Calculated Dose Distributions Research Articles

National pilot-study on verification of calculated absorbed dose distribution to be delivered in advanced radiotherapy treatment

Dosimetry audits in radiation oncology are indicated in the Council Directive 2013/59/EURATOM as one of several measures to ensure high quality of absorbed dose delivery in radiation therapy. Therefore, a national pilot-study was prepared and conducted for an on-site dosimetry audit on the 2D pre-treatment verification methodology. The aim was to explore the possibility of introducing such audits at the national level and examine the feasibility of extending such a concept.The main activities performed were developing and verifying methodology to be applied elsewhere, assembling a survey related to the application of advanced radiotherapy techniques, point and 2D absorbed dose measurements, and acquiring data for on-site and off-site data validation. The measurements of 2D absorbed dose distributions of different complexities were performed using local and auditor's (reference) equipment. The beam output, dose linearity, and field output factors were determined using a reference set of equipment only.Eight high-energy photon beams were evaluated. The participating centres fulfilled the recommended criterion of ±2% for beam output. Seven beams fulfilled the dose linearity criterion. Comparison of field output factors exhibited out-of-tolerance discrepancies only for the smallest field size of 2 × 2 cm2.For the evaluation of 2D absorbed dose distributions, the results obtained with local equipment showed that all absorbed dose distributions had gamma (γ) passing rate ≥95% for the 3%/2 mm tolerance criterion. However, the γ passing rates obtained with the reference equipment were lower for most verified beams. Some of the analysed absorbed dose distributions did not fulfil the recommended γ passing rate acceptance criterion. γ passing rates have shown a statistically significant difference for 3%/2 mm and 2%/2 mm criteria with p = 0.0117 and p = 0.0212, respectively, comparing the results obtained by reference and local equipment.External audits related to the 2D dosimetrical pre-treatment verification of calculated dose distributions provide the advantage of being independent of the equipment and methodology used locally. Such audits can be a valuable tool for the evaluation and improvement of local practices in the application of advanced radiotherapy techniques.

PUFFIn – A user friendly fast interface for calculating and visualizing the dose distribution in materials

This article describes a new graphical user interface that uses the PENELOPE Monte Carlo code to calculate dose distributions in materials. It is named PUFFIn, for the Penelope User-Friendly Fast Interface and was developed as an educational and scoping analysis tool for non-experts in radiation modeling. PUFFIn enables the user to visualize and compare the dose distributions in objects (e.g., sterilized healthcare products) irradiated with cobalt-60 gamma-rays, electron beam (E-beam) or X-rays. From such comparisons, the user can determine the most efficient product and/or packaging designs for any given radiation field – whether for conceptual or existing products and packaging.PUFFIn is distributed in a complete, self-contained package of software, including the PENELOPE radiation transport code, a standard graphics package, and a set of simple exercises. The package is available to any user at no cost and requires a minimal amount of training compared to other similar software. PUFFIn's capabilities are described, as well as validation measurements performed at Texas A&M University E-beam facility and the Aerial E-beam Facility in France.

Carbon-Iodine Polydiacetylene Nanofibers for Image-Guided Radiotherapy and Tumor-Microenvironment-Enhanced Radiosensitization.

Radiotherapy is a mainstay treatment used in clinics for locoregional therapy, although it still represents a great challenge to improve the sensitivity and accuracy of radiotherapy for tumors. Here, we report the conjugated polymer, polydiiododiacetylene (PIDA), with an iodine content of 84 wt %, as a highly effective computed tomography (CT) contrast agent and tumor microenvironment-responsive radiosensitizer. PIDA exhibited several key properties that contribute to the improvement of precision radiotherapy. The integrated PIDA nanofibers confined within the tumor envelope demonstrated amplified CT intensity and prolonged retention, providing an accurate calculation of dose distribution and precise radiation delivery for CT image-guided radiotherapy. Therefore, our strategy pioneers PIDA nanofibers as a bridge to cleverly connect a fiducial marker to guide accurate radiotherapy and a radiosensitizer to improve tumor sensitivity, thereby minimizing potential damage to surrounding tissues and facilitating on-demand therapeutic intervention in tumors.

Multi-institutional investigation into the robustness of intra-cranial multi-target stereotactic radiosurgery plans to delivery errors.

