Influence of resorbable poly(L-lactide) bone plates and screws on the dose distributions of radiotherapy beams.

Metallic bone plates have been shown to affect radiation in vitro. Although no damage has ever been demonstrated in vivo these plates may cause dose enhancements and shielding of the adjacent tissue. Resorbable high molecular weight as-polymerized poly(L-lactide) (PLLA) bone plates have recently been used for reconstruction in the maxillofacial area. To determine their influence on dose distribution, a 4-hole bone plate and screws of PLLA were exposed to electron and photon beams. A tissue-equivalent phantom of perspex was irradiated and measurements were made with LiF thermoluminescent dosimeters. No significant changes in dose deviations could be determined when the dose distribution in the homogeneous phantom was compared with that of the phantom in which the PLLA material was placed. From this study it can be concluded that the PLLA material can be regarded as tissue-equivalent and can, thus, be safely used for fracture fixation of bone fragments when postoperative irradiation is anticipated.