bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐457: Multi‐Mode Model ‐ A Consistent Approach for Conventionally Fractionated Radiotherapy and Stereotactic Body Radiotherapy
Authors: Ma C
Published: June 2012

Purpose: The accuracy of dosimetric analysis and outcome comparison between conventionally fractionated radiation therapy(CFRT) and stereotactic body radiotherapy(SBRT) requires reliable radiobiological modeling. The aim of this work was to further improve the multi‐mode model(MMM) for both CFRT and SBRT. Methods: MMM assumes the existence of different modes of cell killing as a Result of radiation damage to different parts of a cell, e.g., a single severe damage to the DNA or two or more small damages to the membrane or DNA. The cell survival probability can then be calculated by s=Product_(i=1,n){1−(1−ê(−d/Di))̂(i)}, where i represents the i‐th mode of cell killing that requires i potentially unrepairable damages to the cell as a result of radiation dose d and Di is the dose that gives 63% probability to cause an unrepairable damage for the i‐th mode. The dose rate effect is included in MMM assuming 1/D_i=(k_i‐ r_i/U), where k_i is the radiation damage rate, r_i the repair rate and U the dose rate. The low‐dose hypersensitivity is also included in the new model. Results: A comparison of the goodness‐of‐fit of the LQ, multitarget, USC and MMM to the survival curve of the H460 non‐small‐cell lung cancer cell line showed the same agreement between USC and MMM with the survival data, which was significantly better than the fits to the LQ and multitarget models. The parameters used for the LQ, multitarget and USC models were alpha=0.33Gy, alpha/beta=10Gy, D_T =6.2Gy, D_0 =1.25Gy and D_q =1.8Gy. The parameters for MMM(n=4) were D_1=4.0Gy, D_2=4.01Gy, D_3=3.08Gy and D_4=41Gy. Conclusions: MMM offers a superior description of the mammalian cell survival curve in both conventional and ablative dose ranges, which can be used for designing new fractionation schemes and predicting and understanding treatment outcomes for both CFRT and SBRT.
SU‐E‐T‐459: Radiobiological Evaluation of Implant Duration and Radionuclide Selection for COMS Eye Plaque Brachytherapy Using an Objective Function
Authors: Gagne N , Rivard M
Published: June 2012

Purpose: The biologically effective dose (BED) of temporary brachytherapy treatments is a function of both chosen radionuclide (R) and implant duration (T). This study endeavored to evaluate BED delivered to the tumor volume and surrounding ocular structures as a function of plaque position (P), prescription dose, R, and T. Methods: Plaque‐heterogeneity‐ corrected dose distributions were generated with MCNP5 for the range of currently‐available COMS plaques using low‐energy radionuclides. These physical dose distributions were imported into the Pinnacle3 TPS using the TG‐43 hybrid technique and used to generate DVHs for a T=7d implant within a reference eye geometry at eight standard treatment positions. The Dale equation was employed to create biologically effective dose volume histograms (BEDVHs), allowing for BED volumetric analysis of all ROIs. Isobiologically‐effective prescription doses were calculated for T=5−0.01d, with BEDVHs subsequently generated for all ROIs using correspondingly reduced prescription doses. Objective functions were created to evaluate the BEDVHs as a function of R and T. Results: Reducing T from 7 to 0.01d for a 10mm plaque produced an average BED benefit of 26%, 20%, and 17% for 103Pd, 125I, and 131Cs, respectively, for all P; 16mm and 22mm plaque results were more position‐dependent. 103Pd produced a 16–35% BED benefit over 125I, whereas 131Cs produced a 3–7% BED detriment, independent of P, T, and plaque size. Additionally, corresponding OAR physical doses were lowest using 103Pd in all circumstances. Conclusions: Shorter implant durations may correlate with more favorable outcomes vs. 7d implants for small and medium lesions. T may be safely reduced if the prescription dose is appropriately diminished. 103Pd offers a substantial 16‐ 35% radiobiological benefit over 125I and 131Cs irrespective of P, T, and tumor size. The objective functions used in this study can be applied to temporary or permanent brachytherapy implants for a variety of disease sites.
SU‐E‐T‐461: Fractionation Schedule Optimization for Lung Cancer Treatments Using Radiobiological and Dose Distribution Characteristics
Authors: Keller H , Meier G , Hope A , Davison M
Published: June 2012

Purpose: Lung cancer radiotherapy treatments employ a wide variety of fractionation protocols. The choice among protocols mostly depends on the size of the target volume (GTV or ITV) and the volume of normal tissue receiving a critical dose. Rigorous mathematical criteria for normal tissue (NT) dose distributions were derived to determine the type of dose per fraction schedule that maximizes linear‐quadratic tumor effect. Methods: Selecting the individual doses per fraction that maximize a linear‐quadratic effect in the tumor while constraining the normal tissue complication probability according to the Lyman‐Kutcher‐Burman model leads to an optimization problem. For time‐independent parameters, the solution is always an equal dose per fraction schedule; depending on parameter values, two different class solutions are suggested: minimal number of fractions clinically realized with hypo‐fractionation, or minimizing dose per fraction clinically realized with standard‐ or hyper‐fractionation. The value of a single scale‐free “bifurcation” number, derived from the DVH of the NT dose distribution suggests which solution is preferred for a given plan with respect to a given normal tissue. The clinical relevance of the bifurcation number in selecting fractionation schemes was tested for 30 patients previously treated for non‐small‐cell lung cancer according to various fractionation protocols. Results: The bifurcation numbers for both lung and esophagus were a good classifier for the hypofractionated and the conventional fractionation groups. The variability of the numbers within patients of the conventional fractionation group was much smaller than the variability of the treated ITV volumes or the ITV to lung volume ratios. The prescribed fractionations were also consisted with the currently accepted alpha‐beta values for tumor (10) and radiation‐induced pneumonities in the lung (4). Conclusions: Model‐based criteria such as the bifurcation number may replace the more empirical volume criteria to decide the optimal fractionation protocol once the dose distribution has been optimized.
SU‐E‐T‐470: Comparison of Proton Treatment Planning and Monte Carlo Calculation Using TOPAS for Liver Cancer
Authors: Moteabbed M , Schuemann J , Paganetti H
Published: June 2012