The use of modulated techniques for intra-cranial stereotactic radiosurgery (SRS) results in highly modulated fields with small apertures, which may be susceptible to uncertainties in the delivery device. This study aimed to quantify the impact of simulated delivery errors on treatment plan dosimetry and how this is affected by treatment planning system (TPS), plan geometry, delivery technique, and plan complexity. A beam modelling error was also included as context to the dose uncertainties due to treatment delivery errors. Delivery errors were assessed for multiple-target brain SRS plans obtained through the Trans-Tasman Radiation Oncology Group (TROG) international treatment planning challenge (2018). The challenge dataset consisted of five intra-cranial targets, each with a prescription of 20Gy. Of the final dataset of 54 plans, 51 were created using the volumetric modulated arc therapy (VMAT) technique and three used intensity modulated arc therapy (IMRT). Thirty-five plans were from the Varian Eclipse TPS, 17 from Elekta Monaco TPS, and one plan each from RayStation and Philips Pinnacle TPS. The errors introduced included: monitor unit calibration errors, multi-leaf collimator (MLC) bank offset, single MLC leaf offset, couch rotations, and collimator rotations. Dosimetric leaf gap (DLG) error was also included as a beam modelling error. Dose to targets was assessed via dose covering 98% of planning target volume (PTV) (D98%), dose covering 2% of PTV (D2%), and dose covering 99% of gross tumor volume (GTV) (D99%). Dose to organs at risk (OARs) was assessed using the volume of normal brain receiving 12Gy (V12Gy), mean dose to normal brain, and maximum dose covering 0.03cc brainstem (D0.03cc). Plan complexity was also assessed via edge metric, modulation complexity score (MCS), mean MLC gap, mean MLC speed, and plan modulation (PM). PTV D98% showed high robustness on average to most errors with the exception of a bank shift of 1.0mm and large rotational errors ≥1.0° for either the couch or collimator. However, in some cases, errors close to or within generally accepted machine tolerances resulted in clinically relevant impacts. The greatest impact upon normal brain V12Gy, mean dose to normal brain, and D0.03cc brainstem was found for DLG error in alignment with other recent studies. All delivery errors had on average a minimal impact across these parameters. Comparing plans from the Monaco TPS and the Eclipse TPS, showed a lesser increase to V12Gy, mean dose to normal brain, and D0.03cc brainstem for Monaco plans (p<0.01) when DLG error was simulated. Monaco plans also correlated to lower plan complexity. Using Spearman's correlation coefficient (r) a strong negative correlation (r≤-0.8) was found between the mean MLC gap and dose to OARs for DLG errors. Reducing MLC complexity and using larger mean MLC gaps is recommended to improve plan robustness and reduce sensitivity to delivery and modelling errors. For cases in which the calculated dose distribution or dose indices are close to the clinically acceptable limits, this is especially important.

Evaluation of a novel CBCT conversion method implemented in a treatment planning system

BackgroundTo evaluate a novel CBCT conversion algorithm for dose calculation implemented in a research version of a treatment planning system (TPS).MethodsThe algorithm was implemented in a research version of RayStation (v. 11B-DTK, RaySearch, Stockholm, Sweden). CBCTs acquired for each ten head and neck (HN), gynecology (GYN) and lung cancer (LNG) patients were collected and converted using the new algorithm (CBCTc). A bulk density overriding technique implemented in the same version of the TPS was used for comparison (CBCTb). A deformed CT (dCT) was created by using deformable image registration of the planning CT (pCT) to the CBCT to reduce anatomical changes. All treatment plans were recalculated on the pCT, dCT, CBCTc and the CBCTb. The resulting dose distributions were analyzed using the MICE toolkit (NONPIMedical AB Sweden, Umeå) with local gamma analysis, with 1% dose difference and 1 mm distance to agreement criteria. A Wilcoxon paired rank sum test was applied to test the differences in gamma pass rates (GPRs). A p value smaller than 0.05 considered statistically significant.ResultsThe GPRs for the CBCTb method were systematically lower compared to the CBCTc method. Using the 10% dose threshold and the dCT as reference the median GPRs were for the CBCTc method were 100% and 99.8% for the HN and GYN cases, respectively. Compared to that the GPRs of the CBCTb method were lower with values of 99.8% and 98.0%, for the HN and GYN cases, respectively. The GPRs of the LNG cases were 99.9% and 97.5% for the CBCTc and CBCTb method, respectively. These differences were statistically significant. The main differences between the dose calculated on the CBCTs and the pCTs were found in regions near air/tissue interfaces, which are also subject to anatomical variations.ConclusionThe dose distribution calculated using the new CBCTc method showed excellent agreement with the dose calculated using dCT and pCT and was superior to the CBCTb method. The main reasons for deviations of the calculated dose distribution were caused by anatomical variations between the pCT and the corrected CBCT.

