Adaptive-predictive organ localization (a-POLO) in the clinic: Updated results in hypofractionated bladder radiotherapy.

Abstract

282 Background: The A-POLO strategy allows the optimal 'plan of the day' to be selected online for radiotherapy (RT) delivery. The methodology is implemented in a phase II study of patients with muscle-invasive bladder cancer who are not suitable for cystectomy/daily RT and are receiving hypofractionated RT. Methods: Planning scans were performed at 0 and 30 minutes post void (CT0 and CT30). Three conformal plans were created (small, intermediate, large) ( Table ). Patients were prescribed 6Gy weekly for 5–6 weeks. A pre-RT cone beam CT (CBCT) scan and online set-up correction were performed. The plan giving the optimal target coverage was selected by 2 observers. Offline plan selection was also carried out by an independent observer. A post-RT CBCT was acquired to calculate the percentage of the CTV covered by 95% of the dose (V95). The mean A- POLO volume was compared to our previous institutional standard PTV (1.5cm isotropic margins) (PTViso). Outcome data were collected. Results: A total of 77 RT fractions were delivered to 14 patients. The small plan was delivered for 38 (49%) fractions and the large for 6 (8%) fractions. The concordance rate between online and offline plan selection was 71/77 (92%). The mean CTV V95 was 99% (patient mean range 97–100%). The mean time between the pre- and post-treatment CBCT was 15 minutes. The mean reduction between PTViso and mean A-POLO PTV was 42% (range 16– 59%). 2 patients had grade (G) 3 (CTCv3.0) treatment-related acute toxicity. There have been no treatment-related G4 acute or G3 late toxicities. With a median follow-up of 7.3 months 10 patients are alive with 8 disease free (1 local and 1 distant relapse). Conclusions: Implementation of A-POLO RT is feasible, well tolerated, and associated with good concordance in 'plan of the day' selection. An individualized treatment plan can be delivered with each fraction to achieve a reduction in PTV compared to PTViso with maintenance of target coverage. [Table: see text] No significant financial relationships to disclose.