Clinical Radiobiology Flashcards
linear accelerator function
generates high energy photons and electrons
How does ionizing radiation kill cancer cells
dsDNA breaks
Cell death mechanism for lymphoma
apoptosis
cell death mechanism for epithelial cells
necrosis
Gross disease dose
higher dose for gross disease
mechanism of radiation resistance
hypoxia
concurrent chemotherapy
increase acute toxicity, minimal effect on long term toxicity
tolerance dose 5/5
dose at which there is 5% risk of toxicity at 5 years
normal tissue toxicity risk factors
- high dose
- intrinsic sensitivity
- large fraction size
- large target volume
- tissue architecture
Late toxicity intrinsic rad sensitivity
Scleroderma
Ataxia Telangiectasia
dsDNA break strand repair
Fractionation
decreases acute effects; multiple decrease for late effects
Secondary cancers
- osteosarcoma
- more common in children
- 5-20 years after treatment
Tissue architecture
Parallel vs. Series
Parallel architecture
liver/lung - can treat small volume to high dose
Series architecture
spinal cord - can not treat small volume to high dose
Prostate cancer
epithelial tumor
7-8 weeks daily treatment
7200 cGy in 40 x 180 cGy fractions
entire prostate
small escalation in dose
improves disease control
increased toxicity
IMRT (abv)
Intensity Modulated Radiation Therapy
IMRT
dose escalation w/ normal tissue sparing
brachytherapy
60-100 seeds; dose escalation; tissue sparing.
why fractionation
allows normal tissue repair;
CyberKnife System
allows for reduced treatment margins
alpha/beta value
estimate of the relative fraction size sensitivity
low alpha/beta (1-3)
tumor is very sensitive to fraction size
high alpha/beta (8-10)
insensitivity to fraction size
alpha/beta of prostate carcinoma
~1.5 Gy - may need to change paradigm to a few high doses
lower than normal tissue
