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Assessing tumor dose dynamics and pre‑treatment dosimetry of lutetium‑177 PSMA‑I&T in men with metastatic castration‑resistant prostate cancer

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What is this trial about?

A plain-language summary of the goals, design and what participants do

A study is being done in men with metastatic castration-resistant prostate cancer, a type of prostate cancer that has spread and no longer responds to hormone therapy. The treatment being tested is a radioactive drug called 177Lu-PSMA-I&T, which is given by an intravenous (through a vein) injection. The amount of the drug is measured in GBq, a unit that tells how much radiation is inside the medicine. This medicine is designed to seek out and deliver radiation directly to cancer cells.

The purpose of the study is to see how the radiation dose to the tumors changes over the course of treatment and whether planning the dose before treatment is practical. Participants will receive the injection, then have a series of imaging scans that look at the amount of radiation in the tumor (called dosimetry). One of the scans used is a PET scan, which shows how active the cancer is, and a measure from that scan called SUV indicates how much of the tracer the tumor absorbs. Over several treatment cycles, doctors will check the size of the tumors and any side effects, while also monitoring routine health checks.

The research process

The trial runs in 8 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Enrollment and Informed Consent

    After agreeing to join the study, you sign an informed consent form that explains the purpose of the trial, the procedures involved, and any possible risks.

    The study team confirms that you meet the eligibility criteria, which include being a male aged 18 years or older with metastatic castration‑resistant prostate cancer.

  2. Step 2

    Baseline Assessments

    You undergo a series of examinations to record your health status before treatment begins. This includes blood tests, vital‑sign measurements, and a physical examination.

    Imaging studies such as a PET scan are performed to document the size of the tumors and their activity, measured as the standardized uptake value (SUV).

  3. Step 3

    Pre‑Treatment Dosimetry

    Special imaging is used to calculate how much radiation the tumors are likely to receive from the upcoming therapy. This step is called pre‑treatment dosimetry and helps the study team plan the dose.

    The results are compared with the baseline imaging to establish a reference point for later measurements.

  4. Step 4

    Administration of Study Drug

    You receive a single intravenous (IV) bolus injection of 177Lu‑PSMA‑I&T. The dose is 7.4 GBq (gigabecquerel, a unit of radioactivity).

    The injection is given through a vein over a short period while the study staff monitor your vital signs.

  5. Step 5

    Immediate Post‑Treatment Monitoring

    After the injection, you remain in the clinic for a short observation period. Blood samples and vital signs are checked to ensure there are no immediate reactions.

    Any symptoms or side effects that arise during this time are recorded as part of the safety assessment.

  6. Step 6

    Post‑Treatment Dosimetry

    Within a few days after the injection, additional imaging is performed to measure the actual radiation absorbed by the tumors. This is called post‑treatment dosimetry.

    The measured tumor dose is compared with the planned dose to evaluate how accurately the treatment was delivered.

  7. Step 7

    Follow‑Up Visits

    You attend scheduled follow‑up visits at intervals defined by the study protocol. During each visit, blood tests, vital‑sign checks, and physical examinations are repeated.

    Repeat PET scans are performed to assess changes in tumor size and SUV, allowing the study team to track the effectiveness of the treatment over time.

    Any new or worsening side effects are documented as adverse events, and their severity and relationship to the study drug are evaluated.

  8. Step 8

    End‑of‑Study Assessment

    At the conclusion of the trial, a final set of assessments is performed, including imaging, laboratory tests, and a complete safety review.

    The collected data are used to determine the primary and secondary outcomes of the study, such as tumor dose per treatment cycle and changes in tumor volume.

Who can join the trial?

