Development and evaluation of a standard for absorbed dose to water from alpha-particle-emitting radionuclides

IF 2.1 3区工程技术 Q2 INSTRUMENTS & INSTRUMENTATION

Metrologia Pub Date : 2023-10-03 DOI:10.1088/1681-7575/acfb89

Ahtesham Ullah Khan, Jeff Radtke, Benjamin R. Palmer, Jennifer Hull, Keith Kunugi, Larry Albert DeWerd

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Abstract

Abstract Targeted radionuclide therapy and brachytherapy with alpha particles has gained significant clinical relevance recently. Absorbed dose traceability to a standard is currently lacking in the dosimetry chain. The short range of alpha particles in water of <100 μm complicates the absorbed dose measurements in the form of significant attenuation and perturbation effects. The aim of this work was to develop and validate a standard for absorbed dose to water from alpha-particle-emitting radionuclides. A dosimetric formalism to realize surface absorbed dose to water per unit activity using a windowless cylindrical parallel-plate ion chamber (IC) was introduced. IC-based and Monte Carlo (MC)-based correction factors were calculated for a planar circular 210 Po alpha-particle emitter. The measured absorbed dose to air was compared to the MC-calculated absorbed dose. A parallel-plate IC with a nominal 4 mm collector diameter composed of polystyrene-equivalent material was utilized as a standard. MC simulations were performed using the TOPAS MC code and finite source size, backscatter, and emission angle divergence correction factors were calculated by modeling the IC and the source. Multiple measurement trials were performed to measure ionization current at air gaps in the 0.3 mm to 0.525 mm range. The proposed dosimetric formalism was employed to calculate the surface absorbed dose to water from a point-like 210 Po source. The recombination and polarity correction factors were measured to be <0.50% when a 150 V mm −1 electric field strength was applied. The MC-calculated and measured absorbed dose to air agreed within 2.05%. The finite source size and backscatter corrections were <10% with the emission angle divergence correction being in the 93%–239% range. The surface absorbed dose to water was measured to be 2.8913 × 10 −6 Gy s −1 Bq −1 with a combined uncertainty of 4.23% at k = 1. This work demonstrated the ability of a windowless parallel-plate IC as a standard for absorbed dose from alpha-particle-emitting radionuclides.

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放射粒子的放射性核素对水的吸收剂量标准的制定和评价

摘要靶向放射性核素治疗和近距离α粒子治疗近年来在临床上具有重要意义。目前在剂量测定链中缺乏对标准的吸收剂量可追溯性。100 μm的α粒子在水中的短范围以显著的衰减和微扰效应的形式使吸收剂量测量复杂化。这项工作的目的是制定和验证α粒子释放放射性核素对水的吸收剂量标准。介绍了一种利用无窗圆柱平行板离子室(IC)实现单位活度对水表面吸收剂量的剂量学形式。计算了平面圆形210 Po粒子发射器的ic修正系数和MC修正系数。将测量的空气吸收剂量与mc计算的吸收剂量进行比较。采用聚苯乙烯等效材料组成的集电极直径为4mm的平行板集成电路作为标准。利用TOPAS MC代码进行MC模拟，通过模拟集成电路和源，计算有限源尺寸、后向散射和发射角发散校正因子。在0.3 mm ~ 0.525 mm范围内进行了多次测量试验，测量了气隙处的电离电流。采用所提出的剂量学公式计算了210 Po点状源对水的表面吸收剂量。当施加150 V mm−1的电场强度时，复合系数和极性校正系数为<0.50%。mc计算和测量的空气吸收剂量在2.05%以内一致。有限源尺寸和后向散射校正为10%，发射角发散校正为93% ~ 239%。测得表面对水的吸收剂量为2.8913 × 10−6 Gy s−1 Bq−1,k = 1时的综合不确定度为4.23%。这项工作证明了无窗平行板集成电路作为α粒子发射放射性核素吸收剂量的标准的能力。

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来源期刊

Metrologia 工程技术-物理：应用

CiteScore

2.80

自引率

25.00%

发文量

137

审稿时长

12 months

期刊介绍： Published 6 times per year, Metrologia covers the fundamentals of measurements, particularly those dealing with the seven base units of the International System of Units (metre, kilogram, second, ampere, kelvin, candela, mole) or proposals to replace them. The journal also publishes papers that contribute to the solution of difficult measurement problems and improve the accuracy of derived units and constants that are of fundamental importance to physics. In addition to regular papers, the journal publishes review articles, issues devoted to single topics of timely interest and occasional conference proceedings. Letters to the Editor and Short Communications (generally three pages or less) are also considered.