Impact of Fluciclovine (18F) Positron Emission Tomography on Target Volume Definition for Post-Prostatectomy Salvage Radiotherapy: Initial Findings from a Randomized Trial

The purpose was to evaluate the role of the synthetic amino acid positron emission tomography (PET) radiotracer fluciclovine ((18)F) in modifying the clinical and planning target volume (CTV and PTV) definition in post-prostatectomy patients undergoing salvage radiotherapy and to evaluate the resulting dosimetric consequences to surrounding organs at risk.

96 patients were enrolled in a randomized prospective intention to treat clinical trial for potential salvage radiotherapy for recurrent prostate cancer after prostatectomy. All patients underwent initial treatment planning based on results from conventional abdominopelvic imaging (computed tomography [CT] or magnetic resonance imaging [MRI]). Patients in the experimental arm(n = 45) underwent planning modification after additionally undergoing abdominopelvic fluciclovine ((18)F) PET/CT. For each patient, the target volume (CTV{prostate bed}[or CTV1{pelvis}/CTV2{prostate bed}] and PTV[or PTV1/PTV2]) that would have been treated prior to fluciclovine ((18)F) registration (PRE) was compared to that after registration (POST). The V40Gy and V65Gy of the organs at risk (Rectum, Bladder[minus CTV], and Penile Bulb) PRE and POST were compared. Statistical comparisons were made using the paired t-test. Radiation Therapy Oncology Group (RTOG) acute genitourinary (GU) and gastrointestinal (GI) toxicity were compared between the control and experimental groups using the chi-square test.

Radiotherapy was planned either to the prostate fossa alone (CTV)[64.8-66.6 Gy][n = 24] or pelvis (CTV1)[45.0 Gy] followed by prostate fossa boost (CTV2)[19.8-25.2 Gy][n = 21]. In each case, the corresponding PTV expansion was 0.8 cm(0.6 cm posterior). For CTV, CTV1, CTV2, PTV, and PTV1, POST volumes were all significantly larger than the corresponding PRE volumes (only PTV2 PRE vs POST volumes were not significantly different). Analysis of Rectum, Bladder[minus CTV], and Penile Bulb V40Gy and V60Gy PRE vs POST demonstrated that only Penile Bulb endpoints were significantly higher after registration. No significant differences in acute GU or GI toxicity were observed.

Inclusion of fluciclovine ((18)F) PET information into the treatment planning process leads to significant differences in target definition with higher doses to the penile bulb but with no significant differences in bladder or rectal dose or acute GU/GI toxicity. Longer follow-up is needed to determine the impact of fluciclovine ((18)F) on cancer control and late toxicity endpoints.

Journal of nuclear medicine : official publication, Society of Nuclear Medicine. 2016 Sep 08 [Epub ahead of print]

Ashesh Jani, Eduard Schreibmann, Peter J Rossi, Joseph W Shelton, Karen Godette, Peter Nieh, Viraj A Master, Omer Kucuk, Mark Goodman, Raghuveer Halkar, Sherrie Cooper, Zhengjia Chen, David M Schuster

Emory University, United States.

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