Use of radiochromic dosimetry film for HDR brachytherapy quality assurance.

An important quality assurance (QA) procedure in high dose rate (HDR) remote afterloading brachytherapy is the verification of the system's control of the source by a direct test with dosimetry medium prior to the patient's first treatment. In this test radiochromic film is placed in direct contact with the applicator and the patient's proposed treatment is then run with their EPROM card. Examination of the film allows a quick appraisal of step size, number of steps, and offset. Advantages of this film include self-development so the image may be viewed immediately, insensitivity to normal room light, and archivability. The cost is about U.S. $2 per clinical case.

X-ray beam energy, scatter, and radiation risk in chest radiography.

Effective doses for patients undergoing chest radiography were computed utilizing updated weighting factors, published organ doses and measured entrance doses. The effective dose decreases with beam energy (kVp) and reaches a minimum value after 100 kVp, with values when a grid is used (6.90 microSv) being 145% higher at this energy than when no grid is used (2.82 microSv). The uncertainties associated with derivation of the tissue weighting factors are shown not to affect the point at which risk is minimized. Use of the effective dose as the measure of risk does not require special treatment of the remainder tissue as with use of effective dose equivalent. The effective dose required for radiographs of constant optical density was examined to incorporate the behavior of the detector's response to energy and compare results to previous work where exit dose was held constant. The effective dose at 120 kVp with a grid (6.84 microSv) is compared to an estimate of that associated with the current kVp distribution (14.55 microSv). Since image quality is enhanced by the grid, its use in conjunction with a beam energy of 120 kVp could maximize the benefit/risk ratio in chest radiography and should be considered for universal implementation. Such adoption could reduce the population risk compared to current practice.

A Clarkson's sector integration routine for personal computers.

A Clarkson's sector integration scheme has been implemented on a personal computer to calculate mean scatter-air ratio (SAR) and mean tissue-air ratio (TAR) for external photon beams of irregular shape. To find where a given radial line from the point of interest intersects the edge of the radiation field, polygon clipping algorithms have been adapted from the field of image processing. The program has calculation run times of approximately 1 s on an 80387 with a math coprocessor for an integration of 36 sectors. The software was validated by comparison to program IRREG, where for various squares and clinical shapes, the agreement was typically 0.7%. The source code is available from the authors.

Rare-earth scatter fractions in chest radiography.

A beam stop technique was used to measure the densitometric scatter fractions under three regions of a humanoid chest phantom utilizing LaOBr and Gd2O2S screens. For these receptors, the scatter fractions under the lung and retrocardiac areas were 13%-36% lower than published values for CaWO4. In the mediastinal area, there was no significant difference between the CaWO4 and rare-earth phosphors. The use of grids reduces the scatter fraction in all three regions by 40%-75%. With and without a grid, radiographic contrast with Gd2O2S was measured utilizing simulated lesions placed above the lung and retrocardiac areas.

Results of surgery and radiotherapy for early breast cancer.

Primary radiotherapy for 127 early breast cancers produced five-year local control of 96.1 percent and NED results of 81.1 percent. Results from a large community cancer center in New Jersey are comparable to results of major university cancer centers.

Mathematical aspects of a rotating point source with an application to megavoltage shielding.

This study developed the mathematics of a rotating point source. The relative dose and the dose rate were numerically evaluated at various positions along the cardinal axes, both with and without a 1-m-thick concrete barrier. The point source model was compared to experimental data gathered at an operational megavoltage radiation therapy facility.

Dosimetric aspects of a 3.3-MV linear accelerator.

Both the design considerations and the dosimetric properties of the Siemens Model 5800 linear accelerator are discussed. This unit is of such an energy (3.3 MV) as to imitate Cobalt-60 teletherapy depth doses. A linear relation of dmax to depth dose at low energies was found for various wave guides and targets. The energy of the unit can be characterized by its nominal accelerating potential of 2.70 MV, its d80 of 5.3 cm, its first half-value layer of 0.8 cm lead and the measured energy of the electron beam at 3.3 MeV. The following selected commissioning aspects are reported: central axis depth dose, relative output factors, beam profiles, wedge factors, virtual source position, back scatter factors, penumbra and build-up region.

The radiation phosphene.

A low flux of X-rays below the Cerenkov energy threshold generates a phosphene by direct action on the retina without a fluorescence in the ocular media. X-rays above the Cerenkov threshold can generate only a faint luminescence in the lens and cornea. From experimental work on humans in 1905 with unencapsulated radium, it is known that approximately 80% of the intensity of the radium phosphene is from the beta-ray component and approximately 20% from the gamma-ray. From calculations of the photon yield due to Cerenkov radiation in the eye from radium, one finds intensities of approximately 90% and approximately 10% for beta and gamma-rays, respectively, if only Cerenkov radiation is considered. Thus, one may conclude that the dominant mechanism of the radium phosphene is Cerenkov radiation, primarily from electrons and not fluorescence as previously speculated. The term "radium phosphene" is a misnomer and should be subsumed along with the X-ray phosphene and particle induced visual sensations under the name "radiation phosphene".

Observations of visual sensations produced by Cerenkov radiation from high-energy electrons.

Ten cancer patients whose eyes were therapeutically irradiated with 6-18 MeV electrons reported visual light sensations. Nine reported seeing blue light and one reported seeing white light. Controls reported seeing no light. Additionally, tests with patients ruled out the x-ray contamination of the electron beam as being important. The photon yield due to Cerenkov radiation produced by radium and its daughters for both electrons and gamma rays was calculated; it was found to account for a turn-of-the-century human observation of the "radium" phosphene. We conclude that the dominant mechanism of this phosphene is Cerenkov radiation, primarily from betas. From our own patient data, based on the color seen and the Cerenkov production rates, we conclude that the dominant mechanism is Cerenkov radiation and that high-energy electrons are an example of particle induced visual sensations.

A Monte Carlo computer model to investigate patient scheduling.

A Monte Carlo computer model was developed to investigate various types of patient appointment schedules for a single channel queue. Input parameters included the incidence of no-shows, the rate of unscheduled walk-ins, the frequency distribution of physician examination times, and the string of appointment times. The results included the frequency distributions of physician utilization rates and the total waiting time of all patients. Five hospital clinics were simulated. Even increment schedules yielded the best trade-off between physician utilization and patient waiting.