Radiation Physics -- Radiation Oncology
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Created by:
minidoc2 on November 14, 2011
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Radiation Physics - Wake Forest, Class of 2012
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480 terms
Terms | Definitions |
|---|---|
 Electron output depends on... | Jaw Settings |
| Embryo-Fetus Exposures | Total Dose Equivalent = 5mSV = 0.5rem Monthly Dose Equivalent = 0.5mSV = .05rem Per gestational period |
| KERMA | Kinetic Energy Released in Matter KERMA = E transferred from beam to medium / mass |
| LET | Linear Energy Transfer Highest for charged particles |
| 1SV = ? rem | 1Sv = 100 rem |
| I-131 Therapy Dose | > 30 mCi |
| Proton SRS | High E (150-250 MeV) Dose modified by spreading range and modifying shape Best Dose Distribution |
| Dose @ 10cm from field edge | 1% of prescribed dose |
| Public Exposures - Continuous/Frequent Exposures - Infrequent Exposures - Students | Continuous/Frequent exposure = 1mSV = 0.1 rem Infrequent Exposures = 5mSv = 0.5 rem Student = 1mSv = .1 rem |
| Occupational Exposures - Dose Equivalent Limit - Lens of Eye - All other organs Cumulative Exposure | - Dose Equivalent Limit = 50mSv = 5rem - Lens of Eye = 150 mSv = 15 rem - All other organs = 500mSv = 50 rem Cumulative Exposure = 10mSv x age = 1rem x age |
| Exposure Rate Constants Co-60 Rn-222 Ra-226 Ir-192 Cs-137 Au-198 Pd-103 I-125 | Co-60 = 13.07 Rn-222 = 10.15 Ra-226 = 8.25 Ir-192 = 4.69 Cs-137 = 3.26 Au-198 = 2.38 Pd-103 = 1.48 I-125 = 1.46 |
| Inverse square law | ... |
| Treated Volume | Volume enclosed by an isodose line that adequately covers the PTV |
| Characteristic x-rays result from... | Vacancies in an electron shell |
| Vascular Brachy Rx Point... | 2mm |
| Effective energy of an x-ray beam | About 1/2 to 1/3 of the kVp |
| Temperature/Pressure Correction | ... |
| Less than 15 cm separation -- what energies? | Co-60, 4-6 MV |
| Backscatter Factor | Dm Phantom / Dm Air Increases with E then decreases Increases with field size |
| Roentgen applies to energies up to... | 3 MeV Ionization in air only |
| Roentgen to C/kg | ... |
| Retina TD5/5 (whole | 4500cGy |
| Skin dose increases when ... | - SSD is decreased - Bolus is used - Field size is increased - Beam is at an oblique incidence |
| Cerrobend | - Melts at 70 degrees C (158 degrees F) - Harder than lead - Bismuth (most), lead, tin cadium (least) |
| Increase in dose to tissues beyond healthy lung (orthovoltage) | + 10% per cm lung |
| Exposure | Roentgen |
| LDR Dose Rate | 40 - 200 rad/hr |
| Activity Equation | ... |
| IORT is collimated with... | - Aluminum collimators - Lucite cones |
| Sievert is a unit of ... | Equivalent Dose |
| Advantages of EPID images | - Improved latitude - Improved constrast - Real-time image display - Digital image storage |
| MRI accuracy | 2 mm |
| Highly Sensitive Tumors | - Oat Cell (Small, round blue cells) - Lymphoma |
| rem conversion to Sv | 100rem = 1 Sv 1rem = 10mSv 1mrem = 10 microSV 1rem = 1cGy = 10mSv |
| Depth dose is a Function of... | 1. Energy increase = DD increase 2. Field size increase = DD increase 3. Depth increase = DD DECREASE 4. SSD increase = DD increase |
| Exposure Rate Constant Co-60 | ... |
| Nuclear radiation with shortest range in tissue | Alpha |
| Time to decay to 1% radioactivity | 6.64 half-lives |
| Lateral scattered 23MV electrons travel | Much more than 6MV secondary electrons |
| Optic Chiasm TD 5/5 (whole) | 50 Gy; RTOG protocols go up to 54-55Gy |
| Brachial Plexus TD 5/5 (whole) | 60 Gy |
| Secondary emissions from photoelectric | - Electrons - Auger Electrons - Characteristic X-rays - Target is BOUND electron |
| Use Factor (U) | Fraction of operating time during which radiation is directed towards a barrier |
| Workload (W) | - Weekly dose delivered @ 1cm from source - rad/week @ 1m - (# patients/week)(dose delivered @ 1m) |
| Linear Attenuation Coefficient (u) | Fraction attenuated per unit length u = .693 / HVL |
| Exposure Rate Constant (Pd-103) | 1.48 Rcm^2 / mCi-h |
| Radiation Exposure Limit (Whole Body XRT Worker) | 5rem/yr = 50mSV/yr |
| OAR & Depth | Decreases with depth beyond 10cm |
| Heel Effect | Intensity of diagnostic beam is less on the anode side than the cathode side. |
| Choice of photon beam energy in a treatment plan is governed by... | - Depth to isocenter - Proximity of PTV to lung - Depth of PTV below surface - Neutron leakage outside the beam |
