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A polar-coordinate-based pencil beam algorithm for VMAT dose computation with high-resolution gantry angle sampling

MEDICAL PHYSICS 2022年第6期49卷 4026-4042页

作者： Tseng, Wenchih Yan, Guanghua Liu, Hongcheng Kahler, Darren Li, Jonathan Liu, Chihray Lu, Bo Univ Florida Dept Radiat Oncol Gainesville FL 32610 USA Univ Florida Dept Ind & Syst Engn Gainesville FL 32610 USA

Purpose Most commercially available treatment planning systems (TPSs) approximate the continuous delivery of volumetric modulated arc therapy (VMAT) plans with a series of discretized static beams for treatment planning, which can make VMAT dose computation extremely inefficient. In this study, we developed a polar-coordinate-based pencil beam (PB) algorithm for efficient VMAT dose computation with high-resolution gantry angle sampling that can improve the computational efficiency and reduce the dose discrepancy due to the angular under-sampling effect. Methods and Materials 6 MV 1x1mm(2) pencil beams were simulated on a uniform cylindrical phantom under an EGSnrc Monte Carlo (MC) environment. The MC-generated PB kernels were collected in the polar coordinate system for each bixel on a 40x40cm(2) fluence map and subsequently fitted via a series of Gaussians. The fluence was calculated using a detectors' eye view with off-axis and MLC transmission factors corrected. doses of VMAT arc on the phantom were computed by summing the convolution results between the corresponding PB kernels and fluence for each bixel in the polar coordinate system. The convolution was performed using fast Fourier transform to expedite the computing speed. The calculated doses were converted to the Cartesian coordinate system and compared with the reference dose computed by a collapsed cone convolution (CCC) algorithm of the TPS. A heterogeneous phantom was created to study the heterogeneity corrections using the proposed algorithm. Ten VMAT arcs were included to evaluate the algorithm performance. Gamma analysis and computation complexity theory were used to measure the dosimetric accuracy and computational efficiency, respectively. Results The dosimetric comparisons on the homogeneous phantom between the proposed PB algorithm and the CCC algorithm for 10 VMAT arcs demonstrate that the proposed algorithm can achieve a dosimetric accuracy comparable to that of the CCC algorithm with average g

关键词： dose calculation algorithm fast Fourier transform pencil beam model polar coordinate system VMAT

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Quantitative evaluation of dosimetric uncertainties associated with small electron fields

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JOURNAL OF MEDICAL IMAGING AND RADIATION SCIENCES 2022年第2期53卷 273-282页

作者： Ali, Imad Kendall, Ethan Alsbou, Nesreen Ahmad, Salahuddin Univ Oklahoma Dept Radiat Oncol Hlth Sci Ctr 800 NE 10th StOKCC L100 Oklahoma City OK 73104 USA Lancaster Gen Hosp Dept Radiat Oncol 2102 Harrisburg Pike Lancaster PA 17601 USA Univ Cent Oklahoma Dept Engn & Phys Howell Hall 221R100 N Univ Dr Edmond OK 73034 USA

Introduction: Although many studies have investigated small electron fields, there are several dosimetric issues that are not well understood. This includes lack of charged particle equilibrium, lateral scatter, source occlusion and volume averaging of the detectors used in the measurement of the commissioning data. High energy electron beams are also associated with bremsstrahlung production that contributes to dose deposition, which is not well investigated, particularly for small electron fields. The goal of this work has been to investigate dosimetric uncertainties associated with small electron fields using dose measurements with different detectors as well as calculations with eMC dose calculation algorithm. Methods: Different dosimetric parameters including output factors, depth dose curves and dose profiles from small electron field cutouts were investigated quantitatively. These dosimetric parameters were measured using different detectors that included small ion chambers and diodes for small electron cutouts with diameters ranging from 1550mm mounted on a 6 x 6cm(2) cone with beam energies from 620MeV. Results: Large deviations existed between the output factors calculated with the eMC algorithm and measured with small detectors for small electron fields up to 55% for 6MeV. The discrepancy between the calculated and measured doses increased 10%-55% with decreasing electron beam energy from 20 MeV to 6 MeV for 15mm circular field. For electron fields with cutouts 20mm and larger, the measured and calculated doses agreed within 5% for all electron energies from 6-20MeV. For small electron fields, the maximal depth dose shifted upstream and becomes more superficial as the electron beam energy increases from 6-20MeV as measured with small detectors. Discussion: Large dose discrepancies were found between the measured and calculated doses for small electron fields where the eMC underestimated output factors by 55% for small circular electron fields with a diame

