Towards a dosimetric framework for therapeutic ultrasound

Figures & data

Table 1. Overview of therapeutic ultrasound applications.

Application	Treatment site	Aim	Acoustic exposure	Guidance	System type	Status
HIFU	Uterine fibroids [31]	Thermal ablation	HI	US/MR	E-C	Clin
	Prostate cancer [32]	Thermal ablation	HI	US/MR	E-C T-R	Clin
	Breast cancer [33]	Thermal ablation	HI	US/MR	E-C	Clin
	Abdominal cancer (liver, kidney, pancreas) [34]	Thermal ablation	HI	US/MR	E-C I-O	Clin
	Bones [35]	Pain palliation, tumour control	HI	US/MR	E-C	Clin
	Brain (essential tremor, Parkinson’s dyskinesia, OCD, depression, epilepsy) [36]	Thermal ablation	HI	MR	E-C	Clin
	Uterus (twin-twin syndrome) [35]	Vascular occlusion by thermal ablation	HI	US	E-C	Preclin
	Eye (glaucoma) [37,38]	Thermal ablation	HI	–	E-C	Clin
Lithotripsy	Kidney, Gall bladder [39]	Stone destruction by mechanical disruption	HP	US	E-C	Clin
Histotripsy [40]	Prostate	Cavitation-induced tissue disruption	HP	US	E-C	Clin
US mediated drug  delivery [41]	Malignant tumours of abdomen	Mechanically or thermally enhanced local drug delivery	MI/LI	US/MR	E-C	Preclin (early trials)
US mediated drug  delivery [41]	Brain (cancer, Alzheimer’s disease)	Breaching of BBB using mechanical effects from microbubbles	MI/LI	MR	E-C	Preclin (early trials)
Fracture healing [42]	Bone	Non-thermal effects	LI	–	E-C	Clin
Physiotherapy [43]	Soft tissues	Improved function via thermal and non-thermal effects	MI	–	E-C	Clin

BBB, blood–brain barrier; Clin, in clinical use; E-C, extra-corporeal; HI, high intensity; MI, medium intensity; LI, low intensity; High pulse pressure amplitude; I-O, intra-operative; preclin, under laboratory investigation; T-R, trans-rectal.

Table 2. Relationship of free field, in situ, dose and effect quantities.

Type of quantity	Description
Free field (water) exposure quantities	These describe the ultrasound field in water and depend only on the source and the acoustic properties of water. Typically they are local pressures, local intensities, beam-shape descriptors, for example.
In situ exposure quantities	These describe the ultrasound field in a medium other than water. The in situ level depends on the source and on the acoustic properties of the medium. Essentially these quantities are similar to those used for free field quantities (e.g. local pressures, local intensities, beam-shape descriptors).
Dose quantities	These quantify the interaction of the ultrasound field with the medium. The magnitude of the dose depends on the in situ exposure level and on the acoustic and other physical properties of the medium.
Effect quantities	These quantify the change in the behaviour or properties of the tissue. The size of the effect depends on the dose and the dose-response of the tissue. (e.g. lesion volume rate, cell surviving fraction, the rate of production of a specified bio-marker).

Table 3. What characteristics of the ultrasound exposure do you think are important for effective therapy in your application?

Exposure characteristics	Agree (%)
General
Frequency and/or spectrum	77.6
Transducer dimensions	45.9
Beam shape	69.4
Exposure time	80.0
Acoustic field
Acoustic power	80.0
Pulse parameters (e.g. burst length, pulse repetition rate)	69.4
Acoustic pressure parameters	56.5
Acoustic intensity parameters	54.1
Heating related
Maximum temperature rise	56.5
Variation of temperature rise with time	47.1
Cavitation related
Amount of stable cavitation	40.0
Amount of collapse cavitation	48.2

Figure 1. Different approaches to describing dose (vertical axis) rated according to specified criteria: (A) familiarity with the concept, (B) perceived relevance to their own applications of ultrasound, (C) perceived relevance to other applications, (D) likely acceptability to the ultrasound community). In each case, the possible responses are listed below each chart. Results are expressed as a percentage from 93 reponses to these questions.

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