| Wedge Factors | - Increase with Field Size & Depth (scatter) - Measured @ Dmax or 10cm |
| Source Leak Testing | - Tested every 6 months - 0.005 uCi or more is considered leakage |
| Advantages of Radiochromic Film | - Tissue Equivalent - Does not require processing - Insensitive to visible light - Response (optical density vs. absorbed dose) is more linear |
| Pt A dose in GYN LDR | 50-60 cGy/hr |
| Perinatal death (at or around time of birth) most likely occurs as a result of irradiation during... | Major organogenesis (21-40 days) |
| LINAC SRS | - Collimation 5mm - 40mm - Multiple arcs - More than 1 isocenter - < 10 MV photons < 1mm accuracy required |
| Exposure Rate Constant Ra-226 | 8.25 Rcm^2 mg-h ** ONLY one to be mg-hr -- all the rest are mCi-h |
| Exposure Rate Constant Cs-137 | 3.26 Rcm^2 / mCi-h |
| Dose Rate Pd-103 | 20-30 cGy/hr |
| Factors that influence relative dose in a medium from a brachy source... | 1. Distance from source 2. Self-attenuation 3. Medium attenuation 4. Scatter build up |
| 1Ci = ? Bq | 3.7 x 10^10 dps (Bq) = 1 Ci |
| Dimension of an atom | 1 Angstrom = 10^-10 meters |
| Film | - Overresponds at low E - Great spatial resolution - H & D curves exposure/dose vs. optical density - opacity 10/1 |
| As the target angle decreases, the focal spot ... | Decreases |
| Coefficient for Equivalent Thickness Bone | 1.65 cm of water = 1 cm of bone |
| Hot Spot for 4MV photons | 20% |
| mA | - Tube current - No effect on energy or depth dose - Only affects dose rate |
| Brain TD 5/5 (whole) | 45 Gy |
| Non-Stochastic Effects (Deterministic) | - Has a threshold - All-or-nothing |
| Alpha Decay | ... |
| Increase in dose to tissue beyond health lung with 20MV x-rays | + 1% per cm of lung |
| Alpha Particles | - "+2" charge - short range in air - interact quickly |
| Electron Output and Inverse Square | Electron output cannot be corrected by the inverse square |
| Decay Constant | 0.693 / half-life |
| Gamma Knife Accuracy | 0.3mm |
| B+ decay | ... |
| Total Scatter Factor Scp | Measured at Dmax |
| Transport Index | Indicates maxiumum dose-rate at 1.0 meter |
| F = ? C | F = 9/5 C + 32 |
| Planning Organ at Risk Volume | Organs at risk with an additional margin to compensate for movements. |
| Energy of coherent scatter photon at 90' | .511 MeV |
| Cesium-132 source decays.... | 2.3% per year (half-life = 37 years) |
| Electrons lose most of their energy in soft tissue by... | Ionization and Excitation |
| Transmission through intraleaf MLC | 4% |
| Given dose SAD Setups | ... |
| Decay Constant | ... |
| Gamma Knife QA | - Interlocks daily -Output monthly -Timer monthly - Leak test semi-annually - Dose profiles annually |
| Standard Deviation | ... |
| Proportional Counters | - Distinguish alphas & betas - Used for neutron events (neutron shielding survey) - Count individual events |
| Dose outside field is caused by... | - Patient scatter - Head scatter - Leakage |
| SI unity of Activity | Becquerel |
| Exposure Rate Constant I-125 | 1.46 Rcm^2/mCi-h |
| Wedge Angle | WA = 90' - (hinge angle/2) |
| Minimum Target Dose | Lowest absorbed dose in target area |
| Max Radiation Exposure to a lends for an XRT worker | 15 Rem/yr = 150mSv/yr |
| Dose outside field increases with... | - Wedges - Increased field size |
| F factor | F Factor converts exposure to dose F (air) = 0.876 cGy/R |
| Half Life of Cs-137 | 30 yrs |
| Binding energy increases as ... | the atom decays to ground state - more stable |
| Reactivity of an atom depends on... | number of electrons in the outer shell |
| Public Continuous Exposure | 1mSv |
| Indirectly ionizing particles... | neutrons |
| Neutrons produced by LINACs | > 10 mV |
| B- Decay | ... |
| Mean energy of electron beam | 2.33 R50 (depth at which dose falls to 50%) |
| Transmission through cerrobend | 3.5 - 5% |
| Photodisintegration | - Photon in, neutron gets knocked out. - Takes ~ 7 MeV to knock out a nucleon & create a photodisintegration neutron - 10 MeV start shielding - Comes from head of machine or in patient - Neutrons become a problem at 15-20 MeV |
| Irradiated Volume | Volume of tissue receiving a significant dose (50% or more of the prescribed dose) |
| Termination of Spinal Cord | L2 |
| Skin dose is dose below skin at | 0.5mm |
| X-ray quantity is proportional to... | maS |
| Effective Half-Life | ... |
