Comparison of planned dose distribution and time consumption between Monte Carlo and ray tracing calculation algorithm in cyberknife

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Comparison of planned dose distribution and time consumption between Monte Carlo and ray tracing calculation algorithm in cyberknife


Author: Tam, Kwok-wah
Title: Comparison of planned dose distribution and time consumption between Monte Carlo and ray tracing calculation algorithm in cyberknife
Degree: M.Sc.
Year: 2012
Subject: Radiation dosimetry.
Radiation -- Dosage.
Lungs -- Cancer -- Radiotherapy.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Health Technology and Informatics
Pages: 143 p. : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record:
Abstract: Background: Accurate dose calculation is essential to radiotherapy especially involving heterogeneous patient anatomy such as lungs, nasopharyngeal region and thoracic spine region. Monte Carlo algorithm is known as the most accurate dose algorithm to deal with heterogeneous medium. The balance between time consumption and dose accuracy related to uncertainty level is evaluated. Methods: Acceptable treatment plans of patients were generated using ray-tracing algorithm (RT) using Multiplan 4.0x in peripheral lung region (n=17), central lung region (n=16), nasopharyngeal region (n=15), thoracic spine region (n=16). The plans were further divided into small and large Planning Target Volume (PTV) group. The plans were recalculated using Monte Carlo (MC) algorithm with 4%, 2% and 1% uncertainty levels. The doses of reference points in different regions were used for preliminary investigation. The PTV coverage, conformality index (CI), homogeneity index (HI), D₂, D₉₅ and D₉₈ were collected for comparison. Besides, the Dmax, D₂, Dmean, V₂₀, V₃₀ were used for organ at risk (OARs) evaluation. The calculation time of Monte Carlo algorithm with different uncertainty levels were recorded for evaluation. The Monte Carlo 1% uncertainty level (MC1) was used as a reference for comparison among different calculation algorithms and uncertainty levels. The results were analyzed for the statistical significance.
Results: In peripheral lung region, there were 17-21% significant (p<0.05) increase in PTV reference points in RT compared with MC1. The PTV parameters showed 4% to 25% increase in MC1. MC4 and MC2 showed 12% and 5% discrepancies respectively in PTV parameters compare with MC1. In central lung region, there were significant (p<0.05) differences (5-24%) in PTV parameters between RT and MC1. The significant discrepancies of MC4 and MC2 with reference to MC1 in PTV parameters lie between 3-16% and 3% respectively. In nasopharyngeal region, the differences between RT and MC1 in PTV CI and HI were 9% and 19% respectively. In MC4 and MC2, there were significant differences of 19% and 9% respectively with reference to MC1. In thoracic spine region, there were 1% to 5% significant differences in PTV parameters in RT compared with MC1. In MC4 and MC2, the PTV coverage and HI were approximately 11% and 30% significant differences compared with MC1. The discrepancies between RT and MC1 on PTV parameters ranged from 11% to 30% with variation of PTV sizes. The average calculation time for MC4, MC2 and MC1 were 709 , 1272 and 3313 seconds. The central lung region required longest calculation time among different treatment regions. Conclusions: The ray-tracing algorithm overestimated the dose especially severe in peripheral lung. The discrepancies between MC4 and MC1 were larger than between MC2 to MC1. The larger differences were presented in small PTV group in peripheral region. The calculation time consumption was depended on the Monte Carlo uncertainty level, treatment region and closely related to the size of PTV.

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