The Lateral Scatter Of Proton Beams In Radiotherapy And Dose Compensation

Proton is considered one of the ideal particles in radiotherapy for its unique dose distribution. The application of proton radiotherapy has been widely implemented internationally and its therapeutic effect is also well received. Compared with photons, protons will deposit more energy in the tumor and minimize the absorbed dose of the surrounding normal tissues at the same time. It plays an important role in protecting the surrounding normal tissues, especially in the treatment of complicated tumors such as head and neck cancer, nasopharynx cancer which are surrounded by critical organs. Besides, it is particularly important to reduce the dose of normal tissues in the children’s radiotherapy. The children are more likely to get radiation induced cancers after radiotherapy because they are more sensitive to radiation than adults. Promotion the proton radiotherapy will bring the patients a better life. In order to make the use of proton therapy successfully, research about dose distribution of protons is necessary.In this work,120-MeV protons entering the water tank were simulated based on the Monte Carlo simulation platform GATE. The dose distribution of protons in the depth and lateral were got. We discussed the lack of absorbed dose due to the lateral scattering on the edge of tumors when using 4cm×4cm proton beams to treat 4cmx4cm rumors. To compensate the dose on the edge we designed new compensation beams. The dose distribution both in and out of the tumors were analyzed for new designed plan and traditional plan which simply expands the irradiation field to 5cmx5cm. We found that compared with 5cm×5cm irradiation field, the new designed plan got the uniform dose in the tumor and lower dose in the surrounding normal tissues.We know that in the clinical radiotherapy Spread Out Bragg Peak composed of a number of pristine Bragg curves are used to cover treatment tumors. In our simulation water phantoms with several thickness were used as a range modulator and the initial 130MeV protons were modulated to generate a SOBP. We used the above-mentioned designed plan and 5cm×5cm irradiation field to generate the SOBP and compared their lateral dose distribution. We found that new designed plan will compensate the dose on the edge of SOBP to some extent. But the dose compensation at different depth are not uniform. Dose of new designed plan is obviously lower in the front of SOBP and slightly lower in the back of SOBP compared with 5cmx5cm irradiation field. The integral dose of tumor area for new designed plan is lower than that of 5cmx5cm irradiation field. Outside the tumor the dose of new designed plan is obviously lower too.