Room: Exhibit Hall
Purpose: To compare proton and Brainlab IMRT plans for small brain tumors (CTV<12 cc) in terms of target coverage and critical organ sparing.
Methods: Ten patients treated with frameless Brainlab hypofractionated IMRT were retrospectively selected for this study. Brainlab plans were created using iPlan treatment planning system (TPS; version 4.1) for Varian TrueBeam STx, and were transferred to Eclipse TPS (version 11) for proton plan dose calculations using Mevion S250 double scattering proton therapy system. The Brainlab plans were generated using a sliding window IMRT technique with 10 to 13 beams in 3 to 5 fractions, while the proton plans consisted of 2 or 3 beams in each case with an aperture and a range compensator fitted for each field. The plans were normalized to cover at least 99% of the CTV with prescribed dose (20 Gy to 40 Gy) and compared by homogeneity index (HI), conformity index (CI), CTV dose (mean and maximum), critical organ (brainstem, brain, optic chiasm, optic nerve, and cochlea) dose (mean and maximum), and dose at 3 mm depth.
Results: HI was smaller by 3.1Â±3.0, while CI was larger by 0.5Â±0.9 in the Brainlab plans. Mean CTV dose, maximum CTV dose, and maximum dose at 3 mm depth were 1.5Â±1.9%, 4.7Â±3.7%, and 11.4Â±19.6% higher for the proton plans, respectively. Mean and maximum doses of critical organs were lower with proton planning, as exemplified by a 15.5Â±16.9% dose decrease of maximum dose in brainstem.
Conclusion: Brainlab generates more homogeneous target dose than proton, but exhibits slightly worse conformity for small brain tumors. Proton plans better spare critical organs, but generally increase maximum surface dose owing to the smaller number of beams. Plan quality strongly depends on target depth, target size, and organ proximity to target which should be considered for selection of patient treatment technique.