bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐378: Radiochromic Film Based Reference Dosimetry System for 192Ir Brachytherapy Sources
Authors: Aldelaijan S , Mohammed H , Tomic N , Liang L , Deblois F , Sarfehnia A , Abdel‐Rahman W , Seuntjens J , Devic S
Published: November 2011

Purpose: Comparison between radiochromic film reference dosimetry system calibration curves established in water and Solid Water(TM) for high dose rate (HDR) 192‐Iridium brachytherapy source is described and assessed. Accordingly, a new reference dosimetry system protocol for HDR 192‐Iridium using the latest EBT‐2 model GAFCHROMIC(TM) film is suggested. Methods: Calibration curves were established in water and Solid Water(TM) using pieces of EBT‐2 GAFCHROMIC(TM) film irradiated with HDR 192‐Iridium brachytherapy source for a dose range from 0 to 50 Gy. A parallel‐opposed beam setup was specially designed to allow the positioning of the HDR source into two channels (catheters) with the film piece positioned mid‐way between them. This setup increases the dose homogeneity region over the film piece and reduces the positional uncertainty with respect to the radiation source. Responses of dosimetry systems were compared for irradiations in water and Solid Water(TM) by scaling the dose between media through Monte Carlo‐calculated conversion factor simulated for the two setups.Results: Monte Carlo calculated conversion factor, which converts dose delivered to the sensitive layer of the film in water to a dose delivered to the sensitive layer of the film in Solid Water(TM), was found to be 0.9941±0.0007. The EBT‐2 GAFCHROMIC(TM) film based reference dosimetry system described in this work can provide an overall one‐sigma uncertainty in measured dose of 2% for doses above 1 Gy Conclusions: Experimental confirmation of the Monte Carlo‐calculated factor that shows dose difference between measurements in water and Solid Water(TM) was provided. The remaining 0.6% difference between measurements in both media shows that Solid Water(TM) is a viable alternative to water as a reference medium in establishing the calibration curve at 192‐Iridium energy. Response curves utilizing green color channel only has shown superior precision if used alone in dosimetry for dose range that extends up to 50 Gy.

This work was supported by the Natural Sciences and Engineering Research Council of Canada contract No. 386009. Saad Aldelaijan would like to acknowledge Saudi Food & Drug Authority for financial support during his graduate studies.
SU‐E‐T‐379: Development of a Monte Carlo Based Correction Strategy for a TG‐43 Based Brachytherapy Treatment Planning System to Account for Applicator Inhomogeneities
Authors: Mathews B , Price M
Published: November 2011

Purpose: To investigate the use of pre‐calculated Monte Carlo (MC) ovoid‐ and source‐based attenuation‐correction factors that would correct a commercially‐available brachytherapy treatment planning system (TPS) generated plan in order to account for any dosimetric effects due to the presence of intracavitary brachytherapy (ICBT) applicators during treatment delivery. Methods: The American Association of Physicists in Medicine Task Group 43 (TG‐43) report was utilized to calculate absolute dose around an Ir‐192 source. MC was utilized to simulate dose distributions resulting from an Ir‐192 source at eight dwell‐positions within Nucletronˈs ICBT CT‐MR Fletcher applicator (with and without a shield surrogate). With these distributions, a library of ovoid‐ and source‐based 3D attenuation‐correction factor datasets characterizing the dosimetric effects of the ICBT applicator was developed. These factors were then applied to correct a brachytherapy TPS‐calculated plan. Plans with different maximum dwell‐time gradients were compared to evaluate the effectiveness of both correction methods with respect to criteria of acceptability being within +/− 2% absolute dose or +/− 2 mm distance‐to‐agreement (DTA). Results: Plans generated by a brachytherapy TPS with a maximum dwell‐time gradient less than 10% can be corrected utilizing either correction method to agree with full simulated Monte Carlo datasets to within criteria. A dwell‐time gradient of 10% is a threshold for the ovoid‐ based correction scheme. The source‐based correction method consistently results in 100% agreement between a corrected plan and the equivalent MC generated plan. Conclusions: No correction scheme is necessary for the ICBT CT‐MR Fletcher compatible ovoid applicator. For a shielded applicator, source‐ based correction factors can be applied to correct a TG‐43 based treatment plan with any set of dwell‐time combinations to match a full MC simulation.
SU‐E‐T‐381: Dosimetric Analysis of Patients Treated with Accelerated Partial Breast Irradiation Using the Mammosite® and SAVI Applicators
Authors: Sehgal V , Zhang J , Dietrich S , Al‐Ghazi M , Wong J , Kuo J , Ramsinghani N
Published: November 2011

Purpose: To present dosimetric data for patients undergoing Accelerated Partial Breast Irradiation (APBI) using the Mammosite® and Strut‐Adjusted Volume Implant (SAVI) applicators. Methods: We have treated 35 patients with Accelerated Partial Breast Irradiation (APBI) using high dose rate brachytherapy. These patients were treated per guidelines specified in the NSABP B‐39/RTOG 0413 protocol. The patients undergoing APBI have been treated with Mammosite® applicator (N=20) and SAVI applicator (N=15). The Mammosite® applicator used for all 20 patients was a single channel applicator. Single or multiple dwell positions were used as warranted by the type of balloon used and other clinical factors. The SAVI Applicator is a single‐entry, multi‐catheter device available in different sizes with 7, 9 and 11 catheters. The use of multiple catheters facilitates dose sculpting to improve treatment plan quality as well as reduce the skin dose. Each treatment plan was evaluated for conformance of the dose to the PTV using commonly used dosimetric parameters. These parameters included balloon/cavity volume, PTV volume, V90, V100, V150 and V200. Results: The median V90 for the treatment plans delivered using the Mammosite® applicator was 99.7% (96.7%–99.8%) whereas it was 98.8% (96%–100.0%) for the patients treated with the SAVI applicator. Other data including the V100, V150, V200 and skin dose will be presented. The impact/ importance of the data presented is that it provides useful information about the range of dosimetric parameters to be expected in treatment planning of APBI cases using these applicators. Conclusions: : Our results indicate that both the Mammosite® and SAVI applicators allow treatment planning and delivery of APBI per the guidelines specified in the NSABP B‐39/RTOG 0413 protocol.
SU‐E‐T‐387: A Biologically Effective Dose Volume Histogram for Optimizing Eye Plaque Brachytherapy
Authors: Gagne N , Leonard K , Rivard M
Published: November 2011

