EARLY CARCINOMA OF THE VOCAL CORDS

KILOVOLTAGE RESULTS; TELECOBALT 60 DOSIMETRY (A PRELIMINARY REPORT)

¹ Chief, Radiotherapy Section, Veterans Administration Hospital, Long Beach, California and Clinical Professor (Radiology), University of California at Los Angeles, School of Medicine.
² Chief, Radiological Physics Section, Veterans Administration Hospital, Long Beach, California and Clinical Instructor, Department of Radiological Sciences, University of California at Irvine, School of Medicine.
³ Professor of Radiology and Chief, Division of Radiation Therapy, University of California at Los Angeles, School of Medicine.

1. Kilovoltage therapy of 32 consecutive cases of carcinoma limited to one or both vocal cords, with no impairment of mobility, has resulted in the gross 4 year survival without disease of 88 per cent of the cases.

2. The field size description for telecobalt 60 units, although clearly set forth by the ICRU, may present the radiation therapist with unique difficulties. If one is to irradiate the volume of interest to within 90% of a desired dose, the location of the 90% isodose line becomes critical.

3. The width of a nominal field (usually measured at the 50% isodose line as recommended by the ICRU) and the width of a dosimetric field that is measured at the 90% isodose line may differ by more than 3 cm. for a small field. Therefore records of field size might give both the nominal and the dosimetric field size for each telecobalt 60 unit.

4. Clinically, it appears desirable to measure telecobalt 60 fields for vocal cord cancer at the 90% isodose line. We prefer a 5 cm.x5 cm. dosimetric field, at the 90% line.

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