PHARM 444: Radiation therapy

how does radiation work?

High energy x-rays are converted to photons in a linear accelerator >>>> photons interact with tissue = displaces e- from orbit creating net positive charge (ionizing radiation) >>> recoil e- interact with water in tissue = creating free radicals = damage to DNA = cell death

what are the 2 types of radiation therapy

1) external beam RT = linear accelerators to focus radiation on cancer sites

2) brachytherapy = internal radiotherapy; implants directly in tumour of body cavity

what is the intent behind using brachytherapy

to deliver a high radiation dose to the tumor while limiting the absorbed dose to surrounding healthy tissues

How often is radiotherapy (RT) usually given?

daily

How long does one RT treatment usually take?

several mins

Do patients become radioactive from External Beam RT?

NO. -- but yes with brachytherapy

Why is RT used in cancer patients?

- improve survival

- improve local control

- decrease symptoms

- improve quality of life

What percent of RT is given with palliative intent?

~50%

Indications for palliative RT (5):

1. Bone metastases

2. Spinal cord compression

3. Brain metastases

4. Advanced lung cancer

5. Superior vena cava syndrome

Criteria for radiation-induced malignancy (4)

1) within or at border of RT field

2) previously normal tissue

3) latent period exists (≥ 3 years)

4) histologically proven different from primary cancer