bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐442: Comparison of Global versus Local Gamma Criteria for Planar Dose IMRT QA
Authors: Ozturk N , Smith B , Aydogan B
Published: November 2011

Purpose: To evaluate the effect of using global vs local gamma analysis on planar dose IMRT QA . Methods: Seven Eclipse IMRT plans, with nine fields each, for head and neck and pelvic cancer were evaluated; planar doses from verification plans calculated on a flat phantom were compared with measurements obtained using a 2D detector array (Matrixx). An in‐house developed software was used to evaluate the measured doses using the local gamma scheme where percent dose difference is calculated relative to dose at each point, as well as the global gamma in which percent dose difference is calculated relative to the maximum dose in the measurement plane. Percent of pixels that passed (gamma >1) were compared and points that failed were investigated. Results: With 3%/3mm gamma criteria and 10% threshold dose, overall passing rate with local gamma was 4.9% (+/− 1.6%) smaller on the average than global gamma rates. Maximum difference in the passing rate was as high as 16%, with an average of 10.3% (+/−3.6%) for all fields; the variation was more pronounced for pelvic plans with simultaneous integrated boost which involved multiple planning target volumes with different prescribed doses. Points failing the local gamma criteria were mostly in lower dose (i.e., about 40–60% of maximum planar dose) and low gradient regions. Conclusions: For planar dose IMRT QA, global gamma analysis gives higher passing rates where points in lower dose and low gradient regions pass the global dose criterion with higher actual percent dose differences between measured and planned doses. Higher percent dose deviations in lower dose regions might possibly be due to deficiencies in IMRT commissioning and/or planning which could have been missed using the global gamma analysis. Users need to be aware of the limitations of the techniques used in the dosimetric analysis of IMRT plans.
SU‐E‐T‐446: The Effect of Breathing Motion on the Delivery of Linac‐Based Intensity Modulated Total Marrow Irradiation (IM‐TMI)
Authors: Surucu M , Kavak G , Wiersma R , Aydogan B
Published: November 2011

Purpose: To evaluate the effect of breathing motion on the delivery of linac‐based intensity modulated total marrow irradiation (IM‐TMI). Methods: An IM‐TMI treatment planning for an anthropomorphic Rando phantom was performed using the three isocenter technique that was previously reported by our group. The chest sub‐plan that targets the ribs, sternum and spine while sparing the lungs, liver, and heart was used to evaluate the effect of breathing on the treatment delivery. The breathing motion was simulated using a motorized stage. IM‐TMI dose measured in a stable phantom first and then in a phantom that was set on motion using three sinusoidal motions with peak‐to‐peak distances of 5 mm superior‐inferior (SI), 10 mm SI, and 5 mm both SI and anterior‐posterior (AP). A total of 46 thermoluminescent detectors (TLDs) were placed in five locations in the target bones and lungs. An additional 8 TLDs were used for dose calibration. The measured doses were corrected using the individual TLD sensitivities. The average TLD doses obtained with motion were compared to that of the stable delivery. In addition, a stereotactic photon diode was used to measure the dose in another target bone location. Results: The ratio of the moving to stable delivery of mean dose were 1.04 (range: 1.01–1.06), 1.06 (1.04–1.07) and 1.03 (1.00–1.04) in target bones while the ratios were 1.00 (0.94–1.09), 1.01 (0.97–1.04) and 1.00 (0.97–1.04) in the lungs for the 5 mm SI, 10 mm SI, and 5 mm SI and AP motions respectively. Conclusions: In this study, 16 out of 18 measurement points showed less than 6% difference with breathing motions in a single fraction. The delivered dose difference was as much as 7% high in bone and 9% low in lung with breathing motion.
SU‐E‐T‐447: Energy‐Dependent Geometric Correction Factor for the MatriXXTM QA Device for Validation of Intensity Modulated Radiation Therapy Plans Utilizing Clinical Gantry Angles
Authors: Kirkpatrick S , Selvaraj R , Gotts H , Oliveira S , Agarwal A
Published: November 2011

Purpose: The MatriXX™ detector array (IBA Dosimetry) is widely used for IMRT validations with a perpendicular beam incidence. At our institution we employ the device using actual beam incidence (clinical gantry angles), which introduces uncertainties into the measurements due to directional dependence of detector response as well as table attenuation. To address these uncertainties, we determined an Energy‐Dependent Geometric Correction Factor (EDGCF) for routine IMRT validations utilizing actual (clinical) gantry angles. Methods: Data for this study was acquired with the IBA MatriXX™ device using a Varian 23iX accelerator. The device was sandwiched in a Solid Water™ phantom and positioned on the Exact Couch table for a range of gantry angles typical of actual IMRT treatments. Measured data was compared to dosimetric calculations using the Eclipse AAA (v8.6) algorithm. Average EDGCF values for typical clinical geometries were determined and IMRT plan validations compared with and without the correction factors. Results: The average EDGCF for all field sizes for 6MV is 1.0473(SD0.0022) and for 10MV is 1.0335(SD0.0034). The small standard deviations (SD) indicate that the directional response of the MatriXX™ device is independent of field size. The average EDGCF for field size 8×8cm and 6MV is 1.0474(SD0.0837) and for 10MV is 1.0319(SD0.0571). Although the EDGCF is weakly dependent on field size the large statistical deviation indicates a high dependence on actual gantry angle. For 25 plans using 6MV photon beams, the mean ratios of planned to measured dose before and after applying the corrections were 0.956(SD0.019) and 1.003(SD0.017) Conclusions: Although it is more precise to use a gantry angle‐dependent correction factor, the fact that clinical gantry angles are patient‐specific would render the correction cumbersome. In our opinion a simple average EDGCF is sufficient to improve the accuracy of the MatriXX™ measurements for comparison to the calculated dose.
SU‐E‐T‐455: Evaluation of the Influence of the Dosimetric Leaf Gap on RapidArc Plans Using Gafchromic Film and Monte Carlo Simulations
Authors: Szpala S , Atwal P , Cao F , Kohl K
Published: November 2011

