The DLog file is a treatment log file that contains the planned segmented treatment table (STT) and the corresponding segment boundary samples, i.e., the actual delivered MU and gantry angle increment for each control point. Results: For the VMAT plans we have treated so far, the average pass rate was 97.3±2.0% and the dose discrepancy at the isocenter was −0.77±0.96%. The difference between the calculated and measured doses at the chosen point on patient skin was −3.1±0.24%. Conclusions: We believe that our QA procedure can minimize the possibility of treatment errors and maximize the patient safety.
SU‐GG‐T‐292: Comparison of Helical TomoTherapy Patient Quality Assurance Using PTW Seven29 and ScandiDos Delta4
Authors: Myers P , Stathakis S , Gutiérrez A , Mavroidis P , Mihailidis D , Papanikolaou N
Published: August 2010

Purpose: The purpose of this project is to compare the Delta4 and Seven29/OCTAVIUS phantoms on the basis of patient Quality Assurance (QA) plans for Helical TomoTherapy. Materials and Methods: The PTW Seven29 2D‐ARRAY inserted into the OCTAVIUS octagonal phantom as well as the ScandiDos Delta4 phantom are intended for the dose validation of IMRT plans in which the dose delivery is from different angles. A total of 20 patient QA plans were delivered using Helical TomoTherapy with the Delta4 and Seven29/OCTAVIUS for comparison. Each plan was compared based on gamma percentage with both the clinical, 3% and 3mm, parameters and more stringent, 2% and 2mm. Results: Using the clinical gamma criteria, 3% and 3mm, the average gamma pass percentage was 96.03% for the Delta4 and 98.00% for the Seven29/OCTAVIUS. Using gamma criteria 2% and 2mm, the average gamma pass percentage were 83.31% and 89.54% respectively. On 14 out of 15 plans for 3% and 3mm, and 11 of 14 for 2% and 2mm, the Seven29/OCTAVIUS had a higher gamma percent than Delta4. Both the Seven29/Octavius and Delta4 had a 90% or greater gamma percent for all plans with 3mm, 3% parameters, and therefore each plan was considered clinically acceptable. Conclusions: In order to deliver the most accurate IMRT treatments to clinic patients, a QA plan must be performed and must pass the clinical standards before delivery. The Seven29/OCTAVIUS and the Delta4 phantoms are comparable in performance based on average gamma passing percents. Based on these measurements however, the Seven29/Octavius gives better results when using the clinical passing criteria of 3%, 3mm as well as the more stringent 2% and 2mm when comparing QA plans with Helical TomoTherapy. Research sponsored by PTW corporation.
SU‐GG‐T‐300: Method for In‐House Leaf‐Dependent MLC Offset Correction
Authors: Mader B , Rice J
Published: August 2010

Purpose: Manufacturer recommended rounded leaf offsets for the Philips Pinnacle treatment planning system are inaccurate for leaves away from the central axis, and for varying energies. The need for an in‐house MLC rounded leaf offset correction is established, as well as a method for determining the offsets for individual MLC leaves. Materials and Methods: A standard picket‐fence test is developed with 2 cm separations across a 25×25 field. Dose distributions are calculated for the test, with 20th leaf offset values for the X = 0.0 position ranging from −2.0 to +2.0 mm from the nominal leaf position, using the manufacturer recommended offset curve for leaves 1–40. Dose profiles are collected along the cross‐plane of the 20th leaf. The picket‐fence test plan is delivered to a film, in phantom at 90cm SSD and 10 cm depth, for 6 and 10 MV energies. Dose profiles are measured through the central axis and superimposed on the calculated profiles produced by the TPS. The profiles are compared for agreement. Results: It was found that the measured dose profiles do not match manufacturer recommended offsets for leaves away from the central axis. If the calibrated leaf (20th) is matched to the tabular data, there is deviation in the picket‐fence test at distances >5.0 cm from the central axis, resulting is dose discrepancies. Manufacturer‐recommended offsets were also observed to be inaccurate for the 10 MV beam, exhibiting an energy‐dependence of the required offset values. Conclusions: It is found that manufacturer recommended rounded leaf offsets are inaccurate and in‐house measurements are required to determine appropriate offsets for groups of leaves near and away from the beam's central axis. It was also found that there is an energy dependence for these offsets. A method for making in‐house corrections is established by using measured and calculated dose distributions.
SU‐GG‐T‐303: Evaluation of the Sensitivity of the Anisotropic Analytical Algorithm (AAA) to the Commissioning Dataset
Authors: Yaldo D , Tailor R , Scarboro S , Sahoo N , Kry S , Kisling K , Followill D , Howell R
Published: August 2010

