Monte Carlo Dose Calculation Algorithm Research Articles

Dosimetric Accuracy of Ray-tracing Algorithm for Treatment of Thoracic Spine Lesions Using Robotic Radiosurgery

Dosimetric Accuracy of Ray-tracing Algorithm for Treatment of Thoracic Spine Lesions Using Robotic Radiosurgery

The use of non-standard CT conversion ramps for Monte Carlo verification of 6 MV prostate IMRT plans

Monte Carlo (MC) dose calculation algorithms have been widely used to verify the accuracy of intensity-modulated radiotherapy (IMRT) dose distributions computed by conventional algorithms due to the ability to precisely account for the effects of tissue inhomogeneities and multileaf collimator characteristics. Both algorithms present, however, a particular difference in terms of dose calculation and report. Whereas dose from conventional methods is traditionally computed and reported as the water-equivalent dose (Dw), MC dose algorithms calculate and report dose to medium (Dm). In order to compare consistently both methods, the conversion of MC Dm into Dw is therefore necessary.This study aims to assess the effect of applying the conversion of MC-based Dm distributions to Dw for prostate IMRT plans generated for 6 MV photon beams. MC phantoms were created from the patient CT images using three different ramps to convert CT numbers into material and mass density: a conventional four material ramp (CTCREATE) and two simplified CT conversion ramps: (1) air and water with variable densities and (2) air and water with unit density. MC simulations were performed using the BEAMnrc code for the treatment head simulation and the DOSXYZnrc code for the patient dose calculation. The conversion of Dm to Dw by scaling with the stopping power ratios of water to medium was also performed in a post-MC calculation process.The comparison of MC dose distributions calculated in conventional and simplified (water with variable densities) phantoms showed that the effect of material composition on dose-volume histograms (DVH) was less than 1% for soft tissue and about 2.5% near and inside bone structures. The effect of material density on DVH was less than 1% for all tissues through the comparison of MC distributions performed in the two simplified phantoms considering water. Additionally, MC dose distributions were compared with the predictions from an Eclipse treatment planning system (TPS), which employed a pencil beam convolution (PBC) algorithm with Modified Batho Power Law heterogeneity correction. Eclipse PBC and MC calculations (conventional and simplified phantoms) agreed well (<1%) for soft tissues. For femoral heads, differences up to 3% were observed between the DVH for Eclipse PBC and MC calculated in conventional phantoms. The use of the CT conversion ramp of water with variable densities for MC simulations showed no dose discrepancies (0.5%) with the PBC algorithm. Moreover, converting Dm to Dw using mass stopping power ratios resulted in a significant shift (up to 6%) in the DVH for the femoral heads compared to the Eclipse PBC one.Our results show that, for prostate IMRT plans delivered with 6 MV photon beams, no conversion of MC dose from medium to water using stopping power ratio is needed. In contrast, MC dose calculations using water with variable density may be a simple way to solve the problem found using the dose conversion method based on the stopping power ratio.

WE‐B‐213AB‐01: AAPM TG1S7: An Overview of Source Modeling and Beam Commissioning for Clinical Monte Carlo

The Monte Carlo method is the most accurate dose calculation method for radiotherapy treatment planning and several commercial vendors have implemented Monte Carlo dose calculation algorithms for photon and electron radiation therapy treatment planning. The AAPM task group 157 was formed to deal with the source modeling and beam commissioning issues for the clinical implementation of Monte Carlo algorithms and a report has been produced to summarize the source models used by the commercial vendors and the beam commissioning recommendations by TG 157. This is the first presentation of this educational session on the TG 157 report and related topics. A brief introduction will be given of the basics of Monte Carlo dose calculation and methods developed for source modeling and beam commissioning for clinical Monte Carlo dose calculation. This will be followed by a brief introduction to the TG157 report that will provide some background information on the two following presentations.Learning Objectives:1. Understand the basics of Monte Carlo radiation transport2. Understand the methods for Monte Carlo source modeling and beam commissioning3. Understand the goals and scope of the AAPM Task Group 157