Purpose: Correct setting the dosimetric leaf gap (DLG) in the planning system is essential for proper calculation of the dose distribution for RapidArc plans. We evaluated the influence of the DLG by using Gafchromic EBT2 film, as well as running Monte Carlo (MC) simulations. Methods: Gafchromic EBT2 film was sandwiched between acrylic slabs, and irradiated during delivery of RapidArc plans. The films were scanned with Epson V700 scanner, corrected for scanner nonuniformity, and converted to dose. The agreement between the dose distribution measured with film (for DLG values ranging from 1.3mm to 5.0mm) was compared to the corresponding dose calculated in Eclipse using the AAA8615 algorithm. After registering the film images to the calculated dose, agreement was quantified by comparing line profiles and examining gamma maps. No normalization or spatial shifting was employed. MC simulations were carried out on a phantom; gamma maps were calculated between the simulated and planned doses. Results: Comparing line profiles from film to the corresponding profiles from AAA revealed the best agreement at DLG of 1.6mm. For larger values of the DLG the AAA calculations overestimated the film profiles, while smaller values underestimated the film data. The gamma maps in the region conformal to the PTV had nearly 100% passing rate for gamma (3%, 3mm). MC simulations yielded an optimum DLG value of 2.2mm Conclusions: EBT2 films proved to be sensitive to detect variations in dose distributions calculated for various values of the DLG. Such sensitivity was only possible in the absence of normalization of the data sets, as the DLG influences the average calculated dose in the PTV. There is a small disagreement of the optimum value of DLG established using these two methods, which may be attributed to the film data being a subset of the MC calculated 3D data set.
SU‐E‐T‐456: Comparison of Dosimetric Effect of Translational Setup Errors for Total Scalp Irradiation Using Conventional Photon‐Electron Combination, IMRT and VMAT Techniques
Authors: Wang H , Wang C , Wong P , Martel M , Chung H , Tung S
Published: November 2011

Purpose: IMRT and VMAT showed superior total scalp coverage and uniformity over conventional photon/electron combination technique. This study is to investigate and compare the dosimetric effects of translational setup errors for these techniques. Methods: Three total scalp irradiation patients were studied. For each patient, three treatment plans were generated using conventional, IMRT and SmartArc VMAT technique. In order to evaluate the dosimetric effect due to translational setup errors, 36 additional plans were calculated for each patient on the planning‐CT image, which included isocenter shift of 2mm and 5mm in lateral (LR), anterior‐posterior (AP) and superior‐inferior (SI) directions for each of the three plans. The dose distributions for target and organs at risk (OAR) (brain, brainstem and spinal cord) from the 36 plans were compared to the original plans and among the three techniques using dose‐volume histograms, tumor‐volume coverage of prescription dose and the maximum OAR dose. Results: Conventional plans were robust to lateral shift (less than 0.8% tumor coverage drop and less than 0.8cGy brain mean dose increases for up to 5 mm isocenter shift) because only lateral beams were used. Tumor coverage drops were apparent when isocenter moved towards posterior and superior scalp. At 2mm shift, tumor coverage drop for VMAT plans were comparable to conventional plans (LR 0.4%, AP 1.4%, SI 2.3%), while for IMRT plans, the coverage dropped 3.3%, 3.0% and 2.6% in LR, AP and SI direction, respectively. At 5mm shift, both IMRT and VMAT plans had significant higher coverage drop than conventional plans with IMRT plans the worst in all directions. OAR dose increases were less than 50cGy for conventional plans, and were up to 150cGy for IMRT and VMAT plans at 2mm isocenter shift. Conclusions: The dosimetric effect were comparable between VMAT and conventional technique when translational setup errors were within 2mm. IMRT plans showed worse effect than VMAT.
SU‐E‐T‐457: Influence of Changing Magnetron and Injector Current on the Beam Characteristics of a Tomotherapy Hi‐Art SYSTEM
Authors: Van De Vondel I , Tournel K , Duchateau M , Reynders T , Van Vaerenbergh S , Boussaer M , Leysen K , Depuydt T , Poels K , Verellen D , De Ridder M
Published: November 2011

