X-ray beam symmetry is specified for which of the following parameters?

X-ray beam symmetry refers to how evenly the radiation dose is distributed around the central axis of the beam, which is crucial for ensuring consistent treatment delivery in radiation therapy. The specification of beam symmetry takes into account both the 10 cm depth in water and points equally distant from the central axis for comprehensive evaluation.

At a 10 cm depth in water, the dose distribution can be tested to ensure that the radiation reaching this depth is uniform, which is critical for effective cancer treatment and minimizing damage to surrounding healthy tissue. In addition, measuring symmetry at points equally distant from the central axis allows for assessment of how the beam behaves off-axis, ensuring that the entire target area receives an appropriate and consistent dose.

Together, both criteria—evaluation at a specific depth in water and at various off-axis points—are essential for accurately characterizing the beam symmetry, making it essential in the context of dose planning and treatment delivery in medical dosimetry. This comprehensive approach helps in avoiding hot or cold spots in the treatment area, which can significantly impact treatment efficacy and patient outcomes.