Quantitative measurements for entrance and exit radiation dose confirmation for cancer patients: An analysis of large cohort of patients

Background: The success of radiation therapy depends on accurate dose delivery to the target. Diode in vivo measurement of entrance and exit dose is a valuable quality assurance (QA) tool to ensure accurate dose delivery.  Materials and Methods: This study was performed at BINO Cancer Hospital, Bahawalpur. Entrance and exit dose measurements were done with p-type diode for various types of cancer patients treated on Co-60 teletherapy unit. These measurements were compared with calculated (planned) dose values. A total of 3285 radiation fields of 723 cancer patients of various sites were included in current investigation. Results: The action level was ± 3 % for current measurements. The average percentage variation between the expected and measured dose was 0.37 with standard deviation 2.08. It was observed that 87.49 % of measurements were within tolerance level. It was also noticed that all dose deliveries fell within ± 5 %. This study showed that exit/wedged/oblique dose measurements were harder than entrance/non wedged/normal incidence dose measurements and more standard deviation were observed for these measurements. Conclusion: The Quantitative entrance and exit absorbed dose verification for cancer patients is beneficial for quality improvement in radiation therapy. A great majority of measurements were found within the acceptable limit. Execution of entrance and exit dose measurement procedure had demonstrated to be very helpful for detecting potential mistakes and avoiding errors due to accurate positioning of patients.