Dosimetric Comparison of Helical Tomotherapy (HT) with Intensity Modulated Radiotherapy (IMRT), Three-dimension Conformal Radiotherapy (3D-CRT) and Conventional Two-dimension Radiotherapy (2D) for Craniospinal Axis Irradiation

Abstract

Purpose: Helical Tomotherapy (HT) can provide radiation beam to a longer treatment field without requirement of matching junction. The goal of this study is to establish the feasibility and measurement of plan quality using physical parameters in craniospinal axis (CSA) irradiation with HT and evaluate the potential dosimetric benefit from eliminating the need for field junction facility compared with IMRT, 3D-CRT and 2D technique. Methods and Materials: Twelve patients who newly diagnosed of primary CNS tumor requiring a CSA irradiation for curative intent proposed were treated with HT, simultaneous integrated boost technique (SIB). The same CT dicom images data sets were transferred to generate of each particular treatment planning with IMRT, 3D-CRT and 2D. The target dosimetric comparisons of CSA irradiation were divided to cranial part (PTV brain), spinal part (PTV spine) and PTV tumor boost, performed by analysis of homogeneity index (HI) and conformity index (CI). The percentage over prescription dose of spinal cord and integral dose from four treatment planning techniques were also compared. Results: Helical Tomotherapy achieved the best homogeneous dosimetric distribution for cranial part of CSA irradiation with mean HI of 44.51% compared with 54.92%, 56.07% and 86.32% for IMRT, 3D-CRT and 2D, respectively. HT also had excellent CI of 0.984 compared with 0.955, 0.976 and 0.830 (P < 0.001). The result of PTV tumor boost was nearly identical to PTV brain. For spinal portion, homogeneity of HT and IMRT revealed equally while the conformation was highest with HT technique. The mean HI was 22.43%, 22.20%, 41.44%, 59.24%, and the mean CI was 0.978, 0.917, 0.929 and 0.753 (P < 0.001) compatible with the lowest spinal cord maximal dose of 122.22% over prescription dose in HT compared with 127.80%, 135.11% and 148.22% for IMRT, 3D-CRT and 2D, respectively. The integral dose to whole body of HT was comparable with 2D technique (264.48 vs 270.82, P = 0.272), significant inferior to 3D-CRT (P = 0.034) while IMRT planned shown significantly highest ID (310.24, P < 0.05). All twelve patients were well tolerated in HT treatment, the mean overall treatment times were 40 days (range from 32 to 53 days). Grade 3-4 hematologic toxicity was the only adverse effect that caused a treatment break. Conclusion: Helical Tomotherapy was feasible for CSA irradiation and had acceptable acute radiation toxicity with shorter overall treatment time. Comparing with other techniques, the dosimetric analysis of HT was excellent in all aspects, except for the integral dose that more inferior than 3D-CRT, but better than step and shoot IMRT. Longer follow-up and further investigation was required to evaluate this concerning issue.