Room: Exhibit Hall | Forum 4
Purpose: A retrospective study of secondary check for non-IMRT and IMRT clinical radiotherapy plans of C-arm and non C-arm linear accelerators was performed.
Methods: 3076 plans were collected from 21 institutions. Commercial software employing the Clarkson algorithm was used for verification after a validation study of measurement, and software comparisons were performed. The doses generated by the treatment planning systems (TPSs) were retrospectively analyzed using the verification software. The mean (Â± two standard deviations) dose differences were compared.
Results: For C-arm linear accelerators, there were larger differences for breast (4.0 Â± 4.0%) and for lung (2.5 Â± 5.8%) than the other sites (0.6 Â± 2.7%). For non C-arm linear accelerators, there was a statistically significant difference (P < 0.01) in dose difference between non-lung (âˆ’0.3% Â± 4.4%) and lung sites (3.5% Â± 6.7 %). Inter-institutional comparisons showed various systematic differences and variations, with different planning techniques for field shape and differences in reference point placement.
Conclusion: The 5% action level may be feasible for verification for all radiotherapy techniques using all linear accelerators. For lung SBRT, AAA showed much larger variation than the algorithms of PBC and Adaptive Convolve. For IMRT and VMAT, the reference point should be within the planning target volume (above âˆ’350 HU). Based on the inter-institutional comparisons, stability of plan quality may be found in verification and care must be taken when determining an institution-specific action level from treatment plans with different field shape settings and incorrectly placed reference point placements.
Funding Support, Disclosures, and Conflict of Interest: This research was partially supported by grants from the Japan Agency for Medical Research and Development (AMED) [grant Number 15ck0106185h0001] and Triangle Products.