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The precise conversion of CT numbers to their electron densities is essential in treatment planning for hadron therapy. Although some conversion methods have already been proposed, it is hard to check the conversion accuracy during practical therapy. We have estimated the CT numbers of real tissues by a calculational method established by Mustafa and Jackson. The relationship between the CT numbers and the electron densities was investigated for various body tissues as well as some tissue-equivalent materials used for a conversion to check the accuracy of the current conversion methods. The result indicates a slight disagreement at the high-CT-number region. A precise estimation of the multiple scattering, nuclear reaction and range straggling of incident particles has been considered as being important to realize higher-level conformal therapy in the future. The relationship between these parameters and the CT numbers was also investigated for tissues and water. The result shows that it is sufficiently practical to replace these parameters for real tissues with those for water by adjusting the density.

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To verify international uniformity in carbon beam dosimetry, an intercomparison programme was carried out at the heavy ion medical accelerator (HIMAC). Dose measurements with ionization chambers were performed for both unmodulated and 6 cm modulated 290 MeV/nucleon carbon beams. Although two different dosimetry procedures were employed, the evaluated values of absorbed dose were in good agreement. This comparison established a common framework for ionization chamber dosimetry between two different carbon beam therapy facilities.

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Abstract. The fl+ decay of 86Mo has been firstly investigated by means of f17 spectroscopy. The 86Mo nuclei were produced by fusion-evaporation reactions of 54Fe (35C1, 1 p2n) and 58Ni (32S, 2p 2n) at beam energies of 103 and t20 MeV, respectively. Three 7 rays of 47.3, 49.8 and 187.0 keV were unambiguously identified to follow the fl+ decay of 86Mo by results of X7 and f17 coincidence and cross-bombardment. A half life and a maximum fl+-ray energy of 86Mo were determined to be 19.6_ 1.1 s and 3.9_+ 0.4 MeV, respectively. A decay scheme of 86Mo is proposed in this article. Furthermore, a decay of S6Nb has been studied using the same combinations of projectiles and targets, and a new fl-decaying isomer 86mNb was observed with a half life of 56.3 _+ 8.3 s.