ESTRO 2023 - Abstract Book

S1655

Digital Posters

ESTRO 2023

2) The required time for the online plan adaptation and total treatment time were (20.1 ± 6.1) min and (26.0 ± 6.3) min, respectively.

Conclusion Daily online adaptive radiotherapy ensures the target coverage, achieving all the dosimetric goals for the actual rectum and bladder on every session. The full online adaptive planning described in this study is feasible within a 30 min slot in the linac.

PO-1907 comparison of dosimetric error due to the tumor motion between TomoTherapy and LINAC-based VMAT

J. Song 1

1 Chonnam National University Medical School, Radiation Oncology, Gwangju, Korea Republic of

Purpose or Objective In this study, we analyzed the difference in dosimetric error due to tumor motion in an ITV-based IMRT process based on the IMRT method using the Delta4 Hexa-Motion system. Among the IMRT methods, the conventional LINAC-based VMAT technique and the helical-based TomoTherapy technique were selected for a comparison analysis of the dosimetric error due to tumor motion. Materials and Methods ITV-based IMRT plans for a total of 10 cases of liver cancer were prepared in TomoTherapy (Tomo) and LINAC-based VMAT. Delivery quality assurance (DQA) plans were created using Delta4 phantom for the verification of dosimetric accuracy of the established Tomo and VMAT plans. DQA measurements were performed in both the static mode and the Hexa-Motion mode by using the Delta4 Hexa-Motion system in Tomo and VMAT. The dose variations were compared and analyzed for each treatment method in order to evaluate the effect of a target motion on the IMRT dosimetric error. Results In the static mode, the average gamma passing rate (GPR) using a 3% dose difference/3 mm distance to agreement criteria was 99.61% in Tomo and 99.35% in VMAT, which confirmed sufficient dosimetric accuracy in both IMRT methods. Figure 1 shows a comparison of GPRs calculated from DQA results in the Hexa-Motion mode between Tomo and VMAT. The calculated average GPR values based on the 3%/3 mm criteria were 90.93% in Tomo and 82.58% in VMAT, indicating that the dosimetric error under the motion conditions was relatively less in Tomo compared with that in VMAT. As shown in Figure 2, the GPR difference values of VMAT were larger in all the cases analyzed, indicating that Tomo had less dosimetric error than VMAT in the motion condition. The average GPR difference in Tomo was 8.68%, which was 8.09% lower than value of 16.77% in VMAT. A t-test was performed to verify whether statistically significant difference occurred in the degree of the GPR value decrease for Hexa-Motion between Tomo and VMAT. The calculated p-value for the GPR differences between Tomo and VMAT was 0.00018, which confirmed the statistical significance of the GPR difference.