Plate Nº 66 · recorded October 10, 2026
Health & Medicine ResearchReported finding
Berkeley Lab Images Alpha Therapy Isotope in First Human Scan
A new PET algorithm called TOF-CGI has produced the first human images of actinium-225, an alpha-emitting radioisotope used in targeted cancer therapy, in a pilot study at Berkeley Lab.
By Elena Vasquez4 min read740 words
In brief
- Researchers produced the first PET scan of a human patient injected with actinium-225, a 10-day-half-life alpha-emitting radioisotope.
- Patients receive roughly 100 times less actinium-225 than a typical PET tracer, making the gamma signal hard to capture.
- In a one-patient pilot, TOF-CGI detected the same prostate tumors as a standard PET scan and saw more actinium-225 decays than SPECT.
- The study was published in the Journal of Nuclear Medicine in 2026 (DOI: 10.2967/jnumed.126.272594).
A team at Lawrence Berkeley National Laboratory has produced the first PET scan of a human patient injected with actinium-225. The alpha-emitting radioisotope powers an experimental cancer therapy. The work, published in the Journal of Nuclear Medicine, centers on a new algorithm called TOF-CGI.
What is targeted alpha therapy?
Targeted alpha therapy, or TAT, is a form of cancer treatment that uses engineered radioisotopes — radioactive atoms — to seek out and destroy cancer cells. Alpha particles are helium nuclei that pack thousands of times more energy than the beta particles used in conventional radiotherapy. That extra punch can shatter a cancer cell's DNA beyond repair.
The catch: alpha particles travel only a few cell widths. TAT only works when the radioisotope reaches the tumor. Clinicians have had no reliable way to confirm the dose arrived where it should.
Why is actinium-225 hard to image?
Actinium-225 is a leading TAT candidate because of its 10-day half-life and its four-alpha decay chain. As it breaks down, it also releases pairs of gamma photons — high-energy light particles — that a scanner could theoretically pick up.
Those photons are weak. Patients receive roughly 100 times less actinium-225 than a typical PET tracer, and the gamma signal is faint. Standard SPECT scanners use heavy metal shields called collimators that lose too much of it.
PET scanners, which detect pairs of gamma photons from positron-electron collisions, have higher sensitivity. They face one problem with actinium-225: the isotope emits no positrons at all.
How does TOF-CGI work?
Researchers led by Javier Caravaca, a staff scientist in Berkeley Lab's Nuclear Science Division, wondered whether a PET scanner could detect actinium-225's gamma pairs directly.
"Traditionally, there have been only two ways to image cancer: SPECT (single-photon emission computed tomography) or PET (positron emission tomography). Although these techniques have led to big advances in cancer imaging, neither has so far met the demanding requirements to image targeted alpha therapy accurately. Our new study is the first to show that there could be a third way to image cancer with the alpha therapy radioisotope actinium-225," Caravaca said.
Caravaca wrote a new image-reconstruction algorithm called TOF-CGI — time-of-flight cascade gamma-ray imaging. It treats each gamma pair as a timestamped signal pointing back to the atom that released it. The algorithm then stitches those signals into a 3D map of where actinium-225 is decaying.
GPU computing at the National Energy Research Scientific Computing Center (NERSC) sped the reconstruction. The team tested it on a Siemens PET scanner alongside collaborators from UC San Francisco and Siemens Medical Solutions U.S. Inc.
What did the human trial show?
The pilot study involved one patient previously diagnosed with prostate cancer through standard PET. After a follow-up scan using TOF-CGI, the algorithm identified the same prostate tumors the original diagnostic scan had caught.
It also detected more actinium-225 decays than SPECT, producing cleaner images. The result is a proof of concept on a single patient, not a clinical tool yet.
What comes next?
Caravaca called the result a first step rather than a finished product.
"This is an exciting first step. Clinicians want to know whether a radioisotope is doing its job. Did it stop the cancer cells from spreading? Or did new tumors emerge? Targeted alpha therapy imaging could help us answer those questions and more, but we still need an imaging modality to match. We think that our TOF-CGI technique could one day help us get there," he said.
His team plans to expand TOF-CGI to other radioisotopes and test it on a full-body PET scanner.
How does this fit Berkeley Lab's role in nuclear medicine?
Berkeley Lab has shaped nuclear medicine since 1935, when physicist Ernest Lawrence invited his brother John, a physician, to study cyclotron-produced radioisotopes for medicine. A year later, John Lawrence treated the first cancer patient with a cyclotron-made isotope.
The lab later produced medical staples such as iodine-131, technetium-99m, and carbon-14. In the 1950s, Hal Anger built the scintillation camera, the forerunner of every modern SPECT and PET machine. A 2015 Berkeley Lab contribution helped build the first total-body PET scanner.
"TOF-CGI brings us a step closer to helping clinicians diagnose and treat cancer in a way that wasn't possible before," Caravaca said.
via Medical Xpress (Source)
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