Room: ePoster Forums
Purpose: Stereotactic radiosurgery (SRS) has been widely employed for brain tumors. Recently, with the implementation of new technologies, multiple intracranial tumors can be treated with a single-isocenter SRS treatment. The purpose of this study was to compare the dosimetric outcomes of different SRS treatment methods for brain tissue dose sparing and tumor dose conformity during multiple brain tumors treatment.
Methods: An index case with 7 intracranial, metastatic target lesions was utilized. IROC SRS brain phantom was used for this study. The total volume of all 7 tumors was 3.33cc with individual volumes ranging from 0.22cc to 1.35cc. Our treatment planning system has the capability of treating multiple lesions with a single isocenter utilizing enhanced dynamic conformal arc optimization. The prescription dose to each target was in accordance with our departmental SRS protocol and varied according to tumor volume with dose range (18-22.5Gy). Four treatment plans, denoted as P1, P2, P3 and P4, were compared, including 6X FFF with Millennium MLC, 10X FFF with Millennium MLC, 6X FFF with HD MLC and 10X FFF with HD MLC, respectively. Prescription doses from the same SRS plan template (6 couch angles) were identical across all four plans. Brain tissue volume with more than 12Gy dose (V12Gy), Mean Brain dose (MBD) and Average tumor conformity index (ACI) were used for comparison.
Results: The V12Gy of P1, P2, P3 and P4 were 21.33cc, 24.76cc, 17.90cc and 19.32cc, respectively. The corresponding V12Gy/total tumor volume ratio were 6.40, 7.43, 5.37 and 5.80. The MBD were 2.01Gy, 2.26Gy, 1.76Gy and 1.89Gy. ACI of these plans were 1.55, 1.72, 1.54 and 1.55.
Conclusion: This study showed HD MLC provided better tumor ACI and better brain tissue dose sparing than Millennium MLC. For the same MLC type, lower energy showed better tumor ACI and brain tissue dose sparing too.