The AAPM/RSNA physics tutorial for residents. X-ray attenuation.

Attenuation is the reduction of the intensity of an x-ray beam as it traverses matter. The reduction may be caused by absorption or by deflection (scatter) of photons from the beam and can be affected by different factors such as beam energy and atomic number of the absorber. An attenuation coefficient is a measure of the quantity of radiation attenuation by a given thickness of absorber. Linear and mass attenuation coefficients are the coefficients used most often. The equation I = Ioe-mu x expresses the exponential relationship between incident primary photons and transmitted photons for a monoenergetic beam with respect to the thickness of the absorber and thus may be used to calculate the attenuation by any thickness of material. The quality or penetrating ability of an x-ray beam is usually described by stating its half-value layer (HVL). Another parameter used to describe the penetrating ability of a beam is the homogeneity coefficient. Among other things, use of added filtration reduces the intensity of the x-ray beam, increases the HVL, decreases patient exposure, and improves image quality for a given radiation dose.

Study of radiation doses to personnel in a cardiac catheterization laboratory.

Radiation safety guidelines and federal regulations (10 CFR Part 20) require that radiation workers who are likely to receive above a certain percentage of the effective dose equivalent limit be monitored and that exposure be maintained as low as reasonably achievable (ALARA). With few exceptions in our hospital, the badges that exceed the Level 1 ALARA limits were worn by personnel in the Cardiology Division. The objective of this study was to determine the reasons for the high personnel dosimeter readings for staff in the cardiac catheterization laboratory and implement corrective measures to keep exposures ALARA. The physicians were double badged. The fluoroscopic time for each patient examination performed by each physician in the catheterization laboratory was tabulated and compared with the exposure on the dosimeters of the person performing the study. Education and retraining of cardiology staff concerning radiation protection and the use of state-of-the-art equipment are major considerations in reducing worker radiation exposure.

Data base management system for a radiation safety program.

A data base management system (DBMS) has been developed that simplifies the retrieval of data concerning radioisotope use at a university and hospital. The system customizes software that is commercially available to perform several functions. Reports can be developed concerning receipt of radioactive materials, radioactive waste disposal, and research proposals submitted by investigators. Reports can be prepared that utilize the software's ability to perform numerical calculations. The main advantage of the DBMS is that it allows the easy retrieval of information that is used in the day-to-day operation of a radiation safety office; it also provides easy access and manipulation of data for the preparation of reports, budget proposals, and justifications for purchases.

Hodgkin's disease, stages I and II: relationship of recurrence to size of disease, radiation dose, and number of sites involved.

A total of 57 patients with Hodgkin's disease limited to above the diaphragm (Stages I and II, A and B) were treated with radiation therapy alone at the University of Florida between 1964 and 1974. Staging laparotomy was done on 24 patients (42%). A total of 16 patients have relapsed, 4 within the treatment fields, 3 marginally, and 9 as extensions. Analysis of dose vs. size showed no in-field failure with disease less than 6 cm in size, with a range of doses. Massive disease continued to recur occasionally, even with higher doses. Most of the massive disease was mediastinal or hilar; the risk of lung or pleural involvement as determined by x-ray and/or biopsy showed a dramatic increase with size of mediastinal/hilar disease. Only 2 (5%) of 43 patients with mediastinal disease less than 6 cm in size had lung or pleural involvement, compared with 10 (71%) of 14 patients with disease greater than 6 cm in size. Both in-field recurrence and generalized relapse were closely related to the number of anatomical sites involved. Treatment programs need to consider tumor size, particularly in the mediastinum, and the number of sites involved.