Craniospinal irradiation for medulloblastoma tumors: Retrospective analysis of dosimetric comparison-An institutional study.

Introduction: The comparative study of dosimetric parameters for craniospinal irradiation (CSI) in medulloblastoma cancer patients has been conducted using three different radiation treatment modalities, such as helical intensity-modulated radiation therapy (RT) (HIMRT), helical three-dimensional (3D) conformal RT (H3DCRT), and volumetric modulated arc therapy (VMAT). Evaluation based on dosimetric parameters has been performed to check the better clinical outcomes of recent treatment techniques over one another.

Materials and methods: In this retrospective study, twenty patients have been taken who were suffering from average-risk medulloblastoma. For these patients, phase 1 and phase 2 treatment plans were generated with HIMRT, H3DCRT, and VMAT using Accuray Precision version 2.0.1.1 and Monaco version 5.51.10 treatment planning software (TPS). For dose calculation, the convolution superposition algorithm is used for HIMRT and H3DCRT and the Monte Carlo algorithm is used for VMAT.

Result: Homogeneity index (HI), conformity index (CI), heterogeneity index (HT), total treatment time (TT), and doses to organs at risk (OARs) have been calculated. Statistical analysis has been performed with a paired-samples test in Statistical Package for the Social Sciences (SPSS) software version 22. For target volume PTV_Brain, Conformity index in different treatment techniques are mentioned (HIMRT = 1.02 ± 0.016, H3DCRT = 1.04 ± 0.015, VMAT = 1.11 ± 0.090), homogeneity indexes is (HIMRT = 0.73 ± 0.088, H3DCRT = 0.39 ± 0.208, VMAT = 0.43 ± 0.102), and Heterogeneity index is (HIMRT = 1.51 ± 0.013, H3DCRT = 1.50 ± 0.017, VMAT = 1.09 ± 0.018). For target volume PTV_Spine Conformity index in different treatment techniques are mentioned (HIMRT = 1.00 ± 0.004, H3DCRT = 1.01 ± 0.013, VMAT = 1.07 ± 0.039), homogeneity indexes is (HIMRT=0.07 ± 0.043, H3DCRT =0.06 ± 0.070, VMAT = 0.23 ± 0.183), and Heterogeneity index is (HIMRT = 1.10 ± 0.12, H3DCRT = 1.11 ± 0.121, VMAT = 1.06 ± 0.007). For target volume Boost_GTV Conformity index in different treatment techniques are mentioned (HIMRT = 1.035 ± 0.016, H3DCRT = 1.04 ± 0.016, VMAT = 1.08 ± 0.05), homogeneity indexes is (HIMRT = 0.80 ± 0.090, H3DCRT = 0.44 ± 0.223, VMAT = 0.56 ± 0.105), and Heterogeneity index is (HIMRT = 1.27 ± 0.006, H3DCRT = 1.26 ± 0.009, VMAT = 1.07 ± 0.009). Total Treatment time (minutes) for phase 1 in different techniques (HIMRT = 17.77 ± 3.974, H3DCRT = 14.83 ± 3.750, VMAT = 9.72 ± 0.713) and for phase 2 treatment time (HIMRT = 1.99 ± 0.306, H3DCRT = 1.68 ± 0.326, VMAT = 3.39 ± 0.918). All techniques, such as HIMRT, H3DCRT, and VMAT, give a uniform and conformal target coverage, but HIMRT shows the best conformal and homogeneous dose distribution and better OAR sparing.

Conclusion: In this study, CSI patients treated with HIMRT showed better results in terms of conformity, homogeneity, and doses to organs at risk.