ABSTRACT
PURPOSE: To estimate the dose required to counteract accelerated proliferation, gamma/alpha, of medulloblastoma (MB) cells during fractionated radiotherapy. MATERIALS AND METHODS: Sixty-five patients with MB (local control rate at 5 years: 73%) treated between 1980 and 1990 at our university hospitals were analyzed. The gamma/alpha was estimated by applying the profile likelihood method to Cox's proportional hazards model including the maximum value of time-incorporated biologically effective dose, tBEDmax. The tBEDmax was conditionally calculated with various settings of alpha/beta, time to kick off accelerated proliferation, Tk, and gamma/alpha. Pretreatment T-stage, log(age+1), extent of removal, and use of chemotherapy and immunotherapy were also included in the multivariate model. RESULTS: When alpha/beta was taken to be 10 Gy, the estimate of gamma/alpha was 0.52 Gy/day (95% confidence limits: 0.29-0.75) for 0 day of Tk and was 0.55 Gy/day (0.30-0.80) for 21 days of Tk. The gamma/alpha values tended to be larger in the T3 subgroup and in the non-total removal subgroup than in all patients, by about 0.05 Gy/day and 0.1 Gy/day, respectively. When alpha/beta was taken to be 25 Gy, the estimated values were about 0.05 Gy/day smaller than these values. CONCLUSION: The estimated gamma/alpha values were considerably large. Therefore, it is preferable to take this consumed dose per day into consideration in planning and conducting treatments for MB.
Subject(s)
Cerebellar Neoplasms/radiotherapy , Medulloblastoma/radiotherapy , Dose Fractionation, Radiation , Female , Humans , Male , Proportional Hazards Models , Radiotherapy Planning, Computer-Assisted , Time FactorsABSTRACT
On a second mail survey (in 1984) concerning radiation-induced cancer following radiotherapy for benign diseases, 86 cases were collected from 95 hospitals in Japan. Adding these to 150 cases collected in the previous survey in 1979, 236 cases were accumulated. This is a report on the analysis of the 236 cases from a clinicopathological viewpoint. Underlying diseases consisted of cervical tuberculous lymphadenitis (125 cases), skin diseases (41 cases), benign thyroid diseases (19 cases), hemangioma (18 cases) and others (33 cases). Radiation-induced cancers, which were defined as cancers originating in the radiation field, including leukemia, consisted of hypopharyngeal cancer (68 cases), skin cancer (61 cases), laryngeal cancer (26 cases), esophageal cancer (23 cases), thyroid cancer (23 cases), salivary gland tumor (8 cases) and others (27 cases). Multiple primary cancers in the radiation field were observed in 7 cases. Average latent period was 28.9 years. It was demonstrated that the older the age at irradiation the shorter the latent period. Based on the population irradiated for benign diseases before 1977, which was collected in the first mail survey, incidence of radiation-induced cancers was estimated to be about 0.9%. The incidence varied with the period of radiotherapy; 1.9% for the period of radiotherapy before 1955, 0.4% for 1956-1965, 0.1% for 1966-1977. Although radiotherapy is now rarely indicated for benign diseases, it was shown in the first mail survey that more than 15,000 cases of benign diseases had been irradiated after 1956. It seems to be reasonable to consider that radiation-induced cancers after radiotherapy for benign diseases may continue to be discovered for several years in the future.