20 criteria

  • You must have a confirmed diagnosis of metastatic castration‑resistant prostate cancer (mCRPC), which means the cancer has spread and no longer responds to hormone treatments, and it must have progressed while you were on Androgen Deprivation Therapy (ADT) (medications that lower testosterone) and an Androgen Receptor Pathway Inhibitor (ARPI) (a drug that blocks the effect of testosterone on cancer cells), but you must not have received the chemotherapy drug docetaxel after the cancer spread.
  • Your amount of tumor and where it is spread must be similar to the first participant in the study. This will be checked with a special scan called [68Ga]Ga‑PSMA PET/CT or PET/MR (a picture of the cancer that uses a substance that sticks to a protein called PSMA) and a blood test called PSA (a protein that many prostate cancers produce). If your tumor burden is very different, you cannot join.
  • You must be able to understand the study information, sign the consent form, and follow all study rules.
  • You must be at least 18 years old.
  • Your overall health score, called ECOG performance status, must be 0 or 1, meaning you are fully active or able to do light work.
  • Doctors must expect that you will live for more than 12 months.
  • Your lab tests must show good organ function, including:
    • Hemoglobin (a measure of red blood cells) ≥ 13 g/dL
    • White blood cells ≥ 4.0 × 10⁹/L
    • Neutrophils (a type of white blood cell) ≥ 1.6 × 10⁹/L
    • Platelets ≥ 150 × 10⁹/L
    • Kidney filtration rate (eGFR) ≥ 50 mL/min
    • Liver enzymes ASAT and ALAT ≤ 1.5 times the normal limit
    • Albumin (a protein made by the liver) ≥ 28 g/L
    • Total bilirubin (a waste product processed by the liver) ≤ 1.5 times normal, or ≤ 40 µmol/L if you have Gilbert’s syndrome (a mild liver condition)
    • You must have had an orchiectomy (surgical removal of the testes) or be currently receiving ongoing hormone therapy to keep testosterone low.
    • If you have a female partner who could become pregnant, you must use reliable birth control, including barrier methods, during the study and for at least six months after the last dose of the radioactive drug.
    • You must have been taking a bone‑strengthening medicine such as a bisphosphonate or denosumab continuously for at least 30 days before joining.
    • A recent [68Ga]Ga‑PSMA PET/CT or PET/MR scan (done within the last 21 days) must show PSMA‑positive metastatic disease that is suitable for the targeted radioactive treatment. This means more than half of the metastases take up more tracer than normal liver tissue, and you must have between 5 and 20 metastatic spots located only in lymph nodes or bone.
    • At least two of your metastases must be large enough (about 2–3 cm), isolated, and no more than 30 cm apart so that a special imaging test called SPECT (a scan that measures radiation) can be used for dosimetry (calculating the radiation dose to the tumor).
    • You must be expected to be able to complete six treatment cycles of the radioactive drug [177Lu]Lu‑PSMA.

Who cannot join the trial?

10 criteria

  • Having received a previous PSMA‑targeted radioligand therapy, which is a special radioactive drug that seeks out prostate cancer cells, makes you ineligible.
  • If you had a blood transfusion (receiving donated blood) within the past 60 days, you cannot join the study.
  • Having a large amount of cancer spread to the bone marrow (the spongy tissue inside bones that makes blood cells) excludes you.
  • Having bone cancer that is causing or is about to cause pressure on the spinal cord (known as spinal cord compression) prevents participation.
  • If you have another type of cancer that could shorten your life expectancy or make it hard to evaluate your prostate cancer, you are excluded.
  • Experiencing incontinence (loss of bladder control) is a reason to be excluded.
  • Having serious other health problems, such as severe heart failure (New York Heart Association class III or IV), a lifelong heart rhythm disorder called prolonged QT syndrome, an uncontrolled infection, or any condition your doctor believes would make study participation unsafe, will exclude you.
  • If you were treated with radium‑223 (a radioactive medication) or received external radiation therapy within the last 3 months, you cannot take part.
  • Using any experimental drug (an investigational agent) within 28 days, or for a period equal to five times its half‑life (the time it takes for half of the drug to leave your body), whichever is longer, makes you ineligible.
  • Having a known allergy (hypersensitivity) to the study’s PSMA‑radioligand drug also excludes you.
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Investigated drugs

177LU-PSMA-I&T is a radioactive medication that is designed to find and attach to a protein called PSMA, which is found on many prostate cancer cells. It is given as a single injection into a vein. Once inside the body, the radioactive part (lutetium‑177) delivers a small amount of radiation directly to the cancer cells that have PSMA, helping to damage or kill them while trying to spare most normal tissue. In this study, the drug is being used to treat men with advanced prostate cancer that no longer responds to hormone therapy. Researchers are measuring how much radiation the tumors receive and checking if they can predict the best dose before treatment starts.

What is already known about the treatment

177LU-PSMA-I&T - 177LU-PSMA-I&T is given as an intravenous bolus injection of a solution for injection, delivering a measured amount of the radioactive compound. It is an experimental radiopharmaceutical that is currently being studied in clinical trials and is not yet approved for routine medical use. The drug is intended for patients with metastatic castration‑resistant prostate cancer, where it seeks to deliver radiation directly to cancer cells that express the PSMA protein. It works by attaching a radioactive lutetium atom to a molecule that binds PSMA, allowing the radiation to damage the tumor cells while sparing most normal tissue, and it belongs to the class of targeted radioligand therapies.

Investigated diseases

Metastatic castration‑resistant prostate cancer - It is a form of prostate cancer that continues to grow despite low testosterone levels achieved by hormonal therapy. Cancer cells have acquired mechanisms to survive without androgen signaling. The disease has spread beyond the prostate gland to distant sites such as bone, lymph nodes, or other organs. Tumor growth in these sites can lead to increasing lesion size and new lesions over time. The condition is characterized by a steady or accelerating increase in tumor burden if left unchecked.
Trial detailsLast updated 15 Oct 2026
Age18+ yearsPhasePhase IITrial ID2026-526519-12-00Estimated enrolment3 patientsSponsorUniversitetssykehuset Nord-Norge HF

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