principles of radiation oncology Essay

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what are the physics behind radiation therapy?
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radiation therapy works due to cellular absorption of radiation, leading to ionization of biologic materials
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ionizing radiation can be classified as ____ or _____ ?
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electromagnetic or particulate
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what are the 2 kinds of electromagnetic radiation? how are they produced?
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gamma rays (produced spontaneously from elements suchs as cobalt/radium), x rays (produced from linear accelerators)
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where would lower voltages of x ray be used? higher?
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lower doses would be head/neck, higher would be pelvis
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what is a unit of radiation deliverance?
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1 gray (100 centigrade)
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what is teletherapy?
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external beam radiation, uses an external machine to deliver radiation -> most common type used
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what is bradytherapy?
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when the radiation source is placed w/in the region to be treated (also called implants, can be temp/permanent)
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what does ionizing radiation do on a biological level? what are most effects of ionizing radiation due to?
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ionizing radiation deposits energy as it traverses the absorbed medium, cutting DNA (directly/indirectly), preventing it from dividing. most effects of ionizing radiation are indirect (about 70%) due to free radical formation, which leads to DNA ligation
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what is the therapeutic ratio?
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all cells (CA/non-CA) can die from DNA damage, but normal cells have a greater ability to repair the damage, so the hope is that normal cells will repair themselves more efficiently. a good therapeutic ratio consists of more CA cells affected by radiation and this would be apparent in radiosensitive tumors
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what is fractionation? why is it done?
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the total radiation dose is fractionated (spread out over time) for several important reasons: fractionation allows normal cells time to recover, while tumor cells are generally less efficient in repair between fractions. fractionation also allows tumor cells that were in a relatively radio-resistant phase of the cell cycle during one treatment to cycle into a sensitive phase of the cycle before the next fraction is given.
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when is fractionation radiation delivered? how is it modulated for palliative care?
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~1.8-2 Gy every day for 1-9 wks depending on if palliative care or not. fraction size is increased and the dosage (total tx time) is decreased for palliative treatment.
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how is dosage determined for radiation therapy?
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what kind of cancer, site of tx, other planned modalities (chemotherapy/sx)
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what radiation dose does lymphoma usually respond to?
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36-40 Gy (don’t worry about too much)
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what radiation dose does epithelial malignacy usually respond to?
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50 Gy (don’t worry about too much)
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what radiation dose does gross disease usually respond to?
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70 Gy (don’t worry about too much)
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what can be treated with radiation?
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almost everything can be treated with radiation, (B. prostate, lung, head and neck, brain tumors, lung cancer, cervical cancer, skin cancer, etc. all effective in radiation treatment)
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where does sx usually fail in tumor tx? radiation?
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sx usually fails to be effective at periphery of tumors, while radiation usually fails at the core – so they work well in concert
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what is preoperative radiation tx? why is it used? disadvantages? when is this commonly done?
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preoperative radiation sterilizes the edges of the resection, so the surgeon knows they’re not cutting through the tumor’s edge. it allows for better (preoperative) oxygenation of the area (less oxygen can lead to more resistant tumor cells). preoperative radiation may also shrink an unresectable tumor to make it resectable. disadvanrages: it can lead to a higher rate of sx complications, pts may have already been irradiated. this is commonly used for GI tumors.
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what is postoperative radiation tx? why is it used? disadvantages? when is this commonly done?
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postoperative radiation is advantageous b/c tx can be given based on operative findings for the tumor. disadvantages include a potential larger field to cover all sites of likely tumor seeding and increased hypoxia (due to sx compromised vasculature). it is commonly used in GI, head and neck, breast CA, and sarcomas
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what are the 3 major branches of oncology?
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medical, radiation and surgical oncology
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how are radiation and chemotherapy combined?
