The Importance of Organ-Specific Setup Uncertainties Assessment for Determination of the Planning Target Volume Margin in Prostate and Cervical Cancer Using Electronic Portal Imaging Device (EPID)

Introduction: The setup uncertainty is a significant issue in radiotherapy that affects the accuracy of the delivered dose to the clinical target volume (CTV). To ensure that the target receives an adequate dose despite setup errors, a setup margin is defined around the CTV to determine the planning target volume (PTV). This study aims to develop a protocol for determining the CTV-to-PTV margin specific to the needs of each radiotherapy department, with a focus on the cervix and prostate. Material and Methods: A total of 300 portal images from 25 cervical cancer patients and 25 prostate cancer patients were aligned with Digitally Reconstructed Radiographs (DRRs). Population errors, both systematic (Σ) and random (σ), were calculated, and the necessary CTV-to-PTV setup margins in the lateral, longitudinal, and vertical directions were estimated using the formulas recommended by the International Commission on Radiation Units and Measurements (ICRU-62), Stroom, and Van Herk. Results: The systematic and random errors fell within the ranges of 2.54-2.91 mm and 1.73-2.11 mm for the cervix, and 2.09-2.35 mm and 1.64-2.0 mm for the prostate. The average margins, as per the ICRU 62, Stroom, and Van-Herk formulas, were 3.27, 6.03, and 7.36 mm for the cervix, and 2.87, 2.60, and 6.22 mm for the prostate, respectively Conclusion: The utilization of calculated margins to delineate the PTV will ensure that the CTV receives an adequate dose. The author recommends organ-specific margins in research, rather than using overall margins, based on the differences between prostate and cervix margins.