Role of [18F]FDG-PET/CT in Evaluation of Tumor Response to Chemoradiation Therapy for Advanced Colorectal Cancer.

OBJECTIVES

The objective is to evaluate the efficacy of F-fluorodeoxyglucose positron emission tomography (F-FDG-PET) computed tomography (CT) in the evaluation of tumor response to preoperative/palliative chemoradiotherapy (CRT) for advanced colorectal cancer; including metastatic cancer at primary presentation and recurrent cancers with local and/or distant metastasis.

MATERIALS AND METHODS

Fifty patients with advanced rectal cancer underwent two point imaging with 18 FDG PET-CT before and after 3 weeks of completion of preoperative/palliative CRT in between 2016 and 2022. Patients with locally recurrent cancer also underwent radical surgery. The assessment consisted of the evaluation of the following metabolic PET parameters: Maximum standardized uptake value (SUV), SUV, metabolic tumor volume (MTV), and total lesion glycolysis (TLG). Response was assessed among the followed patients using RECIST 1.1 criteria.

OBSERVATIONS AND RESULTS

There was a significant decline in the mean post therapy SUV and SUV as compared to baseline ( = 0.0001). Twenty-six out of 50 (52%) patients were classified as responders. A significant decrease in all parameters (SUV, SUV, TLG, and MTV) from baseline was observed in responders of the study when comparing with nonresponders ( < 0.05). Besides SUV and SUV, the mean posttherapy TLG was significantly reduced in responders than nonresponders ( = 0.0065).

CONCLUSION

PET-CT is a useful combined anatomic and functional imaging modality in monitoring tumor response to preoperative/palliative CRT in advanced rectal cancer, whether primary or recurrent, including metastatic cancers at presentation. Posttherapy SUV and TLG in particular are significantly associated with treatment response.