Absorbed dose determination for high energy photon and electron beams at a PRIMUS linear accelerator using the documents DIN 6800-2 and TRS-398.

The International Atomic Energy Agency in Vienna has recently published a new Code of Practice for absorbed dose determination in external beam radiotherapy (Technical Reports Series No. 398). This code claims to fulfill the need for a systematic and internationally unfied approach to the calibration of ionization chambers, as well as to the use of these detectors in determining the absorbed dose to water for the radiation beams used in radiotherapy. In Germany, the corresponding national norms are laid down in DIN 6800-2. Therefore, it appeared necessary to compare in detail the procedures and results obtained according to these two documents. The comparison was performed for a 6 MV and 15 MV photon beam, as well as for a 12 MeV and 18 MeV electron beam. Although a series of differences could be ascertained, in particular in the numerical values of the various perturbation factors, the agreement of the final results remained well within the expected uncertainty range. Nevertheless, it is suggested to modify DIN 6800-2 in order to make it more easily applicable to a hospital environment, to incorporate the progress of knowledge in the data involved, and to achieve a better adherence to international recommendations.