Session Item

Report the successful completion of a UK-based Compassionate Access Programme to provide daily adapted MR-guided (MRgRT) stereotactic ablative radiotherapy (SABR) for pancreatic cancer, including patient selection criteria, planning approach and tumour characteristics. Demonstrate the dosimetric benefits of MRgRT and report acute toxicity rates in this cohort.

Eligibility included patients with borderline resectable, locally advanced, medically inoperable, and locally recurrent disease; good organ function; ECOG PS 0-2; and no frank luminal invasion. For each treatment course dosimetric data was available from baseline treatment plans calculated on the anatomy at simulation; predicted doses from the baseline plan calculated on the daily anatomy; and treatment plans based on daily anatomy. UK SABR Consortium organ at risk (OAR) constraints were used alongside those accepted internationally. All patients were offered an online system to collect patient reported outcome measures (PROMs).

Fifty patients were accepted for treatment following multidisciplinary team review. Median age was 71 (max 89, minimum 40) and 28/50 (56%) were male. The most common (46/50, 92%) prescription dose was 40 Gy in 5 fractions on alternate days. Median GTV volume was 49.6 cc (min 12.7 cc, max 273.1 cc). Forty-nine patients completed treatment. The rate of grade 3+ acute toxicity was 10%. Late toxicity, local control and survival outcomes will be reported.

For baseline treatment plans, median target coverage was 77.9% (minimum 52.4%, maximum 95.0%) with no violations of mandatory OAR dose constraints (median OAR V36 = 0.0 cc). Predicted treatment plans showed increased doses to critical OARs (median OAR V36 = 0.6 cc, V33 = 1.2 cc). Using adaptive MRgRT, the re-optimized treatment plans showed no violations of mandatory OAR dose constraints (median OAR V36 = 0.0 cc, V33 = 0.01 cc) whilst maintaining target coverage (median 75.5%, min 48.5%, maximum 98.9%).

Adaptive MRgRT SABR is feasible with acceptable rates of acute toxicity in the setting of a UK-based Compassionate Access Programme. Daily plan re-optimisation allows for OAR dose constraints to be met without compromise of target coverage. These results have informed the design of a prospective dose escalation study.