64. Clinical Assessment of Tumor/ Tissue Responses of Heavy Ions by Radiobiological Basis and Volume Effect for Treatment Optimization

Takashi Nakano, Atsuko Abe, Tatsuya Ohono, Atsuro Terahara, Shinitiro Sato and Suho Sakata

Keywords: heavy ion therapy, treatment, cervical cancer

Acute reaction of intestine was evaluated by frequency and intensity of diarrhea. This reaction due to carbon was significantly smaller than that by photon treatment. The dose volume histogram of the intestine by carbonbeam treatment was significantly smaller than by photon treatment. Chromosomal aberrations of lymphocytes of irradiated patients were analyzed according to the radiation biologic effect. RBE of carbonbeam treatment for chromosomal aberrations of human lymphocytes seems to be approximately 3.

Acute response analysis for cervical cancer patients treated with carbon beam therapy.
Acute reaction of bowel of 22 patients treated with carbon beam therapy was undertaken using the Dose Volume Histogram Analysis Method. The degree and frequency of the diarrhea and bowel movement were compared to those of conventional photon treatment.
Diarrhea developed significantly 3-4 weeks after initiation of radiation, and disappeared with medication. The incidence and degree of the diarrhea were significantly smaller in carbon beam treatment than the conventional photon treatment. There was no significant correlation beteeen acute small intestine reaction and Dose Volume Histogram of small intestine. Similarly, there was no significant correlation beteeen diarrhea and Dose Volume Histogram of large intestine.
Late reaction of rectum and intestine was analyzed by the Dose Volume Histogram Analysis Method. Grade of rectal bleeding and fistula formation, etc. were counted as late reaction according to RTOG late reaction score. Tumor volume irradiated with larger than 65 Gy showed an increase in late reaction. However, there was no apparent trend that patients with large DVH had higher incidence or higher grade of late reaction. Therefore, further intensive analysis in terms of hot spot dose distribution will be required.