Effects of titanium mesh implant on dosimetry during Gamma Knife radiosurgery

Calvarial reconstruction following resection of tumors involving the skull is often followed by stereotactic radiosurgery. Prior studies have addressed the effects of various cranioplasty materials on dose distributions in linac-based radiosurgery. We aim to determine the effects of titanium mesh implants on Gamma Knife dose. Radiation backscatter and transmission were measured for eight types of titanium mesh using film, ion chamber, and Theratron Co-60 teletherapy device. A single mesh was selected for Gamma Knife irradiation using a CaSO4 skull filled with ballistics gel. Dose profiles for reconstructed and intact skulls were compared with the planning system prediction at 2.5 and 5.5 cm depth. Titanium contact backscatter and transmission dose perturbations ranged from -18% to 23%. Radiation dose measured at 1.5 cm below the calvarial implant increased by 0.5% to 3.3% relative to bone. Measured Gamma Knife dose profile diameters agreed with expected profiles. Maximum dose within the intact phantom was 3% less than planned due to skull attenuation. Maximum dose within the reconstructed phantom was between the intact phantom and planned doses. Titanium mesh implants and hydroxyapatite cranioplasty result in minimal alteration (< 3%) in the delivered Gamma Knife dose.