Principles of Supervoltage (2 Million Volts) Rotation Therapy

Abstract

The Efficiency of a particular form of radiation therapy is gauged by its ability to produce rather homogeneous dose distribution within the tumor region with minimal irradiation of the surrounding tissues. Supervoltage rotation therapy with 2 Mv x-rays has been found by Trump, Hare, and associates (1, 2) to produce efficient dose distributions. The principles and special advantages of supervoltage rotation therapy will be illustrated by the report of a case of chordoma of the body of the fourth lumbar vertebra. The therapeutic problem was to deliver a large tumor-lethal dose of radiation (approximately 7,000 r) to a deep-seated lesion which lay not only near the center of the torso but also close to the cauda equina. Case Report W. T. H., a white male aged 44 years, in June 1952 suddenly experienced sharp pain in the lumbar region and posterior right thigh, interfering with locomotion. Radiographic examination (Fig. 1) disclosed an osteolytic tumor of the anterior and right half of the body of the fourth lumbar vertebra. There was perforation of the cortex of the bone, with lateral extension of the disease into the soft tissues. On Sept. 4, 1952, through a right transverse flank incision, the vertebra was exposed retroperitoneally. A biopsy needle removed some grayish, jelly-like tissue, which was diagnosed histologically (by Dr. Henry L. Jaffe) as “chordoma” (Fig. 2). The therapeutic problem is illustrated in Figure 3. The tumor, measuring 4 cm. in diameter, lay 1 cm. from the cauda equina, the tolerance dose for which is 5,000 r in five to eight weeks. The anterior border of the tumor was 3 cm. from the intestines, whose tolerance dose is 4,500 r in a like period. It was deemed necessary, on the basis of our previous experience, to deliver to this tumor a dose of approximately 7,000 r. From Nov. 20, 1952, to Jan. 6, 1953, twenty-six x-ray treatments were given with a two-million-volt resonant transformer generator. With rotation technic, a tumor dose of 7,200 r was delivered in forty-seven days to a cylindrical volume of tissue measuring 6 cm. in diameter and 6 cm. high, which encompassed the tumor. The dose to the spinal cord ranged from 3,800 to 4,400 r. At the conclusion of treatment, the pain had disappeared. Radiographic examination one month later showed healing sclerosis of the lesion and restoration of normal contour of the body of the vertebra (Fig. 4). This remains unchanged to date (December 1954). There was no erythema of the skin and no evidence of spinal cord damage two years after irradiation. The therapeutic problems in the above case are typical of those which can be efficiently solved by means of supervoltage rotation therapy. Before describing the technic employed at the Hospital for Joint Diseases, let us consider the treatment of the above chordoma by other methods. Non-Rotation Treatment Technics