Medical Physics Unit, McGill University, Montreal, QC, Canada.
Medical Physics Unit, McGill University, Montreal, QC, Canada.
Pract Radiat Oncol. 2021 Jan-Feb;11(1):e114-e121. doi: 10.1016/j.prro.2020.07.005. Epub 2020 Aug 11.
Intraoperative radiation therapy (IORT) using the INTRABEAM, a miniature x-ray source, has shown to be effective in treating breast cancer. However, recent investigations have suggested a significant deviation between the reported and delivered doses. In this work, the dose delivered by INTRABEAM in the TARGIT breast protocol was investigated, along with the dose from the Xoft Axxent, another source used in breast IORT.
The absorbed dose from the INTRABEAM was determined from ionization chamber measurements using: (a) the manufacturer-recommended formula (Zeiss V4.0 method), (b) a Monte Carlo calculated chamber conversion factor (C method), and (c) the formula consistent with the TARGIT breast protocol (TARGIT method). The dose from the Xoft Axxent was determined from ionization chamber measurements using the Zeiss V4.0 method and calculated using the American Association of Physicists in Medicine TG-43 formalism.
For a nominal TARGIT prescription of 20 Gy, the dose at the INTRABEAM applicator surface ranged from 25.2 to 31.7 Gy according to the C method for the largest (5 cm) and smallest (1.5 cm) diameter applicator, respectively. The Zeiss V4.0 method results were 7% to 10% lower (23.2 to 28.6 Gy). At 1 cm depth, the C and Zeiss V4.0 absorbed doses were also larger than those predicted by the TARGIT method. The dose at 1 cm depth from the Xoft Axxent for a surface dose of 20 Gy was slightly less than INTRABEAM (3%-7% compared with C method). An exception was for the 3 cm applicator, where the Xoft dose was appreciably lower (31%).
The doses delivered in the TARGIT breast protocol with INTRABEAM were significantly greater than the prescribed 20 Gy and depended on the size of spherical applicator used. Breast IORT treatments with the Xoft Axxent received less dose compared with TARGIT INTRABEAM, which could have implications for studies comparing clinical outcomes between the 2 devices.
使用微型 X 射线源 INTRABEAM 的术中放射治疗（IORT）已被证明对治疗乳腺癌有效。然而，最近的研究表明，报告剂量和实际剂量之间存在显著偏差。本研究旨在调查 TARGIT 乳房方案中 INTRABEAM 的实际剂量，以及另一种用于乳房 IORT 的 Xoft Axxent 源的剂量。
通过使用电离室测量，确定 INTRABEAM 的吸收剂量：（a）采用制造商推荐的公式（蔡司 V4.0 方法），（b）使用蒙特卡罗计算的电离室转换因子（C 方法），以及（c）符合 TARGIT 乳房方案的公式（TARGIT 方法）。通过使用蔡司 V4.0 方法，从电离室测量确定 Xoft Axxent 的剂量，并使用美国医学物理学家协会 TG-43 格式进行计算。
对于最大（5cm）和最小（1.5cm）直径的应用器，TARGIT 处方 20Gy 的名义值，根据 C 方法，INTRABEAM 应用器表面的剂量范围分别为 25.2 至 31.7Gy。蔡司 V4.0 方法的结果低 7%至 10%（23.2 至 28.6Gy）。在 1cm 深度，C 和蔡司 V4.0 吸收剂量也大于 TARGIT 方法的预测值。Xoft Axxent 在表面剂量为 20Gy 时，在 1cm 深度的剂量略低于 INTRABEAM（与 C 方法相比，为 3%-7%）。例外的是 3cm 应用器，其中 Xoft 剂量明显较低（31%）。
TARGIT 乳房方案中 INTRABEAM 实际输送的剂量明显高于规定的 20Gy，并且取决于使用的球形应用器的大小。与 TARGIT INTRABEAM 相比，Xoft Axxent 进行的乳房 IORT 治疗接收的剂量较少，这可能对比较两种设备之间临床结果的研究产生影响。
