Dahn Margaret L, MacDonald R Lee, Cherpak Amanda, Allen Stefan, Dahn Hannah M
Dalhousie University Faculty of Medicine, Canada.
Department of Medical Physics, Canada.
Clin Transl Radiat Oncol. 2025 Jun 9;54:100992. doi: 10.1016/j.ctro.2025.100992. eCollection 2025 Sep.
Online adaptive radiation (ART) is a novel treatment approach that allows for a new daily treatment plan based on cone beam CT (CBCT) imaging. This daily adaptation facilitates precise tumor and organ-at-risk (OAR) localization and minimizes the impact of interfractional motion, allowing for planning target volume (PTV) margin reduction. Isotropic PTV margins for localized non-stereotactic adaptive prostate radiation performed on an ETHOS linear accelerator with HyperSight have been reduced from standard 7 mm to 5 mm. This study assesses the impact of margin reduction by evaluating the dose metrics of patient reference plans, as well as daily treated plans, for 7 mm vs 5 mm PTV margins.
Patients with prostate cancer receiving moderately hypofractionated adaptive radiation were initially treated with a 7 mm PTV margin (n = 10). This retrospective study generated 5 mm PTV margin treatment plans (n = 10) for these patients for comparison. In addition, a full adaptive 20 fraction treatment course was simulated with margin reduction to identify differences not recognized with reference plan comparison alone.
Bladder V40.8 and V48.6 but not V60 were significantly reduced in 5 mm treatment plans compared to 7 mm treatment plans. However, when daily treated plan data was examined bladder V60 was lower for the 5 mm PTV case. Similarly, rectum doses V24.6-V57 but not V60 were significantly reduced in 5 mm PTV margin treatment plans. Further differences were identified when looking at the daily treated plan data as opposed to simply comparing reference plans.
In the era of online ART, with significant data available, such as daily treated plan dosimetry, analysis of reference plans alone may not be sufficient. PTV margin reduction, made possible due to the use of online ART, reduced the volume of bladder and rectum receiving <60 Gy, which may reduce toxicity and secondary malignancy risk.
在线自适应放疗（ART）是一种新型治疗方法，可根据锥形束CT（CBCT）成像制定新的每日治疗计划。这种每日适应性调整有助于精确确定肿瘤和危及器官（OAR）的位置，并将分次间运动的影响降至最低，从而可以缩小计划靶体积（PTV）边界。在配备HyperSight的ETHOS直线加速器上进行的局部非立体定向自适应前列腺放疗中，各向同性PTV边界已从标准的7毫米降至5毫米。本研究通过评估患者参考计划以及每日治疗计划中7毫米与5毫米PTV边界的剂量指标，来评估边界缩小的影响。
接受中度低分割自适应放疗的前列腺癌患者最初接受7毫米PTV边界的治疗（n = 10）。这项回顾性研究为这些患者生成了5毫米PTV边界的治疗计划（n =）用于比较。此外，模拟了一个完整的20次分割适应性治疗疗程，并缩小边界，以识别仅通过参考计划比较无法发现的差异。
与7毫米治疗计划相比，5毫米治疗计划中的膀胱V40.8和V48.6显著降低，但V60未显著降低。然而，在检查每日治疗计划数据时，5毫米PTV病例的膀胱V60较低。同样，在5毫米PTV边界治疗计划中，直肠剂量V，但V60未显著降低。与简单比较参考计划相比，在查看每日治疗计划数据时发现了进一步的差异。
在在线ART时代，有大量可用数据，如每日治疗计划剂量测定，仅分析参考计划可能不够。由于使用在线ART，PTV边界缩小，减少了接受<60 Gy剂量的膀胱和直肠体积，这可能降低毒性和继发性恶性肿瘤风险。