WE‐B‐213AB‐02: AAPM TG‐157 Recommendations on Beam Commissioning for Clinical Monte Carlo Dose Calculation

Monte Carlo (MC) dose calculation algorithms are currently available for routine clinical planning in several commercial treatment planning systems. As noted in the AAPM Task Group Report No. 105 on issues associated with clinical implementation of MC dose algorithms, there are several fundamental differences between MC and other algorithms that need to be considered in the clinical commissioning process. The AAPM Task Group 157 was formed to provide comprehensive information on the factors relevant to source modeling and beam commissioning of MC dose algorithms. The TG‐157 report was charged to provide prescriptive guidelines to medical physicists as they embark on acceptance testing and clinical commissioning of these algorithms prior to clinical use. This lecture will focus specifically on the topic of beam commissioningLearning Objectives:1. Understand the basic components of the MC dose algorithm which need to be considered during clinical commissioning. Understand the beam commissioning requirements associated with different beam models.2. Understand the types of verification measurements necessary for accurate clinical commissioning of MC beam models and the criteria for acceptable agreement between calculations and measurements.3. Understand the issues associated with accurate benchmark measurements for beam modeling, especially under circumstances of charged particle disequilibrium.

OC-0466 VIRTUAL SOURCE MODELLING OF PHOTON BEAMS FOR MONTE CARLO BASED RADIATION THERAPY TREATMENT PLANNING

OC-0466 VIRTUAL SOURCE MODELLING OF PHOTON BEAMS FOR MONTE CARLO BASED RADIATION THERAPY TREATMENT PLANNING

Dosimetric Verification Using Monte Carlo Calculations for Tissue Heterogeneity-Corrected Conformal Treatment Plans Following RTOG 0813 Dosimetric Criteria for Lung Cancer Stereotactic Body Radiotherapy

The recently activated Radiation Therapy Oncology Group (RTOG) studies of stereotactic body radiation therapy (SBRT) for non-small-cell lung cancer (NSCLC) require tissue density heterogeneity correction, where the high and intermediate dose compliance criteria were established based on superposition algorithm dose calculations. The study was aimed at comparing superposition algorithm dose calculations with Monte Carlo (MC) dose calculations for SBRT for NSCLC and to evaluate whether compliance criteria need to be adjusted for MC dose calculations. Fifteen RTOG 0236 study sets were used. The planning tumor volumes (PTV) ranged from 10.7 to 117.1 cm(3). SBRT conformal treatment plans were generated using XiO (CMS Inc.) treatment planning software with superposition algorithm to meet the dosimetric high and intermediate compliance criteria recommended by the RTOG 0813 protocol. Plans were recalculated using the MC algorithm of a Monaco (CMS, Inc.) treatment planning system. Tissue density heterogeneity correction was applied in both calculations. Overall, the dosimetric quantities of the MC calculations have larger magnitudes than those of the superposition calculations. On average, R(100%) (ratio of prescription isodose volume to PTV), R(50%) (ratio of 50% prescription isodose volume to PTV), D(2 cm) (maximal dose 2 cm from PTV in any direction as a percentage of prescription dose), and V(20) (percentage of lung receiving dose equal to or larger than 20 Gy) increased by 9%, 12%, 7%, and 18%, respectively. In the superposition plans, 3 cases did not meet criteria for R(50%) or D(2 cm). In the MC-recalculated plans, 8 cases did not meet criteria for R(100%), R(50%), or D(2 cm). After reoptimization with MC calculations, 5 cases did not meet the criteria for R(50%) or D(2 cm). Results indicate that the dosimetric criteria, e.g., the criteria for R(50%) recommended by RTOG 0813 protocol, may need to be adjusted when the MC dose calculation algorithm is used.

