Oscar Ardenfors1, Alexandru Dasu2, Jan Lillhök3, Linda Persson3, Irena Gudowska4. 1. Medical Radiation Physics, Department of Physics, Stockholm University, Box 260, 171 76 Stockholm, Sweden. Electronic address: oscar.ardenfors@fysik.su.se. 2. The Skandion Clinic, von Kraemers allé 26, 752 37 Uppsala, Sweden. 3. Swedish Radiation Safety Authority, Solna Strandväg 96, 171 16 Stockholm, Sweden. 4. Medical Radiation Physics, Department of Physics, Stockholm University, Box 260, 171 76 Stockholm, Sweden.
Abstract
PURPOSE: To determine out-of-field doses produced in proton pencil beam scanning (PBS) therapy using Monte Carlo simulations and to estimate the associated risk of radiation-induced second cancer from a brain tumor treatment. METHODS: Simulations of out-of-field absorbed doses were performed with MCNP6 and benchmarked against measurements with tissue-equivalent proportional counters (TEPC) for three irradiation setups: two irradiations of a water phantom using proton energies of 78-147 MeV and 177-223 MeV, and one brain tumor irradiation of a whole-body phantom. Out-of-field absorbed and equivalent doses to organs in a whole-body phantom following a brain tumor treatment were subsequently simulated and used to estimate the risk of radiation-induced cancer. Additionally, the contribution of absorbed dose originating from radiation produced in the nozzle was calculated from simulations. RESULTS: Out-of-field absorbed doses to the TEPC ranged from 0.4 to 135 µGy/Gy. The average deviation between simulations and measurements of the water phantom irradiations was about 17%. The absorbed dose contribution from radiation produced in the nozzle ranged between 0 and 70% of the total dose; the contribution was however small in absolute terms. The absorbed and equivalent doses to the organs ranged between 0.2 and 60 µGy/Gy and 0.5-151 µSv/Gy. The estimated lifetime risk of radiation-induced second cancer was approximately 0.01%. CONCLUSIONS: The agreement of out-of-field absorbed doses between measurements and simulations was good given the sources of uncertainties. Calculations of out-of-field organ doses following a brain tumor treatment indicated that proton PBS therapy of brain tumors is associated with a low risk of radiation-induced cancer.
PURPOSE: To determine out-of-field doses produced in proton pencil beam scanning (PBS) therapy using Monte Carlo simulations and to estimate the associated risk of radiation-induced second cancer from a brain tumor treatment. METHODS: Simulations of out-of-field absorbed doses were performed with MCNP6 and benchmarked against measurements with tissue-equivalent proportional counters (TEPC) for three irradiation setups: two irradiations of a water phantom using proton energies of 78-147 MeV and 177-223 MeV, and one brain tumor irradiation of a whole-body phantom. Out-of-field absorbed and equivalent doses to organs in a whole-body phantom following a brain tumor treatment were subsequently simulated and used to estimate the risk of radiation-induced cancer. Additionally, the contribution of absorbed dose originating from radiation produced in the nozzle was calculated from simulations. RESULTS: Out-of-field absorbed doses to the TEPC ranged from 0.4 to 135 µGy/Gy. The average deviation between simulations and measurements of the water phantom irradiations was about 17%. The absorbed dose contribution from radiation produced in the nozzle ranged between 0 and 70% of the total dose; the contribution was however small in absolute terms. The absorbed and equivalent doses to the organs ranged between 0.2 and 60 µGy/Gy and 0.5-151 µSv/Gy. The estimated lifetime risk of radiation-induced second cancer was approximately 0.01%. CONCLUSIONS: The agreement of out-of-field absorbed doses between measurements and simulations was good given the sources of uncertainties. Calculations of out-of-field organ doses following a brain tumor treatment indicated that proton PBS therapy of brain tumors is associated with a low risk of radiation-induced cancer.
Authors: Linda Eliasson; Jan Lillhök; Torbjörn Bäck; Robert Billnert-Maróti; Alexandru Dasu; Malgorzata Liszka Journal: Front Oncol Date: 2022-08-02 Impact factor: 5.738