J. N. Bradbury

Computed tomography using proton energy loss

An experiment has been performed to demonstrate the feasibility of proton computed tomography. The proton energy loss was used to measure the projections of the relative stopping power of the phantom. High quality reconstructions were obtained from scans of 19 cm and 30 cm diameter performance phantoms. Comparison with reconstructions from an EMI CT-5005 X-ray scanner showed the proton technique is more dose efficient by a large factor.

Proton computed tomography of human specimens

The experimental procedure and results of a comparative study of the imaging characteristics of proton and X-ray CT scans are presented. Scans of a human brain and heart are discussed. The proton produced images are found to be similar in information content while providing a decided dose advantage.

Tuning of the First Section of the Biomedical Channel at LAMPF

Results are presented from the tuning of the first section of the Biomedical Channel at LAMPF; the work centers about the use of the third bending magnet as a magnetic spectrometer. The momentum resolution at the intermediate focus is given in detail. The performance of a wedge degrader that compresses the wide momentum acceptance of the first section is discussed. The output ¿- rate is also given.

Dosimetry of pion therapy beams.

Cellular, animal, and human radiobiology studies are in progress at the Los Alamos Meson Physics Facility as part of a joint University of New Mexico and Los Alamos Scientific Laboratory pion therapy project. To support these activities, dosimetry has been performed on many different pion beam configurations. The effect of both static and dynamic momentum spreaders and of collimators on beam profiles, depth-dose distributions, and peak-to-plateau ratios have been studied. The absorbed dose is obtained by the application of Bragg-Gray cavity theory to ionization chamber measurements. Calculations have been made for the effective W values and average mass-stopping-power ratios needed for the Bragg-Gray equation. Kerma corrections are applied to transform the dose from the chamber wall to dose in muscle.

Dose outside the treatment volume for irradiation with negative pions

Irradiation of humans with negative pions requires a knowledge of the absorbed dose and radiation quality outside the primary pion beam. In conjunction with early clinical trials at LAMPF, experimental data have been obtained with microdosimetric techniques and multiwire proportional counters. Theoretical calculations have been made for the neutron contribution to the dose and are consistent with these data. Measurements were made with in 40 cm x 51 cm x 76 cm water phantom for a negative pion beam of initial momentum of 170 MeV/c, deltap = +/- 3MeV/c. The absorbed dose outside the treatment volume is the result of: (1) neutrons and photons from the pion interactions,(2) treatment room background and (3) peripheral muons, electrons and pions in the primary beam. The first two components are nearly isotropic and are congruent to 0.02% of the peak dose at a distance of 24 cm from the treatment volume; the third component is anisotropic and varies from 0.01 to 0.1% of the peak dose. Collimation of the bean increases the dose outside the treatment volume typically by 50%.

Current status of clinical pion radiotherapy.

An RBE for acute skin reaction to peak pions, for a specific fractionation scheme, has been established at 1.40-1.44. The time of development of acute skin reactions varied in 2 patients with 30 metastatic skin nodules treated with doses varying from 1,175 to 1,951 peak pions and 2,350 to 3,901 rads of 100 kVp x rays. The reactions reached their peak approximately one week apart at all dose levels with both forms of radiation. No untoward effects have been seen in epidermis or subcutaneous tissues as late as 169 days after the start of treatment. All nodules disappeared and have not returned 169 days after treatment. There is a strong suggestion that the response of thick tumors is sensitive to the proportion of high LET radiation deposited at various levels in the tumor.

Tuning the Beam Shaping Section of the LAMPF Biomedical Channel

The Biomedical Channel at LAMPF is used for radiotherapy with negative pi mesons. A discussion is given of the transport properties of the beam-shaping section of the channel. Large emittance beams produced by the first section are matched to specific output requirements by tuning the last five quadrupole magnets using a combination of measurements and calculations.

Characterization of the radiation environment at a new proposed irradiation facility at LAMPF

A new irradiation facility is being planned at the Clinton P. Anderson Meson Physics Facility (LAMPF). Irradiations will be possible both in the direct proton beam (∼760 MeV) and in a spallation neutron flux generated at the LAMPF beam stop area. As an aid in the design of the facility and an aid to potential experimenters, the radiation environment expected in this area was characterized by calculation. The Monte Carlo Code for the Transport of Neutrons and Photons (MCNP) and the High-Energy Transport Code (HETC) were employed to calculate the flux and energy spectrum of neutrons, protons, pions, muons, and photons generated by 760-MeV protons incident on components along the beam line in the Target Station A-6 area. In the direct proton beam a current density of 20 μA/cm2 can be realized. The maximum total neutron flux outside the beam line between 1 eV and 800 MeV was determined as 4.9 × 1013 neutrons cm−2 s−1 (± 2.2%). The calculated spallation neutron spectrum resembles a fission spectrum with the addition of substantial numbers of higher energy (⩾ 1 MeV) neutrons. The maximum secondary proton flux was calculated as 1.18 × 1012 protons cm−2 s−1 (± 3.2%). The maximum pion, muon, and photon fluxes along the beam line were calculated to be 5.68 × 1010 π+ cm−2s−1 (± 14.4%), 8.21 × 108μ+ cm−2s−1 (± 51.5%), and 1.4 × 1013 photons cm−2s−1 (± 8%), respectively. Additionally, calculations were done that predict transmutation product generation in a variety of materials including a ferritic stainless steel. These products, most notably He, have been identified as being effective in determining microstructural evolution of materials under high-energy neutron (14-MeV) irradiation as is present in fusion reactors. It is felt that this new facility will be useful in the study of material for fusion applications.

Pion Beam Development for the LAMPF Biomedical Project

Common to both static and dynamic patient irradiations at the LAMPF linac is the problem of maintaining good quality control of beams form a secondary channel. A major contributor to therapy beam variation has been change in electron contamination due to the change in target geometry and proton beam steering. The electron variation problem is described and a solution is presented that has been realized as a result o a new target geometry that allows some control of the electron fraction. (GHT)

An automated dosimetry data-acquisition and analysis system at the LAMPF pion therapy facility.

An automated data-acquisition and analysis system has been developed for dosimetry measurements on the pion therapy beam at the Clinton P. Anderson Meson Physics Facility Biomedical Channel in Los Alamos using a PDP-11/45 computer and CAMAC interface. Initialization, test, and monitor programs allow the user to set the physical limits of scanner travel, test the data lines, calibrate the analog signals for the scanner position, and monitor the analog versus digital values of the scanner position during operation. Data-acquisition programs scan beams in one, two, and three dimensions. Many options are available to the user in selecting the scan parameters and in changing some of these parameters during scanning. Data-analysis programs provide reproduction of stored data, comparison of linear scans, beam profiles along any line of a planar or volume scan, and isodose distributions from any planar scan or from any planar scan or from any plane of a volume scan. Other programs summarize stored data files and search for specific data according to the users instruments.