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1. What is the energy range for superficial (Crookes tube) therapy machines?
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2. What machines had "hot cathode" tubes and generated medium energy ranges?
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Radiation Therapy QA
Quality Assurance information for Radiation Therapy
| Question | Answer |
|---|---|
| 1. What is the energy range for superficial (Crookes tube) therapy machines? | 50 to 100 kV |
| 2. What machines had "hot cathode" tubes and generated medium energy ranges? | Orthovoltage or deep therapy machines |
| 3. What is the energy range for orthovoltage machines? | 150 - 500 kV |
| 4. What are the five main components of a typical linear accelerator? | drive stand, gantry, patient support assembly (PSA), electronic cabinet, and console |
| 5. What are the 4 major components of the drive stand? | Klystron or magnetron, waveguide, circulator, and water cooling system |
| 6. What is a klystron? | it is an amplifier of microwaves that are produced by a radio-frequency drive ; used for 10MV and above |
| 7. What is a magnetron? | it is a source of microwaves; used for 6MV and below |
| 8. What is a waveguide? | a series of tubes/pipes that transport microwaves to the accelerator guide |
| 9. What are major components of the gantry? | electron gun, accelerator guide, treatment head |
| 10. What are the components of the treatment head? | bending magnet, x-ray target, flattening filter, scattering foil, monitor chambers, optical distance indicator, primary and secondary collimators |
| 11. In a linear accelerator, what components helps create a uniform electron beam? | scattering foil |
| 12. In a linear accelerator, microwave amplification occurs in the: | klystron |
| 13. On a conventional simulator what can be used to reduce unwanted scatter radiation? | beam-restricting diaphragms |
| 14. The conventional simulator design was meant to mimic what other piece of equipment? | It was meant to simulate the mechanical, geometric, and optical conditions of a variety of treatment units |
| 15. Gantry, x-ray head and collimator, x-ray tube and generator, imaging device, and couch are all components of what simulator? | Conventional or fluoroscopic-based simulator |
| 16. On a conventional simulator, what defines the edge of the treatment field? | field-defining wires |
| 17. Every image taken in conventional simulation should show evidence of what? | collimation by displaying a 1 to 2 cm clear border of unexposed film |
| 18. A typical image intensifier contains what four major components? | film holder, image intensifier, television camera, and video monitor |
| 19. True or False: A conventional simulator could potentially produce CT images. | True if the machine has a CT mode. |
| 20. What are the two major methods of CT data acquisition? | slice by slice and volumetric (spiral) CT |
| 21. In CT simulation, what does aperture size refer to? | The diameter of the hole into which the patient is positioned |
| 22. Each small square on a CT image is called what? | pixel |
| 23. Window selection determines what in CT simulation? | It determines what anatomy will be seen. |
| 24. What are the two window selections that can be made? | window level & window width |
| 25. _______________ represents the range of grey scale on a CT image? | Window width |
| 26. What does window level represent? | It represents the center of the window width |
| 27. A pixel is a two-dimensional representation of what? | a corresponding tissue volume or voxel |
| 28. On a conventional simulator, localizing lasers and ODI checks should be performed when and within what tolerance? | daily and 2mm |
| 29. On a conventional simulator, rotation isocenter checks should be performed how often and be within what tolerance? | annually and 2mm |
| 30. Radiographic checks should be performed ______________ on a conventional simulator. | annually |
| 31. Orientation of gantry lasers on a CT simulator should be performed when? | monthly or after laser adjustments |
| 32. On a CT simulator what should have a QA procedure run annually? | Table indexing and position, gantry tilt accuracy, gantry tilt position accuracy, scan localization, radiation profile width |
| 33. The table vertical and longitudinal motion on a CT simulator should be checked when and be within what tolerance? | monthly and within 1mm over the range of table motion |
| 34. For CT simulator image quality, image noise should be checked when and be within what tolerance? | daily and be within the manufacturer's specifications |
| 35. What are the three major categories of a quality assurance procedure on treatment machine? | Dosimetry, mechanical, and safety |
| 36. The emergency off switches should be checked how often? | monthly |
| 37. The audiovisual monitor should be checked ___________ for _____________. | daily for functionality |
| 38. X-ray output constancy and electron output constancy should be checked __________ and the tolerance is _________. | monthly and within 2% |
| 39. Acceptance testing requires _________________. | a comparison of output and performances values as measured against what the manufacturer promised. |
| 40. Light field and radiation field congruence should be checked: | monthly |
