Purpose

Hippocampal-sparing whole brain radiotherapy (HS-WBRT) aims to preserve neurocognitive functions in patients undergoing brain radiotherapy (RT). Volumetric modulated arc therapy (VMAT) involves intensity-modulated RT using a coplanar arc. An inclined head position might improve dose distribution during HS-WBRT using VMAT.

Materials and methods

This study analyzed 8 patients receiving brain RT with inclined head positioning. A comparable set of CT images simulating a non-inclined head position was obtained by rotating the original CT set. HS-WBRT plans of coplanar VMAT for each CT set were generated with a prescribed dose of 30 Gy in 10 fractions. Maximum dose to the hippocampi was limited to 16 Gy; to the optic nerve, optic chiasm, and eyeballs this was confined to less than 37.5 Gy; for the lenses to 8 Gy. Dosimetric parameters of the two different plans of 8 patients were compared with paired t-test.

Results

Mean inclined head angle was 11.09±0.73. The homogeneity (HI) and conformity (CI) indexes demonstrated improved results, with an average 8.4±10.0%(p= 0.041) and 5.3±3.9%(p= 0.005) reduction, respectively, in the inclined vs. non-inclined position. The inclined head position had lower hippocampi D min (10.45±0.36 Gy), D max (13.70±0.25 Gy), and D mean (12.01±0.38 Gy) values vs. the non-inclined head position (D min= 12.07±1.07 Gy; D max= 15.70±1.25 Gy; D mean= 13.91±1.01 Gy), with 12.8±8.9%(p= 0.007), 12.2±6.8%(p= 0.003), and 13.2±7.2%(p= 0.002) reductions, respectively. Mean D max for the lenses was 6.34±0.72 Gy and 7.60±0.46 Gy, respectively, with a 16.3±10.8% reduction in the inclined position (p= 0.004). D max for the optic nerve and D mean for the eyeballs also decreased by 7.0±5.9%(p= 0.015) and 8.4±7.2%(p= 0.015), respectively.

Conclusion

Inclining the head position to approximately 11 during HS-WBRT using VMAT improved dose distribution in the planning target volume and allowed lower doses to the hippocampi and optic apparatus.