Purpose: To compare Monte Carlo (MC) calculated and planned dose distributions (pencil beam algorithm) for patients with liver cancer treated with proton radiation therapy. Methods: Six patients with unresectable Hepatocellular carcinoma were chosen from the institutional protocol list. We applied the newly developed TOPAS (Tool for Particle Simulation) Monte Carlo (MC) tool and an in‐house (mcauto) program, which connects the planning system with the MC. Two beams, typically right lateral (RL) and anterior‐posterior (AP), were simulated for each patient with a total prescribed dose of 58 Gy. The calculated absolute dose was determined by separately simulating an SOBP dose in a water phantom for normalization to the prescription dose. The difference between MC and planned dose were calculated and Dose Volume Histograms (DVHs) for the critical organs with non‐negligible dose (whole liver, heart, small and large bowel and chest wall) were analyzed. Results: The resulting dose distributions were in quite good agreement. The main discrepancy in all cases was observed in the lateral penumbrae. These discrepancies can mainly result from the range compensator gradient and tissue composition. The Dose Volume Histograms (DVHs) also presented good agreement between doses for the CTV as well as all the OARs. The difference in D95 ranged from 0.7–1.5 Gy that is translated to 1.3–2.5% of the prescribed dose. Conclusions: TOPAS Monte Carlo tool presented an efficient and accurate method for dose calculation in liver and to validate clinical treatment planning. Discrepancies with doses calculated using the pencil beam algorithm were seen but were generally quite small.
SU‐E‐T‐471: Beam Properties of an In‐Room Proton Therapy Accelerator
Authors: Bloch C , Hill P , Klein E
Published: June 2012

Purpose: To quantify basic beam properties of the first gantry‐mounted proton therapy accelerator, situated in the treatment room and delivering beam to the patient without any intermediate bending magnets. Methods: Monte Carlo simulations for prototype beamlines of the Mevion S250TM proton therapy system were performed using MCNPX. For each configuration, open profiles in air were determined at 3 different positions for 3 range settings (216 profiles). Similarly, half‐beam‐blocked profiles were determined for the same settings (216 profiles). Additionally, beam axis fluence profiles in air were determined for 3 range settings (72 profiles). Finally, Bragg peak depth‐dose curves in water were determined for 3 range settings (72 profiles). Using these 576 profiles, several beamline parameters were determined for each proton range and configuration, including virtual SAD, effective source size, and effective SAD. Additionally, Bortfeld's analytic approximation of the Bragg curve was fit to each depth‐dose curve to determine R0, σ and ε. The 72 values determined for each parameter were compared within each configuration and across all configurations. Results: Within any configuration, the change in range was too small (=2.5 cm) to have a large effect on any of the extracted parameters. Comparing parameters among configurations revealed smooth trends. These parameters were then fit as a function of range. Conclusions: The simplicity of this system results in beams with greater similarity among configurations as compared to other proton therapy systems. Because a beam with fixed initial energy is degraded only by tissue‐equivalent materials, range straggling and beam divergence are nearly constant across all beamline configurations. Beam parameters change smoothly as functions of proton range, with no major discontinuities between configurations. This suggests that the entire machine may be fully and accurately characterized in a treatment planning system by fewer measurements than would normally be required.
SU‐E‐T‐473: Performance Assessment of the TOPAS Tool for Particle Simulation for Proton Therapy Applications
Authors: Perl J , Shin J , Schuemann J , Faddegon B , Paganetti H
Published: June 2012

