Whole brain radiotherapy with hippocampal avoidance and simultaneous integrated boost for brain metastases: a dosimetric volumetric-modulated arc therapy study

Abstract

To develop a feasible volumetric modulated arc therapy (VMAT) treatment in whole brain radiotherapy (WBRT) with a simultaneous integrated boost (SIB) and hippocampal (HP) sparing in 1-5 brain metastases (BMs). Ten patients with 20 BMs received a WBRT prescription of 20 Gy, SIB dose on BMs of 40 Gy/5 fractions. PTVWBRT was generated from brain minus BMs-PTVs (PTVSIB) and planning organ at risk volume to HP. All plans were evaluated in: homogeneity index (HI), target coverage (TC), maximum dose to prescription dose ratio (MDPD), prescription isodose to target volume ratio (PITV) and paddick conformity index (CI). We also evaluate D100%, mean and maximum doses to HP. Planning objectives were for PTVWBRT, D2% = 25 Gy with acceptable deviation of 26.7 Gy and D98% ≥ 16.7 Gy; for PTVSIB D95% ≥ 38 Gy; for HP, D100% = 6 Gy with acceptable deviation of 6.7 Gy, Dmax = 10.7 Gy with acceptable deviation of 11.3 Gy, a mean dose of 8 Gy. Mean number of BMs was 2 (range 1-5). Mean values for BMs were volume of PTVSIB = 5.1 ± 4.9 cc, dose to 95% of PTVSIB 39.3 ± 0.9 Gy, HI 0.083 ± 0.03, TC 0.96 ± 0.24, CI 0.78 ± 0.17. Mean MDPD was 1.06 ± 0.02 and PITV 0.96 ± 0.24. For WBRT, mean target volume was (13.46 ± 2)*10(2) cc, mean dose to 90% of PTVWBRT 19.8 ± 0.2 Gy, mean HI 0.42 ± 0.12 and TC 0.78 ± 0.11. Mean and maximum HP doses were 7.7 ± 0.3 Gy and 10.5 ± 0.5 Gy. Mean dose to 100% of HP volume (D100%) was 6.7 ± 0.3 Gy. WBRT plus SIB with HP avoidance with VMAT was feasible. All dosimetric parameters were satisfied for PTVWBRT and PTVSIB.