ESTRO 2025 - Abstract Book

S2797

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

quality for patients with benign disease. This is relevant for this cohort as they are typically younger and healthier than other SRS patients and thus more susceptible to the risk of developing a radiation-induced secondary cancer [1]. Material/Methods: Three previously treated patients with different benign pathologies were selected for examination including meningioma, acoustic neuroma and pituitary adenoma. Several HyperArc plans were created by systematically varying plan parameters, including the removal of a non-coplanar arc, MU suppression and varying the strength of the aperture shape controller (ASC). The ASC is a tool in Eclipse which controls the complexity of the multileaf collimator apertures. Plan quality was assessed by comparing plan quality metrics against the clinical reference plan. Metrics included the PTV coverage (PTV V100%), prescription dose conformity index, gradient index and relevant OAR doses. Extracranial dose was measured as discrete absorbed doses using thermoluminescent dosimeters (TLDs) and the anthropomorphic phantom, Rando (Alderson Research Laboratories, CA, USA). TLDs were placed on the midline anterior surface, at distances of 15cm, 30cm, 43cm and 70cm inferior to target. At 30cm, TLDs were placed at depth and on the posterior surface. These discrete doses were compared to the doses calculated in Eclipse. Results: The plans that resulted in the largest reduction in extracranial dose without compromising plan quality were those with the vertex arc removed. See Table 1 and Figure 1. Plans with the non-coplanar oblique arcs removed had comparable plan quality to the corresponding reference plan but resulted in increasing extracranial dose. The MU suppressed plans showed reduction in extracranial dose, but only where more than a 30% reduction in MU from the reference plan was achievable, and plan quality was compromised. Varying the ASC had little effect on extracranial dose. There was reasonable agreement between the measured and calculated doses given the low dose magnitude being measured.