Room: Exhibit Hall
Purpose: To shield the fetus from radiation exposure during an IMRT treatment to the brain, per TG 36 and TG 158.
Methods: A mobile shield on wheels was designed to straddle the treatment couch and hold up to 5 HVLs of lead. The cart, based off of a design by Dr. Podgorsak at Roswell Park Cancer Institute, was made of aluminum and fitted with approximately 2 HVLs (2.5 cm) of lead sheets. Lead shielding covered four sides: top, right, left, and front. The front piece was custom fit around the patient curvature 10 cm superior to the fundus. Before starting treatment, various treatment plans were delivered on an in-house water equivalent phantom to determine the desired shielding quantity and planning technique. Several dose reduction techniques were explored per TG 158. Once the shield was assembled, measurements were made with and without shielding using a farmer chamber at the approximate location of the fundus. On the first day of treatment, OSLD measurements were taken at the fundus, umbilicus, and pubis under 0.5 cm bolus per TG 36.
Results: Ion chamber measurements were made pretreatment on an in-house water equivalent phantom with and without the shielding in place. The chamber was placed 50 cm from the isocenter at a depth of dmax. The measurement showed a 45% reduction in dose with the shielding in place. Patient measurements were taken with OSLDs at the fundus, umbilicus, and pubis per TG 36 and measured a dose for the entire course of treatment of 1.5 cGy, 0.9 cGy, and 0.9 cGy respectively.
Conclusion: By using treatment planning techniques described in TG 158 and a mobile shield on wheels described in TG 36, dose reduction to the fetus was achieved while maintaining a quality treatment plan.