Document Type : Original Paper
Department of Oncology, Komfo Anokye Teaching Hospital, Kumasi, Ghana
Departments of Medical Physics, School of Nuclear and Allied Science, University of Ghana- Atomic Campus, Ghana
National Radiotherapy and Nuclear Medicine Centre, Korle-bu Teaching Hospital, Accra, Ghana
Introduction: One of the useful standard quality assurance techniques in radiation therapy is monitoring entrance doses in in-vivo dosimetry. An overall tolerance limit of 5% of the absorbed radiation dose has been recommended by the International Commission of Radiological Units. The implementation of an in vivo dosimetry still remains as a challenge to clinical medical physicists. As a result, the practice of constant monitoring of patients undergoing radiation therapy in most of the radiotherapy departments in Africa has not been given much attention. The study aimed at the evaluation of in-vivo entrance dosimetry using diodes to verify the accuracy of the radiation delivered to patients, compared to prescribed doses.
Material and Methods: In this paper, a protocol for in vivo dosimetry using a two flat surface Sun Nuclear Corporation diode in a radiotherapy department has been implemented in equinox Cobalt 60 beams. A water phantom calibrated was performed using the International Atomic Energy Agency standards (TRS 398). Calibration coefficients were determined with diodes using a Perspex phantom to derive correction factors. A total number of 137 patients’ doses were measured with the diodes during the treatment of 4 different sites.
Results: The average deviation between the measured and expected entrance dose performed by the phantom studies was 5% (0.34±1.8%) in almost all cases.
Conclusion: The developed protocol in this study indicates that in vivo dosimetry using silicon diodes is reliable, which can be adopted as a universal quality assurance tool in the radiotherapy departments. Moreover, measurements with diodes can be acquired online which produces an instant readout and is relatively cheaper as compared to the ion chamber.