串联式β发射型血管内近距离治疗源串的GAF薄膜剂量测定法。

Iftimia Ileana, Devlin Phillip M, Chin Lee M, Baron J M, Cormack R A

Department of Radiation Oncology, Brigham and Women's Hospital, Dana-Farber Cancer Institute and Children's Hospital, Harvard Medical School, 75 Francis Street, Boston, Massachusetts 02115-6110, USA.

Med Phys. 2003 Jun;30(6):1004-12. doi: 10.1118/1.1573206.

Coronary artery brachytherapy may require treatment of lesions longer than a single source length. A treatment option is tandem positioning of the single source. This study presents relative dosimetric measurements of a cardiovascular brachytherapy source and the dosimetric characteristics in the junction region of tandem treatments. Measurements were carried out using a Novoste Beta Cath 90Sr/90Y 40 mm beta source in a plastic water phantom. Radiochromic MD-55-2 film, calibrated using both 6 MV photon and 6 MeV electron beams from a linear accelerator, was used as the dosimeter. Dose distributions around a single source and in the junction region of tandem irradiation were measured. Measurements of the near field dose as close as 1.2 mm from the source are presented. Significant over- or underdoses in the junction region of tandem irradiation were quantified. At a radial distance of 2 mm from the longitudinal axis of the source, the dose value in the middle of the junction region, normalized to the dose at 2 mm midline single source, was about 182% for a 2-seed overlap and 16% for a 2-seed gap, respectively. Dose distributions in the junction region as a function of source overlap and radial distance have fairly high gradients and exhibit characteristic patterns. The fraction of prescription dose was found to have a sigmoidal dependence on overlap size, for radial distances ranging between 1.2 and 3 mm. The parameters of these sigmoids, quantified as functions of radial distance, could be used to provide quick and reasonable over/underdose estimates, given any potential overlap or gap in the junction area, with an uncertainty within 10%.

冠状动脉近距离放射治疗可能需要治疗长度超过单个放射源长度的病变。一种治疗选择是单个放射源的串联定位。本研究展示了心血管近距离放射治疗源的相对剂量测量以及串联治疗交界区域的剂量学特征。测量是在塑料水模体中使用诺沃斯特Beta Cath 90Sr/90Y 40毫米β放射源进行的。使用经直线加速器的6兆伏光子束和6兆电子伏电子束校准的放射变色MD - 55 - 2薄膜作为剂量计。测量了单个放射源周围以及串联照射交界区域的剂量分布。给出了距离放射源近至1.2毫米处的近场剂量测量结果。对串联照射交界区域的显著剂量过高或过低情况进行了量化。在距放射源纵轴2毫米的径向距离处，交界区域中部的剂量值，相对于2毫米中线单个放射源处的剂量进行归一化后，对于两颗种子源重叠的情况约为182%，对于两颗种子源有间隙的情况约为16%。交界区域的剂量分布作为源重叠和径向距离的函数具有相当高的梯度并呈现出特征模式。发现对于1.2至3毫米的径向距离范围，处方剂量分数对重叠大小呈S形依赖关系。这些S形曲线的参数，作为径向距离的函数进行量化，可用于在交界区域存在任何潜在重叠或间隙的情况下，快速且合理地估计剂量过高/过低情况，不确定性在10%以内。