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Quantitative evaluation of dosimetric uncertainties associated with small electron fields

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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Independent dose calculations for the CORVUS MLC IMRT

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Medical Dosimetry 2001年第2期26卷 135-141页

作者： Ayyangar, Komanduri M. Nizin, Paul S. Saw, Cheng B. Gearheart, Darren Shen, Bin Enke, Charles A. Department of Radiation Oncology University of Nebraska Medical Center Omaha NE United States Department of Radiology Baylor College of Medicine Houston TX United States

Two independent dose calculation methods have been explored to validate MLC-based IMRT plans from the NOMOS CORVUS system. After the plan is generated on the CORVUS planning system, the beam parameters are imported into an independent workstation. The beam parameters consist of intensity maps at each gantry angle. In addition, CT scans of the patient are imported into the independent workstation to obtain the external contour of the patient. The coordinate system is defined relative to the alignment point chosen in the CORVUS plan. The 2 independent calculation methods are based on a pencil beam kernel convolution and a Clarkson-type differential scatter summation, respectively. The pencil beam data for a 1 × 1-cm beam, as formed by the multileaf collimator, were measured for the 6-MV photon beam from a Siemens PRIMUS linear accelerator using film dosimetry. In the pencil beam method, the dose at a point is calculated using the depth and off-axis distance from a given pencil beam, corrected for beam intensity. The scatter summation method used the conversion of measured depth dose data into scatter maximum ratios. In this method, the differential scatter from each pencil beam is corrected for the beam intensity. Isodose distributions were generated using the independent dose calculations and compared to the CORVUS plans. Although isodose distributions from both methods show good agreement with the CORVUS plan, our implementation of the differential scatter summation approach seems more favorable. The 2 independent dose calculation algorithms are described in this paper. © 2001 American Association of Medical Dosimetrists.

关键词： CORVUS system dose calculation algorithm IMRT MLC Photon beam

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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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Review of electron beam therapy physics

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PHYSICS IN MEDICINE AND BIOLOGY 2006年第13期51卷 R455-R489页

作者： Hogstrom, Kenneth R. Almond, Peter R. Louisiana State Univ Dept Phys & Astron Baton Rouge LA 70803 USA Mary Bird Perkins Canc Ctr Baton Rouge LA 70809 USA Univ Texas MD Anderson Canc Ctr Dept Radiat Phys Houston TX 77030 USA

For over 50 years, electron beams have been an important modality for providing an accurate dose of radiation to superficial cancers and disease and for limiting the dose to underlying normal tissues and structures. This review looks at many of the important contributions of physics and dosimetry to the development and utilization of electron beam therapy, including electron treatment machines, dose specification and calibration, dose measurement, electron transport calculations, treatment and treatment-planning tools, and clinical utilization, including special procedures. Also, future changes in the practice of electron therapy resulting from challenges to its utilization and from potential future technology are discussed.

关键词： dose calculation algorithm CHEST WALL IRRADIATION HIGH-ENERGY ELECTRONS MONTE-CARLO CODE PARALLEL IONIZATION CHAMBERS LITHIUM FLUORIDE doseMETERS MULTIPLE-SCATTERINGTHEORY FLUENCE CORRECTION FACTORS COMBINED-MODALITY THERAPY TREATMENT PLANNING SYSTEM

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OPTIMUM TREATMENT MODE APPLIED TO POST-OPERATIVE CERVICAL CANCER FOR 5F-IMRT PLAN BASED ON FOUR VARIABLES IN VARIAN ECLIPSE TPS

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JOURNAL OF MECHANICS IN MEDICINE AND BIOLOGY 2016年第7期16卷 1650095-1650095页

作者： Li, Jun Tang, Xiao-Bin Zhang, Xi-Zhi Gui, Long-Gang Ge, Yun Chen, Da Chai, Lei Nanjing Univ Aeronaut & Astronaut Dept Nucl Sci & Engn Nanjing 210016 Jiangsu Peoples R China Subei Peoples Hosp Jiangsu Prov Radiotherapy Ctr Yangzhou 225001 Jiangsu Peoples R China Nanjing Univ Sch Elect Sci & Engn Nanjing 210023 Jiangsu Peoples R China Jiangsu Higher Educ Inst Collaborat Innovat Ctr Radiat Med Nanjing Jiangsu Peoples R China

Purpose: This study aimed to determine the dosimetric effect on the target volume, organs at risk (OARs) and normal tissues based on the different choice for four types of mechanical variables, i.e., treatment position, dose calculation algorithm, mulitleaf collimator (MLC) motion mode and X-ray energy;and to investigate the optimum treatment mode applied to post-operative cervical cancer for 5-field intensity-modulated radiation therapy (5F-IMRT) technique. Methods: The dosimetric difference on the target volume and OARs under the influence of four types of variables were initially compared by changing one variable at a time. Then, based on the above compared results, we compared the dosimetric difference on planning target volume (PTV) and OARs between group A composed of the superior four variables and group B composed of the relatively inferior four variables. The dosimetric parameters included dose distribution of the target volume, OARs and normal tissues, conformal index (CI), homogeneity index (HI), monitor units (MU) and beam-on time (T). The independent and paired t-tests were used for statistical analysis, and the threshold for statistical significance was P <= 0.05. Results: Compared with the supine position, the maximum dose of PTV (Dmax-PTV), the maximum dose of small intestine (Dmax-small intestine) and V-50 of bladder V50-bladder) were all lower in prone position. In contrast with the pencil beam convolution (PBC), CI of PTV (CLPTV) was larger while HI of PTV (HLPTV) was lower, both V50-bladder and the maximum dose of rectum (Dmax-rectum) were lower using anisotropic analytical algorithm (AAA). Moreover, the same results were obtained using sliding window (SW) compared with multiple static segments (MSS). The mean dose of PTV (Dmean-PTV) and CLPTV was larger while the maximum dose of the spinal cord (Dmax-spinal cord), V50-bladder and the maximum dose of femoral heads were lower with 15 MV X-rays compared with 6 MV X-rays. In comparison with group B

