¹⁸F-fluorocholine PET-guided target volume delineation techniques for partial prostate re-irradiation in local recurrent prostate cancer

Abstract 

Background and purpose

We evaluate the contribution of ¹⁸F-choline PET/CT in the delineation of gross tumour volume (GTV) in local recurrent prostate cancer after initial irradiation using various PET image segmentation techniques.

Materials and methods

Seventeen patients with local-only recurrent prostate cancer (median=5.7years) after initial irradiation were included in the study. Rebiopsies were performed in 10 patients that confirmed the local recurrence. Following injection of 300MBq of ¹⁸F-fluorocholine, dynamic PET frames (3min each) were reconstructed from the list-mode acquisition. Five PET image segmentation techniques were used to delineate the ¹⁸F-choline-based GTVs. These included manual delineation of contours (GTV_man) by two teams consisting of a radiation oncologist and a nuclear medicine physician each, a fixed threshold of 40% and 50% of the maximum signal intensity (GTV_40% and GTV_50%), signal-to-background ratio-based adaptive thresholding (GTV_SBR), and a region growing (GTV_RG) algorithm. Geographic mismatches between the GTVs were also assessed using overlap analysis.

Results

Inter-observer variability for manual delineation of GTVs was high but not statistically significant (p=0.459). In addition, the volumes and shapes of GTVs delineated using semi-automated techniques were significantly higher than those of GTVs defined manually.

Conclusions

Semi-automated segmentation techniques for ¹⁸F-choline PET-guided GTV delineation resulted in substantially higher GTVs compared to manual delineation and might replace the latter for determination of recurrent prostate cancer for partial prostate re-irradiation. The selection of the most appropriate segmentation algorithm still needs to be determined.

Keywords: PET/CT, ¹⁸F-fluorocholine, Image segmentation, Gross tumour volume, Recurrent prostate cancer