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Secondary neutron dose during proton therapy using spot scanning
Uwe Schneider1, Stefano Agosteo, Eros Pedroni
1Division of Medical Physics, Department of Radiation Oncology and Nuclear Medicine, City Hospital Triemli, CH-8063 Zürich, Switzerland. uwe.schneider@psi.ch
Summary
Secondary neutrons from proton radiotherapy are minimal with spot scanning. Neutron dose in healthy tissue is slightly higher than photon therapy but still very low, offering significant dose sparing benefits.
Area of Science:
- Medical Physics
- Radiation Oncology
- Nuclear Interactions
Background:
- Secondary neutrons are produced during proton radiotherapy.
- Neutron dose is often overlooked in treatment planning.
- Spot scanning proton therapy is an advanced treatment modality.
Purpose of the Study:
- To estimate neutron dose in patients during spot scanning proton therapy.
- To compare neutron dose from spot scanning vs. scatter foil techniques.
- To assess the clinical significance of neutron dose in proton radiotherapy.
Main Methods:
- Measurements using Bonner sphere and CR39 detectors in a water phantom.
- Monte Carlo simulations with the FLUKA code.
- Irradiation with 177-MeV protons.
Main Results:
- Spot scanning shows at least a 10-fold dose advantage over scatter foil techniques.
- Neutron dose equivalent at the Bragg peak is ~1% of the treatment dose.
- Neutron doses in healthy tissues are approximately 0.004 Sv and 0.002 Sv per Gy for large and medium volumes, respectively.
Conclusions:
- Neutron dose in the treatment region is negligible with spot scanning.
- Neutron dose in healthy tissue is slightly elevated compared to photon therapy but remains very low.
- Proton therapy offers substantial dose sparing benefits despite minimal neutron contributions.