Which Dose Specification Should Be Used for NRG Radiation Therapy Trials: Dose-to-Medium or Dose-to-Water?

PURPOSE

To compare the doses calculated by the Analytical Anisotropic Algorithm (AAA), Acuros dose-to-medium, and Acuros dose-to-water for the patients with lung cancer treated at our institution and show that further investigation and clarification are needed about what dose specifications should be used for NRG clinical trials.

METHODS AND MATERIALS

Twenty-one patients with lung cancer who previously received intensity modulated radiation therapy or volumetric modulated arc therapy-based treatments at our institution were analyzed by recalculating their plans for each one with the AAA algorithm (reviewed and approved by our radiation oncologists) and with both reporting modes of the Acuros algorithm. All plans used the same monitor units as the original approved plan and a 2.5-mm grid size. For each patient, D of clinical target volume (CTV) and CTV coverage ratios in each plan were compared, and dose distributions and dose-volume histograms calculated by AAA, Acuros dose-to-water (D), and Acuros dose-to-medium (D) were compared as well.

RESULTS

Differences between CTV D calculated by AAA and Acuros D were larger than the differences between AAA and Acuros XB D for all patients. When D of CTV was evaluated, the largest difference between AAA and Acuros D was 14.12% and between AAA and Acuros XB D was 3.68%. The average differences between the CTV D calculated by AAA and Acuros D was 5.39%. Coverage ratio between Acuros D and AAA ranges from 51.08% to 100% with an average of 91.32%; coverage ratio between Acuros D and AAA ranges from 87.2% to 100.41% with average of 98.94%; coverage ratio between Acuros D and Acuros D ranges from 58.58% to 100% with an average of 92.03%.

CONCLUSIONS

The present study shows large and systematic differences in doses calculated by AAA and Acuros D. Therefore, further investigation and clarification are needed about which dose reporting mode should be used.