Multiple Cryoprobes Research Articles

Local Ablation Therapy for Hepatocellular Carcinoma: Clinical Significance of Tumor Size, Location, and Biology.

Local ablation therapy, encompassing radiofrequency ablation (RFA), microwave ablation, and cryoablation, has emerged as a crucial strategy for managing small hepatocellular carcinomas (HCCs), complementing liver resection and transplantation. This review delves into the clinical significance of tumor size, location, and biology in guiding treatment decisions for HCCs undergoing local ablation therapy, with a focus on tumors smaller than 3 cm. Tumor size significantly influences treatment outcomes, with larger tumors associated with poorer local tumor control due to challenges in creating sufficient ablative margins and the likelihood of microvascular invasion and peritumoral satellite nodules. Advanced ablation techniques such as centripetal or no-touch RFA using multiple electrodes, cryoablation using multiple cryoprobes, and microwave ablation offer diverse options for HCC treatment. Notably, no-touch RFA demonstrates superior local tumor control compared with conventional RFA by achieving sufficient ablative margins, making it particularly promising for hepatic dome lesions or tumors with aggressive biology. Laparoscopic RFA proves beneficial for treating anterior subphrenic HCCs, whereas artificial pleural effusion-assisted RFA is effective for controlling posterior subphrenic HCCs. However, surgical resection generally offers better survival outcomes for periportal HCCs compared with RFA. Cryoablation exhibits a lower incidence of vascular or biliary complications than RFA for HCCs adjacent to perivascular or periductal regions. Additionally, aggressive tumor biology, such as microvascular invasion, can be predicted using magnetic resonance imaging findings and serum tumor markers. Aggressive HCC subtypes frequently exhibit Liver Imaging Reporting and Data System M features on magnetic resonance imaging, aiding in prognosis. A comprehensive understanding of tumor size, location, and biology is imperative for optimizing the benefits of local ablation therapy in managing HCCs.

On the development of an optimized multiprobe cryo-ablation plan using immerse boundary method and genetic algorithm

Cryosurgery is becoming an effective method to treat undesired tumor tissue via the application of extremely low temperature coolant flowing through a probe. To maximize cryoinjury in the targeted tumor region, multiple cryoprobes are simultaneously employed to freeze the surrounding tumor tissues. In order to minimize cryosurgical injury to the surrounding health tissues, the cryoprobe localization for each specific tumor is critical. We developed finite difference analysis to calculate the freezing process during cryosurgery. According to our experimental data, the simulation results from the Pennes equation coupled with immersion boundary method (IBM) are consistent with the experimental data, with a maximum error of ±8.12%.We further incorporate a genetic algorithm as a planning tool to address the problem in connection to be interactive positioning of the cryoprobes and the freezing process duration during the pre-operative stage. Several optimization scenarios are judiciously investigated to emphasize different performance variables. Key results have revealed that this computerized approach is highly efficient one for selecting optimized multiple operational parameters.

Pulmonary Cryoablation Zones: More Aggressive Ablation Is Warranted In Vivo

The objective of our study was to determine the effective cryoablation zone when treating pulmonary tumors in vivo and to create pulmonary-specific ablation maps to guide clinical procedure planning. Ablation volume was measured retrospectively in human patients after pulmonary tumor cryoablation with a triple-freeze protocol. Single-probe ablations were performed with 17-, 14-, and 13-gauge cryoprobes; multiple-probe ablations were performed with two or three 17-gauge probes. Statistical comparisons of ablation volumes to manufacturer reference values were calculated using the Wilcoxon rank-sum test. Comparisons of ablation sizes by the number of probes were evaluated by the Kruskal-Wallis test. Mean volume of in vivo lung ablation with a single 17-gauge cryoprobe measured 3.0 cm3, which is a statistically significant difference compared with the in vitro -20°C isotherm volume of 22.6 cm3 (p < 0.01). Mean ablation volume of larger 13- and 14-gauge cryoprobes were 4.3 and 1.8 cm3, respectively, both of which are smaller than the in vitro -20°C isotherm volume. Mean cryoablation zone was not significantly affected by distance to the pleura (p = 0.54) or distance to a vessel (p = 0.55). Ablation volume was significantly increased (p < 0.01) with the use of multiple cryoprobes, at a rate of a 10.8-cm3 increase per additional probe. The increased ablation zone size was more attributable to increased short-axis width (9.6-mm increase per probe) compared with long-axis length (5.6-mm increase per probe). The in vivo effective pulmonary cryoablation zone is significantly smaller than the manufacturer-published in vitro isotherm. Larger ablation margins in lung are best achieved by using multiple cryoprobes.

