A validation of carbon fiber imaging couch top modeling in two radiation therapy treatment planning systems: Philips Pinnacle3 and BrainLAB iPlan RT Dose
Department Texas Oncology, Radiation oncology, Tyler 910 East Houston Street, Texas 75702, USA
Radiation Oncology 2012, 7:190 doi:10.1186/1748-717X-7-190Published: 9 November 2012
Carbon fiber (CF) is now the material of choice for radiation therapy couch tops. Initial designs included side metal bars for rigidity; however, with the advent of IGRT, involving on board imaging, new thicker CF couch tops without metal bars have been developed. The new design allows for excellent imaging at the expense of potentially unacceptable dose attenuation and perturbation.
We set out to model the BrainLAB imaging couch top (ICT) in Philips Pinnacle3 treatment planning system (TPS), to validate the already modeled ICT in BrainLAB iPlan RT Dose treatment planning system and to compute the magnitude of the loss in skin sparing.
Using CF density of 0.55 g/cm3 and foam density of 0.03 g/cm3, we demonstrated an excellent agreement between measured dose and Pinnacle3 TPS computed dose using 6 MV beam. The agreement was within 1% for all gantry angle measured except for 120o, which was 1.8%. The measured and iPlan RT Dose TPS computed dose agreed to within 1% for all gantry angles and field sizes measured except for 100o where the agreement was 1.4% for 10 cm × 10 cm field size. Predicted attenuation through the couch by iPlan RT Dose TPS (3.4% - 9.5%) and Pinnacle3 TPS (2% - 6.6%) were within the same magnitude and similar to previously reported in the literature. Pinnacle3 TPS estimated an 8% to 20% increase in skin dose with increase in field size. With the introduction of the CF couch top, it estimated an increase in skin dose by approximately 46 - 90%. The clinical impact of omitting the couch in treatment planning will be dependent on the beam arrangement, the percentage of the beams intersecting the couch and their angles of incidence.
We have successfully modeled the ICT in Pinnacle3 TPS and validated the modeled ICT in iPlan RT Dose. It is recommended that the ICT be included in treatment planning for all treatments that involve posteriors beams. There is a significant increase in skin dose that is dependent on the percentage of the beam passing through the couch and the angle of incidence.