Room: Exhibit Hall | Forum 3
Purpose: The commonly used TG-43 formalism cannot account for tissue heterogeneities and lack of sufficient-backscatter. Introduction of deterministic Acuros-based algorithm in Eclipse with voxelized density mapping provides heterogeneous dose distributions within the treatment area such as air, bone or muscle and predicts dose similar to Monte Carlo calculation. Aim of this report was to quantify dosimetric differences of TG-43 calculation and AcurosBV algorithm for vaginal cuff cylinder and cervical T&O HDR plans.
Methods: TG-43 and AcurosBV dose distributions for image-based (1.25mm CT scans) inverse optimized plans were calculated for 15 vaginal cuff and 10 cervical cancer patients. Prescription doses were 7 Gy and 5.5 Gy/fraction to â‰¥90% of HR-CTV for vaginal cuff and cervical patients, respectively. Dosimetric parameters were compared including HR-CTV coverage, D2cc of rectum, bladder and normal tissue (5mm envelope from HR-CTV) and vaginal cuff, sigmoid point and point A doses. In addition, overall calculation times were recorded.
Results: Vaginal cuff patients showed an average percentage difference in HR-CTV coverage of 0.6% (p-value<0.001) higher with TG-43. However, the cylinder apex dose was typically 10-20% higher for the AcurosBV due to lack of attenuation in the air filled channel. For cervix patients, TG-43 systematically overestimated calculated dose by greater than 2-4% (p-values<0.001) for target coverage and all evaluated OAR parameters compared to AcurosBV. AcurosBV calculation times were approximately 5 and 10 minutes for vaginal cuff and cervix plans.
Conclusion: All studied parameters showed statistically significant differences between TG-43 and AcurosBV dose calculation with p-values<0.05. Utilizing AcurosBV, heterogeneous brachytherapy dose distributions can be obtained. However, increased calculation times may be restrictive for busy clinics. The largest investigated difference, up to 20%, occurred in the sigmoid and vaginal cylinder apex point doses. Isolating the difference due to attenuation from heterogeneities and its connection to basal cuff reoccurrence is under future investigation.