On methods for radiometric surveying in radiotherapy bunkers

Area of Science:

• Medical Physics
• Radiation Oncology
• Health Physics

Background:

• Radiometric surveys are standard in radiotherapy bunkers for shielding verification and regulatory compliance.
• The increasing adoption of Intensity Modulated Radiation Therapy (IMRT) necessitates re-evaluation of shielding due to altered radiation leakage.
• Existing radiometric survey methods require adaptation to account for increased leakage impacting secondary walls.

Purpose of the Study:

• To compare two distinct radiometric survey methods for assessing dose rates in secondary walls considering IMRT.
• To analyze the impact of different 'time of beam-on' assumptions on dose rate calculations.
• To propose an optimized radiometric survey procedure based on the secondary wall's use factor (U).

Main Methods:

• Two methods were evaluated: one assuming 'time of beam-on' affects both leakage and scattered radiation, the other affecting only leakage.
• Dose rates were calculated and compared for secondary walls with different use factors (U).
• The study analyzed overestimation and underestimation of dose rates based on the chosen method and U value.

Main Results:

• The first method (affecting both components) significantly overestimates dose rates for secondary walls with U=1.
• For secondary walls with U<1, the first method can lead to both overestimation and underestimation, contingent on project parameters.
• The accuracy of dose rate assessment is highly dependent on the specific method and the secondary wall's use factor.

Conclusions:

• An optimized radiometric survey procedure is proposed, tailored to the use factor (U) of the secondary wall.
• Accurate dose rate assessment in IMRT facilities requires careful consideration of leakage radiation and appropriate survey methodology.
• The findings contribute to improved radiation safety and regulatory compliance in radiotherapy settings using IMRT.