Purpose: Clinical optimization of eye plaque brachytherapy is currently limited to tumor coverage, standardized prescription dosage, and dose calculations to ocular structures. The biologically effective dose (BED) of brachytherapy treatments is a function of implant duration and chosen radionuclide. A novel method would propose to evaluate eye plaque brachytherapy implants based on BED delivered to the tumor volume and surrounding normal ocular structures.Methods: Using the equation introduced by Dale for temporary low dose rate (LDR) brachytherapy implants, 16 mm COMS‐eye plaque patient DVH data were converted to biologically‐effective dose volume histograms (BEDVH). These data were calculated for Pd‐103, I‐125, and Cs‐131 for different implant durations. Therapeutic ratios were derived from comparing BED results as a function of implant duration for tumors and normal ocular structures (lens, lacrimal gland, and optic nerve). Isobiologically‐effective physical doses were created for different implant durations and radionuclides. Results: The BEDVH curves were dependent on implant duration and less sensitive to radionuclide choice. In comparison to a 7‐day implant, maximum BED for a 1‐day implant increased by a factor of 2–3 for normal ocular structures; for the tumor, maximum BED increased by a factor of 4.5. These factors decreased with increasing implant duration, and were not significantly radionuclide‐dependent. Conclusions: A method was introduced to evaluate and further optimize eye plaque dosimetry through analysis of BED delivered to the tumor and adjacent normal tissue volumes. This method is readily adaptable to other temporary or permanent brachytherapy implants in a variety of clinical situations.
SU‐E‐T‐389: Energy Deposition Characteristics of Beta‐Emitter P‐32 and Photon Emitter Pd‐103
Authors: Li Texin , Tong Shidong , Gong Jason , Fountain Lynn , Duffy Edward
Published: November 2011

Purpose: Comparing the energy deposition characteristics of beta‐emitter P‐32 and photon emitter Pd‐103 to evaluate potential improvement in prostate brachytherapy dosimetry.Materials /Methods: Energy deposited by an activity A after total decay is calculated by 1.44T1/2AE, where E is the energy emitted by a single disintegration. The total energy deposited in the target will be 1.44T1/2AE F, where F is the absorbed fraction (AF). Absorbed fraction is defined as the fraction of emitted energy absorbed in the target. It increases monotonously with target volume. Monte Carlo calculated AF data for uniformly distributed spherical targets, 1 for P‐32 and clinically obtained AF, 2 from Pd‐103 permanent prostate brachytherapy are used in this study. Results: A unity activity (1 mCi) of P‐32 will deliver 7.38 joules, while the same activity of Pd‐103 will deliver 0.26 joules. The total energy deposited in a volume of 20 cc will be 6.90 joules for P‐32 and 0.11 joules for Pd‐103. As the volume of the target increases to 60 cc, the total energy deposited for P‐32 will be 7.06 joules, and 0.14 joules for Pd‐103 respectively. Conclusion: From the preliminary comparison, P‐32 is about 50 to 60 times more efficient in utilizing energy than Pd‐103. This high efficiency will reduce total activity needed to achieve desired dosage in the target. Also, the fact that most energy is absorbed locally in the target suggests that the dose to healthy tissue outside the target can be significantly reduced. Further study is needed in order to fully realize these potential dosimetric advantages.
SU‐E‐T‐393: A Novel 4D Dosimetric Characterization of a Common 103‐Pd Brachytherapy Source with Mobile Internal Components
Authors: Baradaran‐Ghahfarokhi M , Mosleh‐Shirazi M , Faghihi R , Hadad K , Bagheri M , Naghshnezhad Z , Meigooni A
Published: November 2011

Purpose: A new method, based on the Finite Element (FE) modeling, has been introduced for dosimetric assessment of the brachytherapy sources with mobile internal component. Methods: Dosimetric characteristic of a commercially available brachytherapy source, Best Double‐Wall Model 2335 103Pd seed, were calculated by Monte Carlo (MC) simulation using the MCNP4c2 and MCNP5 codes according to the updated AAPM Task Group 43 (TG43U1) protocol, following finite element (FE) modeling to predict displacements of the seedˈs internal radioactive components in different orientations of the seed encountered in clinical practice (4D dosimetry). The complete seed geometry and materials together with a published 103Pd spectrum were used to perform finite‐element modeling using ABAQUS v.6.8.1 software and dosimetric characterization of the source using MCNP4c2 and MCNP5 codes. Results: Using FE modeling, change of seed orientation resulted in displacements of the seedˈs internal components. For the case of the Model 2335 103Pd seed, this has a negligible effect on the dose rate constant and radial dose function (<1%) but the consequences on the 2D anisotropy function was greater (up to 16.2% at small angles). Conclusions: There are no clinically significant variations in the dose rate constant and radial dose function due to the uncertainty of the internal position of the structures for the Model 2335 103Pd seed. However, the uncertainty in the 2D anisotropy function at smaller angles is larger than what has been reported, due to the motion of the internal components. Using this 4D dosimetry method is suggested to determine the dosimetric characteristics of each new brachytherapy seed with mobile internal components.