First clinical application of image-guided intraoperative electron radiation therapy with real time intraoperative dose calculation in recurrent rectal cancer: technical procedure

Intraoperative radiation therapy (IORT) is a radiation technique applying a single fraction with a high dose during surgery. We report the first abdomino-pelvic application of an image-guided intraoperative electron radiation therapy with intraoperative real time dose calculation based on the individual intraoperative patient anatomy. A patient suffering from locoregionally recurrent rectal cancer after treatment with neoadjuvant re-chemoradiation was chosen for this approach. After surgical removal of the recurrence, an adequate IORT applicator was placed as usual. A novel mobile imaging device (ImagingRing, MedPhoton) was positioned around the patient covering the region to be treated with the IORT-applicator in place. It allowed the acquisition of three-dimensional intraoperative cone-beam computed tomography images suitable for dose calculation using an automated scaling (heuristic object and head scatter as well as hardening corrections) of Hounsfield units. After image acquisition confirmed the correct applicator position, the images were transferred to our treatment planning system for intraoperative dose calculation. Treatment could be accomplished using the calculated dose distribution. We herein describe the details of the procedure including necessary adjustments in the typically used IORT equipment and work flow. We further discuss the pros and cons of this new approach generally overcoming a decade long limitation of IORT procedures as well as future perspectives regarding IORT treatments.

Evolution of 3D X-Ray Dose Computation Algorithms

Radiation treatment planning of individual cancer patients relies on the accurate computation of dose distributions in irradiated tissue. Inaccurate dose maps have the potential to mislead clinical decision-making and compromise the balance between effective tumour control and side effects in surrounding normal tissue. In the context of this conference, 3D dosimetry is important for the experimental validation of computed dose distributions. Dose computation methods for external beams of high energy x rays have evolved over the past decade with computer simulation models more closely aligned with the fundamental physics of x-ray scattering and absorption in heterogeneous tissue. In this article, we first present a historical review from a Canadian perspective, followed by an introductory intuitive description of contemporary algorithms used in clinical treatment planning: (1) Convolution-superposition algorithm fundamentally based on the Green’s function method; (2) Stochastic Monte Carlo simulation of x-ray interactions in tissue, and (3) Deterministic numerical solution of a system of Boltzmann transport equations. In principle, all these methods solve the same problem of predicting x-ray scattering and absorption in heterogeneous tissue. However, the mathematical tools differ in their approach and approximations to achieve sufficient speed for routine clinical application. In the conclusion of this article, the evolution of 3D x-ray dose computation is summarized, in terms of accuracy and computational speed.

Delivery time reduction for mixed photon-electron radiotherapy by using photon MLC collimated electron arcs

Objective. Electron arcs in mixed-beam radiotherapy (Arc-MBRT) consisting of intensity-modulated electron arcs with dynamic gantry rotation potentially reduce the delivery time compared to mixed-beam radiotherapy containing electron beams with static gantry angle (Static-MBRT). This study aims to develop and investigate a treatment planning process (TPP) for photon multileaf collimator (pMLC) based Arc-MBRT. Approach. An existing TPP for Static-MBRT plans is extended to integrate electron arcs with a dynamic gantry rotation and intensity modulation using a sliding window technique. The TPP consists of a manual setup of electron arcs, and either static photon beams or photon arcs, shortening of the source-to-surface distance for the electron arcs, initial intensity modulation optimization, selection of a user-defined number of electron beam energies based on dose contribution to the target volume and finally, simultaneous photon and electron intensity modulation optimization followed by full Monte Carlo dose calculation. Arc-MBRT plans, Static-MBRT plans, and photon-only plans were created and compared for four breast cases. Dosimetric validation of two Arc-MBRT plans was performed using film measurements. Main results. The generated Arc-MBRT plans are dosimetrically similar to the Static-MBRT plans while outperforming the photon-only plans. The mean heart dose is reduced by 32% on average in the MBRT plans compared to the photon-only plans. The estimated delivery times of the Arc-MBRT plans are similar to the photon-only plans but less than half the time of the Static-MBRT plans. Measured and calculated dose distributions agree with a gamma passing rate of over 98% (3% global, 2 mm) for both delivered Arc-MBRT plans. Significance. A TPP for Arc-MBRT is successfully developed and Arc-MBRT plans showed the potential to improve the dosimetric plan quality similar as Static-MBRT while maintaining short delivery times of photon-only treatments. This further facilitates integration of pMLC-based MBRT into clinical practice.

