School of Physical Sciences, University of Adelaide, Adelaide, SA, Australia.
Department of Radiation Oncology, Royal Adelaide Hospital, Adelaide, SA, Australia.
J Appl Clin Med Phys. 2024 Feb;25(2):e14182. doi: 10.1002/acm2.14182. Epub 2023 Oct 14.
Uncertainties in radiotherapy cause deviation from the planned dose distribution and may result in delivering a treatment that fails to meet clinical objectives. The impact of uncertainties is unique to the patient anatomy and the needle locations in HDR prostate brachytherapy. Evaluating this impact during treatment planning is not common practice, relying on margins around the target or organs-at-risk to account for uncertainties.
A robust evaluation framework for HDR prostate brachytherapy treatment plans was evaluated on 49 patient plans, measuring the range of possible dosimetric outcomes to the patient due to 14 major uncertainties.
Patient plans were evaluated for their robustness to uncertainties by simulating probable uncertainty scenarios. Five-thousand probabilistic and 1943 worst-case scenarios per patient were simulated by changing the position and size of structures and length of dwell times from their nominal values. For each uncertainty scenario, the prostate D and maximum doses to the urethra, D , and rectum, D , were calculated.
The D was an average 1.16 ± 0.51% (mean ± SD) below nominal values for the probabilistic scenarios; the D metric was 2.24 ± 0.90% higher; and D was greater by 0.48 ± 0.30%. The D and D metrics were more sensitive to uncertainties than D , with a median of 79.0% and 84.9% of probabilistic scenarios passing the constraints, compared to 96.5%. The median pass-rate for scenarios that passed all three metrics simultaneously was 63.4%.
Assessing treatment plan robustness improves plan quality assurance, is achievable in less than 1-min, and identifies treatment plans with poor robustness, allowing re-optimization before delivery.
放疗中的不确定性会导致剂量分布偏离计划，从而导致治疗无法达到临床目标。这种不确定性的影响因患者解剖结构和 HDR 前列腺近距离治疗中的针位而异。在治疗计划中评估这种影响并不常见，通常依赖于靶区或危及器官周围的边界来考虑不确定性。
评估了一种针对 HDR 前列腺近距离治疗计划的稳健性评估框架，对 49 个患者计划进行了评估，测量了由于 14 个主要不确定性因素导致患者可能出现的剂量学结果范围。
通过模拟可能的不确定性情况来评估患者计划的稳健性。通过改变结构的位置和大小以及驻留时间的长度来模拟每个患者的 5000 个概率和 1943 个最坏情况场景。对于每个不确定性场景，计算前列腺 D 和最大剂量到尿道、D 和直肠、D 。
概率场景下，D 的平均值比名义值低 1.16 ± 0.51%（平均值 ± 标准差）；D 度量值高 2.24 ± 0.90%；D 高 0.48 ± 0.30%。D 和 D 度量值比 D 更敏感于不确定性，79.0%和 84.9%的概率场景符合约束条件，而 96.5%的场景符合 D 度量值。同时通过所有三个度量值的概率场景的中位数通过率为 63.4%。
评估治疗计划的稳健性可以提高计划质量保证，在不到 1 分钟的时间内完成，并识别出稳健性差的治疗计划，以便在交付前进行重新优化。
