Nuclear Science and Techniques

Abstract: Radiation for targeting liver tumors can be challenging because of the damage that it can cause to sensitive organs such as heart and kidney. To calculate the dose received by noninvolved organs, a modeling of the patient’s entire body is necessary. Therefore, in this study, a human Oak Ridge National Laboratory-Medical Internal Radiation Dose phantom was used for liver proton therapy simulation. The results show that the optimum proton energy interval covering the whole tumor was in the range of 90–120 MeV. A spread-out Bragg peak was built by adding Bragg peaks to cover the liver tumor volume, and beam parameters recommended by the International Commission on Radiation Units and Measurements (ICRU) were evaluated. The flux of secondary particles was calculated on the surface of the tumor, and two-dimensional dose distributions for protons, neutrons and photons were shown. Finally, the total doses of protons, photons and neutrons in tumor and 14 noninvolved organs were calculated. The results indicated that the ratio of received dose to the normal tissue of the liver concerning the spherical tumor of 2 cm in radius was approximately 0.01. This ratio for organs such as gall bladder, heart and kidney was approximately 8.4 × 10−5, 5.1 × 10−5 and 2.34 × 10−5. Secondary particles such as neutrons and photons deposit their energies to organs located far from the treatment volume, thus increasing the risk of secondary cancers. The research results indicated that the secondary particles dose was quite small in liver proton therapy. All the calculations were performed using Monte Carlo N-Particle Transport Code (MCNP).

Key words: Proton therapy, Liver, Spread-out, Bragg peak, Secondary particles, Noninvolved organs