Lecture 9 2/18/25 Flashcards
What is a gray?
absorption of one joule of radiation energy per kilogram of matter
What is the basis of radiation biology?
we cause damage in the DNA within tumor cells to prevent cell division and cause cell death; ideally want to cause double strand breaks
Which tumor types will show a faster response to radiation treatment?
those with higher mitotic activity
How do most tumor cells die?
via necrosis
Why is it important that lymphoma cells die via apoptosis?
this type of cancer is more likely to show a quick response to radiation therapy
What are the four Rs of radiation therapy?
-repair
-repopulation
-redistribution
-reoxygenation
What are the characteristics of repair?
-the most important aspect of radiation
-repair of damage caused by radiation occurs in both tumor and normal cells
-thought that normal cells repair better/faster; want to time treatments so that normal cells are repaired while tumor cells are still damaged
What are the characteristics of repopulation?
-50-60% of normal cells killed with each fraction of radiation are recovered due to compensatory proliferation of tissue
-tumor cells are thought to repopulate at a slower rate; better to keep treatments shorter together to take out more cells/prevent proliferation
-local control and long term survival are better when treatments are closer together
What are the characteristics of redistribution?
-has to do with where in the cell cycle normal and tumor cells are
-cells in G2/M phase are sensitive and die
-cells in S/G1 phase are not as sensitive and survive
-radiation can initiate G1/S blocks and G2/M blocks
-cells that were in S/G1 during one treatment could be in G2/M in a future treatment and be killed then
What are the characteristics of reoxygenation?
-upwards of 50% of tumors have hypoxia
-oxygenated cells are more sensitive to radiation
-aerated cells can be killed off to allowing hypoxic cells to become aerated again; can kill off aerated cells with each treatment and allow cycle to continue
What are the characteristics of definitive radiation?
-long term tumor control
-daily treatments
-small daily doses that add up to high total dose
What are the characteristics of palliative radiation?
-shorter survival time
-typically weekly treatments
-high daily doses that ultimately add up to a lower total dose
What are the characteristics of acute side effects?
-occur during radiation therapy
-deterministic/occur once a threshold level of radiation has been achieved
-related to total dose of radiation
-related to stem cell damage
-worst effects seen in rapidly dividing tissues
-begin during third week of treatment and last 2-3 weeks after treatment
What are the special acute side effects?
-tear glands/dry eye
-lung tissue/pneumonitis
-brain tissue/edema
What are the treatment options for acute side effects?
topical:
-clean radiation site
-ointments
-vitamin E oil
oral:
-NSAID
-gabapentin
-tramadol
-opioids if severe
What are the characteristics of late side effects?
-stochastic/random events
-related to fraction size; more likely with larger fractions
-can cause necrosis, fibrosis, and secondary tumors
What are the treatment options for late side effects?
-extensive surgery
-euthanasia
How does SRS stereotactic radiotherapy differ from SBRT stereotactic radiotherapy?
SRS:
-single fraction
-used for neuro tissue
SBRT:
-multiple fractions
-used for tissues other than neuro
-most common in vet med patients
What are the characteristics of stereotactic radiotherapy?
-delivery of ablative doses of radiation
-multiple tiny fields
-normal tissues receive minimal dose
-tumor area receives high dose
What are the benefits of stereotactic radiotherapy?
-less acute side effects
-shorter course of radiation
-less anesthesia/sedation needs
What are the pitfalls of stereotactic radiotherapy?
-not all tumors can be treated via this method
-must have a target
-scar lines cannot be treated
-late effects related to fraction size can develop months to years later
What is the late side effect seen when treating pituitary tumors?
blindness 8 to 12 months post-treatment
What are the late side effects seen when treating nasal tumors?
-osteonecrosis
-seizures
What are the late side effects when treating osteosarcoma?
-fractures
-skin fibrosis/necrosis
