Dosimetric comparisons of craniospinal axis irradiation using helical tomotherapy, volume-modulated arc therapy and intensity-modulated radiotherapy for medulloblastoma

BACKGROUND: To evaluate the potential dosimetric gains of helical tomotherapy (HT) versus intensity-modulated radiotherapy (IMRT) and volume-modulated arc therapy (VMAT) for craniospinal axis irradiation (CSI) of medulloblastoma. METHODS: A total of 36 treatment plans were calculated retrospectively for 12 patients with medulloblastoma receiving CSI using HT with TomoTherapy Hi-Art Software (Version 2.0.7) (Accuray, Madison, WI, USA). For each case, the other two different delivery techniques were re-planned with IMRT/VMAT optimized with Eclipse treatment planning system (TPS) (Version 11.0.31). Homogeneity index (HI) and conformity index (CI) of the planning target volume (PTV) and organs at risk (OARs) sparing were analyzed. Differences in plans were evaluated using paired-samples t-test for various dosimetric parameters. RESULTS: HT yielded the highest CI in all PTV coverage including PTV of gross tumor volume (PGTV) (HT: 0.7163; VMAT: 0.6688; IMRT: 0.6096), PTVbrain (HT: 0.8490; VMAT: 0.8384; IMRT: 0.7815) and PTVspine (HT: 0.5904; VMAT: 0.5862; IMRT: 0.5797). Meanwhile, HT yielded better HI in PGTV (HT: 0.0543; VMAT: 0.0759; IMRT: 0.0736), PTVbrain (HT: 0.5525; VMAT: 0.5619; IMRT: 0.5554) and PTVspine (HT: 0.0700; VMAT: 0.0782; IMRT: 0.0877). As for OARs, HT demonstrated marked superiority in critical organs including maximal/mean doses of brainstem PRV, optical chiasm and optic nerves. CONCLUSIONS: For CSI of medulloblastoma, HT offers superior outcomes in terms of PTV conformity, PTV homogeneity and critical OAR sparing as compared with IMRT/VMAT.