| Photon Energy of Ra-226 | 0.83 MeV |
| HVL (mm Lead) for I-125 | 0.025mm |
| Range of electrons in lead | 2 MeV/mm |
| Internal Target Volume (ITV) | Internal margin added to CTV to compensate for internal motion. |
| Highly Sensitive Cells | - Sperm - Erythrocytes - Crypt cells - Bone marrow |
| Stochastic effects | - Random events (e.g. carcinogenesis) - Increase dose, increase probability |
| Average Life | T avg - 1.44 x half-life |
| SI unit of radiation exposure | Coulomb/kilogram |
| The photoelectric effect is proportional to... | Z cubed + 1/E-cubed |
| Gap Formula | ... |
| Gross Tumor Volume (GTV) | - Gross demonstrable extent and location of tumor. - Primary tumor, metastatic lymphadenopathy, or other metastases. |
| Exposure Rate Equation | Exposure Rate = Activity x Exposure Rate Constant x 1/d^2 |
| Stereotactic Linac Accuracy | 1.0 cm |
| Memory used to manipulate CT images | RAM |
| 1 byte (B) equals | 8 bits |
| Rest mass of 1 amu | 931 MeV |
| Geiger-Mueller Detectors | - Detect presence of radiation - Have a large signal size - Have a long dead time |
| Rectum TD 5/5 (whole) | 60 Gy |
| Beta particle penetration | - 0.5 cm/MeV in tissue - 800 times as far in air |
| Maynord's F Factor | ... |
| What is the most significant influence of dose near a brachy source? | Inverse Square |
| Ra-226 to Cs-137 Conversion | 10mg Ra = 25mCi Cs-137 |
| Sternal Angle/Carina | T4 |
| Photon Energy Rn - 222 | 0.83 MeV |
| Linac Timer Error | 0.10 Mu |
| 1.0 cm Pb = ? Cerrobend | 1.2 cm Cerrobend |
| I-131 Radiation Type & Half Life | Beta Decay Half-life 8.05 days |
| Prostate Location | Anterior - Pubic Symphysis Lateral - Greater Trochanter |
| Directly Ionizing Radiation | - Protons - Alpha Particles - Beta Particles - Positrons - Photons |
| When a sector is skipped in an arc technique | High dose area is shifted away from the skipped sector |
| Methods of Radioisotope Production | - Separation from spent reactor fuel rods (S-137 & Sr-90) - Bombarding with neutrons in a reactor Ir-192 & Co-60 - Bombarding with protons in a cyclotron-positron emitters - Elution of metastable daughter from parent T99(m) |
| Gamma Decay | Isomeric Transition (Co-60 -> Tc 99m) 1. n/p same 2. n,z,a same 3. gamma ray emitted from NUCLEUS |
| Photon mass attenuation coefficient varies with... | - Photon energy - Linear attenuation coefficient/density - Measured in cm^2/g |
| Absorbed dose is measured in... | Rad & Gray |
| Dmax 6 MeV electron | 1.2 cm |
| Co-60 Leakage | - 10mR/hr MAX - 2mR/hr AVG |
| Dimension of Nucleus | 10^-14m (10 to the minus 14th power) |
| Photoelectric Effect | Dependent on Z-cubed up to 50 keV |
| Contralateral Breast Limit | 200 cGy |
| Absportion | - Process whereby energy is transferred from a photon beam to electrons in a medium |
| Radiation Exposure Non-Occupational/Public Total Body | - 0.1 rem/yr - 1 mSv/yr |
| Photon Energy Ir-192 | 0.38 MeV = 380 keV |
| Backscatter Factor | TAR @ Dmax |
| Half Life Ir-192 | 73.8 Days |
| Kidney (TD 5/5 to whole kidney) | 23 Gy |
| TAR, TMR, TPR depends on... | 1. Energy -- as energy increases TAR increases 2. Field Size -- as field size increases TAR increases 3. Depth -- as depth increases TAR decreases |
| Photon Energy Sr-90/Y-90 | 2.2 MeV Beta |
| Clinical Target Volume (CTV) | - Demonstrated tumor & any other tissue with presumed tumor - Represents true extent & location of tumor |
| Flattening Filter | - Flattens at d = 10 cm - Steeper for 18x than 6x - Hardens beam on CAX |
| Attenuation Equation | ... |
| Electron Capture | ... |
| Exposure is measured in ... | Roentgen |
| Average Annual Exposure Radiation Worker Total Body | 1 rem/yr 10 mSv/yr |
| Energies less than 10 MV, PDD @ d=10 cm decreases by... | 3-4% per cm |
| X-Ray quality improves with... | Filtration |
| X-Ray Contamination of Electron Beams | - Increases with energy - Caused by Bremstrahlung |
| Prostate Seed RX I-125 | - Primary = 144 - 160 Gy - Boost - 120 Gy |
| Lens (TD 5/5 - whole lens) | 1000 cGy |
| Half-Life of I-125 | 59.4 days |
| Femoral Head TD 5/5 (whole) | 5200 cGy |
| Photon beam calibration is done in... | Water |
| CT # of bone | 1000 cGy |
| Photoelectric Effect | ... |
| F-Factor | - Roentgen to rad conversion factor - Greater for high - Z materials - Greater for low energy - 0.876 for Co-60 photons in air |
| Half-Life of I-131 | - 8 days - Thyroid Ablation |
| A 2 bit binary number gives | four bits of information |