Keywords: Palladium‐103, Brachytherapy, Monte Carlo simulation, Finite Element modeling, TG43U1
SU‐E‐T‐395: Feasibility Study of a Novel Technique to Measure Instantly the Strength of 125I Seeds Being Implanted
Authors: Tanaka K , Tateoka K , Asanuma O , Endo S , Sato K , Takeda H , Kamo K , Hori M , Hareyama M , Takada J
Published: November 2011

Purpose: Final goal is to develop a technique to detect the 125I seed and measure its strength during implantation process. This will be a backup tool for QA by offering an additional measurement apart from the pre‐operation measurement. In actual implantation, the speed of the seed varies because it is conducted manually. In order to develop a simple and stable system usable in any speed, this study supposes to use single detector and repeat short‐time measurements. This report summarizes a feasibility test. Methods: The 125I seeds　(Oncra Inc. Oncoseed 6711) was moved in speeds up to 200 mm/s by an electric actuator. Its strength was measured with a NaI detector (1″diam. × 1″) set at 170 mm from the needle guiding the seed. The requirement for the counting time was investigated to estimate the strength regardless the seed speed. Results: In the measurement where the seed was set static in needle, the change in counting rate of the NaI detector was 4 % at the 30 mm‐long region along the needle, while the counting rate rapidly decreased outside the region. It is desirable to start‐stop the measurement while the seed is within this region. Assuming 200 mm/s as the maximum speed, 7 to 8 measurements can be performed for the counting time of 20 ms, 3 measurements at 50 ms, 1 measurement at 100 ms. By using the average of the measured results while the seed was within the region, the estimated seed strength agreed within 10 % between the speeds 0 and 200 mm/s at counting time of 100 ms or less. Conclusion: This report shows the feasibility in principle to estimate the 125I seed strength during the implantation operation, regardless the seed velocity.
SU‐E‐T‐397: Development of An Ultrasound‐Based Prostate Model to Aid in CT‐Based Dosimetry in Prostate Brachytherapy
Authors: Tam C , Spadinger I , Thomas S , Chng N , Morris W , Keyes M , Moradi M , Lobo J , Salcudean T
Published: November 2011

Purpose: To determine whether the reliability of calculated dose metrics in permanent implant prostate brachytherapy, performed on post‐operative CT, can be improved though the use of a semi‐automatic prostate model based on intra‐operative ultrasound. Methods: Intra‐operative trans‐rectal ultrasound (TRUS) data was collected from clinical subjects undergoing low dose rate prostate brachytherapy. Seed verification in TRUS data was acquired through seed cloud reconstruction in fluoroscopy data collected at the same time. A simplified 3‐D prostate model was constructed from prostate boundary contours determined on TRUS images, and deformed to account for the effects of expected anatomical movement and deformation between data sets. Volume registration between the post‐operative pelvic CT scan, obtained as part of routine QA procedures in which a seed implant plan reconstruction is performed, and TRUS data is determined through seed matching. The transformed and transposed prostate model is used to generate CT contours that inform the QA dose metrics D90 and V100 that determine implant quality. Results: Preliminary results have shown that CT prostate contours generated using ultrasound‐ based models are within the expected variability of those drawn manually by experienced radiation oncologists, which is the current standard practice in prostate brachytherapy QA. Methods for improving the registration and model accuracy, and evaluating the performance, are currently in progress. Conclusions: Prostate boundaries are notoriously difficult to discern on CT images due to poor soft tissue contrast. Dose metrics derived from CT contours are subject to considerable inter‐ and intra‐observer variability, which affects the overall assessed treatment quality. We have found that an ultrasound‐based semi‐automatic prostate model can be registered to the CT and used to generate objective and reproducible CT contours. If applied in a clinical setting, this method could potentially improve treatment QA by setting a consistent definition of treatment volume.
SU‐E‐T‐403: Investigation of Electron Dose Calculation Using the Lateral Buildup Ratio Method
Authors: Gebreamlak W , Tedeschi D , Alkhatib H
Published: November 2011

Purpose: To calculate the percentage depth dose of any irregular shape electron block using the lateral build‐up‐ratio method.Methods: Percentage depth dose (PDD) curves were measured using 6, 9, 12, and 15 MeV electron beam energies for applicator cone sizes of 6×6, 10×10, 14×14, and 20×20 cm2. Circular cutouts for each cone were prepared from 2.0 cm diameter to the maximum possible size for each cone. In addition, three irregular cutouts were prepared. The scanning was done using a water tank and two diodes ‐ one for the signal and the other a stationary reference outside the tank. The water surface was determined by scanning the signal diode slowly from water to air and by noting the sharp change of the percentage depth dose curve at the water/air interface.Results: The lateral build‐up‐ratio (LBR) for each circular cutout was calculated from the measured PDD curve using the open field of the 14×14 cm2 cone as the reference field. Using the LBR values and the radius of the circular cutouts, the corresponding lateral spread parameter (sigma) of the electron shower was calculated. The PDD curves of the irregular cutout sizes were calculated using the sigma values of the 2 cm and the 3 cm diameter cutout sizes. Finally, the calculated PDD curves were compared with measurements of the irregular cutouts Conclusions: The PDD curves for the irregular cutout calculated using the sigma value of the 2.0 cm diameter cutout agreed with the measured PDD curves within 2% for 6MeV and 4% for 12 MeV. On the other hand, using the average sigma values of the 2 and 3 cm diameter cutouts reduced the difference by a factor of two. The result of the calculated sigma value showed that at a given depth and energy, the sigma value increases with cutout size.
SU‐E‐T‐406: Use of Portal Dosimetry with EPID for Quality Control of RapidArc
Authors: Goncalves V , Vieira A , da Cruz J , Sakuraba R
Published: November 2011