3:40 PM Abstract No. 47 Characterization of in vivo ablation zones following percutaneous pulmonary cryoablation: expected and experimental findings

To determine the in vivo ablation zone when treating pulmonary tumors with cryoablation, with attention to differences in probe type, probe number, and anatomical factors. CT imaging was reviewed retrospectively following cryoablation of lung tumors using Galil Medical cryoprobes with a triple freeze protocol. Postprocedure volume of the ablation zone was calculated by measuring the maximum axial diameter (2a) and 90° orthogonal diameters (2b and 2c), and applying the formula for volume of an ellipsoid: 4/3*πabc. Statistical comparison was calculated using a student’s t-test or 1-way ANOVA. Linear regression was used to model ablation size with respect to probe number or distance to pleura or vessel. Graphical plots were created using the equation for an ellipse: x2/a2+y2/b2 = 1. Mean volume of in vivo lung ablation with a single 17-gauge cryoprobe measured 3.0 cm3(95% CI [2.3, 3.6], n = 15), a significant difference compared to the manufacturer published -40°C isotherm volume of 7.1 cm3 in room temperature gel (p<0.001). Mean ablation volume of a larger 13-gauge cryoprobe was 4.3 cm3 (95% CI [1.7, 6.9], n = 2), which was not significantly different compared to the smaller 17-gauge probe (p = 0.22). Mean cryoablation zone was not significantly affected by nodule distance to the pleura (p = 0.54) or distance to a vessel larger than 3 mm in diameter (p = 0.55). Ablation volume was significantly increased (p<0.001) with the use of multiple cryoprobes, at a rate of 10.8 cm3 increase per additional probe (2 probes: 12.9 cm3, 95% CI [8.2, 17.6], n = 24; 3 probes: 25.3 cm3, 95% CI [8.0, 42.6], n = 5). The increased ablation zone size with multiple probes was more attributable to increased short axis length (9.6 mm increase per probe) compared to the long axis (5.6 mm increase per probe). The in vivo effective ablation zone differs significantly from manufacturer supplied specifications in pulmonary cryoablation. Ablation zone volume is increased by utilizing more cryoprobes, but not affected by cryoprobe gauge or proximity to pleura or vessel.

Computational study of the effects of arterial bifurcation on the temperature distribution during cryosurgery

BackgroundThermally significant blood flows into locally cooled diseased tissues and warm them during cryosurgery so that the iceball is often hard to cover the whole diseased volume. This paper is aimed at investigating the effects of large arterial bifurcation on the temperature distribution during cryosurgery through simulation method.MethodsA parametric geometry model is introduced to construct a close-to-real arterial bifurcation. The three-dimensional transient conjugate heat transfer between bifurcated artery and solid tissues with phase change during cryosurgery is performed by finite volume method.ResultsThe discussion was then made on the effects of the relative position between cryoprobe and artery bifurcation, the inlet velocity of root artery and the layout of multiple cryoprobes on the temperature distribution and iceball evolution. The results show that the thermal interaction between blood flow and iceball growth near bifurcation is considerable complex. The thermal effects of bifurcation could modulate the iceball morphology, severely weaken its freezing volume and prevent the blood vessel from being frozen.ConclusionThe present work is expected to be valuable in optimizing cryosurgery scheme of the situation that the bifurcated artery is embedded into the disease tissue.

