Which imaging modality do you prefer when monitoring disease status for patients with prostate cancer undergoing 177-Lu PSMA treatment?

At the present time, I generally use contrast-enhanced CT of the chest/abdomen/pelvis and whole-body Tc-bone scan (every 12 weeks) for monitoring. While it is attractive to consider serial PSMA-PET imaging for monitoring disease response to 177Lu-PSMA-617, there is currently no FDA indication to use PSMA-PET scans in this manner. I also do not generally use FDG-PET in this setting either. Remember, PSA declines can also be used as a reasonable indicator of efficacy of radioligand therapies, in conjunction with imaging modalities and clinical symptoms.

Imaging weeks or months later probably serves no useful purpose. What may be far more useful is SPECT for dosimetry imaging right after the first dose, to determine the absorbed dose in Gy to the tumors and the OAR. Then, if OAR doses permit, one may administer a higher dose of Pluvicto that may lead to longer remission. Or, those tumors underdosed by Pluvicto may be administered external RT, also to prolong remission.

These patients are monitored by bone scan and cross-sectional imaging and PSA. PSMA PETCT is not approved for monitoring of mCRPC, nor should be paid for outside of a clinical trial setting. Cross sectional imaging is either CT or MRI with response assessment in accordance with PCWG3 guidelines.

NaF is rarely used.

FDG PET is useful for understanding if there are non-PSMA avid prostate cancer lesions.

Question to answer here is, what is the purpose of the test and what would you do with the results?

Recall that PCWG criteria was developed in prostate cancer to avoid changing therapies early (and potentially unnecessarily) leaving patients with limited future options and causing harm.

There are three ways to assess disease, biochemical test (PSA), imaging (PSMA PET, CT, Bone scan), and clinical evaluations (patient history with symptoms reported and signs identified).

Generally, PSA is very sensitive, PSMA PET would be less sensitive than PSA but still very sensitive and CT with contrast and bone scan would be less sensitive. Clinical evaluation would be least sensitive to "measure disease" but most likely most important to patients.

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