Medical Research: Emerging Concepts and Applications Vol. 1

This study examined the accuracy of entrance radiation dose delivery in patients receiving Cobalt-60 radiotherapy for head and neck cancer using a p-type diode dosimetry system, with the aim of adopting diode-based in-vivo dosimetry as a quality assurance protocol. Four p-type ISORAD diodes were tested and calibrated using a Cobalt-60 radiotherapy unit employed for the treatment of malignant diseases. The diode response was calibrated and evaluated before patient measurements were performed. Entrance dose measurements were obtained at the depth of maximum dose for each treatment field and were compared with the corresponding dose calculated by the treatment planning system for each individual beam. The study included 22 patients with head and neck cancer and a total of 45 treatment fields. The action level for the comparison between measured and calculated entrance doses was set at ±5%. Approximately 97.77% of the measurements for head and neck treatments were within this action level. For the 45 measurements, the average discrepancy between diode-measured and treatment-planning-system-calculated entrance dose was 3.23%, with a corresponding standard deviation of 3.05%. One measurement exceeded the ±5% action level and required review before continuation of treatment. The findings indicate that real-time diode readings were practical for clinical use, did not add substantial measurement time and provided direct dose information before treatment delivery. Within the scope of this study, p-type diode in-vivo dosimetry supported verification of entrance dose delivery and helped identify discrepancies between measured and calculated doses during Cobalt-60 radiotherapy for head and neck cancer.