Second primary tumors after radiotherapy for malignancies. Treatment-related parameters.

PURPOSE: The aim of the present analysis was to identify radiotherapy-related parameters that influence the development of second malignancies. PATIENTS AND METHODS: Between 1969 and 1989, about 31,000 patients were treated in Dresden with low voltage (< or = 180 kV X-rays) or telecobalt radiotherapy or a combination of both. Of these 203 were readmitted after earlier radiotherapy, for radiotherapy of a newly developed malignancy. Based on definitive diagnosis of a secondary tumor and completeness of documentation 53 patients were selected for further analysis. This included the spatial relation between the new tumor and the primary treatment fields, and the incidence in relation to the dose at the site of origin. The material does not allow for risk estimation.
RESULTS: Primary malignancies comprised breast and gynecological tumors in female, and tumors of prostate, head and neck and lymphomas in male patients. Second tumors developed mainly in corpus uteri, respiratory, gastrointestinal and urinary tract. The high incidence of 9.9% second primary corpus/cervix uteri tumors in patients with primary breast cancers suggests a common etiology. The majority of second tumors was observed within the margin of the planning target volume (PTV), which was defined as the volume 2.5 cm inside to 5 cm outside the field margin proper. Inside the PTV developed < 10%, outside 11% of the second tumors. With regard to dose the majority of second tumors was observed in the region receiving < 6 Gy.
CONCLUSIONS: A significant number of second primary tumors is found in the volume receiving < or = 6 Gy, i.e. at the margins of the PTV. This should be considered for multiple field radiotherapy and IMRT, where the relevant volumes may be substantially increased.