Department of Radiation Oncology, Allegheny General Hospital, Pittsburgh, PA 15212-4772 , USA.
J Appl Clin Med Phys. 2010 Jun 10;11(3):3228. doi: 10.1120/jacmp.v11i3.3228.
The objective of this work is to evaluate the interfractional biological effective dose (BED) variation in MammoSite high dose rate (HDR) brachytherapy. Dose distributions of 19 patients who received 34 Gy in 10 fractions were evaluated. A method was employed to account for nonuniform dose distribution in the BED calculation. Furthermore, a range of alpha/beta values was utilized for specific clinical end points: fibrosis, telangiectasia, erythema, desquamation and breast carcinoma. Two scenarios were simulated to calculate the BED value using: i) the same dose distribution of fraction 1 over fractions 2-10 (constant case, CC), and ii) the actual delivered dose distribution for each fraction 1-10 (interfractiondose variation case, IVC). Although the average BED difference (IVC - CC) was < 0.7 Gy for all clinical endpoints, the range of difference for fibrosis and telangiectasia reached -11% to +3% and -9% to +9% for one of the patients, respectively. By disregarding high inhomogeneity in HDR brachytherapy, the conventional BED calculation tends to overestimate the BED for fibrosis by 16% on average, while it underestimates the BED for erythema (7.6%) and desquamation (10.2%). In conclusion, the BED calculation accounting for the nonuniform dose distribution provides a more clinically relevant description of the clinical delivered dose. Though the average BED difference was clinically insignificant, the maximum difference of BED for late effects can differ by a single fractional dose (10%) for a specific patient due to the interfraction dose variation in MammoSite treatment.
本研究旨在评估 MammoSite 高剂量率（HDR）近距离放疗中分次间生物学有效剂量（BED）的变化。评估了 19 名接受 34 Gy/10 分次的患者的剂量分布。采用一种方法来计算 BED 时考虑非均匀剂量分布。此外，还针对纤维化、毛细血管扩张、红斑、脱屑和乳腺癌等特定临床终点，使用一系列α/β值。模拟了两种情况来计算 BED 值：i）将第 1 分次的剂量分布应用于第 2-10 分次（恒定情况，CC），和 ii）为每个第 1-10 分次实际应用的剂量分布（分次间剂量变化情况，IVC）。尽管对于所有临床终点，平均 BED 差值（IVC-CC）<0.7 Gy，但对于其中一名患者，纤维化和毛细血管扩张的差值范围分别达到-11%至+3%和-9%至+9%。由于忽略了 HDR 近距离放疗中的高不均匀性，常规 BED 计算往往会高估纤维化的 BED 约 16%，而低估红斑（7.6%）和脱屑（10.2%）的 BED。总之，考虑非均匀剂量分布的 BED 计算为临床所给予的剂量提供了更具临床相关性的描述。尽管平均 BED 差值在临床上无意义，但由于 MammoSite 治疗中的分次间剂量变化，对于特定患者，晚期效应的最大 BED 差值可能会相差单个分次剂量（10%）。
