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Commissioning of a Custom Fetal Lead Shield for Radiotherapy

A Owrangi

A Owrangi*, D Roberts , E Covington , J Hayman , K Masi , C Lee , J Moran , J Prisciandaro , Univ Michigan Medical Center, Ann Arbor, MI


TU-G-CAMPUS-T-3 (Tuesday, July 14, 2015) 4:30 PM - 5:00 PM Room: Exhibit Hall

Purpose: To evaluate the peripheral dose (PD) to a fetus during radiation therapy of pregnant patients when using a newly designed fetal lead shield (FLS).

Methods: A custom FLS has been designed and fabricated for our department. The FLS (1.1 TVLs for 6 MV) is mounted on a mobile frame and can be adjusted vertically with a motor actuator. PD measurements were acquired for multiple simple square fields and for a variety of potential treatment sites a pregnant patient may be treated for including brain, head and neck (H&N) and thorax. For measurements of the brain, H&N, and thorax, an ionization chamber and OSLDs were positioned on average at a distance of 48, 29 and 26 cm, respectively, from the edge of treatment fields to mimic the approximate position of the fundus.

Results: Based on our measurements, applying a 90° collimator rotation and using tertiary MLCs to define the field aperture in combination with jaws resulted in an average dose reduction of 60%. When using these planning strategies in combination with the FLS, on average, the PD was reduced by additional 25% for simple square fields and 20% for clinical plans.

Conclusion: The custom FLS is a safe, effective, and relatively easy system to position. Commissioning measurements have demonstrated that the PD to the fetus can be significantly reduced when using the FLS. The comprehensive dataset obviates the need for individual patient pre-treatment dose measurements as long as the geometry falls within the commissioning limits.

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