The examination of optimal positron emitting nuclide in the estimation of attainment depth within the body of RI beams by positron camera

The (10)C and (11)C beam stop position in a homogeneous phantom was measured using the range verification system in HIMAC. This system was developed to clear uncertainty of beam range within the patient body in heavy ion radiotherapy. In this system, a target is irradiated with RI beams ((11)C or (10)C) and the distribution of the beam end-points are measured by a positron camera. To inspect the precision of the measurement, three experiments were done, simple PMMA phantom irradiation, empirical beam stop position measurements using a range shifter and boundary irradiation using PMMA and lung phantom. Results of the first two experiments were consistent. Consequently, a 0.2 mm standard deviation of statistical error measurement was possible with 250 determinations. For the third experiment, we compared the precision using (10)C and (11)C beams. The boundary of the PMMA and lung phantom was irradiated with both beams to maximize the positron range effect in the beam range measurement. Consequently, no significant difference was observed between the two beams in spite of the different positron range. Thus, we conclude that the (10)C beam was useful for clinical application because of its good statistics owing to the short half-life.