Variability In Prostate Volume As Determined By Mri Versus Ultrasound And Its Impact On Treatment Recommendations For Patients With Favorable-Risk Prostate Cancer

249 Background: Prostate volume affects whether patients qualify for brachytherapy (desired size ≥20mL and ≤60mL) or active surveillance (desired PSA density ≤0.15). This study examines variability in prostate volume as determined by contoured axial ultrasound slices, ultrasound ellipsoid (HxWxL) calculation, and endorectal coil MRI (erMRI) ellipsoid calculation, and quantifies the impact of this variability on treatment recommendations for men with favorable-risk prostate cancer.The study examined 72 patients who presented consecutively for consideration of brachytherapy for favorable-risk prostate cancer who had 3 volume estimates from direct contouring on ultrasound axial slices (2.5mm thickness), the ultrasound ellipsoid method, and the erMRI ellipsoid method.Average gland size by the contoured ultrasound, ellipsoid ultrasound, and eMRI methods were 34.22, 37.15, and 39.58 mLs, respectively. All pairwise comparisons between methods were significant (all p<0.02). Of the 68 patients who anatomically qualified for brachytherapy on ellipsoid ultrasound measures (size ≥20mL and ≤60mL), 22 (32.35%) did not qualify on eMRI (5 patients <20 mL, 11 patients >60 mL) or contoured ultrasound measures (7 patients <20 mL, 3 patients >60 mL). 40 patients (55.56%) were very low risk (PSA density ≤0.15 ng/dl) as calculated using ellipsoid ultrasound volumes, while 35 (48.61%) and 39 patients (54.17%) were very low risk using contoured ultrasound and eMRI volumes, respectively.The ultrasound ellipsoid and erMRI ellipsoid methods appeared to overestimate ultrasound contoured volume by an average of 8.56% and 15.65% respectively. 32.35% of those who qualified for brachytherapy based on ellipsoid ultrasound volume would be disqualified based on ultrasound contoured and/or erMRI volume. As treatment recommendations increasingly rely on estimates of prostate size, clinicians must consider method of volume estimation.