Evaluation on the effect of dosimetry using a depth of calibration point or a depth of temporary dose maximum in high energy electron beams.]

The Japan Society of Medical Physics (JSMP) has published a new dosimetry protocol "JSMP-01" for the calibration of radiotherapy beams. This protocol provides a new definition of the calibration point (depth) in order to obtain the absorbed dose at a reference point (D(r)) by the calculation in high energy electron beams. This study evaluated the difference in the absorbed dose at the depth dose maximum (D(dmax)) and D(r) calculated from the absorbed dose at the calibration point. Further, the difference in the absorbed dose (D(dmax)) at "measured maximum depth (d(max))" was evaluated using "temporary maximum depth (d(max*))." In the experiment at a depth interval of 0.1 g cm(-2), no difference was observed between D(dmax) and D(r). However, in the experiment at a depth interval of 0.3 g cm(-2) the differences between D(dmax) and D(r) increased to 6.4% and 5.2% at 4 MeV and 6 MeV, respectively. Subsequently, at all energy levels the difference between D(dmax) and D(r) of all energy was more than 3% at a depth interval of 0.4 g cm(-2). The differences between D(dmax) and D(dmax*) were 2.68% and 4.50% at 6 MeV and 9 MeV, respectively, for this depth interval.