Oncology - Radiation Flashcards
*Gastrointestinal (GI) lymphoma diagnosed in cats is most frequently low/high grade and B-cell/T-cell in origin?
low, T-cell
*Lymphoma is currently diagnosed most commonly in older, feline leukemia virus (FeLV) positive/negative cats.
negatiive
*Most commonly used oral chemotherapeutic to treat low grade GI lymphoma in cats?
Prednisone and chlorambucil
*Diagnostic test utilized to determine clonality of lymphocyte population?
PCR (PARR)
What are the realistic challenges for radiation therapy in veterinary oncology?
Availability, logistics/time, cost, side effects, and perception
When are X-rays produced?
when charged particles (such as electrons) strike dense material and suddenly decelerate
When are gamma rays produced?
when naturally unstable atomic nuclei decay
What is the direct action on DNA of radiation?
It breaks the double strand
What is the indirect action on DNA of radiation?
70% of biologic effect of RT comes from free-radical formation
The biologic effects of radiation result from what?
damage of DNA
In order of decreasing sensitivity, what is the degree of tissue susceptibility to radiation?
Blood-forming organs, reproductive organs, skin, bone and teeth, muscle, and the nervous system
In a general sense, what cells are more susceptible to radiation?
rapidly dividing cells because they have less time to repair
In what phase of replication are cells most sensitive to radiation?
Cells in the Late S phase, G2, or Active mitosis
- The most important mechanism by which external beam radiation therapy causes DNA damage and results in cell death is via:
a. Direct action of ionizing radiation causing double strand breaks in the cellular DNA
b. Thermal damage to cells caused by ionizing radiation
c. Indirect action of ionizing radiation via free radical induction and subsequent DNA damage
d. Inhibition of topoisomerase II
c. Indirect action of ionizing radiation via free radical induction and subsequent DNA damage
We see acute/chronic radiation side effects more often.
acute
What are some examples of acute radiation side effects?
Moist desquamation of skin, mucositis, conjunctivitis, colitis, proctitis, rhinitis, and more
How do you manage acute radiation side effects?
Based on the symptoms they are showing
Pain medication for acute radiation side effects are central/peripheral.
central
What tissues are commonly effected by acute radiation side effects?
rapidly dividing cells/tissues
What tissues are commonly effected by chronic radiation side effects?
Late responding tissues - lens, bone, fibrous tissue, and nerves
In tissues affected by chronic radiation, DNA damage results in _____ catastrophe months to years after radiation.
mitotic
- Which of the following would be a possible early side effect following radiation therapy in a dog with a nasal tumor?
a. Cataract OS
b. Oral mucositis
c. Necrosis of the hard palate
d. Change in hair color in area treated
b. Oral mucositis
What tumors can radiation therapy be used for?
Nasal, oral/craniofacial, brain, ear canal, thyroid, mediastinal, bone/spinal, mast cell tumors, soft tissue sarcomas, urinary bladder, prostate, and anal sac
What is the indication for palliative-intent radiation therapy?
Absence of curable disease OR when co-morbidities preclude definitive-intent RT
What is the goal of palliative-intent RT?
Improve/maintain quality of life
What is the goal of definitive-intent RT?
Deliver enough dose to achieve durable local tumor control
Maximize quantity and quality of life
True or False: Radiation therapy is only used after surgery.
False - it can be used before or after surgery
What are the pros to palliative-intent RT?
Low cost, convenient schedule, and low risk of severe acute toxicity
What are the cons to definitive-intent RT?
Expensive, inconvenient schedule, and may be associated with bad side effects
What are the pros and cons to stereotactic RT?
Expensive, convenient schedule, low risk of severe acute toxicity
What are some common types of external beam RT?
Clinical/manual setup
3-dimensional conformal RT
Intensity-modulated RT
Stereotactic RT
What are the advantages to clinical/manual point calculation?
Less expensive, treat microscopic disease, and even distribution when treating cuboid structures
What are the disadvantages to clinical/manual point calculation?
Over/under dosing more common, uneven distribution of dose for complex shapes, and no dose painting/shaping
What is the clinical utility of clinical/manual point calculation?
Microscopic disease of extremities, rostral maxilla or mandible, and palliative radiation of many sites
What are the advantages of intensity-modulated RT (IMRT)?
More effectively spare normal tissue, minimize radiation effects, and treats gross or microscopic disease
What are the disadvantages to IMRT?
requires advanced accelerator/technology
What is the clinical utility of IMRT?
Nasal/oral, brain, body wall, and urinary tract tumors
What are the advantages to sterotactic radiotherapy?
Treatment is completed in 1-5 fractions and minimizes acute radiation side effects
What are the disadvantages to stereotactic radiotherapy?
Requires advanced equipment/technology and cannot treat microscopic disease/requires gross tumor
What is the clinical utility of stereotactic radiotherapy?
Brain, nasal, bone, thyroid, lung, mediastinal, heart-based tumors
Palliative treatment at almost any site
How does stereotactic radiotherapy work?
It uses onboard imaging and dynamic collimation to deliver high doses of targeted radiation
