Prediction of prostate cancer to urethra distance by a pretreatment nomogram: urethral thermoprotection implication in cryoablation

MRI predicts prostatic urethral involvement in men undergoing radical prostatectomy: implications for cryo-ablation of localized prostate cancer

PURPOSE

To determine whether multi-parametric magnetic resonance imaging (mpMRI) can reliably predict proximity of prostate cancer to the prostatic urethra in a contemporary series of men undergoing radical prostatectomy (RP) at two academic centers.

METHODS

Clinical characteristics of consecutive men undergoing pre-operative mpMRI prior to RP and whole-mount axial serial step-sectioned pathology examination at two academic centers between Jun 2016 and Oct 2018 were analyzed retrospectively. Every tumor was characterized by its pathologic minimum distance to the prostatic urethral lumen (pMDUL). Only the cancer closest to the urethra represented the prostatic urethral index lesion. The radiologic minimum distance of the index lesion to the prostatic urethral lumen was measured and noted as ≤ 5 mm versus  > 5 mm. The sensitivity, specificity, positive and negative predicting values (PPV and NPV) and area under the receivers operating characteristics curve (AUC) were calculated for performance of mpMRI for predicting pMDUL ≤ 5 mm.

RESULTS

Of the 163 surgical specimens examined, 112 (69%) exhibited a pMDUL ≤ 5 mm. These men had significantly higher grade group (GG) and advanced pathological and clinical stage. The rates of high PI-RADS score and presence of gross extracapsular extension were also significantly greater for the group with pMDUL ≤ 5 mm. The AUC, sensitivity, specificity, PPV, and NPV were 0.641, 51.8, 76.5, 82.9, and 42.4%, respectively, for mpMRI to predict pMDUL < 5 mm.

CONCLUSIONS

Nearly 70% of men undergoing RP present with tumor within 5 mm of the prostatic urethra. These tumors present higher risk characteristics, and mpMRI exhibited moderate performance and high PPV in their pre-operative detection. Physicians performing partial gland ablation should take these results into consideration during treatment selection and planning.

The Value and Evaluability of the PCA3 Urine Assay in Prostate Carcinoma is Independent of the Tumor Localization

INTRODUCTION

The prostate cancer gene 3 (PCA3) test is based on the analysis of tumor cell mRNA in urine. As an exprimated urinary marker, its retrieval is subject to certain physical aspects like palpation pressure and detachment force during the squeezing of cells. Other potential factor of influence may be the distance the cells have to cover until they reach the urethra. Thus, it was investigated whether the localization of the tumors within the prostate with regard to the urethra and the seminal colliculus influences the PCA3 score.

METHODS

Prostatectomy specimens of 55 organ-confined prostate cancer patients were processed according to the Stanford protocol. For each prostatectomy specimen, a three-dimensional reconstruction including the surface of the prostate, the tumor areas and the urethra was created. By model simulating, virtual concentric tubes were placed around the urethra and spherical volumes were virtually positioned around the seminal colliculus at diameters of 8, 16 and 32 mm. Depending on localization, tumor volumes may or may not protrude into the tubes or spherical volumes. For each respective diameter, PCA3 levels were compared between the subgroup with and without protrusion of tumor tissue into the tube or spherical ball.

RESULTS

For none of the diameters, whether in tubes or spherical balls, were patients without intersection volumes-hence showing peripherally located tumors-found to have lower PCA3 levels. No clinical or histopathological parameter correlated with the PCA3 score.

CONCLUSION

The location of the tumor mass in the prostate with respect to the urethra or the seminal colliculus did not to affect the PCA3 score. Hence, the location of the tumor does not limit the validity of the PCA3 score, and even for exclusively peripherall y located tumors, this possible influencing factor did not lead to an artificial modulation of the PCA3 score.

A Monte Carlo study of I-125 prostate brachytherapy with gold nanoparticles: dose enhancement with simultaneous rectal dose sparing via radiation shielding

We investigate via Monte Carlo simulations a new ¹²⁵I brachytherapy treatment technique for high-risk prostate cancer patients via injection of Au nanoparticle (AuNP) directly into the prostate. The purpose of using the nanoparticles is to increase the therapeutic index via two synergistic effects: enhanced energy deposition within the prostate and simultaneous shielding of organs at risk from radiation escaping from the prostate. Both uniform and non-uniform concentrations of AuNP are studied. The latter are modeled considering the possibility of AuNP diffusion after the injection using brachy needles. We study two extreme cases of coaxial AuNP concentrations: centered on brachy needles and centered half-way between them. Assuming uniform distribution of 30 mg g^-1 of AuNP within the prostate, we obtain a dose enhancement larger than a factor of 2 to the prostate. Non-uniform concentration of AuNP ranging from 10 mg g^-1 and 66 mg g^-1 were studied. The higher the concentration in a given region of the prostate the greater is the enhancement therein. We obtain the highest dose enhancement when the brachytherapy needles are coincident with AuNP injection needles but, at the same time, the regions in the tail are colder (average dose ratio of 0.7). The best enhancement uniformity is obtained with the seeds in the tail of the AuNP distribution. In both uniform and non-uniform cases the urethra and rectum receive less than 1/3 dose compared to an analog treatment without AuNP. Remarkably, employing AuNP not only significantly increases dose to the target but also decreases dose to the neighboring rectum and even urethra, which is embedded within the prostate. These are mutually interdependent effects as more enhancement leads to more shielding and vice-versa. Caution must be paid since cold spot or hot spots may be created if the AuNP concentration versus seed position is not properly distributed respect to the seed locations.