Author Questions Flashcards
Questions at the end of every session
MHC class 2 receptors present antigens to be recognized by the following immune cell type:
A) Myeloid-derived suppressor cells
B) Natural Killer cells
C) CD8+ “Cytotoxic” T cells
D) CD4+ “Helper” T cells
E) B cells
D) CD4+ “Helper” T cells
Anti-PD1 and Anti-CTLA4 target the following type of tumor reactive immune cells:
A) Myeloid-derived suppressor cells
B) CD8+ “Cytotoxic” T cells
C) CD4+ “Helper” T cells
D) B cells
E) B and C
E) B and C
Both CD8+ “Cytotoxic” T cells and CD4+ “Helper” T cells
A radiation oncology resident is designing a clinical trial combining radiotherapy and immune checkpoint inhibitor for melanoma. Which of the following approaches have shown promise in clinical trials:
A) SBRT, 8Gy x 3, immediately followed by anti- PD1 or anti-PDL1
B) Conventionally fractionated radiation with concurrent anti-PD1 or anti-PDL1
C) Conventionally fractionated radiation, immediately followed by anti-PD1
D) All of the above
E) A and C
E) A and C
Conventionally fractionated radiation with concurrent anti-PD1 or anti-PDL1 does not work.
A scientist has developed a radioprotector compound that acts by scavenging free radicals in the cell. For which type of radiation would the relative radioprotective effect likely be the greatest?
A – Photons
B – Neutrons
C – Equal protection for photons and neutrons
D – Neither would be radioprotected by this compound
A - Photons
Photons are low LET, and their greatest (~70%) effects are indirect (via formation of free radicals). Thus, free radical scavengers would be more effective on those.
Which one of the following is a radiolysis product of water responsible for the molecular damage caused by the indirect action of ionizing radiation?
A - e (aq)
B - 1O2
C - OH -
D. OH*
E - O2-
Question 1: (I-2 in ASTRO 2023 study guide)
I-2) Which one of the following is a radiolysis product of water responsible for the molecular damage caused by the indirect action of ionizing radiation?
A. e(aq)
B. 1O2
C. OH-
D. OH*
E. O2-
D 65-75% of the damage caused by indirect action is mediated by the hydroxyl radical, OH*. Little biological damage is caused by the hydrated electron (eaq; Answer Choice A). 1O2 is produced primarily by photosensitizers and, rarely, by ionizing radiation (Answer Choice B). Neither OH- nor O2- are primary radiolysis products, although O2- can be produced secondarily by reaction of eaq with O2 (Answer Choices C and E). Mitchell JB, et al. Radiation, Radicals, and Images. Ann N Y Acad Sci. 899:28-43, 2000. Pubmed
Huber, K, Woloshak, G, Rosenstein B. 2023 Astro Radiation and Cancer Biology Study Guide. 2023. American Society for Radiation Oncology. Available from: https://www.astro.org/ASTRO/media/ASTRO/AffiliatePages/arro/PDFs/RadBio_StudyGuide_23.pdf
Which of the following ionization processes represents the principal interaction with tissue for X-rays used in radiotherapy?
