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Dosimetric Impact of Statistical Uncertainty On Monte Carlo Dose Calculation in Monaco TPS Volumetric Modulated Arc Therapy for Lung Cancer

P Mohandass

P Mohandass1,2*, D Khanna2 , D Manigandan1 , M Kumar1 , A Puri1 , N Bhalla1 , (1) Fortis Cancer Institute, Fortis Hospital, Mohali, Punjab,India (2) Karunya University, Coimbatore, Tamilnadu, India


SU-I-GPD-T-403 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To study the dosimetric impact of statistical uncertainty (SU) per plan on Monte Carlo calculation in Monaco™ TPS during volumetric modulated arc therapy (VMAT) for lung cancer.

Methods: Three lung cancer patients treated with 60Gy/30 fractions were chosen for the study. VMAT plans were generated with Monaco™ treatment planning system (TPS-V5.10) for Elekta Synergy™ linear accelerator with 1cm leaf width. Plans were generated using dual partial arcs with 2% statistical uncertainty per plan. By keeping all other parameters constant, plans were recalculated only by varying the SU, 0.5, 1, 2, 3, 4, and 5%. For plan evaluation, conformity index (CI), Homogeneity index (HI) to planning target volume (PTV), dose coverage to PTV (D98%) was analyzed. Mean and max dose to organ at risk (OAR) was analyzed for spinal cord, pericardium, both lungs-PTV, esophagus and liver. The normal tissue volume receiving dose >5Gy & >10Gy and normal tissue integral dose (NTID) (patient volume-PTV), calculation time (mins) and gamma pass rate (<1.00)(3%/3mm) were compared.

Results: CI and HI improve as the SU increases 0.5 to 5%. CI was 1.0001±0.064, 1.0035±0.063, 1.0110±0.054, 1.0107±0.054, 1.0112±0.054 and 1.0112±0.054 for SU 0.5, 1, 2, 3, 4, and 5%, respectively. HI was 0.1121±0.009, 0.1144±0.010, 0.1251±0.010, 0.1323±0.011, 0.1323±0.011 and 0.1329±0.012. No significant dose difference was observed in Dmean to PTV, both lungs-PTV dose, mean dose to pericardium, esophagus, liver and normal tissue volume receiving dose >5Gy&>10Gy and NTID. Decrease in dose calculation time was observed with increase of SU; 11.8±2.8, 3.0±2.1, 2.1±1.1, 1.9±1.1, 1.7±0.8 and 1.7±1.5mins. Gamma pass rate was observed as 99.63±0.43%, 98.10±1.90%, 98.53±1.16%, 98.20±1.80%, 98.50±1.20% and 98.66±1.36%.

Conclusion: For lung VMAT plans, SU can be accepted up to 3% per plan with reduced calculation time without compromising target coverage, OAR doses and plan delivery by accepting variations in point dose and inhomogeneous dose within target.

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