ESTRO 2023 - Abstract Book

S1533

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ESTRO 2023

[Fig. 1]

Results The agreement between measured ATT and TPS computed ATT was within 1% for all gantry angles for all models of the couch except at gantry angle 110°, where the field passes through the edges of the couch. Although more complex couch models showed increasingly better agreement between the measured and the TPS-calculated ATT, model 4 showed the lowest mean absolute percentage deviation (MAPD) for all energies [Table 1].

Parts of the couch are usually excluded from the CT field of view; therefore, accurate calculations cannot be possible without modeling the couch in TPS.

Three pelvic plans (2 full arcs, 4 partial arcs, 3DCRT) with model 1-3 were compared. No significant changes in PTV coverage or OAR dose were observed in the full arcs VMAT plans. The result of the analysis of the VMAT plan with 4 arcs passing through the edges of the couch shows a slight difference in PTV coverage, while the 3DCRT plan with two fields crossing the edges of the couch shows the largest difference in PTV coverage. No significant changes in OAR dose were observed. Conclusion We suggest to use the couch model 1 in clinical practice although it demonstrates a higher MAPD of 0.98% for 6 MV compared to both model 3 and model 2 (MAPD 0.64% and 0.81% respectively) as a multi-density couch model enhances the risk of not placing high-density parts of the couch top consistently throughout the complete treatment course. Fields for 3DCRT passing solemnly through the edges of the couch should be avoided.

For high-accuracy treatments such as SBRT where higher accuracy is needed couch model 3 might play a role.