Seasonal Photon Output Trend from Linear Accelerator in Sokoto, North-Western Nigeria

Background: Linear accelerators are so sensitive to variability of temperature, pressure, humidity and dust; thus, weather factors can cause common errors in photon output which in turn can compromise constancy and consistency in precise delivery of tumor dose. Dose checker is such a dose-measuring devices that has an inbuilt correction factor for bunker temperature and pressure changes which ensures the photon output is within the accepted values to the patient. The aim of the study is to find the effect of seasonal changes on Linac and its influence on the patient. Methods: This is a retrospective study and daily records of 6 and 15 MV photon output with their corresponding temperature and pressure from January 2019 and December 2021 were extracted and reviewed. Precision mercury-in-glass thermometer and Barometer (OPUS 10 THI) were used to keep daily records of bunker temperature and pressure while their seasonal behaviours were recorded. Mean values of each month of the year was calculated and arranged according to three seasons of the year; results were represented in graphs, tables and bar charts. Results: The overall mean photon outputs were 0.997 and 0.828 cGy/MU for 6 and 15 MV respectively. The deviation of photon outputs from their reference values were ±2% for 6MV and ±3% for the 15MV energy. The mean bunker temperature was 27.07oC. The overall mean bunker pressure was 977.23 hpa. During harmattan season the temperature and pressure ranged between 26.8-25.4oC and 978-976.1 hpa respectively. In hot season bunker temperature was between 25.7-29.5oC and pressure was between 976.1-975.0 hpa. For the wet season, the temperature was between 29.5-25.7oC, and the corresponding bunker pressure ranged between 980.0-976.3 hpa. Conclusion: The seasons of year influenced variation in bunker temperature and pressure with corresponding seasonal photon output variation despite the use of dose checker. Low photon outputs were recorded during harmattan and hot seasons while higher outputs were recorded during wet season. Keywords: Season; Trend; Photon output, Linear Accelerator