High-precision radiotherapy for craniospinal irradiation: evaluation of three-dimensional conformal radiotherapy, intensity-modulated radiation therapy and helical TomoTherapy.

This study aimed to establish the feasibility of intensity-modulated radiation therapy (IMRT) in craniospinal irradiation (CSI) using conventional linear accelerator (IMRT_LA) and compare it dosimetrically with helical TomoTherapy (IMRT_Tomo) and three-dimensional conformal radiotherapy (3DCRT). CT datasets of four previously treated patients with medulloblastoma were used to generate 3DCRT, IMRT_LA and IMRT_Tomo plans. A CSI dose of 35 Gy was prescribed to the planning target volume (PTV). IMRT_LA plans for tall patients were generated using an intensity feathering technique. All plans were compared dosimetrically using standardised parameters. The mean volume of each PTV receiving at least 95% of the prescribed dose (V(95%)) was >98% for all plans. All plans resulted in a comparable dose homogeneity index (DHI) for PTV_brain. For PTV_spine, IMRT_Tomo achieved the highest mean DHI of 0.96, compared with 0.91 for IMRT_LA and 0.84 for 3DCRT. The best dose conformity index was achieved by IMRT_Tomo for PTV_brain (0.96) and IMRT_LA for PTV_spine (0.83). The IMRT_Tomo plan was superior in terms of reduction of the maximum, mean and integral doses to almost all organs at risk (OARs). It also reduced the volume of each OAR irradiated to various dose levels, except for the lowest dose volume. The beam-on time was significantly longer in IMRT_Tomo. In conclusion, IMRT_Tomo for CSI is technically easier and potentially dosimetrically favourable compared with IMRT_LA and 3DCRT. IMRT for CSI can also be realised on a conventional linear accelerator even for spinal lengths exceeding maximum allowable field sizes. The longer beam-on time in IMRT_Tomo raises concerns about intrafraction motion and whole-body integral doses.