| Standard thickness of Cerrobend in therapy | 7.5 cm |
| Consequences of larger pixel format | - More memory for storage - More processing time - More time to transmit images |
| Dmax 4 MV X-rays | 1.0 cm |
| Compton Effect | ... |
| Electron Interactions | - Ionization greater with low Z materials - Excitation - ??? - Bremstrahlung - high E & high Z |
| A Beam Spoiler is used to | Increase dose in buildup region while maintaining some skin sparing |
| Maximum Target Dose | - Hightest does within target - Must be greater than 2 cubic centimeters |
| Electron Scatter | - Multiple Coulomb scattering - Low energy e- and high Z materials create largest amount of scatter |
| Small Intestine TD 5/5 (whole) | 4000 cGy |
| Increase in Dose to Tissues Beyond Health Lung (4MV x-rays) | +3% per cm lung |
| Lateral scatter equilibrium in an electron beam exists when the field size is... | of the order of electron energy |
| Electromagnetic Radiation With Highest Frequency | Gamma |
| Total Dose Equivalent (Embryo/Fetus) | 5 mSv |
| Energy of Coherent Scatter at 180' | 0.25 MeV |
| Public Infrequent Exposure | 5 mSv |
| HVL (mm Lead) - Pd-103 | 0.008 mm |
| Isomer | - Metastable Atom - Identical atoms @ different energy levels - Photon emitted from nucleus |
| Orthovoltage | - 150-500 kVp - HVL 1-4 mmCu Dmax = surface |
| Gantry/Collimator | +/- 1' |
| Hot Spots | - Area outside target that receives dose higher than RX dose - Must be greater than 2cm-squared |
| Characteristic X-Ray Energy | Defined by energy differences of electron shells |
| Umbilicus | L3-L4 = Aortic Bifurcation |
| Activity | Becquerel and Curie |
| Absorbed Dose | Gray + Rad |
| 1 Kilobyte | 2^10 bytes ; 1024 bytes |
| 1 Megabyte | 2^20 bytes |
| OAR 6x vs. 18x | Greater for 6x |
| HVL (mm Lead) Cs-137 | 5.5mm |
| Pair Production | ... |
| Effective Z of air in photoelectric region | 7.6 |
| Surface Dose for 15 keV | 90% |
| Rest Mass of Electron | 0.511MeV |
| Resistant Tumors | - Melanoma - Glioblastoma |
| Neutrons have a high quality factor because... | They are indirectly ionizing and transfer their energy to protons, which have a large mass and are densely ionizing |
| Fetal Dose Limit | - 0.5 rem/yr = 0.05 rem/mo - 5 mSv/yr = 0.5 mSv/mo |
| HVL (mm Lead) Ra-226 | 12 mm |
| Dose @ 1 m from field edge | 0.1% of prescribed dose |
| Dose @ 30 cm from field edge | 0.2 % of prescribed dose |
| Exposure Rate Constant Rn-222 | 10.15 Rcm^2 / mCi-h |
| Binding energy increases with... | Z and proximity to nucleus |
| Dynamic Wedge Factors | Are a function of both the start and end jaw positions |
| Surface Dose (18E & 22E) | 93% |
| Electron backscatter from internal shielding | - Increases with Z - Decreases with increase in energy - is absorbed in a low Z material lining |
| Suprasternal Notch | T2 - T3 |
| Half-Life Ra-226 | 1600 years |
| Tray factor | Output with tray / output with open Tray factors increase with increasing energy (more transmission) |
| TBI Rx Dose | 1000 - 1200 cGy |
| Electron Arcs | - Velocity effect decreases surface dose, increases depth, increases x-ray contamination - Extend field width 15' to retain penumbra - Shielding thickness E/2 + 1mm Pb |
| Skin TD 5/5 (100cm square) | 5000 cGy |
| Controlled Area | Exposure of persons is monitored by radiation protection of 0.1 rem/week. |
| Tenth Value Layer | Amount of material required to reduce beam intensity to one-tenth its original value. TVL = 3.3 HVL |
| Power Equation | - Power = Voltage (current) - Measured in watts |
| Median Target Dose | Value between min & max absorbed dose values within the target. |
| Co-60 source size | 1.5 - 2 cm |
| Exposure | Total charge of ions of one sign, liberated by photons per unit mass in air. |
| Non-controlled area | Unsupervised by radiation protection = 0.01 rem/wk |
| CT # Air | -1000 |
| Time to decay to 10% radioactivity | 3.32 Half Lives |
| Mass attenuation due to compton interactions depends on... | Electron density |
| B+ decay | ... |
| Phantom Scatter (Sp) | - Not directly measurable - Increases with field size |
| Penumbra transmission through collimator & block | - Collimator = 0.5% - Block = 3% |
| Advantages of multiple field treatments | - Maximization of target dose - Minimization of normal tissue dose - Applicability in all clinical situations |
| Spatial Resolution of PET | 3-4 mm in axial plane |
| CT Accuracy | 1 mm |
