Dose reduction of hippocampus using HyperArc planning in postoperative radiotherapy for primary brain tumors |
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Institution: | 2. Department of Medical Physics and Engineering, Osaka University Graduate School of Medicine, Suita, Japan;2. Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, TX, 77030, USA;3. RaySearch Laboratories, Stockholm, Sweden;1. Department of Radiation Medicine, Northwell Health, Lake Success, NY, 11042, USA;2. Department of Oncology, University of Calgary, Calgary, AB, Canada;3. Tom Baker Cancer Centre, Calgary, AB, Canada;2. Department of Radiation Oncology, Baylor Scott & White Health, Temple, Texas, USA;2. Department of Radiation Oncology, Nova Scotia Health, Halifax, Nova Scotia, B3H2Y9 Canada;3. Department of Radiation Oncology, Dalhousie University, Halifax, Nova Scotia, B3H2Y9 Canada;4. Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, B3H2Y9 Canada |
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Abstract: | To compare dosimetric parameters for the hippocampus, organs at risk (OARs), and targets of volumetric modulated arc therapy (VMAT), noncoplanar VMAT (NC-VMAT), and HyperArc (HA) plans in patients undergoing postoperative radiotherapy for primary brain tumors. For 20 patients, HA plans were generated to deliver 40.05 to 60 Gy for the planning target volume (PTV). In addition, doses for the hippocampus and OARs were minimized. The VMAT and NC-VMAT plans were retrospectively generated using the same optimization parameters as those in the HA plans. For the hippocampus, the equivalent dose to be administered in 2 Gy fractions (EQD2) was calculated assuming α/β = 2. Dosimetric parameters for the PTV, hippocampus, and OARs in the VMAT, NC-VMAT, and HA plans were compared. For PTV, the HA plans provided significantly lower Dmax and D1% than the VMAT and NC-VMAT plans (p < 0.05), whereas the D99% and Dmin were significantly higher (p < 0.05). For the contralateral hippocampus, the dosimetric parameters in the HA plans (8.1 ± 9.6, 6.5 ± 7.2, 5.6 ± 5.8, and 4.8 ± 4.7 Gy for D20%, D40%, D60% and D80%, respectively) were significantly smaller (p < 0.05) than those in the VMAT and NC-VMAT plans. Except for the optic chiasm, the Dmax in the HA plans (brainstem, lens, optic nerves, and retinas) was the smallest (p < 0.05). In addition, the doses in the HA plans for the brain and skin were the smallest (p < 0.05) among the 3 plans. HA planning, instead of coplanar and noncoplanar VMAT, significantly reduces the dosage to which the contralateral hippocampus as well as other OARs are exposed without compromising on target coverage. |
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