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

0167-8140/$ see front matter 2009 Elsevier Irelan doi:10.1016/j.radonc.2009.08.037 * Corresponding author. Address: Division of Nucle sity Hospital, CH-1211 Geneva 4, Switzerland. E-mail address: habib.zaidi@hcuge.ch (H. Zaidi). Background and purpose: We evaluate the contribution of F-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 = 5.7 years) after initial irradiation were included in the study. Rebiopsies were performed in 10 patients that confirmed the local recurrence. Following injection of 300 MBq of F-fluorocholine, dynamic PET frames (3 min each) were reconstructed from the list-mode acquisition. Five PET image segmentation techniques were used to delineate the F-choline-based GTVs. These included manual delineation of contours (GTVman) 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 (GTV40% and GTV50%), signal-to-background ratio-based adaptive thresholding (GTVSBR), and a region growing (GTVRG) 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 F-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. 2009 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 93 (2009) 220–225