Purpose: To investigate the impact of systematic errors in applicator reconstruction on DVH parameters of different organs at risk (OARs) and target volumes (TV) in intracavitary brachytherapy (ICBT) using GEC ESTRO EMBRACE protocol.
Methods: : Retrospectively, 10 patient plans of ICBT were taken in this study in which Nucletron CT and MR imaging compatible ring applicator of 3cm ring diameter and 6 cm tandem length (Nucletron, Veenendaal, The Netherlands) were used. Planning and contouring of OARs (Bladder, Rectum, Sigmoid) and TVs (HRCTV) were done on Oncentra TPS (Nucletron) with MRI images and applicator geometry was reconstructed manually and considered as zero position. Further, systematic errors were introduced in the spatial coordinates of applicator geometry by translating the applicator in -5 mm to +5 mm in a step size of 1 mm from the zero position in x-, y- and z-axis respectively by using an in-house program. The impact of systematic errors was quantified using DVH parameters of different OARs and TVs respectively.
Results: The mean value of relative percentage variation of dosimetric parameters for 0.1cc, 1cc, 2cc, and 5cc volumes of the bladder, rectum, sigmoid colon and D90%, D98% and V90% for HRCTV in x-, y- and z- directions were calculated and shown in Table 1.
Conclusion: The reconstruction of applicator geometry is very sensitive to the systematic errors that significantly affect the doses of OARs and TVs. This study reveals the quantitative impact of systematic errors on the OARs and TVs doses.