Does Cone Beam Computed Tomography Decrease CTV Margins in Prostate Cancer Radiation Treatment?

The document reports on a study that aimed to determine the degree of interfraction prostate displacements and daily set-up errors in prostate cancer radiotherapy using cone beam computed tomography imaging (CBCT). The study involved 14 patients with locally advanced prostate cancer who underwent daily CBCTs during the first week of treatment. The displacements were analyzed in three directions: left-to-right (LR), superior-inferior (SI), and anterior-posterior (AP). The results showed median displacements of 2 mm (LR), 3 mm (SI), and 3 mm (AP), with a displacement of less than 3 mm in 75.1%, 60.3%, and 50.3% of patients, respectively. The study concluded that a margin of 3 mm around the Clinical Target Volume (CTV) can be applied only if an on-board imaging system is used for further controls during treatment, as minimal displacement of the target volume was observed after replanning. The greatest variations were in the superior-inferior direction, while the left-to-right variations were the lowest, suggesting that different margins in the three directions should be considered.