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Induced radioactivity in patients from betatron irradiation

Brookhaven National Laboratory, Upton, New York 11973

J. Meltzer, M.D.

Nassau County Medical Center, State University College of Medicine at Stony Brook, East Meadow, New York 11554

B. E. Archambeau, M.D.

University of Chicago, Chicago, Illinois 60606

J. O. Archambeau, M.D.

City of Hope National Medical Center, Duarte, California 91010, USA

This excerpt was created in the absence of an abstract.

The nuclear binding energy averages 7–8 MeV per nucleon. If a nucleus is penetrated by a quantum of energy which exceeds this average binding energy, the nucleus may lose one or more of its nucleons. The residual nucleus may be radioactive. As early as 1949, induced radioactivity in tissue from a 24 MeV synchrotron was demonstrated by Mayneord et al. (1949). This induced radioactivity results from the nuclear photo-effect and accounts for less than 1% of the total energy absorbed from a bremsstrahlung spectrum whose average energy is 10 to 15 MeV (Joyet, 1965). Since this correlates with energy levels used clinically in betatron irradiation, the induced activity may be useful in clinical applications, including correlation of the activity distribution and ultimately the dose distribution with that prescribed by the clinician. A similar visualization procedure for a therapeutic proton beam has been demonstrated using an on-line positron camera (Bennett et al., 1978).

The 33 MeV Brown Boveri betatron at Montefiore Hospital and Medical Center was utilized for this research in a clinical setting. Patients already undergoing radiation with standard treatment fields and fractionation schedules of 200–300 cGy (rad) were randomly selected for measurements of induced radioactivity.

Immediately after treatment the patient was brought to an enclosed area adjacent to the betatron room. A sodium iodide crystal was positioned on each side of a movable bed on which the patient rested (Fig. 1).

Received for publication January 1, 1980. Revision received July 1, 1980.