S1795
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
algorithm requires a monotonically increasingCT number-mass density curve, the materials Bone 50% and Bone 20% of the Catphan were not included in the calibration. On the other hand, a postal audit of the CT number calibration was conducted. Details of this audit are described by Nakao et al.1,2 It uses a water- equivalent phantom including a tough lung, a tough bone and a water plug. A stoichiometric CT number calibration with this phantom was reported by the audit institute. Simulation CT scans of 10 patients were selected from our database (prostate, head and neck, breast, lung and brain). No patients had prostheses or metal implants in the region of interest. For each one, a clinical plan was calculated using three CT number- mass density calibration curves: 1) curve reported by the audit institution (Curve_AUDIT), 2) curve based on the Catphan phantom (Curve_CTP), and 3) stoichiometric CT number calibration derived from the Catphan phantom (Curve_STOICH). The three plans calculated for each patient kept the same monitor units and field fluences, i.e., only the CT number-mass density calibration curves were changed for each calculation.Values of D2%, D50% and D98% for the planning target volume (PTV), and D2% and D50% for the organs-at-risk (OARs) were collected for the three plans computed for each patient. Dx% is the absolute dose to x% of the volume. For each metric, the Dx% values obtained using the Curve_CTP and Curve_STOICH were compared against the corresponding Dx% values obtained using the Curve_AUDIT. Percent differences in absolute values ( ∆ ) were reported. Results: Figures 1 and 2 show the absolute percent differences ( Δ ) for each metric. The symbol × denotes the average value in the plots. Average differences of ≥ 1.5% were obtained when using Curve_CTP, while differences were within 0.2% when using Curve_STOICH.
Conclusion: Delineation systematic uncertainties obtained in this study are compatible with values reported in the literature.5 Such uncertainties should be considered for the planning target volume margin. The script developed by Dupont et al is a valuable tool to assess the target delineation uncertainty on multiple CBCT images. References: 1 Pract Radiat Oncol. 2022 Mar-Apr;12(2):e144-e152.2 Phys Med. 2024 May:121:103368)3 Med Phys. 1999
Jun;26(6):931-404 Semin Radiat Oncol. 2004 Jan;14(1):52-64.5 Semin Radiat Oncol. 2005 Jul;15(3):136-45. Keywords: prostate, SBRT, adaptive
Digital Poster 53 Dose calculation accuracy using a CT number calibration curve created using a stoichiometric CT number calibration method JUAN-FRANCISCO CALVO-ORTEGA 1,2 , MINORU NAKAO 3,4 , SANDRA MORAGUES-FEMENIA 1 1 RADIATION ONCOLOGY, HOSPITAL QUIRÓNSALUD BARCELONA, BARCELONA, Spain. 2 RADIATION ONCOLOGY, HOSPITAL QUIRÓNSALUD MÁLAGA, MÁLAGA, Spain. 3 Department of Radiation Oncology, Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan. 4 Department of Radiation Oncology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan Purpose/Objective: To investigate the accuracy of the dose calculation performed by a treatment planning system (TPS) using a CT number-mass density calibration curve obtained with a stoichiometric method. Material/Methods: The Acuros XB v. 16.1 algorithm (dose-to-medium) of the Eclipse TPS is used in our department for clinical dose calculations. A general protocol was established in a GE Optima 660 CT scanner for radiotherapy patient simulation. A CT number-mass density calibration curve was created for this protocol using the commercial Catphan 604 phantom. As the Acuros
Made with FlippingBook - Share PDF online