High Risk for Skeletal Events

The goal of this clinical trial is to learn whether radiotherapy (i.e. treatment with ionizing radiation to destroy cancer cells) can prevent symptoms in patients with metastatic cancer, having high-risk bone metastases that currently result in no or only mild symptoms. High-risk bone metastases are bone metastases at high-risk of developing bone complications, such as fractures or myelum compression. The main questions this study aims to answer are: * Can preventive radiation of high-risk asymptomatic or minimally symptomatic bone metastases (and observation or medication) decrease the number of skeletal related events (i.e. bone complications due to bone metastases) in patients with metastatic cancer? * Can preventive radiation of high-risk asymptomatic or minimally symptomatic bone metastases (and observation or medication) decrease the need for hospitalization related to such bone metastases, improve overall survival and (health-related) quality of life? * What are the side effects of preventive radiation of high-risk asymptomatic or minimally symptomatic bone metastases? Researchers will compare 2 treatment groups in order to answer the questions listed above: 1 group treated with medication or observation alone (group A) and 1 group treated with medication or observation and preventive radiotherapy (group B). Participants will * be screened to assess whether they are eligible to participate in the study. * be randomized (i.e. drawn) into the 2 treatment groups mentioned above. * be treated with preventive radiotherapy if they were drawn in treatment group B. * need to attend follow-up visits (may be via teleconsultation) at 1, 3, 6, 12, 18 and 24 months after date of randomization during which safety and efficacy is monitored. During these follow-up visits, the general health condition of the participant is evaluated, the occurrence of any bone complication, the medications taken by the participant are registered, the degree of pain and location of the high-risk bone metastases are determined and possible side effects are registered. Furthermore, the participant needs to complete 2 questionnaires at each visit regarding his/her quality of life.