Standardization of Stereotactic MR-Guided Adaptive Radiation Therapy Planning for Prostate Cancer

PURPOSE/OBJECTIVE(S)

To assess the impact of a standardized planning class solution (PCS) in stereotactic MR-guided adaptive radiation therapy (SMART) for prostate cancer on efficiency and robustness for daily adaptive radiation therapy treatments.

MATERIALS/METHODS

Data collection of 20 previous SMART prostate plans: number of objective structures, number of beam segments, treatment delivery time (TDT) and the plan adaption robustness (PAR). The PAR was scored from 1 to 3 for the robustness of the plan to re-adapt and achieve similar dose metric scores to the baseline plan on all fractions. These scores were, 1: a single re-optimization required, 2: cost-function adjustments required and 3: medical physics advice required. Five medical dosimetrists provided preferences for objective structures and the optimization thresholds used. A PCS was created based on this data and implemented into SMART prostate plans between October 2022 and December 2022. A consecutive sample of 20 patients (PCSpost) were then retrospectively compared with the previous 20 patients prior to the PCS (PCSpre).

RESULTS

The PCS showed minimal difference in the TDT and segment number mean ± (standard deviation), 9.5 ± (0.7) mins and 77.8 ± (6.9) segments PCSpost respectively compared to 9.5 ± (0.8) mins and 80.8 ± (5.9) segments PCSpre. However, the PCS resulted in a considerable reduction in PAR, with 11 patients requiring only a single re-optimization for each fraction to achieve dose metric targets compared to 7 PCSpre patients. Also, the median PAR score was 1 in PCSpost compared to a score of 2 with PCSpre. The PCS had good compliance with the criteria met in 18/20 patient baseline plans. Feedback surveys showed positive results for efficiency saving from multiple disciplines; in therapeutic radiographers from reduced PAR, medical physicists increased automation in plan checking and consistent planning guidelines for medical dosimetrists.

CONCLUSION

The PCS is in clinical use, results have shown improved treatment adaption efficiency and robustness. Fewer re-optimizations per treatment were required onset to achieve similar dose metrics than before its implementation.

Evaluation of hypofractionated adaptive radiotherapy using the MR Linac in localised pancreatic cancer: protocol summary of the Emerald-Pancreas phase 1/expansion study located at Oxford University Hospital, UK

INTRODUCTION

Online adaptive MR-guided radiotherapy allows for dose escalation to pancreatic cancer while sparing surrounding critical organs. We seek to evaluate the safety of delivering hypofractionated five-fraction, three-fraction and single-fraction MR-guided stereotactic ablative radiotherapy (SABR) to the pancreas.

METHODS AND ANALYSIS

This is a single-centre three-arm phase 1 non-randomised safety study. Patients with localised pancreatic cancer will receive either 50 Gy in five (biological equivalent dose (BED10)=100 Gy), 39 Gy in three (BED10=90 Gy) or 25 Gy in a single fraction (BED10=87.5 Gy) MR-guided daily online adaptive radiotherapy. Each fractionation regimen will be assessed as independent cohorts to determine tolerability, assessed continuously using Bayesian conjugate posterior beta distributions. The primary endpoint of the study is to establish the safety of five-fraction, three-fraction and single-fraction MR-guided hypofractionation SABR in localised pancreatic cancer by assessing dose-limiting toxicities. Secondary endpoints include overall survival, progression-free survival, local control rates, overall control rate, resection rates, long-term toxicities and freedom from second-line chemotherapy. This study plans to also explore imaging and immune biomarkers that may be useful to predict outcome and personalise treatment. The trial will recruit up to 60 patients with a safety run-in.

ETHICS AND DISSEMINATION

The trial is approved by the West Midlands-Black Country Research Ethics Committee 22/WM/0122. The results will be disseminated via conference presentations, peer-reviewed scientific journals and submission to regulatory authorities. The data collected for the study, including individual participant data, will be made available to researchers on request to the study team and with appropriate reason, via octo-enquiries@oncology.ox.ac.uk. The shared data will be deidentified participant data and will be available for 3 years following publication of the study. Data will be shared with investigator support, after approval of a proposal and with a signed data access agreement.

TRIAL REGISTRATION NUMBER

ISRCTN10557832.