J.M. Sisterson

Multiple Coulomb scattering of 160 MeV protons

Abstract We have measured multiple Coulomb scattering of 158.6 MeV protons in fourteen materials from beryllium to uranium including brass and several plastics. Targets ranged from thin (negligible energy loss) to very thick (greater than the mean proton range). The angular distribution was measured by means of a single diode dosimeter scanned typically over two decades of dose falloff. Each data set was fitted with a Moliere scattering distribution (using Bethes tables) to extract a characteristic angle θM as well as a Gaussian distribution to extract a characteristic angle θ0. As expected in the small angle region, the Gaussian fits about as well as the Moliere shape. The θM values were compared with Molieres predicted value ( χ c B 2 ) including Fanos correction for scattering by atomic electrons and using Molieres formalism to account for energy loss and/or compound targets or mixtures. The distribution of the deviation from theory for 115 independent measurements is approximately normal, with a mean value − 0.5 ± 0.4% and an rms spread of 5%. The θ0 values were compared with Highlands formula and with an “improved Highland” formula of Lynch and Dahl, using our own generalization to thick targets. The overall accuracy of Highlands formula is slightly worse than that of Moliere theory. The distribution of the deviation from theory for 115 independent measurements is normal, with a mean value − 2.6 ± 0.5% and an rms spread of 6%. The Lynch formula gives nearly the same average statistics though details of the fit are different. Some data were taken for very thick targets (thickness greater than 97% of the mean proton range) where only a fraction of the incident protons emerge. Here the characteristic angle appears to level off or even to fall slightly with target thickness perhaps due to the filtering out of large-angle protons. These measurements are presented but were excluded from the comparison with theory. We have reviewed six other published proton measurements, partially reanalyzing four whose authors claimed that Moliere theory either did not apply (because of thick targets) or was incorrect. These experiments range from 1 MeV to 200 GeV incident energy. Averaging each measurement including our own over everything but target material we obtain 39 independent measurements of the deviation from theory whose distribution is normal with a mean value − 0.3 ± 0.5% and an rms spread of 3%. We conclude that Moliere theory with the Fano correction is accurate to better than 1% on the average for protons. Systematic discrepancies on the order of a few percent with target thickness and/or target material cannot be ruled out at present. In particular there is some indication that the theory may be ≈ 4% high for the highest-Z materials.

Quantifying the diffusion kinetics and spatial distributions of radiogenic ^4He in minerals containing proton-induced ^3He

Apatite, titanite and olivine samples were bombarded with a ~ 150 MeV proton beam to produce ~ 10^8 atoms/mg of spallation ^3He. High-precision stepped-heating experiments were then performed in which the artificial ^3He and, for apatite and titanite, the natural radiogenic ^4He were measured to characterize the diffusive behavior of each isotope. Helium-3 diffusion coefficients are in excellent agreement with concurrently and/or previously determined He diffusion coefficients for each mineral. Our results indicate that proton-induced ^3He is uniformly distributed and that radiation damage associated with a proton fluence of ~ 5 x 10^(14) protons/cm^2 does not cause noticeable changes in ^4He diffusion behavior in at least apatite and titanite. Proton-induced ^3He can therefore be used to establish He diffusion coefficients in minerals with insufficient natural helium for analysis or those in which the natural ^4He distribution is inhomogeneous. In addition,step-heating ^4He/^3He analysis of a mineral with a uniform synthetic ^3He concentration provides a means by which a natural ^4He distribution can be determined.

Conservative treatment of uveal melanoma: probability of eye retention after proton treatment.

Enucleation was performed after proton treatment in 57 of 1006 (5.7%) uveal melanoma patients treated with proton beam therapy at the Harvard Cyclotron Laboratory between July 1975 and December 31, 1986. Only 2% of 99 patients with small tumors and 4% of 566 patients with intermediate size tumors underwent enucleation after treatment; 10% of 341 patients with large tumors lost the treated eye. No eyes were removed after 52 months, with 89% of enucleations performed during the first 36 months after treatment. Eye retention rates at 60 months were 89.1 +/- 3.0% for the entire group, and 97 +/- 3.7%, 92.7 +/- 3.1%, and 78.3 +/- 7.0% in patients with small, intermediate, and large tumors, respectively. Significantly greater enucleation rates were observed in patients with large tumors than in those with intermediate tumors (p = less than .0001), in patients with tumor height greater than 8 mm relative to those with tumors less than or equal to 8 mm, p = (less than .0001), with tumor diameter greater than 16 mm compared to less than or equal to 16 mm, (p = less than .0001), and with tumor involvement of the ciliary body compared to involvement of the choroid only (p = less than .0001). Possible strategies to decrease the likelihood of enucleation in patients at apparently increased risk of losing the eye after conservative therapy, that is, those with large tumors involving the ciliary body, might include a lower total dose, a more protracted treatment course, or a lower radiation dose and adjuvant treatment with chemotherapy and/or immunotherapy, with hyperthermia, or with other radiation sensitizers.

Proton beam penumbra: effects of separation between patient and beam modifying devices.

