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Dosimetric and Radiobiological Comparison of Conventional and Monte Carlo Treatment Plans of Lung Tumors Using SBRT

S Stathakis

S Stathakis1*, P Mavroidis2 , B Tuazon1 , D Defoor1 , N Kirby1 , N Papanikolaou1 , (1) Cancer Therapy and Research Center, San Antonio, TX, (2) University North Carolina, Chapel Hill, NC


SU-F-T-623 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: This study aims at estimating the dosimetric differences of Pinnacle and Monte Carlo (MC) calculation algorithms in computing the dose distributions in lung cancer SBRT cases. Furthermore, to interpret the dosimetric findings into expected tissue response rates in order to estimate their clinical impact.

Methods: 17 patients were studied and for each one, two treatment plans (one from Pinnacle and one MC) were created. The structures that were used for the optimization were: PTV, ipsilateral and contralateral lungs, spinal cord, heart, esophagus and stomach. The same dosimetric constraints were used for both pairs of plans. These dosimetric indices were used for the comparison of the two calculation modalities. Additionally, the TCP and NTCP values of the different targets and organs at risk (OAR) were calculated and compared together with the complication-free tumor control probability.

Results: The proposed plan evaluation shows that the plans by Pinnacle deliver higher doses to the OAR than MC. The same is observed for the PTV (minimum dose and BEUD: 58.3 vs. 55.1Gy, respectively). However, these dosimetric differences are translated to negligible differences in TCP and NTCP.

Conclusion: The results of this work indicate that for the fractionation scheme of 18Gy in 3 fractions, the treatment plans in Pinnacle and Monte Carlo show minor differences in the doses to the organs at risk (in all the cases the doses by MC were lower than those calculated by Pinnacle). Those doses are predicted to cause 0.0% of side effects. On the other hand, the findings of the analysis indicate that Pinnacle calculation is shown to deliver higher dose to the PTV than MC. However, the dosimetric differences do not appear to have a measurable impact in the expected TCP rates of the targets.

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