Palliative radiation therapy for the head/neck regionMedical editor Jan Folkvard Evensen
Oslo University Hospital
Patients with advanced cancer and short expected survival time may benefit from both symptom-relief and prevention by radiation therapy. In some cases, radiation treatment may also extend survival.
Normal tissue has a greater ability to repair itself between fractionations compared to tumor tissue. Radiation therapy is therefore given with one or few fractions with good effect and little side effects. In this way, a high total dose is given to the tumor tissue but injury to healthy tissue is still limited.
It is very important that acute side effects are minor and of short duration.
Palliative radiation therapy is used both for primary tumors, local recurrence, and metastases.
- Incurable cancer in the head/neck region.
- Clear association between metastasis(es) and symptom(s).
- Relieve symptoms
- Prevent symptoms
|Definitions of target volumes according to ICRU (International Commission on Radiation Units and Measurements)
|CTV (Clinical Target Volume)
||Tissue volume that contains a GTV and/or subclinical microscopic malignant disease, which has to be eliminated.
|ITV (Internal Target Volume)
||Volume encompassing the CTV and IM. (ITV = CTV + IM)
|PTV (Planning Target Volume)
||Geometrical concept. Defined to select appropriate beam sizes and beam arrangements, taking into consideration the net effect of all the possible geometrical variations and inaccuracies in order to ensure that the prescribed dose is actually absorbed in the CTV. Its size and shape depend on the CTV but also on the treatment technique used, to compensate for the effects of organ and patient movement, and inaccuracies in beam and patient setup.
|OAR (Organ at Risk)
||Normal tissues whose radiation sensitivity may significantly influence treatment planning and/or prescribed dose.
|PRV (Planning Organ at Risk Volume)
||Includes margin around the OAR to compensate for changes in shape and internal movement and for set-up variation.
|TV (Treated Volume)
||Volume enclosed by an isodose surface.
|IV (Irradiated Volume)
||The volume that receives a dose that is significant in relation to normal tissue tolerance.
|CI (Conformity Index)
||Relationship between TV and PTV (TV/PTV).
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.
Fractionation and total dose will depend on whether the patient has received radiation therapy in the same area previously.
If the problem is locoregional, for example a recurrence, the first attempt will be 20 fractions of 1.5 Gy, 10 fractions per week.
If the tumor responds and the patient tolerates treatment, an additional series with the same fractionation can be attempted after 14 days.
Metastases causing symptoms outside the head/neck region, such as painful bone metastases, can be treated with higher fractions, possibly 10 fractions of 3 Gy.
Most side effects occurring during treament are due to normal organs included in the radiation field. The dose levels used for pure symptom relief are, however, held low to minimize the risk for acute side effects.
The total dose is at a level to minimize the risk for late effects.
Good follow-up is important to achieve adequate relief of symptoms and usually takes placed with the patient's local hospital or primary care doctor.