A - Pair production
B - Photoelectric effect
C - Compton process
D - Photodisintegration
E - Coherent scattering
C
For photons in the energy range used typically in radiotherapy, the Compton process is predominant. In the Compton process, a high-energy photon interacts with an atom to cause ejection of an outer shell electron (referred to as a recoil electron) and a scattered photon. The energy of the incident photon is distributed between the scattered photon and the kinetic energy of the recoil electron. The Compton interaction may occur when photon energies range from 150 keV to 3 MeV although it also occurs to some extent at lower energies of 100-150 keV. Pair production occurs when a photon of greater than 1.02 MeV interacts with a nucleus to form an electron-positron pair. This amount of energy is just sufficient to provide the rest mass of the electron and positron, 0.51 MeV each. Excess of energy above 1.02 MeV will be possessed by these two particles, which produce ionizations as they travel in the material. As the positron comes to rest, it interacts with an electron in an annihilation reaction and is replaced by two photons, each having an energy of 0.51 MeV and moving in opposite directions. Pair production becomes an important form of interaction above about 10 MeV. The photoelectric effect is predominant for photons that have energies less than approximately 100-150 keV, typical of X-rays used in diagnostic radiology. In the photoelectric process, a photon interacts with an inner orbital electron and is completely absorbed. The electron is ejected from the atom becoming a free photoelectron. The kinetic energy of the ejected electron is equal to the energy of the incident photon minus the binding energy of the electron that has been ejected. The vacancy left in the shell by the ejected electron is filled in by the transition of an electron from an outer shell and is accompanied by the emission of a characteristic X-ray, whose energy represents the difference in the energy levels of the shells involved in the electron transition. When the excess energy derived from the transition of the electron from the higher to the lower energy state is transferred to an orbital electron that is ejected, this is referred to as an Auger electron. Photodisintegration occurs at photon energies much higher than those used in either diagnostic radiology or radiation therapy. In this process, a high-energy photon interacts with the nucleus of an atom resulting in the emission of one or more nucleons. An electron is not ejected through coherent scattering and not ejected through coherent scattering and no energy is transferred in this type of interaction, only the direction of the incident photon is altered.
(ASTRO 2020 Study Guide: Radiation-Matter Interactions)
Woloshak, G, Huber, K, Barker, C, Rosenstein B, et al. 2020 Astro Radiation and Cancer Biology Study Guide. 2020. American Society for Radiation Oncology. Available from: https://www.astro.org/ASTRO/media/ASTRO/AffiliatePages/arro/PDFs/Radiobiology_StudyGuide21.pdf
The largest contributor to radiation exposure of the US population each year is:
A - Radon
B - Cosmic radiation
C - Computed Tomography
D - Industrial activity
E - Consumer products
XXIX-8) A Per the National Council on Radiation Protection and Measurements (NCRP), Report No. 160, the average annual radiation dose per person in the United States is approximately 6.2 millisieverts (mSv) or 620 millirem (mrem). The majority (37%) of this dose can be attributed to background radiation sources including Radon and Thoron. These gases are created when other naturally occurring elements undergo radioactive decay. Cosmic radiation contributes 5% of the average annual dose (Answer Choice B). An additional 48% of the average dose to an individual in the United States is from medical procedures (not including dose received during therapeutic radiation). Of these, Computed Tomography (CT) scans comprise approximately 24% of radiation dose (Answer Choice C). Industrial activity contributes only a very small amount of the average annual dose to the average American (<0.1% or 0.003mSv).
Consumer products contributes approximately 2% of the average annual dose (Answer Choice E) Radiation Sources and Doses. United States Environmental Protection Agency. https://www.epa.gov/radiation/radiation-sources-and-doses
Huber, K, Woloshak, G, Rosenstein B, et al. 2023 Astro Radiation and Cancer Biology Study Guide. 2023. American Society for Radiation Oncology. Available from: https://www.astro.org/ASTRO/media/ASTRO/AffiliatePages/arro/PDFs/RadBio_StudyGuide_23.pdf
Question 4: Which of the following results from the recombination of the initial water radiolysis products?
A. Solvated electron
B. Solvated proton
C. Hydrogen ion
D. Water
E. Only A and B
D
The main initial products of resulting from irradiation of pure water are the short-lived free radicals, hydrogen radical (H) (10%), hydroxyl radical (OH) (45%), and solvated electrons (e-aq ) (45%).
These react with DNA or with each other. Therefore, OH + H –> H2O
The remaining recombination reactions of free radicals are:
e-aq + e-aq +2 H2O –>H2 + 2 OH-
OH + OH –>H2O2
H + H –>H2
These reactions always compete with reactions that lead to direct damage of the biological molecules.
