リニアックを用いた線量計の校正

DOI 被引用文献1件 参考文献9件

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  • Calibration of ionization chambers using a linear accelerator

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Accuracy of cavity-gas calibration factors Ngas for ionization chambers using high-energy photon and electron beams from a linear accelerator was evaluated by comparing with in-air calibration using a 60Co beam. For in calibration with a linear accelerator, fluctuations in beam energy and output, and changes in beam flatness and symmetry become important problems. To overcome these problems, we investigated a new method with a tip-to-tip calibration procedure in a phantom and with an exchange between a calibrated PTW-Farmer chamber and a calibration Fanner chamber. For the 8 PTW-chambers (with acrylic wall), Ngas ratios and the uncertainties (2 SD) of the improved in-phantom calibration for the in-air 60Co calibration were 0.999± 0.005 for a 60Co beam,1.000 ± 0.005 for 4 MV x-rays,0.999 ± 0.005 for 10 MV x-rays, and 0.998 ± 0.006 for 15 MeV electrons, respectively. The uncertainties (2 SD) in Ngas ratios among beam energies were within ±0.3%. On the other hand, for 2 NE-chambers (with graphite wall), the deviations among the beam energies were observed because of errors of the physical data for the wall correction factors Pwall. Therefore, it was concluded that when the discrepancies in Pwall values do not occur, from the results for the PTW -chambers, the accuracy of our calibra tion method for ionization chambers with a linear accelerator is equivalent to the in-air 60Co calibration.

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