关键词： Dosimetric uncertainties Small field electron dosimetry dose calculation algorithm Bremsstrahlung Commissioning data

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The influence of basic plan parameters on calculated small field output factors-A multicenter study

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PHYSICA MEDICA-EUROPEAN JOURNAL OF MEDICAL PHYSICS 2021年 88卷 98-103页

作者： Falco, Maria Daniela Fusella, Marco Clemente, Stefania Fiandra, Christian Gallio, Elena Garibaldi, Cristina Bagala, Paolo Borzi, Giuseppina Casale, Michelina Casati, Marta Consorti, Rita Delana, Anna Esposito, Marco Malatesta, Tiziana Menghi, Enrico Reggiori, Giacomo Russo, Serenella Stasi, Michele Mancosu, Pietro Univ G dAnnunzio SS Annunziata Hosp Dept Radiat Oncol Chieti Italy Veneto Inst Oncol IOV IRCCS Med Phys Dept Via Gattamelata 64 Padua Italy Azienda Osped Univ Federico II Unit Med Phys & Radioprotect Naples Italy Univ Turin Dept Oncol Radiat Oncol Turin Italy European Inst Oncol IRCCS Unit Radiat Res IEO Milan Italy Univ Campus Biomed Roma Via Alvaro del Portillo 200 Rome Italy REM Radioterapia Via Penninazzo 11 Viagrande CT Italy Azienda Osped Santa Maria Terni Struttura Semplice Fis Sanitaria Terni Italy Azienda Osped Univ Careggi Med Phys Unit Florence Italy S Filippo Neri Hosp Med Phys Unit ASL Roma 1 Rome Italy Osped S Chiara APSS Trento Serv Fis Sanitaria Trento Italy Azienda USL Toscana Ctr Med Phys Unit Via Antella 58 I-50012 Florence Italy Osped Fatebenefratelli S Giovanni Calibita Rome Fis Med Rome Italy Ist Romagnolo Studio Tumori Dino Amadori IRST Srl Med Phys Unit Ist Ricovero & Cura Carattere Sci Meldola FC Italy Humanitas Clin & Res Hosp Med Phys Unit Radiat Oncol Dept Rozzano Milan Italy AO Ordine Mauriziano Med Phys Dept Turin Italy

Purpose: The influence of basic plan parameters such as slice thickness, grid resolution, algorithm type and field size on calculated small field output factors (OFs) was evaluated in a multicentric study. Methods and materials: Three computational homogeneous water phantoms with slice thicknesses (ST) 1, 2 and 3 mm were shared among twenty-one centers to calculate OFs for 1x1, 2x2 and 3x3 cm2 field sizes (FSs) (normalized to 10x10 cm2 FS), with their own treatment planning system (TPS) and the energy clinically used for stereotactic body radiation therapy delivery. OFs were calculated for each combination of grid resolution (GR) (1, 2 and 3 mm) and ST and finally compared with the OFs measured for the TPS commissioning. A multivariate analysis was performed to test the effect of basic plan parameters on calculated OFs. Results: A total of 509 data points were collected. Calculated OFs are slightly higher than measured ones. The multivariate analysis showed that Center, GR, algorithm type, and FS are predictive variables of the difference between calculated and measured OFs (p < 0.001). As FS decreases, the spread in the difference between calculated and measured OFs became larger when increasing the GR. Monte Carlo and Analytical Anisotropic algorithms, presented a dependence on GR (p < 0.01), while Collapsed Cone Convolution and Acuros did not. The effect of the ST was found to be negligible. Conclusions: Modern TPSs slightly overestimate the calculated small field OFs compared with measured ones. Grid resolution, algorithm, center number and field size influence the calculation of small field OFs.

