Same-day consultation, simulation and lung Stereotactic Ablative Radiotherapy delivery on a Magnetic Resonance-linac.

Abstract

Magnetic resonance-guided radiotherapy (MRgRT) with real-time intra-fraction tumor motion monitoring allows for high precision Stereotactic Ablative Radiotherapy (SABR). This study aimed to investigate the clinical feasibility, patient satisfaction and delivery accuracy of single-fraction MR-guided SABR in a single day (one-stop-shop, OSS). Ten patients with small lung tumors eligible for single fraction treatments were included. The OSS procedure consisted of consultation, treatment simulation, treatment planning and delivery. Following SABR delivery, patients completed a reported experience measure (PREM) questionnaire. Prescribed doses ranged 28-34Gy. Median GTV was 2.2cm3 (range 1.3-22.9cm3). A gating boundary of 3mm, and PTV margin of 5mm around the GTV, were used with auto-beam delivery control. Accuracy of SABR delivery was studied by analyzing delivered MR-cines reconstructed from machine log files. All 10 patients completed the OSS procedure in a single day, and all reported satisfaction with the process. Median time for the treatment planning step and the whole procedure were 2.8h and 6.6h, respectively. With optimization of the procedure, treatment could be completed in half a day. During beam-on, the 3mm tracking boundary encompassed between 78.0 and 100% of the GTV across all patients, with corresponding PTV values being 94.4-100% (5th-95th percentiles). On average, system-latency for triggering a beam-off event comprised 5.3% of the delivery time. Latency reduced GTV coverage by an average of -0.3 %. Duty-cycles during treatment delivery ranged from 26.1 to 64.7%. An OSS procedure with MR-guided SABR for lung cancer led to good patient satisfaction. Gated treatment delivery was highly accurate with little impact of system-latency.