Examination of the dosimetric effects of the headrest used in radiotherapy by different algorithms

Abstract

INTRODUCTION: The use of immobilization devices is imperative in radiotherapy to ensure proper positioning of the patient and correct application of the treatment. Headrests are frequently used to restrict the movement of a patient and to provide comfortable laying during the treatment. The aim of the present study was to examine the effect of a headrest on dose distribution by including the headrest in the body structure using two different algorithms. METHODS: The body structures on seven patient images were contoured with and without headrest. Dose distribution within the body was calculated for each patient using both Collapse Cone (CC) and Monte Carlo (MC) algorithms for cases where the headrest was included in the body structure and removed. The obtained results were compared with the gamma analysis method. RESULTS: The headrest has some effect on the dose distribution. Specifically, the results of the gamma analysis indicate that when the headrest was included in the body structure doses to the body were somewhat reduced. Since the CC algorithm does not allow calculation of secondary photons and scattered radiation sufficiently accurate in a low density environment, the similarity results of the CC algorithm were higher in the gamma analysis than those of the MC algorithm. DISCUSSION AND CONCLUSION: In order to accurately calculate the radiation dose, all the materials through which the radiation passes during the treatment must be specified in a treatment planning system. It is concluded that even if the immobilization devices are of low-density material, they have some effect on the dose distribution within a patient and should be included in the treatment planning system.