| > 20 cm separation - what energies are used? | 10 MV or higher x-ray |
| Increase filtration | - Decreased dose rate - Decreased # of lower energy photons - Increased HVL |
| CT # of Water | 0 |
| Co-60 Timer Error | 0.02 minutes |
| Fractionation results in... | - Allows for normal tissue recovery - Causes more damage to tumor than OAR |
| Mean Lethal Dose | Dose to reduce surviving fraction to 10% of irradiated cells |
| IORT Single Fx Dose | 1000 - 2000 cGy |
| Dose @ Dmax / Midpoint Dose | - Increase thickness, increase ratio - As E decreases, increase ratio - As field size increases, decreases ratio |
| Surface Dose - 6 keV | 75% |
| Planck's Constant | 6.62 x 10 ^-34 J sec |
| Effects of electron contamination | - Increases surface dose - Increases dose in build-up - Increases for increasing SSD - Increases with field size |
| Liver TD 5/5 (whole) | 30 Gy |
| When internal conversion occurs... | - Z and A remain the same - Energy transferred to an inner shell electron, which is ejected |
| Coherent Scatter | - Independent - Happens at 30 keV - 30 MeV |
| Half-Life of Pd-103 | 17.0 days |
| Which is hotter SSD or SAD treatments? | SAD treatments |
| Contact Therapy | - 40-50 kVp - HVL < 1mm AL Dmax - surface |
| Use Factor (U) | Fraction of operating time beam is directed toward the barrier. |
| Coefficient of Equivalent Thickness of Lung | 0.25 cm water = 1 cm of lung |
| Level of cricoid cartilage | - C6 - Junction of larynx to trachea & pharynx to esophagus |
| Binding energy per nucleon | Determines the stability of the nucleus. |
| Half-Life of Free Neutron | 12 min |
| Surface Dose - 9 MeV | 80% |
| Scatter dose at any point in a phantom can be determined by... | - Scatter air ratio - Scatter maximum ratio |
| Photoelectric interacting photon energy | - Equal to or just greater than binding energy of electron. |
| LINAC focal spot size | 0.5 - 3.0 mm |
| High Energy Beam Calibration Chamber | Farmer Type |
| RBE | RELATIVE BIOLOGICAL EFFECTIVENESS - Increases with LET - Highest for charged particles |
| Oxygen Enhancement Ratio | - Oxygen enhances cell kill - Greater for X-rays than neutrons - Dose without oxygen / Dose with oxygen ... to cause the same effect |
| Electron Binding Energy | - Decreases with increasing shell # - Increases with increasing atomic # - Equal for the same shell for all isotopes of the same element |
| Degrees C = ? Degrees F | C = 5/9 (F - 32) |
| Penumbra for Co-60 | 15 mm |
| SRS penumbra | - Best with Gamma Knife - Worsens with additional shots and arcs |
| HVL (mm Lead) Ir-192 | 2.5 mm |
| BSF Co-60 | 1.036 |
| Penumbra (Cerrobend vs. MLC) | Cerrobend provides a tighter penumbra than MLC |
| For dose points that lie beyond an area of inhomogeneity, the prominent effect is... | Attenuation of primary beam |
| Mean energy of an electron | 2.33 MeV/cm x R50 |
| CT # fat | -100 |
| Paris System | - Uniform loading - Non-uniform dose - No crossing - Parallel planes |
| SI unite of dose equivalent | Sievert |
| Integral Dose | - Measure of total energy absorbed in the treated volume - Mass x dose (kg-rad) - Keep to minimum - Decreases as energy increases |
| Xiphoid Process | T9-T10 |
| LD 50/30 Humans | 450 cGy |
| Monthly Linac Output | 2% |
| Sievert Integral | - Calibrates brachy source doses of Cesium and Radium INCLUDES: - Air - Inverse Square - Filtration EXCLUDES: - Self absorption - Tissue attenuation - Tissue scatter |
| Colon TD 5/5 (whole | 45 Gy |
| Fricke Dosimeter | - Works via calorimetry - Provides absolute dose measurement - Has a large range |
| Therapeutic Ratio | - Ratio of tissue tolerance to tumor lethal dose - Less than 1 for resistant tumors - Larger than 1 for sensitive tumors - Can be modified with radiosensitizers and radioprotectors |
| Paterson-Parker | - Non-uniform distribution produces uniform dose +/- 10% - Area reduced by 10% for each uncrossed end |
| Surface Dose - 12 MeV electrons | 85% |
| Standquist Curves | - Radiation Biology model based on skin tolerances |
| I-125 dose-rate | 5-10 cGy/hr |
| Monthly Flatness | 3% of 80% of field at a depth of 10 cm |
| Monthly Symmetry | 2% of 80% of field at a depth of 10 cm |
| Dose beyond beam edge is influenced by... | - Photon side scatter - Electron Transport - Collimator Transmission |
| HDR Unit Source | 10 Ci Ir-192 |
| Relationship between speed, wavelength, and frequency... | c = λν |
