The Dosimetry Dilemma: Why Many Sites Aren’t Ready for Radioligand Trials

Why Why Dosimetry Is Getting Attention

Radiopharmaceutical development is moving quickly. Radioligand therapies are gaining traction across oncology, and more programs are entering clinical trials. At the same time, expectations around dose optimization and treatment understanding are becoming more defined.

In this environment, dosimetry is getting more attention. Not because it is the biggest challenge, but because it often reveals whether a site can actually run a radioligand therapy trial as intended [1].

At a basic level, dosimetry measures how radiation distributes through the body after treatment. It helps teams understand how much dose reaches tumors and how much affects healthy tissue. This information supports safety assessments, dosing decisions, and overall treatment strategy. The science itself is well established. However, implementing it consistently across clinical sites remains difficult [1][2].

That is where the real issue begins.

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The Real Challenge: Coordination, Not Theory

The challenge is not just the science. It is the coordination required to make dosimetry work in a real world trial setting.

To perform dosimetry properly, sites often need multiple imaging timepoints using PET or SPECT scans. These scans must be scheduled at specific intervals after treatment. Radiopharmacy teams must prepare radioactive drugs within narrow time windows. Imaging teams must capture consistent, high quality data. Clinical and research teams must coordinate patient visits and ensure protocol adherence. Data must then be processed and analyzed using specialized expertise.

Each step depends on the others. If one part of the process is delayed or misaligned, the entire workflow can be affected.

In radiopharmaceutical therapy, radiation is not delivered in a fixed way like external beam radiation. Instead, it depends on how the drug distributes within each patient’s body. That makes imaging and measurement essential, but it also introduces variability and operational complexity [3].

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Why Even “Qualified” Sites Struggle

Because of this complexity, even well equipped sites can struggle to execute dosimetry effectively.

A site may have PET or SPECT scanners, nuclear medicine staff, and radiation safety oversight. On paper, it appears ready. But if departments are not aligned, the workflow can break down. Imaging may not be scheduled within protocol windows. Data processing may be delayed. Teams may need to rely on external support for analysis or interpretation.

When that happens, dosimetry becomes difficult to execute. More importantly, it becomes inconsistent.

This is not just a technical issue. It is an operational one.

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Dosimetry as a Signal of Site Readiness

Importantly, this is not just a dosimetry problem. It is a site readiness problem.

Dosimetry highlights whether a site can coordinate across oncology, nuclear medicine, imaging, radiopharmacy, and research teams. If those groups are not working within a structured and integrated workflow, even routine steps become difficult. Small delays can affect imaging windows. Missed timepoints can impact data quality. These issues can quickly extend beyond dosimetry and affect the entire study [1].

For many sponsors, this is where the gap becomes visible. Sites may meet baseline requirements, but lack the operational integration needed to execute complex protocols reliably.

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The Growing Pressure from Regulatory Expectations

Regulatory expectations are also evolving. FDA’s Project Optimus is placing greater emphasis on dose optimization in oncology drug development. In parallel, guidance for therapeutic radiopharmaceuticals reinforces the importance of understanding dose and treatment effects during clinical development.

This increases the need for reliable and consistent data collection across sites. It also raises the bar for what “trial-ready” truly means in practice [5].

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Why This Matters for Sponsors

For sponsors, this creates a practical challenge.

Site selection cannot rely only on equipment lists or institutional reputation. The more important question is whether a site can execute the full workflow. Can it manage multiple imaging visits within strict time windows? Can it coordinate across departments without introducing delays? Can it deliver consistent, high quality data across patients and timepoints?

If the answer is uncertain, dosimetry is often where that weakness becomes visible first [4].

Theragnostic Insight - Dosimetry is not the only bottleneck in radiopharmaceutical development. In many cases, it is not even the primary one. But it is often the point where underlying gaps become impossible to ignore.

At Theragnostic Insights, we focus on how protocols translate into real world execution. That includes evaluating site workflows, coordination across teams, and readiness to support radioligand therapy trials at scale. By identifying workflow gaps early, development teams can reduce activation delays and improve trial execution.

Dosimetry does not just measure radiation. It shows whether a site is truly ready to run a radioligand therapy trial.

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‍Stay tuned for more in this mini-series: Clinical Capacity Crisis: The Hidden Bottleneck in Radiopharma Development.
In the coming weeks, we’ll continue exploring the clinical capacity crisis holding back radiopharmaceutical innovation; from regional access gaps to operational gridlock and infrastructure blind spots. Don’t miss the next post as we map out the road to a truly trial-capable ecosystem.

1.     The Trial Site Gap: Why Radiopharmaceutical Innovation Is Hitting a Wall

2.     Geography Is Destiny: The Clinical Access Gaps in Radiopharmaceutical Research

3.     Operational Gridlock: Where Radiopharmaceutical Trials Break Down on Site

4.     Beyond the Badge: Rethinking What “Trial-Ready” Really Means in Radiopharma

5.     Infrastructure as Investment Strategy: Clinical Site Access and Radiopharma ROI

6.     Built for What’s Next: Redefining Clinical Site Design for Theragnostic Trials

7.     Speed as Strategy: How Site Scarcity Is Slowing Radiopharmaceutical Pipelines

8.     One Roof, Many Bottlenecks: Why Fragmented Site Models Undermine RLT Trials

9.     The Dosimetry Dilemma: Why Many Sites Aren’tReady for Radioligand Trials

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References:

[1] O’Donoghue J et al., 2022. Dosimetry in Radiopharmaceutical Therapy. Journal of Nuclear Medicine

[2] Ramonaheng KR et al., 2023. Activity Quantification and Dosimetry in Radiopharmaceutical Therapy with Reference to 177Lutetium. Frontiers in Nuclear Medicine

[3] Graves SA et al., 2021. Dosimetry for Optimized, Personalized Radiopharmaceutical Therapy. Seminars in Radiation Oncology

[4] Zanzonico P., 2025. Dosimetry for Radiopharmaceutical Therapy: Practical Implementation. American Journal of Roentgenology

[5] FDA Oncology Center of Excellence, 2025. Oncology Therapeutic Radiopharmaceuticals: Dosage Optimization During Clinical Development. U.S. Food and Drug Administration

[6] Shanmugiah J et al., 2026. Personalised Dosimetry in Nuclear Medicine: Bridging Physics, Biology and AI for Next Generation Radiopharmaceutical Therapy. Springer Nature

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