Biomedical subjects
Publications and source records attributed to R A Shore.
We show that, for any function f in which Kleene's O is computable, the ordering of Turning degrees (i.e., degrees of difficulty of computation of functions) is not isomorphic to the ordering of degrees of functions from which f is computable. This refutes a well-known conjecture of H. Rogers, Jr., and others.
Monte Carlo calculations have been made to determine the energy delivered to a phantom by neutrons escaping from the head of a Varian Clinac 35 medical accelerator at an SSD of 1 m. The energy was sorted into two regions: inside and outside a volume defined by a circular beam of area 100 and 600 cm2. For the two beam sizes, the energies outside the treatment volume were 12 and 8.7 g-rad (per photon rad) respectively. Room scattering increased these values by about 20%. These energies are smaller than those delivered by scattered photons by more than ten times.
Monte Carlo calculations have been made to determine the energies delivered by photons and neutrons to the human body irradiated by collimated photon beams. The beams were monoenergetic and ranged from 100 keV to 40 MeV. The energy deposition in the body was sorted into two regions: inside and outside the irradiated volume. Most of the results obtained were for a beam size of 100 cm2 although some calculations were also made to 600 cm2 beams. The effect of beam size on energy deposition in the two regions was investigated for 60Co gamma rays. Graphs are presented which give the integral doses delivered by neutrons and photons to the two regions for therapy beams of various energies. These graphs can be used to calculate the integral doses which are delivered inside and outside the treatment volume for photon spectra from most medical accelerators. Calculations of energy deposition were also made for the spectra from two particular accelerators. These were done using Monte Carlo as well as by simply "folding" the spectra into the results for monoenergetic photons. The results obtained by both methods were in good agreement and indicated that the integral doses deposited outside the treatment volume by neutrons are more than two orders of magnitude smaller than those deposited by scattered photons.