Purpose: The TOPAS Tool for Particle Simulation was developed to make Geant4 Monte Carlo simulation more readily available for research and clinical physicists. Before releasing this new tool to the proton therapy community, several test have been performed to ensure accurate simulations in a variety of proton therapy setups. Methods: TOPAS can model a passive scattering or scanning beam treatment head, model a patient geometry based on CT images, score dose, fluence, etc., save and replay a phase space, provides advanced graphics, and is fully four‐dimensional (4D) to handle variations in beam delivery and patient geometry during treatment. An innovative control system meets requirements for ease of use, reliability and repeatability without sacrificing flexibility. To test the TOPAS code, we modeled proton therapy treatment examples including the UCSF eye treatment beamline (UCSFETB), the MGH STAR radiosurgery beamline and the MGH gantry treatment head in passive scattering and scanning modes. The simulations included time‐dependent geometry and time‐ dependent beam current delivery. Results: At the UCSFETB, time‐ dependent depth dose distributions were accurately simulated with time‐ varying energy modulation from a rotating propeller. At the MGH STAR beamline, distal and proximal ranges agreed within measurement uncertainty and the shape of the simulated SOBP followed measured data. For the MGH gantry treatment head in passive scattering mode, SOBPs were simulated for the full set of range modulator wheel and second scatterer combinations. TOPAS simulation was within clinical required accuracy. For the MGH nozzle in scanning mode, a variety of scan patterns were simulated with fluence maps generated for cases including beam current modulation, energy modulation and target tracking. Conclusions: Our results demonstrate the functionality of TOPAS. They show agreement with measured data and demonstrate the capabilities of TOPAS in simulating beam delivery in 3D and 4D. This work was supported by IH/NCI under R01 CA 140735‐01
SU‐E‐T‐477: Influence of Eye Size on Radiation Absorbed Dose Delivered to Non‐ Targeted Tissues during Stereotactic Radiosurgery for Age‐Related Macular Degeneration
Authors: Cantley J , Chell E , Firpo M , Hanlon J , Lee C , Bolch W
Published: June 2012

Purpose: This work determines how variations in eye size will influence the radiation absorbed dose delivered to non‐targeted tissues within the eye during stereotactic radiosurgery of age‐related macular degeneration (AMD) using the IRay™ treatment. Methods: Stylized models of the eye were created with axial lengths of 20, 22, 24, 26, and 28mm. Each model was based upon the reference eye model from NCRP Report 130 and then scaled appropriately for each axial length. Models were incorporated with MCNPX radiation transport code in order to simulate the three beam IRay™ delivery system. Simulation results were assessed for both the mean absorbed dose and dose‐volume histograms (DVH) for both target (macula) and non‐ targeted eye tissues, including the lens, retina, central retinal artery, and optic nerve. Results: For each of the three beams, an average dose of 8Gy was delivered to the macula resulting in a total average dose of 24Gy for each eye model. The lens of the eye received a total average dose ranging from 146 to 189mGy, with the larger doses occurring in the smaller eye models since the beams traverse through the sciera closer to the limbus. The distal tip (1.5mm) of the central retinal artery received a total average dose ranging from 499 to 567mGy, with the larger doses occurring in the larger eye models due to increased scatter resulting from longer tissue path length to the nominal target. The optic nerve received a total average dose ranging from 207 to 225mGy, with the larger doses occurring in the smaller eye models. Conclusions: The small variation in dose to the lens, central retinal artery, and optic nerve suggests that eye size does not significantly affect radiation dose to non‐targeted eye tissues. This work was sponsored by Oraya Therapeutics.
SU‐E‐T‐479: Skin Dose from Flattening Filter Free Beams: A Monte Carlo Investigation
Authors: Zhang G , Javedan K , Moros E , Latifi K , Feygelman V , Moffitt H. Lee
Published: June 2012

Purpose: Flattening filter free (FFF) beams in radiotherapy have advantages such as shorter treatment delivery time and lower out‐of‐field dose compared with conventional flattened beams. This study investigates in detail the skin dose induced by FFF beams from a TrueBeam accelerator (Varian Medical Systems, Palo Alto, CA) using Monte Carlo method. Methods: Phase space files generated using real geometry of a TrueBeam accelerator above the jaws, were used as the input radiation source files in beam simulation for various field sizes using BEAMnrc. Phase space files for various field sizes were generated at the phantom surface. DOSXYZnrc was used for dose calculations in phantom and in patient using the generated phase space files as source input files. Results: The calculated percentage depth dose curves and profiles in water agreed with measurements within ± 2% for the high dose region and ±2 mm in the penumbra. The peak fluence of a 6 MV FFF beam with the same electron beam incident on the target is about 3 times that of a flattened beam . The mean energy of a 6 MV FFF beam is 0.92–0.95 MeV while it is 1.18–1.30 MeV for the flattened beam. Due to the mean energy difference, the dose in a 6 MV FFF beam is about 6% (of the maximum dose, or 12% of local dose) higher at depth of 1 mm compared with a flattened beam. Conclusions: Due to the lower mean photon energy, in an FFF beam the surface (skin) dose is slightly higher compared to the conventional flattened beam of the same field size.
SU‐E‐T‐481: Dosimetric Effects of Tissue Heterogeneity in Proton Therapy: Monte Carlo Simulation and Experimental Study Using Animal Tissue Phantoms
Authors: Liu Y , Zheng Y
Published: June 2012

Purpose: Accurate determination of proton dosimetric effect for tissue heterogeneity is critical in proton therapy. Proton beams have finite range and consequently tissue heterogeneity plays a more critical role in proton therapy. The purpose of this study is to investigate the tissue heterogeneity effect in proton dosimetry based on anatomical‐based Monte Carlo simulation using animal tissues. Methods: Animal tissues including a pig head and beef bulk were used in this study. Both pig head and beef were scanned using a GE CT scanner with 1.25 mm slice thickness. A treatment plan was created, using the CMS XiO treatment planning system (TPS) with a single proton spread‐out‐Bragg‐peak beam (SOBP). Radiochromic films were placed at the distal falloff region. Image guidance was used to align the phantom before proton beams were delivered according to the treatment plan. The same two CT sets were converted to Monte Carlo simulation model. The Monte Carlo simulated dose calculations with/without tissue omposition were compared to TPS calculations and measurements. Results: Based on the preliminary comparison, at the center of SOBP plane, the Monte Carlo simulation dose without tissue composition agreed generally well with TPS calculation. In the distal falloff region, the dose difference was large, and about 2 mm isodose line shift was observed with the consideration of tissue composition. The detailed comparison of dose distributions between Monte Carlo simulation, TPS calculations and measurements is underway. Conclusions: Accurate proton dose calculations are challenging in proton treatment planning for heterogeneous tissues. Tissue heterogeneity and tissue composition may lead to isodose line shifts up to a few millimeters in the distal falloff region. By simulating detailed particle transport and energy deposition, Monte Carlo simulations provide a verification method in proton dose calculation where inhomogeneous tissues are present.
SU‐E‐T‐483: Delay Treatment or Switch to Different Machines? Dosimetric Effect and Tumor Control Probability
Authors: Lin T , Fan J , Hossain M , Ma C
Published: June 2012

