58. The Dose - Volume Histogram Analysis for Pelvic Tumor Using Carbon Ion Radiotherapy

Takeshi Yanagi, Tadashi Kamada, Hiroshi Tsuji, Shigeru Yamada and Hirohiko Tsujii

Keywords: carbon ion radiotherapy, pelvic tumor

It is important to conform an irradiation beam only to a tumor, and to minimize the dose to the normal tissues around it. International interests exist in the use of charged particles in cancer radiotherapy, because of its good dose distribution. The aim of this study is to confirm the merits of the dose distribution of carbon ion beams compared to photon beams by simulating treatment planning analyzed by dose volume histograms (DVHs).

In comparative treatment planning, two types of pelvic tumor were selected; case 1/sacrum chordoma (volume: 701ml) and case 2/ recurrent rectal cancer (2267ml). Plans for of carbon and conventional photon beams were simulated using CT scans for each pelvic tumor, and the results were analyzed using DVH. In standard photon planning, 3,4,5,7 ports were used in case 1, and 2,3,4,5,6 ports in case 2, and the margin for the planning target volume (PTV) was given to cover the clinical target volume (CTV) with 80 - 100% of the prescribed dose. In carbon planning, 3 ports were used, and the minimum target dose given was at least 90% of the prescribed dose.

As a result, for the target volume, the carbon plans provided good coverage with a homogeneous dose around the maximum dose in both cases. Volumes of both bowels and bladders could be reduced at any dose levels in the carbon plans. Whole irradiated volumes of each case were less at low or middle dose level for carbon ion beams than for photons. Significantly higher dose could be given to 95% of the target with carbon beams than in photons for the bowel dose <50GyE. The use of carbon ion beams provided improved target dose homogeneity and reduced doses to critical structures compared to conventional photon beams. The use of carbon ion beams provides superior dose localization characteristics to those of photons.