Speaker
Description
Currently at our centre, the stereotactic program uses 6 MV cFF and forward planning techniques: cones for SRS, conformal MLC for SRT. Patients are immobilized with either the non-invasive Aktina stereotactic frame or a thermoplastic mask. Treatment localization is performed with CBCT. We are implementing DCAT and VMAT for SRT with 6 MV FFF to reduce treatment time, treat larger non-spherical lesions, and treat multiple lesions simultaneously. We investigated using different beam geometries, 1 arc, 3 arcs and 5 arcs, for both one and two lesions. Planning was completed in Monaco 5.11 and delivery with Elekta Agility MLC. Fluence measurements were taken with MapCheck and compared to TPS. Absolute dose measurements were acquired with an ion chamber at 4 off axis distances in the Steev phantom and compared to TPS. We selected 3 non-coplanar arcs as the preferred beam geometry. DCAT and VMAT both produced clinically acceptable plans that met our institutional guidelines. DCAT plans had fewer total MU and had higher DTA/dose passing rates and had fewer delivery interrupts. VMAT plans could achieve better OAR sparing when critical structures are near the lesion. Optimization time was similar, as both methods used a 1 mm dose grid. In conclusion, acceptable SRT plans can be produced with 3 non-coplanar arcs and the FFF beam using both DCAT and VMAT techniques.
