A combination of pretherapy imaging and dosimetry may help patients with refractory differentiated thyroid cancer obtain the maximum benefit from radioactive iodine treatments following redifferentiation therapy, according to a novel study published by Taprogge et al in The Journal of Nuclear Medicine.
Background
While the majority of patients with differentiated thyroid cancer respond well to initial treatment with radioactive iodine—which has been utilized in this patient population for over 80 years—some patients require further administration. After several treatments, 5% to 10% percent of patients no longer respond to treatment and often have poor prognoses with a median overall survival of 3 to 5 years.
“The drug selumetinib has shown potential to restore or enhance the uptake of radioactive iodine treatment in patients,” highlighted lead study author Jan Taprogge, PhD, Principal Radioisotope and Imaging Physicist in the Department of Physics at The Royal Marsden National Health Service Foundation Trust. “In this study we aimed to investigate whether selumetinib could resensitize these [patients with] differentiated thyroid cancer to radio[active] iodine,” he added.
Study Methods and Results
In the new multicenter phase II trial, researchers assigned patients with iodine-refractory differentiated thyroid cancer—who had one or more lesions with no measurable iodine uptake or an iodine-avid lesion that progressed within 12 months of radioactive iodine treatment—to undergo baseline iodine-123 [I-123]–sodium iodide [NaI] single photon-emission computed tomography (SPECT)/CT imaging and receive selumetinib orally twice daily for 4 weeks. In this novel approach, a small amount of radioactive iodine was used. The researchers then conducted follow-up I-123–NaI SPECT/CT imaging to determine whether the patients experienced increases in I-123–NaI to their thyroid lesions after taking selumetinib.
Pretherapy and posttherapy dosimetry were performed, and the range of absorbed doses was assessed. If the treatment was absorbed well, therapy was warranted, and the researchers were able to calculate a personalized treatment dosage for each patient.
Conclusions
A wide variation in the radiation delivered to different areas of the thyroid cancer was found among patients. However, the researchers reiterated that this variability could be accurately predicted from pretherapy scans with just a small amount of the radioactive drug.
“It is likely that the response to treatment is largely dependent on how much of the injected radiation is delivered to the disease as absorbed doses, and the range of radiation doses delivered may partly explain the variation in outcomes. The ability to predict the radiation doses delivered to areas of [the] disease implies that this could be considered when planning treatment [strategies] and that treatments may be tailored to individual patients,” underscored Dr. Taprogge.
The researchers concluded that the methods developed for this study—in particular the close collaboration between medical centers to collect and share images and radiation dosimetry results—may open the door to more informed treatments that could improve outcomes. These methods can be applied to the wider field of molecular radiotherapy and could significantly improve the clinical and cost effectiveness of existing and new radiotherapeutics.
Disclosure: For full disclosures of the study authors, visit jnm.snmjournals.org.
