ESTRO 2023 - Abstract Book

S1742

Digital Posters

ESTRO 2023

1 GSI, Biophysics, Darmstadt, Germany; 2 Shanghai Proton and Heavy Ion Center, Medical Physics, Shanghai, China

Purpose or Objective 4D reconstruction and evaluation of the dose delivered in thoracic patients treated with pencil beam scanning(PBS) proton and carbon ion beams. Materials and Methods Thirteen plans of eleven patients (lung cancer and tracheobronchial adenoid cystic carcinoma) who were treated at our center were included. Clinically used scanning proton and carbon ion beam plans were generated by Syngo TPS based on average CT (phases: 20%-exhale, end-exhale, and 20%-inhale). 4D planning CT, daily breathing monitoring records, and gated treatment beam delivery records were collected for three proton and ten carbon plans. A total of 49 fraction-based 4D dose reconstructions were performed by using TRiP4D TPS. 4D accumulated dose metrics(D95% and D2%) for CTV on the end-exhale phase were compared with static plans recalculated by TRiP4D TPS. Motion amplitude of targets(MA), mean water equivalent range deviation(RD) of each field, and gamma between 4D and static doses (criteria 2%/2mm) was also analyzed.

Figure 1. Beam delivery sequence and gating signal. Patient motion amplitude is shown in black line, beam on/off signal is shown in red line. Red circle represents irradiated spots while black circle represents the corresponding motion states of each scanning spot. Results The mean values(SD) of Δ D95%, Δ D2% calculated between 4D dose and static dose were -1.9%(1.2%) and 0.9%(0.3%). The mean(SD) of MA and RD was 1.76 mm(1.26 mm) and 0.05 mm(0.64 mm). The mean(SD) gamma passing rate ( γ -PR) between the 4D dose and the static dose was 96.68%(2.51%). The motion-induced reduction of D95% per fraction was within -2.57% except for case 8. The Δ D95% of case 8 was -5.75%, and the corresponding target MA, RD, and γ -PR was 4.0 mm, 1.5 mm and 89.70%, which is also the worst among all evaluated cases. The Pearson’s correlation coefficients between Δ D95 and MA, between Δ D95 and RD, and between Δ D95 and γ -PR were –0.678, -0.669, and 0.750, respectively. Good agreement was found in the 4D dose among fractions.

Figure 2 Comparison of DVH curves for CTV between the static-dose and fraction based 4D-doses. Fraction doses are shown in dashed line, while static dose is shown in solid line.