Dosimetry in At-Risk Organs After 177Lu-PSMA-617 Treatment for Castration-Resistant Prostate Cancer

In a sub-trial of the VISION study, presented in Poster Session A: Prostate Cancer at the 2022 American Society of Clinical Oncology (ASCO) Genitourinary Cancer Symposium, researchers sought to quantify the absorbed dose of the radioligand, 177Lu-PSMA-617, in organs at risk for radiotoxicity among patients with metastatic castration-resistant prostate cancer (mCRPC). According to lead author, Ken Herrmann, MD, and colleagues, 177Lu-PSMA-617 dosimetry results were consistent with previously documented ranges, and adverse events (AEs) affecting organs were “infrequent and of low-to-moderate severity.”

Twenty-nine eligible patients received 177Lu‑PSMA‑617 (7.4 GBq per cycle) plus standard of care every six weeks at four German centers. Dosimetry outcomes were based on biodistribution, measured via planar whole-body scintigraphy scans and single-photon emission computed tomography/computed tomography (SPECT/CT) scans, as well as blood and urine samples.

In the session, Dr. Herrmann reported that absorbed doses of radiation per unit activity were the highest in the lacrimal glands (2.1 Gy/GBq), followed by the salivary glands (0.63 Gy/GBq). On average, the kidneys received slightly lower doses (0.43 Gy/GBq), while the dose in the blood-based red marrow was much lower (0.035 Gy/GBq). During cycle one, 20% of the patients experienced one hematological AE of Common Terminology Criteria for Adverse Events (CTCAE) of grade ≥2 and two patients had a grade 1 salivary gland AE. Conversely, no patients experienced any lacrimal gland toxicity or a renal AE of grade ≥2.

Though the main VISION trial found 177Lu-PSMA-617 significantly improved overall survival (OS) and progression-free survival (PFS) compared to SOC, the possibility of inflicting radiotoxicity on high-risk organs was a concern. Fortunately, according to Dr. Herrmann’s presentation, “these findings indicate that patients with metastatic castration-resistant prostate cancer receiving 177Lu-PSMA-617 should be at low risk of radiation-induced AEs.”