Verification and Monitoring of Radiation using Invivo and In-vitro Dosimetry in External Beam Radiotherapy in Libya

Abstract

Radiation therapy has been used in the treatment of cancer patients since its discovery in 1895, and these techniques were always in continuous scientific and technical development. It was necessary to introduce diode in-vivo dosimetry for radiation measurements to control the dose administered to patients. The patient simulating device, planning system and treatment machine are tested regularly according to set protocols developed by national and international organizations. Even though these individual systems are tested for errors which can be made in the transfer between the systems. The best quality assurance for the system is at the end of the treatment planning chain. In vivo dosimetry is used as a quality assurance tool for verifying dosimetry as either the entrance or exit surface of the patient undergoing external beam radiotherapy. It is a proven reliable method of checking overall treatment accuracy, allowing verification of dosimetry and dose calculation as well as patient treatment setup. The aim of the study was to calculate entrance dose obtained by the treatment planning system with measured dose using diode detectors and discover discrepancies lager than ±5% between the calculated dose and the measured. Calibration of the diode was done using Cobalt-60 teletherapy machine, linearity and calibration factors were determined. Measurements were preformed in Perspex phantom for calibration procedure. In vivo dosimetry represents a technique that has been widely employed to evaluate the entrance/exit dose to the patient mainly in radiotherapy. The analysis of all available measurements gave a mean percent deviation of 0.91% and average discrepancy 3.178 ±0.507 (±15.97%). A great majority of measurements were found within the acceptable limit±5%. Diode dosimeters are considered the best methods for in vivo dosimetry is simple, cost effective, provides immediate results and is a useful quality assurance tool for verification of absorbed dose delivered during patient treatment on Co-60 machine, also diode need to be calibrated against an accurate dosimetric reference, such as an ionization chamber, to determine the calibration factor and we conclude that using diode for in vivo dosimetry requires careful attention.