Comparative Effectiveness of Radiotherapy versus Focal Laser Ablation in Patients with Low and Intermediate Risk Localized Prostate Cancer

Toward mechatronic MRI-guided focal laser ablation of the prostate: Robust registration for improved needle delivery

BACKGROUND

Multiparametric MRI (mpMRI) is an effective tool for detecting and staging prostate cancer (PCa), guiding interventional therapy, and monitoring PCa treatment outcomes. MRI-guided focal laser ablation (FLA) therapy is an alternative, minimally invasive treatment method to conventional therapies, which has been demonstrated to control low-grade, localized PCa while preserving patient quality of life. The therapeutic success of FLA depends on the accurate placement of needles for adequate delivery of ablative energy to the target lesion. We previously developed an MR-compatible mechatronic system for prostate FLA needle guidance and validated its performance in open-air and clinical 3T in-bore experiments using virtual targets.

PURPOSE

To develop a robust MRI-to-mechatronic system registration method and evaluate its in-bore MR-guided needle delivery accuracy in tissue-mimicking prostate phantoms.

METHODS

The improved registration multifiducial assembly houses thirty-six aqueous gadolinium-filled spheres distributed over a 7.3 × 7.3 × 5.2 cm volume. MRI-guided needle guidance accuracy was quantified in agar-based tissue-mimicking prostate phantoms on trajectories (N = 44) to virtual targets covering the mechatronic system's range of motion. 3T gradient-echo recalled (GRE) MRI images were acquired after needle insertions to each target, and the air-filled needle tracks were segmented. Needle guidance error was measured as the shortest Euclidean distance between the target point and the segmented needle trajectory, and angular error was measured as the angle between the targeted trajectory and the segmented needle trajectory. These measurements were made using both the previously designed four-sphere registration fiducial assembly on trajectories (N = 7) and compared with the improved multifiducial assembly using a Mann-Whitney U test.

RESULTS

The median needle guidance error of the system using the improved registration fiducial assembly at a depth of 10 cm was 1.02 mm with an interquartile range (IQR) of 0.42-2.94 mm. The upper limit of the one-sided 95% prediction interval of needle guidance error was 4.13 mm. The median (IQR) angular error was 0.0097 rad (0.0057-0.015 rad) with a one-sided 95% prediction interval upper limit of 0.022 rad. The median (IQR) positioning error using the previous four-sphere registration fiducial assembly was 1.87 mm (1.77-2.14 mm). This was found to be significantly different (p = 0.0012) from the median (IQR) positioning error of 0.28 mm (0.14-0.95 mm) using the new registration fiducial assembly on the same trajectories. No significant difference was detected between the medians of the angular errors (p = 0.26).

CONCLUSION

This is the first study presenting an improved registration method and validation in tissue-mimicking phantoms of our remotely actuated MR-compatible mechatronic system for delivery of prostate FLA needles. Accounting for the effects of needle deflection, the system was demonstrated to be capable of needle delivery with an error of 4.13 mm or less in 95% of cases under ideal conditions, which is a statistically significant improvement over the previous method. The system will next be validated in a clinical setting.

Laser technology in urologic oncology

Laser technology has been used in Urology since the 80s with a lot of different applications in endoscopic and open surgery. With the developments of the technology and the introduction of new active medium and source of laser energy, this technology have become the gold standard not only in stone surgery but even in benign prostate enlargement (BPE) surgical treatment. Regarding urologic oncology, laser energy has now reached an important role in focal therapy and in conservative treatment. The possibility of having better functional outcomes without any relevant impact on oncological results led to an increased use of laser in penile surgery, with a significant mention in urological guidelines for this option. In urothelial cancers as well, both in conservative management of upper tract tumors that in the treatment of non muscle invasive bladder cancer, a clear role of these relatively new source of energy have been demonstrated. Finally, both in prostate that in renal cancer the strategy of focal therapy may take advantage from this precise and fine technology. In this review we analyzed and described the applications of laser energy in urological cancers with a specific focus on penile, urothelial and prostate cancer.

Current evidence for focal laser ablation and vascular-targeted photodynamic therapy for localized prostate cancer: review of literature published in the last 2 years

PURPOSE OF REVIEW

Currently, a significant number of patients are diagnosed with unilateral and apparently unifocal low or intermediate-risk prostate cancer (PCa). These patients are suitable for focal therapy, thus preventing radical treatment side effects without affecting cancer control. Among focal therapy energy sources, laser-based technologies have shown promising outcomes. We aimed to summarize recent data on focal laser ablation (FLA) and vascular-targeted photodynamic therapy (VTP) for PCa.

RECENT FINDINGS

We selected eight studies reporting data on 1155 patients with PCa who underwent laser-based focal therapy. Five studies were on FLA and three on VTP (six prospective and two retrospective series); four reported both oncologic and functional outcomes whereas in three only oncologic and one only functional outcomes were discussed. Follow-up protocols and durations varied widely among the studies. PCa recurrence rates ranged between 20 and 56%. Urinary and erectile function were preserved after treatment, and complications were mild and transient. A lack of high-quality data on long-term oncological outcomes still remains, thus further highlighting the need for prospective controlled studies.

SUMMARY

FLA and VTP are well tolerated procedures with excellent functional outcomes. However, both procedures showed a significant rate of PCa recurrence, thus demonstrating a certain grade of oncologic control failure of the procedure and/or nonoptimal patients' selection.

Focal therapy for localized prostate cancer - Current status

Focal therapy (FT) has recently gained popularity for the treatment of localized prostate cancer (PCa). FT achieves cancer control by targeting the lesions or the regions of the cancer and avoids damage to the surrounding tissues thus minimizing side effects which are common to the radical treatment, such as urinary continence and sexual function, and bowel-related side effects. Various ablative methods are used to deliver energy to the cancerous tissue. We review the different modalities of treatment and the current state of FT for PCa.