In various common cancers, the skeleton is a preferred site of metastasis. These bone metastases are the most common cause of cancer-related pain, which significantly impair quality of life. It is postulated that the clinical target volume (CTV) of painful bone metastases consists of cancer cells and tumor-associated host cells: the tumor-host ecosystem. Advances in biological imaging (positron emitting tomography PET) might allow us to selectively identify the tumor-host ecosystem within the anatomical boundaries of a bone metastasis. These findings suggest the potential of intentionally non-homogenous dose escalation (dose painting by numbers) to improve pain control. The hypothesis is that fluorodeoxyglucose positron emitting tomography (FDG-PET) can detect the intra-bone metastasis regions confined with tumor-associated host-cell compartments responsible for metastasis-related pain. The primary objective is to improve pain control with biological image-guided stereotactic body radiotherapy compared to conventional radiotherapy.

Inclusion Criteria:

• Painful bone metastasis of solid tumors
• Pain score minimum of 2 on a scale of 10
• A maximum number of painful bone metastases: 3 or more
• Life expectancy > 3 months
• Age minimum 18 years old
• Signed informed consent

Exclusion Criteria:

• Tumor histology (renal cell and melanoma vs. other solid tumors)
• VAS pain score (<5 vs. 6-10).
• Bisphosphonate use (yes vs. no)
• Opioid analgesics (yes vs. no)
• Corticosteroid use (yes vs. no)
• Spine vs non-spine localisation