Effect of inhomogeneity in a patient's body on the accuracy of the pencil beam algorithm in comparison to Monte Carlo

Yamashita, Takashi; Akagi, Takashi; Aso, T.; Kimura, Akinori; Sasaki, Takashi

doi:10.1088/0031-9155/57/22/7673

Cited by 37 publications

(31 citation statements)

References 37 publications

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“…The shortcoming of PB algorithms to accurately predict dose in low density media has been described previously 27 , 32 , 45 , 46 , 47 , 48 , 49 . In a recent study of 304 irradiations performed at 221 different institutions, Kry et al (49) observed an overestimate of 4.9% in PB algorithms compared to measurement in the Radiological Physics Center (RPC) thorax phantom used for RTOG credentialing; these results agree favorably with those reported here.…”

Section: Discussionsupporting

confidence: 86%

Commissioning and initial stereotactic ablative radiotherapy experience with Vero

Solberg

Medin

Ramirez

et al. 2014

J Applied Clin Med Phys

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The purpose of this study is to describe the comprehensive commissioning process and initial clinical performance of the Vero linear accelerator, a new radiotherapy device recently installed at UT Southwestern Medical Center specifically developed for delivery of image‐guided stereotactic ablative radiotherapy (SABR). The Vero system utilizes a ring gantry to integrate a beam delivery platform with image guidance systems. The ring is capable of rotating ± 60° about the vertical axis to facilitate noncoplanar beam arrangements ideal for SABR delivery. The beam delivery platform consists of a 6 MV C‐band linac with a 60 leaf MLC projecting a maximum field size of 15×15 cm2 at isocenter. The Vero planning and delivery systems support a range of treatment techniques, including fixed beam conformal, dynamic conformal arcs, fixed gantry IMRT in either SMLC (step‐and‐shoot) or DMLC (dynamic) delivery, and hybrid arcs, which combines dynamic conformal arcs and fixed beam IMRT delivery. The accelerator and treatment head are mounted on a gimbal mechanism that allows the linac and MLC to pivot in two dimensions for tumor tracking. Two orthogonal kV imaging subsystems built into the ring facilitate both stereoscopic and volumetric (CBCT) image guidance. The system is also equipped with an always‐active electronic portal imaging device (EPID). We present our commissioning process and initial clinical experience focusing on SABR applications with the Vero, including: (1) beam data acquisition; (2) dosimetric commissioning of the treatment planning system, including evaluation of a Monte Carlo algorithm in a specially‐designed anthropomorphic thorax phantom; (3) validation using the Radiological Physics Center thorax, head and neck (IMRT), and spine credentialing phantoms; (4) end‐to‐end evaluation of IGRT localization accuracy; (5) ongoing system performance, including isocenter stability; and (6) clinical SABR applications.PACS number: 87.53.Ly

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Section: Discussionsupporting

confidence: 86%

Commissioning and initial stereotactic ablative radiotherapy experience with Vero

Solberg

Medin

Ramirez

et al. 2014

J Applied Clin Med Phys

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“…Using Monte Carlo (MC) simulations in phantom geometries, Sawakuchi et al (Sawakuchi et al 2008) analyzed range degradation effects as a function of proton energy and geometric complexity. Range degradation can lead to an underestimation of the doses to critical structures distal to the target particularly in low-density regions (Yamashita et al 2012). In a review on range uncertainties, Paganetti estimated the uncertainties due to dose calculations alone to be between 2.7% (for homogeneous patient geometries such as liver fields) and 4.6% (for heterogeneous patient geometries such as head & neck fields) of the proton range when using standard analytical dose calculations.…”

