Transurethral ultrasound applicators with dynamic multi‐sector control for prostate thermal therapy: In vivo evaluation under MR guidance

Abstract

The purpose of this study was to explore the feasibility and performance of a multi-sectored tubular array transurethral ultrasound applicator for prostate thermal therapy, with potential to provide dynamic angular and length control of heating under MR guidance without mechanical movement of the applicator. Test configurations were fabricated, incorporating a linear array of two multisectored tubular transducers ͑7.8-8.4 MHz, 3 mm OD, 6 mm length͒, with three 120°independent active sectors per tube. A flexible delivery catheter facilitated water cooling ͑100 ml min −1 ͒ within an expandable urethral balloon ͑35 mm longϫ 10 mm diameter͒. An integrated positioning hub allows for rotating and translating the transducer assembly within the urethral balloon for final targeting prior to therapy delivery. Rotational beam plots indicate ϳ90°−100°acoustic output patterns from each 120°transducer sector, negligible coupling between sectors, and acoustic efficiencies between 41% and 53%. Experiments were performed within in vivo canine prostate ͑n =3͒, with real-time MR temperature monitoring in either the axial or coronal planes to facilitate control of the heating profiles and provide thermal dosimetry for performance assessment. Gross inspection of serial sections of treated prostate, exposed to TTC ͑triphenyl tetrazolium chloride͒ tissue viability stain, allowed for direct assessment of the extent of thermal coagulation. These devices created large contiguous thermal lesions ͑defined by 52°C maximum temperature, t 43 = 240 min thermal dose contours, and TTC tissue sections͒ that extended radially from the applicator toward the border of the prostate ͑ϳ15 mm͒ during a short power application ͑ϳ8−16 W per active sector, 8-15 min͒, with ϳ200°or 360°sector coagulation demonstrated depending upon the activation scheme. Analysis of transient temperature profiles indicated progression of lethal temperature and thermal dose contours initially centered on each sector that coalesced within ϳ5 min to produce uniform and contiguous zones of thermal destruction between sectors, with smooth outer boundaries and continued radial propagation in time. The dimension of the coagulation zone along the applicator was well-defined by positioning and active array length. Although not as precise as rotating planar and curvilinear devices currently under development for MR-guided procedures, advantages of these multi-sectored transurethral applicators include a flexible delivery catheter and that mechanical manipulation of the device using rotational motors is not required during therapy. This multi-sectored tubular array transurethral ultrasound technology has demonstrated potential for relatively fast and reasonably conformal targeting of prostate volumes suitable for the minimally invasive treatment of BPH and cancer under MR guidance, with further development warranted.

Phase-shift perfluorocarbon agents enhance high intensity focused ultrasound thermal delivery with reduced near-field heating

“…In some countries, HIFU is approved to treat prostate cancer, and in the U.S., HIFU is approved by the Food and Drug Administration for the treatment of uterine fibroids (Ringold, 2004;Gedroyc and Anstee, 2007;Lukka et al, 2011). HIFU is also under preclinical investigation as a potential treatment option for tumor malignancies located in brain, liver, prostate, pancreas, bone, and breast (Hill and terHaar, 1995;Kennedy, 2005;Pauly et al, 2006;Wu et al, 2007;Kinsey et al, 2008;Maleke and Konofagou, 2008;Liberman et al, 2009;Fischer et al, 2010;Jang et al, 2010;Maleke and Konofagou, 2010;McDannold et al, 2010;Tempany et al, 2011). Because HIFU requires no invasive procedures, radiation, or chemotherapy, it offers advantages over standard cancer therapy.…”

Approaches for modelling interstitial ultrasound ablation of tumours within or adjacent to bone: Theoretical and experimental evaluations

“…The simulated size and shape of thermal lesions, defined as cross-sectional area of the 52°C contour [54], were compared to the measured lesions described above.…”

Theoretical evaluation of the treatment effectiveness of a novel coaxial multi-slot antenna for conformal microwave ablation of tumors

“…Microwave ablation (MWA) is an efficacious therapy for liver cancer [2][3][4][5][6][7][8]. The cancer cells are heated above 52°C which leads to their immediate death during the MWA process [9][10][11][12][13][14]. The goal of MWA is to create heat in the cancerous tissue without damaging surrounding normal tissue [15,16].…”