ESTRO 2025 - Abstract Book

S2718

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

Conclusion: Automated plan generation with our tool yielded high-quality treatment plans within a fraction of typical planning times, allowing for increased efficiency and standardization of the planning process.

Keywords: automation, DVH prediction, plan challenge

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Digital Poster Dose increase to eyelid from backscatter due to a use of a tungsten eye shield in a 6 MeV electron beam George X Ding Radiation Oncology, Vanderbilt University, Nashville, USA Purpose/Objective: To protect the lens and cornea of eye when treating the eyelid, an eye shield made of tungsten and aluminum is often used in the total skin electron radiation therapy (TSET). The 2 mm tungsten eye shield is recommended for used for 6 MeV electron beams. The user will need to determine an acceptable amount of backscatter to decide whether to use a commercially available thinner or thicker aluminum cap as shown in Figure 1. It is important to know the amount of dose increase due to the backscatter from a tungsten eye shield when a different thickness of an aluminum cap is used because it is a challenging task to put it under eyelid especially when a thicker aluminum cap is used. Using the Monte Carlo simulation this study evaluates the dose enhancement to eyelid from backscatter as a function of the aluminum cap thickness from 0 to 2 mm.

Material/Methods: The Monte Carlo Simulations are performed using the EGSnrc system with user code BEAMnrc/DOSXYZnrc[1] for generating a 6 MeV beam and dose calculations. The accuracy of the simulated 6 MeV electron beam was previously validated against measurements[2]. Results: Figure 2 shows the dose variations without and with a 2 mm eye shield with different thickness of aluminum cap thickness resulting from a 6 MeV electron beam incident on water phantom where 2 mm thick tungsten starts at 6 mm and ends at 8 mm; 1 mm aluminum thick starts at 5 mm and ends at 6 mm; and 2 mm thick aluminum starts at 4 mm and ends at 6 mm. The incident electron beam field size and SSD are 10x10 cm 2 and 100 cm respectively. The size of layers of aluminum and tungsten slabs are 19x19 mm 2 in the direction that is perpendicular to the beam central axis. The doses are normalized to the maximum dose without the eye shield. It is seen that the dose enhancement from the backscatter is clinically significant ranging from dose increase of 28%, 42% and 50% for including 2 mm aluminum, 1 mm aluminum and no aluminum cap respectively.