Predicting complete response to neoadjuvant CRT for distal rectal cancer using sequential PET/CT imaging

Area of Science:

• Oncology
• Radiology
• Medical Imaging

Background:

• Positron emission tomography/computerized tomography (PET/CT) offers advanced diagnostic insights beyond standard imaging for rectal cancer.
• PET/CT may help identify patients with rectal cancer who are likely to achieve complete tumor regression after neoadjuvant chemoradiation therapy (CRT).

Purpose of the Study:

• To identify specific PET/CT features associated with complete tumor response following neoadjuvant CRT in rectal cancer patients.
• To evaluate the predictive value of baseline and follow-up PET/CT scans in assessing treatment response.

Main Methods:

• A prospective single-center trial (NCT 00254683) included 99 patients with distal rectal cancer (cT2-4N0-2M0).
• Patients underwent baseline PET/CT, followed by neoadjuvant CRT (54 Gy and 5-fluorouracil-based).
• Follow-up PET/CT scans were performed at 6 and 12 weeks, with clinical response assessment blinded to radiological data.

Main Results:

• Complete pathological response (pCR) was observed in 7 patients, and complete clinical response (cCR) in 16 (23 total complete responders).
• Baseline primary tumor Standard Uptake Value (SUV) was a significant predictor of pCR.
• Depth of rectal wall uptake at baseline and the change in maximum SUV (SUVmax) between baseline and 12-week scans were independent predictors of complete response (pCR or cCR).
• A decrease in SUVmax >67% by week 6 or >76% by week 12 predicted complete response.

Conclusions:

• PET/CT imaging at baseline, 6, and 12 weeks provides valuable information for predicting complete tumor regression after neoadjuvant CRT.
• These findings suggest PET/CT can help stratify rectal cancer patients based on their likelihood of achieving a complete response to neoadjuvant therapy.