What occurs in the anterior region of overlap when using a pair of wedged treatment fields with a wedge angle much smaller than the ideal one?

When using wedged treatment fields, the goal is usually to achieve an optimal dose distribution throughout the treatment area. In scenarios where the wedge angle applied is much smaller than the ideal one, the intended dose modulation may not be achieved effectively. Instead, in the anterior region of overlap—which is where the two wedged fields intersect—there tends to be an accumulation of dose due to the converging beams.

This occurs because the lesser angle does not sufficiently create the necessary tilt to adequately spread out the dose, leading to a situation where the dose is more concentrated or higher in that overlapping area compared to other regions. The result is a high dose region that can potentially exceed the prescribed limits, which could have implications for treatment and surrounding healthy tissues.

Thus, the interaction of the wedged fields at a smaller angle results in an undesired high dose concentration in the anterior region of overlap, which is critical for dosimetrists to consider when planning treatment to avoid overdose in that area.