Graphics Processing Unit-Based Bioheat Simulation to Facilitate Rapid Decision Making Associated with Cryosurgery Training
- May 3, 2015
Cryoablation for Localized Prostate Cancer using 17 gauge Cryoneedles:
Aaron E. Katz, MD
Cryosurgery is a rapidly evolving minimally invasive treatment modality for localized prostate cancer. Early devices utilized a liquid nitrogen system, which allowed rapid freezing of tissue to -200°C, but there was an unacceptably high rate post-operative complications. Monitoring and targeting ice ball formation was imprecise. Urinary incontinence, rectourethral fistulas, and urethral sloughing and stricture were common, and an open perineal incision was occasionally used. Adoption of urethral warmers and the implementation of transrectal ultrasound (TRUS) for percutaneous probe placement significantly advanced this technology. Ice ball formation could now be monitored with ultrasound to ensure complete prostate ablation while reducing damage to adjacent tissue. Liquid nitrogen technology was then replaced with second generation cryosurgery technology using pressurized argon gas that allowed for rapid temperature cooling and thawing. Real-time control of ice ball formation improved precision of tissue ablation and further minimized harm to adjacent tissue.
The transition to gas also permitted the advent third generation cryosurgery using ultra-thin 17-guage (1.5 mm diameter) cryoneedles that can be percutaneously passed through a brachytherapy-like template.
Due to many technologic advances, cryosurgery has evolved into a very durable and minimally invasive treatment option for men with prostate cancer who defer radical surgery and radiation. In one of the largest published series, Long et al assessed cancer-related outcomes of 975 patients treated with cryoablation between 1993 and 1998 as the primary treatment for localized prostate cancer. After median follow-up of 2 years, biochemical recurrence free survival (bRFS) (defined as PSA < 1.0) for low, moderate and high risk patients was 76%, 71% and 61% , respectively, with the overall positive biopsy rate of 18%. Several other studies reported similar results with bRFS ranging from 59% to 92%.6-9 Even among high-risk patients with a PSA ≥ 10 ng/mL and/or Gleason sum score ≥ 8, cryosurgical ablation seems to offer a durable response with 6-year bRFS probability of 81.7% and overall survival of 100%.
Patients with radioresistant or recurrent prostate cancer following radiation therapy are often faced with a difficult decision regarding their further treatment options. Operating in an irradiated field has proved to technically challenging with a much greater morbidity than non-salvage procedures. In a review of 15 published series, salvage prostatectomy was associated with an mean estimated blood loss 992 cc, 3.7 hours of operating time, 6.6% rectal injury, 18% bladder neck contracture, and 45% incontinence.11 By avoiding the need for open surgery, salvage cryosurgery has emerged as a promising modality for salvage local therapy.
Pisters et al reported on the initial MD Anderson salvage cryosurgery experience using liquid nitrogen-based 3.4 mm probes (AccuProbe, CryoMedical sciences, Rockville, MD) in 150 men.12 The complications were not trivial as morbidity included urinary incontinence (73%), obstructive symptoms (67%), impotence (72%) and severe perineal pain (8%). Fortunately, outcomes have dramatically improved with more contemporary series using updated technology. Ghafar et al reported on a series of 38 patients who underwent salvage cryosurgery using a second generation, argon gas based cryotechnique (CRYOCare system, Endocare, Inc, Irvine, CA) utilizing 2.4 mm needles .13 These patients experienced a nearly 10-fold lower incidence of incontinence (7.9%). The most common complaint was rectal pain in 39.5% of patients. Other complications included hematuria (7.9%), scrotal swelling (10.5%), and LUTS (15.8%). The bRFS in this series was 66% at 12 months.
Han et al have recently reported on their experience with third generation cryosurgery in 106 men.14 A brachytherapy template was used with technique similar to the present study. Again, no dilation for needle tracts or closure of puncture sites with suturing was necessary. All but 2 patients were discharged home on the same day. bRFS was at 1 year was 78% for low risk patients and 71% for high risk patients. Pelvic pain was reported in 5.9%, urge incontinence (no pads) in 5.1%, urethral sloughing in 5.8%, and impotence in 87%. Overall, morbidities were more prevalent among patients undergoing salvage therapy (15%) versus primary therapy (85%).
Whereas chronic pelvic and rectal pain was associated with prior early generation cryosurgeries, patients rarely complain of this symptom after the use of the ultra-thin cryoneedles. This is likely the benefit of no longer making skin incisions and dilating skin tracts. Furthermore, the use of a brachytherapy template allows better placement of cryoneedles and temperature probes for more accurate creation of an ice ball. Better care can also be made to avoid rectal wall injuries. Rectourethral fistulas are simply non-existent with modern cryosurgery. Morbidity across the board has been greatly reduced, except with regard to erectile dysfunction.
Erectile dysfunction is the most common complication of cryosurgery due to freezing of the neurovascular bundles during complete gland cryoablation. Erectile function may not be lethal in some instances and return of erectile function has been reported in a small percentage (13%) of men who were potent before cryosurgery.16 In men with low volume disease who wish to spare their erections, focal cryoablation has become a new option. In 2002, Onik et al first reported a pilot series of 9 men with unilateral low volume prostate cancer.17 Repeat prostate biopsies of the contralateral side were done to verify unilateral cancer. Focal cryoablation of the affected side only was performed to spare the contralateral neurovascular bundle. At a median follow up 36 months, 7 of the 9 men maintain their erectile function. Bahn et al later reported a 89% potency rate in a cohort of 29 men, mean age 64 and mean PSA 4.95 ng/mL, with a 96% no evidence of disease at mean follow up 70 months.18 In our present series, we were able to present similar potency results. Nine of the 26 men who underwent focal cryoablation were potent prior to the operation, and 7 patients (78%) were able to maintain their erectile function. The precision required for cryoablation of the cancer while sparing the contralateral neurovascular bundle would be all but impossible without 17 gauge cryoneedles.
Third generation argon based systems with 17 gauge cryoneedles represents the next era in prostate cryosurgery. Morbidity is vastly minimized, and focal cryoablation gives men hope of maintaining their erections.