ESTRO 2024 - Abstract Book

S4374

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

2704

Digital Poster

EBH abdominal SBRT: inter- and intrafraction motion using two commercial monitoring systems

Cristina Ansón 1 , Pablo Carrasco 1 , Sonia Bermejo 2 , Jessica Jimenez 2 , Noé Ventosa 2 , Josep Balart 2 , Núria Jornet 1 , Pedro Gallego 1 , Jaime Pérez-Alija 1 , Natalia Tejedor 1 , Helena Vivancos 1 , Agustín Ruiz 1 , Marta Barceló 1 , Fátima Leo 1 , Alejandro Domínguez 1 , Víctor Riu 1 , Gemma Sancho 2 1 Hospital de la Santa Creu i Sant Pau, Medical Physics, Barcelona, Spain. 2 Hospital de la Santa Creu i Sant Pau, Radiation Oncology, Barcelona, Spain

Purpose/Objective:

The aim of this study is presenting our initial experience in using SGRT in combination with IGRT for patient positioning and monitoring during abdominal SBRT treatments in expiration breath-hold (EBH). In addition, we compare the analysis of inter and intra-fraction set-up errors using the 3D surface mapping with SGRT versus a reflecting block.

Material/Methods:

Twelve patients with pancreatic or hepatic tumors treated in EBH with SBRT technique in 3 and 5 fraction schemes were included in the study. Treatment plans consisted of 2 10X-FFF VMAT arcs delivered in a TrueBeam unit (Varian).

Six of them were monitored using Align-RT SGRT system with Real-Time Coach (RTC) visual feedback system (group A) and 6 using RSGC Varian reflecting block with Visual Coach Device (VCD) feedback system (group B). The initial set up was performed using SGRT and tattoo marks for groups A and B respectively, followed in both groups by a CBCT (pre-CBCT) applying six-degree table corrections. Additional CBCTs were performed between the 2 treatment arcs (mid-CBCT) and at the end of the treatment session (post-CBCT) for both groups. Six-degree shifts from the CBCT’s online registration were recorded to assess inter- and intrafraction motion. The tolerances used for the real-time deltas (RTD) in Align-RT were ±1.5 mm for VERT; ±2 mm for LAT, LNG, MAG and ±2º for ROT, PITCH and ROLL. The gap amplitude used in RSGC system was set to 3 mm.

Results:

Shifts from the CBCT’s registration are shown in figure 1 and figure 2.

Interfraction motion (pre-CBCT) resulted smaller for group A (SGRT) than group B (tattoos, reflecting block) in all directions. The mean of the translation vector magnitude was 0.42(SD 0.10) cm for group A and 1.0(SD 0.41) cm for group B. Shifts resulting from the mid-CBCT and post-CBCT registration showed a lower intrafraction motion for patients of group A (SGRT). The mean of the translation vector magnitude was 0.21(SD 0.20) cm and 0.07(SD 0.16) cm for group A meanwhile for group B was 0.39(SD 0.25) cm and 0.43(SD 0.21) for mid-CBCT and post-CBCT respectively.