3'-deoxy-3'-[ ¹⁸ F]fluorothymidine PET quantification of bone marrow response to radiation dose

Purpose: The purpose of this study was to quantify the relationship of bone marrow response to radiation dose, using 3'-deoxy-3'-[ ¹⁸ F] fluorothymidine ([ ¹⁸ F]FLT)-labeled uptake quantified in positron-emission tomography (PET) scans. Methods and Materials: Pre- and post-Week 1 treatment [ ¹⁸ F]FLT PET images were registered to the CT images used to create the radiation treatment plan. Changes in [ ¹⁸ F]FLT uptake values were measured using profile data of standardized uptake values (SUVs) and doses along the vertebral bodies located at a field border where a range of radiation doses were present for 10 patients. Data from the profile measurements were grouped into 1 Gy dose bins from 1 to 9 Gy to compare SUV changes for all patients. Additionally, the maximum pretreatment, the post-Week 1 treatment, and the dose values located within the C6-T7 vertebrae that straddled the field edge were measured for all patients. Results: Both the profile and the individual vertebral data showed a strong correlation between SUV change and radiation dose. Relative differences in SUVs between bins >1 Gy and <7 Gy were statistically significant (p < 0.01, two-sample t test). The reduction in SUV was approximately linear until it reached a reduction threshold of 75%-80% in SUV for doses greater than 6 Gy/week for both the dose-binned data and the vertebral maximum SUVs. Conclusions: The change in SUV observed in head and neck cancer patients treated with chemoradiation shows the potential for using [ ¹⁸ F]FLT PET images for identifying active bone marrow and monitoring changes due to radiation dose. Additionally, the change in [ ¹⁸ F]FLT uptake observed in bone marrow for different weekly doses suggests potential dose thresholds for reducing bone marrow toxicity.