Monte Carlo simulated correction factors for high dose rate brachytherapy postal dosimetry audit methodology

IF 3.4 Q2 ONCOLOGY
Krzysztof Chelminski , Alexis Dimitriadis , Roua Abdulrahim , Pavel Kazantsev , Evelyn Granizo-Roman , Jonathan Kalinowski , Shirin Abbasi Enger , Godfrey Azangwe , Mauro Carrara , Jamema Swamidas
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Abstract

Background and Purpose

Full-scatter conditions in water are impractical for postal dosimetry audits in brachytherapy. This work presents a method to obtain correction factors that account for deviations from full-scatter water-equivalent conditions for a small plastic phantom.

Material and Methods

A 16 × 8 × 3 cm phantom (PMMA) with a radiophotoluminescent dosimeter (RPLD) at the centre and two catheters on either side was simulated using Monte Carlo (MC) to calculate correction factors accounting for the lack of scatter, non-water equivalence of the RPLD and phantom, source model and backscatter for HDR 60Co and 192Ir sources.

Results

The correction factors for non-water equivalence, lack of full scatter, and the use of PMMA were 1.062 ± 0.013, 1.059 ± 0.008 and 0.993 ± 0.009 for 192Ir and 1.129 ± 0.005, 1.009 ± 0.005 and 1.005 ± 0.005 for 60Co respectively. Water-equivalent backscatter thickness of 5 cm was found to be adequate and increasing thickness of backscatter did not have an influence on the RPLD dose. The mean photon energy in the RPLD for four HDR 192Ir sources was 279 ± 2 keV in full scatter conditions and 295 ± 1 keV in the audit conditions. For 60Co source the corresponding mean energies were 989 ± 1 keV and 1022 ± 1 keV respectively.

Conclusions

Correction factors were obtained through the MC simulations for conditions deviating from TG-43, including the amount of back scatter, and the optimum audit set up. Additionally, the influence of different source models on the correction factors was negligible and demonstrates their generic applicability.
蒙特卡罗模拟高剂量率近距离放射邮政剂量测定审计方法的校正系数
背景和目的水中的全散射条件对于近距离放射治疗中的邮政剂量测定审核来说是不切实际的。材料和方法使用蒙特卡洛(Monte Carlo,MC)模拟了一个 16 × 8 × 3 厘米的模型(PMMA),模型中心有一个放射性光致发光剂量计(RPLD),两侧有两根导管,计算出校正系数,校正系数考虑了散射不足、RPLD 和模型的非水等效性、放射源模型以及 HDR 60Co 和 192Ir 放射源的反向散射。结果对于 192Ir 和 60Co,非水等效、缺乏完全散射和使用 PMMA 的校正系数分别为 1.062 ± 0.013、1.059 ± 0.008 和 0.993 ± 0.009,对于 192Ir 和 60Co,分别为 1.129 ± 0.005、1.009 ± 0.005 和 1.005 ± 0.005。研究发现,5 厘米的水等效后向散射厚度是足够的,增加后向散射厚度对 RPLD 剂量没有影响。在全散射条件下,4 个 HDR 192Ir 源在 RPLD 中的平均光子能量为 279 ± 2 keV,在审计条件下为 295 ± 1 keV。对于 60Co 光源,相应的平均能量分别为 989 ± 1 keV 和 1022 ± 1 keV。结论通过 MC 模拟获得了偏离 TG-43 条件的校正因子,包括后向散射量和最佳审核设置。此外,不同源模型对校正因子的影响可以忽略不计,这也证明了校正因子的通用性。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Physics and Imaging in Radiation Oncology
Physics and Imaging in Radiation Oncology Physics and Astronomy-Radiation
CiteScore
5.30
自引率
18.90%
发文量
93
审稿时长
6 weeks
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