Prostate thermal therapy with high intensity transurethral ultrasound: The impact of pelvic bone heating on treatment delivery

Wootton, Jeffery; Ross, Anthony B.; Diederich, Chris J.

doi:10.1080/02656730701744794

Cited by 31 publications

(44 citation statements)

References 84 publications

(119 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…7͒. Furthermore, as demonstrated in experiments and theory of previous studies of tubular applicators, it is possible to extend penetration to 15-20 mm radial with increased power and longer treatment times, 20,24,27,30 indicating that future optimization of design and treatment delivery strategies can be performed to potentially treat larger glands up to ϳ5 cm width if necessary. However, the radial divergence of the acoustic energy from tubular radiators may limit effective penetration for glands greater than ϳ5 cm.…”

Section: Discussionmentioning

confidence: 89%

“…[24][25][26] Planar and curvilinear ultrasound applicators appear to provide good penetration and control of thermal lesions; however, due to an inherent narrow acoustic beam width ͑ϳ4 mm͒, they require scanning and treatment times from ϳ10 to Ͼ30 min to ablate large regions of the prostate as demonstrated within canine prostate in vivo, in phantom, and in simulations. [24][25][26]29,30 Treatment durations could be increased if pelvic bone is in close proximity to the gland, due to selection of higher frequencies and lower powers in order to reduce bone heating. 30 Mechanical manipulation of the applicators during treatment can create problems and inaccuracies with proton resonance frequency ͑PRF͒ based MR temperature imaging because phase subtraction methods are very sensitive to movement in a series of images.…”

Section: Introductionmentioning

confidence: 99%

“…[24][25][26]29,30 Treatment durations could be increased if pelvic bone is in close proximity to the gland, due to selection of higher frequencies and lower powers in order to reduce bone heating. 30 Mechanical manipulation of the applicators during treatment can create problems and inaccuracies with proton resonance frequency ͑PRF͒ based MR temperature imaging because phase subtraction methods are very sensitive to movement in a series of images. As the numbers of sequential rotation steps and heat treatment durations increase, the more likely it is that applicator movement, tissue movement, image phase drift, or a change in prostate dimensions will create significant inaccuracies in temperature measurement.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

et al. 2008

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: Discussionmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

et al. 2008

Self Cite

View full text Add to dashboard Cite

show abstract

“…[45][46][47][48][49] However, the literature does not have many reports on the use of a linefocused acoustic device for thermal therapy except for a 1990 patent by Lele, who proposed it for hyperthermia applications (nonablative temperatures), and the more recent development of slightly focused curvilinear applicators for transurethral prostate thermal therapy. [50][51][52] Lele's patent mentioned the potential advantage of lower intensities afforded by line-focusing over point-focusing transducers. To our knowledge, however, strongly line-focused ultrasound applicators have not been studied for noninvasive thermal therapy applications other than hyperthermia.…”

Section: Discussionmentioning

confidence: 99%

SonoKnife: Feasibility of a line‐focused ultrasound device for thermal ablation therapy

et al. 2011

View full text Add to dashboard Cite

Purpose: To evaluate the feasibility of line-focused ultrasound for thermal ablation of superficially located tumors. Methods: A SonoKnife is a cylindrical-section ultrasound transducer designed to radiate from its concave surface. This geometry generates a line-focus or acoustic edge. The motivation for this approach was the noninvasive thermal ablation of advanced head and neck tumors and positive neck nodes in reasonable treatment times. Line-focusing may offer advantages over the common point-focusing of spherically curved radiators such as faster coverage of a target volume by scanning of the acoustic edge. In this paper, The authors report studies using numerical models and phantom and ex vivo experiments using a SonoKnife prototype. Results: Acoustic edges were generated by cylindrical-section single-element ultrasound transducers numerically, and by the prototype experimentally. Numerically, simulations were performed to characterize the acoustic edge for basic design parameters: transducer dimensions, line-focus depth, frequency, and coupling thickness. The dimensions of the acoustic edge as a function of these parameters were determined. In addition, a step-scanning simulation produced a large thermal lesion in a reasonable treatment time. Experimentally, pressure distributions measured in degassed water agreed well with acoustic simulations, and sonication experiments in gel phantoms and ex vivo porcine liver samples produced lesions similar to those predicted with acoustic and thermal models. Conclusions: Results support the feasibility of noninvasive thermal ablation with a SonoKnife.