Modified from question from the ASTRO 2023 study guide
Original question from: Huber, K, Woloshak, G, Rosenstein B, et al. 2023 Astro Radiation and Cancer Biology Study Guide. 2023. American Society for Radiation Oncology. Available from: https://www.astro.org/ASTRO/media/ASTRO/AffiliatePages/arro/PDFs/RadBio_StudyGuide_23.pdf
- Which of the following particles is most efficient at directly ionizing the deoxyribonucleic acid backbone?
A) Carbon ion
B) Proton
C) Alpha particle
D) Co60 gamma ray
C
High LET radiation types have an increased propensity for direct ionization of biomolecules, including the induction of clustered lesions. Low LET radiation types are more likely to impact biomolecules (including DNA) through indirect ionization via hydroxyl radicals or other radiolysis species.
Approximate LET values according to Hall (keV/uM)
- 14 MeV Carbon ion: 12
- 150 MeV Proton: 0.5
- 2.5 MeV alpha particle: 166
- Co60 gamma ray: 0.2
- The lifetime of an OH* radical is approximately:
A. 10-15 second
B. 10-9 second
C. 10-1 second
D. 1 second
E. 1 minute
B
The initial ionization process takes approximately 10-15 second (this can be either ionization of water (radiolysis) or direct ionization of a biomolecule like DNA. If radiolysis occurs, the primary radicals (H20+, e-aq) produced by the ejection of an electron from water typically have a lifetime of 10-10 second. Subsequent interaction of these primary radicals with water results in H3O+ and OH* , which has a lifetime of approximately 10-9 second. The DNA radicals formed through direct or indirect ionization of DNA (base radicals or sugar-phosphate ionization) have a lifetime of approximately 10-5 second.
Timescales by process
Biology (e.g., DNA damage) – microseconds (usec) to decades
Chemistry (e.g., radiolysis species and derivatives) - picoseconds to nanoseconds
Physics (e.g., initial ionization event) – femtoseconds
Modified from ASTRO study guide question
Original question from:
Huber, K, Woloshak, G, Rosenstein B, et al. 2023 Astro Radiation and Cancer Biology Study Guide. 2023. American Society for Radiation Oncology. Available from: https://www.astro.org/ASTRO/media/ASTRO/AffiliatePages/arro/PDFs/RadBio_StudyGuide_23.pdf
Radiobiology refers to which of the following:
A) The study of different physical sources of radiation
B) The study of how electromagnetic radiation interacts with biological
systems
C) The use of radiological imaging to define the anatomy of living
organisms
D) None of the above
B) The study of how electromagnetic radiation interacts with biological
Which of the following statements is true regarding clinical responses
to radiation
A) Effects are fully realized within a matter of weeks after radiation is
administered
B) The tumor’s genetic profile is the sole determinant of radiation
sensitivity
C) Both tumor cell and normal tissue responses contribute to the clinical
response to radiation, which can take years to fully manifest
D) None of the above
C) Both tumor cell and normal tissue responses contribute to the clinical
Clinical scenarios when you might use your radiation and cancer
biology knowledge
A) Estimating normal tissue dose tolerances during a course of re-
irradiation
B) Making clinical decisions about dose/fractionation
C) Determining whether radiation plans need to be modified when a
patient’s germline genetic testing identifies an unexpected
pathogenic mutation in TP53
D) Deciding how to manage timing of a recently approved targeted
cancer therapy drug with a course of palliative radiotherapy
E) All of the above
E) All of the above
Which of the following proteins inhibits the intrinsic pathway of apoptosis?
1) BAX
2) P53
3) PUMA
4) BCL-2
4)BCL-2
What is the primary mechanism by which radiation therapy kills follicular lymphoma cells?
1)Senescence
2)Pre-mitotic apoptosis
3)Ferroptosis
4)Necroptosis
2) Pre-mitotic apoptosis
