Long-term use of an isotope check source for verification of ion chamber calibration.

A radioactive check source is recommended for operational and constancy checks of dosimetry systems used for the calibration of therapeutic x-ray generators, including linear accelerators. Eight years of data have been analyzed for two ion chambers (and their associated electrometers) irradiated at fixed geometry in such a device. These dosimetry systems have also been calibrated every 2 years at a single Accredited Dosimetry Calibration Laboratory. Our analysis suggests that when a check source is used, and the results are consistent, the interval between formal calibrations can be lengthened.

Cerebral metastases: value of reirradiation in selected patients.

Fifty-two adult patients were selected to receive a second course of cranial radiation therapy to relieve symptoms caused by recurrent cerebral metastases. To be selected, patients had to (a) have remained in relatively good general condition for at least 4 months after their initial course of radiation therapy and (b) experience renewed deterioration of their neurologic condition. Initial treatment typically consisted of 3,000 cGy administered in 10 fractions over 2 weeks to the whole brain. Reirradiation most commonly consisted of 2,500 cGy in 10 fractions. Twenty-two patients (42%) responded to reirradiation and improved by at least one level in their neurologic function status. Survival after second therapy averaged 5 months. The authors conclude that reirradiation of cerebral metastases should be considered for patients who remain in good general condition but who experience neurologic deterioration 4 or more months after satisfactory response to initial palliative cerebral radiation therapy.

Analysis of multiple prognostic factors in patients with stage IB cervical cancer: age as a major determinant.

To evaluate the prognostic importance of age in patients with Stage IB cervical cancer we reviewed the results of 131 patients treated between 1974 and 1985. Patients ranged in age from 25 to 87 (mean 48) and were followed for a median of 65 months. One hundred twenty-five patients had complete follow-up information for survival analysis. Patients were divided into two groups; Group A comprising 43 patients less than or equal to age 40 and Group B comprising 88 patients greater than age 40. Both Group A and Group B patients were comparable with respect to all covariables studied. The 5-year actuarial survival for the 125 patients studied was 80%, whereas that for Group A (42 patients) and Group B (83 patients) was 54% and 91%, respectively (p = .0001). The 5-year survival for 100 surgical patients was 79% and that for Group A (36 patients) and Group B (64 patients) was 53% and 90%, respectively (p = .0001). The 5-year survival for 25 patients treated with curative RT was 65% and that for Group A (six patients) and Group B (19 patients) was 42% and 90%, respectively (p = .005). Eighteen patients were treated with adjuvant RT following surgery and their 5-year survival was 69% with three out of nine Group A and nine out of nine Group B patients alive at 65 months (p = .004). In 18 patients with pelvic nodal involvement, the 5-year survival was 48% compared to 84% in patients with negative nodes (p = .007). The difference in survival at 5 years between Group A (nine patients) and Group B (nine patients) with positive nodes was 25% and 75%, respectively. Finally, there was an increase in both local and distant failure in Group A patients. Our data illustrate that age has a profound influence on survival in women with Stage IB cervical cancer independent of potentially confounding variables.

The prognostic significance of residual pigmentation following radiotherapy of epidemic Kaposi's sarcoma.

The response to radiotherapy of epidemic Kaposi's sarcoma (EKS) is unusual in that irradiated regions are frequently left with a persistent purple stain, reminiscent of the color of the original tumor, but with no tumor mass. To date there are no published data to indicate whether the persistence of pigmentation can be predicted beforehand or if it has any prognostic import. We reviewed the response to treatment of 118 EKS lesions that were irradiated at New York University (NYU) Medical Center between 1981 and 1986. A total of 86 responded to treatment by complete clearance of the mass. Of these, 29 left residual purple pigmentation within the treatment portal, while 57 did not. Complete response (CR; without residual pigmentation) occurred more often in patients who had higher Karnofsky scores at the time of treatment. However, in terms of ultimate local control or survival, there were no differences between patients whose lesions cleared completely v those in whom pigmentation remained. We conclude that persistent pigmentation represents only a benign remnant of irradiated EKS and has no prognostic import.

Radiofrequency hyperthermia: the design of coil transducers for local heating.

Simple and complex coils have been designed and built for use as radiofrequency transducers for local and regional hyperthermia. The heating from such coils is produced by currents generated in the dielectric by the electromagnetic field radiated from the coil elements. The heating rate profile, as a function of phantom depth, is dependent upon the size and geometry of the coil, its proximity to the dielectric, and the transducer current. Since the fields of simple pancake coils are inhomogeneous, either complex geometries or some method of smoothing is required. A simple solution is to move the coil over the region to be heated or to use multiple applicators. However, many satisfactory heating patterns have been derived for stationary coils designed to heat well-defined subcutaneous volumes to a depth of 3-5 cm. Thermometry studies in static saline-gelatin phantoms demonstrate extensive heating ranges and flexibility since the coils couple with the dielectric through air.

Postoperative irradiation of pterygia: an unexpected effect of the time/dose relationship.

Factors which might determine the outcome of treatment of pterygia were examined. Unexpectedly, patients beginning radiation therapy greater than or equal to 4 days after surgery exhibited fewer recurrences than those irradiated within 3 days of surgery. This finding raises questions about the mechanism and method of postoperative irradiation in this condition.

Adjustable compensators for whole-brain irradiation.

A compensator for use in irradiating the whole brain with parellel opposed lateral fields was made from a stack of thin tempered aluminum plates. This configuration gives a wide latitude of degrees of compensation and can accommodate a broad range of head sizes. Dosimetry studies indicate that overcompensation may be desirable to reduce the dose to the mid-coronal plane of the skull and scalp without seriously affecting the dose uniformity in the treatment volume.

Development of optical process for accessing three-dimensional patient topology.

A commercial optical system developed by Solid Photography, Inc., has been used to generate precise paraffin--polyethylene tissue compensators. A program with the objective of constructing a medical facility has been undertaken to access patient topology for treatment planning, tissue-compensator fabrication, and patient positioning verification on the treatment table. Currently, patients are taken to a specially equipped studio where a series of microprocessor-controlled reticles are projected on the surface to be analyzed and photographs are taken automatically for computer processing. The topology data then drives a machine tool to sculpt the tissue compensators and may be transmitted via acoustic-coupled terminals to a treatment-planning computer at the Medical Center. The tissue compensators have been found to conform accurately to patient contours. At present, data bases can be generated to accommodate volumes of approximately 70,000 cm3.

Patient immobilization with a low-temperature splint/brace material.

The authors describe a low-temperature plastic which is useful for the construction of immobilizing devices where beam orientation is critical.

Extended expression for tissue-maximum ratio fitted to the Varian Clinac-4 and Clinac-6 accelerators.

An expression which generates tissue maximum ratio (TMR) data for the Varian Clinac-4 and Clinac-6 accelerators is presented. This semiempirical expression can be programmed easily for radiotherapy computer systems or the new generation of scientific calculators. Our technique leads to good agreement with the published data, as demonstrated by a total average percent deviation of the measured TMR values of -0.115% for the Clinac-4 and -0.002% for the Clinac-6.

Steel trimmer for use with 60Co tangential fields.

A prototype steel trimmer provided by Atomic Energy of Canada Limited was modified for use with tangenital wedged 60Co fields. The trimmer virtually eliminated the penumbra of the wedged fields, permitting a more uniform irradiation of the chest wall. There was no significant change in the wedge transmission factors for the trimmed and untrimmed fields.