A dosimetric comparison of two high-dose-rate brachytherapy planning systems in cervix cancer: standardized template planning vs. computerized treatment planning.

PURPOSE: High-dose-rate brachytherapy is an important component of the curative treatment for cervical cancer. Some institutions use standardized template planning (STP), based on a precalculated table of dose rates, instead of computerized treatment planning (CTP), based on digitized orthogonal X-ray films. STP can be used as a backup check in case of computer hardware malfunction, and/or as a way to minimize treatment planning time. We performed a dosimetric comparison of STP and CTP to determine dose differences at point A and the International Commission on Radiation Units and Measurements Report 38 bladder and rectal reference points. METHODS AND MATERIALS: We retrospectively reviewed the treatment plans of 62 patients (135 applications) treated with a tandem and two ovoids using the CTP method. For each of these plans, we calculated the dwell times required to deliver the same prescription dose had STP been used. We also used the planning computer to vary tandem and ovoid geometry and develop a table of dose rates based on geometric parameters. RESULTS: The mean dose at point A was 7.6 Gy using CTP, increasing to 8.4 Gy when the STP approach was used (p<0.05). The mean doses at the International Commission on Radiation Units and Measurements Report 38 bladder and rectal points were both 4.5 Gy with CTP and increased to 4.9 and 5.0 Gy, respectively using STP (p<0.05). Our table of dose rates showed significant dose rate dependency on the applicators geometry. CONCLUSIONS: Our study shows that if the STP approach had been used, a significantly higher dose would have been delivered, and that STP tables accounting for differences in implant geometry should be carefully considered.

Effects of neurosurgical titanium mesh on radiation dose.

The purpose of this study was to determine the dosimetric impact of a neurosurgical titanium mesh in patients treated with 6- and 18-MV photon beams. The effects of a 0.4-mm-thick titanium mesh on the dose profile at 3 regions within a solid water phantom were measured using extended dose range-2 (EDR2) film for 6- and 18-MV photon beams. All measurements were performed with the titanium mesh placed at a depth of 1.5 cm in the phantom. Films were exposed immediately above the mesh, immediately below the mesh, and at a depth of 5 cm from the surface of the phantom. The films were scanned using a scanning densitometer. In the region directly above the titanium mesh, there was an increase in dose of 7.1% for 6-MV photons and 4.9% for 18-MV photons. Directly below the titanium mesh, there was an average decrease in dose of 1.5% for 6-MV photons and an increase of 1.0% for 18-MV photons. At 5-cm depth, for 6- and 18-MV photons, there was a decrease in dose of 2.2% and 0.6%, respectively. We concluded that for cranial irradiation with high-energy photons, the dosimetric impact of a 0.4-mm titanium mesh is small and does not require modification in treatment parameters.