What Dose Specification Should be used for NRG Radiation Therapy Trials, Dose-to-Medium or Dose-to-Water?

Abstract Purpose To compare the doses calculated by AAA, Acuros dose-to-medium and Acuros dose-to-water for the lung patients treated at our institution and show that further investigation and clarification are needed about what dose specification should be used for NRG clinical trials. Methods and Materials Twenty-one lung patients who previously received IMRT or VMAT-based treatments at our institution were analyzed by recalculating their plans for each one with AAA algorithm (reviewed and approved by our Radiation Oncologists) and with both reporting modes of Acuros algorithm. All plans used the same monitor units (MU) as original approved plan and 2.5mm grid size. For each patient, D100 of clinical target volume (CTV) and CTV coverage ratios in each plan were compared and dose distributions and DVHs calculated by AAA, Acuros dose-to-water Dw,m and Acuros dose-to-medium Dm,m were compared as well. Results Differences between CTV D100 calculated by AAA and Acuros Dm,m were larger than the differences between AAA and Acuros XB Dw,m for all patients. When D100 of CTV was evaluated, the largest difference between AAA and Acuros Dm,m was 14.12%, and between AAA and Acuros XB Dw,m was 3.68%. The average differences between the CTV D100 calculated by AAA and Acuros Dm,m was 5.39%. Coverage ratio between Acuros Dm,m and AAA ranges from 51.08% to 100% with an average of 91.32%; coverage ratio between Acuros Dw,m and AAA ranges from 87.2% to 100.41% with average of 98.94%; coverage ratio between Acuros Dm,m and Acuros Dw,m ranges from 58.58% to 100% with an average of 92.03%. Conclusion The present study showed large and systematic differences in doses calculated by AAA and Acuros Dm, m. Therefore, further investigation and clarification are needed about which dose reporting mode should be used.