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Evaluation of a Commercial Tungsten Eye Shield for Orthovoltage Beams Using Gafchromic Film

M Shafiq ul Hassan1, H Chen1*, J Bond1, D Allen1, Z Chen1, (1) Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, Connecticut, USA


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To evaluate the dose behind a commercial tungsten eye shield for Orthovoltage x-ray beams and compare it with the existing tungsten eye shield used in our clinic.

Methods: Medium sized tungsten eye shields, with external diameters of 23 mm (new vendor) and 19.1 mm (existing), were evaluated. Eye shields were placed on squared pieces of Gafchromic films in the central axis of the field on the surface of 10 cm thick solid water block (30x30cm2). Films were exposed with and without eye shield for 120 kV, 250 kV energies combined with three different filters and with collimated field sizes (FS) of 5x5cm2, 10x10cm2 and glass cone (4-cm diameter), respectively. Source to skin distance (SSD) for collimated field size and glass cone were 50 cm and 30 cm respectively. Gafchromic film was calibrated with respective Orthovoltage x-rays and acquired films were analyzed using FilmQA Pro software. Doses were calculated and compared for the two sets of eye shields.

Results: For 120 kV (Filter1, HVL = 4.2 mm Al), doses were 11% and 16.5% for both eye shields at 5x5cm2 and 10x10cm2 FS, respectively. For 250 kV (Filter 2, HVL = 0.54 mm Cu), doses for 5x5cm2 were 11% and 13% for the new and existing shields, respectively, while doses for 10x10cm2 were about 20% for both eye shields. For 250 kV (Filter 6, HVL=1.85mmCu), doses were about 12% for both shields for 5x5cm2, and for 10x10cm2, doses were 13.6% and 18.4% for the new and existing shields. For 120 kV with 4 cm Glass Cone (HVL = 2.1 mm Al), doses were 6.5% for both eye shields.

Conclusion: Doses behind the new internal eye shield were similar as the existing eye shield for most energies with different filter combinations. It can be used safely to replace the existing eye shields.

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