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chemotherapy (given before/after radiation) can function as a radiation sensitizer, improve local radiation control, and *help with organ preservation (esp w/head, anal, bladder, and breast CA)*
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what characterizes side effects associated with radiation therapy in the short (acute) term? long term? what influences these side effect?s
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in the short term, radiation side effects occur in rapidly renewing tissues (mucosa, skin, small intestine), while being treated and disappear 4-6 weeks later. long term side effects (epithelial/stromal/vascular) show up ~6 months after therapy. tx size, fraction size, dose recieved all influence side effect characteristics.
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what is the “volume” of a tumor? what portion of this is targeted by radiation?
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concentric regions extending out rom the tumor consisting of the gross tumor, the microextensions, the biological margin, and the geometrical port margin <- all of which has to be within the tx margins
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what is the 2D imaging technique?
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an older way imaging technique where one slice was used to determine tumor volume
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what is the shrinking field technique?
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start w/a large area, and decrease it as tumor shrinks (while increasing dosage)
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what characterizes pt assessments during radiation tx?
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pt visits minimally once a week to make sure they are tolerating well, then are seen up to one month after treatment finished to check and see if acute side effects have cleared, then see every six months up to two years out, then see once a year so haven’t developed a reoccurrence or second or third malignancy
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what are different versions of external beam radiation therapy?
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conventional ex beam RT, IMRT, IGRT, and stereotactic RT
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how are conventional RT fields generated? what are the fields of tx that are administered with this imaging technique?
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conventional RT using a flurosimulator or w/a CATSCAN (can be 2 or 3D) to provide tumor imaging for 4 field tx (ant, post, and R laterals) and the multi-leaf collimator (MLC) conforms to the correct area for each radiation administration
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what is IMRT?
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intensity modulator radiation therapy is where the the MLC changes its configuration as the tx is delivered to wrap the beam around tumors using very high radiation doses – often used in head tx. it can also be used to differentially treat different structures within the same administration.
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what is IGRT? what is it commonly used for? what does it mean if it is sterotactic?
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image guided radiation therapy – means you can actually see what you are treating while you are treating it, which is commonly used for brain metastasis, other primary CNS lesions, peripheral lung NSCLC, and intr-abdominal lesions <- for high dose/small volume tx. radiation therapy is stereotactic if different beams are converging from different angles
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what is respiratory gating? what is it used in tx of?
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IGRT that takes into account lung movement during tx of peripheral lung tumors (NSCLC), so the beam is only fired when the tumor is in one position and turns off when it moves out of that field
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what are 3 versions of brachytherapy?
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permanent implants, temporary implants and intra-operative radiation therapy (IORT)
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how would brachytherapy be used for prostate CA?
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ultrasound inserted into the rectum, radioactive seeds are inserted through the peritoneum using a needle grid, and then the status is checked periodially with CAT scans or other imaging
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how would brachytherapy be used for cancers such as a sarcoma whose margins are still not clear after sx?
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trochars are put in to mark the target areas for radiation treatment, catheters are then put in and iridium is administered
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what is a cyberknife?
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linear accelerator on robotic arm with image recording in real time to take pt’s movements into account
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what is tomotherapy?
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this looks and functions like CT, but can also deliever radiation. it allows specificity of tx and is good for treating skin lesions
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what is the gamma knife?
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the “grandfather” of stereotactics, it has colbalt sources behind large doors and is used exclusively on CNS lesions (will probably be phased out)
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what is a proton unit used for?
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heavy particle tx, is able to produce a “Brag Peak” which deposits energy in high doses to a defined area and then leaves (does not linger over surrounding tissue)
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what is used in 90% of current radiation tx?
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linear accelerators
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what is high dose radiation (HDR) used for?
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this can be used in brachytherapy to mechanically push out catheters and is good for gynecologic malignancies, it is not as restrictive to the pt’s lifestyle, and it provides good shielding for the rest of the body tissues (esp with eBx)
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what are the most cancers treated with?
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combined modalities (sx, chemo, radiation)

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