Integration of radiobiological modelling and indices in comparative plan evaluation: A study comparing VMAT and 3D-CRT in patients with NSCLC

Publication date: Available online 1 March 2018
Source:Practical Radiation Oncology
Author(s): Soumyajit Roy, Iulian Badragan, Sheikh Nisar Ahmed, Michael Sia, Jorawur Singh, Gaurav Bahl
PurposeTo generate an algorithm to calculate radiobiological end-points and composite indices and use them to compare volumetric modulated arc therapy (VMAT) and three-dimensional conformal radiotherapy (3D-CRT) techniques in patients with locally advanced non-small cell lung cancer (LA-NSCLC).MethodsThe study included 25 patients of LA-NSCLC treated with 3D-CRT at our center between January 1, 2010 and December 31, 2014. The planner generated VMAT plans using clones of the original CT and regions of interest (ROI) volumes, which did not include the original 3D plans. Both 3D-CRT and VMAT plans were generated using the same dose-volume (DV) constraint worksheet. The DVH parameters for PTV (planning target volume) and relevant organs at risk (OAR) were reviewed. The calculation engine was written in the "R" programming language; the user interface was developed with the "shiny" "R" web library. DVH data was imported into the calculation engine and tumor control probability (TCP), normal tissue complication probabilities (NTCP), composite cardio-pulmonary toxicity index (CPTI), morbidity index i.e. MI=∑j=1^{#ofrelevantOARs}(wj∗NTCPj), uncomplicated TCP (UTCP=TCP∗∏k=1#ofOARs1−NTCPK100 and therapeutic gain i.e. TG=TCP∗(100−MI) were calculated.ResultTCP was better with 3D-CRT (12.62% vs. 11.71%, p<0.001), while VMAT demonstrated superior NTCP-esophagus (p=0.02), NTCP-spinal cord (p=0.001) and NTCP-heart/perfusion defect (p=0.016). There was no difference in NTCP-lung (p=0.221) and NTCP-heart/pericarditis (p=0.129) between two techniques. VMAT showed substantial improvement in MI (p=0.01), CPTI (p=0.03) and TG (p=0.035) and trend towards superiority in UTCP (p=0.057).ConclusionThe study highlights the utility of the radiobiological algorithm and summary indices in comparative plan evaluation and demonstrates some benefits of VMAT over 3D-CRT.



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