Relationship between the Patients’ Setup Errors with Dosimetric and Radiobiologic Parameters in Whole Breast Radiotherapy

Zahra  Alijani; Kourosh  Ebrahimnejad Gorji; Ali Shabestani  Monfared; Abbas Rahimi  Alisaraee; Ali  Esmaeeli; Fatemeh  Niksirat

doi:10.18502/fbt.v10i3.13155

Zahra Alijani Student Research Committee, Babol University of Medical Sciences, Babol, Iran
Kourosh Ebrahimnejad Gorji Department of Medical Physics Radiobiology and Radiation Protection, School of Medicine, Babol University of Medical Sciences, Babol, Iran
Ali Shabestani Monfared Cancer Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran
Abbas Rahimi Alisaraee Department of Radiotherapy, Guilan University of Medical Sciences, Rasht, Iran
Ali Esmaeeli Department of Physics, Islamic Azad University, Rasht, Iran
Fatemeh Niksirat Department of Medical Physics Radiobiology and Radiation Protection, School of Medicine, Babol University of Medical Sciences, Babol, Iran

DOI: https://doi.org/10.18502/fbt.v10i3.13155

Keywords: Whole Breast Radiotherapy; Setup Errors; Intensity-Modulated Radiation Therapy; Field-In-Field; Radiobiological Parameters.

Abstract

Purpose: This study aimed to investigate the effect of the patients’ setup errors on dosimetric and radiobiologic parameters for left-sided Whole-Breast Irradiation (WBI) in three different radiotherapy techniques, including Intensity-Modulated Radiation Therapy (IMRT), Field-In-Field (FIF), and Conventional Wedge (CW).

Materials and Methods: Computed Tomography (CT) images of 10 female patients with early-stage left-sided breast cancer were used to simulate different radiotherapy techniques (IMRT, FIF, and CW). The dosimetric parameters; Conformity Index (CI), Homogeneity Index (HI), the dose received by at least 95% (D_95%) of Planning Tumor Volume (PTV), the volume of lung and heart that respectively received at least 20% (V_20%) and 40% (V_40%) of the prescribed dose, as well as, the radiobiologic parameters, including Tumor Control Probability (TCP) and Normal Tissue Complication Probability (NTCP) were assessed for setup errors in patients. The setup errors were assessed by shifting the isocenters and gantry angles of the treatment plans.

Results: The D_95% of the PTV for an isocenter misplacement plan in the posterior direction decreased by 66.99 (IMRT), 71.86 (CW), and 68.25% (FIF). The TCP of the PTV was reduced by 26.66, 39.16, and 36.97% for IMRT, CW, and FIF techniques, respectively. Increasing gantry angle by a ±10 degree caused a 43%, 41%, and 41% decrease in the D_95% of IMRT, FIF, and CW techniques, respectively. The TCP values decreased about 18% in all three techniques with a ±10 degree gantry angle shift; however, the NTCP values of the heart and lungs increased for all three methods. The CI and HI values had significantly more changes with increasing setup errors in the IMRT than in the two techniques.

Conclusion: The radiobiologic parameters in IMRT were less sensitive to setup errors compared to FIF and CW techniques. The radiobiological parameters can help estimate the setup errors along with physical parameters during breast radiotherapy.