Verification of absorbed dose using diodes in cobalt-60 radiation therapy

The objective of this work was to enhance the quality and safety of dose delivery in the practice of radiation oncology. To achieve this goal, the absorbed dose verification program was initiated by using the diode in vivo dosimetry (IVD) system (for entrance and exit). This practice was implemented at BINO, Bahawalpur, Pakistan. Diodes were calibrated for making absorbed dose measurements. Various correction factors (SSD, dose non-linearity, field size, angle of incidence, and wedge) were determined for diode IVD system. The measurements were performed in phantom in order to validate the IVD procedure. One hundred and nineteen patients were monitored and 995 measurements were performed. For phantom, the percentage difference between measured and calculated dose for entrance setting remained within +/- 2 % and for exit setting +/- 3 %. For patient measurements, the percentage difference between measured and calculated dose remained within +/- 5 % for entrance/open fields and +/- 7 % for exit/wedge/oblique fields. One hundred and nineteen patients and 995 fields have been monitored during the period of 6 months. The analysis of all available measurements gave a mean percent deviation of +/- 1.19 % and standard deviation of +/- 2.87 %. Larger variations have been noticed in oblique, wedge and exit measurements. This investigation revealed that clinical dosimetry using diodes is simple, provides immediate results and is a useful quality assurance tool for dose delivery. It has enhanced the quality of radiation dose delivery and increased/improved the reliability of the radiation therapy practice in BINO.