Purpose: Develop a methodology for RapidArc QA using Eletronic Portal Dosimetry Device (EPID) Methods: The RapidArc delivers intensity‐modulated radiation with different monitor units (MUs) at varying dose rates while multileaf collimator (MLC) leaves are continuously moving as the gantry is simultaneously rotating with varying speed. The quality assurance before treatment should be performed to confirm that the accelerator will reproduce what was planned.We developed a technique for using the EPID to quality assurance of RapidArc. This technique consists of converting the original motion of the MLC in a fixed gantry, keeping the MLC movements, monitor units, and fractional doses of each control point as the original plan, which can then be calculated and measured with EPID. Absolute dose measurements with ionization chamber in a water equivalent phantom were performed for validation of this technique. For planar dose distribution two comparisons were performed using as reference the gamma function (3 % / 2 mm): EPID (static field × original arc) and static field (EPID × Matrix − IBA). We evaluated the dependence of the EPID response with dose rate and with the moving gantry. Our score to approve are gamma maximum less than 3 and gamma area with value greater than 1 is less then 5%. For absolute dosimetry the score is below 3%. Results: After analyzing 120 cases, the maximum gamma was 2,8 and the mean value 1,6 and for gamma area, the maximum gamma was 4,2%. For absolute dosimetry all plans were below 3%. Was also observed that these values of gamma maximum accured in tongue‐and‐groove region, showing that the planning system is not properly modeled this effect. Conclusions: After analyzing 120 cases, the results show this methodology is appropriate for quality control of RapidArc plans.
SU‐E‐T‐408: RapidArc Dose Verification Using Ferrous Xylenol‐Orange Gels and Optical CT
Authors: Babic S , Hajdok G , Jordan K
Published: November 2011

Purpose: To perform a 3D dosimetric verification of a RapidArc™ treatment using Ferrous Xylenol‐orange (FX) gels and optical CT. Methods: Two FX gels from the same batch were prepared using 0.3 mM ferrous‐ammonium‐ sulphate, 0.05 mM xylenol‐orange, 65 mM sulfuric acid and 6% by mass porcine gelatin dissolved in distilled water. Upon preparation, the FX gel solution was poured into two separate 0.5 mm thick PFA Teflon‐walled cylinders (9.6 cm diameter, 10 cm height). One FX gel was used for RapidArc™ verification. The RapidArc™ treatment plan created with Eclipse v.8.9 software (Varian Medical Systems), consisted of 6 MV x‐ray beams delivered with a single 360° gantry rotation by Varian Clinac 21IX, and a target dose of 237 cGy. A second FX gel was irradiated with a 12 MeV electron beam to independently calibrate the dose response. Both FX gels were read out using a commercial optical cone‐beam CT scanner at a central wavelength frequency of 590 nm (Vista, Modus Medical Devices). Optical CT reconstructions at 0.5 mm3 voxels were averaged to provide 1 mm3 voxels for comparison with the planned data. Results: In the target volume of comparable slices, planned and measured dose distributions (in units of cGy) are in agreement within 2–3%. In the low dose volume region, the planned dose data is generally less compared to the measured gel data by about 5%. Contrast is slightly reduced in the cone‐beam CT gel images which may be due to residual stray light. The data reveals that larger volumes of gel (>2 L) will be needed for the verification of large target and low dose volumes. Conclusions: FX gel dosimetry with optical CT readout provides accurate volumetric dose verification and quality assurance that will lead to the safe clinical implementation of complex radiotherapy applications such as RapidArc™.
SU‐E‐T‐409: What Does Gamma Dose Evaluation Criteria Mean: A Novel Method for Delivery Uncertainty Included in Dose Distribution, Plan Evaluation and Dose Prescription in Radiation Therapy
Authors: Zhu M , Papiez L , Rangaraj D
Published: November 2011