Implementation of geant4 application for tomography emission Monte Carlo Code in the calculation of dose distribution in external radiation therapy

Implementation of geant4 application for tomography emission Monte Carlo Code in the calculation of dose distribution in external radiation therapy

Deep learning-based fluorescence image correction for high spatial resolution precise dosimetry

Objective. While radiation-excited fluorescence imaging has great potential to measure absolute 2D dose distributions with high spatial resolution, the fluorescence images are contaminated by noise or artifacts due to Cherenkov light, scattered light or background noise. This study developed a novel deep learning-based model to correct the fluorescence images for accurate dosimetric application. Approach. 181 single-aperture static photon beams were delivered to an acrylic tank containing quinine hemisulfate water solution. The emitted radiation-exited optical signals were detected by a complementary metal-oxide semiconductor camera to acquire fluorescence images with 0.3 × 0.3 mm2 pixel size. 2D labels of projected dose distributions were obtained by applying forward projection calculation of the 3D dose distributions calculated by a clinical treatment planning system. To calibrate the projected dose distributions for Cherenkov angular dependency, a novel empirical Cherenkov emission calibration method was performed. Total 400-epoch supervised learning was applied to a convolutional neural network (CNN) model to predict the projected dose distributions from fluorescence images, gantry, and collimator angles. Accuracy of the calculated projected dose distributions was evaluated with that of uncorrected or conventional methods by using a few quantitative evaluation metrics. Main results. The projected dose distributions corrected by the empirical Cherenkov emission calibration represented more accurate noise-free images than the uncalibrated distributions. The proposed CNN model provided accurate projected dose distributions. The mean absolute error of the projected dose distributions was improved from 2.02 to 0.766 mm·Gy by the CNN model correction. Moreover, the CNN correction provided higher gamma index passing rates for three different threshold criteria than the conventional methods. Significance. The deep learning-based method improves the accuracy of dose distribution measurements. This technique will also be applied to optical signal denoising or Cherenkov light discrimination in other imaging modalities. This method will provide an accurate dose verification tool with high spatial resolution.

Monte Carlo investigation of dose distribution of uniformly and non-uniformly loaded standard and notched eye plaques.

To investigate the effect of using non-uniform loading and notched plaques on dose distribution for eye plaques. Using EGSnrc Monte Carlo (MC) simulations, we investigate eye plaque dose distributions in water and in an anatomically representative eye phantom. Simulations were performed in accordance with TG43 formalism and compared against full MC simulations which account for inter-seed and inhomogeneity effects. For standard plaque configurations, uniformly and non-uniformly loaded plaque dose distributions in water showed virtually no difference between each other. For standard plaque, the MC calculated dose distribution in planes parallel to the plaque is narrower than the TG43 calculation due to attenuation at the periphery of the plaque by the modulay. MC calculated the dose behind the plaque is fully attenuated. Similar results were found for the notched plaque, with asymmetric attenuation along the plane of the notch. Cumulative dose volume histograms showed significant reductions in the calculated MC doses for both tumor and eye structures, compared to TG43 calculations. The effect was most pronounced for the notch plaque where the MC dose to the optic nerve was greatly attenuated by the modulay surrounding the optic nerve compared to the TG43. Thus, a reduction of optic nerve D95% from 14 to 0.2Gy was observed, when comparing the TG43 calculation to the MC result. The tumor D95% reduced from 89.2 to 79.95Gy for TG43 and MC calculations, respectively. TG43 calculations overestimate the absolute dose and the lateral dose distribution of both standard and notched eye plaques, leading to the dose overestimation for the target and organs at risk. The dose matching along the central axis for the non-uniformly loaded plaques to that of uniformly loaded ones was found to be sufficient for providing comparable coverage and can be clinically used in eye-cancer-busy centers.

