ESTRO 2023 - Abstract Book

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ESTRO 2023

in DIT versus 43.9 Gy in MIT (p=0.0001).

The heart receives fewer doses using the MIT. However, the difference was not significant for Dmoy and V10%, but it was significant for V2% (14.2 versus 16.5, p = 0.04). Both techniques gave similar results regarding the sparing of the ipsilateral lung, there was no difference in mean dose, V17% and V28%. The maximal spinal cord dose was significantly less with the MIT (9.6 versus 15.7, p=0.036). The median number of monitor units (MU) was and 920.76 [581-1292] for MIT and 1018.92 [618-1750] for DIT (p=0.036). The irradiation time is shorter in the MIT, as there was no need to reposition the therapeutic table then to minimise the set-up errors and all these increase the reproducibility. Conclusion The MIT allows the avoidance of hot spots and assures a better coverage of target volumes. Otherwise, MIT and DIT were almost comparable in terms of doses to OARs. The treatment time is reduced and the reproducibility of positioning is precise and simple. J. Kraft 1 , S. Weick 1 , K. Breuer 2 , P. Lutyj 2 , K. Bratengeier 1 , F. Exner 1 , A. Richter 2 , J. Tamihardja 1 , D. Lisowski 1 , B. Polat 2 , M. Flentje 3 1 University Hospital Wuerzburg, Department of Radiation Oncology, Wuerzburg, Germany; 2 University Hospital Wuerzburg, Department of Radiation Oncology , Wuerzburg, Germany; 3 University Hospital Wuerzburg, Department of Radiation Oncology Wuerzburg, Wuerzburg, Germany Purpose or Objective Treatment plan comparison of hippocampal-avoidance whole brain radiotherapy with simultaneous integrated boost (HA- WBRT+SIB) for treatment of multiple brain metastases between an O-ring and a conventional C-arm linac regarding overall plan quality, dose distribution and adherence to a specified study protocol. Materials and Methods 12 treatment plans for irradiation of multiple brain metastases with HA-WBRT+SIB planned with Pinnacle at a C-arm Elekta Synergy Agility linac were replanned with Eclipse for treatment at an O-ring Varian Halcyon linac. Radiotherapy was applied with a 4-arc volumetric modulated arc therapy (VMAT) and treatment planning was performed on both units according to the experimental arm of the HIPPORAD study protocol (30 Gy in 12 fractions to the whole brain, 51 Gy integrated boost for brain metastases and sparing of the bilateral hippocampal region). Dose-volume histogram metrics for target volume coverage and organ at risk sparing was performed and evaluated regarding their compliance with the study protocol requirements. Additionally, gradient index, homogeneity index and conformity index were calculated. Results 12 patients with a median age of 58.5 (36 to 88) years and a median number of 9 (6 to 17) metastases were included in this analysis. The most common entity was NSCLC (n=6), followed by breast cancer (n=3). For both linacs the required specifications of the HIPPORAD study protocol were fully met for the target volumes (PTVwholebrain and PTVmetastases). There were only minor statistical differences within the achieved planning goals for both linacs, including better performance of meeting the required 30 Gy in PTV wholebrain for the Halcyon-Eclipse plans compared to the Synergy- Pinnacle plans (Dmean: Halcyon 30.27 vs Synergy 31.43 Gy, p < 0.001). However, violations of the study protocol demands were observed for some organs at risk constraints. In total, we observed 8 major deviations and 3 minor deviations for the Halcyon treatment plans and 8 major and 5 minor deviations for the Synergy plans. For the conformity index (CI), homogeneity index (HI) and the gradient index (GI), Synergy-Pinnacle plans were slightly in favour, except for the CI for PTVmetastases, where Halcyon-Eclipse plans were superior. PO-2010 Comparison of Varian Halcyon and Elekta Synergy for HA-WBRT+SIB in multiple brain metastases