ABSTRACT
Objective: The purpose of this study was to quantitatively assess the systematic and random errors in radiation therapy for pelvic tumor patients of different somatotypes and seek an individualized mathematic basis for defining the planning target volume(PTV) and planning organ at risk volume(PRV) in 3 dimensional space.Methods: Thirty patients with pelvic tumor were immobilized by thermoplastic body mask in a spine position and divided into four somatotypes according to their body mass indexes(BMI).CT simulations were performed and digitally reconstructed radiographs(DRR) were generated as the reference image.To define the appropriate PTV-and PRV-margins for intensity modulation radiated therapy(IMRT),inter-fractional set-up errors and intra-fractional organ motions were quantitatively evaluated in the right-left(R-L),anterior-posterior(A-P) and cranial-caudal(C-C) directions.And the frequency of shift in the three directions were observed.Results: For the pelvic tumor patients with different BMIs,the inter-fractional set-up errors of the emaciated,moderate,overweight and obese somatotypes were 1.8,1.8,2.2 and 2.7 mm in the R-L direction,2.2,1.8,3.6 and 2.8 mm in the A-P direction,and 2.4,2.1,2.7 and 2.6 mm in the C-C direction.The intra-fractional organ motions of the four somatotypes were 1.9,1.9,2.3 and 2.5 mm in the R-L,2.1,2.2,2.9 and 3.0 mm in the A-P,and 1.8,1.9,2.2 and 2.5 mm in the C-C direction.Conclusion: In the pelvic irradiation,the definition of PTV and PRV should be individualized.