Uday Bharat Patel MBBS, BSc, Presenter: Nothing to Disclose

David J. Collins, Abstract Co-Author: Nothing to Disclose

Irene Chong MRCP, FRCR, Abstract Co-Author: Nothing to Disclose

Dow-Mu Koh MBBS, Abstract Co-Author: Nothing to Disclose

Diana Tait MRCP, FRCR, Abstract Co-Author: Nothing to Disclose

Gina Brown MD, MBBS, Abstract Co-Author: Nothing to Disclose

To measure serial changes in tumor ADC values after chemoradiotherapy (CRT) in patients enrolled into a surveillance protocol of deferred surgery following response to chemoradiotherapy.

We prospectively studied patients undergoing imaging and clinical surveillance following a good response to preoperative CRT. The primary endpoint of the trial is to demonstrate that surgery can be deferred and even permanently deferred in patients that show complete response. Using high resolution T2 weighted imaging we outlined tumor/treated tumor/tumor scar and used them to define the region of interest (ROI) on ADC map. Analysis of  ROIs on ADC maps was undertaken using Diffusion View™ software to determine: 1. Changes in ADC values from 6 weeks to 36 months after completion of radiotherapy. 2. Characteristic ADC values in patients with complete response on long term surveillance. 3. Characteristic ADC values in patients with tumor regrowth whilst on surveillance.  Between patient ADC measurement variabilty was assessed by 3 observers identifying ROIs independently  

 Of the 25 patients enrolled, 10 had active tumor at some point in surveillance while 15 had clinically and biopsy proven complete response to treatment.   Cases with active tumor during follow-up. Patients with biopsy proven recurrent disease or recently finishing chemoradiotherapy were found to have ADC values > 1.5 X 10-3/s (low - intermediate signal).    Complete response to CRT. Fibrotic areas of scarring had ADC values < 1 X 10-3/s (very low - low signal).   Analysis. Mean ADC values in images showing tumor ranged between 1.44 –2.65 X 10-3/s. Mean ADC values in images showing fibrosis ranged between 0.53-1.35 X 10-3/s. A significant difference between these two groups was found p=0.025 (Mann-Whiney U test). Setting a threshold of ADC=1.5 X 10-3/s or above, enabled identification of all patients with recurrent disease. 43/53 (81%) of patients with a stable region of fibrosis were identified using a threshold ADC of up to 1.1 X 10-3/s.  

In our study tumor showed intermediate signal on ADC images, with values greater than 1.5 X 10-3mm/s. Regions of post CRT fibrosis showed low signal intensity, with values generally less than 1.1 X 10-3/mm2.   

Serial ADC quantification following CRT in rectal cancer is a promising method for monitoring disease.

Patel, U, Collins, D, Chong, I, Koh, D, Tait, D, Brown, G, Serial ADC Measurements in Rectal Cancer Patients Deferring Surgery Following Chemoradiotherapy—Detecting Residual Disease, Complete Response and Tumor Regrowth.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8011686.html