关键词： TPS commissioning Output factors Grid resolution Slice thickness dose calculation algorithm

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Impact of TPS calculation algorithms on dose delivered to the patient in proton therapy treatments

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PHYSICS IN MEDICINE AND BIOLOGY 2019年第7期64卷 075016-075016页

作者： Molinelli, Silvia Russo, Stefania Magro, Giuseppe Maestri, Davide Mairani, Andrea Mastella, Edoardo Mirandola, Alfredo Vai, Alessandro Vischioni, Barbara Valvo, Francesca Ciocca, Mario Fdn CNAO Str Campeggi 53 I-27100 Pavia Italy Univ Milan I-20133 Milan Italy Heidelberg Ion Beam Therapy Ctr Neuenheimer Feld 450 D-69120 Heidelberg Germany

To estimate the impact of dose calculation approaches adopted in different treatment planning systems (TPSs) on proton therapy dose delivered with pencil beam scanning (PBS). Treatment plans for six regular volumes in water and 15 clinical cases were optimized with Syngo-VC13 and exported for forward recalculation with Raystation-V7.0 pencil beam (RS-PBA) and Monte Carlo (RS-MC) algorithms and with the independent Fluka-MC engine. To verify clinical consistency between the two TPS dosimetric outcomes, the average percentage variations of clinical target volume (CTV) D-98%, D(50)(% )and D-2(%), adopted for plan prescription and evaluation, were considered. Ionization chamber measurements served as a further reference for comparison in homogeneous conditions. CTV dose volume histogram (DVH) analysis and gamma evaluation with 3 mm-3% agreement criteria quantified the dose deviation of TPS calculation algorithms, in heterogeneous conditions, against the Fluka-MC code. CTV D-50%, representing the plan dose prescription goal, was higher on average over H&N cases of (3.9 +/- 0.9)% and (2.3 +/- 0.6)% as calculated with RS-PBA and RS-MC, respectively, compared to Syngo. For tumors located in the pelvis district, average D-50% variations of (1.6 +/- 0.7)% and (1.2 +/- 0.7)% were found. Syngo underestimated target near maximum doses with respect to all computation systems. calculation accuracy in heterogeneous conditions of RS-PBA H&N plans resulted poor when a range shifter was required. Target DVH and gamma-analysis showed excellent agreement between RS-MC and Fluka-MC, with gamma-pass rates >98% for all patient groups. Different TPS dose calculation approaches mainly affected dose delivered in H&N proton treatments, while minor deviations were found for pelvic tumors. RS-MC proved to be the most accurate TPS dose calculation algorithm when compared to an independent MC simulation code.

关键词： proton therapy dose calculation algorithm treatment planning

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Monte Carlo dose verification for a single-isocenter VMAT plan in multiple brain metastases

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Medical Dosimetry 2019年第4期44卷 e51-e58页

作者： Hoshida, Kento Araki, Fujio Ohno, Takeshi Tominaga, Hirofumi Komatsu, Kazuki Tamura, Kentaro Graduate School of Health Sciences Kumamoto University Kumamoto 862-0976 Japan Department of Health Sciences Faculty of Life Sciences Kumamoto University Kumamoto 862-0976 Japan Varian Medical Systems Tokyo 103-0026 Japan Ion Beam Therapy Center SAGA HIMAT Foundation Tosu 841-0033 Saga Japan

