A retrospective comparison of intensity-modulated arc therapy and 3-dimensional conformal approaches in the planning of grade 3 gliomas

Purpose: To evaluate the extent to which intensity-modulated arc therapy (IMAT) for high-grade gliomas is comparable with three-dimensional conformal radiotherapy (3DCRT) in relation to the dose delivered to normal brain tissue (NBT), planning target volume (PTV) conformity and the dose delivered to brainstem and optic chiasma. Method: A total of 16 randomly selected 3DCRT treatment plans of grade 3 gliomas were re-planned using an IMAT planning technique and dose–volume histograms were compared. Primary outcomes were maximum, mean, 1/3 and 2/3 doses to NBT outside the PTV. Also the maximum, mean, D50 and D20 doses to PTV. Secondary outcomes were maximum and mean doses to the brainstem and optic chiasm. Wilcoxon signed rank test was used to compare data. Results: IMAT led to a statistically significant increase in mean dose to NBT (34·4 versus 33·3 Gy, (p=0·047) but a statistically significant reduction in maximum dose to NBT (62·7 versus 63·8 Gy, p=0·004) compared with 3DCRT. IMAT led to statistically significant reductions in maximum, D50 and D20 doses to the PTV (63·3 versus 64·7 Gy, p=0·001; 60·0 versus 60·7 Gy, p=0·001 and 60·5 versus 61·8 Gy, p=0·002, respectively). No statistically significant differences were seen in doses to brainstem and optic chiasm. Conclusion: IMAT is at least comparable with 3DCRT in relation to minimising dose to NBT and ensuring good PTV conformity. Doses delivered to organs at risk using IMAT were also comparable with 3DCRT. This study supports the continued use of IMAT for the treatment of high-grade gliomas