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Energy spectra, sources, and shielding considerations for neutrons generated by a flattening filter‐free Clinac
Author(s) -
Kry Stephen F.,
Howell Rebecca M.,
Titt Uwe,
Salehpour Mohammad,
Mohan Radhe,
Vassiliev Oleg N.
Publication year - 2008
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2905029
Subject(s) - electromagnetic shielding , dosimetry , neutron , spectral line , flattening , energy (signal processing) , physics , nuclear physics , radiation protection , optics , medical physics , nuclear medicine , medicine , quantum mechanics , astronomy
Neutron production is an unwanted result of high‐energy radiation therapy and results in secondary exposure of patients and radiation therapists to radiation. Recent studies have shown that delivering therapy using a standard medical accelerator with the flattening filter removed may reduce neutron fluence by nearly 70% over the course of prostate intensity‐modulated radiation therapy (IMRT). In the current study, theA197 u Bonner sphere technique was used to compare the neutron spectrum produced when the filter is present and when it is absent. In addition, the following was calculated: (1) the neutron‐shielding parameters of source strength and ambient dose equivalent( H 0 )and (2) using the Monte Carlo technique, the sources of neutron production in the accelerator head. It was found that the neutron spectrum was nearly constant, regardless of the presence of the flattening filter; however, the total fluence and ambient dose equivalent over the course of prostate IMRT were more than 70% lower when the filter was removed. Similarly, shielding parameters were lower when the filter was removed. Finally, the primary collimator and jaws accounted for the majority of neutron production, both with and without the flattening filter; however, with the flattening filter removed, the upper jaw accounted for much more neutron production relative to when the filter was present. Ultimately, removal of the flattening filter may offer several clinical advantages, including a reduction in the dose from neutrons to the patient and to radiation personnel.