Percutaneous Cryoablation for the Treatment of Primary and Metastatic Lung Tumors: Identification of Risk Factors for Recurrence and Major Complications

PurposeTo identify risk factors for local recurrence and major complications associated with percutaneous cryoablation of lung tumors. Materials and MethodsAll cases between April 2007 and September 2014 at 1 institution were retrospectively reviewed. Procedures were performed using computed tomography guidance and a double freeze-thaw protocol. Tumor progression was determined via World Health Organization guidelines, and complications were classified using SIR reporting standards. Measures of efficacy were calculated via Kaplan-Meier analysis. Predictors of local progression and major complications were identified by Cox proportional hazards and logistic regression. ResultsThere were 47 tumors (25 primary, 22 metastatic) treated with median follow-up of 11.1 months. Mean diameter before treatment was 2.4 cm, and an average of 2.1 cryoprobes were used per procedure. Major complications (most commonly, pneumothorax requiring chest tube) occurred in 12 (25%) cases, and minor complications occurred in 13 (27%) cases. Median time to local progression was 14 months (16 mo for primary tumors and 10 mo for metastatic tumors), and median overall survival was 33 months (43 mo for patients with primary tumors and 22 mo for patients with metastatic tumors). On multivariate analysis, tumor diameter > 3 cm was associated with local progression (hazard ratio = 3.2, P = .013), and use of multiple cryoprobes (relative risk [RR] = 7.2, P = .045) and previous local therapy (RR = 15, P = .030) were associated with major complications. ConclusionsPercutaneous cryoablation of lung tumors is technically feasible with a complication rate comparable to other percutaneous ablation techniques. Percutaneous cryoablation is more efficacious and has fewer complications when offered to patients with small, previously untreated lesions.

Parallel Algorithm for Solving 3-D Freezing Problems in Biological Tissues during Cryosurgery

Treatment planning based on numerical prediction before or during cryosurgery is an indispensable way to achieve exactly killing of tumor. However, conventional sequential computation is difficult to meet the challenge of real-time assistance with complex treatment plans. In this study, two parallel numerical algorithms, i.e. explicit finite difference scheme and alternating direction implicit scheme, based on an effective heat capacity method are established to solve three-dimensional phase change problems in biological tissues subjected to freezing of multiple cryoprobes. The results as well as speedup of parallel computing were compared. It was shown that the parallel algorithms developed in this study can be used to perform rapid prediction of temperature distribution for cryosurgery, and that parallel computing is hopeful to assist cryosurgeons with prospective parallel treatment planning in the near future.

Are Multiple Cryoprobes Additive or Synergistic in Renal Cryotherapy?

To investigate the relationship between multiple cryoprobes was investigated to determine whether they work in an additive or synergistic fashion in an in vivo animal model because 1.47 mm (17-gauge) cryoprobes have been introduced to the armamentarium for renal cryotherapy. Laparoscopic-guided percutaneous cryoablation was performed in both renal poles of 3 pigs using 3 IceRod cryoprobes. These 12 cryolesions were compared with 12 cryolesions using a single IceRod cryoprobe. Each cycle consisted of two 10-minute freeze cycles separated by a 5-minute thaw. The iceball volume was measured using intraoperative ultrasonography. The kidneys were harvested, and cryolesion surface area was calculated. The lesions were fixed and excised to obtain a volume measurement. Statistical analysis was used to compare the single probe results multiplied by 3 to the multiple probe group for iceball volume, cryolesion surface area, and cryolesion volume. The iceball volume for the first freeze cycle for the single cryoprobe multiplied by 3 was 8.55 cm3 compared with 9.79 cm3 for the multiple cryoprobe group (P=.44) and 10.01 cm3 versus 16.58 cm3 for the second freeze (P=.03). The cryolesion volume for the single cryoprobe multiplied by 3 was 11.29 cm3 versus 14.75 cm3 for the multiple cyroprobe group (P=.06). The gross cryolesion surface area for the single cryoprobe multiplied by 3 was 13.14 cm2 versus 13.89 cm2 for the multiple probe group (P=.52). The cryolesion created by 3 simultaneously activated 1.47-mm probes appears to be larger than that of an additive effect. The lesions were significantly larger as measured by ultrasonography and nearly so (P=.06) as measured by the gross cryolesion volume.

