Conrad Mireille, Dal Bello Riccardo, van Timmeren Janita E, Andratschke Nicolaus, Wilke Lotte, Guckenberger Matthias, Tanadini-Lang Stephanie, Balermpas Panagiotis
Institute of Radiation Physics, Lausanne University Hospital, Rue du Grand-Pré 1., 1007 Lausanne, Switzerland.
Department of Radiation Oncology, University of Zurich, Rämistrasse 100, 8091 Zurich, Switzerland.
Clin Transl Radiat Oncol. 2023 Apr 1;40:100624. doi: 10.1016/j.ctro.2023.100624. eCollection 2023 May.
Treatment of head and neck cancer on linear accelerators with on-board magnetic resonance imaging (MR-linac) might be beneficial to reduce side effects and increase accuracy. For many head and neck cancer patients, dose coverage of the often superficially located planning target volumes (PTVs) is required. This study examines the impact of the electron return effect (ERE) on the surface dose in MR-guided radiotherapy (MRgRT) compared to conventional radiotherapy.
For this bicentric dosimetric study, 14 cases of laryngeal carcinomas with PTVs reaching up to the skin surface were included. For each patient, five different plans were compared, two VMAT plans (with and without a 5 mm bolus) and three IMRT MRgRT plans (0.35 T, 1.5 T and 0 T, each without bolus). Dose distributions were also validated with film measurements.
A similar coverage on the most superficial 3-5 mm of the PTV was achieved in the VMAT plans with bolus and the MRgRT plans for both 0.35 T and 1.5 T. However, coverage on this region was usually not achieved for VMAT without bolus and the 0 T plans. The film measurements on phantoms confirmed the results with the relative error never exceeding the calculated differences between the plans.
The present study could demonstrate that the ERE for both commercially available MR-linac variants provides sufficient coverage of the superficial tissue layers in MRgRT-plans for laryngeal carcinoma.
在直线加速器上使用机载磁共振成像(MR直线加速器)治疗头颈癌可能有助于减少副作用并提高准确性。对于许多头颈癌患者,需要对通常位于浅表的计划靶区(PTV)进行剂量覆盖。本研究探讨了与传统放疗相比,电子回返效应(ERE)对磁共振引导放疗(MRgRT)中表面剂量的影响。
在这项双中心剂量学研究中,纳入了14例PTV延伸至皮肤表面的喉癌病例。对每位患者比较了五种不同的计划,两种容积调强弧形治疗(VMAT)计划(有和没有5mm厚的 bolus)以及三种调强放射治疗(IMRT)MRgRT计划(0.35T、1.5T和0T,均无bolus)。剂量分布也通过胶片测量进行了验证。
在有bolus的VMAT计划以及0.35T和1.5T的MRgRT计划中,PTV最浅表3 - 5mm处的剂量覆盖情况相似。然而,没有bolus的VMAT计划和0T计划通常无法实现该区域的剂量覆盖。体模上的胶片测量结果证实了该结果,相对误差从未超过计划之间的计算差异。
本研究表明,两种市售MR直线加速器变体的ERE在MRgRT计划中为喉癌提供了足够的浅表组织层剂量覆盖。