ESTRO 2024 - Abstract Book

S4043

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

1 K.E.I. Deurloo, R.J.H.M. Steenbakkers, L.J. Zijp, et al. Quantification of shape variation of prostate and seminal vesicles during external beam radiotherapy. Int J Radiat Oncol Biol Phys, 2005; 61 228-238.

2 Lucy Kershaw , Laila van Zadelhoff , Wilma Heemsbergen et al. Image Guided Radiation Therapy Strategies for Pelvic Lymph Node Irradiation in High-Risk Prostate Cancer: Motion and Margins. Int J Radiat Oncol Biol Phys. 2018; 100(1): 68-77.

1553

Digital Poster

An in-vivo dosimetry clinical decision model for adaptive radiotherapy of nasopharyngeal carcinoma

Long Yang, Zhenhao Li, Jiazhou Wang, Weigang Hu

Fudan University Shanghai Cancer Center, Department of Radiation Oncology, Shanghai, China

Purpose/Objective:

Adaptive Radiation Therapy (ART) could adjust the treatment plan based on changes in patient anatomy and tumor location continuously and improve treatment accuracy. However, current trigger indicators for ART used in clinical practice do not reflect the issues that clinicians concerned. This study aims to develop a clinically and anatomically relevant online patient QA solution and determine trigger indicators for ART using daily CT scans and EDID-based in vivo dosimetry.

Material/Methods:

54 fractions from 11 patients with nasopharyngeal cancer treated with IMRT at our center were enrolled. The 2D in vivo dose distribution was obtained through EPID to generated 3D dose distribution by using a reconstruction algorithm. Automatic segmentation was used to get OARs, and PTVs were recontoured by an experienced physician in daily CT. The dose-volume indices were calculated, then the percent deviations between the reconstructed dose distributions and original plans were determined, while the 95% interval of them were seen as range for tolerance levels. Finally, our QA solution was validated on an additional 6 clinical patients.

Results:

In nasopharyngeal cancer, the tolerance range of the QA metrics for ΔD95, ΔD2, ΔDmean of PTV-C were [- 4.13%,0.35%], [-1.40%,1.85%], [-2.51%,1.27%], for ΔD95, ΔD2, ΔDmean of PTV-LN66 were [-4.65%,0.10%], [- 2.47%,1.75%], [-0.65%,2.63%], for ΔD95, ΔD2, ΔDmean of PTV-60 were [-0.82%,-8.26%],[-1.89%,1.34%],[- 0.2.88%,0.60%], for ΔD95, ΔD2, ΔDmean of PTV-54 were [-0.82%,-6.87%],[-1.62%,3.45%],[-6.08%,0.66%]. In validation, the 71% of all patients' treatment fractions had one or fewer indicators outside the tolerance range, and 7% had four or more indicators outside the tolerance range while we need to action when four or more indicators are out of tolerance range.