Purpose: Introducing a radiobiological index based on early tumor regression during neo-adjuvant radio-chemotherapy (RCT, including oxaliplatin) of rectal adenocarcinoma and testing its discriminative power in predicting the tumor response. Methods: Seventy-four patients were treated with Helical Tomotherapy following an adaptive (ART) protocol (41.4 Gy/18 fr, 2.3 Gy/fr) delivering a simultaneous integrated boost on the residual tumor in the last 6 fractions up to 45.6 Gy. T2-weighted MRI were taken before (MRIpre) and at mid (MRImid) therapy and the corresponding tumor volumes were considered (Vpre,Vmid). The “Early Regression Index” (ERITCP=-ln[(1-(Vmid/Vpre))Vpre]) was introduced and its discriminative power was assessed in terms of AUC, sensitivity/specificity, positive/negative predictive value (PPV/NPV). Two end-points were considered: (a) pathological complete response (pCR) or clinical complete response followed by watch-and-wait, (cCR); (b) limited response (residual vital cells (RVC) in the surgical specimen >10%). Results: Complete data were available for 65 patients: pCR, cCR and RVC >10% were 20, 2 and 19 respectively. The discriminative power of ERITCPwas moderately high (AUC = 0.81/0.75 for /pCRorcCR/RVC >10% respectively, p <0.0005). ERITCPwas highly sensitive (86–89%) with very high NPV (90–94%). The discriminative power of ERITCPwas confirmed on a subgroup of 44/65 patients when considering tumor volumes delineated by a skilled radiologist. Conclusion: A radiobiologically consistent index based on early regression showed high performances in predicting the pathological response after neo-adjuvant RCT for rectal cancer with relevant potentialities for ART/treatment customization. © 2018 Elsevier B.V.
Fiorino, C., Gumina, C., Passoni, P., Palmisano, A., Broggi, S., Cattaneo, GM., Di Chiara, A., Esposito, A., Mori, M., Raso, R., Ronzoni, M., Rosati, R., Slim, N., De Cobelli, F., Calandrino, R., & Di Muzio, NG. (2018). A TCP-based early regression index predicts the pathological response in neo-adjuvant radio-chemotherapy of rectal cancer. Radiotherapy and Oncology, 128(3), 564-568. https://doi.org/10.1016/j.radonc.2018.06.019