Adaptive Proton Therapy for Pediatric Patients: Improving the Quality of the Delivered Plan With On-Treatment MRI

Abstract

Pencil-beam scanning proton therapy is particularly sensitive to anatomic changes, which may negatively affect plan quality. We hypothesized that magnetic resonance imaging (MRI)-based adaptation can improve plan quality for pediatric patients. By evaluating 230 MRI scans acquired in treatment position during proton therapy, we found that onefourth of patients exhibited anatomic change, more than half of which result in suboptimal delivered plans. This highlights the potential role for MRI-guided proton Purpose: Pencil-beam scanning proton therapy is particularly sensitive to anatomic changes, which may affect the delivered dose distribution. This study examined whether offline adaptation using on-treatment magnetic resonance imaging (MRI) scan during proton therapy could improve plan quality for pediatric patients. Methods and Materials: Pediatric patients with at least 1 MRI scan in the treatment position (MRI tx ) during proton therapy between January 2017 and July 2019 were retrospectively reviewed. Patients underwent MRI and computed tomography simulation. Cases were planned with scenario-based optimization with 3 mm/3% positional/ range uncertainty. Patients demonstrating anatomic change on MRI tx were recontoured. The original plans were applied to the anatomy-of-the-day for dose recalculation (delivered plans). Plans were subsequently reoptimized offline, using original beam angles and dose-volume constraints (adapted plans). Delivered plans were compared with adapted plans to detect significant changes in plan quality, defined as a 5% decrease in the clinical target volume (CTV) receiving 95% of the prescription dose (V95) or a 5% increase in the dose-volume parameter used as an organ-atrisk constraint. Results: Seventy-three pediatric patients were eligible, with 303 MRI scans (73 simulation and 230 MRI tx scans) available for analysis. The median MRI tx scans per patient was 3 (range, 1-7). Twenty patients (27%) showed anatomic change, with 11 (55%) demonstrating a significant change in delivered plan quality. Significant changes were noted on MRI tx from week 2 (n Z 3) or week 3 (n Z 8). Seven of these 11 patients

Facilitating MR-Guided Adaptive Proton Therapy in Children Using Deep Learning-Based Synthetic CT

“…We have previously described our offline MRI-guided adaptive proton therapy workflow [ 1 ]. During proton therapy, patients undergo offline MRI tx to detect anatomic changes that affect delivery accuracy.…”

“…The enhanced-dose sculpting capability of pencil-beam scanning proton therapy is associated with increased sensitivity to anatomic changes. Although 27% of pediatric patients demonstrate anatomic changes during therapy, current treatment planning methods do not effectively account for anatomic variation [ 1 ]. This could potentially result in suboptimal delivered plans, defined as inadequate coverage of tumor or increased dose to healthy structures.…”

The potential role of MR-guided adaptive radiotherapy in pediatric oncology: Results from a SIOPE-COG survey

“…Data by Merchant et al have demonstrated the important role of weekly MR surveillance examinations in children with craniopharyngioma receiving RT to allow for re-planning in the case of cystic change during the course of treatment [34] . Similarly, ad hoc offline MR may be used to inform the need for proton re-planning in pediatric patients with intracranial or extracranial tumors [35] . However, cystic changes occurring in between MRI examinations can be missed for a number of fractions, hence the potential benefit of daily MR imaging.…”

Magnetic resonance imaging (MRI) guided proton therapy: A review of the clinical challenges, potential benefits and pathway to implementation

“…Inter-fraction anatomical changes include tumour motion [41,42], tumour target volume change (due to tumour growth, regression or change in oedema) [43][44][45], and changes in position of normal organs, all of which affect tissue density within the beam path resulting in range uncertainties and issues with tumour coverage. These inter-fraction changes are better detected on MRI than X-ray imaging.…”

“…These inter-fraction changes are better detected on MRI than X-ray imaging. A paediatric cancer study assessing MRI detected anatomical changes during proton therapy found that 27% of paediatric patients had anatomical changes in their gross tumour volume or in the tissue density within the beam path, and over half of these resulted in a significant deterioration in plan quality [45]. Rhabdomyosarcomas and low grade gliomas had the highest rate of anatomical change at 100% and 24%, respectively.…”