A study of proton therapy on malignant tumors

We irradiated proton beams on the ears of rabbits and the Harding-passey mouse melanoma and observed their morphological change. We used 52 MeV proton beams from the INS-FM cyclotron. We adjusted the energy of the proton beams to be at the plateau part of the Bragg curve, at the half-way point of the Bragg peak, and at the Bragg peak. The amount of radiation was 5000rad in each case. The Harding-Passey mouse melanoma was transplanted into the subcutan of a three week old mouse. In this experiment, we used tumors, the diameter of which grew up to 1.5-2cm in 2-3 weeks after the transplantation. Using the electromicroscope, we observed both lightly and severely damaged cells. Using proton irradiation with the Bragg peak located at depth of 1mm in the rabbit's ears, we studied the change in the tissue. Irradiated epidermis fell off and was eroded because of radiation damage, but the rear surface of the rabbit's ears was only slightly damaged. On the other hand, the melanoma cells were severely damaged with the proton beams with a dose of 5000 rad when they were located at the peak of the Bragg curve. Unlike the gamma ray irradiation, the proton beam caused severe damage of the nuclei in a short time in comparison with the damage to the protoplasma. We next irradiated the melanoma of mice at the plateau of the Bragg curve. Studying the melanin granules in melanoma with an electromicroscope, we found no essential change in the process of producing melanin in melanoma. At the same time, the inner structure of the Gogi vacuoles and large granuloma, the melanoma in the protoplasma remained almost normal, without any marked change. (J.P.N.)