Modern imaging methods in radiation therapy planning

Introduction: Prostate-specific membrane antigen (PSMA) is a transmembrane protein that may be expressed on the surface of prostate cancer (PC) cells.It enables a more sensitive and specific diagnosis PC, compared to conventional anatomical imaging.Aim: The integration of PSMA-based imaging in the personalized radiotherapy of PC patients and the evaluation of its impact on target volume definition if stereotactic body radiotherapy (SBRT) is planned for locally recurrent or oligometastatic disease.Patients and methods: The data from 363 examinations were analyzed retrospectively.Inclusion criteria were histologically verified PC and clinical data suggesting local recurrence or distant metastasis.Whole-body 99m Tc-PSMA-I&S single-photon emission computed tomography (SPECT)/CT or 18 F-JK-PSMA-7 positron emission tomography/computer tomography (PET/CT) was carried out, and the evaluation of the scans and biological tumor volume contouring was performed at the Department of Nuclear Medicine.The target volume delineation on topometric CT (TCT) scan was performed at the Department of Oncotherapy.The comparison of the two volumes was performed by image fusion and registration.Results: From 363 PSMA isotope-based examinations, 84 lesions of 64 patients were treated with SBRT.In 50 patients, 70 lesions were examined for intermodality comparison.The target volume defined by the PSMA density was significantly smaller than the tumor size defined by the TCT scan: GTV CT (gross tumor volume on the TCT), 27.58 ± 46.07 cm 3 ; BTV PSMA (biological target volume on the PSMA-based examination), 16.14 ± 29.87 cm 3 .During geometrical analyses, the Dice similarity coefficient (DSC) was 0.56 ± 0.20