Genitourinary Cancer

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SU_29_2293 - Largest axial dimension of tumor on T2W endorectal MRI is associated with biochemical outcome in men treated with external beam radiation therapy for prostate cancer

Sunday, October 21
1:15 PM - 2:45 PM
Location: Innovation Hub, Exhibit Hall 3

Largest axial dimension of tumor on T2W endorectal MRI is associated with biochemical outcome in men treated with external beam radiation therapy for prostate cancer
S. Liauw1, G. Kauffmann2, P. Patel2, and A. Oto2; 1The University of Chicago, Department of Radiation and Cellular Oncology, Chicago, IL, 2University of Chicago, Chicago, IL

Purpose/Objective(s): Endorectal MRI (eMRI) can help stratify risk in men who undergo external beam RT (EBRT) for prostate cancer. Radiographic extracapsular extension (ECE) and seminal vesicle invasion (SVI) have previously been associated with treatment failure after EBRT, however these imaging features may be more difficult to interpret. We explored the value of a potentially more practical, consistently measurable radiographic marker for outcome, largest axial size of the tumor nodule.

Materials/Methods: 97 men with NCCN intermediate or high risk prostate cancer underwent multi-parametric eMRI prior to EBRT, prior to any neoadjuvant hormonal therapy. Men with suspected radiographic lymph node involvement (n=13) were excluded, leaving 84 men for analysis. Median age was 69. Median PSA was 10.1; Gleason score was 6, 7, or 8-10 in 8%, 70%, 21%, respectively. 64% had NCCN high-risk disease. RT was given using daily image guidance to a median dose of 78 Gy, with concurrent hormonal therapy (ADT) in 56% for a median 9 mo (range 3-28). Size was measured on the axial slice representing the largest tumor nodule on T2W imaging, and analyzed with respect to freedom from biochemical failure (FFBF, nadir+2) in univariate and multivariate (MVA) analysis. ECE and SVI were also graded by a body radiologist in blinded fashion on a 4 point scale for suspected involvement, but were not tested against FFBF in this analysis.

Results: At a median follow-up of 56 months, FFBF-5y was 91%. 44% of men had suspected ECE, and 10% had SVI. The largest axial dimension of tumor was median 11 mm (IQR 6-18, range 0-52). Larger size was related to risk of ECE (p<0.0001) and SVI (p<0.0001). Tumor size was associated with FFBF when analyzed as a continuous variable on logistic regression (p=0.0009). Men with largest size ≤15 mm had FFBF-5y of 97% vs. 82% if > 15 mm; this size cutoff was associated with FFBF in men treated without ADT (92% vs 42%, p=0.0083) or with ADT (100% vs 89%, p=0.0393). In men treated with EBRT alone, there were no failures up to a size of 8 mm, and in men treated with EBRT and ADT, there were no failures up to 17 mm. On MVA, size (RR 1.12 per mm, p=0.0012) was the factor most strongly associated with FFBF when controlling for NCCN risk category (p=0.4731) and ADT (p=0.0696).

Conclusion: Measurement of largest axial size of a prostatic nodule on T2W is a simple radiographic measurement that is strongly associated with outcome. Size on eMRI may be a useful tool to help make clinical decisions on the use of ADT in men treated with EBRT.

Author Disclosure: S. Liauw: None. G. Kauffmann: None. A. Oto: Research Grant; Philips, Guerbet. Honoraria; Profound Healthcare.

Stanley Liauw, MD

University of Chicago

Disclosure:
Employment
University of Chicago: Associate Professor: Employee

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