[Dosimetry, control and irradiation of rat cervical spinal cord]

ABSTRACT

In radiobiology, the most important physical radiation quantity to predict the effect of irradiation of a biological specimen is the absorbed dose to the tissue of interest. In this project an irradiation set up was designed and verification of set up and dosimetry procedure was performed to deliver a precise X-ray dose to the small field of rat cervical spinal cord. AAPM-TG61 [American association and physician in medicine radiation therapy committee task group 61] protocol was used for dose measurement and we tailored a rat like phantom from polyethylene for dosimetry verification. The ionization chamber in this study was a farmer type and the X-ray generator was an orthovoltage Siemens machine working at 200 KVp potential. Dosimetry was done in air and phantom. An special jig was also built to fix the animals during irradiation which could help the treatments to be reproducible. Simulation and portal films were obtained to verify the irradiation field. The average value of dose rate in specified geometries by measurement was 146.54 cGy/min [SD=0.109]. While the dose determined by calculation was 95.145 cGy/min [SD=0.105], the comparison between these 2 methods shown a small discrepancy of 0.50% [P<0.001], which lies within the error limit of +/- 5.3% as mentioned by ICRU. Using protocol of AAPM TG-61 can provide an accurate dosimetry with minimum ambiguity. Application of appropriate correction factors and protocols can increase the accuracy and decrease the irradiation errors in radiobiological studies