Influence of smoothing algorithms in Monte Carlo dose calculations of cyberknife treatment plans: A lung phantom study

The Monte Carlo dose calculation algorithm yields accurate dose distributions in heterogeneous media and interfaces. The Monte Carlo calculation algorithm provided in the Multiplan Cyberknife treatment planning system (Accuray, Sunnyvale, CA, USA) has five different dose-smoothing algorithms in it. As the principle of smoothing of these algorithms is different, they can produce a disparity in the final dose distribution. The aim of the present study is to analyze the influence of these Monte Carlo smoothing algorithms in the final dose distribution of cyberknife treatment plans. An anthropomorphic lung phantom with a tumor mimicking ball target was taken for this study. The basic optimization was performed with the Ray tracing algorithm. The Monte Carlo calculations were introduced with each smoothing algorithm on the basic plan and the plans were compared. The Monte Carlo doses were found to be lesser than the Ray tracing doses. The dose conformity index was above 4 for all the smoothing algorithms, while it was only 1.19 for Ray tracing. The least coverage of 6.34 was obtained for a weighted average algorithm. The deviation between the V100% values of different smoothing algorithms was higher than the deviation in V80%. The deviations between the smoothing algorithms are higher in the high-dose regions, including the prescribing isodose, than the low-dose regions of the target, as well as in the organs at risk (OAR).

Ray-Trace is Inferior to Monte Carlo Dose Calculation Algorithm for Intracranial Robotic Radiosurgical Treatment: A Comparative Dosimetry Study

Ray trace (effective path length method; EPL) is inferior to the Monte Carlo (MC) dose calculation algorithm when treating tumors at tissue interfaces of varying densities, such as lung tumors. We hypothesized that the anatomic complexity of the skull base would introduce similar uncertainties, due to the multiple tissue interfaces in this location (e.g. bone, brain, and air). We set out to determine whether differences between the EPL and the MC dose calculations were more pronounced for lesions of the skull base when compared to those within the substance of the brain and what dosimetric and anatomic characteristics influence these differences.

Validation of an electron Monte Carlo dose calculation algorithm in the presence of heterogeneities using EGSnrc and radiochromic film measurements

The purpose of this study is to validate Eclipse's electron Monte Carlo algorithm (eMC) in heterogeneous phantoms using radiochromic films and EGSnrc as a reference Monte Carlo algorithm. Four heterogeneous phantoms are used in this study. Radiochromic films are inserted in these phantoms, including in heterogeneous media, and the measured relative dose distributions are compared to eMC calculations. Phantoms A, B, and C contain 1D heterogeneities, built with layers of lung‐ (phantom A) and bone‐ (phantoms B and C) equivalent materials sandwiched in Plastic Water. Phantom D is a thorax‐anthropomorphic phantom with 2D lung heterogeneities. Electron beams of 6, 9, 12 and 18 MeV from a Varian Clinac 2100 are delivered to these phantoms with a 10×10 cm2 applicator. Monte Carlo simulations with an independent algorithm (EGSnrc) are also used as a reference tool for two purposes: (1) as a second validation of the eMC dose calculations, and (2) to calculate the stopping power ratio between radiochromic films and bone medium, when dose is measured inside the heterogeneity. Percent depth dose (PDD) film measurements and eMC calculations agree within 2% or 3 mm for phantom A, and within 3% or 3 mm for phantoms B and C for almost all beam energies. One exception is observed with phantom B and the 6 MeV, where measured PDDs and those calculated with eMC differ by up to 4 mm. Gamma analysis of the measured and calculated 2D dose distributions in phantom D agree with criteria of 3%, 3 mm for 9, 12, and 18 MeV beams, and criteria of 5%, 3 mm for the 6 MeV beam. Dose calculations in heterogeneous media with eMC agree within 3% or 3 mm with radiochromic film measurements. Six (6) MeV beams are not modeled as accurately as other beam energies. The eMC algorithm is suitable for clinical dose calculations involving lung and bone.PACS numbers: 87.10.Rt, 87.55.km

MO-D-BRB-07: Phantom Validation and Clinical Application of Monte Carlo for Small Field SBRT

