S2092
Physics - Image acquisition and processing
ESTRO 2026
(l-TL) and lower action limits (l-AL) according to the AAPM TG-218 [2]. Material/Methods: A dataset of 30 patients undergoing whole-breast IMRT in DIBH was analysed. Each treatment was characterized by hypofractionation with a dose of 2.67 Gy across 15 fractions. Patient setup was performed using surface-guided radiation therapy (SGRT) and then verified with 2D portal imaging. For each fraction, starting from the second one, EPID images were acquired and analysed using the EPID-IVTD methodology, expressed in terms of gamma passing rate (GPR). Global 3%/5 mm criterion with a 10% dose threshold was used. The first delivered fraction was used as the reference image for all subsequent comparisons. l-TL and l-AL values were then derived for routine clinical monitoring purposes. Results: The maximum, mean, and minimum GPR values were 100%, 97.55%, and 77.4%, respectively. The calculated l-AL and l-TL were 86.53% and 90.98%, respectively. Among all data, 3.13% of GPR values were below l-AL, 4.17% were between l-AL and l-TL, and 93.14% were above l-TL. The figure presents the results of EPID- IVTD analysis, shown as a histogram of the GPR values obained from the gamma analysis. Conclusion: The EPID-IVTD method, previously applied to free- breathing breast treatments [1], proved suitable for monitoring the quality of DIBH IMRT treatments as well. The l-AL and l-TL represent practical alert and alarm thresholds for identifying potential deviations in treatment delivery. Further investigations are ongoing to better understand the origin of low GPR values, with a particular focus on inter-fraction patient setup variations. References: [1] Zirone, Lucia, et al. "In vivo transit dosimetry methodology for whole breast intensity modulated radiation therapy." Journal of Applied Clinical Medical Physics 26.5 (2025): e70072.[2] DENG, Jia, et al. Evaluating AAPM - TG - 218 recommendations: Gamma index tolerance and action limits in IMRT and VMAT quality assurance using SunCHECK. Journal of Applied Clinical Medical Physics, 2024, 25.6: e14277. Keywords: in vivo transit dosimetry, DIBH, Breast
Halcyon IR 6s (2.9), Halcyon IR 60s (2.0), and conventional TrueBeam (1.7). A moderate inverse correlation (R ² =0.45) was observed between image noise and contouring confidence, indicating that lower noise levels were associated with higher confidence in contouring OARs (Figure 2B).
Conclusion: Observer confidence was related to image noise, as quantified by the SD of CT numbers. HyperSight CBCT scans acquired with a 6-second protocol and IR reconstruction led to lower image noise and higher contouring confidence compared to longer acquisition protocols and conventional TrueBeam CBCT scans. Keywords: cone-beam CT imaging, contouring, lung cancer EPID-IVTD for Breast IMRT in DIBH: Evaluation of Feasibility and Determination of Lower Tolerance Limits Martina Pace 1 , Bonanno Elisa 1 , Giuseppina Rita Borzì 1 , Nina Cavalli 1 , Andrea Girlando 2 , Sara Panebianco 1 , Giuseppe Stella 3 , Lucia Zirone 1 , Carmelo Marino 1 1 Medical Physics department, Humanitas Istituto Clinico Catanese, Misterbianco, Italy. 2 Radiotherapy department, Humanitas Istituto Clinico Catanese, Misterbianco, Italy. 3 Physics and Astronomy Ettore Majorana, University of Catania, Catania, Italy Digital Poster Highlight 4451 Purpose/Objective: In vivo transit dosimetry using an Electronic Portal Imaging Device (EPID-IVTD) represents an effective approach for verifying the accuracy of radiotherapy delivery. In a previous study [1], we developed and clinically implemented a standardized EPID-IVTD method for whole-breast IMRT treatments performed under free-breathing conditions. The aim of the present work is to apply the same methodology to breast IMRT treatments delivered under deep inspiration breath-hold (DIBH) conditions, in order to evaluate its feasibility and to establish lower tolerance
Made with FlippingBook - Share PDF online