Purpose: If the Linac is unavailable during the IMRT treatment schedule, the patient can be switched to a different Linac or prostpond treatment until the origonal Linac is available. The resulting dosimetric difference is estimated and the compromise in the TCP is estimated for both scenarios. This work investigates the feasibility and rationale of switching patients between different accelerators for IMRT in contrast to prostponing the treatment. Methods: We performed Monte Carlo simulations of photon beams from different Linac models and vendors. Prostate and head and neck treatment plans for Siemens Primus, Primart, Artiste and Varian‐21Ex/IX accelerators are studied in this work. Dose distributions for given plans are recalculated using different beam data with the same nominal energy from different Linacs. We have compared DVHs, the maximum, the minimum and the mean dose to the target and critical structures due to switching accelerators. In the process of switching a treatment plan to a different accelerator, there are issues, such as optimum penumbra compensation, dose distribution at the boundary of target and critical structures and multileaf collimator (MLC) leaf width effects, needed to be considered and verified with measurements. In making the final decision whether to switch machines, the TCP based on a linear‐quadratic model with time factor is considered. Results: Two DVHs of two plans from Varian and Siemens models are delivered on different machines. Slight dose coverage differences have been observed. TCP estimation with both delayed and without delayed treatments is calculated. Undesired drop of TCP is observed with treatment gap. Conclusions: Based on the analyses done in this work, it is therapeutically more beneficial to switch a patient to a different machine than to postpone a treatment until the original machine is available, especially for fast growing tumors such as head and neck cancers.
SU‐E‐T‐485: Validation of Acuros XB Dose Calculations in SBRT Lung Planning with Monte Carlo Methods
Authors: Bush K , Wang L , Mok E
Published: June 2012

Purpose: The Acuros XB (AXB) Advanced Dose algorithm (Varian Medical Systems) represents a dramatic shift in clinical photon dose calculation methodology from pencil‐beam superposition/convolution methods. Early studies evaluating the accuracy of the algorithm in lung have found good agreement with both measurement and Monte Carlo based dose calculations. In this study, a dosimetric validation of Acuros is performed for clinical SBRT lung planning cases using Monte Carlo (MC) calculations as a benchmark. Methods: MC simulations using BEAMnrc/DOSXYZnrc were carried out for 8 AXB calculated 6/10 MV arc plans delivered on a TrueBeamTM STx linac in high‐dose‐rate flattening filter free mode. Clinical planning constraints were applied in each case with plans normalized to achieve 95% PTV coverage. Metrics used in the evaluation include: maximum and minimum GTV/PTV dose, PTV isodose coverage, conformity and dose profile comparisons. To understand the impact of moving toward to AXB calculations in SBRT lung planning, calculations using the Analytical Anisotropic Algorithm (AAA) are presented for each plan. Results: For both 6 and 10MV energies, consistent mean GTV dose and PTV isodose coverage was observed for AXB and MC calculations. GTV mean dose was observed to deviate by <2% for all cases. Isodose coverage for MC simulations ranged from 92%–98%. AAA was also in agreement with MC simulations within the GTV to within 2%. AXB and MC maximum and minimum PTV dose differences were larger (up to 9%) but not of clinical concern. In several cases, AXB exhibited a significant improvement in dose calculation accuracy in the lung region surrounding the GTV over AAA, particularly with lung densities < 0.1 g/cc. Conclusion: AcurosXB provides increased accuracy in modelling dose deposition for SBRT lung over AAA and is found to be in good agreement with MC calculations.
SU‐E‐T‐486: Volume and Location Dependence on the Difference Between Monte Carlo and Pencil Beam Dose Calculations for Lung Stereotactic Body Radiation Therapy
Authors: Zhuang T , Djemil T , Qi P , Magnelli A , Stephans K , Videtic G , Xia P
Published: June 2012

