Quantitative analysis of mean ADC in cervix cancer patients during chemoradiotherapy

Abstract

Purpose or Objective A pilot study to evaluate changes in mean apparent diffusion coefficient (ADC) as a quantitative imaging biomarker during chemoradiotherapy prior to implementation on the MR Linac (MRL). Material and Methods A sample of 6 patients undergoing curative-intent concurrent chemoradiotherapy (CRT) for locally advanced cervical cancer (LACC) were enrolled into a prospective observational imaging study. Sagittal T2 weighted (T2W) and diffusion weighted imaging (DWI) sequences were obtained at three time points during external beam radiotherapy (EBRT). These were in addition to the regular imaging protocol. Conventional ADC maps were calculated and co-registered to the T2W images. A radiologist delineated the tumour volume of interest on the T2W sequences and mean ADC values were calculated. Patients with serial tumour volume reduction at diagnostic MR imaging were classified as imaging-based responders using the Response Evaluation Criteria in Solid Tumors (RECIST) criteria1,2 Results Patients 1-5 were all responders and patient 6 was a nonresponder. The responders demonstrate a serial increase in mean ADC values during chemoradiotherapy with a positive correlation (Spearman’s rs = 0.69; t=3.42; p=0.005). CRT affects the tumour microarchitecture and integrity of cell membranes. ADC, which measures the rate of water mobility, increases after successful therapy because cell density decreases and reflects cell death3.The solitary non-responder (Patient 6) did not demonstrate this trend with a fall in mean ADC value at the third time point. This tumour was a high grade, poorly differentiated, adenosquamous carcinoma which may explain the poor response. Conclusion During CRT, cervical tumour mean ADC values serially increase in those patients responding to treatment. This pattern was not seen in the non-responding patient. This supports the role of serial functional imaging during chemoradiation as a biomarker, and will inform our protocols when commissioned on the MRL which has a similar 1.5T magnet to the diagnostic MR used in this study.