| Question 1: There are several reasons for updating the TG-51 protocol. Which of the following is NOT one of them?
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| Reference: | McEwen et al., “Addendum to the AAPM’s TG-51 protocol for clinical reference dosimetry of high-energy photon beams,” Med. Phys. 41:041501, 2014.
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| Choice A: | There have been advances in reference dosimetry since publication of TG-51. |
| Choice B: | The update prescribes a new, improved formalism for beam calibration. |
| Choice C: | Accurate Monte Carlo based kQ factors are now available. |
| Choice D: | TG-51 deliberately avoided uncertainties. |
| Question 2: One of the main reasons for recommending the use of cylindrical chambers for reference dosimetry of electron beams, even with energy less than 6 MeV, is:
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| Reference: | Muir and Rogers, “Monte Carlo calculations of electron beam quality conversion factors for several ion chamber types,” Med. Phys. 41:111701, 2014.
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| Choice A: | Cylindrical chambers are not as stable as plane-parallel chambers. |
| Choice B: | Perturbation corrections for cylindrical chambers are variable for similar chambers. |
| Choice C: | Beam quality conversion factors, kQ, are now well known from Monte Carlo calculations and include Pgr, simplifying the calibration procedure. |
| Choice D: | Clinical medical physicists are not comfortable using cylindrical chambers for electron beam reference dosimetry. |
| Question 3: What will be the change in the TG-21 determination of absorbed dose to water following the recommendations of ICRU 90? |
| Reference: | The International Commission on Radiation Units and Measurements, “Key data for ionizing radiation dosimetry: measurement standards and applications,” Journal of the ICRU, volume 14, no. 1, ICRU report 90 (2016).
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| Choice A: | No change. |
| Choice B: | Less than 0.5%. |
| Choice C: | Approximately 0.7%. |
| Choice D: | More than 1%. |
| Choice E: | TG-21 (Air kerma-based) dose determination is no longer recommended. |
| Question 4: Why is the dose to tissue different than the dose to water?
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| Reference: | The physics of Radiology. Johns and Cunnigham. Charles C Tomas publishing, Springfield Il. 1983. |
| Choice A: | Because they have different densities. |
| Choice B: | Because they have different chemical compositions. |
| Choice C: | Because they exist in different states. |
| Choice D: | Because tissue is at a higher temperature than typical water tank water. |
| Question 5: A 1% correction between dose to water and dose to tissue: |
| Reference: | IROC Houston, (2010, September 20) Water or tissue – revisited. Accessible at http://rpc.mdanderson.org/RPC/newsletter/September%202010%20water_4C1EF9.pdf |
| Choice A: | Has been consistently applied by the medical physics community for photon beams. |
| Choice B: | Has been consistently applied by the medical physics community for electron beams. |
| Choice C: | Has been inconsistently applied by the medical physics community. |
| Choice D: | Is never necessary. |
| Choice E: | Is not necessary for electron beams. |
| Question 6: Collapsed Cone Convolution photon algorithm as described by Ahnesjo and Aspardakis1 is expected to approximate dose to tissue because:
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| Reference: | Ahnesjo A, Aspradakis MM. Dose calculations for external photon beams in radiotherapy. Phys Med Biol. 1999;44(11):R99-155.
2. Wieslander E, Knöös T. Dose perturbation in the presence of metallic implants: treatment planning system versus Monte Carlo simulations. Phys Med Biol. 2003;48(20):3295.
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| Choice A: | The energy deposition kernel used for C/S is assigned the tissue material and density. |
| Choice B: | The mass energy absorption coefficient for TERMA calculation is based on tissue radiological properties. |
| Choice C: | The superposition/convolution equation models the dose distribution in 3 dimensions by taking the local density into account for lateral dose spread calculations. |
| Choice D: | The TERMA decrease with depth is accounted for by using CT# to electron density conversion. |