Purpose: Stereotactic body radiotherapy has been an efficacious treatment modality for early stage non‐small cell lung cancer. The accuracy of dose calculations is in question due to the presence of inhomogeneity. It was required in several clinical trials to calculate dose without heterogeneity correction. However, to better correlate the outcomes with the planned dose, accurate dose calculation with heterogeneity correction is highly desirable. Methods: We compared the recalculated dose with Monte Carlo (MC) algorithm to the original Pencil Beam (PB) calculations for clinical lung SBRT plans. Thirty‐one clinical plans that followed protocol guidelines were retrospectively investigated. Dosimetric parameters D1, D95 and D99 for the PTV and D1 for organs at risk were compared. Correlations of mean lung dose and V20 of lungs between two calculations were investigated. Results: Compared to the PB calculations without heterogeneity correction in clinical plans, we found that in terms of D95 of PTV, (1) the two calculations resulted in similar D95 for edge tumors with volumes greater than 25.1cc; (2) an average overestimation of 5% in PB calculations for edge tumors with volumes less than 25.1cc; and (3) an average overestimation of 9% or underestimation of 3% in PB calculations for island tumors with volumes smaller or greater than 22.6 cc, respectively. With heterogeneity correction, the PB calculation resulted in an average reduction of 23.8% and 15.3% in D95 for island and edge lesions respectively compared to the MC calculation. For organs at risks, no clinical meaningful differences were found among all the comparisons. Excellent correlations for mean dose and V20 of lungs were observed between the two calculations. Conclusions: Using a single scaling factor to account for the differences in using heterogeneity correction may not be sufficient. To understand dose‐response relation in Lung SBRT, accurate dose calculation such as the Monte Carlo algorithms is highly recommended.
SU‐E‐T‐487: Spatial Assessment of Dose Distributions for Patients with Lung Cancer Treated with Stereotactic Ablative Radiotherapy (SABR)
Authors: Liu D , Chen D , Chetvertkov M , Altman M , Li H , Wen N , Glide‐Hurst C , Ajlouni M , Levin K , Movsas B , Chetty I
Published: June 2012

Purpose: We hypothesize that PTV margin dose is an important factor for local tumor control. We evaluated dose distributions for patients originally treated with pencil‐beam (PB)‐based plans and retrospectively calculated with Monte Carlo (MC) method, with emphasis on the spatial region between the ITV and PTV (PTV‐margin), where the largest dose differences were expected. Methods: Forty‐six stage I–II lung cancer patients with 51 lesions treated with SABR were retrospectively analyzed (23 central and 28 peripheral tumors). All patients received 4DCT imaging, and an ITV was generated from the maximum intensity projection and subsequent review of four 4DCT phases. An isotropic 3mm ITV‐to‐PTV margin was used. The iPlan TPS was used to generate the original treatment plans using PB‐based heterogeneity correction. MC doses were recalculated using the same MUs as in the PB plan. Dose distributions for the ITV, PTV‐margin, and PTV were analyzed using generalized equivalent uniform dose (gEUD) with a = − 20. Student's paired t‐test elucidated differences between PB and MC‐based gEUD and the two different tumor locations. Results: Mean ITV and PTV volumes were 24.2 cc (range: 2.2 to 99.3 cc) and 50.4 cc (range: 6.4 to 229.7 cc), respectively. The mean gEUDs of ITV, PTV‐margin and PTV, normalized to PB‐based 100% isodose were 1.02+/−0.04, 1.01+/−0.04 and 1.01+/−0.04 for PB‐based plans, compared to 0.94+/−0.06, 0.88+/−0.08 and 0.90+/−0.08 (all p<0.05) for MC‐based plans. The maximum overestimations with the PB algorithm in the PTV‐margin average dose were 10.4% and 19.6% (p < 0.05) for peripheral tumor cases and central tumor cases, respectively. Conclusions: PB‐based dose distributions showed the highest dose overestimation (relative to MC) in the PTV‐margin spatial region. Analysis of spatial dose differences is an important precursor toward assessment of patterns‐of‐local failure, to be investigated in future work to explore possible association between dose and regions of failure. Acknowledgement: supported in part by grants from NIH R01 CA106770 and from Varian Medical Systems.
SU‐E‐T‐495: Monte Carlo Dose Verification of Passive Scattering Proton Therapy for Prostate Cancer
Authors: Giantsoudi D , Paganetti H
Published: June 2012

Purpose: To verify the clinical pencil beam dose calculation algorithm for passive scattering proton therapy using field with large range in tissue, i.e. in prostate cancer, using a Monte Carlo (MC) simulation system. Methods: Previously treated prostate cancer cases were randomly selected from our patient database. All patients received the same dose prescription of 50Gy (25 fractions) to planning treatment volume including the seminal vesicles (PTV1), followed by 28Gy (14 fractions) boost to the prostate gland only (PTV2). Patient and beam geometry were imported to our MC simulation platform (TOPAS ‐ TOol for PArticle Simulation) and the dose of each individual beam, as well as their weighted sum, were calculated and compared to pencil beam algorithm‐based calculation from the clinical treatment planning system (XiO). Results: Preliminary results from four patient cases show overall good agreement between the pencil beam and MC calculations. However, a small but systematic overestimation of the dose, as calculated by the pencil beam calculation algorithm, was noticed for the target structures (<2% difference in D95 for PTV1 and PTV2), compared to the MC calculation. The inverse was observed for the OARs (rectum and bladder) for which the dose seems to be somewhat underestimated by the pencil beam calculation algorithm (up to 3.75% difference in the volume covered by the 70Gy and 75Gy isodose lines). Furthermore, systematic difference in the range calculation was noticed: the pencil beam calculation algorithm results in larger proton range, in the order of 3–4mm, compared to the MC calculations for all beams and patients studied. This can be attributed to the bone anatomy in the path of the beams (femoral heads). Conclusions: Routine MC dose calculation has the potential to improve delivery accuracy in proton therapy of prostate cancer and influence the analysis of currently ongoing clinical trials of protons versus IMRT. Funded by NIH/NCI R01 CA140735
SU‐E‐T‐496: Monte Carlo Simulation of a 6MV Varian Truebeam Without Flattening Filter Linac
Authors: Song T , Zhou L , Jiang S
Published: June 2012