| Curie (Ci) | 1 g Ra-226 = 1 Ci 1 Ci = 3.7 x 10^10 disintegrations per second 1 mg Ra-226 = 1 mCi = 3.7 x 10^7 dps 1 Ci = 3.7 x 10^10 Bq |
| Quimby | - Uniform source distribution - Along & Away - Area reduced by 7.5% for each uncrossed end |
| Picket Fence Test | Checks leaf positions that are out of calibration |
| Chamber measurements must be corrected for | - Saturation - Polarity - Temperature/Pressure |
| Factors needed to select correct PDD for a superficial treatment | 1. HVL 2. SSD |
| Surface dose for a 6 MV beam | 15% - 40% depending on field size |
| Ratio of scatter @ 1m to entrance dose to patient | 1:1000 |
| Photon energy of Co-60 | 1.17 MeV 1.33 MeV Average Energy is 1.25 MeV |
| Penumbra | Distance between the 80% and the 20% IDL. |
| Prostate seed RX for Pd-103 | Primary - 115 Gy Boost - 90 Gy |
| Compton initial interacting photon energy | Much larger then electron binding energy |
| Dmax for 18 MV x-rays | 3.5 cm |
| Source Inventory Contains | - Source identity - Source configuration - Source strength |
| Transient Equilibrium | - Half-life of parent is not much different than half-life of daughter; occurs at about 1.5 days |
| MDR Dose Rate | 200 - 1200 rad/hr |
| Isotopes | - Have same # protons - Have same # electrons - Chemically identical |
| HDR Dose Rate | > 1200 rad/hr |
| Shape of H & D Curve | ... |
| Planning Target Volume (PTV) | Includes CTV with IM + setup margin |
| Output Factor -- Circle vs. Rectangle of Same Area | Output is greater for circle |
| Maximum Scatter Energy | 0.511 MeV |
| Dmax 1.25 MeV (Co-60) | 0.5 cm |
| Speed of light (c) | 3.0 x 10^8 m/s |
| Wedge Angle | WA = 90 degrees - (hinge angle/2) |
| Penumbra Equation | ... |
| Effective energy of an X-ray beam | - Energy of a monoenergetic beam that would give the same HVL |
| Dmax of 9 MeV electron | 2.0 cm |
| Esophagus TD 5/5 (whole) | 55 Gy |
| I-125 decays by... | Electron Capture |
| HVL (mm Lead) for Au-198 | 2.5 mm |
| Photoelectric photon loses... | All energy |
| Main component of a computer that processes all data... | CPU |
| Hounsfield Units | ... |
| Half Life Rn-222 | 3.83 days |
| 1mCi = ? Bq | 3.7 x 10^7 dps (Bq) |
| Becquerel | 1 Bq = 1 dps = 1 atom/sec 1 Ci = 3.7 x 10^10 Bq |
| B- Decay | ... |
| Secular Equilibrium | Half-life of parent is much greater than half-life of daughter -- occurs at about 20-25 days. |
| Co-60 unit dose rate | 240 cGy/min |
| Modal Target Dose | Absorbed dose that occurs most frequently within the target |
| Internal Conversion | ... |
| Hot spot Co-60 | 30% |
| Atomic Mass # | #n + #p = # nucleons |
| Point A | - 2 cm up from os, 2 cm over from tandem - Where uterine vessels cross the ureter - Prescription Point |
| Half life Co-60 | 5.26 years |
| Dose equivalent is measured in... | Rem % Sv |
| HDR Source Positioning Accuracy | 1 mm |
| Dmax for 250 keV | Surface |
| SRS Dose | - Volume dependent in that bigger volumes get smaller doses - Gamma knife prescribe to 50% line - LINAC - prescribe to 80% line |
| Fraction of Activity Remaining is Equal to... | ... |
| HVL (mm lead) Rn-222 | 12 mm |
| Radiation Exposure -- Public One-Time Max | - 0.5 rem/yr - 5 mSv/yr |
| Linear Quadratic Formula | Rad Bio model based on biological effective dose (BED) |
| Shoulder of cell survival curve represents... | - Repair of sublethal damage - No damage due to small radiation doses - Absent for high LET radiation |
| LD 50/60 Humans | 300 rad |
| Dose decrease beyond bone (Co-60) | 4% per cm |
| TLDs | - Dose-rate independent - Large range - Personnel monitoring - Patient dosimetry - Must be stored properly |
| Thyroid Cartilage | C4-C5 |
| Ion Chamber Uses | - Surveys & Calibrations - Brachy patient survey - Source calibration - LINAC calibration - Shielding surveys |
| Dose perturbation behind inhomogeneity depends on... | - Size - Shape - Electron Density - Effective Atomic # |
| Cell Death | - Cell losing some specific function in case of non-proliferating cells - Caused by lethal damage to DNA & other critical structures |
| TBI Dose-Rate | 5-10 cGy/min |
| GI Syndrome | 10-100Gy |
| Electron Energy Loss | 2 MeV/cm |
| Increase in dose to tissues beyond health lungs (Co-60 γ rays) | + 4% per cm in lung |
| Scintillation Detectors | - Light is proportional to E - NaI used for high count rates - NaI used for contamination surveys & thryoid uptakes - Liquid scintillation counters used for B surverys |
| Transpyloric Plane | Pancreas = L1 |
