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Onco 3 Radiation

sihirlifil's version from 2018-05-01 11:26

Intro & Tx

Question Answer
Radiation therapy backgroundRecognized specialty 1994
Important component of multimodal approach to treating cancer (e.g. couldn’t do sx, want to reduce tumor size)
Radiation therapy = _________ radiationElectromagnetic
Important aspects of radiationEquipment (intricate!)
Basic mechanism of action of ionizing radiation
Results of irradiating various tumors
Associated acute & late SEffx
What are some significant advances to radiation?Using megavoltage radiotherapy
Daily radiation therapy protocols
Administration of higher total doses
Use of CT (tumor imaging, radiation therapy planning)
External beam equipment =Xrays, gamma rays, electrons delivered by either orthovoltage or megavoltage
Types of radiation therapyTeletherapy
Teletherapy = ?Delivered from a distance
Teletherapy: how does orthovoltage work?Xrays generated, bombarding metal object (100-200 kVp)
Maximum radiation delivered at skin surface
Limited to lesions <2-3cm depth. Short surface-to-skin difference
Differential absorption of radiation dose
Teletherapy: ORTHOVOLTAGE primarily suited for?Superficial tumors that do not involve adjacent bone
Teletherapy: advantages of ORTHOVOLTAGEGood for surface tumors!
Minimal structural facility requirements
Teletherapy: disadvantages of ORTHOVOLTAGEDifferential absorption (bone > soft tissue)
Too superficial for many tumors
Teletherapy: how does MEGAVOLTAGE work?Cobalt 60 gamma rays from a radioactive source: Linear accelerator (LINAC) can produce electrons & photons, large source --> skin distance, skin-sparing effect
t1/2 = 5.26 years!
Teletherapy: advantages of LINAC? (megavoltage)Versatile
Computerized treatment planning
Treat deep & superficial tumors
Ability to treat large fields over vital organs (amt of scatter produced not damaging to spleen, liver, etc)
Teletherapy: disadvantages of LINAC? (megavoltage)Expensive, special facility, quality assurance
Brachytherapy =Delivered from short distances. Radioisotopes applied to/within a tumor
Brachytherapy: what implants are used?Iridium 192
Iodine 125
Cesium 137
Brachytherapy: AdvantagesSingle anesthetic
Continuous radiation
Sparing of normal tissues, higher dose to tumor
Shorter hospitalization
Brachytherapy: DisadvantagesLack of availability
Challenge in dosimetry (don’t know if same amount delivered all the way through)
What kind of radiation?
Brachytherapy (equine sarcoids)
Brachytherapy: e.g. of systemicIodine 131
153-Samarium-EDTMP (Quadramet)
How does I-131 work?Taken up by hyperfunctional thyroid cells. Emits gamma-radiation & high-energy electrons
Used in tx of hyperthyroidism in cats & thyroid carcinoma in dogs
Caveat for I-131 treatmentRADIATION ISOLATION! NOT for diabetics or kidney failure cats! Can’t access patient for 3-7d… sometimes longer
How does 153-Samarium-EDTMP work? used for?(targeted radiopharmaceutical developed at MU-Columbia) Bone-seeking radionucleotide (EDTMP) localizes in areas of increased osteoblastic activity (active areas of bone remodeling). Used for OSA in dogs (limb sparing), pain palliation for metastatic bone lesions (lung, breast, OSA, prostate)
SEffx of 153-Samarium-EDTMPPROFOUND thrombocytopenia & neutropenia
What kind of radiation?
Strontium 90 (applicator)
Brachytherapy: e.g. of applicatorsStrontium 90
How does Strontium 90 work?Emits beta particles
Limited to 3mm thickness
Indications for Strontium 90SCC, eosinophilic granulomas (cats) (equine squames, sarcoids)
Principles: most critical target =DNA! (Double-stranded breaks of nuclear DNA are the most important cellular effect of radiation. This breakage leads to irreversible loss of the reproductive integrity of the cell and eventual cell death)
Perturbation of cellular homeostasis --> cell death
Affects all cells undergoing division (S phase resistant, G2 phase sensitive)
What’s going on here?
Mitotic death
Cells die after irradiation after 1 or more mitotic attempts (optimal effx of radiation w/in a few weeks to months, Don’t kill cells until they get ready to divide. some cells sitting in G0 phase so not dividing for a long time)
4 R’s of radiobiologyREPAIR of sublethal dmg
REPOPULATION with tumor cells (resistant)
REOXYGENATION of hypoxic cells (makes radiation a little easier to deliver)
REDISTRIBUTION of cells throughout cell cycle (gets to point that’s not susceptible to radiation so give multiple doses)
Radiation planning/tx principles (9)Patient evaluation (general condition)
Tumor imaging (CT)
Tumor dx
Selection of therapy (brachhy, tele, systemic)
Portal radiography
Postradiation evaluation
Size & location of 1ry
Presence/absence & extent/incidence of regional or distant metastasis
Early vs late stage cancer
Treatment considerations: total doseDepends on tumor type (want to spare normal tissue)
4500-6500 cGY (1 gray = 100 rads = 100 cGy)
Treatment considerations: fractionation means?# of doses patient will receive
Fractionation: higher dose/fraction = ? lower dose?Higher = more severe LATE effects
Smaller may spare late-responding tissues
Fractionation: most radiation therapy performed how?MWF for 10-12 tx, or M-F for 4wks
How to select a patient?Tumors commonly tx’d w/ radiation therapy
Goal of intent: palliative vs. definitive (curative)
Facilities & equipment
Normal tissue tolerance
Bastic principles of radiation oncology
Name dese tumors
Melanoma, lymphoma, epulis, squame
Cancer patient management: considerationsLoco-regional tumor control vs control of potential metastatic dz (chemo vs sx and/or radiation therapy)
Multimodality treatment: considerationsOwner wishes & commitment
Probability of local/locoregional tumor control
Predicted fxnl & cosmetic outcome
Other concurrent health problems
Potential for metastasis (proven antitumor activity of adjunctive chemotherapy)
Tumors commonly tx’d w/ Radiation therapyUnlikely to metastasize but difficult to control locally!
Exception: oral melanoma, high grade sarcomas
Multidisciplinary approach: e.g. logistics?Full course chemo 1st, then follow up w/ RTX
Full course radiation 1st, then follow w/ chemo
Admin a couple doses of chemo, then RTX between, then follow up w/ chemo
(Advantages of (neo)adjuvant post-op RTX? DISadv?)(ADV: Better sx staging, total dose can be based on residual tumor burden, sx resection easier, tissue heals better
DISADV: delay in post-op tx if healing problems)
Acute radiation effects: occur primarily in?Tissues w/ RAPIDLY proliferating cells! Oropharyngeal mucosa, nasal mucosa, skin, SI, bladder mucosa, BM
When do acute radiation effects start? last how long?Start during course of therapy, last for 2-3 weeks after tx is over
ACUTE EFFX: skinDesquamation, epilation

