Units 5 and 6 Physics II

The hinge angle of an "ideal" treatment situation of two wedged fields is 45°, select the appropriate wedge angle: A. 60° B. 45° C. 30° D. 15°

A

Compared to kV cone beam CT, mV cone beam CT images provide: A. Better contrast B. Better resolution C. Less susceptibility to artifacts due to high z objects D. Better correlation to electron density E. A and B AB. C and D AC. All of the above

AB

For a wedge beam A. The wedge angle is defined as the angle of the physical wedge filter B. The wedge factor generally increases with field size and depth C. The central axis percent depth dose generally increases compared to the open beam of the same dimensions D. The Isidore curves are tilted through the same angle at all depths E. A and B AB. B and C AC. A, B, C AD. All of the above

AB

According to ICRU specification, which of the following is correct? A. For multi-beam arrangements the dose should be specified at the intersection point if the central axes of the beam B. The target dose should be specified at the deepest region of the target, for a single SSD photon beam C. For rotational photon therapy involving arcs of 270° and larger, the dose should be specified at the center of rotation if the beam D. The dose for parallel opposed photon beams should be specified midway between the beam entrance points E. a and b AB. a and c AC. a c and d AD. All of the above

AC

Rotational x ray beam therapy is acceptable: A. When the external contour of the patient is fairly cylindrical B. When blocking is required to shield sensitive structures C. When target volume is small D. When target volume is centrally located E. a and b AB. a and c AC. a c and d AD. All of the above

AC

Surface dose would increase for what conditions in a mV beam? A. Increasing field size B. Reducing shadow tray-to-surface distance C. Inserting a 1 mm thick lead in the beam under the shadow tray D. Increasing beam obliquity E. a and b AB. b and d AC. a and d AD. a, b and d AE. All of the above

AD

Which of the following statements is/are true? An isodose curve can: A. Have a concavity B. Cross another curve of a different value C. Cover the entire patient D. Exceed 100% E. Have more than one incidence (eg. two separate 95% isodose lines) in a single plane AB. a b and c AC. a c and d AD. a c d and e AE. All of the above

AD

Compared to CT, MRI provides better: A. Quality of images for bone or calcification B. Quality of images for soft tissue or tumors C. Spatial resolution D. Correlation with electron density

B

Compared to CT, PET images provide better: A. Geometric accuracy B. Differentiation of malignancy tumor and normal tissue C. Correlation with electron density D. Spatial Resolution

B

For isocentric parallel opposed equally weighted photon fields: A. The target dose specification point is the depth of dmax B. There is reproducibility of setup with less chance of geometric Miss C. Treating one field per day is less harmful to normal tissues than treating both fields per day D. The peripheral dose increases with increasing energy for constant midline dose

B

Which of the following statements are true regarding target volume delineation according to ICRU 62? A. Treatment fields are blocked to the PTV, which includes the CTV plus uncertainties in daily patient setup B. The treatment volume is larger than the CTV, but smaller than the irradiated volume C. The minimum target dose is defined as the lower dose within the PTV, provided this dose converts a minimum area of 2cm

B

In a wedged pair technique: A. Thin ends of the wedges must be placed adjacent B. Wedged angle if each wedge must be half the hinge angle C. Hot spots generally occur under the thin ends of the wedges D. The dose within the target volume is uniform within */-5% E. a and c AB. b and c AC. c and d

C

A compensator designed for irregular surface compensation: A. Has the same thickness (g/cm3) along ray lines as the tissue deficit B. Provides the same depth dose distribution as expected with flat surface C. Has a compensator ratio that is independent of compensator-to-surface distance D. Should be placed at compensator-to-surface distance of 20 cm or greater to maintain skin-sparing effect of mV photon beams

D

According to ICRU specifications, the wedge angle is defined at: A. Depth of 50% isodose line B. Depth of 80% isodose line C. Depth of dmax D. 10 cm depth E. B and C

D

Compared to the dose at central axis, the dose at the geometric field border at the same depth is approximately: a. 100 +/- 3% b. 95% c. 80% d. 50% e. 2%

D

How many HVLs are required to reduce the primary beam of 2% if it's initial value? A. 3.76 B. 4.32 C. 5 D. 6 E. 7.5

D

Select an arrangement in the increasing order of volume (CTV, GTV, ITV, PTV) A. CTV, GTV, ITV, PTV B. ITV, GTV, CTV, PTV C. GTV, CTV, PTV, ITV D. GTV, CTV, PTV

D

calculate the optimal wedge angle for a wedged pair plan with beams directed at 60° from one another: A. 15° B. 30° C. 45° D. 60° E. Need more info to calculate

D

Which of the following is/are true regarding wedge filters? A. The wedge angle is equivalent to the angle of the wedge, when converted to water-equivalent thickness B. The wedge angle is defined as the angle of the wedge profile measured at depth of 10 cm in water C. Physical wedge factors vary only slightly with field size, depth, and lateral distance D. The surface dose for wedge filters increase the skin dose beyond 50% of dmax due to electron contamination produced by the filters E. The wedge angle is defined the same for physical and nonphysical wedges

E