Clinical Medicine Flashcards
What are the different types of radiation used for therapy?
Ionizing radiation - electromagnetic (x rays, photons) or particulate (electrons, protons, neutrons, charged particles)
What are the two general uses of radiation in cancer treatment?
Used for local treatment, targeting area of known disease plus margin of normal tissue
Treats area of most likely local/regional spread of disease
What are the units of measurement for radiation exposure?
Orthovoltage/supervoltage
Roentgen - related to ability of x rays to ionize air
Rad - unit of absorbed dose, absorption of 100 ergs/g
Gray - energy absorption of 1 joule/kg
What is the mechanism of radiation effects on tissue?
Directly ionizing - charged particles can disrupt atomic structure of absorber and directly produce chemical and biological changes
Indirectly - electromagnetic give up energy to absorber to produce charged particles
Where in the cell does treatment of cancer act?
Photon interacts with atom or molecule which produces ion radical which produces free radical which damages DNA
Single or double stranded breaks but double more important
Repair not as efficient in cancer cells
What are the four modifiers of the radiation response?
Cell cycle
Type of radiation
Oxygen enhancement
Fractionation
How does the cell cycle enhance the effects of radiation?
Cells most sensitive to radiation in m and g2 phase
Least sensitive in late s phase
Intermediate sensitivity in g1 and early s
Drugs that increase proportion of cells in m and g2 will increase effects of radiation
How do types of radiation enhance effects of radiation?
Densely ionizing radiation (alpha particles or low energy neurons) - survival exponential function of dose, compact area
Sparsely ionizing radiation (x rays) - dose response curve is initial linear, then shoulder, then becomes straight at high doses, more spread out - less likely to hit DNA
How does oxygenation enhance the effects of radiation?
Cells more sensitive to radiation when they are in oxygen rich environment
Large tumors outgrow blood supply and cause central hypoxia - radiation kills peripheral better
Drugs that increase oxygen content can increase radiation response
How does fractionation enhance the response to radiation?
Single dose of radiation has greater kill than same dose in multiple smaller fractions due to repair of sub lethal damage b/w doses
Therapy is a balance - multiple smaller doses preferred
What are the four different fractionations?
Standard - once a day, 5 days per week
Hyperfractionation - decreases dose per fraction and increases total dose delivered
Accelerated fractionation - decreases total treatment time with no changes in number of fractions, total dose or dose/fraction
Accelerated hyperfractionation - combo of both altered schemes
What are the early side effects of radiation therapy?
Occur within days or weeks in tissues with rapid turnover
Rapidly repaired and may be reversible
CNS - fatigue, nausea, hair loss, swelling
Head and neck - dry mouth, taste change, skin irritation
Thorax - esophagitis, pneumonitis, pericarditis
Abdomen - nausea, vomiting, nephritis, hepatitis
Pelvis - diarrhea, dysuria, bone marrow suppression
What are the late effects of radiation therapy?
After months of years on slowly proliferating tissues
May improve but never completely repaired
CNS - damage to brain tissue
Head and neck - permanent xerostomia, osteoradionecrosis of mandible, myelitis
Thorax - fibrosis, myelitis
Abdomen - necrosis of small bowel, kidney, liver
Pelvis - hematuria or rectal bleeding, fibrosis
What are the two methods of delivery of radiation?
Teletherapy = external beam irradiation - radiation generated with electricity, electrons accelerated then rapidly decelerated in target material to produce x rays, directed at tumor from outside body - if not on surface multiple beams directed to intersect at site (target volume)
Brachytherapy - radiation source placed in body, mostly in GYN malignancies esp cervical cancer, intracavitary or interstitial
What are the three general categories of info required to make treatment decisions for cancer patients? What do you use to do this?
Site and extent of disease
Type of tumor
Patient characteristics that may limit possible treatment methods
Histopathology and stage
What are petechiae pathognomonic of?
Thrombocytopenia
What are special areas to pay attention to on physical exam of a bleeding disorder patient?
Skin and mucous membranes (mucous membranes could indicate CNS involvement - bad)
Spleen
Lymph nodes
Joints
What are disorders of primary hemostasis characterized by?
Early bleeding
Mucocutaneous bleeding
Abnormal platelet count, function or morphology
Failure to stop bleeding after initial injury
What platelet count is considered low?
Less than 10,000
What is pseudothrombocytopenia?
Artifactual clumping of platelets in response to EDTA in collection tube
Uses different tube to rule out
How does platelet volume help clue the cause of thrombocytopenia?
Young platelets and those produced during periods of high turnover are larger
What are the three broad causes of thrombocytopenia?
Decreased production
Increased destruction
Sequestration
What are causes of decreased platelet production and what would you see on peripheral blood smear?
Bone marrow infiltration - see dacrocytes
End stage cirrhosis - deficiency of thrombopoietin - see spur cells
Nutritional - b12 or folate deficiency, iron deficiency
Sepsis
What are some causes fond increased destruction of platelets?
Immune thrombocytopenia (ITP) DIC TTP HUS Vasculitis Will see schistocytes
What should you look for in the peripheral smear of thrombocytopenia?
Platelet clumping at feather edge - rule out pseudothrombocytopenia
Schistocytes –> microangiopathic process w fibrin deposition
Dacrocytes and nucleated RBCs –> bone marrow infiltrate
Spherocytes and microspherocytes –> ITP
Macrocytosis - liver disease?
Microcytosis, hypochromia
What is ITP and how is it diagnosed?
Development of antibodies against platelets
HIV individuals have high incidence
Testing for antibodies not helpful for diagnosis
Diagnosis of exclusion - physical exam and blood tests normal
What are the classifications of ITP?
Autoimmune - primary (classic, HIV related, hep c related) or secondary (SLE, lymphoproliferative disorders, solid tumors)
Drug induced
Infection induced post transfusion purpura
Neonatal isoimmune
Aloo immune
How does drug induced thrombocytopenia happen?
Drugs induce anti platelet antibodies that are dependent on presence of drug
What is heparin induced thrombocytopenia?
Virulent form of thrombocytopenia associated with high risk of arterial and venous thrombosis
Antibodies against platelet factor 4-heparin complex that activates platelets
Diagnosed by measuring HIT antibodies
What are signs and symptoms of acquired platelet function disorders?
Superficial ecchymoses out of proportion to any degree of trauma