SU-E-T-413: Dosimetric Evaluation and Clinical Implementation of IPlan Monte Carlo Algorithm For Lung Stereotactic Ablative Radiotherapy (SABR)
Purpose: To evaluate, validate and compare dosimetric accuracy of commercially available iPlan Monte‐Carlo(MC) dose algorithm for lung‐SABR. Due to short comings of Pencil‐Beam(PB) algorithm in regions of tissue inhomogeneity and advent of faster computing environment, ability to use more accurate MC based dose calculation algorithms is becoming more of a reality. This study presents a comparative analysis of dose calculations with 6MV using iPlan PB and MC algorithms with measured data utilizing lung anthropomorphic phantom.Materials & Methods: For treatment planning and dose measurement purposes a QUASAR™ phantom with lung inserts and Ion‐Chamber drills was utilized. Three different PTVs were drawn in phantom; two were in lungs and one in homogeneous region in midline of phantom. SABR planning were performed using three different techniques: DynamicArc, ConformalBeams and IMRT for each PTV. For planning purposes NovalisTx with HDMLC, 6MVSRS were used. Three different Ion‐Chambers; 0.6cc, CC01 and CC13 were utilized to measure doses. PTV‐maximum, PTV‐minimum, PTV‐mean doses and Ion‐Chamber mean doses were collected from plans which were calculated using PB‐corrected, PB‐uncorrected and MC. Results: Agreement between MC and Ion‐Chamber measurement were −1.1–1.64% (mean0.6%), 0.5–1.55% (mean1.17%) and −2.7−0.4% (mean‐0.55%) for DynamicArc, ConformalBeams and IMRT respectively. Deviations between PB‐corrected and measured values were 1.81–6.83% (mean4.4%), 2.73–8.63% (mean5.13%) and −1.28−1.24% (mean0.13%) for DynamicArc, ConformalBeams and IMRT respectively. Deviations between PB‐uncorrected and measured values were −2.36– −3.8% (mean‐2.96%), −1.88–− 3.04% (mean‐2.46%) and −3.88–−7.1% (mean‐5.29%) for DynamicArc, ConformalBeams and IMRT respectively. The mean deviations for all techniques were 0.4%,3.22%,−1.93% for MC, PB‐corrected and PB‐uncorrected respectively. PTV dose comparison between different algorithms has also been analyzed. Conclusions: This phantom study shows excellent agreement between doses calculated using iPlan Monte‐Carlo versus measurements for 6MV beam in lung equivalent material. MC algorithm not only predicts accurate dose at isocenter but also at borders of tumors where Pencil‐Beam overestimates the doses.