Gross tumor volume and clinical target volume in prostate cancer: How do satellites relate to the index lesion

Purpose: There is an increasing interest for dose differentiation in prostate radiotherapy. The purpose of our study was to analyze the spatial distribution of tumor satellites inside the prostate.

Methods and materials: 61 prostatectomy specimens were stained with H&E. Tumor regions were delineated by the uro-pathologist. Volumes, distances and cell densities of all delineated tumor regions were measured and further analyzed.

Results: Multifocal disease was seen in 84% of the patients. The median number of tumor foci was 3. The median distance between the index lesion and the satellites was 1.0 cm, with a maximum of 4.4 cm. The index lesions accounted for 88% of the total tumor volume. The contribution of tumor foci<0.1 cm(3) to the total tumor volume was 2%. The median cell density of the index lesion and all satellites, regardless of size, were significantly higher than that of the prostate.

Conclusions: Satellites do not appear in a limited margin around the index lesion (GTV). Consequently, a fixed CTV margin would not effectively cover all satellites. Thus if the aim is to treat all tumor foci, the entire prostate gland should be considered CTV.