RESUMO
PURPOSE: Volumetric modulated arc therapy (VMAT) has generally been perceived as too time and resource intensive for palliative radiation therapy mainly because of the need for extensive organs at risk contouring. Dose-limiting conformity-based objectives can be automatically generated and are commonly used to conform isodoses closely around the target volumes during inverse planning. The aim of this study was to determine if conformity-based objectives can be used to create VMAT plans for lumbosacral spine palliative radiation therapy without organs at risk contours, which will improve conformity, dose homogeneity, and speed of delivery compared with standard forward planning approaches. METHODS: A total of 25 patients were retrospectively replanned using three different planning techniques: (1) anterior-posterior parallel opposed pair (POP); (2) single isocenter anterior-posterior half-beam block junctioned to three fields, posterior and two laterals (JUNC); and (3) VMAT single arc. Treatment volume included L1-S5 vertebrae prescribed to 20 Gy in five fractions. Conformality index, homogeneity index, contour, planning, and treatment time were compared for each technique. RESULTS: Planning target volume V95 ≥95% was maintained for all 75 replans. VMAT was superior to POP and JUNC in terms of conformality (POP 2.0 vs. JUNC 1.8 vs. VMAT 1.2; P < .01) and homogeneity (POP 1.1 vs. JUNC 1.1 vs. VMAT 1.0; P < .01). Planning times for POP were the lowest (3.2 minutes). VMAT and POP had similar delivery times (1.5 minutes), which were approximately half the JUNC delivery time (3.2 minutes). CONCLUSIONS: Conformity-based VMAT was dosimetrically superior to conventional field-based planning and reduced delivery time. This reduction in normal tissue dose as well as reduced time spent on the treatment couch can potentially improve the quality of life in palliative patients receiving radiotherapy to the lumbosacral spine.
