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Influence of Statistical Uncertainty On Monaco Monte-Carlo Dose Calculation

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S Sharma

S Sharma*, V Subramani , P Kumar , N Gopishankar , S Bhaskar , S Pathy , S Thulkar , S Chander , All India Institute of Medical Sciences, New Delhi, Delhi


SU-I-GPD-T-399 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Aim is to evaluate influence of statistical uncertainty on Monte-Carlo dose calculation of Monaco 5.11 treatment planning system (TPS).

Methods: Phantom with contoured C-Shape structure set was downloaded from AAPM website provided with TG119 report. VMAT plan was created for C-Shape test case using Monaco TPS for 6MV Elekta Versa-HD linear-accelerator. Dose prescription and constraints were as per TG119. After optimisations C-Shape plan was calculated with different statistical-uncertainty (i) 0.5%, 1.0%, 3.0% and 5.0% per control point and (ii) 0.5%, 1.0%, 3.0% and 5.0% per calculation. Base plan was calculated with 0.5% per control point. Plan analysis was done using dose volume parameters i.e. PTV-D95, PTV-D10, Core-D10, MU required to deliver plan, number of histories considered in dose calculation and time taken in calculation. Plans were measured with I’matriXX 2D-detector using My-QA software. 2D-Gamma analysis was done using 3%/3mm criteria.

Results: Variations in PTV doses for different statistical-uncertainties with respect to 0.5% per control point were within PTV-D95: 82cGy(1.64%); PTV-D10: 14.8cGy(0.28%); Core-D10: 3.7cGy(0.15%). MU required to deliver a plan (920 MU) were observed same with different statistical-uncertainty. Number of histories: 55904581, 13976145, 1552905, 559046 and 1402641, 350660, 97057, 97057; Calculation time (min): 106.56, 26.43, 4.15, 1.28 and 2.91, 1.50, 0.38, 0.38 were observed as above for 0.5% - 5.0% per control point and per calculation statistical-uncertainty respectively. Calculation time increases with decrease in statistical-uncertainty (due to more number of histories). 2D-Gamma pass rate was ranging from 98.1% to 98.9% for analysed statistical-uncertainties. Statistical-uncertainty 0.5% per control point showed higher Gamma pass-rate (98.9%).

Conclusion: Minor variation (<1.64%) in dose-volume parameters was observed with different statistical-uncertainties, whereas Monitor unit remain same. 3.0% per control point and 0.5% per calculation resulted in almost similar results and found optimal with reasonable calculation time in terms of plan quality and delivery accuracy (gamma pass-rate).

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