Optimizing pelvic and lumbar treatment metastases using multiple isocenters with VMAT on the halcyon 2.0

Bone metastases are a major clinical problem, mainly in breast and prostate cancers, which comprise the majority of cancer cases. With technological advances that improve precision and efficacy, radiotherapy is an essential palliative solution. In this study, two radiotherapy planning techniques were evaluated, the longitudinal isocenter (LONI), and the three-isocenters (3ISO) that combine the lateral isocenters for pelvis and longitudinal isocenters for lumbar metastases, using the Halcyon^TM2.0 machine with the volumetric modulated arc therapy (VMAT) technique. Dosimetric parameters such as conformity index (CI), homogeneity index (HI), (dose coverage (D_95%), dose max (D_MAX), monitor units (MUs), and conformation number (CN) were analyzed. No significant difference in dose conformity between the two studied techniques was observed. However, remarkable results in terms of dose homogeneity were achieved in the application of the 3ISO modality, with an improvement of 42.8%. Additionally, D_95% for 3ISO was 96.26% against 92.71% for LONI. Regarding CN, which considers both dose coverage and healthy tissue optimization, 3ISO technique resulted in an improvement of 12.3%. It is noted, however, that 3ISO requires more time and accurate patient positioning to guarantee optimal outcomes.