Patients
This was a prospective study conducted in the period between December 2018 and November 2020. Forty patients with histopathologically proven primary colorectal cancer at any age ranging between 20 and 80 years with no sex predilection were enrolled in this study. The diagnosis of colorectal carcinoma in these patients was established based on their symptomatology, clinical examination, colonoscopy, and biopsy.
Patients with claustrophobia, metal implants (as cochlear implants), cardiac defibrillators and pacemakers, first trimesteric pregnancy, or post-surgical resection of colorectal cancer were excluded from this study. Approval of the institutional review board and written informed consents from all patients were obtained before the start of this study.
Technique of magnetic resonance imaging
1.5-Tesla MRI machine (Siemens Magnetom Sempra) was used for the examination using pelvic 8-channel phased array coil. The patients were advised to have an enema 1–2 h prior to the examination. The patient was lying on the examination couch in lateral decubitus and foly’s catheter was inserted with luminal distention by about 150–200 ml warm gel. The patient then return to the supine feet first position, the pelvic phased array coil is connected, and ear blugs and immobilization foam pads were applied. Buscopan (20 ml) was administrated intravenously to control the peristalsis, and sagittal scout images are obtained parallel to the coil. The imaging sequences included T2-weighted fast spin-echo axial images (T2WIs) with fat suppression [using echo time (TE) 89.2 ms, repetition time (TR) 2100 ms, slice thickness, 4.0 mm, field of view (FOV) 34.0 cm, matrix 256 × 224], non-contrast T1-weighted axial images (T1WIs) with fat suppression [using TE 1.78 ms, TR 3.73 ms, slice thickness 5 mm, FOV 310–370 mm, flip angle 13°, bandwidth 31.25 kHz, asset factor 2, NEX 1, matrix 288 × 160], fat suppressed dynamic contrast-enhanced T1-weighted images [using TE 1.7 ms, TR 210 ms, bandwidth 31.25 kHz, FOV 34.0 cm, flip angle 80°], and DWIs for the rectum or the colon [using TE 63.5 ms, TR × 7 ms, RR interval 7, b = 0 , 400 and 800 s/mm2, trigger window 20%, minimum trigger delay, minimum inter-sequence delay, FOV 34.0 cm, slice thickness 5 mm, spacing 1 mm, asset factor 2, NEX 8, matrix 128 × 128]. Reconstruction of all axial images to 256 × 256 matrix after scanning was done. For each lesion, mean ADC was calculated by manually drawing a region of interest smaller in size than the lesion not including adjacent normal tissue.
Neoadjuvant chemoradiotherapy
Forty-five grays per 25 fractions preoperative pelvic radiation therapy (1.8 Gy per day) over the course of 51/2 or 6 weeks. Subsequent 5.4 Gy per three fractions boost was delivered to the primary neoplasia. Concurrent intravenous injection of two cycles of 5-fluorouracil (500 mg/m2/d) with radiation therapy for 3 days during the 1st and 5th weeks of radiation therapy was also given to the patients.
Follow-up by MRI
Twenty patients out of forty were examined by MRI with diffusion after completion of chemoradiotherapy. The tumor in all the followed up twenty patients was in the rectum.
Image interpretation
The MRI images were interpreted by two consultant radiologists of 6- and 13-year experience in pelviabdominal MRI. They reported the findings after reviewing conventional MRI alone and after reviewing conventional MRI with DWI and ADC value calculation.
In follow-up studies, CR was reported in conventional MRI when there is no mass or mural thickening seen and non-CR was reported when there is visualized residual tumor tissue. When DWI added to the conventional images, CR was reported when there was no high signal in the site of corresponding tumor and non-CR was reported when there is residual high signal in the site of corresponding tumor. After calculation of ADC value, a cutoff value of 1.20 × 10−3 mm2/s was used to discriminate CR from non CR. This value was used considering the results of previous study done by Kim et al. [2].
Biopsy after chemoradiotherapy
The primary tumor response to the chemoradiotherapy was graded as follows: “pathologic complete response” (which means no residual tumor cells found in the sample) or “pathologic non-complete response/residual tumor” varying from limited tumor cells to a solid residual tumor mass. Post-therapeutic pathological staging was compared to the MRI staging.
Statistical analysis
A post hoc power analysis was done using the G∗Power software version 3.1.9.4, with a sample of size 20, considering an effect size equal to 0.5, an alpha level of 0.05, and the resulting power 69.5%. Software (SPSS for Windows, version 10.0.1, 1999; SPSS, Chicago, III) was used for statistical analysis. The results were expressed as mean ± standard deviation or number (%). Comparison between mean values of ADC in the studied groups was performed using the one-way ANOVA test, followed by the Tukey test for multiple comparisons whenever a statistical significance was detected by the ANOVA. The standard diagnostic indices including sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy (diagnostic efficacy) were calculated as described by Galen (1980). P value less or equal to 0.05 was considered significant and less than 0.01 was considered highly significant. A summary of study methodology is shown in Fig. 1.