Volumetric-modulated Dynamic WaveArc therapy reduces the dose to the hippocampus in patients with pituitary adenomas and craniopharyngiomas

Publication date: Available online 13 April 2017
Source:Practical Radiation Oncology
Author(s): Megumi Uto, Takashi Mizowaki, Kengo Ogura, Yuki Miyabe, Mitsuhiro Nakamura, Nobutaka Mukumoto, Hideaki Hirashima, Masahiro Hiraoka
PurposeReducing the radiation dose to the hippocampus is important in patients with brain tumors in order to preserve cognitive function. The Vero4DRT system can realize a new irradiation technique, termed volumetric-modulated Dynamic WaveArc therapy (VMDWAT), which allows the safe use of sequential noncoplanar volumetric-modulated beams without couch rotation. Since VMDWAT appears to reduce the hippocampus dose in patients with pituitary adenomas and craniopharyngiomas, we performed a planning study to compare the dose distribution of volumetric-modulated arc therapy using only a coplanar arc (coVMAT) and VMDWAT.Methods and materials.CoVMAT and VMDWAT plans were created for 30 patients with pituitary adenomas and craniopharyngiomas. The prescription dose was 52.2Gy in 29 fractions, with 99% of each planning target volume covered by 90% of the prescribed dose. Optimization was performed for maximal reduction of the dose to the hippocampus. Treatment time was defined as the beam-on time.ResultsThe mean equivalent dose in 2-Gy fractions to 40% of the volume of the bilateral hippocampus (EQD40%) for coVMAT/VMDWAT were 9.90/5.31Gy, respectively (p<0.001). The mean EQD40% in VMDWAT was less than 7.3Gy, which is the threshold for predicting cognitive impairment. While the volume of normal brain receiving 5Gy (V5) was significantly larger in VMDWAT, compared to coVMAT, the normal brain volume receiving 10, 15, 20, 25, 30, 35, 40, 45, and 50Gy (V10–50) was significantly smaller in VMDWAT. The conformity and homogeneity indices were significantly better in VMDWAT. The mean VMDWAT treatment time was longer compared to coVMAT (70.1 vs. 67.1seconds, respectively).ConclusionsWhile VMDWAT increased brain V5 and the treatment time compared with coVMAT, it significantly reduced the dose to the hippocampus and brain V10–50 and improved target conformity and homogeneity. VMDWAT could be a promising treatment technique for pituitary adenomas and craniopharyngiomas.



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