Dosimetric Study in Tomotherapy Based on AAPM TG 119 Structures: A Longitudinal Moving Phantom Case

Abstract

Purpose: To evaluate the dosimetric impact due to longitudinal motion in phantom on of the Tomotherapy machine.Material and Methods: This study used Cheese and Delta4 phantom+ placed on a respiratory motion platform. They moved in longitudinal directions using various amplitudes from 2, 4, 6, 8, to 10 mm. The period of that movement was 4 and 6 s at field width of 25 and 50 mm, respectively. The C-shaped complex target was modified according to the American Association of Physicists in Medicine (AAPM) Task Group (TG) 119. The planning verifications were evaluated through point dose, gamma index value, and dose-volume histogram (DVH).Results: For all movement variations, the discrepancy of the dose measurements was about -1.254 to -14.421%. The range of gamma index value was 61.2 ±1.23% to 100±0.00. The DVH evaluation showed that the homogeneity index (HI) and the minimum dose to receive by 95% (D95%) of the target structure were 0.247 to 0.389 and -0.061 to -0.271 Gy respectively. The maximum dose (DMax) of the organ at risk (OAR) structure was 0.082 to 0.327 Gy. Conclusions: The motion could induce dose discrepancies on Tomotherapy dose distribution. The selection of the jaw field width in Tomotherapy was crucial for intensity-modulated radiotherapy (IMRT) techniques with moving targets. For larger field width, the dose discrepancy between the planned and measured dose showed an excellent result for gamma index and dose coverage.