Field survey on output for X-ray therapeutic accelerators took place three times in Saitama Prefecture. The result of the field survey in 1997 showed the different rate from the designated dose at peak depth of 35 beams in 18 institutions. As different rate within +/-5% stood 91.4% in all beams, so different rate within +/-3% stood 85.7% in the same beams. The average different rate from the designated dose at peak depth was 11.06%. The standard deviation of the same condition was 3.72.The result of the field survey in 2005 showed the different rate from the designated dose at correction depth of 36 beams in 18 institutions. As different rate within +/-5% stood 100% in all beams, so different rate within +/-3% stood 91.6% in the same beams. The average different rate from the designated dose at correction depth was +0.80%. The standard deviation of the same condition was 1.46.We understood that the different rate from the designated dose at radiotherapeutic institutions decreased and even the value of the standard deviation was decreasing, by receiving 3 times of field surveys that was held in Saitama Pref. Also we understood that the beam numbers of different rate within +/-5% and the beam numbers of different rate within +/-3% were going up. We recognized that the good result of accurate dose is obtained more, by doing a continual field survey. The field survey was carried out in 2006 in Tochigi Prefecture and was the insufficient result in 10% of institutions.
In order to support a routine QA of the CT number for treatment planning, we developed a phantom and a sample holder for easy handling. At most particle radiotherapy facilities in Japan, the CT number is calibrated by the poly-binary calibration method using liquid samples of 100% ethanol and 40% K(2)HPO(4) which are set in a cylindrical water phantom. However it is hard to remove air bubbles from the calibration liquid sample and maintain its stable concentration for a long time. So much time is needed for QA of the CT number. The new sample holder, which we developed, was able to keep a stable concentration of the liquid for more than 300 days. Consequently, the CT number of each sample, which was set in a water equivalent solid phantom, was the same as the CT number in a water phantom within 7 HU. In addition, we developed software which could measure the CT number of each sample semi-automatically and could calculate the calibration coefficients between the CT number and water equivalent length (WEL). Using this software, we could check the calibration result instantly at the time of CT data acquisition. These tools should be useful to carry out calibration of the CT-WEL routinely in a short time.
