Protons vs IMRT
Secondary radiation doses of intensity-modulated radiotherapy and proton beam therapy in patients with lung and liver cancer

https://doi.org/10.1016/j.radonc.2011.01.018Get rights and content

Abstract

Purpose

To compare the secondary radiation doses following intensity-modulated radiotherapy (IMRT) and proton beam therapy (PBT) in patients with lung and liver cancer.

Methods and materials

IMRT and PBT were planned for three lung cancer and three liver cancer patients. The treatment beams were delivered to phantoms and the corresponding secondary doses during irradiation were measured at various points 20–50 cm from the beam isocenter using ion chamber and CR-39 detectors for IMRT and PBT, respectively.

Results

The secondary dose per Gy (i.e., a treatment dose of 1 Gy) from PBT for lung and liver cancer, measured 20–50 cm from the isocenter, ranged from 0.17 to 0.086 mGy. The secondary dose per Gy from IMRT, however, ranged between 5.8 and 1.0 mGy, indicating that PBT is associated with a smaller dose of secondary radiation than IMRT. The internal neutron dose per Gy from PBT for lung and liver cancer, 20–50 cm from the isocenter, ranged from 0.03 to 0.008 mGy.

Conclusions

The secondary dose from PBT is less than or compatible to the secondary dose from conventional IMRT. The internal neutron dose generated by the interaction between protons and body material is generally much less than the external neutron dose from the treatment head.

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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