Focused ultrasound & histotripsy

Focused ultrasound uses an extracorporeal transducer to concentrate acoustic energy inside the body, either heating tissue to coagulation (HIFU) or, in histotripsy, driving cavitation that mechanically fractionates the tumour without heat. HIFU is approved for prostate cancer focal therapy and uterine fibroids. Histotripsy (HistoSonics Edison, FDA 2023) mechanically liquefies liver tumours, with early evidence of immune activation, and trials extend to kidney and pancreas. The approach is completely non-invasive and uses no ionising radiation. Its constraints are the acoustic window, since ribs and bowel gas block the beam, and the fact that long-term oncologic data are limited, so durability of tumour control is the open question. The simple version is that tightly focused sound waves destroy a tumour from outside the body.