PET/CT with 3'-deoxy-3'-[18F]fluorothymidine for lung cancer patients receiving carbon-ion radiotherapy

The aim of this study was to investigate the clinical value of 3'-deoxy-3'-[F]fluorothymidine-positron emission tomography/computed tomography (FLT-PET/CT) for lung cancer patients receiving carbon-ion radiotherapy.

Twenty consecutive patients with lung cancer underwent FLT-PET/CT before and after carbon-ion radiotherapy. Fifty minutes after intravenous injection of approximately 300 MBq of FLT, PET/CT data were acquired. Maximal standardized uptake value of the tumor was measured, from which the reduction rate of tumor FLT uptake was calculated. After treatment, the patients were followed (17-42 months for survivors) for the development of recurrence and survival.

Primary responses to carbon-ion radiotherapy were partial in 13 patients, stable disease in six patients, and nonevaluable in one patient. Although tumor FLT uptake significantly decreased after treatment (P < 0.001), the presence of radiation pneumonitis hampered its precise evaluation. During the follow-up period, nine patients developed recurrence, and seven patients died including two deaths from other causes. Pretreatment FLT uptake of patients who developed recurrence and who died of lung cancer were significantly higher than that of patients who did not (P = 0.008 and 0.007, respectively). Kaplan-Meier analysis using a cut-off value also supported the prognostic value of pre-carbon-ion radiotherapy FLT-PET/CT.

This investigation suggests that FLT-PET/CT is feasible in evaluating lung cancer patients undergoing carbon-ion radiotherapy. The presence of radiation pneumonitis can influence tumor FLT uptake and needs special attention. Pre-carbon-ion radiotherapy FLT-PET/CT seems to have a prognostic value and may contribute to decision-making on the treatment strategy.