MDCB LATEST 2026 PRACTICE EXAM QUESTIONS AND
ANSWERS MARKED A+
✔✔The surface dose for an 18 MeV electron beam, based on a 10x10 cm2 field size, is:
(A) 75%.
(B) 85%.
(C) 95%.
(D) 105%. - ✔✔(C) 95%.
✔✔The surface dose for 6 MeV electron beam, based on a 10x10 cm2 field size, is:
(A) 60%.
(B) 70%.
(C) 80%.
(D) 90%. - ✔✔(C) 80%.????
✔✔The measured and computer generated isodose curves should agree within:
(A) +/- 3%, 2mm.
(B) +/- 2%, 3mm.
(C) +/- 2%, 2mm.
(D) +/- 3%, 3mm. - ✔✔(C) +/- 2%, 2mm.
✔✔An Ir-192 HDR source is being utilized in conjunction with a breast balloon for a
breast
treatment. What would be the typical prescription dose per fraction for this treatment?
(A) 340cGy at the balloon surface
(B) 340cGy at .5cm from the balloon surface
(C) 340cGy at 1.0cm from the balloon surface
(D) 340cGy at 2.0cm from the balloon surface - ✔✔(C) 340cGy at 1.0cm from the
balloon surface
✔✔Radiation damage to the fetus resulting in severe birth defects would most often
occur when radiation was delivered at which time post-fertilization?
(A) 0 - 2 weeks
(B) 3 - 12 weeks
(C) 13 - 24 weeks
(D) 23 - 32 weeks - ✔✔(B) 3 - 12 weeks
✔✔Two missed treatment days due to linear accelerator malfunction:
(A) may be compensated by adding the same or even more fractions to the treatment
course with weekend treatment if possible.
(B) may allow some tumors with high growth fractions and long cell cycle times to
recover
through repopulation.
(C) are of major clinical relevance in most cases.
(D) may be made up by increasing the fraction size for the remainder of the treatment
, course. - ✔✔(A) may be compensated by adding the same or even more fractions to the
treatment
✔✔For a 4-field box technique, which of the following will deliver the lowest dose to the
femoral
heads?
(A) 100 source-to-surface distance (SSD), equal dmax dose to all fields
(B) 100 source-to-surface distance (SSD), equal target dose to all fields
(C) 100 source-to-axis distance (SAD), equal air dose to all fields
(D) 100 source-to-axis distance (SAD), equal target dose to all fields - ✔✔(A) 100
source-to-surface distance (SSD), equal dmax dose to all fields
✔✔The relative skin dose for a given energy photon beam:
(A) decreases with increasing field size.
(B) increases with increasing field size.
(C) increases with decreasing field size.
(D) stays the same with any field size. - ✔✔(B) increases with increasing field size.
✔✔The tissue-maximum ratio (TMR) is used in place of the tissue-air ratio (TAR) for
megavoltage
beams because, as energy increases, the:
(A) scatter effects are not fully taken into account.
(B) dose in free space becomes difficult to measure.
(C) depth of maximum dose shifts.
(D) effective primary beam energy cannot be measured. - ✔✔(B) dose in free space
becomes difficult to measure.
✔✔The expression LD 50/60 refers to a whole-body dose which is lethal to 50% of the
irradiated
subjects within 60 days. With regard to the hematopoietic syndrome:
(A) The LD 50/60 for healthy, young adults is approximately 325 cGy.
(B) The application of medical care, such as antibiotic treatment, has no effect on the
LD
50/60.
(C) An allogenic marrow transplant is not likely to be life-saving if the exposure was
greater
than 2 (two) times the LD 50/60.
(D) In humans, the principal cause of death is anemia. - ✔✔(A) The LD 50/60 for
healthy, young adults is approximately 325 cGy.
✔✔The rationale for using a hyperfractionated course of radiation therapy is:
(A) cancer cells have a lower alpha/beta value.
(B) normal late responding tissue has a lower alpha/beta value.
