Pictorial essay: normal variants, lesions, and pitfalls in 68Ga-PSMA PET imaging of prostate cancer

Whole-Body 177Lu-Prostate-Specific Membrane Antigen Scan Pattern With Excess Free 177Lu-Chloride in a Metastatic Castration-Resistant Prostate Cancer Patient

A 56-year-old man with metastatic castration-resistant prostate cancer was referred for radioligand therapy with Lu-prostate-specific membrane antigen. In the third cycle, a posttherapy whole-body scan showed unexpected skeletal and joint uptake apart from his known metastatic lesions. This observation raised suspicion for possible impurity (mainly free lutetium) in the applied radiopharmaceutical product. After contacting the radiopharmaceutical company, we were informed that the radiochemical purity of the used batch of Lu-prostate-specific membrane antigen had been 95%. This is the first report of excess free lutetium scan pattern and its complications in a patient undergoing radioligand therapy.

Medical Event: Accidental Oral Administration of 177Lu-PSMA to a Patient With Hyperthyroidism

A 74-year-old woman with hyperthyroidism was referred for radioiodine therapy. The patient was accidentally given 60 mCi of Lu-PSMA orally instead of I. Upon discovery of this medical event, we immediately started radiation protective actions including hydration, antiemetics, and laxatives. The patients did not have any symptoms. Static acquisition was performed from the abdominal-pelvic and head and neck regions at 20 and 90 hours after ingestion, which showed prominent intestinal activity and mild systemic activity in the kidneys, bladder, salivary, and lacrimal glands.

68Ga-PSMA PET/CT in prostate cancer patients - patterns of disease, benign findings and pitfalls

Background

68Ga-PSMA PET/CT has an important role in assessment of prostate cancer patients with biochemical recurrence and is evolving in staging high- and intermediate risk disease. The aim of present study was to describe the metastatic patterns and frequency of involved sites of prostate cancer and to assess the incidence of benign Ga68-PSMA avid PET/CT findings in a large patient population.

Methods

68Ga-PSMA PET/CT studies performed in two tertiary medical centers over a period of 24 months were retrospectively reviewed. The incidence and location of pathological 68Ga-PSMA avid foci, suspicious to represent malignancy, as well as those of unexpected benign foci of increased 68Ga-PSMA activity were documented and analyzed.

Results

There were 445 68Ga-PSMA studies in 438 men (mean age 72.4, range 51–92 years) with prostate cancer referred for biochemical failure (n = 270, 61%), staging high-risk disease (n = 112, 25%), response assessment (n = 30, 7%), follow-up (n = 22, 5%) and suspected bone metastases (n = 11, 2%). 68Ga-PSMA avid disease sites were observed in 319 studies (72%), in 181 studies (67%) for biochemical recurrence, 94 studies for staging (84%) (p < 0.05), in 22 studies for response assessment (73%), 10 follow up studies (45%) and in five patients with suspected bone metastases (45%). 68Ga-PSMA avid lesions were most commonly detected in the prostate (n = 193, 43%), loco-regional spread (n = 51, 11%), abdomino-pelvic nodes (n = 129, 29%) and distant metastases (n = 158, 36%), including bone metastases (n = 11, 25%), distant lymphadenopathy (n = 29, 7%) and other organs (n = 18, 4%). Distant 68Ga-PSMA-avid metastases were commonly seen in patients with biochemical recurrence (14/21 lesions), but were not seen in patient referred for staging (p < 0.013). There were 96 non-malignant 68Ga-PSMA avid foci in 81 studies, most common in reactive lymph nodes (n = 36, 38%), nonmalignant bone lesions (n = 21, 22%), thyroid nodules (n = 9, 9%), ganglions (n = 9, 9%) and lung findings (n = 8, 8%).

Conclusion

The distribution of 68Ga-PSMA avid metastatic lesions is similar to data previously reported mainly from autopsy with comparable detection rates, indicating 68Ga-PSMA PET/CT is an accurate detection tool in patients with metastatic prostate cancer. If confirmed by further prospective studies 68Ga-PSMA PET/CT should be included in the guidelines to evaluate disease extent in these patients.