H. G. Blosser

A superconducting cyclotron for neutron radiation therapy.

The physical and clinical specifications of a neutron therapy facility utilizing a superconducting cyclotron are presented. The cyclotron and its support system are described. Details of the operation of the cyclotron in a hospital environment are given; the requirements of the helium liquifier and cryogenic system are described together with a summary of its mode of operation. The simplicity of the cyclotron control system is discussed. The physical characteristics of the neutron beam are described. The central axis percent depth dose curve is equivalent to that of a 4 MV x-ray beam. The depth of maximum dose occurs at approximately 9 mm depth and the surface dose is between 40% and 45%. The multirod collimator allows for the production of irregularly shaped fields of size up to 26.5 x 30 cm, without excessive exposure to operating personnel.

The Michigan State University Superconducting Cyclotron Program

Status of the superconducting cyclotron program is reviewed as of September 1978. A number of design details have changed since the previous conference. Novel features have been checked in a variety of prototype test facilities.

Medical accelerator projects at Michigan State University

The authors report on three medical accelerator projects at Michigan State University. One involves construction of a 100-MeV superconducting cyclotron for neutron therapy. In the second, a conceptual design has been prepared for a 250-MeV superconducting synchrocyclotron for proton therapy. The third consists of preliminary studies of a compact 1600-MeV superconducting cyclotron system for heavy ion therapy.<<ETX>>

A multirod collimator for neutron therapy

PURPOSE To design, construct, and commission a multirod collimator for producing irregularly shaped fields in neutron radiation therapy. To demonstrate the reliability and applicability of this device to routine use with a superconducting cyclotron for neutron therapy. METHODS AND MATERIALS A multirod collimator has been designed, constructed, and thoroughly tested to investigate its radiological properties; neutron transmission characteristics, beam profiles, and penumbral widths as a function of field size and depth in a phantom, and the spatial resolution of the rod array, have been measured. A wide variety of irregularly shaped fields, used routinely in neutron radiation therapy, have been produced, including fields that incorporate partial transmission blocks. The performance of the collimator has been closely monitored over a period of 20 months to accurately assess reliability. RESULTS The multirod collimator has been in routine use for 32 months, and during this time a total of 7025 neutron fields has been treated. For the latter 20 months of this period, detailed performance records show that collimator failure has caused 28.4 h of downtime during the patient treatment day. Only 5.25 h of this downtime was experienced in the last 12 months (0.22% of the available treatment time). The results of collimator attenuation and beam profile measurements show that the radiological properties of the collimator are comparable to those of other collimator systems used for neutron radiation therapy. Isodose measurements in a water phantom show that the spatial resolution of the rods is superior to that of the leaves used in neutron multileaf collimators. The ability of the multirod collimator to produce many irregularly shaped fields commonly encountered in neutron radiation therapy has been demonstrated. Shaped fields for prostate, head and neck, soft tissue sarcomas, lung, thyroid, rectum, bladder, colon, breast, pancreas, and gynecological tumors have been produced. For some prostate cases, the device has been used to produce partial transmission blocks. CONCLUSIONS A novel multirod collimator has been designed, constructed, and successfully applied in the routine treatment of neutron radiation therapy patients.

Design Characteristics of the K=800 Superconducting Cyclotron at M.S.U.

Design work on the proposed K=800, KF= 400, superconducting cyclotron at MSU has progressed to the point where overall machine characteristics are firmly established. The main purpose1 of the machine is to serve as a booster for the K=500 cyclotron, now under construction. In this respect, let us recall that the design goal is to achieve maximum beam energies of 200 MeV/n for fully stripped light ions, and typically 30-40 MeV/n for heavy ions like uranium. Energy variability down to about 50 MeV/n and 4-5 MeV/n, again for light and heavy ions respectively, is also required to ensure some overlap with beam energies delivered by the K = 500 in stand-alone mode.

Focusing properties of superconducting cyclotron magnets

Abstract Superconducting main coils combined with conventional sectored iron pole tips constitute a promising design configuration for a new generation of compact, low-cost, heavy-ion cyclotrons. This paper gives results of focusing strength calculations for such cyclotrons for a variety of possible pole tips. The focusing is found to be highly sensitive to the average strength of the magnetic field, moderately sensitive to the magnet gap in the hills, and relatively independent of the number of sectors, the relative width of hill and valley and the magnet gap in the valleys. Spiraling of the magnet pole tips increases the focusing but substantially less than expected. Several of these properties are strikingly different from the corresponding properties of conventional low field magnets. The focusing limit of high field magnets leads to a linear dependence of the energy per nucleon on the charge-to-mass ratio of the ion over much of the operating range which contrasts with the usual quadratic dependence.

Synchrocyclotron Improvement Programs

A number of groups are engaged in improvement of synchrocyclotrons in order to increase beam current and improve extraction efficiency and beam precision. This paper reviews the major problems involved in such improvements and the solutions contemplated by the several groups. Goals are beams of 10?a or more with extraction efficiency of at least 50% and a tenfold gain in spatial and energy definition of the beams.

Compact Superconducting Cyclotrons for Neutron Therapy

A compact superconducting cyclotron is being constructed for use as a neutron based cancer therapy facility in a major Detroit hospital . The project involves a number of novel design solutions which are described in the paper.

Invited Paper Problems and Performance in the Cyclotron Central Region

A good central region yields a compact, dense, well-centered beam in a phase interval which will optimize the following acceleration and extraction processes. This paper reviews the role of various central region features in attaining desired beam properties. Results of careful calculations are shown to closely agree with observed beam properties.

Design Study for a Compact 200 MeV Cyclotron

A preliminary study has been carried out for a variable energy, 200 MeV cyclotron which is designed for both nuclear physics and medical research. The operational and structural features of this machine are modeled closely on our present 50 MeV cyclotron. The magnet would have the same gap, but twice the diameter (3m) and twice the number of trim coils (17), and it would have four (instead of three) sectors with sufficient additional spiral. The rf system would operate in the 10–20 MHz range, with two 90° dees carrying up to 70 kV. This cyclotron would produce protons at energies up to 200 MeV, and other ions to corresponding energies. By extending our present phase selection and single turn extraction techniques to this cyclotron, the energy resolution of the extracted beam would be: E/(ΔE)=7000. With proton currents of about 2 μA, the beam emittances would be 0.3 mm‐mrad radially and 2.5 mm‐mrad axially. The estimated cost of the cyclotron itself would be around two million dollars.