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Program Information

Varian Surface Applicator Leakage Measurements

M Talmadge

M Talmadge*, P Halvorsen , I Iftimia , Lahey Clinic, Burlington, MA


PO-BPC-Exhibit Hall-18 (Saturday, March 5, 2016)  Room: Exhibit Hall

To experimentally quantify the magnitude and extent of leakage radiation surrounding the Varian Surface Applicators (Varian Medical Systems, Palo Alto, CA) when loaded with an Ir-192 high dose rate source.

Peripheral measurements were made using Gafchromic EBT3 film (Ashland Inc., Wayne, NJ) as well as Optically Stimulated Luminescent Dosimeters (OSLD) (Landauer Inc., Glenwood, IL) and compared to the predictions of the Varian Acuros BV treatment planning system (Varian Medical Systems, Palo Alto, CA). The OSLD system was calibrated using 6MV x-rays whereas the film-based measurements were normalized linearly based the film’s response at a prescription depth of 4mm as the absolute dose at this point was validated during commissioning. All measurements were made using a single source dwell position at 15mm from the distal end of the source path, consistent with clinical use.

Given the inherent uncertainties presented by large dose gradients around the applicator, the measured results are in reasonably good agreement with those predicted by the treatment planning system; however, the film measurements indicate that the spatial extent of the leakage radiation field around the applicators may be greater than that predicted by the treatment planning system.

There is non-negligible leakage radiation surrounding the proximal portion of the Varian Surface Applicators that should be taken into account during clinical use when evaluating potential dose to nearby tissues that may be in the proximal direction along the source path relative to the treatment-surface.

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