Candela-Juan C, Karlsson M, Lundell M, Ballester F, Tedgren Å Carlsson
Radiation Oncology Department, La Fe University and Polytechnic Hospital, Valencia 46026, Spain and Department of Atomic, Molecular and Nuclear Physics, University of Valencia, Burjassot 46100, Spain.
Division of Radiological Sciences, Department of Medical and Health Sciences, Linköping University, Linköping SE 581 85, Sweden.
Med Phys. 2015 May;42(5):2132-42. doi: 10.1118/1.4916685.
During the first part of the 20th century, (226)Ra was the most used radionuclide for brachytherapy. Retrospective accurate dosimetry, coupled with patient follow up, is important for advancing knowledge on long-term radiation effects. The purpose of this work was to dosimetrically characterize two (226)Ra sources, commonly used in Sweden during the first half of the 20th century, for retrospective dose-effect studies.
An 8 mg (226)Ra tube and a 10 mg (226)Ra needle, used at Radiumhemmet (Karolinska University Hospital, Stockholm, Sweden), from 1925 to the 1960s, were modeled in two independent Monte Carlo (MC) radiation transport codes: geant4 and mcnp5. Absorbed dose and collision kerma around the two sources were obtained, from which the TG-43 parameters were derived for the secular equilibrium state. Furthermore, results from this dosimetric formalism were compared with results from a MC simulation with a superficial mould constituted by five needles inside a glass casing, placed over a water phantom, trying to mimic a typical clinical setup. Calculated absorbed doses using the TG-43 formalism were also compared with previously reported measurements and calculations based on the Sievert integral. Finally, the dose rate at large distances from a (226)Ra point-like-source placed in the center of 1 m radius water sphere was calculated with geant4.
TG-43 parameters [including gL(r), F(r, θ), Λ, and sK] have been uploaded in spreadsheets as additional material, and the fitting parameters of a mathematical curve that provides the dose rate between 10 and 60 cm from the source have been provided. Results from TG-43 formalism are consistent within the treatment volume with those of a MC simulation of a typical clinical scenario. Comparisons with reported measurements made with thermoluminescent dosimeters show differences up to 13% along the transverse axis of the radium needle. It has been estimated that the uncertainty associated to the absorbed dose within the treatment volume is 10%-15%, whereas uncertainty of absorbed dose to distant organs is roughly 20%-25%.
The results provided here facilitate retrospective dosimetry studies of (226)Ra using modern treatment planning systems, which may be used to improve knowledge on long term radiation effects. It is surely important for the epidemiologic studies to be aware of the estimated uncertainty provided here before extracting their conclusions.
在20世纪上半叶，镭-226是近距离放射治疗中使用最广泛的放射性核素。回顾性精确剂量测定以及患者随访对于增进对长期辐射效应的了解至关重要。本研究的目的是对20世纪上半叶瑞典常用的两种镭-226源进行剂量学特征描述，用于回顾性剂量效应研究。
1925年至20世纪60年代在瑞典斯德哥尔摩卡罗林斯卡大学医院镭疗科使用的一根8毫克镭-226管和一根10毫克镭-226针，在两个独立的蒙特卡罗（MC）辐射传输代码geant4和mcnp5中进行建模。获取了这两种源周围的吸收剂量和碰撞比释动能，由此得出稳态平衡状态下的TG-43参数。此外，将这种剂量学形式的结果与在水模体上放置由五根针置于玻璃外壳内构成的浅表模具的MC模拟结果进行比较，试图模拟典型临床设置。还将使用TG-43形式计算的吸收剂量与先前基于西弗积分报告的测量值和计算值进行比较。最后，用geant4计算了置于半径1米水球中心的镭-226点状源在远距离处的剂量率。
TG-43参数[包括gL(r)、F(r,θ)、Λ和sK]已作为补充材料上传至电子表格，并提供了一条数学曲线的拟合参数，该曲线给出了距源10至60厘米之间的剂量率。TG-43形式的结果在治疗体积内与典型临床场景的MC模拟结果一致。与用热释光剂量计进行的报告测量值比较显示，沿镭针横轴的差异高达13%。据估计，治疗体积内吸收剂量的相关不确定性为10%-15%，而远处器官吸收剂量的不确定性约为20%-25%。
本文提供的结果有助于使用现代治疗计划系统对镭-226进行回顾性剂量测定研究，这可用于增进对长期辐射效应的了解。对于流行病学研究来说，在得出结论之前了解本文提供的估计不确定性肯定很重要。