The purpose of this study was to verify the accuracy of dose calculation algorithms of a treatment planning system for a single-isocenter volumetric modulated arc therapy (VMAT) plan in multiple brain metastases, by comparing the dose distributions of treatment planning system with those of Monte Carlo (MC) simulations. We used a multitarget phantom containing 9 acrylic balls with a diameter of 15.9 mm inside a Lucy phantom measuring 17 × 17 × 17 cm³. Seven VMAT plans were created using the multitarget phantom: 1 multitarget plan (MTP) and 6 single target plans (STP). Three of the STP plans had a large jaw field setting, almost equivalent to that of the MTP, while the other plans had a jaw field setting fitted to each planning target volume. The isocenter for all VMAT plans was set to the center of the phantom. The VMAT dose distributions were calculated using the analytical anisotropic algorithm (AAA) and were also recalculated through Acuros XB (AXB) and MC simulations under the same irradiation conditions. The AAA and AXB methods tended to overestimate dosage compared with the MC method in the MTP and in STPs with large jaw field settings. The dose distribution in single-isocenter VMAT plans for multiple brain metastases was influenced by jaw field settings. Finally, we concluded that MC-VMAT dose calculations are useful for 3D dose verification of single-isocenter VMAT plans for multiple brain metastases. © 2019 American Association of Medical Dosimetrists

关键词： dose calculation algorithm Monte Carlo method Multiple brain metastases Three-dimensional gamma analysis Volumetric modulated arc therapy

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Verification of Acuros XB dose algorithm using 3D printed low-density phantoms for clinical photon beams

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JOURNAL OF APPLIED CLINICAL MEDICAL PHYSICS 2018年第3期19卷 32-43页

作者： Zavan, Rodolfo McGeachy, Philip Madamesila, Joseph Villarreal-Barajas, Jose-Eduardo Khan, Rao Tom Baker Canc Clin Dept Med Phys Calgary AB Canada Washington Univ Sch Med Dept Radiat Oncol St Louis MO USA

The transport-based dose calculation algorithm Acuros XB (AXB) has been shown to accurately account for heterogeneities primarily through comparisons with Monte Carlo simulations. This study aims to provide additional experimental verification of AXB for clinically relevant flattened and unflattened beam energies in low density phantoms of the same material. Polystyrene slabs were created using a bench-top 3D printer. Six slabs were printed at varying densities from 0.23 to 0.68 g/cm(3), corresponding to different density humanoid tissues. The slabs were used to form different single and multilayer geometries. dose was calculated with Eclipse AXB 11.0.31 for 6MV, 15MV flattened and 6FFF (flattening filter free) energies for field sizes of 2 x 2 and 5 x 5 cm(2). EBT3 film was inserted into the phantoms, which were irradiated. Absolute dose profiles and 2D Gamma analyses were performed for 96 dose planes. For all single slab configurations and energies, absolute dose differences between the AXB calculation and film measurements remained <3% for both fields in the high-dose region, however, larger disagreement was seen within the penumbra. For the multilayered phantom, percentage depth dose with AXB was within 5% of discrete film measurements. The Gamma index at 2%/2 mm averaged 98% in all combinations of fields, phantoms and photon energies. The transport-based dose algorithm AXB is in good agreement with the experimental measurements for small field sizes using 6MV, 6FFF and 15MV beams adjacent to various low-density heterogeneous media. This work provides preliminary experimental grounds to support the use of AXB for heterogeneous dose calculation purposes.

关键词： 3D Printing Acuros XB dose calculation algorithm experimental verification radiochromic film

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A novel lateral disequilibrium inclusive, (LDI) pencil-beam based dose calculation algorithm: Evaluation in inhomogeneous phantoms and comparison with Monte Carlo calculations

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MEDICAL PHYSICS 2011年第3期38卷 1627-1634页

作者： Wertz, Hansjoerg Jahnke, Lennart Schneider, Frank Polednik, Martin Fleckenstein, Jens Lohr, Frank Wenz, Frederik Heidelberg Univ Mannheim Med Ctr Dept Radiat Oncol D-68167 Mannheim Germany

