Role of 68-Ga-PSMA-PET/CT in pelvic radiotherapy field definitions for lymph node coverage in prostate cancer patients.

To evaluate the distribution of metastatic lymph nodes (LN) detected on 68Ga-PSMA-positron emission tomography/computed tomography (PET/CT) in treatment-naïve prostate cancer (PC) patients and to analyze the LN coverage rates of the pelvic fields defined in the GETUG trial and RTOG guidelines and a pelvic field extending superiorly from the L4/L5 interspace.

68Ga-PSMA-PET/CT images obtained at diagnosis of 138 PC patients were retrospectively analyzed. The number and locations of 68Ga-PSMA-positive LNs were co-registered with one single-planning CT. The numbers, locations, and sizes of LNs located outside the three pelvic volumes were investigated for the entire cohort and for patients with LN metastasis in the pelvic area only.

A total of 441 PSMA-PET-positive LN metastases were identified. The most frequent metastatic LNs were internal iliac LNs (25.2%). Para-aortic and presacral LNs outside the three pelvic fields were present in 20 (14.5%) and 22 patients (15.9%), respectively. The LN coverage rates according to the GETUG trial, the RTOG guidelines, and the pelvic field extending superiorly from L4/L5 were 44.2%, 52.2%, and 71, respectively, in the entire cohort and 51.7%, 61 and 83.1%, respectively, in patients with only pelvic LN metastasis. The number of metastatic LNs was a predictive factor for LNs located outside the three pelvic fields.

Extending the cranial margin of the pelvic field from L5/S1 to L4/L5 increases the accuracy of pelvic field irradiation in approximately 20% of patients, highlighting the importance of proximal common iliac irradiation, particularly in patients with multiple LN metastasis.

Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology. 2020 Aug 27 [Epub ahead of print]

Cem Onal, Gokhan Ozyigit, Ozan Cem Guler, Pervin Hurmuz, Nese Torun, Murat Tuncel, Yemliha Dolek, Yagiz Yedekci, Ezgi Oymak, Burak Tilki, Fadil Akyol

Department of Radiation Oncology, Adana Dr. Turgut Noyan Research and Treatment Center, Baskent University Faculty of Medicine, Adana, Turkey. Electronic address: ., Department of Radiation Oncology, Hacettepe University Faculty of Medicine, Ankara, Turkey., Department of Radiation Oncology, Adana Dr. Turgut Noyan Research and Treatment Center, Baskent University Faculty of Medicine, Adana, Turkey., Department of Nuclear Medicine, Adana Dr. Turgut Noyan Research and Treatment Center, Başkent University Faculty of Medicine, Adana, Turkey., Department of Nuclear Medicine, Hacettepe University Faculty of Medicine, Ankara, Turkey., Division of Radiation Oncology, Iskenderun Gelisim Hospital, Hatay, Turkey.