Purpose: This study investigates the influence of the magnetron and injector current on the beam characteristics of a Tomotherapy system. Methods: Treatment on tomotherapy is time‐based : the gantry rotates while the beam is on and all beam modulation is performed by the MLC. This implies that maintaining output stability is crucial. However, daily changes in output have been observed of up to 2.5% depending on external (pressure, temperature) or internal (component wear or instability). The output is tuned by adjusting the magnetron and injector current. This however, has an influence on both beam energy and profile but to which extent or magnitude has not been clear. Therefor, 144 measurements were performed by altering the magnetron current from 86,75A to 101,7A in 6 equal steps and by altering the injector current from 277,5mA to 612mA in 8 equal steps. Beam profile was measured using Tomodose (Sun Nuclear corp.). The Quality index was calculated using the absorbed dose ratio at depth 20cm and 10cm in rectangular slabs of solid water phantom with an SSD of 85cm. To estimate the influence on the cone profile the ratio between two volumes (on‐axis and off‐axis) was calculated. Results: With a magnetron current change of 14A the average quality index difference was 1.63%. Varying the injector current with 334.5mA causes the average quality index to change with 1.43%. Dose variation at 10cm from the central axis in lateral direction was 3% when changing the injector current by 334.5mA and 1.9% when changing the magnetron current by 14A Conclusions: Modifying magnetron and injector current does not have a major effect on the quality index. The lateral dose profile sagging is the most important finding since this will have an effect on off‐axis located targets. Injector current variation has more influence on the profile than magnetron current variation.
SU‐E‐T‐460: Impact on Delivered Dose Accuracy of a Moving Target in Different Types of Plan
Authors: He Rui , Edwards Jason , Dieck Geoff , Liu Tianxiao , Yang Chunli
Published: November 2011

Purpose: To investigate the impact on delivered target dose of tumor motion inside of the lung. The delivered dose of a moving target was measured and compared among 3D conformal, low‐modulated IMRT, VMAT and high‐ modulated IMRT and VMAT plan.Method: A Dynamic Thorax Phantom (Model 008A) from CIRS Tissue Simulation & Phantom Technology was scanned using Philips CT scanner with both standard and 4D mode. The GTV, the implanted 3 cm target in the left lung of the phantom, was drawn based on both 4D CT MIP and standard CT mode. To simplify the process, PTV is the same as 4D‐GTV in this phantom planning study. The prescription is 2 Gy for one fraction and dose normalization is to isocenter, where the chamber (TN31014_00703 from PTW, Freiburg, Germany) located. Five different plans were generated using Pinnacle treatment planning system version 9.0 for 6 MV photon beams from Elekta Beam Modulator LINAC with MLC leaf width of 4 mm. A measured chamber dose is compared to the calculated dose to the chamber volume. The volume of the target from 4D CT is compared to the volume detected from CBCT. Results: The chamber measurement shows the difference between measured and planned are −0.28%, 0.91%, −0.08%, 4.36% and 1.02% respectively. The volume of GTV from 4DCT is 32.5 cm3, 11.5 cm3 from standared and 23.7 cm3 from CBCT. Conclusions: An increased difference between measured and planned is observed with increasing modulation of the IMRT and VMAT plan. The difference in volume detected by daily CBCT and by 4DCT needs to be followed up and a guideline in daily IGRT needs to be worked out. More detailed studies with film dosimetry to address the effect in 2D dose distribution is underway.
SU‐E‐T‐461: Using Foldable Gold Anchor Markers for IGRT Fiducial Tracking
Authors: Shao H , Yang J , Feng J
Published: November 2011

Purpose: Tracking gold markers is a direct method of tumor localization in IGRT. Foldable gold anchor markers can be inserted using narrow needle (22 or 25 gauge) with less morbidity. We explored the feasibility of using anchor makers for IGRT.Methods: The anchor markers are either 10 mm or 20 mm long gold wires. Small notches every 2.0 mm in the wire allow the wire to fold into a dense ball shape when injected, whose angled edge makes fiducial migration less possible. Alternatively, different combination of advancing stylet and retracting needle can place the gold wire into the tissue as either a linear or a tadpole shaped marker. In our phantom study, three 20‐mm wires were placed into a bolus and each folded into ball, linear and tadpole shapes. The bolus was placed on top solid water phantom and scanned. The visualization of these markers on different imaging devices (OBI, cone beam CT, portal image, Acculoc and Cyberknife imaging tracking system) are evaluated. Clinical experience includes lung, liver, prostate and pancreases. The tracking ability of the imaging system on the anchor is evaluated.Results: All markers are clearly visible with kilo‐voltage imaging devices. In our Cyberknife test, anchor markers were visible under default X‐ray parameters. The precision of the lock‐on is within 1 mm, except for the linear marker. When employs mega voltage (MV) portal images with Acculoc system, the ball shaped anchor marker is the most visible in identification and linear one is the least. In clinic, no toxicity was observed resulting from the fiducial placement Conclusions: The gold anchor markers appear comparable with traditional solid gold markers.
SU‐E‐T‐462: Microscopic Fractions of Dose Enhancement: Size Dependence Study to Gold Nanoparticle Using Monte Carlo
Authors: Marques T , Scuch F , Baffa O , Nicolucci P
Published: November 2011

Purpose: To quantitatively compare fractions of dose enhancement in microscopic ranges (m‐DEF) due to gold nanoparticles (AuNP) with different sizes using Monte Carlo simulation. Material and Methods: PENELOPE Monte Carlo code was used to perform simulations of dose deposition. The history condensation parameters of the event‐by‐event electron simulations were set as 0.05 maximum fraction of energy loss and 0.05 maximum fraction of angular deviation per interaction. Two clinical energy spectrums were considered in this study: Ir‐192 HDR brachytherapy source and 200kV ortovoltage beam. Six AuNP spherical sizes were simulated from 10nm to 150nm. Nanoparticles were positioned inside a virtual 8μm spherical cell and total gold concentration was 0.01% mass fraction. Doses were recorded inside the cell and m‐DEFs were calculated as the ratio between total dose deposited inside the cell with and without nanoparticles. Results: A non‐linear relation was found between nanoparticle size and m‐DEF to both clinical beams considered. The m‐DEF found to 50nm particles enclosed to the cell in 200kV and Ir‐192 simulations were 1.73 and 1.56, respectively. This value becomes lower than 1.20 when 150nm nanoparticles are considered to both energy beams. When particles in a range from 10nm to 40nm are considered, the m‐DEF found was lower than 1.40, being higher to 200kV beam. Standard deviations are around 5% to 10nm simulations and decreases fast with particle size, reaching 1% to 150nm AuNP particles. Conclusions: Microscopic dose enhancement fractions are dependent to gold nanoparticle size and this relation can be studied by Monte Carlo when properly statistical analysis is applied. An optimized size of gold nanoparticle can be determined according to radiation therapy beam of interest. The size dependence of m‐DEF has its origin in the range of the electrons created inside the AuNPs that delivery doses inside the cells, being more expressive to large sizes.
SU‐E‐T‐649: A Software Tool for Multi‐Modality and Multi‐Fractionation Biological Composite Plan Evaluation
Authors: Zhao B , Lack D , Spencer B , Miller S , Burmeister J , Liu Q
Published: November 2011

