Time-Dose Relationships in Hodgkin's Disease

The concept of time-dose dependence in radiation therapy has received considerable attention in recent years. Some authors have concentrated on the clinical, qualitative approach; others, particularly Du Sault (2–4), have attacked the problem from an experimental, quantitative point of view. Radiotherapy has reached a level of sophistication today such that the mere prevention of normal tissue necrosis and increasing of the patient's systemic tolerance during treatment are only basic, preliminary problems. Increased understanding of radiobiology has opened new avenues of successful therapy in terms of dose rate, time intervals between treatments, and total time of irradiation. Time-dose relationships are also relative to the question of palliative irradiation. As radiotherapists, we desire a dose of radiation that will give maximum tumor response and/or patient relief in as short a time as possible; however, each case must be individualized. Though frequently the histology of the lesion may be the same in different patients, the total extent of tumor and the anticipated life expectancy will definitely affect the total tumor dose administered and the time that can sensibly be expended in its administration. Hodgkin's disease, because of its particular natural history and demonstrated radiosensitivity, offers interesting and challenging features to the radiotherapist. Many investigators no longer consider the disease invariably fatal, and treatment of Stage I Hodgkin's disease demands vigorous irradiation to enlarged regional fields with prolonged fractionation. At the other extreme, advanced disease generally requires smaller doses and shorter treatment periods. One important fact, however, must be considered. Even in advanced cases, where a progressive course of illness must be accepted, the radiotherapist must seek to deliver to each area under treatment a conclusive course. There is no reason, from the point of view of either the patient's comfort and therapeutic benefit or of the therapist's expenditure of energy, to have to re-treat areas already treated. Herein lies one of the paradoxes of a radiosensitive tumor. Very low doses can result in immediate tumor regression and apparent “cure” only to have disease reappear at the treatment site in a less radiosensitive state and in the presence of needed irradiation elsewhere. A time-dose guide giving us good flexibility of overall treatment time and total dose, potentially assuring a “cure” in localized disease and, at least, preventing local portal recurrence in advanced disease, would be helpful. Murphy (14) feels that a time-dose schedule should be rather loose, due to varying degrees of sensitivity of the disease. He is not specific as to quality of radiation employed, but states that 3,000 to 4,500 rads in nineteen to twenty-four days is appropriate for Stage I, 1,800 to 2,400 rads in sixteen to nineteen days for Stage II, and 1,200 to 1,800 rads in eight to twelve days for Stage III.