Principles of Radiation Therapy Flashcards
Physiology of radiation therapy: Indirect effect
Photons pass through cellular water AND generate free radicals that disrupt DNA helix
Physiology of radiation therapy: Direct effect
Photons pass through biologic tissue and produce ionizations that directly interact with DNA
Definition of Fractionation
Total doses of radiation divided into multiple smaller doses over days/weeks
True or False: Normal cells can better repair sublethal damage caused by radiation than cancer cells
True
External Beam Radiotherapy method
photon beams externally generated and applied to a field of radiation
Brachytherapy method
radioisotope placed into the patiet
Brachytherapy intracavitary treatment dosing
Dose varies inversely to distance between source and point squared. D = 1/(distance)2. Closer tissue receives more radiation
Cells affected by ACUTE radiation Toxicity
Rapid Turnover Cells - Mucosa, bone marrow, skin, hair
Cells affected by LATE radiation Toxicity
Slow turnover cells - Connective tissue, muscles, nerves
Acute radiation Toxicity
Diarrhea, anemia, neutropenia
Late radiation Toxicity
Fibrosis, vaginal narrowing, adhesions
At what stage of cervical cancer is RT the initial therapy
Stage IB3
Indications for adjuvant radiotherapy following surgery for Cervical cancer
Stage IB3, > 4 cm tumor, positive LVSI, positive stromal invasion
Indications for adjuvant radiotherapy AND Chemosensitization
Stage IB3, positive lymph nodes, positive margins, Parametrial involvement
Course for External beam radiation: How many Rads (cGy) per treatment day
180 rads (cGy)