Purpose: Patients receive radiotherapy composed of different modalities. For example, EBRT followed by HDR brachytherapy boost or mixed photon and particle therapies. For such cases, where different fractionation schemes or modalities with different RBEs are used, generation of a 3D composite equivalent biological dose distribution in 2 Gy fractions (EQD2) is desirable. Currently this function is unavailable in commercial planning platforms. The goal of this work was to develop a software tool capable of creating the 3D composite EQD2 dose distribution for multiple modalities. Methods: Matlab‐based software was developed. DICOM‐RT files exported from different planning systems were imported into the software. The physical dose distribution is converted to an EQD2 distribution at voxel levels using the linear‐quadratic model or induced‐repair model. Radiobiological parameters such as alpha/beta ratio and RBE for each structure are changable by the user. Dose matrices from different modalities are aligned and a composite EQD2 dose matrix is generated. This matrix is written back into DICOM format for import into a commercial planning system or in‐house software for plan evaluation. As a demonstration, two cervical cancer test cases were planned with both EBRT in Eclipse and HDR brachytherapy in Oncentra MasterPlan and evaluated. Results: The software provides the 3D composite EQD2 distribution. This simplifies the evaluation of multi‐modality treatments with different fractionation schemes for clinicians. For the two test cases, the D90 for targets and D2cc for the organs‐at‐risk were evaluated. These results were able to be directly interpreted according to published guidelines. The composite plan can also be evaluated in in‐house software using published data of tumor control and normal tissue complication probabilities. Conclusions: The software provides 3D composite biological dose from multiple modalites. This information can help in the evaluation of treatments, assist in creating optimal treatment plans and predict the overall treatment outcome.
SU‐E‐T‐650: Impact of Machine Output Rate on Effective Dose Rate and Biologically Equivalent Fraction Size in Total Body Irradiation (TBI)
Authors: Stewart RD , Kalet A , Laramore GE
Published: November 2011

Purpose: Examine the feasibility and biological significance of increasing machine output rates in extended‐distance Total Body Irradiation (TBI). Methods: Biologically equivalent doses for TBI are derived from the LQ cell survival model. Effective dose rates and corrected fraction size for a mini‐TBI (i.e., 1 fraction × 2 Gy to patient mid‐line) delivered using 4 and 8 beams are computed as a function of machine output rate. The number of beams used for a TBI tends to increase with increasing patient size because of the clinical constraint of no more than 1000 MU per beam. All of the reported results include a 1 minute gap between beams and a (conservative) 5 minute gap for patient repositioning. Results: For a 4 beam treatment, increasing the machine output rate from 200 to 400 MU/minute reduced the fraction delivery time by 36% (28 to 18 minutes), and only increased the effective dose rate from 7 to 11 cGy/minute. For 8 beams, the fraction delivery times for 200 and 400 MU/min are 52 minutes (3.85 cGy/min) to 20 minutes (6.16 cGy/min), respectively. Increasing the machine output rate from 200 to 400 MU/min is unlikely to require more than 2–5% reduction in fraction size (alpha/beta = 1 Gy). The size of the required correction decreases as alpha/beta increases. Conclusions: Patient‐specific planning to correct for differences in beam number (patient size) are unlikely to alter the determination of biologically equivalent fraction sizes by more than 5%, which is well within the +/− 10% uniformity specified in many TBI protocols. A clinical trial to evaluate patient safety and treatment efficacy for machine output rates as high as 600–700 MU per minute are reasonable. Such a trial has the potential to substantially to increase patient comfort and reduce facility and labor costs without jeopardizing treatment effectiveness or safety.
SU‐E‐T‐657: Quantitative Tumour Control Predictions for the Radiotherapy of Non‐Small‐Cell Lung Tumours
Authors: Nahum A , Uzan J , Jain P , Malik Z , Fenwick J , Baker C
Published: November 2011