Purpose: Pencil-beam (PB) based dose calculation for treatment planning is limited by inaccuracies in regions of tissue inhomogeneities, particularly in situations with lateral electron disequilibrium as is present at tissue/lung interfaces. To overcome these limitations, a new "lateral disequilibrium inclusive" (LDI) PB based calculation algorithm was introduced. In this study, the authors evaluated the accuracy of the new model by film and ionization chamber measurements and Monte Carlo simulations. Methods: To validate the performance of the new LDI algorithm implemented in Corvus 09 (R), eight test plans were generated on inhomogeneous thorax and pelvis phantoms. In addition, three plans were calculated with a simple effective path length (EPL) algorithm on the inhomogeneous thorax phantom. To simulate homogeneous tissues, four test plans were evaluated in homogeneous phantoms (homogeneous dose calculation). Results: The mean pixel pass rates and standard deviations of the gamma 4%/4 mm test for the film measurements were (96 +/- 3)% for the plans calculated with LDI, (70 +/- 5)% for the plans calculated with EPL, and (99 +/- 1)% for the homogeneous plans. Ionization chamber measurements and Monte Carlo simulations confirmed the high accuracy of the new algorithm (dose deviations <= 4%;gamma 3%/3 mm >= 96%) Conclusions: LDI represents an accurate and fast dose calculation algorithm for treatment planning. (C) 2011 American Association of Physicists in Medicine. [DOI: 10.1118/1.3557952]

关键词： dose calculation algorithm lateral electronic disequilibrium heterogeneity correction pencil beam dose verification

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A depth dose study between AAA and AXB algorithm against Monte Carlo simulation using AIP CT of a 4D dataset from a moving phantom

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REPORTS OF PRACTICAL ONCOLOGY AND RADIOTHERAPY 2018年第5期23卷 413-424页

作者： Soh, Roger Cai Xiang Tay, Guan Heng Law, Wen Siang Lee, James Cheow Lei Natl Univ Canc Inst Dept Radiat Oncol Singapore Singapore Nanyang Technol Univ Div Phys & Appl Phys Singapore Singapore Natl Canc Ctr Div Radiat Oncol Singapore Singapore

Aim: To identifying depth dose differences between the two versions of the algorithms using AIP CT of a 4D dataset. Background: Motion due to respiration may challenge dose prediction of dose calculation algorithms during treatment planning. Materials and methods: The two versions of depth dose calculation algorithms, namely, Anisotropic Analytical algorithm (AAA) version 10.0 (AAAv10.0), AAA version 13.6 (AAAv13.6) and Acuros XB dose calculation (AXB) algorithm version 10.0 (AXBv10.0), AXB version 13.6 (AXBv13.6), were compared against a full MC simulated 6X photon beam using QUASAR respiratory motion phantom with a moving chest wall. To simulate the moving chest wall, a 4 cm thick wax mould was attached to the lung insert of the phantom. Depth doses along the central axis were compared in the anterior and lateral beam direction for field sizes 2 x 2 cm(2), 4 x 4 cm(2) and 10 x 10 cm(2). Results: For the lateral beam direction, the moving chest wall highlighted differences of up to 105% for AAAv10.0 and 40% for AXBv10.0 from MC calculations in the surface and buildup doses. AAAv13.6 and AXBv13.6 agrees with MC predictions to within 10% at similar depth. For anterior beam doses, dose differences predicted for both versions of AAA and AXB algorithm were within 7% and results were consistent with static heterogeneous studies. Conclusions: The presence of the moving chest wall was capable of identifying depth dose differences between the two versions of the algorithms. These differences could not be identified in the static chest wall as shown in the anterior beam depth dose calculations. (C) 2018 Greater Poland Cancer Centre. Published by Elsevier Sp. z o.o. All rights reserved.