Purpose: This study focuses on the possible clinical impacts and the trustworthy of calculated dose distributions evaluated by measured gamma criteria and potential use of plan‐specific gamma value. Method and Materials:A MATLAB‐based program was developed to calculate the upper‐ and lower‐bounds of dose distributions measured by certain gamma value (e.g. 3%‐3mm) on a voxel‐by‐voxel basis. Calculated data were imported to CERR for analyses. 15 IMRT plans for prostate, lung, and head‐ and‐neck tumors (5 for each site) were analyzed using (3%‐3mm) (the standard adopted by the authorsˈ institute). The mean dose to PTV, bladder, rectum, and parotid; maximum dose to cord, and V20 of lung are compared. Additional gamma values (2%‐3mm and 4%‐4mm) were utilized to compare the dosimetric impacts of different gamma criteria. Results: The upper‐ and lower‐ bounds vary in a wide range. For a standard gamma (3%‐3mm), the lower‐bounds of PTV‐mean are 3.01%–4.34%, 3.06%–15.6%, and 4.22%–8.28% lower than planned value for prostate, lung, and head‐and‐neck plans, respectively. The upper‐bounds increased by 2.74–7.86 Gy and 3.49–5.65 Gy for bladder‐mean and rectum‐mean doses, respectively. The cord‐max increased by 0.2–9.2 Gy and 0.74–3.02 Gy for lung and head‐and‐neck plans. The upper‐bounds of lung V20 increasing varies between 2.5% (from 4.8% to 7.3%) and 4.8% (from 62.7% to 67.6%). The upper‐bounds for parotid‐ mean increased by 0.9–9.07 Gy for head‐and‐neck plans. For various gamma applied to a lung plan, the upper‐bounds range from 39.91%–43.70% for left‐lung V20 and 27.10%–31.10% for right‐lung V20. Gamma variation for other two sites was also analyzed. Conclusion: This study provides a fast evaluation of dosimetric impact of gamma criteria to a treatment plan. The results reveal that the same gamma value can cause different dosimetric consequences for individual plan. This method can also be used to select appropriate gamma value based on the robustness of the plan.
SU‐E‐T‐414: Treatment Delivery with High‐Intensity Flattening‐Filter‐Free Beams for Head‐And‐Neck Cancers: Performance Assessment of Automated IMRT versus VMAT
Authors: Duan J , Shen S , Popple R , Wu X , Brezovich I
Published: November 2011

Purpose: With high‐intensity flattening‐filter‐free (FFF) beams and thenew automation feature of the TrueBeam accelerator (Varian Medical Systems), delivery of fixed‐field IMRT is substantially shortened. We compare treatment delivery time of automated IMRT to highly efficient VMAT for head‐and‐neck cancers. Methods: Ten patients with Stage III–IV squamous cell carcinoma of the head and neck were planned and treated with seven‐equi‐spaced‐field IMRT and two‐arc RapidArc using 6MV flattened and 6 and 10MV FFF beams at maximum dose rates of 600, 1400 and 2400MU/minute, respectively. Prescription doses are 70Gy to the primary and 54Gy to the nodal target in 35 fractions. Delivery time, defined as beam‐on time plus beam‐hold time between fields, was assessed for the three different beams in two delivery modes. Results: The mean delivery times are 2.21 minutes for RapidArc and 4.10 minutes for automated IMRT, substantially shorter than 8 – 10 minutes for IMRT without automation. High dose rate FFF beams provided no benefit to RapidArc delivery time as gantry speed limited the actual dose rate. IMRT delivery benefited moderately from the high dose rate of FFF beams with average delivery times of 4.56 minutes for 6MV flattened, 3.93 minutes for 6MV FFF and 3.80 minutes for 10MV FFF beams, respectively. The benefit of higher dose rate was significantly offset by the fact that FFF beams required 1.6 to 3.3 times the MUs of flattened beams. Conclusions: For HN cancers with conventional fractionation schemes, high intensity FFF beams have little impact on RapidArc and moderate benefit to IMRT delivery times. However, IMRT delivery efficiency is substantially improved with the automation feature. High intensity beams have potentially greater benefit for hypo‐fractionated treatment.
SU‐E‐T‐415: Investigation of VMAT Patient Specific Quality Assurance Action Levels
Authors: Mancuso G , Fontenot J , Parker B , Neck D , González G , Gibbons J
Published: November 2011

Purpose: To examine the appropriateness of patient specific IMRT quality assurance (QA) action levels for use in VMAT QA. Methods: QA measurements were evaluated for the test geometries provided in AAPM Task Group Report 119. The structure sets were copied onto a cylindrical water‐equivalent phantom. Using the Philips Pinnacle treatment planning system, IMRT and VMAT treatments were planned. The plans were delivered and the resulting dose distributions were measured (1) in 2 planes and at 3–4 points in the cylindrical phantom using radiochromic film and ion chamber, respectively, and (2) using a commercial 2D diode array. Ion chamber and diode array measurements were taken five times each, and film measurements were taken three times. Measured planar doses were analyzed using gamma analysis with criteria of 3%/3mm. Measured point doses were analyzed using percent difference. Differences between IMRT QA and VMAT QA results were tested for significance using a Studentˈs t‐test. Results: The radiochromic film results showed averages of 98.9%±1.0% and 99.1%±0.9% (p=0.47) of measured doses within 3%/3mm of calculated doses for IMRT and VMAT plans, respectively. Ion chamber results showed average differences between measured and calculated point doses of − 0.95%±1.5% and −1.8%±1.8% (p<0.01) for IMRT and VMAT plans, respectively. The diode array results showed averages of 98.7%±0.5% and 98.6%±0.7% (p=0.70) of measured doses within 3%/3mm of calculated doses for IMRT and VMAT plans, respectively. Conclusion: Differences between IMRT QA and VMAT QA results were not statistically significant for planar doses measured with radiochromic film and 2D diode array. The average difference between measured and calculated point doses was smaller in IMRT plans (p<0.01); however, the average point dose differences for both IMRT and VMAT were less than 2%. These results suggest that current action levels used in our clinic for evaluating IMRT QA may be applicable to VMAT QA.