Purpose: Radiotherapy of non‐small‐cell lung tumours (NSCLC) is undergoing significant advances due to conformal planning, respiration‐ motion strategies, hypofractionation and isotoxic prescription‐dose individualisation (Fenwick et al 2009; Panettieri et al 2011). In order to maximise the efficacy of these various approaches a model for predicting local‐control probability as a function of the (absolute, total) dose distribution, number of fractions, tumour volume and overall treatment time is essential. Methods: We have taken three contrasting dose and fraction regimens (CHART; the Martel data; our own Clatterbridge clinical experience: 55 Gy in 20 fractions) together with the published (and our won unpublished) local control data and modelled all these data using the Marsden quasi‐mechanistic, LQ‐based, population TCP model (Nahum, Webb, Sanchez‐Nieto 1993, 2000). ‘Best‐fit’ model parameters were derived using a Matlab optimisation routine. Results: The fit is virtually “exact” as the figure demonstrates; the ‘best‐fit’ parameters are alpha = 0.307 per Gy, sigma_alpha = 0.037 Gy‐1, T_K = 20.9 days, Td = 3.7 days with alpha/beta= 10 Gy and rho_clon =10̂7 cm‐3 as the fixed parameters. Conclusions: The Marsden TCP model together with the above ‘best‐fit’ parameters is now ready to be used, togetrher with our in‐ house BioSuite software (Uzan et al 2011) to design radiobiologically optimised NSCLC protocols such as twice‐a‐day fractionation for larger, centrally located tumours and intermediate fraction number (8 to 15) schedules for tumours too large for the 3–5 fraction SBRT approach.

This work was partially supported by Cancer Research UK
SU‐E‐T‐659: Maximizing the Therapeutic Effect of a Fractionated Treatment with Delivery of Inhomogeneous Daily Dose Distributions
Authors: Trofimov A , Niemierko A , Efstathiou JA
Published: November 2011

Purpose: To evaluate potential gain in therapeutic effect from delivery of daily inhomogeneous fractional dose distributions in proton therapy, using pencil beam scanning. Methods: For a sample case of prostate cancer, we consider a standard course of 39 fractions of 2 Gy (78 Gy total), and a hypofractionated course of 20 fractions of 3 Gy (assuming alpha/beta=1.5, the equivalent dose in 2 Gy fractions (ED2Gy) is 77.1 Gy). Two sets of dose distributions were planned: (1) the standard approach, with a uniform dose (100% of prescription) delivered in every fraction to the entire target; (2) delivery of inhomogeneous fractional dose (IFD) distributions, which varied within the target volume between 65% and 135% of the nominal prescription. For IFD, the daily distributions were optimized in such a way that the two hemispheres of the prostate (split sagittally through the urethra) received, in alternating fractions, either 65% or 135% of the nominal fractional dose (e.g., 1.3 and 2.7 Gy), while the urethra received approximately 100% (e.g., 2 Gy) daily. The equivalent uniform dose (EUD), and ED2Gy were compared for different plans. Results: In the IFD course, the whole prostate received a nearly uniform dose over every 2 fractions, however ED2Gy was higher than with standard uniform dose: 81.9 Gy (5% increase) for the conventional, and 82.6 Gy (7% increase) for the hypofractionated course. Rectal and bladder EUD increased by <5%, while urethral EUD was unchanged. Conclusions: In treatment of prostate and other sites, improved therapeutic outcome can be expected with delivery of inhomogeneous daily dose distributions, while administering the prescribed uniform dose to target over the entire course of treatment. The extent of expected gain is dependent on model parameters (alpha/beta, EUD‐a, etc.), and dose distributions may potentially be designed to maximize the gain specifically for a certain assumed range of parameters.

No disclosures or conflict of interest. Supported by the Federal Share of program income earned on C06‐CA059267, Proton Therapy Research and Treatment Center.
SU‐E‐T‐660: Does CMS XiO Electron Monte Carlo Model of a Siemens Artiste Linac Produce Accurate Dose Distribution for a Highly Irregular Electron Field?
Authors: Kostourkov I L , Croft K W
Published: November 2011

Purpose: To evaluate the ability of CMS XiO Electron Monte Carlo algorithm (eMC) to accurately simulate irregularly shaped electron fields from a Siemens Artiste linear accelerator. Methods: Irregular electron fields where defined using a 1.5 cm thick Cerrobend cutout. For accuracy, the pattern was cut using a milling machine. eMC calculated planar dose distributions for 6, 9, 12, 15 and 18 MeV electron beams produced by Siemens Artiste linear accelerator were compared with measurements done with EBT Gafchromic films. All measurements and dose calculations were performed at the depth of maximum dose of the particular beam, at a standard SSD of 100 cm. The EBT films were scanned with Epson Perfection V7000 scanner. The red channel data of the 48 bit TIFF images was extracted, calibrated, corrected and analyzed with in‐house developed software. Results: The differences between eMC and the measurements were found to be within the gamma‐criteria of 2% dose and 2mm distance‐to‐agreement, including in the areas under the Cerrobend cutout. These differences decrease with increasing electron beam energy. Compared to the commonly used electron Pencil Beam algorithm, eMC produced significantly more accurate dose distributions for all regions of the irregular field, as well as under the cutout. Conclusions: The new CMS XiO eMC algorithm is capable of calculating dose distributions for highly irregular fields with an accuracy expected from photon beam calculation algorithms. Additional tests are under way to verify the performance of eMC for inhomogeneous medium and the calculation of dose output for a range of clinical electron fields.
SU‐E‐T‐662: Further Development of a Power Approximation of Range‐Energy Relationship for Therapeutic Proton Beams
Authors: Shi C. , Zheng Y , Liu Y
Published: November 2011

