Lead shielding thickness for dose reduction of 7‐ to 28‐MeV electrons

The relative percent dose reduction by lead of 7‐ to 18‐MeV electrons with a Siemens betatron and of 19‐ to 28‐MeV electrons with a Sagittaire linear accelerator has been measured with a thin‐wall buildup chamber for 6.3×6.3‐ and 10.5×10.5‐cm field sizes at the chamber position for the normal treatment source‐to‐skin distance (SSD) of each machine. The thickness of lead necessary to attenuate the open beam by 95–98% was then determined of 7‐ to 28‐MeV electrons. The required thickness of lead to attenuate 95% of the 7‐ to 28‐MeV electron beam ranged from 2.3 to 18 mm for the 6.3×6.3‐cm field and from 2.4 to 23 mm for the 10.5×10.5‐cm field, respectively. For 98% attenuation, thicknesses from 2.6 to 25.0 mm for the 6.3×6.3‐cm field and from 2.8 to 27.5 mm of lead for the 10.5×10.5‐cm field were necessary.