Image Guided Planning for Prostate Carcinomas With Incorporation of Anti-3-[18F]FACBC (Fluciclovine) Positron Emission Tomography: Workflow and Initial Findings From a Randomized Trial

Abstract

Purpose: (18)F-Fluciclovine (anti-1-amino-3-[(18)F]fluorocyclobutane-1-carboxylic acid) is a novel positron emission tomography (PET)/computed tomography (CT) radiotracer that has demonstrated utility for detection of prostate cancer. Our goal is to report the initial results from a randomized controlled trial of the integration of (18)F-fluciclovine PET-CT into treatment planning for defining prostate bed and lymph node target volumes.

Methods and materials: We report our initial findings from a cohort of 41 patients, of the first enrolled on a randomized controlled trial, who were randomized to the (18)F-fluciclovine arm. All patients underwent (18)F-fluciclovine PET-CT for the detection of metabolic abnormalities and high-resolution CT for treatment planning. The 2 datasets were registered first by use of a rigid registration. If soft tissue displacement was observable, the rigid registration was improved with a deformable registration. Each (18)F-fluciclovine abnormality was segmented as a percentage of the maximum standard uptake value (SUV) within a small region of interest around the lesion. The percentage best describing the SUV falloff was integrated in planning by expanding standard target volumes with the PET abnormality.

Results: In 21 of 55 abnormalities, a deformable registration was needed to map the (18)F-fluciclovine activity into the simulation CT. The most selected percentage was 50% of maximum SUV, although values ranging from 15% to 70% were used for specific patients, illustrating the need for a per-patient selection of a threshold SUV value. The inclusion of (18)F-fluciclovine changed the planning volumes for 46 abnormalities (83%) of the total 55, with 28 (51%) located in the lymph nodes, 11 (20%) in the prostate bed, 10 (18%) in the prostate, and 6 (11%) in the seminal vesicles. Only 9 PET abnormalities were fully contained in the standard target volumes based on the CT-based segmentations and did not necessitate expansion.

Conclusions: The use of (18)F-fluciclovine in postprostatectomy radiation therapy planning was feasible and led to augmentation of the target volumes in the majority (30 of 41) of the patients studied.

Copyright © 2016 Elsevier Inc. All rights reserved.

Figures

Fig. 1

Use of deformable registration to register 18F-fluciclovine to the simulation computed tomographic (CT) scan. (a) Simulation CT scan at the level of a lymph node with positive uptake in positron emission tomography (PET)-CT, with an arrow marking the location. (b) Rigid registration of the CT component of the PET scan. Although the rigid registration matches the bone and muscles, it cannot model lymph node displacement between the scans. (c) Deformable registration. (d) Quality of the displacement field inspected to ensure smooth and anatomic plausible warping of standardized uptake value (SUV) activity. (e) PET mapped to the simulation CT dataset with rigid registration. (f) The same activity warped with deformable registration and iso-SUV levels.

Fig. 2

Lesion segmentation. The region of interest and segmentation of maximum standardized uptake value (SUV) with the region is shown for (a) a prostate bed lesion and (b) a lymph node lesion. (c) A histogram of threshold frequencies selected across all patients, with 50% of standardized uptake value (SUV)max being the most common value used for segmentation.

Fig. 3

Creation of image guided plans. 18F-Fluciclovine imaging shown in (a) was used to modify an initial plan (b) to boost the dose to the iliac node abnormality (c). The color scale ranges from 0 to 77 Gy.

Fig. 4

Image guidance and standard target volumes. Blue lines show the standard volumes; green line shows their modification based on the standardized uptake value (SUV) segmentations that are displayed in light blue. (a) The abnormality in the left external iliac node was not included at all in the initial plan. (b) Abnormalities in the left inguinal and right iliac nodes were adjacent to the initial segmentation. (c) The left presacral abnormality was fully contained within the initial segmentation and did not require edits. (A color version of this figure is available at www.redjournal.org.)

Fig. 5

Dose-volume histogram (DVH) changes with selection of maximum standardized uptake value (SUV) thresholds. (a) The 40%, 50%, and 60% SUVmax isocontours overlaid with the dose for the axial slice depicted in Fig. 4b. (b) Corresponding DVHs for the left inguinal. (c) DVHs for the external iliac lesion shown in Fig. 4a.