Purpose: The purpose of this work is to further develop a power approximation of energy‐range relationship for therapeutic proton beams based on range‐energy tables from Janniˈs Data, ICRU Data, and Monte Carlo simulated Data. Methods: The energy deposition in water was simulated with MCNPX. The energy tally in MCNPX physics cards included the total energy. The proton source was defined as a pencil beam with uniformly distributed in area. The proton energy in simulation ranged from 40 MeV to 250 MeV with increments of 5 MeV. A three dimensional dose matrix was simulated with voxel dimension of 1×1×1 mm̂3. A central‐axis‐slice for each individual simulation was used for range analysis. Results: The range difference between Janniˈs and ICRU data increased from sub‐millimeter to ∼4 mm as energy changed from 40 MeV to 250 MeV with average difference as 1.08%. The Monte Carlo simulation data lies between Janniˈs Data and ICRU data with average 0.57% below Janniˈs Data, and average 0.50% above ICRU Data. The range‐energy table from Janniˈs, ICRU and Monte Carlo Simulation are all in very good agreement with each other, with coefficients of correlation between 0.9999 to 1.000. The relationship between proton range and energy can be fitted by a power approximation. Generally the power relation can be expressed by R = a*Êp. With unit of R in mm and E in MeV, the factor a and the exponent p in proton energy‐range power approximation were determined to be 0.023, 1.763 from Janniˈs Data, 0.022, 1.770 from ICRU Data, and 0.0225, 1.766 from MC simulation. Conclusions: Monte Carlo simulation provided very close agreement to the two widely used proton range‐energy tables. The approximation of range‐energy power relationship based on Monte Carlo data provide slightly different factor a and exponent p from those based on Janniˈs and ICRU Data.
SU‐E‐T‐663: Extended TrueBeam Patient‐Independent Phase Space Library for the 6X, 6XFFF, 10X and 10XFFF Radiotherapy Beams
Authors: Constantin M , Sawkey D , Mansfield S , Salop A , LoSasso T , Svatos M
Published: November 2011

Purpose: To develop a patient‐independent IAEA‐compliant phase space database using accurate geometry representation of the treatment head components imported from CAD (Computer‐Aided‐Design) drawings and a physics list exploration for the specific materials of the linac treatment head. Methods: Geant4.9.4 was employed to simulate the TrueBeam 6X, 6XFFF, 10X and 10XFFF photon beams. Electron beam transport in the linac was simulated with Parmela and used as input into dose calculations. Geometry components were tessellated solids, i.e. Generalized‐Dynamic‐Markup‐Language files, extracted from mechanical CAD drawings. A phase space scorer was implemented above the upper jaws on a cylindrical surface. The simulations were run on the Amazon Elastic Compute Cloud. Dose calculations in a water phantom (with 6×6×4 mm3 voxels) were performed using two physics lists, Standard Option‐0 and Low‐Energy Livermore/Penelope, with a 10um range‐cut. The Urban93 and Goudsmit‐Saunderson models were considered for electron multiple‐scattering, while Tsai and 2BN models for electron Bremsstrahlung angular generators. Results: The maximum dose difference between simulation and experiment was <1% for the percent depth dose curves and <3% for in‐field dose profiles. For large fields, the simulated dose profile horns were smaller by 2% for the 6X beam and larger by 3% for the 10X beam compared to the experiment. Simulations using the Goudsmit‐Saunderson model reproduced the experiment with higher accuracy than Urban93, causing a 3x CPU increase. No CPU penalty or accuracy differences were observed in simulations using the Tsai versus the 2BN angular generators. The Standard Option‐0 list has the advantage of providing 2x CPU speedup and can be used with a range cut of 0.1mm for medical physics applications above 1MeV, ensuring the same accuracy as the Low‐Energy Livermore/Penelope list. Conclusions: We developed an extended TrueBeam phase space database using high precision geometry implementation from CAD that can be used for future medical physics user applications.

Work supported by Varian Medical Systems
SU‐E‐T‐664: Accuracy of Patient Dose Calculation in Proton Therapy of Lung Cancer: A Comparison of Monte Carlo and Pencil Beam Computations
Authors: Mirkovic D , Titt U , Mohan R
Published: November 2011

Purpose: The analytical, semi‐empirical algorithms are used widely for proton treatment planning in the current clinical practice. The aim of this study is the assessment of possible dosimetric uncertainties in these algorithms in highly heterogeneous areas of the thorax. Methods: In this study we use a detailed Monte Carlo model of the passive scattering proton therapy (PSPT) beam line together with a computed tomography (CT) based model of the patient anatomy to investigate the heterogeneity‐induced dosimetric uncertainties in PSPT treatment planning. A CT scan and a treatment plan were used to assemble the input files for the Monte Carlo code MCNPX. The total energy deposition inside the patient volume was computed with statistical uncertainty of less than 2% and converted to dose‐in‐water. The results were compared to the dose computed by the clinical treatment planning system (TPS). The corresponding dose in the water phantom was computed using both the TPS and the Monte Carlo model and used to calibrate the absolute dosimetry in the Monte Carlo model. Results: While there is acceptable agreement between the TPS and the Monte Carlo dose in the water phantom, there are noticeable differences caused by heterogeneities. The regions of largest differences are the points around and beyond the distal edge and points around the lateral penumbra. These are most pronounced when the beam passes through or is stopped in the low density regions of the lung, and increase with the range of the beam and the amount of the heterogeneities in the beam path. Conclusions: In some lung cases the actual target coverage and the accuracy of dose to lung tissues around and beyond the distal edge of the proton beam, calculated with conventional algorithms, may be suboptimal.
SU‐E‐T‐665: Analytical Source Model for Modulated Electron Radiation Therapy
Authors: Papaconstadopoulos P , Alexander A , Connell T , Seuntjens J
Published: November 2011