Purpose: Small field dosimetry is challenging in homogeneous medium and extremely difficult in an inhomogeneous medium. Monte Carlo dose calculation algorithms are considered as the most accurate for treatment planning. We present our validation of the Monte Carlo algorithm in the Accuray Multiplan system using measurements in a cork phantom. We also recalculated Ray Tracing treatment plans with the Monte Carlo algorithm and compared to SBRT dose tolerance limits. Methods: In our validation measurements with a cork phantom, an Exradin A16 ion chamber was used for collimators from 60mm to 20mm on a CyberKnife, and a PTW 60012 stereotactic diode for collimators from 60mm to 5mm. A literature review of more than 500 published SBRT dose tolerance limits was partitioned into high-risk and low-risk categories. Two hundred CyberKnife treatment plans were recalculated using Monte Carlo and compared to the dose limits. The DVH Evaluator software tool was used to generate DVH Risk Maps for 25 critical structures throughout the body, which superimpose a) published dose tolerance limits b) unified high-risk and low-risk trends and c) published adverse event doses, onto Monte Carlo patient doses to assess risk of adverse events. Results: The Monte Carlo calculations matched the Exradin A16 measurements to within 2.5% for field sizes down to 20mm, and matched the PTW 60012 measurements to within 2.5% for all field sizes down to 5mm. Recalculated treatment plan data is within the expected range of published SBRT dose tolerance limits, providing optimism for clinical use. Conclusions: The Accuray MultiPlan Monte Carlo algorithm is accurate even for small fields in heterogeneous media. The range of doses calculated by Monte Carlo for our patient data is compatible with published SBRT dose tolerance limits. SBRT dose tolerance limits should be fine-tuned by Monte Carlo dose calculations in long-term statistical followup studies. Disclosure: The first author has developed the DVH Evaluator software.

TU-C-BRB-11: A Fast and Accurate GPU Based Patient-Specific RapidArc QA Package

Purpose: The goal of this study is to develop a fast and accurate GPU‐based RapidArc QA package which consists of two dose calculation engines and 3D gamma index calculation code. Methods: The dose calculation package includes a GPU‐based Monte Carlo dose calculation algorithm, based on a dose calculation code, DPM and a GPU‐based FSPB algorithm with 3D‐ density correction. It also includes a GPU‐based gamma index calculation algorithm. To test this QA package, five treatment plans for typical tumor sites treated with RapidArc have been created and delivered to a water phantom on the RapidArc treatment unit. During the delivery, the gantry angle and leaf positions for each leaf pair were recorded at 50ms intervals in the two separate MLC Dynalog files, while the gantry angle and dose rate for each control point were recorded in the Clinac log file. With two sets of delivery log files, we generated inputs for our two GPU‐based dose calculation algorithms. The dose distribution was calculated on patient's planning CT and compared with the planning dose distribution from the treatment planning system using the GPU‐based 3D gamma index code. The computational time for each step was recorded to test the efficiency. Results: For all cases, the calculated 3D dose distributions agreed well with the TPS calculated doses. Dose calculation part can be completed within 2.5 minutes using both algorithms and dose evaluation can be finished within a few minutes. Conclusions: We have developed a fast and accurate patient‐ specific RapidArc QA package. The algorithms in this package are specifically optimized for the GPU architecture to achieve high computation efficiency. The results of patient tests suggest that the accuracy and running time of the package have met the clinical requirement for RapidArc QA. We acknowledge Varian Medical Systems, Inc. for its support.

