[18F]fluoromisonidazole and a New PET System With Semiconductor Detectors and a Depth of Interaction System for Intensity Modulated Radiation Therapy for Nasopharyngeal Cancer
Purpose: The impact of a new type of positron emission tomography with semiconductor detectors (New PET) on an 18F-fluoromisonidazole (FMISO)-guided intensity-modulated radiation therapy (IMRT) plan was investigated by comparing the plan with the use of a state-of-the-art PET/computed tomography system (PET/CT) in nasopharyngeal cancer (NPC) patients. Methods and Materials: Twenty-four patients with non-NPC malignant tumors (control group) and 16 patients with NPC were subjected to FMISO-PET. The threshold of the tumor-to-muscle (T/M) ratio in each PET scan was calculated. The hypoxic volume within the gross tumor volume was determined using each PET ([NewPET]GTVh and [PET/CT]GTVh, respectively). Dose-escalation IMRT plans prescribing 84Gy to each GTVh were carried out. Results: The threshold of the T/M ratio was calculated to be 1.35 for New PET and 1.23 for PET/CT. The mean volume of [NewPET]GTVh was significantly smaller than that of [PET/CT]GTVh (1.5±1.6cc vs. 4.7±4.6cc, respectively, P =0.0020). The dose-escalation IMRT plans using New PET were superior in dose distribution to those using PET/CT. Dose escalation was possible in all 10 New PET-guided plans but not in one PET/CT-guided plan, because the threshold dose to the brainstem was exceeded. Conclusion: New PET was suggested to be useful for accurate dose escalation in FMISO-guided IMRT for patients with NPC
