OBT Treatment Planning & Dosimetry 3

Question 1

In intensity-modulated optical beam therapy (IMOBT), which algorithm type iteratively adjusts beam fluence maps to satisfy dose objectives for targets and organs at risk?

Accepted Answer

Inverse planning optimization algorithm

Answer

Inverse planning optimization algorithms work backward from dose objectives to determine the optimal fluence map weights.

Question 2

The concept of equivalent square field is used in dosimetry to:

Accepted Answer

Convert rectangular field scatter factors to those of a square field with equivalent area-to-perimeter ratio

Answer

The equivalent square method uses the area-to-perimeter ratio (A/P) to find a square field with equivalent scatter characteristics to a rectangular field.

Question 3

Which heterogeneity correction method accounts for the 3D scatter contribution from tissue density variations surrounding the calculation point?

Accepted Answer

Convolution-superposition method

Answer

The convolution-superposition method convolves the energy fluence with a dose spread kernel to account for 3D scatter from heterogeneities.

Question 4

A plan review shows that the maximum dose (Dmax) to the spinal cord exceeds the tolerance by 5 Gy. The MOST appropriate next step is to:

Accepted Answer

Add a beam or modify beam angles to reduce cord dose while maintaining target coverage

Answer

Modifying beam geometry or adding beams can redistribute dose away from critical structures while maintaining target coverage.

Question 5

In optical beam therapy planning, the concept of 'normalization' refers to:

Accepted Answer

Scaling all dose values so that a reference point or volume receives the prescribed dose

Answer

Normalization scales the entire dose distribution so that the chosen reference (e.g., isocenter or D50 of PTV) equals the prescription dose.

(OBT) Optical Beam Therapy Certification Practice Test

(OBT) Optical Beam Therapy Certification Practice Test

OBT Treatment Planning & Dosimetry 3