| Electron depth dose measurements in water are carried out by... | - Ionization chamber - Silicon diode |
| X-Ray contamination of electron beams | - 2 - 5% for a 16 MeV beam - Caused by interactions with high Z components inside accelerator |
| CNS Syndrome | > 50 Gy |
| Mandible TD 5/5 (whole) | 60 Gy |
| Physical Penumbra depends on... | - Geometric penumbra - Collimator Transmission - Lateral photon scatter (patient) - Lateral electron transport (patient) |
| Dose Buildup | - Is NOT linear - Very steep in initial portion of build-up - Leads to skin sparing |
| 1R = ? rad | 1 R = 0.873 rad |
| Increase in dose to tissue beyond healthy lung with 6MV xrays | + 2.5% per cm lung |
| Brainstem TD 5/5 (whole) | 50 Gy |
| Dose decrease beyond bone with 4MV photons | 3% per cm |
| TD 5/5 bladder (whole) | 65 Gy |
| Bits per pixel required in a CT image to represent the full range of CT numbers | 12 bits/pixel |
| Dose decrease beyond bone 10MV | 2% per cm |
| Photon Energy I-125 | 0.028 MeV = 28 keV |
| What is the acceptable block transmission of the primary beam? | 5% |
| Quimby System | - Uniform loading - Non-uniform dose - Crossing needles - Along & Away - Higher dose in center than periphery |
| Water phantom for measuring isodose distribution must extend at least ___ laterally & deep beyond the field of measurement | 10 cm |
| Depth Dose | % DD = Dose @ Depth / Dose @ Dmax |
| Pair Production | - Depends on Z^2 - Must be energy > 1.022 Mev |
| Attenuation of Cerrobend is... | About 15% less than lead |
| 1 Gy is equal to... | - 1 J/kg - 100 rads - 1000 mGy - 1 Sv/QF |
| Energies greater than 10MV PDD @ d = 10 cm decreases by ... | 2% per cm |
| Hematopoietic Syndrome | - 1-10 Gy - Survivable |
| HVL (mm lead) Co-60 | 11 mm |
| What improves dose homogeneity for TBI? | - Using highest beam energy & beam-spoiler - AP/PA beams - Tissue compensators for extremities - Using large SSD/SAD - Adding compenating material over the lungs |
| 1 SV = ? rem | 1 SV = 100 rem |
| T2 MRI | - No contrast - Shows swelling and edema - Swelling, edema, and CSF hows up white |
| Mag Factor | Image ÷ Object |
| Half Life of Au-198 | 2.7 days |
| Isotone | - Same # neutrons - Different # p - Different A - Different atom |
| Law of Bernie & Tribundeau | Radiosensitivity varies with: - Cell proliferation - rapidly dividing are sensitive - Future cell division - long-diving futures more sensitive - Inversely with differentiation - less differentiated are more sensitive |
| Dmax with 6 MV X-rays | 1.5 cm |
| Optic Nerve TD 5/5 (whole) | 50 Gy |
| Heavy Charged Particles | - Maintain direction - Have a defined range - Have a Bragg curve |
| Parotid Gland TD 5/5 (whole) | 32 Gy |
| 4 R's of Radiotherapy | 1. Repair 2. Repopulation 3. Reoxygenation 4. Redistribution |
| Depth of Dmax for a photon beam is approximately equal to... | - Depth at which dose & kerma are equal - Maximum range of secondary electrons - Depth at which electronic equilibrium occurs |
| Avagadro's Number | 6.023 x 10^23 atoms per gram |
| Superficial X-rays | - 50 to 150 kVp - HVL = 1-8 mm Al - Dmax = Surface |
| Exposure Rate Constant for Au-198 | 2.3 Rcm^2 per mCi-h |
| Craniospinal Couch Angle | ... |
| Penumbra - Accelerator | 8 mm |
| Pt B Dose | 1/3 of Pt A dose |
| Shades of gray in 1 byte | 256 shades of gray |
| Dmax 10 MV X-rays | 2.5 cm |
| A H&D curve represents | Dependency of optical density on dose |
| Facts about MRIs | - MRI signal differentiates between differences in hydrogen content. - Can image metabolic activity - Only ferromagnetic materials cause problems - Radiographs have better resolution |
| Isotope | - Same # protons - Different # neutrons - Different A - Same Z - Same atom |
| Pacemaker Limit | 2 Gy |
| Compensators | Provide same distribution @ 1 depth - overcompensate at shallow depths - Under compensate at deep depths Preserve skin sparing 15 cm away Compensator thickness < tissue replacement thickness |
| Dose Equivalent | Rem < - > Sievert |
| Jugulodigastric Lymph Nodes | Superior to angle of the mandible; Drains tonsils & tongue |
| PDD | Dose depth ÷ Dmax @ SSD |
| Cumulative Dose in Brachytherapy | 1.44 x T 1/2 x Initial Dose rate |
| Arc Therapy | - Good for small deep-seated tumors - Should not be used if: large volume, non-cylindrical, off-center - Past pointing for partial arcs - Smaller skin dose |