show abstract

“…[1][2][3][4][5][6] Mild hyperthermia (40)(41)(42)(43)(44)(45) • C) can induce direct cytotoxicity in tumors, radiosensitize cancer cells by impairing DNA repair mechanisms, and enhance blood flow in tumor microenvironments to increase tumor oxygenation and facilitate drug delivery. 7 It may also be used to enhance localized drug delivery 8 and gene therapy 9 as reported in some recent investigations.…”

Section: Introductionmentioning

confidence: 99%

Model‐based feasibility assessment and evaluation of prostate hyperthermia with a commercial MR‐guided endorectal HIFU ablation array

et al. 2014

Self Cite

View full text Add to dashboard Cite

Purpose: Feasibility of targeted and volumetric hyperthermia (40-45• C) delivery to the prostate with a commercial MR-guided endorectal ultrasound phased array system, designed specifically for thermal ablation and approved for ablation trials (ExAblate 2100, Insightec Ltd.), was assessed through computer simulations and tissue-equivalent phantom experiments with the intention of fast clinical translation for targeted hyperthermia in conjunction with radiotherapy and chemotherapy. Methods: The simulations included a 3D finite element method based biothermal model, and acoustic field calculations for the ExAblate ERUS phased array (2.3 MHz, 2.3 × 4.0 cm 2 , ∼1000 channels) using the rectangular radiator method. Array beamforming strategies were investigated to deliver protracted, continuous-wave hyperthermia to focal prostate cancer targets identified from representative patient cases. Constraints on power densities, sonication durations and switching speeds imposed by ExAblate hardware and software were incorporated in the models. Preliminary experiments included beamformed sonications in tissue mimicking phantoms under MR temperature monitoring at 3 T (GE Discovery MR750W). Results: Acoustic intensities considered during simulation were limited to ensure mild hyperthermia (T max < 45• C) and fail-safe operation of the ExAblate array (spatial and time averaged acoustic intensity I SATA < 3.4 W/cm 2 ). Tissue volumes with therapeutic temperature levels (T > 41 • C) were estimated. Numerical simulations indicated that T > 41• C was calculated in 13-23 cm 3 volumes for sonications with planar or diverging beam patterns at 0.9-1.2 W/cm 2 , in 4.5-5.8 cm 3 volumes for simultaneous multipoint focus beam patterns at ∼0.7 W/cm 2 , and in ∼6.0 cm 3 for curvilinear (cylindrical) beam patterns at 0.75 W/cm 2 . Focused heating patterns may be practical for treating focal disease in a single posterior quadrant of the prostate and diffused heating patterns may be useful for heating quadrants, hemigland volumes or even bilateral targets. Treatable volumes may be limited by pubic bone heating. Therapeutic temperatures were estimated for a range of physiological parameters, sonication duty cycles and rectal cooling. Hyperthermia specific phasing patterns were implemented on the ExAblate prostate array and continuous-wave sonications (∼0.88 W/cm 2 , 15 min) were performed in tissue-mimicking material with real-time MR-based temperature imaging (PRFS imaging at 3.0 T). Shapes of heating patterns observed during experiments were consistent with simulations. Conclusions: The ExAblate 2100, designed specifically for thermal ablation, can be controlled for delivering continuous hyperthermia in prostate while working within operational constraints.

show abstract

Prostate thermal therapy with high intensity transurethral ultrasound: The impact of pelvic bone heating on treatment delivery

Abstract: Pubic bone heating during ultrasound thermal therapy of the prostate can be substantial in certain situations. Successful realization of this therapy will require patient-specific treatment planning to optimally determine power and frequency in order to minimize bone heating.

Cited by 31 publications

References 84 publications

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

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

SonoKnife: Feasibility of a line‐focused ultrasound device for thermal ablation therapy

Model‐based feasibility assessment and evaluation of prostate hyperthermia with a commercial MR‐guided endorectal HIFU ablation array

Contact Info

Product

Resources

About