The importance of additional geometrical verification with auto beam hold function in prostate cancer irradiation

Abstract

This paper aims to determine the need for additional imaging verification when using the auto beam hold function in radiotherapy of prostate cancer patients with inserted gold fiducial markers. Forty patients who underwent irradiation of the prostate and twenty with prostate and pelvic lymph node radiotherapy were included in the retrospective study. Intrafraction shifts during irradiation were compared with the auto beam hold function in the translational directions. The function was used with time tracking (5 seconds), a tolerance limit for marker deviations (4 mm), and bone structures in the large irradiation field (5 mm). The need for additional image verification was higher in the larger irradiation field group. When translational shifts were analysed, a statistically significant difference in the vertical direction was found in the group with only prostate irradiation (p = 0.013). A statistically significant difference in the lateral direction was found in the group with a larger irradiation field (p = 0.021). Translational shifts were not statistically significantly different between the two groups (p > 0.05). Conclusion: Intrafraction shifts of the prostate increase the need for additional imaging verification. The use of the auto beam hold function is effective in reducing errors.