The benefit of MR‐only radiotherapy treatment planning for anal and rectal cancers: A planning study

Abstract

Introduction: Limited evidence exists showing the benefit of magnetic resonance (MR)-only radiotherapy treatment planning for anal and rectal cancers. This study aims to assess the impact of MR-only planning on target volumes (TVs) and treatment plan doses to organs at risks (OARs) for anal and rectal cancers versus a computed tomography (CT)-only pathway. Materials and methods: Forty-six patients (29 rectum and 17 anus) undergoing preoperative or radical external beam radiotherapy received CT and T2 MR simulation. TV and OARs were delineated on CT and MR, and volumetric arc therapy treatment plans were optimized independently (53.2 Gy/28 fractions for anus, 45 Gy/25 fractions for rectum). Further treatment plans assessed gross tumor volume (GTV) dose escalation. Differences in TV volumes and OAR doses, in terms of Vx Gy (organ volume (%) receiving x dose (Gy)), were assessed. Results: MR GTV and primary planning TV (PTV) volumes systematically reduced by 13 cc and 98 cc (anus) and 44 cc and 109 cc (rectum) respectively compared to CT volumes. Statistically significant OAR dose reductions versus CT were found for bladder and uterus (rectum) and bladder, penile bulb, and genitalia (anus). With GTV boosting, statistically significant dose reductions were found for sigmoid,small bowel,vagina,and penile bulb (rectum) and vagina (anus). Conclusion: Our findings provide evidence that the introduction of MR (whether through MR-only or CT-MR pathways) to radiotherapy treatment planning for anal and rectal cancers has the potential to improve treatments. MR-related OAR dose reductions may translate into less treatment-related toxicity for patients or greater ability to dose escalate.

The Role of MRI and PET/CT in Radiotherapy Target Volume Determination in Gastrointestinal Cancers—Review of the Literature

“…Another study investigating the role of MRI in radiotherapy treatment planning for anal and rectal cancers was conducted by Bird et al The gross tumor volume (GTV) contoured using MRI was smaller compared to the CT volumes (reduced by 13cc). The organs at risk (OAR) such as the bladder, penile bulb and genitalia received statistically significantly lower doses when delineated on MR in comparison with CT, which could translate into a reduction in radiation-induced toxicity for MR-based delineation [29].…”

Radiation induced therapeutic effects in cancerous and tumor cells: A review

“…Therefore, dose-escalating radiotherapy (RT), intensity-modulated radiotherapy (IMRT), imageguided radiotherapy (IGRT), and hypofractionated radiotherapy have been used to reduce toxicity. 88,89 Similarly, MR-associated OAR-dose reduction leads to less toxicity or greater potential for dose escalation due to patient treatment . Balloons are used to treat rectal cancer and reduce acute toxicity.…”

Contouring practices and artefact management within a synthetic CT-based radiotherapy workflow for the central nervous system.

“…In an MR-only RT workflow, these so-called synthetic CT (sCT) images substitute the planning CT scans. This workflow not only eliminates the registration uncertainties but also simplifies the clinical workload as only one image examination, namely MR imaging, is needed for RT planning [4][5][6]. An MR-only RT workflow can be enabled by a two-step implementation process: firstly with a commissioning phase, to test whether the sCT image can perform equally as a CT scan in a clinical environment, and secondly with a validation phase, to develop new workflow guidelines as part of a quality assurance (QA) management program that would oversee the safe usage of the sCT images in RT.…”