Locoregional radiation therapy
The irradiated volume should be limited to the absolute minimum. This requires CT dose planning for treatment.
Before the first treatment session, a customized plastic mask is made for the patient to immobilize the head/neck area.
A CT examination is then performed while the patient is wearing the mask to label tumor tissue and organs at risk.
In the head/neck region, there are many organs at risk with limited tolerance for radiation, such as the:
- spinal cord
- brain stem
- parotid gland
- optic chiasm
- internal ears
- optic nerves
A uniform dose distribution over the target volume is ideal with complete avoidance of critical organs. In practice, however, this is impossible to achieve. There will always be a compromise between what is possible and desired.
Preparation for simulation which involves modeling and drawing of radiation fields takes about one week. When this is completed, the patient is ready to start radiation treatment.