This work is supported in part by a sponsored research agreement with Elekta, Inc.
SU‐E‐T‐419: Clinical Protocol for the Use of Scrotal Shields in IMRT Treatment of Anal Cancer
Authors: Wu Q , McMahon R , Hood R , Willett C , Czito B
Published: November 2011

Purpose: To implement a clinical protocol for the use of scrotal shields for anal cancer IMRT treatment. Methods and Results: (1) Simulation The patient is immobilized in a full‐body alpha‐cradle mold in the frog‐leg position. Further, the mold is built up near the shield to provide a stable and reproducible setup. The planning CT images are taken in 2 sets with patient in the same position: first one with shield to capture the actual position and shape of the shield, and the second without shield for actual planning and dose calculation. These two image sets are then fused for treatment planning and DRR generation.(2) IMRT planning To avoid irradiation of the PTV through the shield, jaw sizes and collimator rotations are manually optimized for each beam. Each beam only covers a portion of the projected PTV while avoiding the shield. When it is favorable to cover the entire PTV from the anterior directions, zero fluence is enforced in the region where the field overlaps with the shieldˈs projection. In the inverse planning process, the shield structure is given a high priority as an avoidance structure so that the fluence through the shield is minimized. With the combination of these steps, the resulted IMRT has a highly conformal dose distribution with 95% of the target volume covered by the prescription dose and a global maximum dose of 112%. (3) IGRT Daily KV imaging ensures the proper alignment of the bony anatomy and the positioning of the shield, with the shield projected on the DRR. Day1 and weekly CBCT imaging further confirms soft tissue target alignment Conclusions: .A clinical procedure for using a scrotal shield in IMRT treatment of anal cancer is described in detailed steps from simulation and planning, to treatment verification and is demonstrated with a clinical patient case.
SU‐E‐T‐420: Sensitivity of the Plan‐Class Specific Correction Factor to the Dose Distribution in Reference Dosimetry of Nonstandard Fields
Authors: Chung E , Soisson E , Seuntjens J
Published: November 2011

Purpose: To analyze the sensitivity of a plan‐class specific correction factor to dose distribution in nonstandard field dosimetry. Methods: Ten different TomoTherapy‐based IMRT fields were created on a water‐filled PMMA cylindrical phantom at the center of which the absorbed dose to water was measured. Dose distribution of each IMRT field was evaluated using three parameters: modulation factor (MF), modified conformal index (COIN) and homogeneity index (HI). The relative dose in each IMRT field was measured using a PTW micro liquid ion chamber. Based on the new dosimetry formalism, the plan‐class specific correction factor was measured for two 0.6 cm3 Farmer‐type chambers (Exradin A12 and NE2571) and a 0.06 cm3 Exradin A1SL chamber. We investigated the dependence of the measured correction factor on the three plan evaluation parameters. Results: Uncertainty on the measurement of the plan‐class specific correction factor was 0.2–0.4 % and 0.2–0.7 % for the Farmer‐type chambers and Exradin A1SL, respectively. When the dose homogeneity was better than 5 % along with values of MF and modified COIN smaller than 2.0 and 0.025, respectively, the correction factor of the IMRT field was not different from unity by more than 0.7 %. For more heterogeneous IMRT fields, the correction factor deviated from unity by up to 2.4 % for the Farmer‐type chambers because of increasing residual gradient effects. For the Exradin A1SL, while it was closer to unity, the correction factor was highly variable in different IMRT fields due to a more significant impact of positioning uncertainties on the response of the smaller chamber. Conclusions: We have shown that the plan‐class specific correction factor can be characterized as a function of plan evaluation parameters, especially for Farmer‐type chambers. This work provides a recipe based on quantifying dose distribution to accurately select air‐filled ionization chamber correction factors for nonstandard fields.
SU‐E‐T‐421: Commissioning and Validation of a Next Generation IMRT QA Method to Provide 3D Delivered‐Dose Verification
Authors: Klaers J , Santanam L , Pereira G , Klein E , Goddu S
Published: November 2011

Purpose: Traditional IMRT quality assurance (QA) methods are incapable of providing complete information about IMRT delivery. Most methods consist of a planar film or diode array measurement for relative dosimetry and 1 ‐2 ionization chamber (IC) measurements made in a homogeneous medium for absolute dosimetry. A new model‐ and measurement‐based IMRT QA tool makes 3D delivered‐dose verification possible through independent dose calculation and 2D fluence measurements, which combine to provide reconstructed dose on a 3D heterogeneous patient dataset. This work aims to commission this new IMRT QA tool and validate its performance relative to traditional QA methods. Methods: The COMPASS system (IBA Dosimetry) consists of a software package for dose calculation and visualization/analysis of measured data acquired using a gantry‐mounted MatriXX Evolution detector array (1020 ICs) and gantry angle sensor. Commissioning included modeling a Varian Truebeam 6 MV photon beam. The system computation algorithm was validated via direct comparison of the COMPASS and Pinnacle‐TPS calculated dose distributions for twelve previously‐treated patient plans (sites: lung, breast, pancreas, head and neck, prostate; delivery types: SMLC‐DMPO, SmartArc). These same plans were measured at the actual treatment beam angles using both the gantry‐mounted MatriXX detector and two ICs placed in a standard cuboidal IMRT solid‐ water phantom. The COMPASS reconstructed dose was validated by comparison of the average PTV dose to the average IC dose measurement, each relative to the TPS expected dose. Results: The COMPASS calculated dose differed from the TPS calculated dose by 0.71+\−0.37%. On average, the measured dose differed from the TPS expected dose by 2.04+\−0.93% for COMPASS and 1.45+\−0.94% for the ICs. Conclusion: The COMPASS computation algorithm is valid and the measured results are comparable with those of the traditional IMRT QA method, while providing more dosimetry information (absolute and relative) in a single measurement and taking patient tissue heterogeneity into account.
SU‐E‐T‐422: Monte Carlo Simulations for Photon Energy Modulation in Radiotherapy
Authors: Park J , Ye S , Kim I , Kim J , Choi C
Published: November 2011

