What is the monthly light/radiation field coincidence tolerance on a side?

• A. 2 mm or 1% on a side
• B. 1 mm or 1% on a side
• C. 2 mm
• D. 3 mm

Answer: (A)

The important idea is making sure the light field you set up matches the actual radiation field, on every side of the field. Monthly, you compare the light-field border to the radiation-field border for both left-right and top-bottom directions. The tolerance is defined as the larger of 2 mm or 1% of the field size, measured on each side. This per-side criterion keeps edge alignment precise across a range of field sizes: for small fields, 2 mm governs; for larger fields, the 1% allowance can become the bigger limit.

That’s why the correct choice reflects both numbers on each side. The other options either give a single fixed value or omit the per-side requirement, which wouldn’t protect against misalignment at the field edges.