Hippocampal-sparing whole-brain radiotherapy using the Elekta equipment

The purpose of this study was to evaluate the feasibility of hippocampal-sparing whole-brain radiotherapy (HS WBRT) using the Elekta Infinity linear accelerator and Monaco treatment planning system (TPS). Ten treatment plans were created for HS-WBRT to a dose of 30 Gy (10 fractions). RTOG 0933 recommendations were applied for treatment planning. Intensity-modulated radiotherapy (IMRT) plans for the Elekta Infinity linear accelerator were created using Monaco 3.1 TPS-based on a nine-field arrangement and step-and-shoot delivery method. Plan evaluation was performed using D2% and D98% for the whole-brain PTV (defined as whole brain excluding hippocampus avoidance region), D100% and maximum dose to the hippocampus, and maximum dose to optic nerves and chiasm. Homogeneity index (HI) defined as (D2%-D98%)/D-median was used to quantify dose homogeneity in the PTV. The whole-brain PTV D2% mean value was 37.28 Gy (range 36.95-37.49 Gy), and D98% mean value was 25.37 Gy (range 25.40-25.89 Gy). The hippocampus D100% mean value was 8.37 Gy (range 7.48-8.97 Gy) and the hippocampus maximum dose mean value was 14.35 Gy (range 13.48-15.40 Gy). The maximum dose to optic nerves and optic chiasm for all patients did not exceed 37.50 Gy. HI mean value was 0.36 (range 0.34-0.37). Mean number of segments was 105 (range 88-122) and mean number of monitor units was 1724 (range 1622-1914). Gamma evaluation showed that all plans passed 3%, 3 mm criteria with more than 99% of the measured points. These results indicate that Elekta equipment (Elekta Infinity linac and Monaco TPS) can be used for HS WBRT planning according to compliance criteria defined by the RTOG 0933 protocol.