ESTRO 2023 - Abstract Book

S248

Saturday 13 May

ESTRO 2023

Conclusion For patients breaching RD thresholds on SS, mean RD was reduced on rescan pCT, however reduction (including all measuring points) was <4mm in both directions. A trend for these patients to sustain a larger rectum throughout treatment was seen, suggesting rescanning may be of limited use. Especially so for 6# patients where mean RD on CBCT was more akin to the rejected SS. This finding may be indicative of the 6# patient group, they are often older with more co-morbidities, both factors known to influence rectal filling. PD-0313 Time analysis of CBCT-guided online adaptive radiotherapy in Prostate cancer treatment workflow C. Votta 1 , A. Boschetti 1 , M. Aquilano 1 , F. Catucci 1 , A. D'aviero 1 , P. Gaias 1 , F. Gruosso 1 , M. Iezzi 1 , M. Marras 1 , S. Menna 1 , D. Piccari 1 , E. Pilloni 1 , D. Piro 1 , F. Preziosi 1 , F. Quaranta 1 , A. Re 1 , N. Ulgheri 1 , V. Verusio 2 , V. Valentini 3 , D. Cusumano 1 , G.C. Mattiucci 1 1 Mater Olbia Hospital, Radiotherapy, Olbia, Italy; 2 Università Cattolica del Sacro Cuore, Istituto di Radiologia, Roma, Italy; 3 Fondazione Policlinico Universitario A. Gemelli IRCCS, Diagnostica per Immagini, Radioterapia Oncologica ed Ematologia, Roma, Italy Purpose or Objective Since August 2021, cone-beam computed tomography (CBCT) -guided online adaptive radiotherapy (oART) is one of our department's treatment options for prostate cancer patients. Different studies show that oART leads to significant dosimetric advantages, both in terms of target coverage and in terms of OAR’s dose sparing. However, the additional steps required for oART can significantly prolong the total treatment time and pose a challenge for day-to-day clinical implementation. This study aimed to evaluate the timing of oART compared to standard non-adaptive radiotherapy (non- ART) in prostate cancer treatment. Materials and Methods A total of 36 prostate cancer patients were treated between August 2021 and September 2022, using Ethos therapy (Varian Medical Systems, Palo Alto, CA, US). All patients were treated with a dose of 67,5 Gy in 25 fractions to the prostate and seminal vesicles; for patients with nodal involvement, an additional total dose of 50Gy was given to the nodes using a simultaneous integrated boost. The total treatment session time (Ttot) was evaluated as the time elapsed from the patient's entry into the bunker to his exit. The time required for the following workflow steps was prospectively documented: patient entry and set-up(Ts), CBCT acquisition and matching (Tm), delivery and exit (Td). For the oART treatment sessions, the CBCT acquisition and contouring (Tc) and planning time (Tp) was also recorded. Results In total, 676 fractions were evaluated: oART were used in 223 (33%) treatment fraction. The mean Ttot for non-ART treatments was 0:12±0:04 (hh: mm). For oART treatments, the Ttot difference was statistically significant (p<0,05) between treatment plans with (oARTn) and without nodes (oARTp); in particular the mean Ttot for oARTp was 0:24±0:06 and the mean Ttot for oARTn was 0:30±0:06 (Figure 1). Time statistics of the different workflow steps are provided in Figure 2. In oART, we spent most of the time on contouring review and manual adjustments with a mean Tc of 0:12±0:04 for oARTn and 0:09±0:04 for oARTp.

Figure 1. Box plot time distribution of Total treatment time