Purpose: To simulate a 6 MV Varian Truebeam linac operating without flattening filter using an existing Phase space file(PhS) with the monte carlo packeage EGSnrc. Methods: An existing PhS file built after simulating the patient‐independent part at the first step in traditional monte carlo simulation was employed. With this PhS being a source, the patient‐dependent part was simulated and the dose distributions were calculated using EGSnrc. The 6 MV dose calculation were performed for field size of 10×10cm2, 20×20cm2, 30×30cm2 and 40×40cm2 in a 54×54×30 cm3 water phantom. The voxel size for the water phantom was 0.6×0.6×0.6cm3. For the 10×10cm2 field, surface buildup calculations were performed using 0.6×0.6×0.3cm3 voxels within 1.8cm of the surface. Dose profiles and percent depth dose(PDD) curves were calculated following 1 billion histories for dose profiles and 500 million histories for PDD curves. Simulation results were compared with measured data for validation. Results: Good agreement between simulations and measurements in water was observed. For the PDD curves, 95% of the calculated data points agree within 2% with the experimental measurements for depths between 1.8cm and 30 cm. In the buildup region, the agreement is within 2%, except several points with the deviation of 5% for the 10×10 cm2 open field. For the lateral dose profiles, the agreement is less than 3% at the depth of 1.3cm, 5cm, 10cm, 20cm and 30cm inside the 80% field size. Conclusions: It demonstrated that the existing phase space file is accurate and the simulation is reliable to be used for clinical patient dose calculations in future investigations. Project supported by the National Natural Science Foundation of China (30970866)
SU‐E‐T‐500: Pencil‐Beam versus Monte Carlo Based Dose Calculation for Proton Therapy Patients with Complex Geometries. Clinical Use of the TOPAS Monte Carlo System
Authors: Schuemann J , Shin J , Perl J , Grassberger C , Verburg J , Faddegon B , Paganetti H
Published: June 2012

Purpose: To investigate the necessity of the verification of dose distributions using Monte Carlo (MC) simulations for proton therapy of head and neck patients and other complex patient geometries. Methods: TOPAS, a TOol for PArticle Simulations that makes MC simulations easy‐to‐use for research and clinical use and is layered on top of Geant4, has been used to simulate the treatments of head and neck patients at the Massachusetts General Hospital (MGH). The resulting dose distributions have been compared to pencil beam calculations based on the XiO treatment planning system. Dose difference distributions were used to highlight areas where the two algorithms did not agree. Dose volume histograms are utilized to investigate the overall agreement of the planned doses in target structures. Results: 21 head and neck patients, both nasopharynx and spinal cord, were investigated. The field complexity ranges from a single field up to 13 fields. For all patients, the dose in the clinical target volume agrees well. Nevertheless, differences in critical structures around the targets have been observed mostly due to range differences between the two algorithms. Conclusions: Pencil beam algorithms provide an accurate description of dose in the target volume. However, we conclude that the differences between MC simulations and pencil beam algorithms in regions outside the target for complex geometries, such as present in head and neck patients, support the necessity of routine use of MC simulations for treatment verifications before treatment. TOPAS is aiming to make such routine simulations available to all researchers and clinics. An automated interface utilizing TOPAS to enable such simulations has been developed at MGH and should become routinely used in the near future for patients with complex geometries. NIH/NCI R01 CA140735
SU‐E‐T‐504: Incident Fluence Reconstruction Based on Monte Carlo Finite‐Size Pencil Beam Model for Dose Guided Radiation Therapy
Authors: LI Gui , WU Yican ,   FDS Team
Published: June 2012

Purpose: In dose guided radiation therapy, incident fluence is one of the important parameters for both influence verification and dose reconstruction. The objective of this investigation was to develop a method to obtain the incident fluence for dose reconstruction in dose guided radiation therapy (DGRT). Methods: An incident fluence reconstruction model based on Monte Carlo Finite‐size pencil beam (MCFSPB) model and “Matthew Effect” Conjugate‐gradient (CG) algorithm was developed, where the MCFSPB model was developed by FDS Team (www.fds.org.cn) and the “Matthew Effect” was proposed to advance the accuracy of CG lgorithm. Then, by measuring dose with amorphous silicon flat panel (a‐Si flat panel), the incident fluence was unfolded. An artifical head phantom was used to test sample. By using the incident fluence to dose calculation with MCFSPB, the 2D and 3D dose was also reconstructed and compared with the measurement dose and the planing dose respectively. The Passing Rate of Dose Difference (PRDD) in 3% was used to learn the accuracy. Results: Two representative cases (6MV and 10MV) with both five beams were used for beam‐by‐beam verification, and the corresponding incident fluence was obtained. By comparing the measurement dose with the calculation dose on measurement plane, the results showed that the PRDD (3%) in field was 100%. And by comparing 3D plannning dose with 3D reconstructed dose, the results indicated that the PRDD (3%) in field was 95%∼98%. Conclusions: The incident fluence reconstruction model based on MCFSPB model and “Matthew Effect” Conjugate‐gradient algorithm was developed. The tested results indicated its accuracy. This study is expected to be applied to 3D dose reconstruction and 3D dosimetric verification in DGRT. Supported by the National Natural Science Foundation under grant No.30900386 and the National Science Foundation of Anhui Province (Nos.090413095 and 111040606Q55).
SU‐E‐T‐505: BrainLab Plan Comparisons: Brain Scan Pencil Beam versus IPlan Monte Carlo
Authors: Kowski M , Edwards J , Bauer L , DuBose R , Powell H
Published: June 2012

