S1698
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
Conclusion: This multicentre initiative demonstrates that standardized protocols combined with plastic scintillator detectors can provide reproducible benchmark data for small field dosimetry. TPS calculations generally underestimated measured doses, consistent with routine detector results. Extreme caution is required for fields smaller than 1 cm due to increased measurement and modelling
cross-checked with spectra generated by XSG and TASMIP software models. Dose-depth profiles for Al and PMMA were compared to determine equivalence (see Figure 1).
uncertainties References:
[1] Kerns, J.R., Followill, D.S., Lowenstein, J., Molineu, A., Alvarez, P., Taylor, P.A., Stingo, F.C. and Kry, S.F. (2016), Technical Report: Reference photon dosimetry data for Varian accelerators based on IROC-Houston site visit data. Med. Phys., 43: 2374- 2386. https://doi.org/10.1118/1.4945697 Keywords: small field dosimetry, scintillator, multicenter
Results: The total HVL obtained experimentally and via simulation was approximately 6.7 mm Al at 70 kV, confirming accurate spectral modeling. PENELOPE simulations closely reproduced the experimental dose-depth curves (Figure 1). The resulting Al-to- PMMA equivalence pairs showed small differences in absorbed dose, which increased slightly with thicker materials due to the detector’s limited radiotransparency. Overall, both experimental and simulated results indicated that Al layers can reliably reproduce the attenuation and dosimetric response of PMMA (Table 1).
Digital Poster 4876
Practical Optimization of kV Imaging in LINACs Using Monte Carlo Methods: Routine Replacement of PMMA by Aluminum ABEL RODRIGUEZ ARANDA 1 , ADRIAN ANDRADES 2 1 MEDICAL-PHYSICS, Lanzarote University Hospital, Arrecife, Spain. 2 Radiotherapy, Las Palmas University Hospital, Las Palmas, Spain Purpose/Objective: In quality assurance (QA) procedures for static kV imaging in linear accelerators (LINACs), polymethyl methacrylate (PMMA) blocks are commonly used as attenuating material. However, PMMA phantoms are heavy, difficult to handle, and not always available in clinical settings. The purpose of this study was to determine whether aluminum (Al), which is lighter and easier to manipulate, could replace PMMA while maintaining equivalent dosimetric behavior, thereby optimizing monthly imaging QA. Material/Methods: Two complementary approaches were applied:Experimental measurements: A standard X-ray tube was used with multiple Al and PMMA thicknesses, along with a UNFORS XI Platinum Plus ionization chamber-electrometer system. The inherent and added half-value layers (HVL) were measured at 70 kV to define the beam spectrum. The detector was placed at 100 cm from the focal spot, and doses were recorded for each PMMA thickness. Equivalent Al thicknesses were then determined by matching the same dose levels obtained with PMMA.Monte Carlo simulation: The experimental setup was reproduced using PENELOPE to validate and extend the findings. Simulations incorporated the measured HVL and were
Conclusion: This study demonstrates that aluminum can effectively replace PMMA for routine QA and static kV imaging calibration in LINACs, significantly simplifying setup
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