| 41. For a linear accelerator the tolerance for variation in collimator rotation around the point of isocenter is: | 2mm |
| 42. The door interlock should be checked: | daily |
| 43. Leak tests of sealed radioactive sources should be conducted at what interval? | 6 month intervals or twice a year |
| 44. When performing a leakage test on a Cobalt 60 machine housing, what radioactivity level should NOT be exceeded? | 0.005 mCi |
| 45. What should be checked weekly on a Cobalt 60 unit? | the source positioning |
| 46. Radiation detectors used with brachytherapy should be calibrated when? | once a month or after repairs |
| 47. When ionization chambers are properly calibrated their accuracy approaches _________. | 2% |
| 48. Due to a properly calibrated ionization chamber's accuracy, it makes them suitable for measurement of ____________________. | the radiation output of therapy equipment |
| 49. Calibration equipment, scanning equipment, dosimetry accessories, and devices are all types of what? | quality control check instrumentation |
| 50. In brachytherapy, source strength should be checked and verified when? | Upon receipt and at an agreed upon interval depending on the half-life |
| 51. What is the tolerance for the daily check of linac output constancy? | 3% |
| 52. How often should field size indicators be checked? | monthly |
| 53. What professional organization for medical physicists is a forerunner in developing minimum QA standards? | AAPM |
| 54. For dynamic MLC QA, why should ion chamber measurements be taken in a solid phantom for patient fields? | to provide a direct independent check of MU calculations |
| 55. Film dosimetry with sufficient spatial resolution for intensity-modulated patterns should be checked because ___________________. | It is a good way to compare the delivered dose distributions to the planned ones |
| 56. To ensure a constant dynamic MLC output and to track long-term stability what should be measured monthly? | Ion chamber and diode array measurements should be taken at different gantry and collimator angles. |
| 57. To provide a visual assessment of dynamic MLC function what should be checked biweekly? | Predesigned fields using film image patterns |
| 58. A periodic dosimetric verification of intensity-modulated fields is performed for dynamic MLC QA to ensure ______________________. | Accuracy of dose patterns and fluence |
| 59. True or False: Specific QA tests should not be performed on each field of a patient's IMRT plan. | False- tests SHOULD be completed on each field to ensure accuracy |
| 60. ____________ through MLCs contributes to increased patient exposure. | Leakage |
| 61. What are 6 disadvantages of an orthovoltage unit? | lack of penetrating ability, high skin dose, low output, large penumbra, doses not homogenous over treatment field, not isocentrically mounted |
| 62. What is D max? | D max is the depth at which electronic equilibrium is reached |
| 63. Is the relationship between D max and energy direct or indirect? | direct |
| 64. What is the SAD of a linear accelerator and Cobalt 60 unit? | linear accelerator SAD is 100cm; Cobalt 60 SAD is 80 cm |
| 65. When using photons what is required to be present in the path of the beam to create a uniform dose distribution? | flattening filter |
| 66. When electrons are produced what must be removed out of the path of the beam, and what must be added to spread the beam? | the target must be removed and a scattering foil must be added |
| 67. What is the average energy of a Cobalt 60 unit? | 1.25 MV; it is comprised of two gamma rays with energies of 1.17 MV & 1.33MV |
| 68. What is a half-value layer (HVL)? | the amount of material needed to reduce radiation transmission by 50% |
| 69. What is the HVL of Co-60? | 1.2 cm of lead |
| 70. How much lead is required to reduce the transmission of a Cobalt 60 beam to approximately 6%? | 4.8 cm of lead |
| 71. What is the D max for a Cobalt 60 unit? | 0.5 cm |
| 72. Approximately, what percentage of Cobalt 60 decays each month? | 1.1% each month |
| 73. When discussing Cobalt 60 units what is timer error? | it is an adjustment made to treatment time to account for the time it takes to move the source in and out of position |
| 74. What are the leakage parameters of a Cobalt 60 machine in the OFF position? | Average not to exceed 2mR/hour at 1 meter; Maximum at any point must not exceed 10mR/hour at 1 meter |
| 75. What are the leakage parameters of a Cobalt 60 machine in the ON position? | must not exceed 0.1% of the useful beam at 1 meter |
| 76. What is the "useful beam" referring to in regards to a Cobalt 60 unit? | It refers to the output and is changed on a monthly basis to account for decay |
| 77. What is geometric penumbra? | the area of unsharpness at the edge of the field |
| 78. What is the relationship (direct/indirect) of geometric penumbra to SSD, source size, and SDD/SCD (source diaphragm distance or source collimator distance)? | SSD-direct, Source size- direct, SDD-indirect |
| 79. What is transmission penumbra? | a) It occurs when straight edge blocks are used for shielding because they do not follow the beam path. Custom blocks do diverge with the beam. |
| 80. How far should Cobalt 60 trimmers or blocks be away from the patient? | at least 15 cm in order to avoid increased skin dose from scatter |
Created by:
cj2218
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