Room: ePoster Forums
Purpose: Evaluate a time-based plan check technique for brachytherapy treatments using Rotte 'Y' or Veneziaâ„¢ applicators.
Methods: For HDR implants, a QA method to catch planning errors has been published using the volume covered by the 100% isodose line (Vâ‚?â‚€â‚€) and a term Ráµ¥=(t x Sk)/Dáµ£â‚“ where t=total dwell time, Sk=air kerma strength, and Dáµ£â‚“=prescription dose. In the study, it was found that Ráµ¥=K x Vâ‚?â‚€â‚€^(2/3) where K is a fit coefficient (U-s-cGyâ?»Â¹-cmâ?»Â²). Combining the equations, the expected implant time can be calculated as a function of Vâ‚?â‚€â‚€. The original manuscript did not consider Rotte 'Y' or Veneziaâ„¢ applicators when generating a coefficient of K=1182 U-s-cGyâ?»Â¹-cmâ?»Â² for implants with 2-3 catheters. Therefore, 39 Rotte 'Y' clinical plans from an equal number of patients and 33 Veneziaâ„¢ institutional library plans were analyzed in this work to assess the appropriateness of the established plan check technique. For the Rotte 'Y' plans, Vâ‚?â‚€â‚€ ranged from 37.3-279.3 cmÂ³ with dose prescriptions of 5.5-9.0 Gy. With the Veneziaâ„¢ applicator, library plans were generated for all available combinations of lunar ovoids and tandems with Vâ‚?â‚€â‚€ ranging from 13.9-86.2 cmÂ³.
Results: Fit coefficients of K=1204 U-s-cGyâ?»Â¹-cmâ?»Â² and K=1163 U-s-cGyâ?»Â¹-cmâ?»Â² were found for the Rotte 'Y' clinical plans and Veneziaâ„¢ library plans, respectively. When applying the published value of K=1182 U-s-cGyâ?»Â¹-cmâ?»Â² for 2-3 catheter plans, it was found that 35/39 Rotte 'Y' clinical plans and 31/33 Veneziaâ„¢ library plans passed the time-based plan test with a difference between predicted Ráµ¥ and actual Ráµ¥ within Â±7%. The pass rate improved to 37/39 for Rotte â€˜Yâ€™ plans and 33/33 for VeneziaTM plans when using applicator-specific fit parameters.
Conclusion: The published plan check technique for 2-3 catheter systems is considered suitable for Rotte 'Y' and Veneziaâ„¢ plans, but higher specificity could be achieved with applicator-specific parameters given sufficient clinical data.