What minimum shielding block thickness is required to reduce the dose in the shielded region to less than 5% of the open field dose?

In radiation therapy and dosimetry, the concept of half-value layer (HVL) is crucial for determining how much shielding is required to reduce radiation exposure. The HVL is defined as the thickness of a specified material (often lead or a similar substance) that reduces the intensity of radiation by half.

To achieve a dose reduction to less than 5% of the open field dose, we need to understand how many half-value layers are needed to reach that level of attenuation. Each HVL reduces the radiation dose to half of its previous value. Therefore, to find the required thickness for a significant dose reduction, one can use the formula that relates the remaining dose to the number of HVLs:

• After 1 HVL, the dose remains at 50%.

• After 2 HVLs, the dose is reduced to 25% (50% of 50%).

• After 3 HVLs, the dose is reduced to 12.5% (50% of 25%).

• After 4 HVLs, the dose is reduced to 6.25% (50% of 12.5%).

• After 5 HVLs, the dose is reduced to 3.125% (50% of