ESTRO 2023 - Abstract Book

S1733

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ESTRO 2023

Materials and Methods Data of ten patients (PTs) clinically treated with VMAT was analyzed. The clinical VMAT plan and its planCT, pre-treatment MRI and five weekly repeated CTs (reCTs) were available. A robust optimized IMPT plan was created retrospectively on this planCT using 7 mm set-up and 3% range uncertainties. Additionally, using these uncertainties, robustness evaluation was performed. The lymph nodes and vagina were manually contoured on the planCTs and using MRI expanded to the ITV. OAR and vagina structures were manually contoured on both planCTs and reCTs. The lymph nodes were deformably warped from the planCT to the reCTs using a deformable hybrid intensity image registration (DIR). Dose distributions were re-calculated on reCTs after rigid image registration and nominal dose distributions were evaluated on the reCTs. Thereafter, robustness evaluations were performed using 3% range and 2 mm set-up uncertainties. Robustness of nominal OAR doses and voxel wise minimum (vox min) D98 vagina and lymph node coverage >94% ¹ of prescribed dose 45 GyRBE were compared for VMAT and IMPT using a Wilcoxon matched-pair signed-rank test. ReCT vox min doses were accumulated by warping reCT doses back to their planCT using DIR and assigning an equal number of fractions to each reCT.

Results Target coverage and OAR dose were similarly robust for IMPT compared to VMAT (Table 1).

Vox min D98 lymph node coverage was <94% for both VMAT and IMPT for only 1/49 reCTs. Vox min D98 vagina coverage was <94% for 5/49 reCTs (2 PTs) for VMAT and 6/49 reCTs (4 PTs) for IMPT. Lymph nodes accumulated vox min D98 was >94% for all VMAT and for 9/10 IMPT treatments and >92% for all IMPT treatments (Figure 1B).