CAN SINGLE ARC SMARTARC VMAT REPLACE DMPO-IMRT FOR COMPLEX TARGETS?

Materials: Ten patients previously treated DMPO-IMRT five for each clinical site were replanned using the SmartArc module of Pinnacle 3 v9.0 (Philips Healthcare, Fitchburg, WI) for an Elekta Synergy linear accelerator (Elekta AB, Stockholm, Sweden) with 1cm MLC leaf width at isocentre. H&N patients were originally planned with a 7-field IMRT technique, to mean doses of 65 Gy and 54 Gy in 30 fractions for primary and nodal planning target volumes (PTVs) respectively. PPN patients were originally planned with a 5-field IMRT technique to mean doses of 60 Gy and 47 Gy in 20 fractions to prostate and pelvic node PTVs respectively. Single arc VMAT plans were produced with the aim of optimisation to at least equal the clinical IMRT plan in terms of PTV coverage and organ at risk (OAR) sparing, although in practice a balance of these factors was necessary. VMAT and IMRT plans were compared in terms of clinical PTV and OAR constraints, treatment delivery time and monitor units (MU) delivered. Plan verification for all VMAT plans and four of the five original H&N IMRT plans was performed by delivering the treatment to a Delta 4 phantom (Scandidos AB, Uppsala, Sweden) and recording the proportion of diodes with a gamma index (3% / 3 mm) of less than or equal to unity.