Radiothérapie à haute dose pour palliation (Hi-D)

This study is being done to see if a new palliative radiotherapy technique can prevent growth or shrink tumors that are bigger than 5cm, for a longer period of time than traditional palliative radiotherapy. The main outcome the investigators are measuring is called "local control"- this refers to how long the treatment is able to stop a cancer from growing. With traditional palliative radiotherapy, radiation is given in smaller doses over multiple, (usually 5 or 10) treatments (called fractions), and the radiation is spread evenly around the tumor. Radiation dose is measured in Gray (Gy). Generally, standard of care/traditional palliative radiotherapy is given as 20 Gy in 5 fractions or 30 Gy in 10 fractions. The new palliative radiotherapy technique the investigators are testing gives a similar radiation dose overall of 27 Gy but gives much higher doses per fraction in only 3 fractions and uses cutting edge technology to concentrate most of the radiation to the center of the tumor. This means that compared to traditional palliative radiotherapy, there is a higher amount of radiation dose that the participant's body and the particularly the center of the tumor is receiving over a shorter period of time. This means a more aggressive treatment for the participants cancer but can also cause an increased risk for side effects. However, because the investigators will concentrate the high doses of radiation only in the center of the tumor, nearby organs do not get too close to the high doses and are spared. The investigators expect that this technique will be as safe as traditional palliative radiotherapy and have a longer duration of effectiveness (longer local control) compared to the older techniques.