Purpose: A device to modulate photon energy during beam‐on time was designed and simulated with the Monte Carlo (MC) method. Method and Materials:A device named energy modulator was a cylinder made of aluminum. The frame of that device was connected with 20 tubes through which mercury could be injected or drained. The mercury thickness inside the device could modulate the photon energy of beam penetrated. Monte Carlo simulations of 6 and 10 MV linac using the EGSnrc code were conducted to evaluate the performance of the device. After the design study, a flattening filter of the linac was replaced with the energy modulator in the MC simulations. At least 5 billion histories were followed for each simulation to create phase‐space files at 100 cm SSD. The thickness of mercury inside the energy modulator varied from 2 mm to 40 mm at the field size of 10 cm by 10 cm. The changes of beam quality were expressed in terms of percentage depth dose (PDD) at the depth of 10 cm and 20 cm in water. Results: As increasing the thickness of mercury, the PDD of 6 MV beam at 10 cm and 20 cm was changed from 63.8% to 68.2% and from 34.5% to 40.2%, respectively. The PDD of 10 MV beam was changed from 68.7% to 73.1% at the depth of 10 cm and 40.2% to 45.7% at the depth of 20 cm. Conclusions: The results of this study showed the feasibility of the energy modulation during beam‐on time, which could be advantageous in dose conformity.
SU‐E‐T‐424: Clinical Validation of a GammaBeam Tomotherapy System Using the Octavius Pre‐Treatment QA Device
Authors: Adnani N , Rudraraju V , Xu L , Smith L P , Cernica G , Romesberg M
Published: November 2011

Purpose: Verify and validate the clinical viability of a GammaBeam Tomotherapy system Methods: A full commissioning of the GammaBeam Tomotherapy unit is performed. This novel radiotherapy system integrates the Co‐60 Equinox machine (Best Theratronics, Canada), MIMiC MLC, AutoCrane and nomoSTATM software (Best Nomos, PA). PDDs, output factors and profiles was acquired and entered into the Corvus GammaBeam treatment planning system. Patient treatment plans for H&N, Pelvis, Brain and Brain SRS were generated. Corresponding pre‐treatment QA plans were calculated and delivered on the Octavius QA phantom (PTW, NY). As acceptance criteria, we applied a gamma analysis with a DTA ranging from 3 mm to 5 mm and a dose difference from 1% to 4% (of local dose). Plan quality is also analyzed in terms of target coverage, organ at risk sparing, skin dose, hot spots, etc., in comparison to serial tomotherapy plans generated on the same CT sets using linac based photon beams. Results: for the H&N plan, acceptance criteria were set to 4%, 5 mm DTA to meet the minimum requirement of more than 90% of points passing. For the Pelvis, 91.6% of points pass the 3%, 3 mm DTA. For Brain and Brain SRS, a gamma analysis based on 2%, 2 mm DTA resulted in 98% and 90.9% of points passing. In the most complex case of H&N, constraints were met with 10% hot spot (within the target) and a skin dose ∼50% of the prescribed dose. Conclusions: investigation has demonstrated that the GammaBeam Tomotherapy system is clinically viable. At maximum source activity (∼15000 Ci), a 2 Gy fraction of the H&N plan took 20 minutes to deliver. Although this time is expected to slowly increase, due to source decay, to reach ∼30 minutes three years later, it remains comparable to linac based tomotherapy treatment times.

Financial support for this work was obtained from Best Medical International.
SU‐E‐T‐427: Verification of the Accuracy of a Commercial Pre‐Treatment IM QA Software
Authors: Gifford K , Hunter L , Ballo M , Kirsner S , Mason B , Nelson C
Published: November 2011

Purpose: To verify the accuracy of a commercial pre‐treatment IMRT software. Methods: Basic beam data, such as OFs and PDDs, for 6MV 18MV were computed on an identical CT data set with the physical de set to 1.0 g/cc for field sizes ranging from 4 × 4 to 30 × 30 cm2 in Pinna (Philips International B.V., Amsterdam, The Netherlands) and Dosim Check (DC) (MathResolutions LLC, Columbia, MD). Eleven patient p previously measured with our current QA technique were re‐meas utilizing the Varian 21EX EPID (Varian Medical Systems, Inc., Palo CA) and recomputed in DC. Absolute doses were compared betw ionometry and those predicted by DC as well as Pinnacle3. 2D iso comparisons were performed between Pinnacle3 and DC in the region o film insert of the battery phantom. Gamma volume histograms computed to compare the dose predicted by DC and Pinnacle3 in 3D. percentage of points less than or equal to a gamma of 1.0 (±3% or ±3 was recorded for each patient plan. Results: Median difference between and ionometry for 6 MV OFs was less than 1.0%. Median differ between DC and ionometry for 18 MV OFs was less than 1.0%. Me difference between DC and ionometry for 6 MV PDDs was 0.5%. Me difference between DC and ionometry for 18 MV PDDs was 0.3%. Me percent difference between ion chamber and Dosimetry Check was (range: −2.4%–2.8%). Median percent difference between Dosimetry C and Pinnacle3 was 1.0% for the same ion chamber position. Median pe of points passing ±3% or ±3 mm was 98.5% (range: 91.7%–99. Conclusions: Dosimetry Check can compute basic beam data to w acceptable clinical accuracy (±2%). Dosimetry Check can compute abso doses in complex IMRT cases to within acceptable clinical accuracy (±5
SU‐E‐T‐429: Clinical Use of ArcCHECK for IMRT and VMAT Delivery QA
Authors: Tyagi N , Yang K , Yan D
Published: November 2011

