(Sunday, 7/14/2019)
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 (V�₀₀) and a term Rᵥ=(t x Sk)/Dᵣₓ where t=total dwell time, Sk=air kerma strength, and Dᵣₓ=prescription dose. In the study, it was found that Rᵥ=K x V�₀₀^(2/3) where K is a fit coefficient (U-s-cGy�¹-cm�²). Combining the equations, the expected implant time can be calculated as a function of V�₀₀. The original manuscript did not consider Rotte 'Y' or Venezia™ applicators when generating a coefficient of K=1182 U-s-cGy�¹-cm�² for implants with 2-3 catheters. Therefore, 39 Rotte 'Y' clinical plans from an equal number of patients and 33 Venezia™ institutional library plans were analyzed in this work to assess the appropriateness of the established plan check technique. For the Rotte 'Y' plans, V�₀₀ ranged from 37.3-279.3 cm³ with dose prescriptions of 5.5-9.0 Gy. With the Venezia™ applicator, library plans were generated for all available combinations of lunar ovoids and tandems with V�₀₀ ranging from 13.9-86.2 cm³.
Results: Fit coefficients of K=1204 U-s-cGy�¹-cm�² and K=1163 U-s-cGy�¹-cm�² were found for the Rotte 'Y' clinical plans and Venezia™ library plans, respectively. When applying the published value of K=1182 U-s-cGy�¹-cm�² for 2-3 catheter plans, it was found that 35/39 Rotte 'Y' clinical plans and 31/33 Venezia™ library plans passed the time-based plan test with a difference between predicted Rᵥ and actual Rᵥ within ±7%. The pass rate improved to 37/39 for Rotte ‘Y’ 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.
Keywords
Brachytherapy, Treatment Planning, Quality Assurance
Taxonomy
TH- Brachytherapy: Calibration & Quality Assurance
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