Shielding Design for Adjacent, Underground Buildings of a Megavoltage Radiotherapy Facility

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiological Engineering

Background:

• Radiotherapy facilities require robust shielding to prevent radiation exposure in adjacent areas, especially from downward irradiation.
• Traditional methods often involve thick concrete floors, leading to increased excavation depth and costs, even without basements.
• Oblique x-ray transmission through floors and walls poses a safety concern in areas adjacent to or below the treatment room.

Purpose of the Study:

• To introduce an analytical method for calculating optimal radiotherapy shielding.
• To determine required wall penetration depth below floor level or additional floor shielding for L-shaped barriers.
• To provide conservative yet optimal shielding design criteria for protecting underground sites.

Main Methods:

• Development of an analytical method to calculate required wall penetration depth.
• Calculation of additional floor shielding for L-shaped barriers, considering earth attenuation.
• Analysis of shielding dimensions based on basic attenuation data and material composition (lead-concrete).

Main Results:

• The required penetration depth for wall barriers is a function of basic attenuation data relative to a reference thickness.
• Shielding dimensions for laminated barriers depend on the relative lead content and attenuation properties.
• The proposed method yields optimal shield dimensions for wall footing and wall-floor shielding.

Conclusions:

• The developed analytical method offers an effective alternative to oversized concrete slab floors in radiotherapy facilities.
• This approach provides conservative shielding design criteria, ensuring safety for underground areas.
• The method optimizes shield dimensions, potentially reducing construction costs and excavation depth.