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Software to Evaluate the Effect of Applicator Translations and Rotations On HDR Plans

M Bakhtiari

M Bakhtiari*, J Schmitt, k zarkoob, V Aroumougame, M Sarfaraz, J Rodgers, RadAmerica, LLC--MedStar Health, Baltimore, MD 21237

SU-E-T-688 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: The rotation and translation of the catheters used in High Dose Rate (HDR) brachytherapy can potentially change the dosimetric outcome of the intended treatment plan. Geometric verification performed before each fraction are not adequate. Tools and techniques should be developed that evaluates the change in dose distribution for possible rotations and translation of the catheters before each treatment.

Methods: A software program was developed that imports the treatment planning systems dicom files, rotates and translates the device based on the values provided by the user, and recalculates the dose distribution in the patients structures. A TG-43 formalism was used to calculate the dose distribution. The program evaluates the dose to selected critical structures to determine if re-planning is necessary. A variety of clinical cases including strut-adjusted volume implant (SAVI), MammoSite, Cantura, Tandom and Ovoids, Cylinder, and skin applicators were studied.

Results: SAVI cases appeared to be the most sensitive to rotations depending on the distance of the chest wall or the skin from the closest dwell position and also to the dwell times. For SAVI cases where the skin or chest wall are at a distance larger than ~1.5 cm from the closest dwell position, the effect of any degree of rotation results in a dosimetric deviation of less than 5%. On the other hand for the cases where the skin is closer than ~1.5 cm from the closest dwell position, a small rotation of 10 degree in some cases results in over dosing as large as 50% to the skin.

Conclusion:The complexity of the plans in SAVI cases leads to a nonlinear dependence of the dosimetric outcome versus amount of rotation and/or translation.

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