The sharp lateral penumbra of a proton beam is often used to spare sensitive normal structures in treating clinical sites in which the target volume abuts, or even wraps around, these structures. Using Monte Carlo calculations and measurements, the factors which influence the penumbra of the proton beam at the Harvard Cyclotron Laboratory were investigated, with particular emphasis on the effects of separation between the patient and any beam modifying devices. Penumbra broadening, characterized by the distance over which the dose rises from 20% to 80% of the central dose, increases with greater amounts of scatterer introduced into the beam line. The broadening due to separation of the beam modifying devices and the patient is essentially linear with increasing air gap; the rate of increase depends on the details of these devices and on the depth of interest in the patient. For a particular portal, most of the parameters which affect the penumbra width are fixed by the patients anatomy and the target volume. Only the thickness of the compensating bolus around the aperture edge and any air gap between the patient and the beam modifying devices can vary. Families of curves relating combinations of bolus thickness and air gap that maintain a constant penumbra width have been developed for guidelines during patient setup.

14C depth profiles in Apollo 15 and 17 cores and lunar rock 68815

Abstract Accelerator mass spectrometry (AMS) was used to measure the activity vs. depth profiles of 14 C produced by both solar cosmic rays (SCR) and galactic cosmic rays (GCR) in Apollo 15 lunar cores 15001-6 and 15008, Apollo 17 core 76001, and lunar rock 68815. Calculated GCR production rates are in good agreement with 14 C measurements at depths below ∼10 cm. Carbon-14 produced by solar protons was observed in the top few cm of the Apollo 15 cores and lunar rock 68815, with near-surface values as high as 66 dpm/kg in 68815. Only low levels of SCR-produced 14 C were observed in the Apollo 17 core 76001. New cross sections for production of 14 C by proton spallation on O, Si, Al, Mg, Fe, and Ni were measured using AMS. These cross sections are essential for the analysis of the measured 14 C depth profiles. The best fit to the activity-depth profiles for solar-proton-produced 14 C measured in the tops of both the Apollo 15 cores and 68815 was obtained for an exponential rigidity spectral shape R 0 of 110–115 MV and a 4π flux (J 10 , Ep > 10 MeV) of 103–108 protons/cm 2 /s. These values of R 0 are higher, indicating a harder rigidity, and the solar-proton fluxes are higher than those determined from 10 Be, 26 Al, and 53 Mn measurements.

MEASUREMENT OF PROTON PRODUCTION CROSS SECTIONS OF 10BE AND 26AL FROM ELEMENTS FOUND IN LUNAR ROCKS

Cosmic rays penetrate the lunar surface and interact with the lunar rocks to produce both radionuclides and stable nuclides. Production depth profiles for long-lived radionuclides produce in lunar rocks are measured using Accelerator Mass Spectrometry (AMS). For a particular radionuclide these production depth profiles can be interpreted to give an estimate for the solar proton flux over a time period characterized by the half life of the radionuclide under study. This analysis is possible if and only if all the cross sections for the interactions of all cosmic ray particles with all elements found in lunar rocks are well known. In practice, the most important cross sections needed are the proton production cross sections, because 98% of solar cosmic rays and {similar_to}87% of galactic cosmic rays are protons. The cross sections for the production of long-lived radionuclides were very difficult to measure before the development of AMS and only in recent years has significant progress been made in determining these essential cross sections. Oxygen and silicon are major constituents of lunar rocks. We have reported already {sup 14}C production cross sections from O and Si for proton energies 25-500 MeV, and O(p,x){sup 10}Be from 58 160 MeV[6]. Here we present new measurements for the cross sections O(p,x){sup 10}Be,O(p,x){sup 7}Be, Si(p,x){sup 7}Be,Si(p,x){sup 26}Al, and Si(p,x){sup 22}Na from {approximately}30 - 500 MeV.

The proton irradiation program at the Northeast Proton Therapy Center

The Harvard Cyclotron Laboratory (HCL) was closed on 1 July 2002. The successful transfer of the research and radiation effects testing program from HCL to the Northeast Proton Therapy Center is described.

Measurements and calculations of the influence of thin inhomogeneities on charged particle beams

The predictions of an analytic technique for calculating fluence and dose distributions beneath thin inhomogeneities are presented for a number of structures, including a rectangular cavity or bar, a cylinder, a disk, and an angled or diffuse edge. Experiments with both electrons and protons for several geometries are presented and compared with predictions based on this technique. We offer some clinical guidelines for avoiding large perturbations due to scattering effects.

The Influence of Thick Inhomogeneities on Charged Particle Beams

Monte Carlo calculations have been performed for charged particle beams incident on density discontinuities which extend for a substantial portion of the particle range. We present dose distributions for energy-modulated proton beams incident on long slivers of bone in tissue. The influence of sliver width and length, and of the angular divergence of the beam, is investigated. Comparable dose distributions are also presented for a pi-meson beam. The significance of the results is related to the problem of assessing the spatial resolution necessary in the measurement of densities in inhomogeneous media in order to guide charged particle radiotherapy.

Clinical use of protons and ion beams from a world-wide perspective

Abstract Proton and ion beams have been used at several centers, worldwide, to treat more than 9000 patients; in all cases accelerators originally designed for nuclear physics research have had to be adapted for this medical application. Now that good long term follow-up data are available, the need to develop specially designed accelerators and facilities dedicated to this form of treatment in a hospital setting is becoming urgent. The design and fabrication of both accelerator and beam delivery systems provide challenges for presently available technologies. Groups in several parts of the world are developing accelerator designs and complete facility designs using the resources available to them. Some of the special features found among them are small superconducting cyclotrons, proton synchrotrons, proton beam lines added to existing neutron therapy facilities and the development of gantries to transport proton beams at any desired angle to the patient.