(armpit high motion, can’t heal)
ACUTE EFFX: mucous mbMucositis, halitosis
ACUTE EFFX: eyeConjunctivitis, KCS, ulcer
ACUTE EFFX: earOtitis
ACUTE EFFX: footPad slough, loss of nail
ACUTE EFFX: GID+, bloody stool
ACUTE EFFX: UrinaryHematuria, polyuria
ACUTE EFFX: LungCough, dyspnea
Tx of acute effxUsually self-limiting, temporary discomfort
WATER-based products, antibx, anti-inflam, oral flushes/rinses (tannins in tea!)
LATE effx of radiation most likely to happen when?AFTER palliation, weeks to YEARS after therapy!
LATE EFFX: skinFibrosis, contraction, leukotrichia
LATE EFFX: eyeCataract, KCS, retinal degeneration
LATE EFFX: jointsDecreased ROM, dry
LATE EFFX: heartPericardial effusion, CHF
LATE EFFX: bonePain, necrosis
LATE EFFX: GIStricture
LATE EFFX: BladderContraction, dysuria
LATE EFFX: CNSSeizures, paralysis, coma
LATE EFFX: any tissueRadiation-induced sarcomas
Tx of late effxSx for cataract removal
Sx debridement/reconstruction
Bougienage or resection of strictures
Treatment considerations: ‘big picture’Geographic location
Time away from home
Financial commitment
Follow up
How is the cost for radiation therapy?Outpatient is less expensive, preferable if possible
National price range: $4500-8000 for 3-4 week course
How does brachytherapy affect hospitalization time?Decreases to 7-10d


Question Answer
What can you do w/ CT scan?Figure out tumor volume, where need to radiate
*Possible complications from CT scansUnder GA every day! could develop tracheitis
How do you know how much of the tumor to take?Gross tumor volume
Clinical target volume (CTV): add margin for microscopic dz
Planning target vol: Another margin for positioning error, organ motion, other types of error
After you have a CT scan, what can you do?Reconstruct 3D image!
Importance of photon beam?Different angles, decide which way is best to deliver radiation & spare normal tissues
(What is there also besides the photon beam)Photon beam mirror
Electron beam lol

How can we figure out which other areas are going to be affected by radiation?Dose volume histogram
How are blocks made?Take tumor burden shape, make same shape to put in machine. Cut it out of Styrofoam, pour (rubber mat w/ lake in it)
What’s this?
Linear accelerator
What’s this?
Positioning cradle. Used to make sure patient is in same position every time (also use crosshairs for exact coordinates)
What’s the left pic? right?
Left = photon beam (delivers a little farther back than electron beam)
Right = electron beam (gets to where node is, still spares skin)
What’s a portal film? Used for what?Double exposed radiograph (non-diagnostic) taken w/ high-energy photons
Can determine if positioning is appropriate
What are these? used for what?
Beam modifiers (15-60* wedges, custom blocks, multileaf collimators) to help spare normal tissue- uneven surfaces, orthogonal beams
What’s this? how does it help?
Multileaf collimator
Piece in blue Styrofoam, poured into sliver thing, push out all at the same time to make hole (only place radiation is delivered)