Section: Introductionmentioning

confidence: 99%

Site-specific range uncertainties caused by dose calculation algorithms for proton therapy

et al. 2014

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The purpose of this study was to investigate the impact of complex patient geometries on the capability of analytical dose calculation algorithms to accurately predict the range of proton fields. Dose distributions predicted by an analytical pencil-beam algorithm were compared with those obtained using Monte Carlo simulations (TOPAS). A total of 508 passively scattered treatment fields were analyzed for 7 disease sites (liver, prostate, breast, medulloblastoma-spine, medulloblastoma-whole brain, lung and head & neck). Voxel-by-voxel comparisons were performed on two-dimensional distal dose surfaces calculated by pencil-beam and Monte Carlo algorithms to obtain the average range differences (ARD) and root mean square deviation (RMSD) for each field for the distal position of the 90% dose level (R90) and the 50% dose level (R50). The average dose degradation (ADD) of the distal falloff region, defined as the distance between the distal position of the 80% and 20% dose levels (R80-R20), was also analyzed. All ranges were calculated in water-equivalent distances. Considering total range uncertainties and uncertainties from dose calculation alone, we were able to deduce site-specific estimations. For liver, prostate and whole brain fields our results demonstrate that a reduction of currently used uncertainty margins is feasible even without introducing Monte Carlo dose calculations. We recommend range margins of 2.8% + 1.2 mm for liver and prostate treatments and 3.1% + 1.2 mm for whole brain treatments, respectively. On the other hand, current margins seem to be insufficient for some breast, lung and head & neck patients, at least if used generically. If no case specific adjustments are applied, a generic margin of 6.3% + 1.2 mm would be needed for breast, lung and head & neck treatments. We conclude that currently used generic range uncertainty margins in proton therapy should be redefined site specific and that complex geometries may require a field specific adjustment. Routine verifications of treatment plans using Monte Carlo simulations are recommended for patients with heterogeneous geometries.

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“…Overall, most parameters evaluated still passed the initial acceptance criteria, although both sets of TLD results were approximately 4% lower than the TPS predicted dose. Previous studies have found an overestimation of the predicted dose by analytical dose calculations (compared with Monte Carlo calculations) [12], particularly near heterogeneities [13,14]. The coronal plane gamma analysis did not meet the proposed criteria, and the sagittal plane gamma analysis, along with the DTA in the anterior-posterior profiles, were only marginally within the proposed passing criteria.…”

Section: Discussionmentioning

confidence: 77%

A New Anthropomorphic Pediatric Spine Phantom for Proton Therapy Clinical Trial Credentialing

Lewis

Taylor

Followill

et al. 2018

International Journal of Particle Therapy

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Purpose: To design and evaluate an anthropomorphic spine phantom for use in credentialing proton therapy facilities for clinical trial participation by the Imaging and Radiation Oncology Core Houston QA Center. Materials and Methods: A phantom was designed to perform an end-to-end audit of the proton spine treatment process, including simulation, dose calculation, and proton treatment delivery. Because plastics that simulate bone in proton beams are unknown, 11 potential materials were tested to identify suitable phantom materials. Once built, preliminary testing using passive scattering and spot scanning treatment plans (including a field junction) were created in-house and delivered 3 times to test reproducibility. The following measured attributes were compared with the calculated values: absolute dose agreement using thermoluminescent dosimeters, planar gamma agreement, distal range, junction match, and right and left profile alignment using radiochromic film. Finally, credentialing results from 10 institutions were also assessed. Results: A suitable bone substitute was identified (Techtron HPV Bearing Grade), which had a measured relative stopping power that agreed within 1.1% of its value calculated by Eclipse. In-house passive scatter testing of the phantom demonstrated that the phantom was suitable for assessing craniospinal irradiation dose delivery. However, the in-house scanning beam results were more mixed, highlighting challenges in treatment delivery. Seven of ten institutions passed the proposed criteria for this phantom, a pass rate consistent with other Imaging and Radiation Oncology phantoms. Conclusions: An anthropomorphic proton spine phantom was developed to evaluate proton therapy delivery. This phantom provides a realistic challenge for centers wishing to participate in proton clinical trials and highlights the need for caution in applying advanced treatments.

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Effect of inhomogeneity in a patient's body on the accuracy of the pencil beam algorithm in comparison to Monte Carlo

Cited by 37 publications

References 37 publications

Commissioning and initial stereotactic ablative radiotherapy experience with Vero

Commissioning and initial stereotactic ablative radiotherapy experience with Vero

Site-specific range uncertainties caused by dose calculation algorithms for proton therapy

A New Anthropomorphic Pediatric Spine Phantom for Proton Therapy Clinical Trial Credentialing

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