SU-E-T-265: Reducing Pacemaker Doses with a Lead Sheet: A Multi-Detector Study.

Purpose: Evaluate the usability of lead shielding to reduce the dose to pacemakers. The efficiency and risk of this type of skin block will be presented.

Methods: A solid water phantom was used and all measurements were made at a depth of 0.5 cm for 6 MV and 23 MV photon beams. Measurements were performed with a parallel plate ion chamber and with a plastic scintillation detector (PSD) prototype. Measurements were made for fields of 10, 20 and 30 cm square. For every field, measurements were made in increment of 5 cm from the center of the field to the edge of the 60 cm long phantom for anterior and posterior beams. All measures have been made with and without a 1.6 mm of lead shielding wrapped in a thermoplastic.

Results: For all measurements, both detectors agree to 0.6%, well within the uncertainties of the detectors. With antero-posterior fields, the benefit of shielding is more important at 23MV (reduction of dose by65%) compared to 6MV (reduction of dose by 46%) when the shielding is out of the field. For distances larger than 35 cm, no benefits are measured. In the case were the lead is completely inside the fields, the dose is increased by the presence of shielding. The same observation is made for postero-anterior fields. For shielding out of field, the dose is slightly increased.

Conclusions: The used of lead shielding with antero-posterior field is advised and provided an easy way to decrease dose to pacemaker. For a postero-anterior field, it is preferable to avoid shielding, but it could be used if it stays outside fields in the case of a multiple beams treatment. PSD has been shown to be an excellent candidate for in vivo monitoring dose to pacemakers and also site like foetus.