Influences of PET/CT on CT-based radiation-treatment-plan of oral cavity cancer

Objective: To evaluate the influences of PET/CT on CT-based radiation-treatment- plan (RTP) and radiotherapy modality of oral cavity cancer.

Methods: Thirty-one oral cavity cancer patients with oral tongue (10), floor of mouth (4), gingiva (6), buccal mucosa (3), hard palate (4) and soft palate (4) were enrolled on the prospective study. 10 of 31 patients had local recurrence disease after surgery. Non-contrast and contrast-enhanced CT scan in treatment position of head-neck for each patient was obtained first. After that, integrated 18F-FDG-PET/CT scan was obtained. Subsequently, CT-based and PET/CT-based RTPs were designed by same radiotherapist. The two RTPs were compared to evaluate the influences of PET/CT on CT-based RTP including the changes of radiation target volume in gross tumor volume (GTV), neck radiation fields and overall radiotherapy modality.

Results: The change of target volume in GTV >15% accounted for 19/31 (61.3%). In 3 of 31 patients (9.7%) neck radiation field were enlarged or added in lower neck because PET/CT showed positive cervical lymph nodes (CT scan negative). In CT-based RTP of a recurrence patient with upper gingival cancer after surgery, both of primary site and neck were designed into radiation fields. After PET/CT scan, the plan changed to radiation to primary site only. The PET/CT showed positive in primary site and negative in neck. After follow-up of ten months, the patient still had not neck disease. 2 of 31 patients (6.4%) changed overall radiation modality from definitive radiation therapy into palliative radiation therapy and chemotherapy because PET/CT showed distinct metastases in lung (1) and bone (1).

Conclusion: PET/CT resulted in a significant change to the CT-based RTP and radiotherapy modality. Additional PET/CT imaging is valuable for improvement of CT-based RTP in oral cavity cancer patients.