Room: Exhibit Hall
Purpose: Tandem-and-ring applicator together with a high-dose-rate (HDR) afterloader remains one popular option to manage the cervical cancer. During the planning step, the catheter digitization is usually done manually by depicting the applicator central canal or the marker wire. However, the actual source path often does not align well with such manual digitization in the ring tube. This work aims to evaluate the dosimetric consequence of the above discrepancy by duplicating the clinical HDR plans using the applicator library modelling where the factory-measured source path is incorporated.
Methods: 12 clinical HDR plans of 5 patients treated in 2017 at our institution were randomly selected for this retrospective study. These fractions were planned using Oncentra Brachy treatment planning system (Elekta Inc, Atlanta, GA) with a per-fraction prescription of 550 or 700 cGy. Each plan was duplicated with the same source activity, dwell positions, and dwell times. Extra coordinate system view was carefully aligned to maintain the consistency between the original and duplicate plan. Doses for the point A (Dâ‚?), the most exposed 2 cc of rectum (Dâ‚‘) and bladder (Dâ‚’), and 90% of the high-risk clinical target volume (Dâ‚‰â‚€) were used as metrics for dosimetric comparison.
Results: When comparing the clinical plans with the ones that used the applicator model and the factory-measured source path, the maximum percentage difference for Dâ‚?, Dâ‚‘, Dâ‚’, and Dâ‚‰â‚€ was 6.7%, 12.1%, 6.5%, and 9.7%, while the average percentage difference amounted to 2.6%, 4.2%, 1.9%, and 4.8%, respectively. By considering the actual source path, the doses to the bladder and rectum almost exclusively increased while the doses to the target and point A decreased.
Conclusion: For accurate dose calculation, we recommend the use of the applicator library modelling together with the factory-measured source path for the planning of tandem and ring HDR treatment.