MO‐F‐BRB‐03: A GPU‐Based Finite‐Size Pencil Beam (FSPB) Algorithm with 3D‐ Density Correction for Radiotherapy Dose Calculation

Purpose: To develop an accurate and efficient finite size pencil beam (FSPB) dose calculation engine for online adaptive radiotherapy. Methods: The new GPU‐based 3D‐density correction FSPB dose calculation engine (g‐DC‐FSPB) is built on our previously published ultrafast FSPB (g‐FSPB) computational framework. The new dose engine correctly accounts for medium heterogeneities by providing both lateral and longitudinal density corrections and its GPU implementation is designed to maximize the data‐ parallel strength of GPU and minimize the memory‐conflict issues. Results: Dosimetric evaluations of the g‐DC‐FSPB dose calculation algorithm against MCSIM Monte Carlo dose calculation algorithm are conducted on 10 IMRT treatment plans with heterogeneous treatment regions (5 head‐and‐ neck cases and 5 lung cases). For head and neck cases, when cavities exist near the target, the improvement with the 3D‐density correction is significant. However, when there are high‐density dental filling materials in beam paths, the improvement is small and the accuracy of the new algorithm is still unsatisfactory. On the other hand, significant improvement of dose calculation accuracy is observed in all lung cases. Especially when the target is in the middle of the lung, the accuracy improvement with the 3D‐density correction is dramatic. Regarding the efficiency, because of the appropriate arrangement of memory access and the usage of GPU intrinsic functions, the dose calculation with the g‐DC‐FSPB algorithm for an IMRT plan on can be accomplished well within 1 second (except for one case) a NVIDIA Tesla C1060 card. Conclusions: We have implemented a GPU‐accelerated 3D‐ density correction FSPB dose calculation engine and systematically evaluated its dosimetric accuracy and computational efficiency. Compared to the original g‐FSPB algorithm, the new g‐DC‐FSPB algorithm significantly improve accuracy with slightly scarification of the computation efficiency (about 5–15% slower in terms of the total computation time), indicating that this algorithm is more suitable for online IMRT replanning.

Influence of electron density spatial distribution and X‐ray beam quality during CT simulation on dose calculation accuracy

Impact of the various kVp settings used during computed tomography (CT) simulation that provides data for heterogeneity corrected dose distribution calculations in patients undergoing external beam radiotherapy with either high‐energy photon or electron beams have been investigated. The change of the Hounsfield Unit (HU) values due to the influence of kVp settings and geometrical distribution of various tissue substitute materials has also been studied. The impact of various kVp settings and electron density (ED) distribution on the accuracy of dose calculation in high‐energy photon beams was found to be well within 2%. In the case of dose distributions obtained with a commercially available Monte Carlo dose calculation algorithm for electron beams, differences of more than 10% were observed for different geometrical setups and kVp settings. Dose differences for the electron beams are relatively small at shallow depths but increase with depth around lower isodose values.PACS numbers: 87.57.Q‐, 87.55.D‐

IMRT for Image-Guided Single Vocal Cord Irradiation

We have been developing an image-guided single vocal cord irradiation technique to treat patients with stage T1a glottic carcinoma. In the present study, we compared the dose coverage to the affected vocal cord and the dose delivered to the organs at risk using conventional, intensity-modulated radiotherapy (IMRT) coplanar, and IMRT non-coplanar techniques. For 10 patients, conventional treatment plans using two laterally opposed wedged 6-MV photon beams were calculated in XiO (Elekta-CMS treatment planning system). An in-house IMRT/beam angle optimization algorithm was used to obtain the coplanar and non-coplanar optimized beam angles. Using these angles, the IMRT plans were generated in Monaco (IMRT treatment planning system, Elekta-CMS) with the implemented Monte Carlo dose calculation algorithm. The organs at risk included the contralateral vocal cord, arytenoids, swallowing muscles, carotid arteries, and spinal cord. The prescription dose was 66 Gy in 33 fractions. For the conventional plans and coplanar and non-coplanar IMRT plans, the population-averaged mean dose ± standard deviation to the planning target volume was 67 ± 1 Gy. The contralateral vocal cord dose was reduced from 66 ± 1 Gy in the conventional plans to 39 ± 8 Gy and 36 ± 6 Gy in the coplanar and non-coplanar IMRT plans, respectively. IMRT consistently reduced the doses to the other organs at risk. Single vocal cord irradiation with IMRT resulted in good target coverage and provided significant sparing of the critical structures. This has the potential to improve the quality-of-life outcomes after RT and maintain the same local control rates.

