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Examination of Dose Volume Effects of Intensity Modulated Radiation Therapy (IMRT) Planning: Toward Biologically Conformal Optimization

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M Chao

M Chao1*, J Wei2 , Y Yuan1 , G Narayanasamy3 , Y Lo1 , J Penagaricano3 , (1) The Mount Sinai Medical Center, New York, NY, (2) City College of New York, New York, New York, (3) University of Arkansas for Medical Sciences, Little Rock, AR


SU-I-GPD-T-658 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To investigate dose volume effects in IMRT planning and scrutinize the structure of heterogeneous dose distribution and its correlation with radiobiological indices, aiming at a novel biological optimization paradigm.

Methods: Non-uniform dose distribution of IMRT plans were perused with the cluster model which represents the aggregation of higher dose in the organ at risk (OAR). The cluster that incorporates spatial details could potentially improve the dose volume histogram (DVH) based normal tissue complication probability (NTCP) model. A Monte Carlo (MC) procedure was implemented to examine the formation of the cluster model realized from the given DVH. Cluster formation via various connectivity choices was studied and the mean size of the largest cluster (MSLC) from MC samples was taken to be a function of the fractional density obtained from the DVH. The correlation between the cluster model and the radiobiological indices such as NTCP and equivalent uniform dose (EUD) was analyzed in clinical cases. OARs examined include upper 5cm esophagus from ten head and neck patients and the rectal wall of ten prostate patients, respectively.

Results: MC study revealed the inverse relationship between the MSLC and the cluster connectivity and the nonlinear changes in cluster size with fractional density regardless of connectivity types. An initially-slow-increase in MSLC that transitioned to an exponential growth with increasing fractional density was persistently observed. The clusters are insensitive to the shape of OARs. Cluster parameters in clinical cases were different from NTCP and EUD values. “Hot spots” from clinical plans fell in the cluster domain as anticipated in the clinical scenario.

Conclusion: Cluster models have the potential to offer insight in dose volume effects of IMRT. Clinical results demonstrated that cluster parameters are not necessarily consistent with NTCP and EUD predictions, which could be due to inherent uncertainties in the NTCP modeling.

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