Purpose: To implement a dynamic, analytical source model for fast and accurate derivation of the beam characteristics on the exit plane of a linear accelerator for modulated electron radiation therapy using a Few Leaf Electron Collimator (FLEC). Methods: An analytical source model (SM) is derived for modulated electron radiation therapy (MERT) by the use of source fluence kernels directly on the linear acceleratorˈs exit plane. The BEAMnrc code was used to identify the most significant radiation sources in MERT. “Virtual” BEAM models were then created, where the different components of the sources were isolated to each other. Monte Carlo simulations of these models were performed to derive the fluence and energy electron distributions on the exit plane. The data were then stored as histograms on a 2D fluence grid (source kernels). Since the source kernels were derived by simulation of a precise accelerator model it is expected that the scattered particles would be accurately predicted. An arbitrary rectangular field can be recreated by superposition of the appropriate source kernels directly on the output plane. Results: Fluence and energy distributions were derived for three field sizes (8 × 8, 2 × 2 and 2 × 8 cm2) and 20 MeV electron beam energy with the SM and compared with the PH‐SP data. Scattered particles from the FLEC agreed well in all cases, while moderate discrepancies were encountered for the primary beam and scattered particles from the jaws. The total reconstructed beam deviation between PH‐SP and SM was less than 1.5% for all cases. Conclusions: The proposed method has shown to reproduce the fluence and energy distributions of small and/or arbitrary rectangular fields within acceptable tolerance. The model is expected to help significantly improve MERT optimization speed while maintaining accuracy in the dose calculations.

Alexander S. Onassis Public Benefit Foundation
SU‐E‐T‐666: Monte Carlo Simulation of Arbitrary Geometries and Heterogeneous Optical Properties for Treatment Planning in PDT
Authors: Sandell J , Zhu T , Finlay J , Liang X
Published: November 2011

Purpose: An important aspect of Photodynamic Therapy (PDT) treatment efficacy is uniformity of light dose. An analytic solution of fluence in a spherical cavity originally presented by Willem Star was further developed to calculate fluence in cavities of arbitrary geometries. To verify our analytic solution in conjunction with a Finite Element Model (FEM) developed in COMSOL, we compare the fluence results for a cavity of arbitrary geometry and heterogeneous optical properties to a Monte Carlo (MC) simulation developed in the MATLAB platform. This verified analytic solution will be applied to a real‐time Infrared (IR) Camera device used as a treatment planning tool for pleural PDT. Methods: The CT scans and IR camera data from four patients enrolled in a Phase I study for HPPH‐mediated Photodynamic Therapy (PDT) are used as the arbitrary cavity geometries which build the framework for the FEM and MC models of fluence. The cavity walls are assigned optical properties measured using a diffuse reflectance spectroscopic system during treatment both before and after the patient receives light dose. Once this cavity environment has been established, and isotropic light source is placed both at a central and off central location in the cavity. The resulting fluence rate calculated from the MC simulation is compared to the results from the FEM simulation. Results: Preliminary results show there is good agreement for spherical cavities of heterogeneous optical properties in the presence of attenuation and multiple scattering. The results of simulations for arbitrary geometries are currently being developed and analyzed. Conclusions: The verification of our FEM model allows us to apply this solution in the clinic with an IR camera which tracks the clinicianˈs treatment in real time. By coupling our fluence model with this new tool we can implement a real‐time fluence monitoring device which may improve uniformity of treatment.
SU‐E‐T‐668: Comparison of the Physical Characteristics of Secondary Electrons and Dose Enhancement from X‐Ray Irradiation of Gold Nanoparticles Using Monte Carlo Simulation
Authors: Leung M , Chow J , Chithrani D , Lee M , Jaffray D
Published: November 2011

Purpose: To investigate secondary electron production in gold nanoparticle (GNP) aided radiotherapy through Monte Carlo simulations, thereby advance the understanding of dose enhancements and their role in improving cell kill. Methods: Using the Geant4 toolkit, simulations were performed with four polyenergetic sources, namely 50 kVp, 250 kVp, Cobalt‐60, and 6 MV, to irradiate a gold sphere of diameters 2, 50, or 100 nm in water. The energy of the secondary electrons and the frequency and type of physics interaction that created them were tracked. This allowed calculation of the absorbed dose and energy deposition inside and outside of the nanoparticle. Results: The presence of a GNP can enhance the production of electrons by approximately 3 orders of magnitude at kV beam energies. For MV beams, the increase in electron production was approximately 10 folds. Considerable dose enhancement occurred when gold was present, at approximately 1000 folds for kV beams, and between 2 to 7 folds for MV beams. The energy deposited was calculated to compare how many additional electrons were generated and take into account their energies. In the kV beams, the addition of a GNP caused significantly greater deposited energy surrounding the nanoparticle by 2 to 3 orders of magnitude. For the MV beams, the increase was approximately 5 folds. The proportion of energy deposition inside the GNP versus the outside was also analyzed. At greater nanoparticle diameters, a larger portion of the overall deposited energy resided within the nanoparticle. Conclusions: We present simulation results that show the presence of GNPˈs can considerably increase the dose and energy deposition outside the nanoparticle, especially at kV energies. This enhancement is also present for MV beams, although to a lesser degree.
SU‐E‐T‐669: Clinical Implementation of a Commercial Monte Carlo Treatment Planning System for Electron Beams
Authors: Vandervoort E , Cygler J
Published: November 2011