HU-based material conversion for BNCT accurate dose estimation

NeuMANTA is a new generation boron neutron capture therapy (BNCT)-specific treatment planning system developed by the Neuboron Medical Group and upgraded to an important feature, a Hounsfield unit (HU)-based material conversion algorithm. The range of HU values was refined to 96 specific groups and established corresponding to tissue information. The elemental compositions and mass densities have an important effect on the calculated dose distribution. The region of interest defined in the treatment plan can be converted into multiple material compositions based on HU values or assigned specified single material composition in NeuMANTA. Different material compositions may cause normal tissue maximum dose rates to differ by more than 10% in biologically equivalent doses and to differ by up to 6% in physically absorbed doses. Although the tumor has a lower proportion of BNCT background dose, the material composition difference may affect the minimum dose of biologically equivalent dose and physically absorbed dose by more than 3%. In addition, the difference in material composition could lead to a change in neutron moderation as well as scattering. Therefore, the material composition has a significant impact on the assessment of normal tissue side effects and tumor control probability. It is essential for accurate dose estimation in BNCT.

Evaluation of intensity-modulated electron FLASH radiotherapy in a clinical setting using veterinary cases.

The increased normal tissue tolerance for FLASH radiotherapy (FLASH-RT), as compared to conventional radiotherapy, was first observed in ultra-high dose rate electron beams. Initial clinical trials in companion animals have revealed a high risk of developing osteoradionecrosis following high-dose single-fraction electron FLASH-RT, which may be related to inhomogeneities in the dose distribution. In the current study, we aim to evaluate the possibilities of intensity-modulated electron FLASH-RT in a clinical setting to ensure a homogeneous dose distribution in future veterinary and human clinical trials. Our beam model in the treatment planning system electronRT (.decimal, LLC, Sanford, FL, USA) was based on a 10-MeV electron beam from a clinical linear accelerator used to treat veterinary patients with FLASH-RT in a clinical setting. In electronRT, the beam can be intensity-modulated using tungsten island blocks in the electron block cutout, and range-modulated using a customized bolus with variable thickness. Modulations were first validated in a heterogeneous phantom by comparing measured and calculated dose distributions. To evaluate the impact of intensity modulation in superficial single-fraction FLASH-RT, a treatment planning study was conducted, including eight canine cancer patient cases with simulated tumors in the head-and-neck region. For each case, treatment plans with and without intensity modulation were created for a uniform bolus and a range-modulating bolus. Treatment plans were evaluated using a target dose homogeneity index (HI), a conformity index (CI), the near-maximum dose outside the target ( ), and the near-minimum dose to the target ( ). By adding intensity modulation to plans with a uniform bolus, the HI could be improved (p=0.017). The combination of a range-modulating bolus and intensity modulation provided a further significant improvement of the HI as compared to using intensity modulation in combination with a uniform bolus (p=0.036). The range-modulating bolus also improved the CI compared to using a uniform bolus, both with an open beam (p=0.046) and with intensity modulation (p=0.018), as well as increased the (p=0.036 with open beam and p=0.05 with intensity modulation) and reduced the median (not significant). By using intensity-modulated electron FLASH-RT in combination with range-modulating bolus, the target dose homogeneity and conformity in canine patients with simulated tumors in complex areas in the head-and-neck region could be improved. By utilizing this technique, we hope to decrease the dose outside the target volume and avoid hot spots in future clinical electron FLASH-RT studies, thereby reducing the risk of radiation-induced toxicity.

Using PRIMO to determine the initial beam parameters of Elekta Synergy linac for electron beam energies of 6, 9, 12, and 15 MeV.

