Program Information
Tuning of AcurosXB Source Size Setting for VMAT Planning with Small Intracranial Targets
S Gardner1*, S Lu2 , C Liu3 , N Wen4 , I Chetty5 , (1) Henry Ford Health System, Detroit, MI, (2) Memorial-Sloan Kettering Cancer Center,Huntington, NY, (3) Henry Ford Hospital, Detroit, MI, (4) Henry Ford Health System, Detroit, MI, (5) Henry Ford Health System, Detroit, MI
Presentations
PO-BPC-Exhibit Hall-1 (Saturday, March 18, 2017) Room: Exhibit Hall
Purpose: To use end-to-end dosimetric measurements with Gafchromic film to evaluate the effects of focal spot size parameter for Acuros dose calculation of small-field SRS lesions.
Methods: A total of 20 VMAT plans (10 with Millennium-120 MLC and 10 with HD-MLC) were generated for cranial SRS patients with target volume range:[0.03cc,13.9cc]). All plans were mapped to a solid water phantom (15 cm thickness; isocenter and film plane at 7.5 depth). Dose calculation was performed with AcurosXB v.13 (1.0mm grid size); five focal spot size settings were tested: 0.5mm, 0.75mm, 1.00mm, 1.25mm,and 1.50mm. For each plan, five calculated doses (corresponding to each focal spot size setting) were compared to measured film dose using quantitative methods [Gamma Analysis(3%,0.3mm,20% threshold criteria)] and qualitative methods (visual dose profile comparison). Film calibration and analysis were performed using in-house calibration methods and software package.
Results: Gamma(3%,0.3mm) analysis passing rate results [mean±st.dev{%}] were as follows. For HD-MLC planning: 97.51±2.38%[0.50mm], 96.25±3.51%[0.75mm], 93.72±4.96%[1.00mm], 84.97±6.93%[1.25mm], and 78.83±7.10% [1.50mm]. For Millenium-120 MLC planning: 95.02±4.68% [0.50mm], 97.22±3.76% [0.75mm], 97.98±3.06%[1.00mm], 95.91±4.33%[1.25mm], 92.46±5.88%[1.50mm]. The variation of spot size parameter impacted the shoulder of the high dose region for all lesion volumes tested; for small volume targets (≤0.30cc), the magnitude of the central lesion dose was also impacted by the spot size used for calculation.
Conclusion: The dose calculation accuracy of DCA and VMAT plans is extremely important for SRS treatment planning. Our results indicate the highest passing rates occur for 0.50mm or 0.75mm spot size setting for HD-MLC and 1.00mm setting for Millennium-120 MLC.
Funding Support, Disclosures, and Conflict of Interest: Henry Ford Health System holds research agreements with Varian and Philips.
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