Prostate biopsy, as the gold standard for prostate cancer diagnosis, can be performed in a guided manner, ranging from finger guidance to TRUS guidance. With the development of imaging technology, mpMRI has shown obvious advantages in prostate cancer diagnosis, especially with implementation of the PI-RIDS, allowing a quantified and standardized diagnosis. Quentin et al. [8] reported that MRI can be used to directly guide prostate biopsy; however, as MRI cannot be performed on patients with metal implants, involves a long scanning time and cannot provide real-time guidance, and requires an expensive, complex, and long biopsy procedure, this method has not been used widely. The emergence of image fusion technology perfectly combines the convenience, ease of operation and low cost of TRUS with the high sensitivity of mpMRI for prostate cancer, addressing the lack of random sampling in systematic puncture biopsy, and has been gradually implemented in clinical practice.

Leveraging TB technology and the MRI screening of patients with PSA 4–10 ng/mL, the positive rate of all 759 patients was 53.10%, higher than that previously reported for SB (positive rate 38.2%) [9]. Some patients were contraindicated for MRI and thus could not undergo mpMRI-TRUS fusion TB. In this study, local anesthesia, transperineal free-arm biopsy was performed, which can be carried out on a large scale for outpatient or daytime patients. The operation time is approximately 15 min and has the advantage of imparting a low risk of bleeding and infection. Patients generally tolerate the procedure well, and the prostate can be punctured with no blind spot.

In this study, the missed diagnosis rate of TB was slightly lower than that of SB, but there was no significant difference; both TB and SB missed approximately 10% of prostate cancers, so TB + SB is currently the best way to perform prostate biopsy.

In the TB missed diagnosis group, a TB missed diagnosis was not significantly associated with patient age but was significantly associated with lower PSA, larger prostate volume, lower PSAD and lower ISUP grade, so early prostate cancer and large prostate volume were more likely to cause TB missed diagnosis.

Among the 37 patients with TB missed diagnoses, the MRIs of 21 prostate cancers diagnosed by SB only showed no abnormalities, which is associated with the sensitivity of MRI; previous studies have concluded that MRI had higher sensitivity to high-risk PCa and tumors longer than 5 mm in diameter [10]. The PCa areas sampled by SB in 9 patients were TB target areas, suggesting that TB did not hit the MRI target area. The possible reasons for this are as follows: (1) Fusion error: different bladder filling state during MRI examination and biopsy, deformation caused by insertion of rectal prostate probe, and operator’s judgment of the datum plane can all affect the fusion of the MR and TRUS images. Consequently, the target lesion region displayed on the TRUS image will be offset from the actual target lesion region on MRI, causing the actual target lesion to be missed. (2) Involuntary patient movement due to pain and discomfort during biopsy [11], causing displayed target lesion deviation. (3) The target lesion area shown on MRI contained both inflammation and cancer tissue, and only the inflammation area was punctured, which resulted in a missed cancer diagnosis; (4) The target lesion was too small to puncture. To reduce the probability of a missed diagnosis for such patients, the following methods could be considered: (1) The patient should empty the bladder before MRI examination and biopsy. (2) The median sagittal plane (urethral plane) should be used as the datum plane for fusion. (3) The local anesthesia should be improved by fully injecting the anesthetic into the area from the perineal skin to the apex region of the prostate, especially on both sides of the nerve vascular bundle. (4) Greater communication should be conducted with the patient before and during biopsy to ease the patient’s anxiety. (5) Larger lesions should be sampled with a greater number of TB needles. (6) The operator should have greater experience in puncturing, in particular, large prostates, small lesions, or lesions in difficult locations (pubic occlusion area, anterior urethral area, base and apex), Pepe et al. [12] found that mpMRI increased the diagnosis of PCa located in the anterior zone of the prostate, where were contained in difficult locations. In the other 7 patients, the PI-RADS scores were underestimated before biopsy, resulting in missed TB of actual PI-RADS 3 areas, which required a careful analysis of the MR images by MRI diagnostic doctors. Khosravi et al. [13] applied artificial intelligence (AI) to the evaluation of MR images and achieved good results. Through full communication between the radiologist and operator and puncturing all suspicious lesions, the positive rate of TB can be further improved.

The ISUP grade of TB and SB samples in the TB+ & SB+ group showed that TB achieved the highest grade in approximately 90% of patients. Prostate cancer is a multifocal tumor, which means there may be several cancer lesions in the prostate. Although every patient was diagnosed with prostate cancer in this group, 45 patients were SB-positive in the non-TB target areas, which means that they experienced missed diagnoses of their prostate cancer lesions. Comparing the missed lesions with the unmissed ones, it was found that the ISUP grade of the TB unmissed lesions was significantly higher than that of the TB missed lesions. Baco et al. [14] suggested that the index lesion be defined as the tumor lesion with the highest Gleason score, or if two or more lesions had the same Gleason score, the index lesion should be defined as the largest lesion. Liu [15] found that index lesions promoted the progression of prostate cancer; therefore, TB likely missed secondary lesions and instead sampled lesions that dominated the overall disease process. Comparing TB missed lesions with MRI in this subgroup and analyzing the causes of each lesion, we found similar results to the TB missed group.

TB has the advantage of requiring fewer needles, and most of the missed lesions were early prostate cancer or secondary lesions. This is similar to the findings of Zhang et al. [16], who found that TB could increase the detection rate of clinically significant prostate cancer while reducing the number of needles. Missed clinically nonsignificant prostate cancer does not necessarily have serious consequences for patients [17]. However, the disease will continue to progress, and these missed cases may delay the treatment of some patients. Pepe et al. [18] reported that 16.2% clinically significant prostate cancers missed by targeted fusion prostate biopsy and a PI-RADS score of 3 or greater. The aim of many existing prostate biopsy studies [19, 20] was to obtain the closest results to radical pathology, to avoid as many missed diagnoses of prostate cancer as possible, and to obtain the true ISUP grade and range of lesions. Patients with clinically significant prostate cancer require positive treatment; patients with clinically nonsignificant prostate cancer can choose the most appropriate intervention or wait for observation according to his or her actual situation and closely monitor the progress of prostate cancer. If a diagnosis is missed during biopsy for these patients, the best treatment opportunity in the progression of the disease may be lost.

The limitations of the present study include: this is a single-center retrospective study; primary objective is diagnoses of any prostate cancer rather than clinically significant prostate cancer; RVS image fusion system is non organ tracking MRI-TRUS fusion system. The patient and/or prostate movement during the biopsy, may significantly influence the precision of targeting. Further, the registration in 3D prostate volume of each biopsy track is difficult to evaluate, consequently it is difficult to confirm the real location of the biopsy cores. If improved fusion system can track organ (prostate) and record the real location of the biopsy cores, the MRI and biopsy findings could be correlated with pathologic large slice after radical prostatectomy, further study will help reduce missed diagnosis of prostate cancer more.

In summary, early prostate cancer, a large prostate, the effect of local anesthesia, patient cooperation, MRI reading, and skill of the operator are possible causes of TB missed diagnoses. Improved imaging technology, additional biopsy experience, improved fusion system, and personalized biopsy plans will help exploit the advantages of TB and further improve the positive rate to that of real prostate pathology.

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