Pilot Study for Palliation of Pain in Bone Metastases by MR-HIFU

Bone is the third most common site of metastases spread after the liver and the lungs, with a great incidence in breast, prostate, lung, kidney and thyroid cancers. For example, 90% of patients dying from breast cancer and most of patients with advanced prostate cancer suffer from bone metastases, which are frequently responsible of chronic pain and lead to an increase in morbidity and mortality with pathological fractures, compression syndrome and hypercalcemia..Moreover, the increasing longevity of patients with cancer resulting from the improvement of the effectiveness of the treatments leads to a higher incidence and prevalence of metastating bone lesions.

Palliative treatment with management of pain and improvement of quality of life remains the first goal of therapy. Current treatments options include systemic drug therapy (chemotherapy, hormonal therapy, analgesics and bi-phosphonates), local invasive treatment (surgery), local mini-invasive treatment with interventional radiological techniques (cimentoplasty, cryotherapy and radiofrequency ablation) and radiation therapy.

External-beam radiation therapy remains the current standard of care for patients with bone metastases in first intention. However, up to 20-30 % of patients treated do not experience pain relief and recurrence of pain appear in 27 % after treatment. Moreover radiation treatment is limited due to accumulation of dose. Since few years, cryotherapy and percutaneous radiofrequency ablation have shown good results in management of pain with bone metastases, however these techniques are still invasive.

In MRI-guided High Intensity Focused Ultrasound (HIFU), the ultrasound generated by the transducer is focused into a small focal tissue volume at specific target locations. During treatment, the beam of focused ultrasound energy penetrates through soft tissue and causes localized temperatures elevation up 55-70°C for a few seconds within the target producing well defined regions of irreversible protein denaturation, cell damage, and coagulative necrosis. A single exposure of focused ultrasound energy is called a "sonication." Multiple sonications are necessary to ablate the targeted tissue. Tight focusing is designed to limit the ablation to the targeted location.

Applying HIFU energy to a patient's lesion requires treatment planning, targeting of the ultrasound (US) beam to desired locations and monitoring of the energy delivery. In some applications this can be performed using diagnostic ultrasound imaging in combination with the HIFU. While diagnostic US provides some anatomical details and helps with procedure planning and treatment targeting, it does not provide 3D planning, means of measuring the temperature increase generated by HIFU, or metrics for quantifying the energy/dose delivered to the treatment zone. Currently, only MR imaging can provide a validated non-invasive temperature measurement and thermal dose quantification in the treated tissue. Furthermore, these real-time MR temperature measurements can be used to control the HIFU system to deliver optimal temperatures to the target locations. The Philips MR-guided focused ultrasound system will provide real-time tissue temperature mapping in multiple planes and control of the temperature delivering dose to the target location. Recent advances in MR temperature mapping make it possible to achieve temperature accuracy of 1°C in stationary soft tissues.