Radical radiotherapy of localised prostate cancer: the relationship between radiation dose and survival

This retrospective study aims to define the effects of different radiation dose levels on survival, local control and toxicity in a series of 208 patients with localised prostate cancer consecutively treated with radical radiation therapy.

From 1982 through 1996, 365 patients with prostate cancer have been consecutively treated with radical radiotherapy in Florence (n = 306) and Arezzo (n = 59). The 208 cases treated until January 1994 with Stage B (125/208, 60%) and C (83/208, 40%) are the objects of the present study. The treatment was most often limited to the prostatic area (81%), using a four-field "box technique" and 25 MV photon beams, up to a total dose of 60-65 Gy (21% of the patients), of 66-69 Gy (26%) and of 70 Gy (53%); conventional fractionation was used (fractional dose: 2 Gy; five fractions/week). Hormonal therapy was also given to 39% of the cases. The possible relationship between dose, stage, grading and survival has been analysed. The survival figures and the types of relapse observed (prostatic, lymphnodal or "biochemical") have been analysed also according to the extent of the target volume and to the prostate-specific antigen (PSA) value at diagnosis, in the entire series or in selected subgroups.

In the whole series and also after radiation alone, the patients with Stage B, with more differentiated tumours and those treated with higher doses to the prostate obtained significantly better survival results. Multivariate analysis confirmed that the dose level has an independent prognostic value. The use of a limited target volume did not produce an excess of pelvic lymphnodal failures. Among the patients more recently treated with radiation alone, the PSA level at diagnosis is strongly related with the risk of local and "biochemical" failure, and also with the relapse-free survival. Toxicity was acceptable, also for the patients treated with higher doses, but late treatment-related damage is more frequent in patients treated on larger volumes.

The results of this retrospective analysis confirm the good results of small volume, high dose radiation therapy of prostatic cancer, even taking into account the possible biases due to the retrospective nature of the study, and the relevance of the PSA level at diagnosis to define the risk of local failure.