Computer simulations on multiprobe freezing of irregularly shaped tumors

Cryosurgery is particularly suitable for the treatment of unresectable liver tumors. However, a major bottleneck is encountered during the treatment of large-sized irregularly shaped tumors. Large and complex liver tumors have varying degree of shape irregularity. Adopting a multiprobe freezing model, simulations for an irregularly shaped liver tumor were conducted. The model, validated with both in-vitro data from an experimental setup, showed good agreement of up to 5.8%. The chosen mathematical treatment and simulation technique permit the study of employing multiple cryoprobes to destroy cancer cells in irregularly shaped tumors. Results from our study indicated that multiple cryoprobes can be strategically positioned to form ice-fronts with various contours that adhere to the shape and size of the tumor. The amount of cell-deaths within the tumor after the −50 °C ice-front can be quantitatively calculated to determine the efficacy of different multiprobe arrangements in order to maximize cell destruction. The paper also underlines a piecewise approach of using several cryoprobes to quickly ‘sculpt’ the desired shape of the ice-front based on the physical morphology of an irregular-shaped tumor. This numerical study forms an essential framework in allowing surgeons to make informed decisions on the most effective surgical protocol based on the degree of irregularity in shape and size of tumor.

Computed tomography-guided cryoablation of pelvic metastasis from uterine leiomyosarcoma

Owing to its ability to place and use multiple cryoprobes simultaneously, cryoablation enables the treatment of tumors of any shape. Cryoablation causes ice crystals to form within cells, inducing membrane rupture and cell death via cellular dehydration and local tissue ischemia. Ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) enable clear visualization of the margins of low-density and solid ice. A case of breast cancer with axillary lymph-node metastasis treated with CT-guided cryoablation has been reported previously.

Parallel Algorithms for Freezing Problems during Cryosurgery

Treatment planning based on numerical simula- tion before cryosurgery is an indispensable way to achieve exactly killing of tumors. Furthermore, intraoperative pre- diction based on monitoring results can lead to more accu- rate ablation. However, conventional serial program is diffi- cult to meet the challenge of real-time assistance with com- plex treatment plans. In this study, two parallel numerical algorithms, i.e. parallel explicit scheme and Alternating Direction Implicit (ADI) scheme using the block pipelined method for parallelization, based on an effective heat capac- ity method are established to solve three-dimensional phase change problems in biological tissues subjected to multiple cryoprobes. The validation, speedups as well as efficiencies of parallelized computations of the both schemes were com- pared. It was shown that the parallel algorithms developed here can perform rapid prediction of temperature distribu- tion for cryosurgery, and that parallel computing is hopeful to assist cryosurgeons with prospective parallel treatment planning in the near future.

Cryoablation as an adjunctive therapy in a multimodality treatment program for malignant pleural mesothelioma.

e17531 Background: Therapy for malignant pleural mesothelioma (MPM) fails to control local/regional disease in most patients and uncontrolled local disease remains a major cause of mortality. Effective novel therapies for multifocal local disease are desperately needed. We hypothesized that cryoablation may help fill this need since it can be used in the pleura/chest wall without the severe pain associated with RF and microwave ablation and without the need for general anesthesia. Methods: We retrospectively reviewed a prospective database and identified patients with localized MPM who had undergone cryoablation. Outpatient CT-guided procedures using single or multiple cryo-probes (up to 4) depending on lesion size were used to deliver two 10 minute cryoablation cycles with an 8 minute thaw period between. We analzyed patient characteristics, morbidity, and response rates. Results: 30 total lesions in 15 MPM patients were treated. 12 patients had prior surgery and were pathologically staged as stage I (2=16.7%), III (8=66.6%) and IV (2=16.7%). N2 disease was present in 6/12 (50%). Lesions in the surgical group were treated at a median of 564 days following surgery (range 201-2,774). Moribidy was limited to one case of skin erythema with a superficial chest wall lesion and one case of significant pain with a paraspinous lesion. Responses were seen in 20 (67%) lesions, stable disease in 5 (16.5%) and progression occurred in only 5 (16.5%). This compares favorably to results from our database with other tumors. Median survival of patients following surgery was 866 days (range 365-2,938) and following cryoablation was 160 days (range 75-444). 6 patients are still alive (50%) and 3 patients had no followup survival information available. Conclusions: Cryoablation can provide excellent palliation for local/regional recurrence following surgery or even primary disease in patients with malignant pleural mesothelioma and should be strongly considered in patients who have limited localized disease and no other viable treatment options. Successful employement of cryoablation potentially may lead to longer survivals in MPM due to improved local disease control. No significant financial relationships to disclose.

