William E. Powers

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.

Bone metastasis from cervical cancer

Background. This retrospective analysis examines the frequency, distribution, and the pattern of disease progression of bone metastasis in patients treated for cervical cancer and the use and results of palliative intent radiation therapy.

Epidural spinal cord compression from metastatic tumor: diagnosis and guidelines for management

Epidural spinal cord compression from metastatic tumors occurs in approximately 5% of cancer patients studied in autopsy series (1). This translated to 18,000 cases annually in the U.S.A. when the cancer death rate was 365,000 cases per year but the number of cases with spinal cord compression is now estimated to be about 25,000 cases per year of the annual 502,000 cancer deaths (5). M oreover, the number ofpatients with this complication is expected to increase because of the advances in cancer treatment that result in increased survival and chronic problems not previously prevalent. Cauda equina compression is included in the discussion since there is no difference in treatment outcome, whether the compression is on the cord or the cauda equina once neurological deficits develop (10, 20). The treatment of epidural spinal cord compression has been relatively unsatisfactory thus far since only approximately one half of patients regain or maintain the ability to walk ( 1). This is due to delayed diagnosis, the lack of clearly established criteria to select treatment modalities, the very limited healing capacity of the injured spinal cord, and the relatively poor local control rate of tumors that produce such injury. With recognition of the markedly diminished quality of life in patients who fail to recover neurologic function, there is an urgent need to re-evaluate the current medical management strategy of this group of patients. The vertebral column is the most common location for metastases to bone from various primary tumor sites because it contains red marrow with extensive circulation including that from Batson’s venous plexus. Metastatic disease is the most common spinal neoplasm (32). The most common primary tumors metastasizing to or involving the spine are lung, breast, prostate, kidney, and hematologic malignancies in decreasing order of frequencies (IO, 15, 21). However, if one considers the tendency for specific malignancies to metastasize to the spine or the epidural space, then multiple myeloma, prostate cancer and renal cell carcinoma seem to have a higher propensity for such metastases than lung cancer, breast cancer or lymphoma ( 15). The primary site of malignancy remains unidentified in approximately 9% of the cases with epidural cord compression. Another 8% of the patients have spinal metastasis as the initial presentation of their malignancy.

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.

Carcinoma of the uterine cervix: The patterns of care study process survey

Abstract The Patterns of Care Study is currently investigating the management of patients with carcinoma of the cervix. This unique effort has required the development of a new method by which patients who have similar extent of disease are grouped. Patterns of care, for patients with similar disease, should be similar. Results indicate that there is substantial variation in care nationwide. The impact of this variation on outcome can provide the basis of educational efforts to improve the quality of patient care.

RBE variation between fast neutron beams as a function of energy. Intercomparison involving 7 neutrontherapy facilities.

In fast neutron therapy, the relative biological effectiveness (RBE) of a given beam varies to a large extent with the neutron energy spectrum. This spectrum depends primarily on the energy of the incident particles and on the nuclear reaction used for neutron production. However, it also depends on other factors which are specific to the local facility, eg, target, collimation system, etc. Therefore direct radiobiological intercomparisons are justified. The present paper reports the results of an intercomparison performed at seven neutrontherapy centres: Orléans, France (p(34)+Be), Riyadh, Saudi Arabia (p(26)+Be), Ghent, Belgium (d(14.5)+Be), Faure, South Africa (p(66)+Be), Detroit, USA (d(48)+Be), Nice, France (p(65)+Be) and Louvain-la-Neuve, Belgium (p(65)+Be). The selected radiobiological system was intestinal crypt regeneration in mice after single fraction irradiation. The observed RBE values (ref cobalt-60 gamma-rays) were 1.79 +/- 0.10, 1.84 +/- 0.07, 2.24 +/- 0.11, 1.55 +/- 0.04, 1.51 +/- 0.03, 1.50 +/- 0.04 and 1.52 +/- 0.04, respectively. When machine availability permitted, additional factors were studied: two vs one fraction (Ghent, Louvain-la-Neuve), dose rate (Detroit), influence of depth in phantom (Faure, Detroit, Nice, Louvain-la-Neuve). In addition, at Orléans and Ghent, RBEs were also determined for LD50 at 6 days after selective abdominal irradiation and were found to be equal to the RBEs for crypt regeneration. The radiobiological intercomparisons were always combined with direct dosimetric intercomparisons and, when possible in some centres, with microdosimetric investigations.

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.

Variation in work-up and treatment procedures among types of radiation therapy facilities: the patterns of care process survey for three head and neck sites.

The PCS Process Survey analyzed radiation therapy facilities to evaluate procedures in work‐up and treatment of patients with cancer of the larynx, tongue, and nasopharynx. Types of facilities are compared to establish bench marks in performance of work‐up and treatment procedures that can be used as a foundation for upgrading care and for adjusting studies to follow this paper. A statistical method is demonstrated that provides a “signature” of relative performance over a standardized set of procedural criteria. Facilities with resident training programs perform nearly all of these procedures much more consistently than do nontraining facilities. Facilities with full‐time head therapists perform most procedures more consistently than do facilities with part‐time heads. A third comparison of large versus small facilities shows that among training facilities size has no effect and that among full‐time facilities size has a slight effect. Among part‐time facilities, however, smaller ones fail to perform most procedures more often than larger facilities. The size difference is confounded with the full‐time/part‐time difference because part‐time facilities are on the average smaller than facilities with full‐time head therapists.

Radiological properties of a prototype multi‐rod collimator for producing irregular fields in photon radiation therapy

A prototype multi-rod collimator for producing irregular fields in photon radiation therapy has been designed and built. The mechanical details of the design and operation of the multi-rod collimator are discussed. Beam profiles for an approximately 10 x 10 cm2 field have been measured at various depths in phantom, and compared with profiles obtained using the secondary collimator jaws alone and with cast metal blocks. The ability of the collimator to produce irregular fields is demonstrated with reference to some commonly encountered therapy fields and the ability to produce central blocks and island blocks is discussed. Isodose curves for selected irregular fields are presented.

Transmission measurements in multi-rod arrays: a design study for a multi-rod collimator

The results of transmission measurements for neutrons, cobalt-60 gamma-rays, and 10 and 15 MV photons made with close-packed arrays of tungsten rods are presented. These results indicate that tungsten rod arrays of reasonable thickness can provide for primary or secondary collimation of all these radiation beams. Development work on a collimation system utilizing the multi-rod concept which is capable of producing irregularly shaped fields and suitable for use in photon or neutron radiation therapy is described.