(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: Impact of Acuros XB algorithm in deep inspiration breath hold techniques used for the treatment of left breast cancer
Methods: A computed tomography (CT) data set of 15 patients in two different respiratory phases (FB and DIBH) treated for left breast cancer was analyzed. Treatment plans were computed using field-in-field technique for tangential fields of 6 MV photon beam energy. The AXB-calculations were performed under identical beam setup and same numbers of monitor units (MUs) used for AAA-calculations.
Results: For lung, the average HU’s were -782.1 ± 24.8 and -883.5 ± 24.9, average mass density (g/cc) were 0.196 ± 0.025 and 0.083 ± 0.032, and average relative electron density were 0.218 ± 0.025 and 0.117 ± 0.025, in FB and DIBH respiratory phases respectively. The dosimetric data shows that, there was no significant difference in PTV coverage (Ï? > 0.05) in DIBH respiratory phase for both algorithms. On contrary, there was significant increase in mean dose, maximum dose and percentage volume of Vâ‚?₀₈ to PTV. Similarly, there was slight increase in OAR’s mean dose for AXB-calculation in comparison to AAA-calculation, except for lung mean dose. In present study, V20Gy for ipsi-lateral and common lung was higher for AXB-calculation in comparison to AAA-calculation. The maximum difference in V20Gy between both algorithms was 1.71 ± 0.82 % and 1.76 ± 0.83 % in FB respiratory phase, 3.34 ± 1.15 % and 3.24 ± 1.17 % in DIBH respiratory phase, for ipsi-lateral and common lung respectively.
Conclusion: Present study indicates that lung electron density reduces due to air filling in DIBH. AXB account more accurately for low-density inhomogeneity present in DIBH respiratory phase for left breast cancer. Thus, AXB-calculation in conjunction with DIBH may results in better estimation of lung toxicities and treatment outcome.
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