Body Composition and Setup Errors in Radiotherapy

This single-center prospective cohort study investigates the association between body composition parameters and setup errors in 120-150 patients receiving radiotherapy with thermoplastic mask immobilization. Body composition (skeletal muscle mass, body fat percentage, phase angle, fat-free mass) will be measured using bioelectrical impedance analysis at baseline and at fraction 20. Setup errors (six degrees of freedom) will be recorded via daily cone-beam computed tomography. The primary outcome is the association between baseline body composition and setup errors. Secondary outcomes include the relationship between body composition changes during radiotherapy and setup error evolution, and identification of threshold values for clinically significant setup error increases. This study will provide evidence on whether body composition-beyond BMI-predicts radiotherapy setup accuracy, potentially enabling personalized immobilization and image-guided strategies.

Inclusion Criteria: * Pathologically confirmed malignancy * Age ≥18 years * Receiving radical or adjuvant intensity-modulated radiotherapy (IMRT) with planned ≥25 fractions * Immobilized with thermoplastic mask * ECOG Performance Status 0-2 * Willing and able to provide written informed consent Exclusion Criteria: * Metal implants (pacemaker, artificial joints) affecting bioelectrical impedance analysis (BIA) measurements * Severe edema or ascites * Inability to cooperate with immobilization or CBCT scanning * Radiotherapy interruption \>5 fractions * Pregnancy or lactation