A dosimetric comparison between three-dimensional conformal radiation therapy and intensity-modulated radiation therapy in the treatment of posterior fossa boost in medulloblastoma.

AIMS: To compare three-dimensional conformal radiation therapy (3DCRT) and intensity-modulated radiation therapy (IMRT) in posterior fossa (PF) boost in children with medulloblastoma (MB); dosimetrically evaluating and comparing both techniques with regard to target coverage and doses to organs at risk.

SETTINGS AND DESIGN: Structured.

SUBJECTS AND METHODS: Seven previously irradiated patients of MB were retrieved and re-planned with both 3DCRT and IMRT techniques. Dosimetric comparison was done by performing two plans for the PF boost for the same patient. Prescription dose and normal tissue constraints were identical for both plans.

STATISTICAL ANALYSIS USED: SPSS, version 19, statistical software package was used. For quantitative data, paired t-test was applied to calculate the difference between two means.

RESULTS: Mean values of planning target volume (PTV); PTV95% and PTV5% in IMRT were 97.19% and 106.07% and for 3DCRT were 96.57% and 106.33%, respectively. The dose homogeneity was better in IMRT (1.091) as compared to 3DCRT (1.100), but was not statistically significant (P = 0.341). Conformity index was comparable in both the plans, i.e., 3DCRT (0.979) and IMRT (0.976) with P = 0.819. IMRT plan provided reduced mean dose to cochlea relative to the 3DCRT plans with P = 0.032 for the right cochlea and 0.020 for the left cochlea. IMRT showed no advantage over 3DCRT in sparing the anterior cranial structures where mean doses to the right and left lens were 0.61 Gy and 0.56 Gy for IMRT and 0.16 Gy and 0.09 Gy for 3DCRT, respectively.

CONCLUSIONS: IMRT technique was able to improve homogeneity index, spare the cochleae, but 3DCRT plans were superior in sparing anterior cranial structures without compromising the dose to PF.