Robert Chuter

Quantifying the dosimetric impact of online daily adaptation for MR-guided RT in cervical cancer

Purpose: This study assessed the inter- and intra-fractional dosimetric impact of MR-Linac-based adaptive radiotherapy for cervical cancer (CC). Methods: A retrospective analysis of five node-negative, locally advanced cervical cancer patients treated under the MOMENTUM study (NCT04075305) using adapt-to-shape (ATS) on an Elekta Unity MR-Linac. Assessing the dosimetric impact of daily online adaptations: (1) comparing dose between daily adapted (MR-adapted) and non-adapted (MR-guided) plans, by quantifying dose differences relative to reference plans (by 2 and 5%) and evaluating adaptation frequency; (2) performing intra-fraction dose evaluations. Dose metrics for targets and organs at risk (OARs) were evaluated following EMBRACE II guidelines. Results: MR-adapted plans improved target coverage or reduced OAR dose in 82–100% of fractions at a 2% dose deviation (and in 25–84% at a 5% deviation), compared to MR-guided plans. Dose reductions for OARs ranged from 2 to 8% for D0.1%, 4.77–16.70% for V4000cGy and 2.10–14.00% for V3000cGy. Intra-fraction analysis showed that the difference between daily planned and delivered doses in all target structures was not clinically significant, ranging from 0.08 to 2.20%, except two fractions that experienced higher deviations (5%) in ITV45. Treatment was well-tolerated, with no Grade 2 or 3 toxicities reported. Interpretation: MR-guided plans required adaptation in 25–100% of the fractions when compared to MR-adapted plans. MR-adapted plans demonstrated enhanced target dose consistency and reduced OAR dose for all patients, highlighting the benefits of daily adaptation. Despite longer treatment times, dose accuracy was preserved. Toxicity results for MRgART in CC appear promising.

The Current use of Adaptive Strategies for External Beam Radiotherapy in Cervical Cancer: A Systematic Review

Variability in the target and organs at risk (OARs) in cervical cancer treatment presents challenges for precise radiotherapy. Adaptive radiotherapy (ART) offers the potential to enhance treatment precision and outcomes. However, the increased workload and a lack of consensus on the most suitable ART approach hinder its clinical adoption. This systematic review aims to assess the current use of adaptive strategies for cervical cancer and define the optimal approach. A systematic review of current literature published between January 2012 and May 2023 was conducted. Searches used PubMed/Medline, Cochrane Library, and Web of Science databases, supplemented with the University of Manchester, Google Scholar, and papers retrieved from reference lists. The review assessed workflows, compared dosimetric benefits, and examined resources for each identified strategy. Excluded were abstracts, conference abstracts, reviews, articles unrelated to ART management, proton therapy, brachytherapy, or qualitative studies. A narrative synthesis involved data tabulation, summarizing selected studies detailing workflow for cervical cancer and dosimetric outcomes for targets and OARs. Sixteen articles met the inclusion criteria; these were mostly retrospective simulation planning studies, except four studies that had been clinically implemented. We identified five approaches for ART radiotherapy for cervical cancer: reactive and scheduled adaptation, internal target volume (ITV)-based approach using library of plans (LOP), fixed-margin approach using LOP, and real-time adaptation, with each approach reducing irradiated volumes without compromising target coverage compared to the non-ART approach. The LOP-based ITV approach is the most used and clinically assessed. Identifying the optimal strategy is challenging due to dosimetric assessment limitations. Implementing cervical cancer ART necessitates strategic optimization of clinical benefits and resources through research, including studies to identify the optimal frequency, and prospective evaluations of toxicity.