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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 cm3, 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. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the European Society of Urogenital Radiology (ESUR) score, the Likert scale, tumor contact length (TCL) > 1 cm, and EPE (extraprostatic extension) grade in predicting EPE at multiparametric magnetic resonance imaging (mp-MRI).Methods: Seventy-nine patients who underwent 3-T MRI and were histopathologically confirmed by microblocks were enrolled in this retrospective study. The index lesions were interpreted by two experienced radiologists. Apparent diffusion coefficient (ADC) values were also noted. Weighted κ statistics were used to compare interreader agreement. Univariate logistic regression analysis was performed to define independent predictors of EPE status. Multivariable logistic regression and receiver operating characteristic (ROC) analysis were performed to compare the MRI-based methods and clinical variables (ISUP grade, prostate volume and PSA density) + MRI-based methods for pathologic EPE prediction by using the area under the curve (AUC) value.Results: The mean age was 64.5 years ± 6.2. 33/79 (41.8%) patients had pathologic EPE. As ESUR score showed weak interreader agreement (κ = 0.537), Likert scale, TCL, and EPE grade showed moderate agreement (κ = 0.608, κ = 0.747, κ = 0.647 respectively). Univariate ROC analysis result showed that all MRI-based score systems, mean ADC value, the ISUP grade, prostate volume, PSA density were the best variables in predicting EPE. ROC analysis results of four MRI-based methods showed good diagnostic performance. At multivariate analysis, all clinical models showed excellent diagnostic performance.Conclusion: All four MRI-based methods had good diagnostic performance. Furthermore, consisting of both qualitative and quantitative parameters and being less reader experience dependent, EPE grade was a promising method in predicting EPE. All clinical models showed excellent diagnostic performance. [ABSTRACT FROM AUTHOR]