VERIFICATION OF ABSORBED DOSE DETERMINED WITH PLANE-PARALLEL CHAMBERSIN CLINICAL ELECTRON-BEAMS FOLLOWING AAPM TASK GROUP-39 PROTOCOL USING FERROUS SULFATE DOSIMETRY

The absorbed dose values determined with the Exradin and PTW-Markus pl ane-parallel chambers were compared to the values obtained with the fe rrous sulphate dosimetry for a number of the Philips SL25 and the Ther ac 20 electron beams. For the plane-parallel chambers, the cavity-gas calibration factor N-gas(pp), was derived by a direct comparison with a calibrated cylindrical chamber using the three different calibration methods as proposed by the newly published AAPM TG 39 protocol. For t he ferrous sulphate dosimetry, an epsilon(m)G value of 352x10(-6) m(-2 ) kg(-1) Gy(-1) was adopted from ICRU Report No. 35. The average ratio of the dose values determined with the plane-parallel chambers and th e dose values determined with the Fricke dosimetry system was 1.001+/- 1.4%. These measurements are consistent with the AAPM TG 39 protocol. (C) 1996 American Association of Physicists in Medicine.