PURPOSEWe aimed to evaluate the prostate volumes calculated as recommended in the PI-RADS v2 and PI-RADS v2.1 guidelines, intraobserver and interobserver variability, and the agreement between the two measurement methods.
METHODSProstate mpMRI examinations of 114 patients were evaluated retrospectively. T2-weighted sequences in the axial and sagittal planes were used for the measurement of the prostate volume. The measurements were performed by two independent observers as recommended in the PI-RADS v2 and PI-RADS v2.1 guidelines. Both observers conducted the measurements twice and the average values were obtained. In order to prevent bias, the observers carried out measurements at one-week intervals. In order to assess intraobserver variability, observers repeated the measurements again at one-week intervals. The prostate volume was calculated using the ellipsoid formula (W×H×L×0.52).
RESULTSIntraclass correlation coefficient (ICC) revealed almost perfect agreement between the first and second observers for the measurements according to both PI-RADS v2 (0.93) and PI-RADS v2.1 (0.96) guidelines. The measurements were repeated by both observers. According to the ICC values, there was excellent agreement between the first and second measurements with respect to both PI-RADS v2 and PI-RADS v2.1 for first (0.94 and 0.96, respectively) and second observer (0.94 and 0.97, respectively). For both observers, the differences had a random, homogeneous distribution, and there was no clear relationship between the differences and mean values.
CONCLUSIONThe ellipsoid formula is a reliable method for rapid assessment of prostate volume, with excellent intra- and interobserver agreement and no need for expert training. For the height measurement, the recommendations of the PIRADS v2.1 guideline seem to provide more consistently reproducible results.The prostate gland is one of the organs for which the disease incidence and prevalence in men increases with age. Prostate volume (PV) has an important role in the evaluation and management of both malignant and benign prostate diseases (
1–
3). In benign prostatic hyperplasia (BPH), prostate volume is used to decide upon treatment and evaluate response to medical therapy (
3–
5). In the diagnosis of prostate cancer, one of the important markers is prostate-specific antigen (PSA), but it has low specificity, and therefore PSA derivatives are used to increase its specificity. One example is PSA density, which is obtained by dividing the PSA value by PV. In the treatment of prostate cancer, PV is important, and the effectiveness of brachytherapy decreases in prostates with a volume greater than 50 mL (
6). Furthermore, PV is used to identify appropriate patients for brachytherapy and select the number of radioactive seeds, and also determine fractionation for external beam radiation, radical prostatectomy operating planning and continence rate counseling, and focal therapy candidacy preparation (
7,
8). For these reasons, it is vital to accurately calculate PV.There are many methods that can be used to calculate PV, with the ellipsoid formula being one of the most preferred since it is easy to apply and highly time-efficient (
1–
4,
9). Many studies have shown that this method has high accuracy due to the elliptic shape of the prostate (
1,
2,
10–
13). The ellipsoid formula is obtained by multiplying the height (anterior-posterior), width (medio-lateral) and length (cranio-caudal) values of the prostate by 0.52. These measurements can be performed by transrectal ultrasonography (TRUS) or magnetic resonance imaging (MRI). TRUS has certain disadvantages, such as being operator-dependent and susceptible to sonographic artifacts (
14). MRI, which has become increasingly popular in recent years, allows for an accurate definition of the prostate boundaries and multiplanar measurements through its high contrast resolution of soft tissues (
1,
5). It also provides more accurate measurements than TRUS (
4,
15,
16).In order to ensure global standardization in the reporting of prostate MRI findings, PI-RADS v2 published in 2015, which is the revised version of PI-RADS 1.0, and the last updated version PI-RADS v2.1 made available in 2019, propose different calculation methods for the measurement of height in obtaining PV (
17,
18). The midaxial plane is recommended for this measurement in PI-RADS v2, while the midsagittal plane is recommended in PI-RADS v2.1. This study aimed to evaluate the interobserver and intraobserver variability of PV calculated by both measurement methods and the agreement between the two measurement methods.
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