Purpose: Monte Carlo (MC) dose modeling techniques are available in the newest version of Brain Lab's IPlan treatment planning system (TPS). Prior to the upgrade, at our facility, BrainLab's BrainScan was the treatment planning system available; pencil beam (PB) modeling is employed by BrainScan. As published in the literature, MC calculations, as compared to the PB algorithm, can generate differences in coverage as much as 20%. With the introduction of the new treatment planning system, treatment parameter comparisons were made with quantitative assessments. Differences due to changes in the dose calculation that could impact patient treatments and outcomes were investigated. Methods: Beam data was collected for the new BrainLab TPS IPLAN under the conditions as outlined in the manufacturer's Version 1.3 data collection, commissioning and acceptance guidelines. Utilizing BrainLab's treatment planning systems, treatment plan comparisons were made. First, PB modeling treatment plans were assessed for each treatment plan with pencil beam modeling in the BrainScan and IPlan TPS. Treatment plans with MC modeling were then compared to PB models. Results: Differences in the dose distribution, DVH values, and monitor units were evaluated between the older version software (BrainScan) and the newer treatment planning system (IPlan). As predicted by the literature, the differences in the MC modeling versus PB modeling were significant depending upon the anatomy (tumor site). Modeling comparison for the treatment plans will be presented for SRS (Stereotactic Radiosurgery) and Stereotactic Body Radiation Therapy (SBRT). Conclusions: Clinical implementation of a new treatment planning system must be approached with caution and with adherence to AAPM recommendations and guidelines. Whenever a new TPS calculation model is introduced, thorough comparison between former and new models should be obtained. An additional recommended test would be to perform an independent, end‐to‐end check of the overall system utilizing the RPC (Radiological Physics Center) phantom.
SU‐E‐T‐507: Dose Calculation Quality of AcurosXB Involving a HD120 MLC Compared with Monte Carlo Methods
Authors: Frauchiger D , Manser P , Bigler R , Geretschläger A , Aebersold D , Fix M
Published: June 2012

Purpose: Advanced radiation therapy requires highly sophisticated dose calculation algorithms such as finite element based Boltzmann solvers or Monte Carlo (MC) methods. MC is commonly accepted as the golden standard method for dose calculation in high energy treatments and thus it is used for benchmarking other algorithms. In this work the quality of dose distribution calculated using the Boltzmann solver based AcurosXB algorithm within Eclipse (Varian Medical Systems) is investigated for volumetric modulated arc treatment (VMAT) plans involving the high definition MLC (HD120 MLC) by comparing doses with the validated Swiss Monte Carlo Plan (SMCP).Materials & Methods: Within SMCP and Eclipse using AcurosXB, 10 VMAT H&N patient plans and corresponding verification plans were recalculated using fixed MUs. In SMCP, radiation transport and dose calculation were performed using VMC++ with a statistical uncertainty of 1%. The voxel size was 2.5 mm for SMCP and AcurosXB and the same material composition data was used for CT conversion. Dose volume histograms (DVH) were used in order to quantify the difference between the dose distributions of the patient plans. In addition, calculated verification plans were compared with measurements carried out with the Delta4 system (Scandidos) by using the gamma evaluation with 3%/3 mm criteria of points having a dose larger than 20% of isocenter dose. Results: DVHs for the patient plans showed good agreement between SMCP and AcurosXB calculations. Overall AcurosXB lead to an underestimation of the median dose values by about 1%. For measured total dose distributions of the verification plans on average 98.6% and 99.0% of the points fullfil the gamma criteria for the dose calculated using AcurosXB and SMCP, respectively. Conclusions: Resulting AcurosXB dose distributions for VMAT H&N plans involving a HD120 MLC are in good agreement with calculated SMCP dose distributions. Conflict of Interest: This work was supported by Varian Medical Systems
SU‐E‐T‐509: Photon Spectrum Modeling of Flattening Filter Free (FFF) Beam and the Optimization of Model Parameters
Authors: Cho W , Kielar K , Xing L , Suh T
Published: June 2012