The purpose of this research was to establish the primary electron beam characteristics for an Elekta Synergy linear accelerator. In this task, we take advantage of the PRIMO Monte Carlo software, where the model developed contains the majority of the component materials of the Linac. For all energies, the Elekta Linac electron mode and 14 × 14 cm2 applicator were chosen. To obtain percentage depth dose (PDD) curves, a homogeneous water phantom was voxelized in a 1 × 1 × 0.1 cm3 grid along the central axis. At the reference depth, the dose profile was recorded in 0.1 × 1 × 1 cm3 voxels. Iterative changes were made to the initial beams mean energy and full width at half maximum (FWHM) of energy in order to keep the conformity of the simulated and measured dose curves within. To confirm simulation results, the Gamma analysis was performed with acceptance criteria of 2 mm - 2%. From the validated calculation, the parameters of the PDD and profile curve (R100, R50, Rp, and field size) were collected. Initial mean energies of 7.3, 9.85, 12.9, and 15.7 MeV were obtained for nominal energies of 6, 9, 12, and 15, respectively. The PRIMO Monte Carlo model for Elekta Synergy was precisely validated. PRIMO is an easy-to-use software program that can calculate dose distribution in water phantoms.

Small field output correction factors at 18MV.

The response of various detectors in the radiotherapy energy range has been investigated, especially for 6 and 10MV energies for small fields, and is summarized in TRS-483. However, data for accelerator energies above 10MV are sparse or unavailable for many detectors, especially for the energy of 18MV. Small variations in field output factors for the commissioning of a treatment planning system can have a high impact on calculation of dosedistributions. Many studies describe an energy dependence of the response for a large number of detectors. We wanted to close the gap for the 18MV energy regime and determined field output correction factors for different detectors at18MV. An ELEKTA Versa HD accelerator at 18MV was used together with a PTW MP3 water phantom at an SSD of 90cm. The following detectors were examined: PTW Semiflex 31021, PinPoint 3D 31022, diode 60012, diode 60008 and microDiamond 60019, Sun Nuclear EDGE detector, IBA PFD, SFD, Razor Chamber, Razor Nano Chamber and Razor Diode, Standard Imaging Scintillator Exradin W2 1x3, W2 1x1 and Gafchromic EBT3 film. The dose response was determined at a depth of 10cm for square fields between 0.5 and 10cm side length. As reference data a composure of radiochromic film data for small fields ( cm) and data of all compatible chambers for larger fields ( cm) was used. The effective field sizes of small fields were determined from profiles obtained on radiochromic film. The obtained field output correction factors obey the rules of the TRS-483protocol. The W2 1x1 scintillator and the Razor Chamber showed the smallest deviations from the reference curve. The shielded diodes (diode 60008, EDGE detector) showed the highest over-response at small fields, followed by PFD, microDiamond and the unshielded diodes (diode 60012, SFD). The ionization chambers exhibited the well-known volume effect, that is, strong under-response at small fields of up to 9% for the PinPoint 3D, 7% for the Razor Chamber and up to 30% for the Semiflex detector for the smallest studied field size. The small chambers showed a polarity effect in axial orientation, especially the Razor Nano Chamber. Corrections at 18 MV are generally larger than those provided by TRS-483, continuing the trend of increasing corrections between 6 and 10 MV also at a higher accelerator energy. Only the PinPoint 3D Chamber showed a slightly smallercorrection. Field output correction factors were determined for square field sizes between 0.5 and 10cm at 18MV. Most detectors needed a larger correction than at 6 and 10MV. Thus, the use of correction factors will improve beam data for18MV.

Optimal values of the Electron Monte Carlo dose engine parameters.

The aim of this study was to indicate the most favorable - in terms of to the time of calculation and the uncertainty of determining the dose distribution - values of the parameters for the Electron Monte Carlo (eMC) algorithm in the Eclipse treatment planning system. Using the eMC algorithm and the variability of the values of its individual parameters, calculations of the electron dose distribution in the full-scattering virtual water phantom were performed, obtaining percentage depth doses, beam profiles, absolute dose values in points and calculation times. The reference data included water tank measurements such as relative dose distributions and absolute point doses. For 63 sets of calculation data created from selected values of the parameters for the eMC algorithm, calculation times were analyzed and the absolute calculated and measured doses were compared. Performing a statistical analysis made it possible to determine whether the differences in the values of deviations between the actual dose and the calculated dose in individual regions of the percentage depth dose curve and the beam profile are statistically significant between the analyzed sets of parameters. Taking into account obtained results from the analysis of the discrepancy between the distribution of the calculated and measured dose, the correspondence of the absolute value of the calculated and measured dose and the duration of the calculation of the dose distribution, the optimal set of parameters was indicated for the eMC algorithm which allows obtaining the dose distribution and the number of monitor units in an acceptable time.

