Program Information
Comparison Between the Dose Distribution for Original Hip Prosthesis and Indigenously Designed Bone Phantom
S Singh1*, K Jassal2 , K Vittal3 , s osman4 , S pal5 , (1) fortis memorial research institute, Gurgaon, haryana, (2) Fortis Memorial Research Institute, Gurgaon, ,(3) Fortis Memorial Research Institute, Gurgaon, Haryana, (4) Fortis Momerial Research Institute, Gurgaon, Haryana, (5) RML, Lucknow, Lucknow, Uttar Pradesh
Presentations
SU-I-GPD-T-443 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To compare the dose distribution on femoral head of prosthesis and bone replica of gypsum embedded in a cylindrical wax phantom.
Methods: Two different wax phantoms were made, one with Ti-Cr alloy hip prosthesis having relative electron density 3.79 g/cm3, and another with gypsum replica of the original prosthesis. This prosthesis was dipped in bee wax having relative electron density 0.958 g/cm3 equivalent to water. The physical density of Gypsum is 2.76 g/cm3 (i.e. equivalent to electron density of bones 3.88 g/cm3 in males and 2.90 g/cm3 in females). Phantoms were imaged in CT scanner (Philips PET Gemini TOF, Amsterdam) with slice thickness of 1.5 mm. A concave structure acting as PTV was drawn adjacent to femoral head of prosthesis and bone replica. VMAT and dMLC plans with 6 MV beam were generated on both the phantoms with Monaco ver. 5.11.01. Two different CT-to-ED conversion files were generated, one gypsum and for Ti-Cr alloy and were assigned respectively during planning. In VMAT two partial arcs and in dMLC five beam plans were generated. The goal of planning was to deliver prescription dose of 30 Gy in 10 fractions to cover 95 % of the PTV volume with 95% of the prescription dose.
Results: The dMLCᴾD95 is 28.82 Gy and dMLCᴾGD95 is 29.16 Gy and VMATᴾPD95 is 29.14 Gy and VMATᴾGD95 is 29.09 Gy for concave PTV. The dMLCᴾPDmean is 10.89 Gy and dMLCᴾGDmean 14.06 Gy and VMATᴾPDmax is 33.97 Gy and VMATᴾGDmax is 32.25 Gy as OAR femoral head.
Conclusion: In MV beams there is significant reduction in dose distribution near the prosthesis and tumor area due to interface effect, provided correct CT-to-ED values are applied.
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