Multicentre dose audit for clinical trials of radiation therapy in Asia.

A dose audit of 16 facilities in 11 countries has been performed within the framework of the Forum for Nuclear Cooperation in Asia (FNCA) quality assurance program. The quality of radiation dosimetry varies because of the large variation in radiation therapy among the participating countries. One of the most important aspects of international multicentre clinical trials is uniformity of absolute dose between centres. The National Institute of Radiological Sciences (NIRS) in Japan has conducted a dose audit of participating countries since 2006 by using radiophotoluminescent glass dosimeters (RGDs). RGDs have been successfully applied to a domestic postal dose audit in Japan. The authors used the same audit system to perform a dose audit of the FNCA countries. The average and standard deviation of the relative deviation between the measured and intended dose among 46 beams was 0.4% and 1.5% (k = 1), respectively. This is an excellent level of uniformity for the multicountry data. However, of the 46 beams measured, a single beam exceeded the permitted tolerance level of ±5%. We investigated the cause for this and solved the problem. This event highlights the importance of external audits in radiation therapy.

[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.