关键词： dose calculation algorithm AXB AAA Monte Carlo

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Assessment of leakage dose in vivo in patients undergoing radiotherapy for breast cancer

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PHYSICS & IMAGING IN RADIATION ONCOLOGY 2018年 5卷 97-101页

作者： Lonski, Peta Kron, Tomas Taylor, Michael Phipps, Alicia Franich, Rick Chua, Boon Peter MacCallum Canc Ctr Melbourne Dept Phys Sci Melbourne Vic Australia RMIT Univ Coll Sci Engn & Hlth Sch Sci Melbourne Vic Australia Peter MacCallum Canc Ctr Radiat Therapy Serv Melbourne Vic Australia Prince Wales Hosp Nelune Comprehens Canc Ctr Randwick NSW Australia Univ New South Wales Fac Med UNSW Sydney Sydney NSW Australia

Background and purpose: Accurate quantification of the relatively small radiation doses delivered to untargeted regions during breast irradiation in patients with breast cancer is of increasing clinical interest for the purpose of estimating long-term radiation-related risks. Out-of-field dose calculations from commercial planning systems however may be inaccurate which can impact estimates for long-term risks associated with treatment. This work compares calculated and measured dose out-of-field and explores the application of a correction for leakage radiation. Materials and methods: dose calculations of a Boltzmann transport equation solver, pencil beam-type, and superposition-type algorithms from a commercial treatment planning system (TPS) were compared with in vivo thermoluminescent dosimetry (TLD) measurements conducted out-of-field on the contralateral chest at points corresponding to the thyroid, axilla and contralateral breast of eleven patients undergoing tangential beam radiotherapy for breast cancer. Results: Overall, the TPS was found to under-estimate doses at points distal to the radiation field edge with a modern linear Boltzmann transport equation solver providing the best estimates. Application of an additive correction for leakage (0.04% of central axis dose) improved correlation between the measured and calculated doses at points greater than 15 cm from the field edge. Conclusions: Application of a correction for leakage doses within peripheral regions is feasible and could improve accuracy of TPS in estimating out-of-field doses in breast radiotherapy.

关键词： Breast radiotherapy TLD Leakage dose dose calculation algorithm

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Dosimetric evaluation of Acuros XB Advanced dose calculation algorithm in heterogeneous media

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RADIATION ONCOLOGY 2011年第2011期6卷 82-82页

作者： Fogliata, Antonella Nicolini, Giorgia Clivio, Alessandro Vanetti, Eugenio Cozzi, Luca Oncol Inst So Switzerland Med Phys Unit Bellinzona Switzerland

Background: A study was realised to evaluate and determine relative figures of merit of a new algorithm for photon dose calculation when applied to inhomogeneous media. Methods: The new Acuros XB algorithm implemented in the Varian Eclipse treatment planning system was compared against a Monte Carlo method (VMC++), and the Analytical Anisotropic algorithm (AAA). The study was carried out in virtual phantoms characterized by simple geometrical structures. An insert of different material and density was included in a phantom built of skeletal-muscle and HU = 0 (setting "A"): Normal Lung (lung, 0.198 g/cm(3));Light Lung (lung, 0.035 g/cm(3));Bone (bone, 1.798 g/cm(3));another phantom (setting "B") was built of adipose material and including thin layers of bone (1.85 g/cm(3)), adipose (0.92 g/cm(3)), cartilage (1.4745 g/cm(3)), air (0.0012 g/cm(3)). Investigations were performed for 6 and 15 MV photon beams, and for a large (13 x 13 cm(2)) and a small (2.8 x 13 cm(2)) field. Results: Results are provided in terms of depth dose curves, transverse profiles and Gamma analysis (3 mm/3% and 2 mm/2% distance to agreement/dose difference criteria) in planes parallel to the beam central axis;Monte Carlo simulations were assumed as reference. Acuros XB gave an average gamma agreement, with a 3 mm/3% criteria, of 100%, 86% and 100% for Normal Lung, Light Lung and Bone settings, respectively, and dose to medium calculations. The same figures were 86%, 11% and 100% for AAA, where only dose rescaled to water calculations are possible. Conclusions: In conclusion, Acuros XB algorithm provides a valid and accurate alternative to Monte Carlo calculations for heterogeneity management.

关键词： dose calculation algorithm Acuros AAA VMC plus inhomogeneity

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