Evaluation of Volumetric Magnetic Resonance Imaging in Determining the Indication for Total Neoadjuvant Therapy in Rectal Cancer.

BACKGROUND

This study aims to evaluate the relationship between volumetric measurements of residual tumor via magnetic resonance imaging (MRI) and pathologic complete response (pCR) in rectal cancer patients undergoing neoadjuvant chemoradiotherapy (nCRT).

METHODS

Patients with locally advanced rectal cancer who had pelvic MRI for clinical staging and completed nCRT followed by radical resection were included. Two experienced radiologists measured tumor volume on MRI obtained before and after nCRT. We compared the pre- and post-CRT tumor volume and measured tumor volume reduction rates.

RESULTS

The median value of tumor volume reduction rate in all patients was 64.7% (min-max - 81.1-98.1%). When the relationship between tumor volume and tumor regression grade (TRG) after nCRT was assessed, it was found that 18 of 21 (86%) patients with a good response (TRG 1) had a post-CRT tumor volume of ≤ 8 cm3 (p = 0.001). While 9 of 10 patients with pCR after nCRT had a tumor volume of ≤ 8 cm3, one patient had pCR despite having a tumor volume greater than 8 cm3 (p = 0.015).

CONCLUSION

The correlation between post-nCRT residual tumor volume and pCR underscores the potential of volumetric MRI as a predictive tool in tailoring rectal cancer treatment. For patients with residual tumor volumes greater than 8 cm, extending neoadjuvant chemotherapy as part of TNT may enhance the likelihood of achieving pCR. This approach advocates for a more personalized treatment strategy, potentially optimizing outcomes for rectal cancer patients.