DW-MRI with Whole Tumor Volume Analysis as A Predictor of Response in Rectal Cancer Treatment

Conclusion

Although MR imaging is extensively used for initial staging of rectal cancer, it has limita-tions when used for restaging following CRT because it is difficult to distinguish fibrosis, desmoplastic response, and colloid from remaining viable tumor. Traditional MR imaging is exclusively utilized for anatomical imaging.

The ADC has been used to describe tumors and measure treatment-induced changes that may occur before morphologic changes do.

Furthermore, by identifying areas of variable diffusivity, histogram analysis of the ADC can evaluate the biologic heterogeneity of a tumor, which may have prognostic and predictive consequences.

Introduction

In men, colorectal cancer is the third most prevalent cancer, while in women, it is the second most common.^(1). To minimize both under- and overtreatment, imaging has become an important tool in preoperative decision-making.⁽²⁾

Rectal Magnetic resonance R imaging has been utilised to assess chemo-radiotherapy (CRT) utilising morphologic and/or functional Magnetic resonance  imaging sequences, however the diagnostic performance of these techniques is variable. Most rectal cancers acquire fibrosis after neoadjuvant (CRT), resulting in lower signal intensity with T2-weighted imaging. ⁽³⁾

The Apparent diffusion coefficient (The ADC) can be used to describe tumours and measure treatment-induced changes that may occur before morphologic changes do. Furthermore, by identifying areas of variable diffusivity, histogram analysis of the ADC can evaluate the biologic heterogeneity of a tumour, which may have prognostic and predictive implications. ⁽⁴⁾

Histogram techniques are especially well suited to assessing tumor heterogeneity because they may detect various micro-environments that are disguised by mean ADC values. The Brownian motion of water molecules is measured using the ADC technique. Reduced diffusion is associated with poor ADC values in solid tumours. ADC levels are higher in post-

treatment malignancies due to cell death and the removal of restrictive barriers, although high ADC values can also be seen in necrotic foci. ⁽⁵⁾

Recent research has discovered that combining the whole-tumor ADC mean with the tumour volume accurately predicts Pathological Complete Response. ^(6).

Other research has shown that the Apparent Diffusion Coefficient value may be used as a quantitative and objective marker to assess the pathologic response of preoperative CRT in rectal cancer^{. (7)}

 Materials and methods

This study included forty patients diagnosed with rectal cancer. They managed according to national treatment protocols. 

Detailed history taking and Magnetic resonance imaging (MRI) including diffusion-weighted imaging (DWI), before and after   CRT was done to all patients. Endoscopy and/or surgery was done to obtain biopsy for histopathological analysis which is the reference standard for pathologic complete response (pCR).

Apparent Diffusion coefficient (ADC) Measurement :

The mean ADC was calculated by positioning multiple regions of interest (ROI) over the tumor in consecutive image sections & then the mean ADC was calculated.

ADC histogram and Whole Tumor Volume Analysis has been done, and comparison of the pre and post CRT was done for evaluation of the skewness and kurtosis of the histogram of the ADC values.

Results

the tumor volume was shown to be substantially correlate with tumor response, with the responding group (33.5 cm³) having a smaller tumor volume than the non-responding group (65 cm³).

Discussion

Rectal cancer treatment has changed from a surgical approach with radiation therapy or combination chemotherapy and radiation therapy (CRT) to the use of neoadjuvant CRT before surgery. The local recurrence rate has decreased, but long-term survival and sphincter preservation rates have increased as a result of this change.

Patients who obtain a full response with CRT should have their therapy altered based on their particular risk of local recurrence, and less invasive treatment options (compared to normal rectal surgery) may be used.

The depth of tumor invasion into the rectal wall or mesorectal fascia can be determined by magnetic resonance imaging (MR imaging). MR imaging is utilized to determine the treatment approach because of its excellent accuracy in detecting local tumor development and lymph node involvement—both of which are critical for decision making.

Rectal cancer is considered one of the most frequent gastrointestinal malignancies, accou-nting for 50 percent to 70 percent of colorectal cancer cases^(8). Surgery, in combination with radiation, chemotherapy, and targeted therapy, are the alternatives during management of  rectal cancer. Accurate staging is a critical step in guiding treatment decisions. TNM stage, tumour differentiation degree, and the presence of peritumor lymphatics, vascular infiltration, and nerve infiltration will all influence the rate of rectal cancer recurrence following surgery.⁽⁹⁾

In our study, the tumor volume was shown to be substantially correlate with tumor response, with the responding group (33.5 cm³) having a

smaller tumor volume than the non-responding group (65cm³).

In harmony with some studies like Lee E. S., et al., (2018) as significant correlations between tumor volume and pathologic complete response pCR have been reported.⁽¹⁰⁾ Regarding these findings, pre-treatment tumor volume and TNM stage were considered as a predictor for post chemotherapy response. In our study, the rectal cancer tumor volume was significantly larger in participants who had pelvic lymph node metastasis, compared to those who did not.