Department of Electrical and Computer Engineering, University of Iowa, 4016 Seamans Center, Iowa City, Iowa 52242.
Med Phys. 2013 Dec;40(12):121703. doi: 10.1118/1.4828778.
To present dynamic rotating shield brachytherapy (D-RSBT), a novel form of high-dose-rate brachytherapy (HDR-BT) with electronic brachytherapy source, where the radiation shield is capable of changing emission angles during the radiation delivery process.
A D-RSBT system uses two layers of independently rotating tungsten alloy shields, each with a 180° azimuthal emission angle. The D-RSBT planning is separated into two stages: anchor plan optimization and optimal sequencing. In the anchor plan optimization, anchor plans are generated by maximizing the D90 for the high-risk clinical-tumor-volume (HR-CTV) assuming a fixed azimuthal emission angle of 11.25°. In the optimal sequencing, treatment plans that most closely approximate the anchor plans under the delivery-time constraint will be efficiently computed. Treatment plans for five cervical cancer patients were generated for D-RSBT, single-shield RSBT (S-RSBT), and (192)Ir-based intracavitary brachytherapy with supplementary interstitial brachytherapy (IS + ICBT) assuming five treatment fractions. External beam radiotherapy doses of 45 Gy in 25 fractions of 1.8 Gy each were accounted for. The high-risk clinical target volume (HR-CTV) doses were escalated such that the D2cc of the rectum, sigmoid colon, or bladder reached its tolerance equivalent dose in 2 Gy fractions (EQD2 with α∕β = 3 Gy) of 75 Gy, 75 Gy, or 90 Gy, respectively.
For the patients considered, IS + ICBT had an average total dwell time of 5.7 minutes∕fraction (min∕fx) assuming a 10 Ci(192)Ir source, and the average HR-CTV D90 was 78.9 Gy. In order to match the HR-CTV D90 of IS + ICBT, D-RSBT required an average of 10.1 min∕fx more delivery time, and S-RSBT required 6.7 min∕fx more. If an additional 20 min∕fx of delivery time is allowed beyond that of the IS + ICBT case, D-RSBT and S-RSBT increased the HR-CTV D90 above IS + ICBT by an average of 16.3 Gy and 9.1 Gy, respectively.
For cervical cancer patients, D-RSBT can boost HR-CTV D90 over IS + ICBT and S-RSBT without violating the tolerance doses to the bladder, rectum, or sigmoid. The D90 improvements from D-RSBT depend on the patient, the delivery time budget, and the applicator structure.
介绍动态旋转屏蔽近距离放疗（D-RSBT），这是一种新型的电子近距离放疗（HDR-BT），辐射屏蔽在放疗过程中能够改变发射角度。
D-RSBT 系统使用两层独立旋转的钨合金屏蔽层，每个屏蔽层的方位角发射角度为 180°。D-RSBT 计划分为两个阶段：锚定计划优化和最佳排序。在锚定计划优化中，通过最大化高风险临床肿瘤体积（HR-CTV）的 D90 来生成锚定计划，假设固定的方位角发射角度为 11.25°。在最佳排序中，将在规定的治疗时间内最接近锚定计划的治疗计划进行高效计算。为 5 名宫颈癌患者生成了 D-RSBT、单屏蔽 RSBT（S-RSBT）和（192）Ir 腔内近距离放疗联合补充间质近距离放疗（IS + ICBT）的治疗计划，假设治疗分为 5 个部分。考虑到外部束放疗剂量为 45 Gy，25 次分割，每次分割 1.8 Gy。将高危临床靶区（HR-CTV）剂量升高，使得直肠、乙状结肠或膀胱的 D2cc 达到其耐受等效剂量 2 Gy 剂量（α∕β=3 Gy 的 EQD2）75 Gy、75 Gy 或 90 Gy。
对于所考虑的患者，假设 10 Ci（192）Ir 源，IS + ICBT 的平均总驻留时间为 5.7 分钟/分次（min∕fx），平均 HR-CTV D90 为 78.9 Gy。为了匹配 IS + ICBT 的 HR-CTV D90，D-RSBT 需要平均增加 10.1 min∕fx 的治疗时间，而 S-RSBT 需要增加 6.7 min∕fx。如果允许 IS + ICBT 病例的治疗时间再增加 20 min∕fx，D-RSBT 和 S-RSBT 可将 HR-CTV D90 分别提高 16.3 Gy 和 9.1 Gy，高于 IS + ICBT。
对于宫颈癌患者，D-RSBT 可以在不超过膀胱、直肠或乙状结肠耐受剂量的情况下提高 HR-CTV D90，优于 IS + ICBT 和 S-RSBT。D-RSBT 的 D90 改善取决于患者、治疗时间预算和施源器结构。
