Program Information
Experimental Validation of a VMAT Planning Technique for Patients with Hip Prosthesis
M Milette1*, L Sporn2 , M Robinson1 , (1) BC Cancer Agency - Centre for the Southern Interior, Kelowna, BC, (2) University of British Columbia, Vancouver, BC
Presentations
SU-G-BRC-9 (Sunday, July 31, 2016) 4:00 PM - 6:00 PM Room: Ballroom C
Purpose: To validate and evaluate the dosimetric accuracy of two different VMAT planning techniques for patients with hip prosthesis of unknown composition.
Methods: A phantom was designed to model a patient with one stainless steel hip prosthesis. PTVs and critical structures contours were copied from a prostate cancer patient. Simultaneous integrated boost VMAT plans covering the prostate and pelvic lymph nodes (50.4Gy and 70Gy in 28 fractions) and sparing the rectum and bladder were generated in Eclipse using AAA dose calculation. Our clinical dose constraints were used for PTV coverage and rectum and bladder sparing. Three VMAT plans were generated. First an unconstrained plan (UN) was created. Two other plans reducing the entrance dose through the prosthesis were developed: a plan using avoidance sector (AV) and a plan with maximum dose constraint on the hip prosthesis (MP). The three plans were measured with gafchromic EBT3 film and analyzed with FilmQAPro software.
Results: The three VMAT plans resulted in an average gamma 2%/2mm of 48.8%, 95.4%, 98.4% (UN, AV and MP plan respectively) and an average gamma 3%/3mm of 76.3%, 99.7%, 99.9% (UN, AV and MP plan respectively). The avoidance sector plan exhibited higher measured doses of up to 3% of the prescription dose at the prosthesis interface. The plan with constraints on the prosthesis showed excellent agreement at the prosthesis interface.
Conclusion: For the phantom presented in this study, VMAT plans with a maximum dose constraint on the prosthesis resulted in best agreement with measured doses.
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