CT body scans obtained on 98 patients before, during, and after radiotherapy were evaluated for their utility in radiotherapy treatment planning and in follow-up after radiotherapy. Twenty-two patients were studied after irradiation. Four received additional treatment, and continuing or platlned treatment was withheld from another four on the basis of CT data. Tumor extent was clearly delineated on CT scan in 48/76 cases (63%), suggestive in 25/76 (33%), and not seen in only three (4%). Utilizing CT data relative to all other available tests, in 75 patients, total treatment volume was altered in 34 (45%), tumor coverage was marginal or inadequate in 35 (47%), and volume of normal tissue irradiated was changed in 34 (45%). CT scan data was judged essential for treatment planning in 41, or 55%, of patients studied. Unsuspected areas of tumor involvement were seen in 32 of 75 cases (43%). Use of the CT scan as a patient contour for radiotherapy treatment planning and alternative techniques for inputting the CT data to treatment planning computers are discussed. A simple inexpensive device to accomplish this is described. Speculations are made regarding the impact of CT scanners on transverse axial tomography units and treatment simulators as well as the potential application of the technique in brachytherapy dose computation.

The internal mammary area has been reviewed on CBT scans from 46 postmastectomy patients, and chest wall thicknesses computed there from the scan. Thicknesses ranged from 10 to 43 mm and 16 to 70 mm on the operated and nonoperated sides, and were weight-related in 38 modified mastectomy patients. Direct Cobalt and 15 MeV electron portals delivered 97-98% of the dose prescribed at 3 cm to a depth of 35 mm, the maximum average thickness on the operated side, while 12 and 10 MeV electrons gave 10 and 20% less at that depth. At 70 mm, underdosage with Cobalt and 15 MeV was 22% and 72%; insignificant doses were delivered with 10 and 12 MeV electrons. Routine determination of chest wall thickness is recommended in patients planned for electron beam treatment, in obese patients, and in patients treated with tangential photon techniques, to avoid underdosage to the internal mammary area. Internal mammary nodes were not routinely visualized, but abnormalities consistent with enlarged nodes were seen in six patients and gross recurrence in another.

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