Protons vs IMRTSecondary radiation doses of intensity-modulated radiotherapy and proton beam therapy in patients with lung and liver cancer
Section snippets
Patient data and treatment planning
We randomly selected three patients with lung cancer and three patients with liver cancer who were to be treated with proton radiotherapy at our institution. All of these patients had undergone treatment planning CT scans (Picker CT-Simulator, UltraZ; Philips Medical System, Best, The Netherlands) of the chest, lower neck, and upper abdomen for identification of targets and normal neighboring organs. An Eclipse proton beam planning system (Varian Medical Systems, Palo Alto, CA) was used to plan
Results
Table 1 shows a comparison of secondary neutron doses with and without a phantom for three directions (A, B and C in Fig. 1) in patients with lung and liver cancer. The neutron dose measured by the type A detector was two or three times higher than the neutron dose measured by the type B and C detectors, indicating that more neutrons are parallel to the Z- than to the X or Y-direction and that the neutrons measured by type A detectors are primarily external neutrons coming from the treatment
Discussion
Utilizing CR-39 detectors, we measured neutron doses based on different orientations and estimated both the external and internal neutron doses at various distances from the isocenter. Our findings indicate that the secondary radiation dose using the scattering mode in proton therapy was lower than that observed using IMRT treatment and that the internal neutron dose from PBT is generally much less than the external neutron dose. These results show that secondary doses were dependent on the
Conclusion
We compared secondary neutron doses produced by proton radiotherapy using the scattering mode with the secondary photon dose from IMRT in lung and liver cancer patients. We found that the secondary dose depended on the distance from the isocenter and that the secondary neutron dose equivalent to the proton absorbed dose during proton therapy depended significantly on a neutron RBE factor. Our results also showed that the internal neutron dose from PBT is generally much lower than the external
Conflict of interest statement
There is no conflict of interest in connection with this work.
Acknowledgments
This work was supported by a research grant from the National Cancer Center, Korea (No. 0910180) and Nuclear Research and Development Program of National Research Foundation of Korea (NRF) funded by Ministry of Education, Science and Technology (MEST) (No. 20090071845).
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