Purpose: To validate the dosimetric accuracy and sensitivity of ArcCheck for IMRT and VMAT QA. Methods: Arccheck is a cylindrical 3D phantom for IMRT and arc delivery. It is a 3D array of 1386 diodes arranged in a helical geometry at a depth of 2.9 cm. The dosimeter was evaluated for dose rate, angular dependence and systematic setup errors. Effect of planning parameters such as couch attenuation and control point (CP) spacing was investigated for various IMRT and VMAT plans. Diodes sensitivity to leaf position errors and gantry errors was studied by simulating errors in various arc delivery plans. Gamma evaluation criteria of 3%, 2mm was used for absolute dose comparison for clinical IMRT and VMAT plans. Results: Diodes show a dose rate dependency of 2% from 600 to 200 MU/min and 5% below 50 MU/min. An angular dependence of 5% was seen for a 20x30 cm2 field size. Prostate and HN IMRT plans delivered at planned angles showed lower gamma passing rate (94.3%) compared to mapcheck measurements (99.3%) delivered at 0° gantry angles. Accounting for couch attenuation in the calculation improved the average passing rate to 97 %. For a 3×40 cm2 static arc the gamma passing rate dropped from 92% to 83% when CP spacing changed from 2° to 6° but larger field sizes were not affected. Introducing a 1 mm setup error in AP, LR and SI direction resulted in 5%, 4.5% and 10% drop in passing rate for a HN VMAT plan. A 2mm leaf position error in one leaf and 3° error in one CP showed 6% and 5% difference in profile comparison for various arc deliveries. Conclusions: ArcCHECK is a robust and sensitive QA tool for IMRT and VMAT delivery. Future work will evaluate a CP by CP analysis to understand complex VMAT deliveries.
SU‐E‐T‐436: Influence of Collimator Rotation on the Dose Verifications in IMRT Fields
Authors: Kumazaki Y , Kato A , Takamatsu S , Tsukamoto N , Sekine H
Published: November 2011

Purpose: To evaluate the influence of collimator rotation on the dose verification in IMRT fields. Methods: We measured the focal spot size of Siemens linac using a narrow slit phantom placed at the isocenter. Transverse dose measurements were performed in the × (cross‐plane) or y (in‐plane) directions perpendicular to the radiation beam with or without collimator rotation, and we calculated dose profile penumbras. We performed the dose verification of TG‐119 prostate plan and Head and Neck plan. We compared the measured dose to the calculated dose using an ionization chamber in the absorbed dose verification, MapCHECK2 in the dose distributions. We compared the results of both dose verifications with or without collimator rotation. Results: The focal spot size in the in‐plane direction is almost twice the size in the cross‐plane. Each focal spot size (FWHM) was 2.8 mm and 1.4 mm, respectively. These denoted the same tendency of the effective source size in treatment planning system (Pinnacle) which was one of the parameters for beam modeling. The dose profile penumbras in‐plane was larger than cross‐plane. For the dose verification of TG‐119 IMRT plans, the differences between absorbed dose with or without collimator rotations in field by field were within about 2%, and no differences were found for total dose both plans. In verification of dose distribution, the pass rates using gamma index (3%, 2mm) at collimator angle of 90 degree were lower than those at collimator angle of 0 degree in the H&N plan, but no significant differences were found for the prostate plan.Conclusion: Our study shows that the focal spot shape of the Siemens linac at our institute is an ellipse. This may have a significant effect on the dose verification of the complex IMRT plan such as H&N plan with collimator rotation.
SU‐E‐T‐440: Assessing the Accuracy of Treatment Planning System Calculated Out‐of‐Target Doses in IMRT and VMAT Plans through 2D Measurements
Authors: Han Z , Nitsch P , Lyatskaya Y , Makrigiorgos M , Marcus K , Zygmanski P
Published: November 2011

Purpose: To quantify the dose uncertainties in the out‐of‐target regions for both VMAT and IMRT. Methods: 12 clinical IMRT (6) and VMAT (6) plans for six patients were created in Varian Eclipse 8.6 and delivered to solid water phantoms containing a 2D ion chamber array — MatriXX. The measured doses in the out‐of‐target regions were compared with TPS calculations. Two types of out‐of‐target regions were considered in this study: type I, with direct irradiations and type II, without direct irradiations. Results: The TPS was found to generally underestimate the out‐of‐target doses for both IMRT and VMAT plans. The mean underestimate was 48.0% and 35.5% for IMRT and VMAT, respectively, in regions without direct irradiations (type II), where the dominant dose contributions are scatter. In regions where direct irradiations are present (type I), the underestimate was significantly smaller, which was 6.5% and 4.0% for IMRT and VMAT, respectively. The percentage dose discrepancy increases as the distance to the field edge increases for both IMRT and VMAT. The dose discrepancies between TPS and measurements also demonstrate a clear dependence on the equivalent square jaw size for both IMRT and VMAT plans. As the jaw size increases, the observed discrepancy increases. This phenomenon is attributed to both open beam and dynamic MLC modeling in the TPS. Conclusions: The accuracy of the out‐of‐target dose by Varian Eclipse TPS for IMRT and VMAT was investigated through 2D phantom measurements. Eclipse was found to underestimate the doses in those regions. The underestimate shows dependence on the types of plans, equivalent field size, and the distance to the field edge. Such an underestimate can have impacts on the evaluation of the OAR and normal tissue sparing.