The Royal Marsden Hospital NHS Trust, London, UK; The Institute of Cancer Research, London, UK.
Guys and St Thomas NHS Trust, London, UK.
Clin Oncol (R Coll Radiol). 2023 Feb;35(2):e135-e142. doi: 10.1016/j.clon.2022.10.008. Epub 2022 Nov 3.
Neoadjuvant chemoradiotherapy followed by surgery is the mainstay of treatment for patients with rectal cancer. Standard clinical target volume (CTV) to planning target volume (PTV) margins of 10 mm are used to accommodate inter- and intrafraction motion of target. Treating on magnetic resonance-integrated linear accelerators (MR-linacs) allows for online manual recontouring and adaptation (MRgART) enabling the reduction of PTV margins. The aim of this study was to investigate motion of the primary CTV (CTVA; gross tumour volume and macroscopic nodes with 10 mm expansion to cover microscopic disease) in order to develop a simultaneous integrated boost protocol for use on MR-linacs.
Patients suitable for neoadjuvant chemoradiotherapy were recruited for treatment on MR-linac using a two-phase technique; only the five phase 1 fractions on MR-linac were used for analysis. Intrafraction motion of CTVA was measured between pre-treatment and post-treatment MRI scans. In MRgART, isotropically expanded pre-treatment PTV margins from 1 to 10 mm were rigidly propagated to post-treatment MRI to determine overlap with 95% of CTVA. The PTV margin was considered acceptable if overlap was >95% in 90% of fractions. To understand the benefit of MRgART, the same methodology was repeated using a reference computed tomography planning scan for pre-treatment imaging.
In total, nine patients were recruited between January 2018 and December 2020 with T3a-T4, N0-N2, M0 disease. Forty-five fractions were analysed in total. The median motion across all planes was 0 mm, demonstrating minimal intrafraction motion. A PTV margin of 3 and 5mm was found to be acceptable in 96 and 98% of fractions, respectively. When comparing to the computed tomography reference scan, the analysis found that PTV margins to 5 and 10 mm only acceptably covered 51 and 76% of fractions, respectively.
PTV margins can be reduced to 3-5 mm in MRgART for rectal cancer treatment on MR-linac within an simultaneous integrated boost protocol.
新辅助放化疗后手术是直肠癌患者的主要治疗方法。标准临床靶区（CTV）到计划靶区（PTV）的边缘为 10mm，用于容纳靶区的内外分次运动。在磁共振集成直线加速器（MR-linacs）上进行治疗允许在线手动重新轮廓和适应（MRgART），从而减少 PTV 边缘。本研究旨在研究原发性 CTV（CTV A；包括 10mm 外扩以覆盖微观疾病的大体肿瘤体积和宏观淋巴结）的运动，以开发用于 MR-linacs 的同步综合增敏方案。
招募适合新辅助放化疗的患者在 MR-linac 上使用两阶段技术进行治疗；仅分析前 5 个阶段 1 的 MR-linac 数据。在治疗前和治疗后 MRI 扫描之间测量 CTVA 的分次内运动。在 MRgART 中，将 1 至 10mm 的各向同性扩展治疗前 PTV 边缘刚性传播到治疗后 MRI，以确定与 95%CTV A 的重叠。如果 90%的分次中重叠>95%，则认为 PTV 边缘可接受。为了了解 MRgART 的益处，使用治疗前成像的参考计算机断层扫描计划扫描重复了相同的方法。
2018 年 1 月至 2020 年 12 月期间共招募了 9 名 T3a-T4、N0-N2、M0 期疾病患者。共分析了 45 个分次。所有平面的中位运动均为 0mm，表明分次内运动最小。发现 PTV 边缘为 3mm 和 5mm 时，分别在 96%和 98%的分次中可接受。与计算机断层扫描参考扫描相比，分析发现 PTV 边缘为 5mm 和 10mm 时，分别仅可接受地覆盖了 51%和 76%的分次。
在 MR-linac 上的直肠癌 MRgART 治疗中，PTV 边缘可以减少到 3-5mm，适用于同步综合增敏方案。
