Arumugam Sankar, Wong Karen, Do Viet, Sidhom Mark
Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute, Sydney, NSW, Australia.
South Western Clinical School, University of New South Wales, Sydney, NSW, Australia.
Front Oncol. 2023 Jul 13;13:1116999. doi: 10.3389/fonc.2023.1116999. eCollection 2023.
To study the feasibility of optimizing the Clinical Target Volume to Planning Target Volume (CTV-PTV) margin in prostate radiotherapy(RT) with a general-purpose linear accelerator using an in-house developed position monitoring system, SeedTracker.
A cohort of 30 patients having definitive prostate radiotherapy treated within an ethics-approved prospective trial was considered for this study. The intrafraction prostate motion and the position deviations were measured using SeedTracker system during each treatment fraction. Using this data the CTV-PTV margin required to cover 90% of the patients with a minimum of 95% of the prescription dose to CTV was calculated using van Herk's formula. The margin calculations were performed for treatment scenarios both with and without applying the position corrections for observed position deviations. The feasibility of margin reduction with real-time monitoring was studied by assessing the delivered dose that incorporates the actual target position during treatment delivery and comparing it with the planned dose. This assessment was performed for plans generated with reduced CTV-PTV margin in the range of 7mm-3mm.
With real-time monitoring and position corrections applied the margin of 2.0mm, 2.1mm and 2.1mm in LR, AP and SI directions were required to meet the criteria of 90% population to receive 95% of the dose prescription to CTV. Without position corrections applied for observed position deviations a margin of 3.1mm, 4.0mm and 3.0mm was required in LR, AP and SI directions to meet the same criteria. A mean ± SD reduction of 0.5 ± 1.8% and 3 ± 7% of V60 for the rectum and bladder can be achieved for every 1mm reduction of PTV margin. With position corrections applied, the CTV D99 can be delivered within -0.2 ± 0.3 Gy of the planned dose for plans with a 3mm margin. Without applying corrections for position deviations the CTV D99 was reduced by a maximum of 1.1 ± 1.1 Gy for the 3mm margin plan and there was a statistically significant difference between planned and delivered dose for 3mm and 4mm margin plans.
This study demonstrates the feasibility of reducing the margin in prostate radiotherapy with SeedTracker system without compromising the dose delivery accuracy to CTV while reducing dose to critical structures.
利用自行研发的位置监测系统SeedTracker，研究在使用通用直线加速器进行前列腺放疗（RT）时优化临床靶区（CTV）到计划靶区（PTV）边界的可行性。
本研究纳入了30例在一项伦理批准的前瞻性试验中接受确定性前列腺放疗的患者。在每个治疗分次期间，使用SeedTracker系统测量分次内前列腺的运动和位置偏差。利用这些数据，使用范赫克公式计算覆盖90%患者且CTV至少接受95%处方剂量所需的CTV-PTV边界。在有和没有对观察到的位置偏差进行位置校正的治疗方案下进行边界计算。通过评估在治疗实施期间纳入实际靶区位置的实际 delivered 剂量，并将其与计划剂量进行比较，研究通过实时监测降低边界的可行性。对CTV-PTV边界在7mm至3mm范围内减小的计划进行了该评估。
应用实时监测和位置校正时，在左右（LR）、前后（AP）和头脚（SI）方向分别需要2.0mm、2.1mm和2.1mm的边界，以满足90%的人群接受CTV 95%剂量处方的标准。在未对观察到的位置偏差进行位置校正的情况下，在LR、AP和SI方向分别需要3.1mm、4.0mm和3.0mm的边界来满足相同标准。PTV边界每减小1mm，直肠和膀胱的V60平均分别降低0.5±1.8%和3±7%。应用位置校正后，对于边界为3mm的计划，CTV D99可以在计划剂量的-0.2±0.3Gy范围内 delivered。在未对位置偏差进行校正的情况下，对于边界为3mm的计划，CTV D99最多降低1.1±1.1Gy，并且对于边界为3mm和4mm的计划，计划剂量和 delivered 剂量之间存在统计学显著差异。
本研究证明了使用SeedTracker系统在前列腺放疗中减小边界的可行性，在不影响向CTV delivered剂量准确性的同时降低了对关键结构的剂量。