Purpose: Several Monte Carlo (MC) based treatment planning systems are commercially available for electron beams and more users are implementing them in the clinical setting. In the case of MC based treatment planning systems in addition to the dose calculation accuracy one also needs to define the additional calculation parameters, such as the calculation voxel size, the choice between the computation of dose‐to‐medium or dose‐to‐water, and the number of histories and/or acceptable level of statistical uncertainty for the voxelized dose distribution. Methods: We report on the influence of these parameters on both calculation time and on the accuracy of calculated dose distributions for the XiO electron Monte Carlo (XiO eMC) software, a new treatment planning system for electron beams developed and commercialized by CMS incorporated. A comparison of radiochromic film measurements with simulated data using different parameters was performed for a complex heterogeneous phantom. Results: Dose calculations in a heterogeneous phantom are in very good agreement with film measurements, provided that appropriate simulation parameters are used (1% average statistical uncertainty, voxel size=2×2×2 mm cubed and dose‐ to‐water is computed). The rapid three‐dimensional dose gradients exhibited for these data highlight the need for a fully 3D dose comparison tool (currently under development) for electron beams treating complex heterogeneous geometries. Using a clinical XiO Linux workstation (8 processors each 3 GHz, 8.29 GB RAM), high resolution (2.5×2.5×2.5 mm cubed) low noise (<1% MRSU) simulations can be obtained in less than 4 and 8 minutes respectively for 9 and 17 MeV beams with a 10×10 cm squared applicator. Conclusions: XiO eMC calculated dose distributions agree very well with the experimental ones in both water tank and heterogeneous phantoms. More investigation may be required, however, to determine the optimal trade off between dosimetric accuracy and clinically acceptable computation times.

Financial support has been provided from Elekta CMS incorporated.
SU‐E‐T‐672: Macro Monte Carlo for Protons: Proof of Principle
Authors: Fix MK , Frei D , Volken W , Born EJ , Manser P
Published: November 2011

Purpose: For electron beams the macro Monte Carlo (MC) technique is well‐established. This work describes the proof of principle of a new macro MC method for proton beams in order to gain computational efficiency. Methods: The proof of principle is performed for the transport of primary protons in water. Pre‐simulations of mono‐energetic proton pencil beams ranging from 10 to 250 MeV impinging perpendicularly on water slabs of different thicknesses (1–10 mm) have been carried out using Geant4. The lateral displacement, the energy‐loss and the direction of all exiting primary protons have been scored and converted into probability density functions (PDFs). The macro MC method consists of stepwise transporting protons by selecting appropriate slab thicknesses and by means of sampling from corresponding PDFs. The sampled energy‐loss is deposited along the path between the entrance and exit positions of the proton for the current step. For validation purposes, different mono‐energetic proton pencil beams impinging on a water phantom, the dose distributions for the primary protons have been calculated using the macro MC transport and Geant4. The resulting integral depth dose curves and dose profiles have been compared. Results: The calculated integral depth dose curves agree better than 1% or 1 mm for all pencil beams considered. The agreement between the dose profiles at several depths in water is within 1% or 1 mm for all energies and depths. The computational efficiency for the macro MC method is about 200 times higher than for Geant4. Conclusions: The results of the dose comparisons demonstrate the very accurate and efficient dose calculation of primary protons using the macro MC method. In future, the macro MC method will be extended to include patient materials and the secondary particle transport in order to allow patient dose calculations for proton beams.

This work was supported by Varian Medical Systems.
SU‐E‐T‐673: Development of Monte Carlo Dose Calculation System for Tumor‐Tracking Irradiation with a Gimbaled X‐Ray Head
Authors: Ishihara Y , Sawada A , Nakamura M , Mukumoto N , Kaneko S , Takayama K , Mizowaki T , Kokubo M , Hiraoka M
Published: November 2011

Purpose: To propose dose calculation model of tumor‐tracking irradiation by gimbals mechanism for MHI‐TM2000 (Vero). Methods: Our MC simulation for a 6 MV photon beam delivered by the MHI‐TM2000 system was performed using EGSnrc. First, the lateral doses (5 × 5 cm2 at 100 mm depth) with pan/tilt rotation were simulated under the SSD of 900 mm. Rotation angles along pan/tilt directions were set in the range of −2.5 to +2.5° at intervals of 0.5°. The corresponding measurements were performed using EDR2 films with water‐equivalent phantoms. Differences between simulated and measured doses were calculated. Furthermore, difference of output characteristic without setup error was estimated using the simulated lateral doses under the reference condition at the maximum and minimum rotation angles. Next, the moving phantom was driven at frequency of 0.25 Hz with amplitude of 10 mm along tilt direction. From the infrared marker positions, the corresponding pan/tilt angles were calculated. Time, phantom position by laser displacement gauge, current angle of pan/tilt, and MU were recorded in the log file. A phase space data at any angles was created from the log file and particle data under the MLC. Finally, both stationary X‐ray head and tumor‐tracking irradiation were simulated under the SSD of 950 mm (4 × 4 cm2 at 50 mm depth). Each of them was compared with the corresponding measurement using EDR2 film. Results: The lateral doses within flat region showed agreement of within 1.1% in any angles. The differences between doses at the minimum angle and at the maximum were within 0.5% and 4.5% in flat and penumbra region, respectively. The averaged differences between the simulated and the measured doses with stationary and tumor‐tracking irradiation were 1.9%. Conclusions: We have developed dose calculation model of tumor‐tracking irradiation for MHI‐TM2000. This study demonstrated our proposed model has acceptable accuracy.

Research sponsored in part by Mitsubishi Heavy Industries, Ltd