(C) cancer cells has a curvier slope on tissue survival curves.
ANSWERS MARKED A+
✔✔The surface dose for an 18 MeV electron beam, based on a 10x10 cm2 field size, is:
(A) 75%.
(B) 85%.
(C) 95%.
(D) 105%. - ✔✔(C) 95%.
✔✔The surface dose for 6 MeV electron beam, based on a 10x10 cm2 field size, is:
(A) 60%.
(B) 70%.
(C) 80%.
(D) 90%. - ✔✔(C) 80%.????
✔✔The measured and computer generated isodose curves should agree within:
(A) +/- 3%, 2mm.
(B) +/- 2%, 3mm.
(C) +/- 2%, 2mm.
(D) +/- 3%, 3mm. - ✔✔(C) +/- 2%, 2mm.
✔✔An Ir-192 HDR source is being utilized in conjunction with a breast balloon for a
breast
treatment. What would be the typical prescription dose per fraction for this treatment?
(A) 340cGy at the balloon surface
(B) 340cGy at .5cm from the balloon surface
(C) 340cGy at 1.0cm from the balloon surface
(D) 340cGy at 2.0cm from the balloon surface - ✔✔(C) 340cGy at 1.0cm from the
balloon surface
✔✔Radiation damage to the fetus resulting in severe birth defects would most often
occur when radiation was delivered at which time post-fertilization?
(A) 0 - 2 weeks
(B) 3 - 12 weeks
(C) 13 - 24 weeks
(D) 23 - 32 weeks - ✔✔(B) 3 - 12 weeks
✔✔Two missed treatment days due to linear accelerator malfunction:
(A) may be compensated by adding the same or even more fractions to the treatment
course with weekend treatment if possible.
(B) may allow some tumors with high growth fractions and long cell cycle times to
recover
through repopulation.
(C) are of major clinical relevance in most cases.
(D) may be made up by increasing the fraction size for the remainder of the treatment
, course. - ✔✔(A) may be compensated by adding the same or even more fractions to the
treatment
✔✔For a 4-field box technique, which of the following will deliver the lowest dose to the
femoral
heads?
(A) 100 source-to-surface distance (SSD), equal dmax dose to all fields
(B) 100 source-to-surface distance (SSD), equal target dose to all fields
(C) 100 source-to-axis distance (SAD), equal air dose to all fields
(D) 100 source-to-axis distance (SAD), equal target dose to all fields - ✔✔(A) 100
source-to-surface distance (SSD), equal dmax dose to all fields
✔✔The relative skin dose for a given energy photon beam:
(A) decreases with increasing field size.
(B) increases with increasing field size.
(C) increases with decreasing field size.
(D) stays the same with any field size. - ✔✔(B) increases with increasing field size.
✔✔The tissue-maximum ratio (TMR) is used in place of the tissue-air ratio (TAR) for
megavoltage
beams because, as energy increases, the:
(A) scatter effects are not fully taken into account.
(B) dose in free space becomes difficult to measure.
(C) depth of maximum dose shifts.
(D) effective primary beam energy cannot be measured. - ✔✔(B) dose in free space
becomes difficult to measure.
✔✔The expression LD 50/60 refers to a whole-body dose which is lethal to 50% of the
irradiated
subjects within 60 days. With regard to the hematopoietic syndrome:
(A) The LD 50/60 for healthy, young adults is approximately 325 cGy.
(B) The application of medical care, such as antibiotic treatment, has no effect on the
LD
50/60.
(C) An allogenic marrow transplant is not likely to be life-saving if the exposure was
greater
than 2 (two) times the LD 50/60.
(D) In humans, the principal cause of death is anemia. - ✔✔(A) The LD 50/60 for
healthy, young adults is approximately 325 cGy.
✔✔The rationale for using a hyperfractionated course of radiation therapy is:
(A) cancer cells have a lower alpha/beta value.
(B) normal late responding tissue has a lower alpha/beta value.
(C) cancer cells has a curvier slope on tissue survival curves.
