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Dosimetric Evaluation and Clinical Implementation of IPlan Monte Carlo Algorithm For Lung Stereotactic Ablative Radiotherapy (SABR)

R Badkul

R Badkul*, D Pokhrel, H Jiang, F Wang, P Kumar, University of Kansas Medical Center, Kansas City, KS

SU-E-T-413 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

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 QUASARâ„¢ 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.

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