Radiation treatment to the brain of lung cancerMedical editor Odd Terje Brustugun MD
Oslo University Hospital
For small cell lung cancer, radiation therapy to the brain is performed as prophylactic treatment when chemotherapy to the primary cancer has resulted in partial or complete response, or as palliative relief treatment for established brain metastases from either small or non-small cell lung cancer.
Based on clinical studies and autopsy data, it is known that up to 25% of all lung cancer patients develop brain metastasis within two years of the diagnosis. 10% of patients with small cell lung cancer have brain metastases at the time of diagnosis and an additional 20 % develop such during treatment.
Radiation is usually given towards the entire brain as opposing directional fields. For 1-3 metastases up to 4 cm in diameter, stereotactic radiation therapy to the tumor(s) may be appropriate. Treatment is given as a single fraction of 15–25 Gy. Total brain radiation is administrated for small cell lung cancer even with only 1–3 metastases, due to the high risk of micrometastases outside the visible metastases. Stereotactic radiation can be administered for this patient group if total brain radiation already has been delivered.
- Complete or partial response of initial therapy in small cell lung cancer
- Established brain metastasis
- Prevent brain metastasis
- Reduce the extent of metastasis
- Relieve and prevent symptoms
|Target volume definitions from ICRU
(International Commission on Radiation Units and Measurements)
GTV (= Gross Tumor Volume)
|Palpable or visible/demonstrative area of malignant growth.
CTV (= Clinical Target Volume)
Clinical target volume
Tissue volume which contains GTV and/or subclinical microscopic malignancy.
ITV (= Internal Target Volume)
Volume containing CTV and a inner margin taking into account inner movements and revisions of CTV.
PTV (= Planning Target Volume)
Geometric volume containing ITV and a Setup margin taking into account assumed variations for patient movements, variations in patient arrangement, and field modeling.
Before the first radiation treatment, an individually adjusted plastic mask is prepared for the head in order to immobilize the patient.
During the CT scan for dosage planning, the patient must stay immobile in a supine position on a thin mattress. He/she must therefore be well medicated for pain, either by premedication or an additional dose of opiates.
Planning of the radiation field (contouring, determining radiation field, necessary adjustments, and checks as well as preparation of documentation) for simulation usually takes a few days.
Simulation in cases of palliative treatment occurs only "virtually," i.e. only as data simulation. The patient will meet for their first treatment a few days after the CT scan.
In the head region, there are many risk organs with limited tolerance for radiation such as:
- spinal cord
- brain stem
- parotid gland
- optic chiasm
- inner ears
- optic nerves
- bulb of the eye
Ideally, a uniform dose distribution over the target volume is achieved with no radiation to critical organs. This is impossible to achieve. A compromise between what is possible and what is desired is therefore made.
Patients with small cell lung cancer who achieved partial or complete response in the thorax 4-6 weeks after concluded chemotherapy should be offered prophylactic radiation to the brain.
2,5 Gy x 10 is given. Five treatments per week are given and the total treatment time is therefore 2 weeks.
For established brain metastases, palliative treatment is given in a dosage of 3 Gy x 10 or 4 Gy x 5. Five treatments per week are administered and the total treatment time is 1-2 weeks.
For 1–3 metastases under about 4 cm, stereotactic radiation therapy is appropriate, usually in one fraction of 15–25 Gy.
Side effects of radiation therapy
Radiation therapy may render the patient more fatigued and lethargic. Reduced appetite, nausea, diarrhea, and pain cause fatigue. The fatigue does not always go away when treatment is over.
Reactions in the skin from radiation are normal and worsen with increasing doses. Soreness may last and/or increase until at least a couple of weeks after treatment is finished.
Radiation therapy to the head causes nausea in rare cases. If the patient is also receiving chemotherapy, nausea may be intensified.
At the start of radiation therapy to the head, the brain tissue can swell leading to headache. Paracetamol and steroids may prevent the headache. Generally when whole brain radiation is being administered, concomitant use of steroids are recommended during the course of radiation to prevent cerebral edema. Steroids may be tapered off after the conclusion of the radiation.
Radiation to the head often causes hair loss. In most cases, hair will grow again after the treatment is concluded. However, large radiation doses can cause permanent damage to hair follicles in which hair and facial hair do not grow back in the radiated areas.