Gross tumor volume is a good predictor of rectal cancer tumor response before chemoradiation with concurrent thermal therapy

Abstract

Background and purpose: This study aimed to evaluate whether we can predict tumor response prior to neoadjuvant chemoradiotherapy (NACR) with concurrent radiofrequency (RF) thermal therapy for rectal cancer. Material and Methods: This study included 80 patients with primary rectal adenocarcinoma localized in the rectum (up to 12 cm from the anal verge) and who received NACR intensity-modulated radiotherapy (IMRT) once daily 5 times/week, 50 Gy delivered to the planning target volume (PTV) in 25 fractions, capecitabine 1700 mg/m2 per day for 5 days per week, and thermic treatment (once a week for 5 weeks with 50 min irradiation). In order to further minimize RF-related complications, we used an initial time of 0 min for the time at which an output limiting symptom occurred as a predicted initial RF output (IRO) and compared this to the tumor response and target volumes (TVs) as defined by computed tomography (CT), magnetic resonance imaging (MRI), and/or 18F-fluorodeoxyglucose positron emission tomography/CT (FDG-PET/CT) findings. A receiver operating characteristic (ROC) curve analysis was used in this study to identify the best-fitted cut-off value for predicted initial radiofrequency output (IRO) and TVs. Results: Gross tumor volume (GTV) correlated significantly with tumor stages, lymph node stages, and pretreatment TNM stages, but not clinical tumor volume (CTV) and PTV. GTV was a better imaging parameter than CTV and PTV for prediction of treatment response in this modality. Patients with predicted IRO ≥ 669.4 Watt, increased body temperature by RF thermal therapy and had a GTV ≤ 31.2 cm3 showed a good indication for this modality. Conclusions: We will be able to select rectal cancer patient prior treatment who respond to chemoradiation therapy with concurrent thermal therapy.