Dose Calculation Accuracy of the Monte Carlo Algorithm for CyberKnife Compared with Other Commercially Available Dose Calculation Algorithms

Monte Carlo dose calculation algorithms have the potential for greater accuracy than traditional model-based algorithms. This enhanced accuracy is particularly evident in regions of lateral scatter disequilibrium, which can develop during treatments incorporating small field sizes and low-density tissue. A heterogeneous slab phantom was used to evaluate the accuracy of several commercially available dose calculation algorithms, including Monte Carlo dose calculation for CyberKnife, Analytical Anisotropic Algorithm and Pencil Beam convolution for the Eclipse planning system, and convolution-superposition for the Xio planning system. The phantom accommodated slabs of varying density; comparisons between planned and measured dose distributions were accomplished with radiochromic film. The Monte Carlo algorithm provided the most accurate comparison between planned and measured dose distributions. In each phantom irradiation, the Monte Carlo predictions resulted in gamma analysis comparisons >97%, using acceptance criteria of 3% dose and 3-mm distance to agreement. In general, the gamma analysis comparisons for the other algorithms were <95%. The Monte Carlo dose calculation algorithm for CyberKnife provides more accurate dose distribution calculations in regions of lateral electron disequilibrium than commercially available model-based algorithms. This is primarily because of the ability of Monte Carlo algorithms to implicitly account for tissue heterogeneities, density scaling functions; and/or effective depth correction factors are not required.

Treatment Planning Accuracy of the CyberKnife Monte Carlo Algorithm Compared to Other Commercially Available Dose Calculation Algorithms

The purpose of this research was to evaluate the clinical implications of Monte Carlo treatment planning for CyberKnife (Accuray Inc.), and to quantitatively compare the CyberKnife Monte Carlo dose calculation algorithm with other commercially available treatment planning algorithms, including ray-tracing for CyberKnife and three algorithms from other treatment planning vendors.

Monte Carlo dose calculation improvements for low energy electron beams using eMC

The electron Monte Carlo (eMC) dose calculation algorithm in Eclipse (Varian Medical Systems) is based on the macro MC method and is able to predict dose distributions for high energy electron beams with high accuracy. However, there are limitations for low energy electron beams. This work aims to improve the accuracy of the dose calculation using eMC for 4 and 6 MeV electron beams of Varian linear accelerators. Improvements implemented into the eMC include (1) improved determination of the initial electron energy spectrum by increased resolution of mono-energetic depth dose curves used during beam configuration; (2) inclusion of all the scrapers of the applicator in the beam model; (3) reduction of the maximum size of the sphere to be selected within the macro MC transport when the energy of the incident electron is below certain thresholds. The impact of these changes in eMC is investigated by comparing calculated dose distributions for 4 and 6 MeV electron beams at source to surface distance (SSD) of 100 and 110 cm with applicators ranging from 6 × 6 to 25 × 25 cm2 of a Varian Clinac 2300C/D with the corresponding measurements. Dose differences between calculated and measured absolute depth dose curves are reduced from 6% to less than 1.5% for both energies and all applicators considered at SSD of 100 cm. Using the original eMC implementation, absolute dose profiles at depths of 1 cm, dmax and R50 in water lead to dose differences of up to 8% for applicators larger than 15 × 15 cm2 at SSD 100 cm. Those differences are now reduced to less than 2% for all dose profiles investigated when the improved version of eMC is used. At SSD of 110 cm the dose difference for the original eMC version is even more pronounced and can be larger than 10%. Those differences are reduced to within 2% or 2 mm with the improved version of eMC. In this work several enhancements were made in the eMC algorithm leading to significant improvements in the accuracy of the dose calculation for 4 and 6 MeV electron beams of Varian linear accelerators.

