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  4. The Dosimetric Uncertainty of Assigning Wrong Material of Hip Prosthesis for RA Plan of Prostate with the Eclipse AcurosXb Algorithm

The Dosimetric Uncertainty of Assigning Wrong Material of Hip Prosthesis for RA Plan of Prostate with the Eclipse AcurosXb Algorithm

S Pokharel*, 21st Century Oncology, Naples, FL

Presentations

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

Room: AAPM ePoster Library

Purpose: To quantify the dosimetric uncertainty of assigning wrong material to Eclipse AcurosXB algorithm


Methods: A prostate case (50.4 Gy, 28 fractions) with bilateral hip prostheses has been chosen for this study. All relevant structures including prostheses and artifacts were contoured and assigned appropriate densities. RA plans with two full arcs without any avoiding sectors were designed by assigning prosthesis material first as a stainless steel and then as a Titanium. Plans were optimized with and without dose reduction objective to the prosthesis, other objectives being same and calculated using Eclipse AcurosXB algorithm (versions 15.6.03). Plans were normalized such that 95% of target volume received 100% of prescription dose.

Results: Significant differences were observed in PTV (minimum, maximum and mean), bladder (V30, V50 and mean) , Rectum (V30, V50 and mean) and Penile Bulb mean dose with the change in prosthesis material and dose reduction objective to it. There was a significant change in PTV (minimum, maximum) dose when optimized with Titanium and calculated as Stainless Steel or vice versa as compared to optimized and calculated with the same material. Other dosimetric indices remain essentially the same.


Conclusion: Selection of correct material and dose reduction objective to prosthesis material is very important for accurate and optimal dose calculation by AcurosXb algorithm. 3 to 5% of under-dosing or overdosing were observed with the selection of wrong material. The best strategy to create a RA plan is to select the correct material and dose reduction objective to prosthesis material. If the material has to be changed , it has to be reoptimized as well. If the prosthesis material is unknown, it is advisable to avoid beam entrance through prosthesis material. This however will result in increase of dose to the other critical structures.

Keywords

Dosimetry

Taxonomy

TH- External Beam- Photons: IMRT/VMAT dose optimization algorithms

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