Introduction to the Monte Carlo dose engine COMPASS for BNCT.

The Monte Carlo method is the most commonly used dose calculation method in the field of boron neutron capture therapy (BNCT). General-purpose Monte Carlo (MC) code (e.g., MCNP) has been used in most treatment planning systems (TPS) to calculate dose distribution, which takes overmuch time in radiotherapy planning. Based on this, we developed COMPASS (COMpact PArticle Simulation System), an MC engine specifically for BNCT dose calculation. Several optimization algorithms are used in COMPASS to make it faster than general-purpose MC code. The parallel computation of COMPASS is performed by the message passing interface (MPI) library and OpenMP commands, which allows the user to increase computational speed by increasing the computer configurations. The physical dose of each voxel is calculated for developing a treatment plan. Comparison results show that the computed dose distribution of COMPASS is in good agreement with MCNP, and the computational efficiency is better than MCNP. These results validate that COMPASS has better performance than MCNP in BNCT dose calculation.

Commissioning of Elekta Infinity™ 6 MV flattening filter-free using Monte Carlo simulation

Commissioning a simulation model of the linear accelerator (Linac) in radiotherapy needs to be done to validate the dose distribution accuracy. For this purpose, the Monte Carlo simulation method is commonly employed, and it involves using the EGSnrc software. This software consists of BEAMnrc for modeling Linac and DOSXYZnrc for calculating dose distribution in a water phantom. This study used Monte Carlo simulation to commission the Linac Flattening Filter-Free (FFF) Elekta Infinity™ 6 MV photon mode. The commissioning results show that the simulated dose distribution satisfied the acceptance criteria of simulation results using initial electron energy of 6.9 MeV at 5 × 5, 10 × 10, and 20 × 20 cm2 field sizes with average local difference of percent depth dose (PDD) of about 2.99%. The dose and dmax increasedwith higher initial electron energy increased, while percentage depth dose (PDD) decreased at smaller field sizes. At larger field sizes, the dose profile widened and the PDD Linac FFF decreased more significantly than PDD Linac Flattening Filter (FF). Additionally, both exhibited differences in the uniformity of dose values in the umbra area. The surface dose for a 10 × 10 cm2 field size was 25.2% and 34.4% for both 6 MV-FF and 6 MV-FFF, respectively.

Dosimetric comparison of VMAT standard optimization (SO) and multi-criteria optimization (MCO) treatment plans with standard mode delivery (STD) or sliding window (SW) for head and neck cancer.

A new development on the RayStation treatment planning system (TPS) allows a plan to be planned by imposing a constraint on the leaf sequencing: all leaves move in the same direction before moving again in the opposite direction to create a succession of sliding windows (SWs). The study aims to investigate this new leaf sequencing, coupled with standard optimization (SO) and multi-criteria optimization (MCO) and to compare it with the standard sequencing (STD). Sixty plans were replanned for 10 head and neck cancer patients (two dose levels simultaneously SIB, 56 and 70Gy in 35 fractions). All plans were compared, and a Wilcoxon signed-rank test was performed. Pre-processing QA and metrics of multileaf collimator (MLC) complexity were studied. All methodologies met the dose requirements for the planning target volumes (PTVs) and organs at risk (OARs). SO demonstrates significantly best results for homogeneity index (HI), conformity index (CI), and target coverage (TC). SO-SW gives best results for PTVs (D98% and D2% ) but the differences between techniques are less than 1%. Only the D2%,PTV-56Gy is higher with both MCO methods. MCO-STD offer the best sparing OARs (parotids, spinal cord, larynx, oral cavity). The gamma passing rates (GPRs) with 3%/3mm criteria between the measured and calculated dose distributions are higher than 95%, slightly lowest with SW. The number of monitor units (MUs) and MLC metrics are higher in SW show a higher modulation. All plans are feasible for the treatment. A clear advantage of SO-SW is that the treatment plan is more straightforward to planning by the user due to the more advanced modulation. MCO stands out for its ease of use and will allow a less experienced user to offer a better plan than in SO. In addition, MCO-STD will reduce the dose to the OARs while maintaining good TC.

PO-1815 CBCT dose distribution calculation with GATE Monte Carlo simulations for lymphoma patients

PO-1815 CBCT dose distribution calculation with GATE Monte Carlo simulations for lymphoma patients