(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: Our aim is to model and validate iBEAM evo couch top for photon beam treatment planning in Monaco TPS.
Methods: The study was performed in Elekta Synergy-S linear accelerator with iBEAM evo and Monaco TPS. CT images of iBEAM evo couch-top acquired and used to delineate carbon fibre (CF), foam core (FC) and side tip (TIP). The delineated structure set stored in the couch library for couch modelling. Couch attenuation measured for 6 and 15MV beams using 10cm thick slab phantom with a farmer chamber as recommended in TG176. Posterior attenuated beams were compared with respective anterior un-attenuated beam for various gantry angles. Appropriate electron density (ED) values of the couch components were reached iteratively and applied to model. The validity of calculated ED verified for 20 different posterior gantry angles. Dosimetric impact of couch model inclusion evaluated for different anatomical sites.
Results: Couch attenuation of 0.35%–5.31% and 0.05%–3.64% for 6 and 15MV open beam, respectively. Maximum attenuation was observed at 110°–120° and 230°–240° gantry angles. The best fit electron density was found to be 0.6, 0.042 and 0.7 for CF, FC and TIP, respectively. The average difference between measured and calculated dose using best fit ED for various gantry angles is 0.02% and 1.02% for 6 and 15MV, respectively. The average target mean dose (Dmean) lowers 1.01% (0.42%–2.24%) by accounting the couch attenuation.
Conclusion: iBEAM evo couch-top model generated with three couch components. The ED values of couch components were found to be 0.6, 0.042 and 0.7 for CF, FC and TIP, respectively. The dosimetric error due to couch attenuation brought down to 0.2% and 1.02% for 6 and 15MV, respectively. The overall couch attenuation depends on the fraction of total MU pass through the couch and the incident angle.
Keywords
Not Applicable / None Entered.
Taxonomy
TH- External beam- photons: Standard field computational dosimetry
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