ESTRO 2024 - Abstract Book

S4307

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

ESTRO 2024

Inmaculada Navarro-Domenech 1 , Beatriz Deben 1 , Concepción Huertas 2 , Beatriz Sanchez 1 , Antonio Lozano 1 , Patricia Arroyo 1 , Daniel Camacho 1 , Carlos Ferrer 2 , Rosa Morera 1 1 Hospital UniversitarioLa Paz, Radiation Oncology, Madrid, Spain. 2 Hospital UniversitarioLa Paz, Department of Radiation Physics, Madrid, Spain

Purpose/Objective:

Hybrid magnetic resonance-guided linear accelerator (MR-Linac) systems allow for real-time adaptive radiotherapy. However, one of the main limitations is that they require more treatment time compared to conventional linear accelerators. We report our experience with treatment times in delivering radiation treatment and identify the factors that have the greatest influence on longer treatment times.

Material/Methods:

We conducted an analysis of treatment times in the first MR-Linac unit installed in Spain. Treatment times were collected prospectively and categorized into the following phases: acquisition time (from patient positioning to image acquisition for daily treatment adaptation), contouring time (including merging the reference plan with the current plan and contour adaptation), planning time (plan adaptation time), verification time (acquiring a new sequence prior to delivering the treatment to ensure no changes in patient positioning during other phases), and treatment time (irradiation time). The studied variables included diagnosis, radiotherapy technique, Planning Target Volume (PTV) volume, total dose, dose per fraction, and monitor units (MU). We analyzed these variables using summary statistics and descriptive analysis. Fisher's test was used for qualitative variables, and Pearson's Chi-square test was employed for categorical variables, with statistical significance set at p<0.05.

Results:

Ninety-one treatments for different locations were analyzed, as shown in Figure 1. The majority (69.2%) of treatments used stereotactic body radiotherapy (SBRT) technique, followed by hypofractionation (27.5%). The median total dose was 36.25 Gy (range 8 to 78.4 Gy), and the median dose per fraction was 7 Gy (range 2 to 20 Gy). The average PTV volume was 202 cc (range 2 to 1305 cc). The mean total time was 38 minutes (range 20 to 56), with acquisition time at 7 minutes (range 5 to 12), contouring time at 9 minutes (range 4 to 18), planning time at 8 minutes (range 4 to 18), verification time at 3 minutes (range 1 to 9), and treatment time at 11 minutes (range 4 to 23). The mean MU per fraction was 1894.5 (range 345 to 3806). Statistical significance was observed in various aspects of treatment times. Specifically, concerning the total time, diagnosis (p=0.03) played a role, with rectal cancer treatment requiring more time, while treatments for lymph node and bone metastases required less time. Additionally, PTV volume (p=0.03) and dose per fraction (p=0.04) showed significant impacts on total time. For acquisition time, smaller volumes were associated with longer times (p=0.03). Contouring time was significantly affected by PTV volume (p=0.01), particularly in cases of rectal tumours with larger volumes. In the planning phase, monitor units (MU) were a statistically significant variable (p=0.03). In the context of treatment time, diagnosis (p=0.003) was influential, with prostate and rectal cancer treatments requiring more time, whereas treatments for bone metastases and liver lesions required less time. Furthermore, total dose (p=0.02), dose per fraction (p=0.01), and MU (p=0.01) were significant factors affecting treatment time.

Figure 1.