News | Nuclear Imaging | June 23, 2016

Molecular Imaging of Neuroendocrine Tumors Optimizes Radiotherapy Dose

Study shows the use of PET and SPECT tailors radionuclide treatment for neuroendocrine cancer patients and reduces the risk of toxicity

neuroendocrine tumors, NET, radiotherapy dose, PET, SPECT, SNMMI 2016

Comparison of Ga-68-DOTATOC PET/CT with Y-90 DOTATOC PET/CT. Although the positron associated with Y-90 is rarely emitted, there is still sufficient signal to acquire a quantitative PET/CT image of Y-90 DOTATOC after a therapeutic administration. The white arrows indicate kidneys and the yellow arrows tumor. Credit: University of Iowa

June 23, 2016 — Aggressive neuroendocrine cancer is something of a dark horse — a rare, elusive and persevering force linked to discouraging long-term survival rates. Researchers at the 2016 Annual Meeting of the Society of Nuclear Medicine and Molecular Imaging (SNMMI) — held June 11-15 in San Diego — presented a molecular imaging technique that allows oncologists to set patients’ radiotherapy doses right at that critical limit of delivering the most powerful kill to neuroendocrine tumors (NETs) while protecting vulnerable vital organs.

The delicate balance of administering the maximum safe dose is called personalized dosimetry, and it can vary widely between patients. This poses a problem for clinicians. A number of radiotherapies that marry a small but potent amount of radioactive material and a targeted molecular compound have been gaining traction as progressive treatments for malignant NETs, which can develop wherever nerve cells and hormone-producing endocrine cells are present (e.g., gastrointestinal tract, pancreas, lungs, thyroid). Scientists are taking pre-emptive action by using already-available molecular imaging systems to determine the optimal dose of one such peptide-receptor radionuclide therapy known as yttrium-90 DOTA0-Tyr3-octreotide (Y-90 DOTATOC).

“DOTATOC is a peptide that binds with somatostatin receptors that are often highly expressed in neuroendocrine cancers,” said Mark T. Madsen, Ph.D., University of Iowa in Iowa City, Iowa. “With molecular imaging, we are able to see whether the DOTATOC imaging agent is taken up by the tumor. If it is, we know that the Y-90 DOTATOC radiotherapy will also reach the tumor and be able to kill tumor cells.”

The objective here is to set the bar for the highest possible therapeutic radiation dose to NETs that does not exceed toxic radiation levels to the kidneys, which take on the brunt of the residual drug that does not bind to its targets. Results of this research showed that the use of positron emission tomography (PET) and single photon emission computed tomography (SPECT), which image physiological functions of the body such as peptide receptor activity, led to dramatically altered dosimetry in all participating patients.

For this study, researchers worked with 12 patients with malignant NETs to find an adaptive approach to personalized dosimetry during three cycles of radiotherapy. All adult patients underwent 4.44 GBq of Y-90 DOTATOC and pediatric patients received 1.85 GBq per m2 during the first course of treatment. Patients were also given an infusion of amino acids as a protective measure against kidney toxicity.

The researchers evaluated blood and renal dosimetry after the first and second courses of radiotherapy to discern the best possible dose of Y-90 DOTATOC for successive courses. Dosimetry was performed by imaging patients with quantitative PET/CT about five hours after administration of Y-90 DOTATOC, followed by quantitative SPECT/CT imaging at 24, 48 and 72-hour intervals after injection. Y-90 burden and kidney mass were determined from reconstructed PET and CT images and verified using phantoms — inanimate objects that act just like patients’ vital organs during imaging and therapy.

The researchers were able to complete 20 dosimetry evaluations for the 12 subjects involved in the study. Y-90 activity accumulation in the kidneys ranged from 1.4 to 3.6 percent. The kidney dose ranged from 0.6 to 2.7 mGy per MBq, and the blood dose ranged from 0.04 to 0.24 mGy per MBq. This led to marked changes in subsequent cycles of treatment. The dose of radiotherapy was not increased for two injections in children, and one patient’s treatment ended after only one course of treatment. For the rest of the subjects, the dose of radiotherapy was increased in eight courses and decreased in three courses. Over all, the prescribed dose of radiotherapy was altered by more than 15 percent in a total of 11 courses of radiotherapy.

“Our approach combines the advantages of quantitative Y-90 PET and SPECT imaging to gather all the information required to accurately estimate kidney dose,” said Madsen. “We expect better outcomes in radionuclide therapy treatment with fewer complications because we will be able to adjust patient dose either up or down as needed.”

While this method of personalized dosimetry was used to determine the maximum dose that is safe for kidneys, this imaging technique could be equally used to determine the most effective dose to combat NETs. Further studies should elucidate how best to apply this technique to improve the standard of neuroendocrine cancer care.

For more information: www.snmmi.org

Related Content

Study Unveils Blueprint for Treating Radiation-Resistant Brain Tumor

NIH-funded researchers showed how gliomas may be treated with radiation and drugs that block DNA repair. Image courtesy of Castro lab, Michigan Medicine, Ann Arbor

 

News | Radiation Therapy | February 19, 2019
February 19, 2019 — Researchers at the University of Michigan recently searched for new brain tumor treatments by exp
Amazon Comprehend Medical Brings Medical Language Processing to Healthcare
News | Artificial Intelligence | February 15, 2019
Amazon recently announced Amazon Comprehend Medical, a new HIPAA-eligible machine learning service that allows...
Videos | Radiation Therapy | February 15, 2019
ITN Associate Editor Jeff Zagoudis speaks with Vinai Gondi, M.D., director of research and CNS neuro-oncology at the
New Targeted Therapy for Recurrent Brain Tumors Implanted for First Time
News | Radiation Therapy | February 15, 2019
University of Minnesota Health (M Health) is the first in the United States to begin offering GammaTile Therapy, a new...
Canon Adds Radiation Therapy Package to Aquilion Prime, Lightning CT Systems
News | Computed Tomography (CT) | February 11, 2019
In the patient-centric world of radiation oncology, it is critical that computed tomography (CT) simulation is...
Elekta Unity MR-Linac Earns FDA Clearance
Technology | Image Guided Radiation Therapy (IGRT) | February 07, 2019
The Elekta Unity magnetic resonance radiation therapy (MR/RT) system recently received 510(k) premarket notification...
University of Oklahoma Cancer Center Begins First Proton Therapy Treatments
News | Proton Therapy | February 01, 2019
Home to the largest and most comprehensive radiation therapy program in Oklahoma, the Stephenson Cancer Center at OU (...
Study Assesses Risk of MRI Exams for Patients With Tattoos
News | Magnetic Resonance Imaging (MRI) | February 01, 2019
A new European study concluded that magnetic resonance imaging (MRI) exams pose little risk for people with tattoos,...
Stereotactic Radiotherapy Improves Long-Term Survival in Stage-IV Cancers
News | Stereotactic Body Radiation Therapy (SBRT) | January 31, 2019
The first report from a phase II, multi-center clinical trial indicates stereotactic radiation can extend long-term...
Philips Collaborates With MIM Software on Radiation Therapy Treatment Planning
News | Treatment Planning | January 31, 2019
January 31, 2019 — Philips announced a collaboration with imaging solutions provider MIM Software Inc.