Lesson: Wedges Module

The formula to help determine the best wedge to use for a wedged pair plan:

WA = 90 – HA/2
or
HA = 180 – 2WA

where the wedge angle (WA) is the best wedge selection for the plan, and the hinge angle (HA) is the angle between the two wedged beams.

For example, if you had two beams that were 90 degrees apart (HA = 90), you could solve for the wedge angle as follows:

WA = 90 – 90/2
WA = 90 – 45
WA = 45 degrees

Or, if you were solving for the hinge angle, and you were using two 30 degree wedges:
HA = 180 – 2(30)
HA = 180 – 60
HA = 120 degrees

As you can postulate, the closer that the angles are together, the greater the degree of wedge that you need. Consequently, as your beams approach opposing angles, the necessity for a wedge decreases.

Note: It is important to remember that these formulas are only used to determine ideal cases where the hinge angle or the wedge angle is the primary reason for dose distribution. This will not work for cases such as breast tangents or larynx cases where it is the anatomy that helps determine the necessity for a wedge.

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