Dosimetric Evaluation of Total Body Irradiations with Helical Tomotherapy: Phantom Study

Abstract

OBJECTIVE In total body irradiations (TBI), it becomes hard getting homogenous dose distribution due to inhomogeneous body shape and tissue density variations. The main goal of the radiotherapy is saving critic organs while achieving a homogeneous dose distribution at target volume. Tomotherapy is a new and one of the most effective technologies used for TBIs. In this study, it was aimed to investigate TBI planned target volume coverage and organ doses using helical tomotherapy. METHODS To simulate rando phantom geometrically, arms and legs created by rice are added to rando phantom and were immobilized by a vacuum bed. The computer tomography images of the lower and upper region of the phantom with a slice thickness of 3 mm were acquired. Thermoluminescent dosimeters (TLDs) were placed entrance-exit, midpoint doses of lens, lungs, and kidneys onto a rando phantom. The treatment plans were prepared and irradiated with helical tomotherapy technique. Results of the measurements and treatment planning system (TPS) doses were compared. All procedures were repeated 3 times and averaged. TPS and TLD doses were evaluated by Wilcoxon test. RESULTS In the plans prepared with the TPS, a homogeneous dose distribution was obtained with a homogeneity index of 0.16 for the upper body and 0.04 for the lower body. When the calculated critical organ doses were compared with the measured organ doses, there was no statistically significant difference between them. CONCLUSION It was seen that saving critical organs and achieving desired dose distribution are possible without blocks in tomotherapy. Doses calculated from TPS and measured by TLD matched.