Purpose: To determine the distribution of photon spectrum on flattening filter free (FFF) beams, novel and fast optimization methods that were applicable on a convolution/superposition dose calculation algorithm were implemented. Methods: Two‐step optimization method was designed to model the virtual photon spectrums for FFF beams. At first, simple functional form of photon spectrums proposed by E. S. M. Ali was modified and used to make rough shapes of photon spectrum. The distributions of photon spectrums were defined at various field sizes (FSs) to consider the changes of the contribution for scattered photons. Percent depth doses (PDDs) at various FSs were used, and collapsed cone convolution (CCC) algorithm was used to calculate PDDs by considering cone‐shaped photon fluence in fields. At next, an arbitrary functional form of photon spectrums where the values of photon intensity itself were free parameters was designed. Line search method was used for optimization and gradient terms at each free parameter were derived from CCC algorithm to enhance the speed of iterations. Results: The mean energies of the optimized spectrums were decreased from 1.40 to 1.21 MeV for 6 MV FFF beams and from 2.45 to 1.27 MeV for 10MV FFF beams as FSs were increased from 3×3 to 40×40 cm2 because of the contributions of scattered photons. The shape of the spectrums were not greatly changed with field sizes, but root mean squared differences (RMSDs) between the measured PDDs and the calculated PDDs using optimized spectrums were increased upto 0.87% as the FSs were decreased to 3×3 cm2. Conclusions: Developed method for spectrum modeling showed good agreements when the PDDs were calculated with the optimized results. Suggested method is proper to the radiation treatment planning systems because it only requires measured PDDs, and based on the analytic dose calculation algorithm. This work was supported by the National Research Foundation of Korea(NRFK)⌉ grant funded by the Korean government (MEST)⌉ (Grant No. K20901000001‐09E0100‐00110⌉), Varian Medical Systems, NCI Grant No.1R01 CA98523⌉, and NSF Grant No. 0854492⌉.
SU‐E‐T‐511: Dose Variations Related to Tumor Size and Location for Pencil Beam and Anisotropic Analytical Algorithms
Authors: Kang J , Yang J , Varlotto J , Saw C , Ma C
Published: June 2012

Purpose: To investigate the tumor geometric relationship to the dose variations of Anisotropic Analytical Algorithm (AAA), pencil beam convolution algorithm with/without modified Bath Power Law(PBMPL)/PB in stereotactic body radiation therapy(SBRT) treatment plans of patients presenting with a solitary primary lung cancer. Materials/Methods: Treatment plans of 14 patients (7 upper lobe, 7 lower lobe) were used for this study. The planning target volume (PTV) size ranges from 3.9c.c. to 156.7c.c. The SBRT treatment plans were composed of 10–12 non‐ coplanar photon beams as per RTOG guidelines. The prescription dose for this study were (i) 4×12Gy, (ii) 5×10Gy, and (iii) 5×11Gy. The Varian Eclipse treatment planning system Eclipse v. 8.9 (Palo Alto, CA) was used for this study. Four‐dimensional CT (4D CT) data were used to define the integral target volume (ITV) on maximum intensity projection. An 5mm circumferential margin was used to create PTV from ITV. Plans were generated with three algorithms. Results: a). For small lesions (PTV occupy less than 1% of the ipsilateral lung volume), the PBMPL plans had overestimated the dose by average 10% compared to AAA. But the PB without any heterogeneity correction agrees well with AAA. b). For big lesions (PTV occupy more than 1% of the ipsilateral lung volume), the PBMPL plans had agreed well with AAA. But the PB without any heterogeneity correction underestimate the dose by average 15% compared to AAA. c). The tumor location (Group1: within 1cm from the lung wall;Group2: 2cm away from the lung wall Group3: in between zone of 1 and 2cm from the lung wall; Group 4:Spread from the lung wall to the 2cm away zone) seems to relate with dose calculation variations among different algorithms. Conclusions: Prescription adjustment is not necessary for PTV less than 1% of ipsilateral lung volume as the recent suggestion by the quality assurance working group of phase III Rosel study of prescription dose reduction of 10% from 60Gy to 54Gy when utilizing AAA instead of PBC.
SU‐E‐T‐515: Comparison of Two Dose‐Specification Methods for the Treatment of Uterine Cervix Cancer with HDR Brachytherapy Using a Tandem and Ring Applicator
Authors: Bhandare N , Yeung A
Published: June 2012

Purpose: To compare the dose to the high‐risk clinical target volume (HRCTV)‐D90 and dose‐limiting structures with the dose prescription to point A (Manchester system) using conventional methods to image‐guided treatment planning with dose optimization and a dose prescription to D90 of the HRCTV. Methods: CT‐MR‐fused image sets for 16 patients (stage IA2‐IIIB) with uterine cervix cancer were obtained for each of 5 fractions of HDR brachytherapy using tandem and ring applicators to generate 2 sets of plans. In the first set, the dose was prescribed to point A with a standard dwell weight pattern reflecting the Manchester system loading pattern. In the second set, the dose was prescribed to D90 of the HRCTV with graphical plan optimization. Parameters of clinical significance (HRCTV‐D90 and dose received by 1.0, 2.0, and 5.0cc of the bladder, rectum, and sigmoid) were compared, as recommended by GEC‐ESTRO. Results: HRCTV‐V for 6 patients was =30cc (largest radius, <2.0cm) and >30cc (largest radius, =2cm) for the others. For the first set of plans, when HRCTV‐V was <30cc, the ratio of doses HRCTV‐D90/dose to point A varied from 1.10 to 1.40. When HRCTV‐V was >30cc, it varied from 0.75 to 0.95. In the second set of plans, HRCTV‐D90 always received the prescription dose. Doses to 2cc of one or more organs at risk exceeded >10% of the limiting doses for 9 patients in the first set of plans but remained <10% in all patients in the second set of plans. A 10–25% dose reduction to 2cc of the bladder and 15–35% to 2cc of the rectum and sigmoid occurred in the second set of plans. Conclusions: Image‐guided brachytherapy with dose optimization yields a prescribed dose to the HRCTV‐D90 while maintaining doses to organs at risk close to their limiting value, offering a dosimetric benefit over the traditional method.