ESTRO 2023 - Abstract Book

S727

Monday 15 May 2023

ESTRO 2023

Figure 1: (1) and (2) are the cumulative planned and delivered doses in XY plane. (3) and (4) are the cumulative planned and delivered doses on YZ plane. (5) and (6) present the gamma-index and the dose difference contribution in XY. (7) shows the passing rate of the spills. The system has been tested in silico on a virtual XCAT 4DCT, with a simulated data stream from the DDS for dose reconstruction. For verification of advanced motion mitigation strategies, we designed RIDOS to be compatible with the recently developed MultiPhase 4D delivery (MP4D). Results The framework successfully achieved the FDC in less than 3 s, i.e., it would enable a delivered dose update during the spill pause. The overall computation time required per spot was ~ 2 ms, where ~ 6 µ s were attributed to raytracing for computing water equivalent depths, the dose calculation took ~ 1.7 ms. The dose warping to the reference motion phase was done once per spill and took ~ 300 µ s. The processing time of gamma-index comparison between the cumulative planned and delivered dose after the spill was of about 0.2 seconds. Both, the real-time calculated planned and delivered doses, were also validated against a research TPS (TRiP98) log-file based dose reconstruction (Fig. 2), showing good agreement with gamma-index passing rate (3mm/3%) > 98%.

Figure 2: Example of TRiP and RIDOS dose distributions in XY.

Conclusion We demonstrated the feasibility of a real-time dose calculation with clinically acceptable precision. The next step will involve experimental tests with carbon and proton beams at the CNAO facility, as well as consideration of more patient data, with variable motion and motion mitigation strategy. In the future, this framework will open the door for possible real-time adaptive particle therapy workflows. Project funded by the Horizon 2020 program, grant agreement N. 955956 (RAPTOR). MO-0880 Early experiences with CBCT-based online adaptive radiotherapy in cervical carcinoma G. Razinskas 1 , S. Wegener 1 , R. Schindhelm 1 , F. Exner 1 , S. Weick 1 , M. Zimmermann 1 , B. Polat 1 , M. Flentje 1 , J. Tamihardja 1 1 University Hospital Wuerzburg, Department of Radiation Oncology, Wuerzburg, Germany Purpose or Objective The Varian ETHOS system enables online adaptive radiotherapy (oART) based on CBCT with daily AI-assisted adaption of the treatment plan to the anatomy of the day. Most clinical treatments focused on the pelvic region in entities like prostate, bladder and anal cancer (Calmels et al. 2022). Cervical cancer is another challenging target for oART due to significant interfractional changes in the position of the uterus and tumor shrinkage and secondly due to changes of rectum and bladder filling. Here, we report the first institutional experiences with cervical cancer oART on the ETHOS system. Materials and Methods Five patients with cervical cancer have been treated with primary chemo-radiotherapy. In total 124 oART fractions between March 2022 and October 2022 have been applied. Treatment of the cervical cancer and the pelvic lymph drainage was prescribed with 25 to 28 fractions, with two patients receiving a homogeneous PTV dose of 1.8 Gy, while three patients received a simultaneous integrated boost to pelvic lymph node metastasis with a second dose level of 2.2 Gy. Additionally, patients received a brachytherapy boost to the primary tumor. Comparison of originally scheduled and online-adapted plans