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Background:
Bone is the third most common organ to which cancer metastasizes, after the lungs and liver. Almost all patients with metastatic prostate cancer harbor skeletal metastases and in breast cancer, bone is the second most common site of metastatic spread, with bone metastases found in 90% of patients dying of breast cancer. Palliation of symptoms is the primary goal of therapy, with multidisciplinary efforts yielding the best results.
The increasing longevity of the population coupled with better therapeutic management of cancer patients contributes to the high incidence and prevalence of metastatic bone lesions. Pain from bone metastases is the most common cause of cancer pain and as more patients are living with bone metastases, improving their Quality of Life (QoL) becomes a major challenge.
Current treatment options for pain control consist of systemic therapy (analgesics, chemotherapy, hormonal therapy and biphosphonates) and local treatments [radiation, surgery and more recently laser ablation and radiofrequency percutaneous ablation Unfortunately, most medical therapies do not achieve long-lasting efficacy, frequently cause side effects or need chronic administration. Although external beam radiation therapy is the current standard of care for cancer patients who present with localized bone pain, 20%–30% of patients treated with this modality do not experience pain relief and in others the palliation is only temporary. QoL of patients with bone metastases is often poor due to unrelenting pain.
Using ExAblate for Pain Palliation of Bone Metastases
The ablation of bone metastatic lesions by focused ultrasound energy presents special considerations due to the special characteristics of the interaction of ultrasound beam with bony tissue. The acoustic absorption of bone tissue is approximately 50 times higher than that of soft tissue and the penetration of ultrasonic energy into the bone is minimal. In addition, the thermal conductivity of the bone is relatively low.
During a bone treatment, the patient is positioned so that the bone to be treated is in a water bath resting on a gel pad. The system is configured so that the targeted bone is in the near-field of the focused ultrasound beam rather than at the focus as in a soft-tissue treatment. The focused ultrasound beam is positioned perpendicular to the bone cortical surface for maximum absorption. During each sonication, the heat absorbed by the bone is capable of ablating the periosteum resulting in pain relief. Treatment progress is monitored using MRI thermal images, and post-contrast images are used following the treatment to confirm ablation.
Potential benefits of ExAblate
Based on preliminary clinical data to date, the ExAblate treatment may potentially offers patients with painful bone metastases the following benefits:
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Single treatment session
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Outpatient treatment
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Fast pain relief
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Effective on both osteolytic and osteoblastic lesions
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Low rate of complications
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No ionizing radiation
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