Application of secondary beams to treatment planning.

A secondary beam facility had been built at the end of last fiscal year and commenced the operation since the second term of HIMAC machine time. Optimum momentum spread was sought so as to compromise two contradictory factors, the blurring of sharp Bragg peak and broadening of the ¹¹C end-point distribution. Three types of irradiation, namely, focused beam irradiation, line irradiation and curved surface irradiation, were tested to see the uniformity of the irradiation field. The field uniformity turned out competent with the assessment of beam end-point in all cases, since it only affects the statistical noise in PET images that degrades indirectly the assessment of end-point. Preliminary irradiation tests were performed on rabbits to see biological half-life of ¹¹C in the thigh muscle of the rear leg.