Impact of dynamic beam delivery of intensity-modulated radiation therapy and volumetric modulated arc therapy on circulating immune cell exposure in glioma.

BACKGROUND AND PURPOSE: To compare how intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) affect circulating blood cells (CBC) depletion in glioma patients. MATERIALS AND METHODS: Twenty-eight glioma patients were retrospectively analyzed. Mean clinical target volume (CTV) was 293.8 ± 152.4 cm3 (μ± σ ). For each clinical IMRT or VMAT plan, a corresponding plan using the alternative technique was generated with identical objectives and constraints. A 4D dynamic blood-flow model simulated cerebral blood flow and time-resolved dose delivery to estimate accumulated dose and CBC depletion. Endpoints included irradiated blood volume (VD>0) and CBC depletion relative to baseline. Linear mixed-effects modeling assessed technique, CTV volume, and their interaction. RESULTS: After one fraction, mean VD>0 was higher with IMRT than VMAT (49.9% ± 7.2% vs 38.6% ± 6.3%; p < 0.00001). IMRT exposed more CBC volume in 24 of 28 patients; the four exceptions had the smallest CTVs. After three fractions, approximately 90% of CBCs were exposed with IMRT versus 77% with VMAT. Estimated CBC depletion was 13.9% with IMRT and 12.8% with VMAT (mean paired difference, 1.0 ± 1.7 percentage points; 95% CI, 0.3-1.7; p = 0.003). Depletion increased with CTV volume for both techniques, with a technique-by-CTV interaction of -0.41 percentage points per 100 cm3 (p = 0.041). CONCLUSIONS: IMRT and VMAT produced different blood dose distributions. However, the mean depletion difference was small relative to estimated intersubject variability and does not establish a clinically meaningful advantage for either technique.