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Dosimetric Evaluation of the Impact of Density Correction On Dose Calculation of Breast Cancer Treatment: A Study Based On RTOG 1005 Cases

J Li*, Y Yu , Thomas Jefferson University, Philadelphia, PA

Presentations

SU-E-T-129 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: RTOG 1005 requires density correction in the dose calculation of breast cancer radiation treatment. The aim of the study was to evaluate the impact of density correction on the dose calculation.

Methods: Eight cases were studied, which were planned on an XiO treatment planning system with pixel-by-pixel density correction using a superposition algorithm, following RTOG 1005 protocol requirements. Four were protocol Arm 1 (standard whole breast irradiation with sequential boost) cases and four were Arm 2 (hypofractionated whole breast irradiation with concurrent boost) cases. The plans were recalculated with the same monitor units without density correction. Dose calculations with and without density correction were compared.

Results: Results of Arm 1 and Arm 2 cases showed similar trends in the comparison. The average differences between the calculations with and without density correction (difference = Without - With) among all the cases were: -0.82 Gy (range: -2.65~-0.18 Gy) in breast PTV Eval D95, -0.75 Gy (range: -1.23~0.26 Gy) in breast PTV Eval D90, -1.00 Gy (range: -2.46~-0.29 Gy) in lumpectomy PTV Eval D95, -0.78 Gy (range: -1.30~0.11 Gy) in lumpectomy PTV Eval D90, -0.43% (range: -0.95~-0.14%) in ipsilateral lung V20, -0.81% (range: -1.62~-0.26%) in V16, -1.95% (range: -4.13~-0.84%) in V10, -2.64% (-5.55~-1.04%) in V8, -4.19% (range: -6.92~-1.81%) in V5, and -4.95% (range: -7.49~-2.01%) in V4, respectively. The differences in other normal tissues were minimal.

Conclusion: The effect of density correction was observed in breast target doses (an average increase of ~1 Gy in D95 and D90, compared to the calculation without density correction) and exposed ipsilateral lung volumes in low dose region (average increases of ~4% and ~5% in V5 and V4, respectively).

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