关键词： Post-operative cervical cancer 5F-IMRT treatment position dose calculation algorithm X-ray energy

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Monte Carlo dose verification of prostate patients treated with simultaneous integrated boost intensity modulated radiation therapy

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RADIATION ONCOLOGY 2009年第2009期4卷 18-18页

作者： Dogan, Nesrin Mihaylov, Ivaylo Wu, Yan Keall, Paul J. Siebers, Jeffrey V. Hagan, Michael P. Virginia Commonwealth Univ Med Ctr Dept Radiat Oncol Richmond VA 23298 USA Univ Arkansas Med Sci Dept Radiat Oncol Little Rock AR 72205 USA Stanford Univ Ctr Canc Dept Radiat Oncol Stanford CA 94305 USA

Background: To evaluate the dosimetric differences between Superposition/Convolution (SC) and Monte Carlo (MC) calculated dose distributions for simultaneous integrated boost (SIB) prostate cancer intensity modulated radiotherapy (IMRT) compared to experimental (film) measurements and the implications for clinical treatments. Methods: Twenty-two prostate patients treated with an in-house SIB-IMRT protocol were selected. SC-based plans used for treatment were re-evaluated with EGS4-based MC calculations for treatment verification. Accuracy was evaluated with-respect-to film-based dosimetry. Comparisons used gamma (gamma)-index, distance-to-agreement (DTA), and superimposed dose distributions. The treatment plans were also compared based on dose-volume indices and 3-D gamma index for targets and critical structures. Results: Flat-phantom comparisons demonstrated that the MC algorithm predicted measurements better than the SC algorithm. The average PTVprostate D-98 agreement between SC and MC was 1.2% +/- 1.1. For rectum, the average differences in SC and MC calculated D-50 ranged from -3.6% to 3.4%. For small bowel, there were up to 30.2% +/- 40.7 (range: 0.2%, 115%) differences between SC and MC calculated average D-50 index. For femurs, the differences in average D-50 reached up to 8.6% +/- 3.6 (range: 1.2%, 14.5%). For PTVprostate and PTVnodes, the average gamma scores were >95.0%. Conclusion: MC agrees better with film measurements than SC. Although, on average, SC-calculated doses agreed with MC calculations within the targets within 2%, there were deviations up to 5% for some patient's treatment plans. For some patients, the magnitude of such deviations might decrease the intended target dose levels that are required for the treatment protocol, placing the patients in different dose levels that do not satisfy the protocol dose requirements.

关键词： Monte Carlo IMRT Plan Simultaneous Integrate Boost Energy Fluence dose calculation algorithm

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On the performances of Intensity Modulated Protons, RapidArc and Helical Tomotherapy for selected paediatric cases

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RADIATION ONCOLOGY 2009年第1期4卷 2-2页

作者： Fogliata, Antonella Yartsev, Slav Nicolini, Giorgia Clivio, Alessandro Vanetti, Eugenio Wyttenbach, Rolf Bauman, Glenn Cozzi, Luca Oncol Inst So Switzerland Med Phys Unit Bellinzona Switzerland London Hlth Sci Ctr London Reg Canc Program London ON Canada Osped Reg Bellinzona & Valli Dept Radiol Bellinzona Switzerland

Background: To evaluate the performance of three different advanced treatment techniques on a group of complex paediatric cancer cases. Methods: CT images and volumes of interest of five patients were used to design plans for Helical Tomotherapy (HT), RapidArc (RA) and Intensity Modulated Proton therapy (IMP). The tumour types were: extraosseous, intrathoracic Ewing Sarcoma;mediastinal Rhabdomyosarcoma;metastastis of base of skull with bone, para-nasal and left eye infiltration from Nephroblastoma of right kidney;metastatic Rhabdomyosarcoma of the anus;Wilm's tumour of the left kidney with multiple liver metastases. Cases were selected for their complexity regardless the treatment intent and stage. Prescribed doses ranged from 18 to 53.2 Gy, with four cases planned using a Simultaneous Integrated Boost strategy. Results were analysed in terms of dose distributions and dose volume histograms. Results: For all patients, IMP plans lead to superior sparing of organs at risk and normal healthy tissue, where in particular the integral dose is halved with respect to photon techniques. In terms of conformity and of spillage of high doses outside targets (external index (EI)), all three techniques were comparable;CI90% ranged from 1.0 to 2.3 and EI from 0 to 5%. Concerning target homogeneity, IMP showed a variance (D-5%-D-95%) measured on the inner target volume (highest dose prescription) ranging from 5.9 to 13.3%, RA from 5.3 to 11.8%, and HT from 4.0 to 12.2%. The range of minimum significant dose to the same target was: (72.2%, 89.9%) for IMP, (86.7%, 94.1%) for RA, and (79.4%, 94.8%) for HT. Similarly, for maximum significant doses: (103.8%, 109.4%) for IMP, (103.2%, 107.4%) for RA, and (102.4%, 117.2%) for HT. Treatment times (beam-on time) ranged from 123 to 129 s for RA and from 146 to 387 s for HT. Conclusion: Five complex pediatric cases were selected as representative examples to compare three advanced radiation delivery techniques. While differences were noted in

关键词： dose Distribution Helical Tomotherapy Conformity Index Simultaneous Integrate Boost dose calculation algorithm

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