Poster — Thur Eve — 55: GRRCC‐Monte Carlo Treatment Planning Research Environment (MCTPRE)

The implementation of Monte Carlo dose calculation algorithms in clinical radiotherapy treatment planning systems has been anticipated for many years however, its introduction into routine clinical practice has been delayed by the extent of calculation time required. With the advent of faster computers, Monte Carlo (MC) algorithms will become a standard calculation algorithm in clinical treatment planning systems. The purpose of this work was to develop a Monte Carlo based radiotherapy treatment planning research environment (MCTPRE) that uses patient‐specific computed tomography (CT) dataset. We have developed a windows based graphical user interface (GUI) that makes it very easy to import patient specific plans from a treatment planning system in either DICOM or RTOG format to a MC treatment planning research environment and can also be used to simulate simple patient specific treatment plans. The MCTPRE uses the BEAMnrcMP Monte Carlo code, which is based on the underlying ESGnrcMP particle transport code to simulate the Varian Clinac 21EX accelerator treatment head for 6 and 15MV photons and 6–20 MeV electron beams. The DOSXYZnrc Monte Carlo code is use for patient specific phantom dose calculations. We compared dose distributions from calculations done with a TPS and with the Monte Carlo code. The GUI incorporating the Monte Carlo code is a very useful research tool for benchmarking treatment planning systems (TPS), testing technique development, and dose verification. Future development will include a direct interface to a TPS.

Poster — Thur Eve — 12: Evaluation of an Electron Monte Carlo Dose Calculation Algorithm for Treatment Planning

Purpose: To evaluate the accuracy of the electron Monte Carlo (eMC) dose calculation algorithm included in the Eclipse treatment planning system. Method and Materials: Multiple tests were planned to explore the system behaviour in configurations encountered in clinical practices. The first series of test were performed in a homogeneous water phantom. Measured and eMC calculated dose distributions were compared for different combinations of energy/applicator/depth. Three different inhomogeneous solid phantoms simulating high and low density materials were constructed to explore various heterogeneity conditions: a small air cylinder, a lung phantom and a chest wall phantom. In this work, the lung phantom, which consists of cork slabs, is described in details. In all cases, comparisons are made between measurements, carried out by means of XV‐2 films, and eMC and Pinnacle computations. Finally, the evaluation of the eMC algorithm for clinical case, a nose cancer, was conducted. Results: The eMC validation in the water phantom and in the lung phantom is shown to be accurate. The maximum observed discrepancy between measurements and eMC is only 2.5%. For the lung case, Pinnacle does not correctly model the electron scattering. The retrospective study of the clinical case, which presents scatter perturbations by air cavities, shows planar dose difference up to 20% between Pinnacle and eMC. Conclusion: eMC algorithm showed good agreements with measurements in simple homogeneous and heterogeneous phantoms. Comparatively to the electron pencil beam algorithms of Pinnacle, the eMC calculations more precisely predict large dose perturbations due to inhomogeneities.

TU-SAM-BRB-05: The Role of Monte Carlo and Other Advanced Dose Calculation Algorithms for Breast APBI

The medical physics community has been faced with a growing body of literature that is exploring the effects of shielding, tissue heterogeneities, interseed attenuation and others in brachytherapy. With new algorithms now identified as possible candidates for clinical implementation or already commercially available, the question of their role in clinical practice is important. Because of its external location and tissue composition, breast is certainly one of the most interesting organs for brachytherapy dosimetry algorithms. This portion of the SAMS session will underline the limitation of the current TG43 dose calculation standard in breast brachytherapy. The notion of scatter condition and tissues heterogeneities will be explored from literature review and with specific clinical examples. The link to basic physical quantities and processes will be made. The choice of treatment isotopes (from 103Pd to 192Ir) or energy (for eBx source) for breast APBI will be recast in the context of uncertainties in the dose calculation protocol. The possible hurdles in integrating advanced dose calculation algorithms in clinical practice will be discussed. Learning Objectives: 1. Understanding the current limitation related to breast brachytherapy dosimetry. 2. Identify situations where Monte Carlo or other advanced dose calculation algorithms could be useful. 3. Identify the underlying dosimetric impact of the choice of treatment isotope or source energy (eBx) in breast brachytherapy