Neutron-induced electronic failures around a high-energy linear accelerator
The CT-on-rails system examined in the current study: a 16-slice GE Lightspeed CT scanner and a Varian 2100 linear accelerator.
The accelerator head encased in 7.6-cm-thick rectangular slabs of borated polyethylene.
The cumulative probability of CT scanner failure as a function of the number of high-energy monitor units (MUs) delivered with the linear accelerator. Data are presented for the accelerator head with no shielding as well as for the accelerator encased in 2.7 and 7.6 cm of borated polyethylene shielding. The solid lines represent the best fits to the data based on Eq. (2). Error bars are included according to Eq. (1), assuming a binomial distribution in the 20 pass/fail measurements of each data point.
The neutron spectrum in the bore of the CT scanner with no shielding, 2.7 or 7.6 cm thick borated polyethylene shielding covering the accelerator head. Error bars denoting the statistical uncertainty in the calculated values are not included because they are approximately the thickness of the line (generally ).
The neutron spectrum in the bore of the CT scanner with 7.6-cm-thick borated polyethylene encasing the linear accelerator head or the CT scanner. Error bars denoting the statistical uncertainty in the calculated values are not included because they are approximately the thickness of the line (generally ).
The relative electronic failure rate as a function of the thickness of borated polyethylene shielding relative to no shielding. The relative failure rate of the CT-on-rails (squares) is compared to the relative neutron spectra/dosimetric properties: thermal fluence, total fluence, fast fluence, ambient dose equivalent , and kerma in silicon (Si kerma).
Neutron field properties at the treatment isocenter and in the bore of the CT scanner. Abbreviations: BPE, borated polyethylene; MU, monitor unit; , ambient dose equivalent; linac, linear accelerator.
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