Abstract
Purpose: Patients with locally advanced rectal cancer (LARC) achieving pathologic complete response (pCR) to neoadjuvant chemoradiotherapy (CRT) have significantly improved long term survival. Preoperative detection of pCR may enable a conservative therapeutic approach in some patients. The purpose of the current prospective pilot study was to assess multiparametric qualitative and quantitative MR, PET, PET-MR and tumor texture features in predicting pCR to CRT in patients with LARC. Material and Methods: Eighteen LARC patients underwent staging with FDG-PET and MR-rectum and 15 had post-CRT restaging. Response was assessed qualitatively and quantitatively. SUV (tumor/background), SUV/ADC, and tumor texture parameters derived via machine learning algorithms (MLA) from PET and multiple MR sequences and were correlated with histopathology. Results: A third of patients had pCR. Sensitivity, specificity & accuracy of PET, MR and combined PET-MR were 90, 60, & 80; 90, 20 & 66.7; 90, 80 & 86.7, respectively. Differences did not reach statistical significance. Quantitatively, only tumor-muscle (SUV/ADC) ratio improved prediction of pCR. Of all texture features assessed using MLA, only the classifier trained on pre-treatment PET was significant (p = 0.034; accuracy, 92.8%). Combined PET and MR texture features did not improve performance. Conclusion: Combined PET-MR may improve specificity compared with PET or MR alone, although this needs to be validated in a larger cohort. Tumor to muscle SUV/ADC ratios post-therapy and texture features on baseline PET show promise in improving prediction of pCR post-CRT in LARC.
Highlights
Pre-operative chemoradiation therapy (CRT) has become the standard of treatment for locally advanced rectal cancer (LARC)
Eligible subjects included patients referred to our institution with locally advanced rectal cancer (T3-T4, N0-N1) based on clinical and imaging studies that were deemed fit to have preoperative chemoradiation and surgery
Eighteen patients with LARC were recruited for this trial, including 12 men and 6 women, with mean age of 59.8 years
Summary
Pre-operative chemoradiation therapy (CRT) has become the standard of treatment for locally advanced rectal cancer (LARC). Following pre-operative radiation, 10% - 30% of patients have no residual tumour in the pathologic specimen following surgery [1]. This is referred to as a complete pathologic response. There has been no single reliable imaging modality to select patients who have had a complete pathologic response before surgery [4]. If this was possible, some patients may be spared a radical resection and permanent colostomy. This would have a significant impact on management of rectal cancer and the quality of life for patients [5]
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