Exploring MR regression patterns in rectal cancer during neoadjuvant radiochemotherapy with daily T2- and diffusion-weighted MRI

Abstract

Background: To date, only limited magnetic resonance imaging (MRI) data are available concerning tumor regression during neoadjuvant radiochemotherapy (RCT) of rectal cancer patients, which is a prerequisite for adaptive radiotherapy (RT) concepts. This exploratory study prospectively evaluated daily fractional MRI during neoadjuvant treatment to analyze the predictive value of MR biomarkers for treatment response. Methods: Locally advanced rectal cancer patients were examined with daily MRI during neoadjuvant RCT. Contouring of the tumor volume was performed for each MRI scan by using T2-and diffusion-weighted-imaging (DWI)-sequences. The daily apparent-diffusion coefficient (ADC) was calculated. Volumetric and functional tumor changes during RCT were analyzed and correlated with the pathological response after surgical resection. Results: In total, 171 MRI scans of eight patients were analyzed regarding anatomical and functional dynamics during RCT. Pathological complete response (pCR) could be achieved in four patients, and four patients had a pathological partial response (pPR) following neoadjuvant treatment. T2-and DWI-based volumetry proved to be statistically significant in terms of therapeutic response, and volumetric thresholds at week two and week four during RCT were defined for the prediction of pCR. In contrast, the average tumor ADC values widely overlapped between both response groups during RCT and appeared inadequate to predict treatment response in our patient cohort. Conclusion: This prospective exploratory study supports the hypothesis that MRI may be able to predict pCR of rectal cancers early during neoadjuvant RCT. Our data therefore provide a useful template to tailor future MRguided adaptive treatment concepts.

Linear Tumor Regression of Rectal Cancer in Daily MRI during Preoperative Chemoradiotherapy: An Insight of Tumor Regression Velocity for Personalized Cancer Therapy

“…Although the survival rate in early stage is high, approximately 80% [ 2 ], loco-regionally advanced stage requires multimodal therapy both pre- and post-surgery in order to improve outcome. The advancement in treatment strategies has been remarkable in the field of rectal cancer, establishing neoadjuvant concurrent chemoradiotherapy (CCRT) as the current standards of care for the locally advanced disease [ 3 , 4 , 5 , 6 , 7 ]. The advances are still in progress and have developed in both ways: treatment intensification, such as total neoadjuvant therapy, and treatment de-intensification, such as the watch-and-wait approach [ 8 , 9 ].…”

Magnetic resonance linear accelerator technology and adaptive radiation therapy: An overview for clinicians

“…Conversely, novel strategies of applying higher RT doses to rectal tumors are emerging as a potential method to allow organ preservation, eliminating surgery in some patients 117 . In addition, recent data have demonstrated that rectal tumors regress during treatment with RT, and this can be seen optimally on MRI 118 . Historically, patients with rectal cancer have been treated with preoperative therapy followed by surgical resection (in some cases, leading to permanent colostomy); however, that paradigm is starting to significantly change.…”

T2 relaxation time for the early prediction of treatment response to chemoradiation in locally advanced rectal cancer

“…After CRT, the tumor volume is further reduced (l-n), and the T2 value is decreased to 52 ms (o, p) (the patchy red areas on the color-coded image represent fibrosis). The postoperative pathology is classified as TRG 1, with no residual tumor cells found in fibrosis (q, hematoxylin-eosin stain, original magnification ×100) Some prospective exploratory studies reported that MRI during neoadjuvant RCT may predict early pCR in rectal cancer patients [31]. A radiomics model that included MRI values before and during radiotherapy showed excellent predictive capability for identifying pCR in LARC patients, with an AUC of 0.93 [24].…”