Department of Radiation Oncology, Olivia Newton-John Cancer Wellness & Research Centre, Austin Health, Heidelberg, Australia; Department of Medical Imaging and Radiation Sciences, Monash University, Clayton, Australia.
Department of Medical Imaging and Radiation Sciences, Monash University, Clayton, Australia.
Med Dosim. 2023;48(4):267-272. doi: 10.1016/j.meddos.2023.07.001. Epub 2023 Jul 26.
The hybrid magnetic resonance image (MRI) scanner and radiation therapy linear accelerator (MR-Linac) has the potential to enhance clinical outcomes for anal cancer (AC) patients with improved soft tissue visualization and daily plan adaption but has planning and delivery limitations due to the incorporation of MRI. We aimed to identify if Elekta Unity MR-Linac-based radiation therapy is feasible for anal cancer. Ten prospectively enrolled AC patients treated with radical chemoradiotherapy were replanned for MR-Linac treatment using departmental planning criteria. For comparison, and to reduce interobserver variability, volumetric modulated arc radiation therapy (VMAT) plans were also created for each patient by the same single senior radiation therapist. Plans were compared using departmental dosimetric plan criteria, as well as conformity and homogeneity indices, monitor units (MUs) and measured plan delivery (beam-on) time. Results were deemed clinically acceptable. Target and organ at risk (OAR) doses were comparable between MR-Linac plans and VMAT plans, although PTV45Gy D98% coverage was compromised in 3 of 10 MR-Linac plans due to caudocranial length exceeding the limits of the MR-Linac. MR-Linac plans had lower MUs, median of 689.1 vs 849.65 (p = 0.002), but took over twice as long to deliver, 529.5s vs 224s (p = <0.0001) as VMAT plans. MR-Linac planning and treatment of AC is feasible for a subset of patients. The current physical limitations of the Elekta Unity system mean patients with large caudocranial elective PTV45Gy target volumes may not be covered dosimetrically to the required clinical standard. Longer image verification and treatment delivery times of the MR-Linac also mean patient selection and intrafractional IGRT are likely to be integral to ensuring high quality clinical outcomes in this rare cancer.
混合磁共振成像(MRI)扫描仪和放射治疗直线加速器(MR-Linac)有可能通过改善软组织可视化和日常计划适应来提高肛门癌(AC)患者的临床结果,但由于 MRI 的加入,存在规划和交付方面的限制。我们旨在确定 Elekta Unity MR-Linac 为基础的放射治疗是否适用于肛门癌。10 名接受根治性放化疗的 AC 患者前瞻性入组,使用部门规划标准为他们重新制定了基于 MR-Linac 的放射治疗计划。为了进行比较,并减少观察者间的变异性,同一位资深放射治疗师也为每位患者创建了容积调制弧形放射治疗(VMAT)计划。使用部门剂量学计划标准,以及适形性和均匀性指数、监视器单位(MU)和测量计划交付(beam-on)时间比较计划。结果被认为是临床可接受的。MR-Linac 计划和 VMAT 计划的靶区和危及器官(OAR)剂量相当,尽管由于头足长度超过 MR-Linac 的限制,10 个 MR-Linac 计划中有 3 个 PTV45Gy D98%的覆盖率受到影响。MR-Linac 计划的 MU 较低,中位数为 689.1MU 对 849.65MU(p = 0.002),但完成治疗的时间长两倍,529.5s 对 224s(p < 0.0001)。MR-Linac 对 AC 的规划和治疗对一部分患者是可行的。Elekta Unity 系统目前的物理限制意味着头足方向上的大的 PTV45Gy 靶区体积较大的患者可能无法达到所需的临床标准的剂量覆盖。MR-Linac 的图像验证和治疗交付时间较长也意味着患者选择和分次内 IGRT 可能是确保这种罕见癌症高质量临床结果的关键。