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Comparison of Dosimetry Characteristic Between Brass Mesh Bolus and Tissue Equivalent Bolus (conventional Bolus)

J Gong

J Gong*, D Pavord, Vassar Brothers Hospital, Poughkeepsie, NY 12601

SU-E-T-268 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To compare the dose characteristic at surface and beneath between a mesh brass bolus and a conventional one, to determine equivalence between those two kinds of bolus.

Methods:Measurements were made with 6MV photons on a Varian 2100C linear accelerator using a PTW parallel plate chamber. Data were collected on surface and beneath by use of various layers of brass mesh bolus against various layers, 0.5 cm increment, conventional bolus at 100 SSD in a solid water phantom perpendicular to the beam central axis. The measurement had identical setup. Surface dose and PDDs were created.

Results:The surface dose is 15% lower using a mesh brass bolus compared with that using a conventional bolus. After 1.5 cm, the dose characteristic approaches the same for these two kinds of bolus. Our test also shows that three layers of the brass bolus has closest PDD profile to 0.5 cm conventional bolus. The different of the dose profile gets smaller at deeper. After 1.5 cm, they can be treated as equivalence(less 5% different). With a brass bolus, the percentage deep dose gets flatter from depth 0.8cm to dmax 1.5 cm.

Conclusion:Mesh bolus does escalate the surface dose. But it is not equivalent to a conventional bolus in the intended area. If we use it as alternate to tissue equivalent bolus material, we would jeopardize 15 % under dose on the skin. More data needs to reveal the long term biological effect using brass mesh bolus before we make a decision for its clinical application.

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