ESTRO 2023 - Abstract Book

S1836

Digital Posters

ESTRO 2023

Coimbatore, India; 4 Kidwai memorial institute of oncology center, Department of Radiation Oncology, Bangaluru, India; 5 Meherbai Tata Memorial Hospital, , Department of Radiation Oncology, Jamshedpur, India Purpose or Objective The purpose of this study is to analyze different dosimetric indices using various formulae in cranial Stereotactic radiotherapy (SRS) treatment planning. Materials and Methods A total 42 targets were constructed from 23 patients with brain metastases treated at our institution selected for this study. Target volumes were chosen up to 30 cc. For simulation, the patients were scanned in head-first supine position with a 1.0 mm slice thickness. Planned target volume (PTV) was delineated by expanding from clinical target volume (CTV) with 3.0 mm isotropic margin. Varian TrueBeam® system with Eclipse™ version 15.6 (Varian Medical Systems, Palo Alto, CA), the volumetric modulated arc therapy (VMAT) with standard millennium 120 leaves with 5.0 mm leaf width were used for treatment planning. Post whole brain radiotherapy treatment, the prescription dose delivered as a sequential boost were 5 to 15 Gy in single or multiple per fractions. All the SRS plans were generated using 6MV photon beam (6MV-FFF), dose rate of 1400 MU/minute, full arc, partial arcs, non-coplanar partical arcs and isocenter at the center of PTV volume. In addition, optimized with the photon optimizer, in which the Acuros XB algorithm with a 1.25 mm grid was used to calculate the dose distribution. The Conformity index (CI), Homogeneity index (HI), and Gradient index (GI) were evaluated using dose volume histogram (DHV) with different mathematical formulae. Results The comparison results of CI, HI and GI with different formulas were depicted in the table 1. For CI values, RTOG, Van’t Riet and Paddick, Inverse of RTOG values were close to 1.0. Whereas Lomax & Scheib and SALT were 0.92 ± 0.06, 0.94±0.05 respectively, achieved lower than 1.0. The HI calculated based on the parameters D98%, D95%, D50%, D2%, D5%, Dmax and Dmin. The results of different types of HI values achieved close similarly ideal values. For GI data scored each individual target for incase multiple lesions. For the dose GI, the results of effective radius and modified GI shows 4.61 ± 1.12, 4.28 ± 1.24 respectively.

Conclusion The present study results concluded that any of the described formula can be used to evaluate the CI, HI and GI for cranial SRS. These different indices can all be objective tools for the evaluation of plan quality. Given the high plan quality and evaluations will be extreme clinical efficiency for the patients.

PO-2061 Dosimetric indexes and its potential relationship with target size and location in SBRT lung cancer.

G. Pozo Rodriguez 1 , S. Fernández Alonso 2 , S. Guardado Gonzalez 3 , E. Cabello Murillo 1 , A. Milanés Gaillet 1 , P. Adaimi Hernández 1 , R. Díaz Fuentes 1 , M. Manzano Rodríguez 1 , Á. Gaitán Simón 1 , A. Ferrando Sánchez 1 , P. Botella Faus 4 , P. García Castañón 5 , D. Rojo Navarrete 1 , J.F. Pérez-Regadera Gómez 3 1 h.U. 12 De Octubre, Medical Physics, Madrid, Spain; 2 h.U.12 De Octubre, Radiation Oncology, Madrid, Spain; 3 h.U. 12 De Octubre, Radiation Oncology, Madrid, Spain; 4 h.U.12 De Octubre, Medical Physics, Madrid, Spain; 5 h.U. La Princesa, Medical Physics, Madrid, Spain Purpose or Objective To evaluate a potential correlation between Paddick (PI) and Gradient (GI) indexes (as defined in ICRU report 91) for lung SBRT treatments against target location within the lung and ITV . Materials and Methods A cohort of 159 lung patients that have undergone SBRT therapy since 2016 have been classified into seven groups regarding its location (table I). Dose to the target has followed an adaptive risk strategy aimed to a minimum BED>100Gy in 90.0% of cases analysed.