Cryoablation for Endophytic Renal Cell Carcinoma: Intermediate-Term Oncologic Efficacy and Safety

PurposeTo evaluate the efficacy and safety of laparoscopic renal cryoablation (LRC) of small endophytic renal cell carcinoma, for which surgical treatment is technically difficult.Materials and MethodsWe enrolled patients with endophytic tumors from a prospectively collected database of 45 renal tumors in 39 patients who had undergone LRC from June 2005 to May 2009. An endophytic tumor was defined as less than 40% of the lesion extending off the surface of the kidney. We evaluated surgical and oncological outcomes.ResultsAmong the treated tumors, 17 tumors (37.8%) were defined as endophytic tumors and 15 tumors from 14 patients were confirmed as renal cell carcinoma (RCC) in the pathologic examination of the tissue biopsy that was conducted at the time of LRC. The mean American Society of Anesthesiologists (ASA) score of the whole patient group was 2.9 (range, 1-4), and 85.7% (12/14) of the patients had an ASA physical status score over 3. The mean tumor size was 2.8 cm (range, 1.7-3.7 cm). The layout of the cryoprobe was carefully planned preoperatively on the basis of radiologic evaluation in all tumors. Multiple cryoprobes (mean, 3.2; range, 2-5) were used. No major complications, including open surgical conversion and nephrectomy due to bleeding, occurred. No patient experienced clinical symptoms of collecting system injuries. During the mean follow-up of 32.6 months (range, 12-51 months), radiologic evidence of tumor recurrence was found in one patient (6.7% for RCC). With the exception of this patient, all other patients have remained free of recurrence or metastasis, as determined by periodic radiologic workups.ConclusionsIn this series of patients with intermediate-term follow-up, LRC for endophytic renal cell carcinoma showed acceptable oncological and surgical outcomes without sequelae in the collecting system.

Lethal Isotherms of Cryoablation in a Phantom Study: Effects of Heat Load, Probe Size, and Number

To assess the effects on the proportions of lethal ice (ie, colder than -30 degrees C) in phantoms with different heat loads created by varying the size and number of cryoprobes spaced 2 cm apart. Thermocouples at 0.5-, 1.0-, and 1.5-cm intervals from 1.7- or 2.4-mm-diameter cryoprobes were held by jigs accommodating a maximum of four cryoprobes. Agar phantoms (N = 24) used three sets of baseline temperatures: approximately 6 degrees C, 24 degrees C, and 39 degrees C. Temperatures during 15-minute freeze cycles were correlated with actual thermocouple locations seen within the ice by computed tomography (CT). Diameters and surface areas of the -30 degrees C lethal isotherm were assessed over time as percentages of the overall ice ball. The high-heat load phantom experiments (39 degrees C) showed the greatest impact on lethal zones by percentage for all probe configurations. At 15 minutes, single-, double-, triple-, and quadruple-probe arrangements of 2.4-mm cryoprobes had average lethal ice diameters of 1.2, 3.3, 4.1, and 4.9 cm, respectively, comprising 13%, 46%, 51%, and 56% surface areas of lethal ice, respectively. Surface areas and diameters of lethal ice made by 1.7-mm cryoprobes were 71% and 84% of those made by 2.4-mm cryoprobes, respectively. Lethal ice resides less than 1 cm behind the leading edge for nearly all probe configurations and heat loads. Single cryoprobes create very low percentages of lethal ice. Multiple cryoprobes overcome the high heat load of body temperature phantoms and help compensate for the lower freeze capacity of thinner cryoprobes.

