Effect of RTOG breast/chest wall guidelines on dose-volume histogram parameters

Abstract

Treatment planning for breast cancer has been traditionally based on clinical landmarks. The Radiation Therapy Oncology Group (RTOG) published consensus guidelines on contouring target volumes (TV) for the breast/chest wall and draining lymphatics. The effect of these guidelines on dosimetric parameters in surrounding organs at risk (OAR) and TVs is unknown. Fourteen patients treated with clinically derived plans from 2007-2011 (Group I) and fourteen patients treated with target volume-based plans from 2011-2012 were selected for comparison (Group II). Treatment plans were constructed based on clinical landmarks (Group I) or TVs (Group II) to a median dose of 50.4 Gy to the breast/chest wall, axilla (Ax), supraclavicular (SCV), and internal mammary (IMN) lymph nodes. The RTOG TVs were then contoured in Group I patients by a single investigator blinded to the dose distributions. Dose-volume histograms (DVH) were computed for the RTOG TVs and OARs in both groups, and DVH parameters were compared. In Group II, coverage improved for the SCV (V90 = 78.0% versus 93.6%, p = 0.02) and intact breast (V95 = 95.6% versus 99.3%, p = 0.007). The dose to the cord, the lung (V20Gy and V30Gy), and contralateral breast (V5Gy) were the same. Finally, the low dose to the heart and lung was decreased in Group II (heart V5Gy= 48.7% versus 27.3%, p= 0.02, heart V10Gy = 33.5% vs. 17.5%, p = 0.01, and ipsilateral lung V5Gy = 84.5% vs. 69.3%, p = 0.001). Overall, our study supports that treatment planning using the RTOG consensus guidelines can improve coverage to certain target volumes compared to treatments based solely on clinical landmarks. Additionally, treatment planning using these target volumes does not increase dose to the contralateral breast, cord, heart, or lungs. Longer follow-up is needed to determine if using these target volumes will affect clinical outcomes.

Figure 1

Composite SCV DVH of patients in Group I (blue) ± one standard deviation (blue dotted lines) compared to the composite SCV DVH of patients in Group II (red) ± one standard deviation (red dotted lines). Mean $\mathrm{V}90=78.0\mathrm{\%}$ (Group I) versus 93.6% (Group II) $(p=0.02)$.

Figure 2

Composite heart DVH (a) of patients with left‐sided tumors in Group I (blue) ± one standard deviation (blue dotted lines) compared to patients with left‐sided tumors in Group II (red) ± one standard deviation (red dotted lines). Mean $\mathrm{V}5\text{Gy}=68.6\mathrm{\%}$ (Group I) versus 39.1% (Group II) $(p=0.0004)$. Composite heart DVH (b) of patients with right‐sided tumors in Group I (blue) ± one standard deviation (blue dotted lines) compared to patients with right‐sided tumors in Group II (red) ± one standard deviation (red dotted lines). Mean $\mathrm{V}5\text{Gy}=22.2\mathrm{\%}$ (Group I) versus 11.5% (Group II) $(p=0.10)$ and mean V20Gy = 5.9% (Group I) vs. 2.0% (Group II) $(p=0.04)$.