Department of Biomedical Engineering, University of Iowa, 1402 Seamans Center for the Engineering Arts and Sciences, Iowa City, IA, 52242, USA.
Department of Radiation Oncology, University of Iowa, 200 Hawkins Drive, Iowa City, IA, 52242, USA.
Med Phys. 2020 Jun;47(5):2061-2071. doi: 10.1002/mp.14101. Epub 2020 Mar 13.
To assess the capability of an intracavitary Yb-based helical multishield rotating shield brachytherapy (RSBT) delivery system to treat cervical cancer. The proposed RSBT delivery system contains a pair of 1.25 mm thick platinum partial shields with 45° and 180° emission angles, which travel in a helical pattern within the applicator.
A helically threaded tandem applicator with a 45° tandem curvature containing a helically threaded catheter was designed. A 0.6 mm diameter Yb source with a length of 10.5 mm was simulated. A 37-patient treatment planning study, based on Monte Carlo dose calculations using MCNP5, was conducted with high-risk clinical target volumes (HR-CTVs) of 41.2-192.8 cm (average ± standard deviation of 79.9 ± 35.8 cm ). All patients were assumed to receive 25 fractions of 1.8 Gy of external beam radiation therapy (EBRT) before receiving 5 fractions of high-dose-rate brachytherapy (HDR-BT). For each patient, Ir-based intracavitary (IC) HDR-BT, Ir-based intracavitary/interstitial (IC/IS) HDR-BT using a hybrid applicator with eight IS needles, and Yb-based RSBT plans were generated.
For the IC, IC/IS, and RSBT treatment plans, 38%, 84%, and 86% of the plans, respectively, met the planning goal of an HR-CTV D (minimum dose to hottest 90%) of 85 Gy (α/β = 10 Gy). Median (25th percentile, 75th percentile) treatment times for IC, IC/IS, and RSBT were 11.71 (6.62, 15.40) min, 68.00 (45.02, 80.02) min, and 25.30 (13.87, 35.39) min, respectively. Ir activities ranging from 159.1-370 GBq (4.3-10 Ci) and Yb activities ranging from 429.2-999 GBq (11.6-27 Ci) were used, which correspond to the same clinical ranges of dose rates at 1 cm off-source-axis in water. Extra needle insertion and planning time beyond that needed for intracavitary-only approaches was accounted for in the IC/IS treatment time calculations.
Yb-based RSBT for cervical cancer met the HR-CTV D goal of 85 Gy in a greater percentage of the patients considered than IC/IS (86% vs 84%, respectively) and can reduce overall treatment time relative to IC/IS. Yb-based RSBT could be used to replace IC/IS in instances where IC/IS treatment is not available, especially in instances when HR-CTV volumes are ≥30 cm .
评估腔内 Yb 螺旋多屏蔽旋转屏蔽近距离治疗（RSBT）输送系统治疗宫颈癌的能力。所提出的 RSBT 输送系统包含一对 1.25 毫米厚的铂部分屏蔽，发射角度为 45°和 180°，它们在施源器内以螺旋模式运行。
设计了一种带有 45°串联曲率的螺旋螺纹施源器，其中包含一个螺旋螺纹导管。模拟了一个 0.6 毫米直径的 Yb 源，长度为 10.5 毫米。对 37 名患者进行了基于蒙特卡罗剂量计算的治疗计划研究，使用 MCNP5，高危临床靶区（HR-CTV）为 41.2-192.8cm（平均值±标准偏差为 79.9±35.8cm）。所有患者均假设在接受 5 次高剂量率近距离治疗（HDR-BT）之前接受 25 次 1.8Gy 的外束放射治疗（EBRT）。对于每位患者，生成了 Ir 腔内（IC）HDR-BT、使用带有 8 个 IS 针的混合施源器的 Ir 腔内/间质（IC/IS）HDR-BT 和 Yb 基于 RSBT 的计划。
对于 IC、IC/IS 和 RSBT 治疗计划，分别有 38%、84%和 86%的计划满足 HR-CTV D（最热 90%点的最小剂量）为 85Gy（α/β=10Gy）的计划目标。IC、IC/IS 和 RSBT 的中位（25 百分位数，75 百分位数）治疗时间分别为 11.71（6.62，15.40）min、68.00（45.02，80.02）min 和 25.30（13.87，35.39）min。使用的 Ir 活度范围为 159.1-370GBq（4.3-10Ci）和 Yb 活度范围为 429.2-999GBq（11.6-27Ci），这与水中源轴 1cm 处相同的剂量率临床范围相对应。在 IC/IS 治疗时间计算中考虑了超出腔内治疗方法所需的额外针插入和计划时间。
与 IC/IS 相比，Yb 基于 RSBT 治疗宫颈癌的 HR-CTV D 目标达到 85Gy 的患者比例更高（分别为 86%和 84%），并且可以相对于 IC/IS 缩短总治疗时间。在无法进行 IC/IS 治疗的情况下，Yb 基于 RSBT 可以替代 IC/IS，特别是在 HR-CTV 体积≥30cm3 的情况下。