Exact analytical solution to three-dimensional phase change heat transfer problems in biological tissues subject to freezing

Analytically solving a three-dimensional (3-D) bioheat transfer problem with phase change during a freezing process is extremely difficult but theoretically important. The moving heat source model and the Green function method are introduced to deal with the cryopreservation process of in vitro biomaterials. Exact solutions for the 3-D temperature transients of tissues under various boundary conditions, such as totally convective cooling, totally fixed temperature cooling and a hybrid between them on tissue surfaces, are obtained. Furthermore, the cryosurgical process in living tissues subject to freezing by a single or multiple cryoprobes is also analytically solved. A closed-form analytical solution to the bioheat phase change process is derived by considering contributions from blood perfusion heat transfer, metabolic heat generation, and heat sink of a cryoprobe. The present method is expected to have significant value for analytically solving complex bioheat transfer problems with phase change.

Percutaneous and Laparoscopic Cryoablation of Small Renal Masses

We reviewed our 4-year experience with percutaneous cryoablation and laparoscopy for treating small renal masses. After institutional review board approval we retrospectively analyzed renal cryoablation procedures performed between March 2003 and October 2007. An in-depth analysis was performed concerning demographics, hospital course and short-term outcome with respect to percutaneous vs laparoscopic cryoablation. A total of 37 patients underwent treatment for 43 renal masses. Of the 37 patients 19 underwent laparoscopic cryoablation (24 tumors) and 18 underwent percutaneous cryoablation (19 tumors) using computerized tomography fluoroscopy. For percutaneous cryoablation a saline instillation was used in 58% of cases to move nonrenal vital structures away from the targeted renal mass. There were 5 cases of hemorrhage requiring transfusion, all of which were associated with the use of multiple cryoprobes. The transfusion rate in the percutaneous and laparoscopic cryoablation groups was 11.1% and 27.8%, respectively. Operative time was significantly longer in the laparoscopic cryoablation group compared to the percutaneous cryoablation group at 147 (range 89 to 209) vs 250.2 (range 151 to 360) minutes, respectively. The overall complication rate (including transfusion) was lower in the percutaneous cryoablation group compared to the laparoscopic cryoablation group (4 of 18 [22.2%] vs 8 of 20 [40%], respectively). Hospital stay was significantly shorter in the percutaneous vs laparoscopic cryoablation group at 1.3 vs 3.1 days, p <0.0001, respectively. Narcotic use in the percutaneous cryoablation group was more than half that used by the laparoscopic cryoablation group (5.1 vs 17.8 mg, p = 0.03, respectively). Among patients with biopsy proven renal cell carcinoma during a median followup of 11.4 and 13.4 months in the percutaneous and laparoscopic cryoablation groups, cancer specific survival was 100% and 100%, respectively, and the treatment failure rate was 5.3% and 4.2%, respectively. Percutaneous cryoablation is an efficient, minimally morbid method for the treatment of small renal masses and it appears to be superior to the laparoscopic approach. Short-term followup has shown no difference in tumor recurrence or need for re-treatment. Of note, hemorrhage was solely associated with the use of multiple probes.

New Modality for Maximizing Cryosurgical Killing Scope While Minimizing Mechanical Incision Trauma Using Combined Freezing-Heating System

Cryosurgery is a minimally invasive surgical technique using extremely low temperature to destroy undesired tissues. A surgical freezing margin of at least 1 cm is often recommended to avoid local tumor recurrence after surgery. For treating slender or elongated solid tumors in a conventional cryosurgery, simultaneous insertion of multiple cryoprobes is a necessity to guarantee an adequate killing scope. However, the risk of mechanical incision trauma may outweigh the benefits of such therapy. To resolve this difficulty, we proposed a new cryosurgical treatment modality, which can significantly maximize the killing scope while minimize the incision trauma, using the recently developed combined cryosurgical-hyperthermia treatment system (CCHTS). The method, named as one time’s percutaneous insertion while multiple times’ freezing∕heating ablation, is rather flexible in administrating a complex cryosurgical process and avoids certain shortcomings of conventional freezing strategies. Owing to the powerful heating function, the present probe can be easily moved back along its original incision tract to the desired positions immediately after initiating the heating. Then, a new iceball can be formed there while the iceballs generated before still remain unmelted in the following cycles. Consequently, a slender iceball could be generated to embrace the whole elongated tumor. This is, however, rather hard to achieve for a conventional cryosurgery with only one single freezing function or using only one probe. To visually demonstrate the feasibility and potential advantage of the present method, proof of concept in vitro gel experiments were performed. In addition, tests and corresponding theoretical simulations were performed on pork tissues. All the results indicate that the elongated iceball could be easily generated by using only one CCHTS probe owing to its strong freezing∕heating capability. In this way, a large number of incisions with multiple probes, commonly adopted in a conventional cryosurgery, can be avoided and the serious mechanical trauma including potential dangers can thus be significantly reduced. Meanwhile, the cost for the operation and postmedical care will be lowered. The present strategies are expected to be valuable in administrating a highly efficient and minimally invasive cryosurgery in the near future.

