ESTRO 2022 - Abstract Book

S726

Abstract book

ESTRO 2022

Our portal dosimetry 3D dose deviations increase with decreasing leaf distances used in complex RT plans. The very small segments can cause true underdosages due to calibration inaccuracies but might also decrease the accuracy of the portal dosimetry model that needs adjustment.

PD-0806 SGRT impact on 2D transit in-vivo dosimetry for breast cancer patients

C. Anson 1 , N. Jornet 1 , P. Gallego 1 , J. Pérez-Alija 1 , A. Latorre-Musoll 1 , N. García 1 , H. Vivancos 1 , M. Barceló 1 , A. Ruiz 1 , F. Leo 1 , P. Carrasco 1

1 Hospital de la Santa Creu i Sant Pau, Medical Physics, Barcelona, Spain

Purpose or Objective Surface-based image guided radiotherapy (SGRT) allows patient positioning and intrafractional motion monitoring. The aim of this study is to report the impact of introducing SGRT for breast cancer patients on the results of 2D transit in-vivo dosimetry (iVD). Materials and Methods In our centre there are one Clinac and three TrueBeam units, one of which provided with the optical SGRT system Align-RT (Vision-RT). The SGRT system is used for patient positioning using the postural video license, taking special attention to arms position as well as the affected breast. During the sessions of patients treated on the machine with SGRT capatilibty, to control intrafraction positioning differences, beam is used with a tolerance deviation of 5 mm in each radial direction and 3º for the three angular directions using Align-RT region of interest (breast). A total of 72 breast cancer patients were enrolled, 50% of them were treated in the unit with SGRT system (W SGRT) and the other 50% in the rest of the units from our centre (WO SGRT). For both groups transit EPID-based iVD was performed once a week when IGRT orthogonal kV-MV images were also acquired. EPID images were analysed automaticallly by PerFraction platform (SunNuclear) using local gamma criteria 5%,7mm, 5%5mm and 3%3mm and 30% threshold. Results A total of 1601 images from 276 fractions were available. Figure 1 shows iVD results for both groups. In-vivo dosimetry gamma rates were higher using SGRT for all the three gamma criteria evaluated. The results given by the percentage of points passing the gamma criteria in quartiles Q1, Q2 (median) and Q3 are respectively: - 5%,7mm gamma: 95.1%, 97.8%, 99.2% for W SGRT and 93.2%, 97.7%, 98.8% for WO SGRT - 5%5mm gamma: 93.5%, 96.4% and 98.4% for W SGRT and 88.5%, 95.7%, 97.9% for WO SGRT. - 3%,3mm gamma: 78.9%, 85.9% and 92.5% for W SGRT and 74.0%, 84.2% and 88.9% for WO SGRT.

Conclusion Real-time monitoring of patient surface and beam control during the whole treatment session accounts for higher in-vivo dosimetry gamma rates obtained using SGRT. This highlights an increase in treatment accuracy.

PD-0807 Clinical plan sensitivity to TPS parameters & complexity metrics that best capture this relationship

F. Brooks 1 , M. Glenn 2 , J. Pollard-Larkin 1 , R. Howell 3 , C. Peterson 4 , C.L. Nelson 5 , C.H. Clark 6 , S.F. Kry 3

1 MD Anderson Cancer Center , Radiation Physics, Houston, USA; 2 University of Washington, Radiation Physics, Seattle, USA; 3 MD Anderson Cancer Center, Radiation Physics, Houston, USA; 4 MD Anderson Cancer Center, Biostatistics, Houston, USA; 5 MD Anderson Cancer Center, Radiation Physics , Houston, USA; 6 University College London Hospitals NHS Foundation Trust, Radiotherapy , London, United Kingdom

Purpose or Objective