Feasibility of tumour-focused adaptive radiotherapy for bladder cancer on the MR-linac

Trimodal Therapy Using an MR–guided Radiation Therapy Partial Bladder Tumor Boost in Muscle Invasive Bladder Cancer

“…Later, authors from the London Institute of Cancer Research developed and reported results of the PERMIT study, which prospectively evaluated the feasibility of online adaptive MRgRT in 5 patients using a hypofractionated simultaneous integrated boost technique treating the partial bladder to 55 Gy and the whole bladder to 46 Gy in 20 fractions on the Elekta Unity platform using PTV margins of 0.5 cm laterally and inferiorly, 1 cm posteriorly, and 1.5 cm anteriorly and superiorly. 22 Both of these studies confirm the feasibility of the adaptive MRgRT approach and report favorable target coverage and normal tissue dosimetry, though neither provided detailed information on toxicity outcomes. Importantly, although the authors appear to have improved the efficiency of the online adaptive reoptimization workflow from their initial cohort, the median total treatment time remained over 30 minutes per fraction.…”

“…Though limited by retrospective analysis, we report a 2-year locoregional control rate of 92% with an MRgRT PBB, which compares favorably to the 3-year local control of 77.5% and 63.5% in the BC2001 and BCON prospective studies, respectively. 24 Notably, neither Hunt et al 21 nor Mitchell et al 22 reported local control rates with their MRgRT experiences.…”

“…Importantly, although the authors appear to have improved the efficiency of the online adaptive reoptimization workflow from their initial cohort, the median total treatment time remained over 30 minutes per fraction. 21 , 22 A disadvantage of the online adaptive approach is the increased resource utilization of physician, physicist, and therapist time as well as prolonged time on the treatment couch for patients. Although Hunt et al 21 reported favorable patient tolerability surveys, the large number of fractions required for definitive RT of MIBC render this prolonged treatment time cumbersome.…”

“…Both of the series from London Cancer Research Institute used adapt-to-shape for all fractions on the Elekta Unity platform, where adapt-to-position was used only for changes in target position on a final verification scan before treatment delivery. 21 , 22 Neither Hunt et al 21 nor Mitchell et al 22 reported an offline analysis comparing predicted dose delivered (ie, base plan delivered on session anatomy) to actual dose delivered.…”

“…Additionally, online adaptive optimization capabilities on platforms such as the Elekta Unity (Elekta AB, Stockholm, Sweden) and ViewRay MRIdian (ViewRay Inc, Oakwood Village, OH) could further facilitate target coverage and normal tissue sparing, and early reports have demonstrated the feasibility of this online adaptive RT strategy for MIBC. 21 , 22 …”