Radiology: MR volume measures predict rectal tumor therapeutic response

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MR volumetric measurements provide a reliable marker of rectal cancer prognosis and can be used to predict disease-free survival and tumor regression grade, according to a study published online March 21 in Radiology.

Low rectal cancer remains a management challenge, according to Stephanie Nougaret, MD, of the department of abdominal imaging at Hopital Saint Eloi in Montpellier, France, and colleagues. These tumors are associated with a higher rate of circumferential resection margin involvement, higher local recurrence rates and poorer survival. Clinicians need a method to differentiate tumors with a good prognosis from those with a poor prognosis to plan therapy and optimize outcomes, the researchers wrote.

Nougaret and colleagues conducted a retrospective analysis of 58 patients with locally advanced low or mid rectal carcinoma.

Two radiologists blinded to clinical information independently reviewed MR data, measuring tumor volume before and after combined chemotherapy and radiation therapy. They compared tumor volume reduction ratio, circumferential resection margin, T stage and occurrence of downstaging with histopathologic response and disease-free survival.   

“Each rectal volumetric examination was performed in approximately five minutes, which increased the reading time of each MR image, but overall, was still acceptable,” wrote Nougaret et al.

The researchers analyzed measurements for the 51 patients with available data, and calculated an optimal cutoff of tumor volume regression of more than 70 percent. “With regard to tumor volume reduction, only two of 30 patients with a volume reduction ratio of more than 70 percent showed recurrence. Fourteen of the 21 patients with a volume reduction ratio of less than 70 percent had recurrence.” This cutoff may be used as a surrogate for clinical response to predict tumor regression grade (TRG) and outcome, they noted.

Nougaret and colleagues also reported differences in tumor volume reduction rates based on patients’ TRG. Patients with a TRG of 1 or 2 had a mean tumor volume reduction rate of 57 cm 3, compared with 83 cm 3 in those with a TRG 3 or 4.  

The researchers emphasized the need for objective evaluation of parameters of tumor response after preoperative therapy. “Our study demonstrated that volumetric measurement of tumors with semiautomated software is a reliable marker for rectal cancer prognosis, especially in low-lying tumors where T stage and circumferential resection margin involvement are less reliable,” they wrote.

Finally, Nougaret and colleagues noted that MR volumetric measurements may be easier and faster to perform and more indicative of survival prognosis than traditional parameters.  Another benefit of the approach for patients with low-lying tumors is that a good response after chemotherapy and radiation therapy enables surgeons to spare the sphincter, which could result in fewer complications and an enhanced quality of life compared with patients who undergo radical resection.