Department of Physics and Medical Physics Unit, McGill University, Montreal, QC, Canada.
Medical Physics Unit and.
Int J Radiat Oncol Biol Phys. 2023 Nov 1;117(3):763-773. doi: 10.1016/j.ijrobp.2023.04.031. Epub 2023 May 5.
The intraoperative radiotherapy in newly diagnosed glioblastoma multiforme (INTRAGO) clinical trial assesses survival in patients with glioblastoma treated with intraoperative radiation therapy (IORT) using the INTRABEAM. Treatment planning for INTRABEAM relies on vendor-provided in-water depth dose curves obtained according to the TARGeted Intraoperative radioTherapy (TARGIT) dosimetry protocol. However, recent studies have shown discrepancies between the estimated TARGIT and delivered doses. This work evaluates the effect of the choice of dosimetry formalism on organs at risk (OAR) doses.
A treatment planning framework for INTRABEAM was developed to retrospectively calculate the IORT dose in 8 INTRAGO patients. These patients received an IORT prescription dose of 20 to 30 Gy in addition to external beam radiation therapy. The IORT dose was obtained using (1) the TARGIT method; (2) the manufacturer's V4.0 method; (3) the C method, which uses an ionization chamber Monte Carlo (MC) calculated factor; (4) MC dose-to-water; and (5) MC dose-to-tissue. The IORT dose was converted to 2 Gy fractions equivalent dose.
According to the TARGIT method, the OAR dose constraints were respected in all cases. However, the other formalisms estimated a higher mean dose to OARs and revealed 1 case where the constraint for the brain stem was exceeded. The addition of the external beam radiation therapy and TARGIT IORT doses resulted in 10 cases of OARs exceeding the dose constraints. The more accurate MC calculation of dose-to-tissue led to the highest dosimetric differences, with 3, 3, 2, and 2 cases (out of 8) exceeding the dose constraint to the brain stem, optic chiasm, optic nerves, and lenses, respectively. Moreover, the mean cumulative dose to brain stem exceeded its constraint of 66 Gy with the MC dose-to-tissue method, which was not evident with the current INTRAGO clinical practice.
The current clinical approach of calculating the IORT dose with the TARGIT method may considerably underestimate doses to nearby OARs. In practice, OAR dose constraints may have been exceeded, as revealed by more accurate methods.
新诊断的多形性胶质母细胞瘤（INTRAGO）临床试验中的术中放射治疗评估了使用 INTRABEAM 接受术中放射治疗（IORT）的胶质母细胞瘤患者的生存情况。INTRABEAM 的治疗计划依赖于根据 TARGeted Intraoperative radioTherapy（TARGIT）剂量学协议提供的供应商提供的水中深度剂量曲线。然而，最近的研究表明，估计的 TARGIT 和所传递的剂量之间存在差异。这项工作评估了选择剂量学形式对危险器官（OAR）剂量的影响。
为了回顾性地计算 8 名 INTRAGO 患者的 IORT 剂量，开发了 INTRABEAM 的治疗计划框架。这些患者在接受外部束放射治疗的基础上，还接受了 20 至 30 Gy 的 IORT 处方剂量。IORT 剂量是使用（1）TARGIT 方法；（2）制造商的 V4.0 方法；（3）C 方法，该方法使用电离室蒙特卡罗（MC）计算的因子；（4）水剂量的 MC；和（5）组织剂量的 MC 来获得的。IORT 剂量被转换为 2 Gy 等效剂量。
根据 TARGIT 方法，在所有情况下均遵守了 OAR 剂量限制。但是，其他形式估计了更高的 OAR 平均剂量，并显示出 1 例脑干剂量限制被超过。添加外部束放射治疗和 TARGIT IORT 剂量导致 10 例 OAR 超过剂量限制。MC 对组织剂量的更精确计算导致了最高的剂量差异，8 例中有 3、3、2 和 2 例（分别为）超过脑干、视交叉、视神经和晶状体的剂量限制。此外，MC 组织剂量方法导致脑干的累积剂量均值超过 66 Gy 的限制，而目前的 INTRAGO 临床实践并未显示出这一点。
目前使用 TARGIT 方法计算 IORT 剂量的临床方法可能会大大低估附近 OAR 的剂量。实际上，更准确的方法揭示了 OAR 剂量限制可能已经被超过。