Purpose: To test the sensitivity of the Eclipse anisotropic analytical algorithm (AAA) to expanded commissioning data that includes small‐field data and data corrected for detector size. Method and Materials: A 0.01 cm3 ionization chamber was used to measure an extended commissioning data set for a 6 MV photon beam including open field profiles (OFP), percent depth dose (PDD), and output factors for field sizes ≥ 1×1 cm2. OFP were processed using mean‐value symmetry and adjusted for detector size effects. OFP were smoothed outside the penumbra region for noise reduction. PDD data were shifted to account for the effective point of measurement and then smoothed. Four unique beam models were commissioned to evaluate the impact of correcting the measured data for detector size as well as small‐field data inclusion. We compared the resulting AAA calculated models with the model based on Golden Beam Data (GBD) provided by Varian Medical Systems. Models were compared using a 1 mm calculation grid. Results: The various models proved to be insensitive to adjustments for detector size effects and also to the inclusion of small‐field data. All models, regardless of the penumbra of input profiles, exhibited nearly identical penumbra in the final calculated model. The algorithm narrowed the penumbra for the model commissioned with GBD i.e. with broad penumbra. Conversely, the algorithm broadened the penumbra for the model commissioned with measured data that were smoothed and corrected for volume averaging effects i.e. data with narrow penumbra. Conclusion: Results suggest that the TPS utilizes a generic model for the penumbra region in calculated models, thus ignoring measured data. The negligible impact of inclusion of small‐field data on the TPS's calculated model may be due to the large relative size of the penumbra region for those fields.
SU‐GG‐T‐305: Evaluation of Some Essential Dosimetric Parameters for Beam Matching of Similar Accelerators
Authors: Bhangle Janhavi , Sathiya Narayanan V.K. , Krishnakumar Namitha , Joseph Jolly , Nirhali Amit , Vaitheeswaran R
Published: August 2010

Purpose: To dosimetrically evaluate beam matching procedure of two similar accelerators using gamma index. Method and Materials: The second accelerator was beam matched with first one using Vendor's acceptance test (ATP) protocol. Depth dose and inline‐crossline profiles were matched within ±1%. In order to quantify the level of agreement between the matched beams we performed a set of measurements including total scatter, collimator scatter, wedge transmission and absolute dose measurement. The ATP specifications are at particular points on the ionization curve for depth dose or profile. Gamma was used to compare planar dose distribution from EDR2 films exposed on both units. For 6MV photon we exposed a film for PDD (10×10cm), beam profile (5,10 and 20cm), a pyramid shape, to compare dosimetric and positional accuracy of MLC a pattern of strips with different MUs at different positions and a diamond shape was exposed. We also exposed a film at tray level to a segmented IMRT field to compare collimator scatter. To account for TPS calculations a film kept in axial plane was exposed to 3DCRT and IMRT plan with actual gantry angles. Absolute dose was measured simultaneously using point chamber. Results: Total scatter, collimator scatter and wedge transmission factors were within ±1%. The absolute dose for 3DCRT and IMRT plan was within ±1% of reference value and within ±3% of TPS value. EDR2 films exposed on both units were analyzed using OmniPro IMRT software. Gamma was calculated for different delta dose and delta distance. The analysis has shown that all these comparisons were in good agreement for delta dose of 2% and delta distance of 2mm. Conclusion: All these tests were done at the commissioning time. We are periodically checking few parameters like PDD, beam profile and MLC accuracy to assure the consistency in beam matching
SU‐GG‐T‐312: Intrabeam‐Intraoperative Radiotherapy Unit Quality Assurarance Measurements with EDR2 Films and Radiological Imaging Technology
Authors: Muralidhar K Raja , Mallikarjun  , Birendra  , Poorniam
Published: August 2010

Purpose: EDR2‐QA films were developed for patient dosimetry in Intraoperative radiotherapy. In this study a method to evaluate the isotropy, PDD, Isodose and beam deflection using EDR2‐QA films and a vidar scanner with RIT Software was developed and tested. Methods and Materials: Intrabeam System is (50KeV, 40μA) intraoperative radiotherapy unit. X‐ray source (XRS) equipped with a 10 cm long (o/ 3.2 mm) probe. Five Films were irradiated for one minute each at a distance of 5cm from the source in all 5 directions (0°, 90°, 180°, 270° and perpendicular to the source) with flat surface facing towards the source. Percentage depth doses were derived by exposing the film vertically down from the source. Results: Horizontal and vertical profiles from films in all directions were taken and compared with the help of RIT software. A difference of 0.7% was found between the profiles at 12cm from the central axis. PDD's were obtained with the film (which was kept vertically down from the source) by normalizing the values at 2 cm depth (known dose) from the surface. These PDD's proved l/r3 and can be implemented on CT. Dose distributions were also derived by RIT software. Films were exposed at different distances from the source and found that these doses are comparable with the doses obtained from Ionization chamber (<1%). Conclusion: Some of these QA procedures can be incorporated as periodic and some can be incorporated as regular QA procedures before taking any patient. These film measurements proved and shown the simple way of checking the Isotropy, PDD, Isodose and beam deflection. These tests also useful to take beam data for planning systems to view the dose on CT images in 2D and 3D, which is not available on the present system.