Inter-fractionated dose uncertainty evaluation during radiation treatment by in vivo dosimetry with diode dosimeters

Backgrounds: Inter-fractionated dose uncertainty is one of causes of errors. Therefore, in vivo dosimetry is recommended for error detection and verifying the accuracy of dose delivery to patients. Objectives: To evaluate inter-fractionated dose uncertainty between prescribed dose obtained from computerized treatment planning system and delivered doses from diode dosimeter. Materials and methods: This study was performed in breast, thoracic, abdominal and pelvic regions of 20 patients. Three dimensional (3D) treatment plans were created by Pinnacle3 treatment planning system version 9.8 and verified by Delta4PT. Gamma index (at 3% dose difference and 3 mm distance to agreement) was set at 90% for acceptant level. Patients were treated with Elekta Precise Linac with 6 or 10 MV and delivered dose was collected in each fraction by p-type diode dosimeter incorporated with VivoSoft version 3.0.1. Results: It was shown that uncertainty of delivered doses were varied from -4.432 to 2.532 percent and from -1.787 to 2.032 percent for entrance and exit dose, respectively. Uncertainty in entrance dose was higher than that of exit dose where the uncertainty in breast and pelvic regions was higher than thoracic and abdominal regions. Conclusion: The study revealed that inter-fractionated dose uncertainty from diode dosimeter compared to computerized treatment planning system was within acceptable level of less than 5%. Therefore, treatment planning verification and in vivo dosimetry were recommended for verifying the accuracy of dose delivery to patients, to reduce errors in dose delivery in patients and improved the efficiency of radiation treatment in radiotherapy. However, diodes should be prior examined in clinic and in vivo dosimetry should be applied with caution. Journal of Associated Medical Sciences 2017; 50(2): 314-322. Doi: 10.14456/jams.2017.32