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Background and Purpose: The individual dosimetry performed for a multicentre European cohort study of second malignant neoplasm following radiotherapy for a solid cancer in childhood demonstrated a large variation in the radiation doses estimated to any site., Materials and Methods: From this study we have extracted the present work, i.e. estimation of doses for patients who underwent radiotherapy for Hodgkin's disease in their childhood. These patients were treated using high energy X-rays from linear accelerators (MV group), gamma-radiation from Cobalt machines (Cobalt group), soft X-rays from orthovoltage machines (kV group) and electron beams from accelerators (MeV group) at six French and UK centres. All patients started their radiotherapy between 1955 and 1985 and about 12% of them received more than one beam quality. Most of the patients were irradiated with large mantle AP/PA or partial mantle fields. Patients with transdiaphragmatic extension were also irradiated using inverted-Y paraaortic fields. The absorbed doses at the 91 skeleton points are used to calculate the mean dose to the active bone marrow., Results: Estimates of the median and mean doses, standard deviations and ranges to 13 specific sites of the body and to the active bone marrow are reported. Depending upon the size and sex of patients, target volume and position and radiotherapy techniques, the estimated doses are highly spread, attaining 0.19-106.07% of the target dose. This study underscores the need for individual dosimetry in epidemiological studies. Comparison with the available measured and calculated doses to the ovary and testis shows good agreement., Conclusion: This study underscores the need for individual dosimetry in epidemiological studies.

The methodology we have developed to study dose distribution outside the target volume during external beam radiotherapy allows us to determine the dose received by the patient arising from leakage radiation and scattered radiation from both the head of the treatment machine and from the treatment room. It also allows us to evaluate the dose due to photon scattering in the patient by means of a dedicated 3-D algorithm permitting computations for the whole body of the patient and taking into account height, sex and anatomical data at the time of the treatment, dosimetric data and lung heterogeneity parameters. This methodology offers solid criteria for recommendations concerning radiation protection.

A true three-dimensional algorithm has been developed at the Gustave Roussy Institute, which can evaluate the dose distribution in inhomogeneous media. In this paper, an explanation is given that, in our view, problems of inhomogeneity cannot be solved without accounting for the third dimension and its contribution to scattered dose calculation.