S1960
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Keywords: HyperSight, Monte-Carlo dose calculation
radiotherapy treatments is a common practice to account for anatomical changes during the treatment course. A high-performance imaging system like HyperSight offers improved image quality, enhanced SNR and an enlarged FOV compared to conventional CBCT systems. This work investigates the suitability of using HyperSight CBCTs installed on C-arm linacs for offline plan adaptation. Material/Methods: Calibration measurements for 1 Siemens Definition CT, 2 Varian Truebeams equipped with a HyperSight CBCT and 6 TrueBeams with conventional on-board imaging platforms were performed. The calibration curve for the CBCTs was defined as the arithmetic mean-value of the measurements for each imaging device and the accuracy of each imaging system was quantified with a CIRS phantom-study using 5 inserts composed of known materials (lung, adipose, muscle, cartilage and bone). Three head and neck cancer cases were identified prospectively. In each case, a minimum of one conventional and one HyperSight CBCT-scan was acquired during the first treatment week. Subsequently both CBCTs were deformably registered to the geometry of the planning CT and the treatment plan was calculated on all image sets using both Acuros XB (AXB) and full-scale MC-calculations with the PENELOPE-based MC-system PRIMO. For benchmarking purposes, a Gamma-analysis (global 1%/1 mm) was performed comparing the resulting AXB and PRIMO dose distributions for each imaging system. Finally, the PRIMO-calculated dose distributions computed on the different CBCT imaging systems was evaluated against the treatment plan calculated on the planning CT. Results: Differences in HU-accuracy between the conventional (HyperSight) CBCT and planning CT was on average 37 units (15 units) with the largest discrepancies found for high-density materials. The lowest gamma pass- rate for benchmarking was 99 % comparing each CBCT modality-pair. Dose-differences for target volumes and OARs between conventional (HyperSight) CBCT and CT were generally within ± 1 % while dose discrepancies > 2 % was found for only 6 (9) out of 52 scored structures. Conclusion: The discrepancy between HyperSight- and CT-acquired HU-values was lower than between conventional CBCT and CT. Preliminary results indicate the comparability between MC-calculated dose distributions on CBCT (conventional and HyperSight) and CT. However, HyperSight provides other benefits, which further qualifies its use in adaptive radiotherapy. Due to the small differences observed in MC-calculated dose distributions between the different modalities, 15 patients are under calculation and evaluation to increase the study power.
Digital Poster 3904
Optimizing radiotherapy of whole breast with simultaneous integrated boost: a comparative evaluation of 3D-CRT vs. VMAT and hybrid techniques Gracinda Johansson 1,2 , Rafat Kojoj 1 , Sewa Surdashi 1 , Emil Fredén 1 , Martin Olin 1 , Eija Dahl 3 , Camilla Wendt 3 1 Medical physics, development and technology, Södersjukhuset, Stockholm, Sweden. 2 Department of clinical science and education, Karolinska Intitutet, Stockholm, Sweden. 3 Department of Oncology, Södersjukhuset, Stockholm, Sweden Purpose/Objective: This study aims to evaluate the performance of VMAT and hybrid techniques in radiotherapy (RT) of the whole breast (WB) with simultaneous integrated boost (SIB). Material/Methods: Ten left-side breast cancer patients that previously received RT for WB with SIB in our institution were selected. These patients underwent planning CT in deep inspiration breath hold. Clinical plans were created in Monaco TPS (Elekta AB, Stockholm, Sweden), using tangential field-in-field (FiF) 3D-CRT technique. VMAT and hybrid plans were retrospectively created. VMAT plans were created using two fields with 3 partial arcs and the hybrid plans were created by combining a FiF for the WB and a VMAT field for the boost(Figure 1). The prescription dose was 2.67 Gy for WB and 3.20 Gy for the boost given in 15 fractions to total dose of 40.05 Gy and 48.0 Gy, respectively. Plan evaluation was made in terms of target dose-coverage and dose-volume (DV) metrics for the OARs, according to our clinical guidelines. The conformity index (CI) to the boost PTV and the NTCP for the heart (late cardiac morbidity) [1], were evaluated across the modalities. A two-sided Wilcoxon signed-rank test with a significant level of 0.05 was carried out.
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