Stereotactic Radiotherapy Treatment of Lymphnodes in Oligometastatic Prostate Neoplasm: Evaluation of the Positioning Setup

Prostate cancer is one of the main male neoplasms and can present in oligometastatic form, characterized by the presence of a limited number of metastases. In this context, stereotactic body radiotherapy (SBRT) represents an effective therapeutic option, capable of delaying the use of prolonged systemic treatments such as hormone therapy. The retrospective observational study, conducted at the AOU of Alessandria, evaluated the reproducibility of the positioning of patients undergoing lymph node SBRT by the use of lower and upper limb immobilization systems. 34 patients with oligometastatic prostate cancer were included, for a total of 206 fractions treated. Positioning errors were detected by daily CBCT images, analyzing translational and rotational displacements along the three axes. The results show an average of translational errors between 0.27 and 0.36 cm and rotational errors between 0.71° and 1.31°, with generally low values. The DIST metric, a three-dimensional positioning accuracy index, showed an average of 0.64 cm, indicative of good reproducibility. The greatest variations were observed in rotations, suggesting the need for further optimization of devices and treatment margins. The conclusions underline the effectiveness of the positioning systems used and the importance of continuous training and systematic monitoring of errors to improve the accuracy of radiotherapy treatment. The study also suggests the opportunity to customize margins and upgrade technology systems to further optimize clinical outcomes.