WE‐C‐M100J‐03: Cryoablation: Scientific Foundation, Treatment Planning and Clinical Practice

Cryoablation: Scientific Foundation, Treatment Planning and Clinical Practice.Interest in and utilization of cryoablation as a primary therapy for many types of cancer has increased markedly in the past decade. The procedure has evolved significantly from a technology perspective with engineering advances yielding greater control of ice formation within the body as well as enhanced visualization. This, coupled with isotherm modeling and treatment planning, has resulted in the ability to accurately target tissue for cryoablation. The organ to which these advances are most often applied is the prostate. This is due to the prostate being a relatively difficult structure to treat. The passage of the urethra through the gland necessitates the use of multiple cryoprobes and the procedure is confounded by the sensitivity of adjacent structures including the neurovascular bundles, external sphincter and rectum. Even with these obstacles, modern prostate cryoablation has emerged both as a primary prostate cancer treatment option and as a salvage therapy following failed radiation therapy.This lecture will review the fundamentals of cryobiology and the seminal work which established clinical endpoints. The technological basis of the procedure will be discussed including both fundamentals of cryoprobe design and compatibility imaging modalities. Lastly, clinical outcomes of the prostate cryoablation will be compared to radical prostatectomy (the gold standard), external beam radiation therapy, brachytherapy and IMRT.Educational goals:1. Understand the damage mechanisms of cryoablation and how they differ from radiation damage.2. Understand the fundamentals of how prostate cryoablation is performed and the technologies used to do so, and3. Understand how the outcomes of cryoablation compare to other treatment modalities.

Computerized planning of cryosurgery using cryoprobes and cryoheaters.

In a typical minimally invasive cryoprocedure, multiple cryoprobes are inserted into the tissue with the goal of maximizing cryoinjury within a predefined target region, while minimizing cryoinjury to the surrounding tissues. A temperature-controlled electrical heater has been developed recently by this research team, in order to assist in limiting the cryoinjury to the target region. The new device has been termed a 'cryoheater,' and it can work with any cryosurgical cooling technique. A prototype computerized planning tool has been presented recently by this research team, which helps to determine the best locations in which to insert the cryoprobes. This prototype was designed for cryoprobes only. The planning procedure utilized a novel iterative optimization technique, based on a force-field analogy. The combination of cryoheaters with computerized planning is the subject matter of this report. The current report includes a review of cryoheater development, and presents an improved cryosurgery planning tool which incorporates cryoheaters.

Computerized Planning for Multiprobe Cryosurgery using a Force-field Analogy

Cryosurgery is the destruction of undesired biological tissues by freezing. For internal organs, multiple cryoprobes are inserted into the tissue with the goal of maximizing cryoinjury within a predefined target region, while minimizing cryoinjury to the surrounding tissues. The objective of this study is to develop a computerized planning tool to determine the best locations to insert the cryoprobes, based on bioheat transfer simulations. This tool is general and suitable for all available cooling techniques and hardware. The planning procedure employs a novel iterative optimization technique based on a force-field analogy. In each iteration, a single transient bioheat transfer simulation of the cryoprocedure is computed. At the end of the simulation, regions of tissue that would have undesired temperatures apply “forces” to the cryoprobes directly moving them to better locations. This method is more efficient than traditional numerical optimization techniques, because it requires significantly fewer bioheat transfer simulations for each iteration of planning. For demonstration purposes, 2D examples on cross sections typical of prostate cryosurgery are given.