Genitourinary Cancer

PD 01 - GU 1 - Poster Discussion - New Data on PET, MRI and Protons for Treating Prostate Cancer

1003 - 68Ga-PSMA PET/CT Mapping Of Prostate Cancer at Initial Staging: Potential Impact On Definitive Radiation Therapy Planning

Sunday, October 21
1:33 PM - 1:39 PM
Location: Room 217 A/B

68Ga-PSMA PET/CT Mapping Of Prostate Cancer at Initial Staging: Potential Impact On Definitive Radiation Therapy Planning
N. Nickols1, J. Calais2, A. U. Kishan3, M. Cao3, J. V. Hegde3, N. Shaverdian3, C. R. King3, M. L. Steinberg4, R. E. Reiter5, M. Rettig4, F. Ceci4, K. Herrmann4, W. P. Fendler4, M. Eiber4, and J. Czernin4; 1VA Greater Los Angeles Health System, Los Angeles, CA, 2Universty of California, Los Angeles, Los Angeles, CA, 3Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, CA, 4University of California, Los Angeles, Los Angeles, CA, 5Department of Urology, University of California, Los Angeles, Los Angeles, CA

Purpose/Objective(s): Standard-of-care imaging for initial staging of prostate cancer (PCa) results in underestimation of disease burden. 68Ga-PSMA-11 PET/CT detects PCa metastasis with superior accuracy with potential impact on definitive radiation therapy (RT) planning for non-metastatic PCa. Our objectives are: i) To determine how often definitive PCa RT planning based on standard target volumes cover 68Ga-PSMA-11 PET/CT defined disease, and ii) To assess the potential impact of 68Ga-PSMA-11 PET/CT on definitive PCa RT planning.

Materials/Methods: This is a post-hoc analysis of an intention to treat population of 73 patients with localized PCa without prior local therapy who underwent 68Ga-PSMA PET/CT for initial staging as part of an Investigational New Drug trial. 11/73 were intermediate-risk (15%), 33/73 were high-risk (45%), 22/73 were very high risk (30%) and 7/73 were N1 (9.5%). Clinical target volumes (CTVs) that included the prostate, seminal vesicles, and pelvic lymph nodes (LNs) using Radiation Therapy Oncology Group (RTOG) consensus guidelines were contoured on the CT portion of the PET/CT by an experienced radiation oncologist blinded to the PET findings. 68Ga-PSMA-11 PET/CT images were analyzed by an experienced nuclear medicine physician. PSMA-positive lesions not covered by planning volumes based on the consensus CTVs were considered to have a major potential impact on treatment planning.

Results: All patients had PSMA-positive primary prostate lesion(s). 25/73 (34%) and 7/73 (9.5%) had PSMA-positive pelvic nodal and distant metastases, respectively. The sites of nodal metastases in decreasing order of frequency were external iliac (20.5%), common iliac (13.5%), internal iliac (12.5%) obturator (12.5%), perirectal (4%), abdominal (4%), upper-diaphragm (4%), and presacral (1.5%). The median size of the nodal lesions was 6 mm (range 4-24 mm). RT planning based on the CTVs covered 69/73 (94.5%) of primary disease and 20/25 (80%) of pelvic nodal disease, on a per-patient analysis.

Conclusion: 68Ga-PSMA-11 PET/CT had a major impact on intended definitive PCa RT planning in 12/73 of patients (16.5%) when RT fields covered the prostate, seminal vesicles and the pelvic LNs, and in 25/66 of patients (37%) when RT fields covered only the prostate and seminal vesicles (without pelvic LNs).

Author Disclosure: N. Nickols: academic affiliation; UCLA. Research Grant; Varian Medical Systems, Nanobiotix, Janssen LLC. Stock; GeneSciences Inc. Stock Options; GeneSciences Inc. J. Calais: None. A.U. Kishan: None. M. Cao: None. J.V. Hegde: Employee; Department of Medicine, UCLA. N. Shaverdian: None. M.L. Steinberg: Honoraria; Accuray. F. Ceci: None. W.P. Fendler: None. M. Eiber: None. J. Czernin: None.

Nicholas Nickols, MD, PhD

Disclosure:
Employment
UCLA: Assistant Professor: academic affiliation; Veterans Affairs: Physician: Employee

Compensation
Janssen LLC: Research Grants; Nanobiotix: Research Grants; Varian Medical Systems: Research Grants

Ownership
GeneSciences Inc: Stock, Stock Options

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