| Effects of field blocking | - Reduces scatter volume - Reduces scatter dose @ depth - Primary dose is relatively unaffected |
| Vascular Brachytherapy Dose | 15 - 20 Gy |
| Energy of a Bremstrahlung X-ray | Any energy up to that of the incident electron |
| Stomach TD 5/5 (whole) | 50 Gy |
| DRR Quality depends on... | - Slice # - Slice thickness - Technique used - Reconstruction algorithm |
| Lung TD 5/5 (whole) | 17.5 Gy |
| Transmission through MLC | 2% |
| Spinal cord TD 5/5 (20 cm) | 47 Gy |
| Energies of Positrons & Betas | Spectrum |
| Electron Range | E/2 |
| Coherent Scattering | - Energy unchanged - Direction changed - Conservation of energy |
| Max Radiation Exposure to Extremities for XRT workers | 50 rem/yr = 500 mSv/yr |
| Point B | 2 cm up from os, 5 cm lateral to midline; represents obturator nodes. |
| IORT | - 1 fx of 10 -20 Gy - 6 MeV - 21 MeV electrons - Increasing energy, flatness worsens, increased penumbra, increased x-ray contamination |
| Total Skin | - 6 field Stanford technique - Shield eyes & nails - Boost perineum, shoulders, folds, breast |
| CT # Lung | -400 |
| How many HVLs yields less than 5% primary beam transmission? | Between 4.5 & 5 HVL |
| Photon energy for Au-198 | 0.412 MeV = 412 keV |
| Collimator Scatter (Sc) | - Measured in air - Increases with field size |
| NaI well chamber | - Measures low level gamma rays - Used in wipe testing |
| Alpha Decay | - Alpha particle = Helium nucleus = He - Usually occurs only for Z > 82 - Typical E (alpha) ~ 4-7 MeV - Each radioactive element has a discrete alpha energy |
| Lowly Sensitive Cells | - Nerve - Muscle |
| T1 MRI | - Tumor - With Constrast - CSF (ventricles) are black - Sagittal sinus is white due to contrast - No edema |
| PET scanners detect... | Annihilation photons |
| 1 Gy = ? rad | 100 rad |
| Co-60 decays... | - 1% per month - 13 % per year |
| TDF Model | Radiation Biology model based on single exposure skin tolerances with time, dose, and fractionation factors built in. |
| Distance Between 2 Points | ... |
| Mean Target Dose | Mean of absorbed dose values within target |
| Photon Energy (Cs - 137) | - 0.662 MeV - 662 keV |
| Patterson-Parker | - Uniform Dose - Non-uniform distribution - Crossing Needles - Peripheral Loading |
| Advantages of a dynamic wedge over a physical wedge | - Same depth dose as open beam - Field height not limited - No heavy lifting - Less dose outside field |
| Half Value Layer | - Amount of material required to reduce beam intensity to half its original value - Monoenergetic HVL1 = HVL2 - Polyenergetic HVL1=HVL2 - HVL = .693/u |
| Increase in dose to tissues beyond healthy lung - 10 MV xrays? | + 2cm per cm lung |
| Isobar | - Same A - Different p - Different n - Different Atoms |
| Focal spot of clinical LINAC | 3 mm |
| Craniospinal Collimator Angle | ... |
| B+ decay occurs in accordance with the laws of | - Electric charge conservation - Energy conservation - Momentum conservation |
| Dmax for 12 MeV electron | 2.5 cm |
| Exposure Rate Constant - Ir-192 | 4.69 Rcm^2 / mCi-h |
| Hot Spot 10MV | 10% |
| Scatter of MV beams increases with... | - Depth - Field Size - Dose Rate |
| Causes of the OAR | - Flattening Filter - Photon Scatter |
| Diodes | - GeLi used to identify isotopes - Semiconductors are very efficient |
| Lasers & ODI | +/- 2mm |
| Photon Energy for Pd-103 | 0.021 MeV = 21 keV |
| Half-Value Layer/Linear Attenuation Coefficient Equation | u = .693 ÷ HVL |
| Dynamic Wedge | - Moving jaw creates wedged effect - Larger wedged field sizes - Any wedge angle |
| Heart TD 5/5 (whole) | 40 Gy |
| Transmission through jaw | 1% |
| Thoreus Filter | - Target * Tin (Sn) - removes low energy photons which would only increase skin dose (increase average effective energy) * Cu -- removes char x-rays produced by target * Al -- removes char x-rays produced by target - Patient Filter decreases output but increased effective energy, leading to better penetration |
| Co-60 | - 1.25 MV - HVL 1.2 cm Pb - Dmax 0.5 cm |
| Divergent blocks reduce | Transmission penumbra |
| FLAIR MRI | - Swelling and edema show up white - CSF is black - Needed to differentiated between edema & CSF |
| Occupancy Factor (T) | Fraction of operating time during which the area of interest is occupied by the individual |
| Electron depth (80%) | E ÷ 3 |
| Scattering Foil | - Primary - spreads out electrons - Secondary - flattens electron beam |
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