Ablative Technologies for Urologic Cancers

Robust and durable aberrative and absorptive phantom for therapeutic ultrasound applications

Phase aberration induced by soft tissue inhomogeneities often complicates high-intensity focused ultrasound (HIFU) therapies by distorting the field and, previously, we designed and fabricated a bilayer gel phantom to reproducibly mimic that effect. A surface pattern containing size scales relevant to inhomogeneities of a porcine body wall was introduced between gel materials with fat- and muscle-like acoustic properties-ballistic and polyvinyl alcohol gels. Here, the phantom design was refined to achieve relevant values of ultrasound absorption and scattering and make it more robust, facilitating frequent handling and use in various experimental arrangements. The fidelity of the interfacial surface of the fabricated phantom to the design was confirmed by three-dimensional ultrasound imaging. The HIFU field distortions-displacement of the focus, enlargement of the focal region, and reduction of focal pressure-produced by the phantom were characterized using hydrophone measurements with a 1.5 MHz 256-element HIFU array and found to be similar to those induced by an ex vivo porcine body wall. A phase correction approach was used to mitigate the aberration effect on nonlinear focal waveforms and enable boiling histotripsy treatments through the phantom or body wall. The refined phantom represents a practical tool to explore HIFU therapy systems capabilities.

Bilayer aberration-inducing gel phantom for high intensity focused ultrasound applications

Aberrations induced by soft tissue inhomogeneities often complicate high-intensity focused ultrasound (HIFU) therapies. In this work, a bilayer phantom made from polyvinyl alcohol hydrogel and ballistic gel was built to mimic alternating layers of water-based and lipid tissues characteristic of an abdominal body wall and to reproducibly distort HIFU fields. The density, sound speed, and attenuation coefficient of each material were measured using a homogeneous gel layer. A surface with random topographical features was designed as an interface between gel layers using a 2D Fourier spectrum approach and replicating different spatial scales of tissue inhomogeneities. Distortion of the field of a 256-element 1.5 MHz HIFU array by the phantom was characterized through hydrophone measurements for linear and nonlinear beam focusing and compared to the corresponding distortion induced by an ex vivo porcine body wall of the same thickness. Both spatial shift and widening of the focal lobe were observed, as well as dramatic reduction in focal pressures caused by aberrations. The results suggest that the phantom produced levels of aberration that are similar to a real body wall and can serve as a research tool for studying HIFU effects as well as for developing algorithms for aberration correction.

Laparoscopic Radiofrequency Ablation versus Partial Nephrectomy for cT1a Renal Tumors: Long-Term Outcome of 179 Patients

OBJECTIVES

To compare the long-term functional and oncological results between laparoscopic radiofrequency ablation (LRFA) and laparoscopic partial nephrectomy (LPN) in selected clinical T1a (cT1a) renal tumor patients.

METHODS

We retrospectively analyzed the medical records of patients with cT1a renal tumors who had LRFA or LPN at our institution between February 2006 and February 2015. Student's t test was used to compare the perioperative data between the two groups. Survival analyses were calculated using the Kaplan-Meier method.

RESULTS

A total of 179 patients were included in the study. Patients in the LRFA cohort were significantly older and had higher American Society of Anesthesiologists sore than in the LPN cohort. The LRFA group had a significantly lower mean blood loss than the LPN group (p = 0.03). The percent decrease of GFR in the LRFA group was significantly lower than in the LPN group (p = 0.021). The 5-year overall, cancer-specific and disease-free survival were 93.3 vs. 94.6%, 98.0 vs. 98.5% and 97.1 vs. 97.3%, for LRFA and LPN, respectively (all p value >0.05).

CONCLUSIONS

The excellent perioperative results, long-term functional and oncological outcomes of LRFA confirm that this technique is safe, nephron sparing and oncologically effective for the treatment of cT1a renal tumors.

Laparoscopic radiofrequency ablation of renal tumors: 32-month mean follow-up results of 106 patients

OBJECTIVE

To report our experience of laparoscopic radiofrequency ablation (RFA) on patients with renal tumors. RFA has been increasingly applied in the management of small renal tumors. However, it was performed mostly via percutaneous approach, with limited cases and a short follow-up period.

METHODS

From February 2006 to March 2008, laparoscopic RFA was performed on 106 renal tumors (size range: 0.9-5.5 cm) in 106 selected patients (74 men and 32 women, age range: 25-81 years). Initial contrast-enhanced computed tomography (CT) examination was performed seven days after the procedure, with subsequent CT assessment at three months, six months, and every six months thereafter. Serum creatinine measurement was conducted along with each time CT examination.

RESULTS

The mean follow-up period was 32 months (range: 12-48). All 106 tumors were biopsied before RFA, of which 90 were diagnosed as renal cell carcinoma (RCC) (84.90%). There was one incomplete ablation. One case with radiographic local recurrence was then proved by pathologic analysis of the nephrectomy specimen to have no cancer cells. The local tumor control rate was 98.1% (104/106). Of the 90 RCC cases, the disease-free survival rate was 97.8% (88/90); both the cancer-specific and the overall survival rate were 100%. No death or renal failure after the procedure has yet been found.

CONCLUSIONS

Our results showed that the laparoscopic RFA on small renal mass was safe, with outcomes of patients comparable with those by partial nephrectomy and percutaneous RFA. Further research and a longer follow-up period are needed to confirm our results.