title: Estimation of the effects of normal tissue sparing using equivalent uniform dose-based optimization.
abstract: In this study, we intend to estimate the effects of normal tissue sparing between intensity modulated radiotherapy (IMRT) treatment plans generated with and without a dose volume (DV)-based physical cost function using equivalent uniform dose (EUD). Twenty prostate cancer patients were retrospectively selected for this study. For each patient, two IMRT plans were generated (i) EUD-based optimization with a DV-based physical cost function to control inhomogeneity (EUDWith DV) and (ii) EUD-based optimization without a DV-based physical cost function to allow inhomogeneity (EUDWithout DV). The generated plans were prescribed a dose of 72 Gy in 36 fractions to planning target volume (PTV). Mean dose, D30%, and D5% were evaluated for all organ at risk (OAR). Normal tissue complication probability was also calculated for all OARs using BioSuite software. The average volume of PTV for all patients was 103.02 ± 27 cm(3). The PTV mean dose for EUDWith DV plans was 73.67 ± 1.7 Gy, whereas for EUDWithout DV plans was 80.42 ± 2.7 Gy. It was found that PTV volume receiving dose more than 115% of prescription dose was negligible in EUDWith DV plans, whereas it was 28% in EUDWithout DV plans. In almost all dosimetric parameters evaluated, dose to OARs in EUDWith DV plans was higher than in EUDWithout DV plans. Allowing inhomogeneous dose (EUDWithout DV) inside the target would achieve better normal tissue sparing compared to homogenous dose distribution (EUDWith DV). Hence, this inhomogeneous dose could be intentionally dumped on the high-risk volume to achieve high local control. Therefore, it was concluded that EUD optimized plans offer added advantage of less OAR dose as well as selectively boosting dose to gross tumor volume.
authors.affiliation: Department of Medical Physics, Karnataka Cancer Therapy and Research Institute, Hubli, Karnataka, India; Research and Development Centre, Bharathiar University, Coimbatore, Tamil Nadu, India.
authors.forename: K
authors.initials: K
authors.lastname: Senthilkumar
authors.affiliation: Department of Radiotherapy, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India.
authors.forename: K J
authors.initials: KJ
authors.lastname: Maria Das
authors.affiliation: Department of Medical Physics, Karnataka Cancer Therapy and Research Institute, Hubli, Karnataka, India.
authors.forename: K
authors.initials: K
authors.lastname: Balasubramanian
authors.affiliation: Department of Medical Physics, Karnataka Cancer Therapy and Research Institute, Hubli, Karnataka, India.
authors.forename: A C
authors.initials: AC
authors.lastname: Deka
authors.affiliation: Department of Medical Physics, Karnataka Cancer Therapy and Research Institute, Hubli, Karnataka, India.
authors.forename: B R
authors.initials: BR
authors.lastname: Patil
keywords: Biological optimization; equivalent uniform dose; in-homogeneity; intensity modulated radiotherapy