Routine contouring of the RTOG recommended target volumes for breast cancer planning was initiated in our clinic in 2011. The purpose of this study was to assess if the dose to surrounding normal tissues was affected when trying to adequately cover the RTOG recommended target volumes. Ten patients who had undergone treatment planning prior to routine contouring of the RTOG target volumes were identified (Group I). For these patients, standard breast fields were constructed based on marks placed at the time of simulation and modified by the attending physician based on the CT anatomy. The RTOG volumes for the breast/chest wall, supraclavicular nodes (SCV), and axilla were then contoured without knowledge of the dose distributions. Subsequently, dose-volume histograms (DVHs) were constructed for these structures. The DVHs of these 10 patients were compared to the DVHs of 10 patients who were planned with the RTOG target volumes contoured prior to treatment planning (Group II). All patients had Stage IIA-IIIC disease and were treated to the breast/chest wall, axilla, SCV, and internal mammary nodes (IMN) to a median dose of 50.4 Gy. The coverage goals were ≥95% of the prescribed dose to ≥ 95% of the target volume for the breast/chest wall, SCV, and axilla and ≥80% of the prescribed dose to ≥ 95% of IMN. Baseline patient characteristics were compared with a chi-squared test and the difference between coverage goals was compared using a student's t-test. Five patients were treated to the chest wall after lumpectomy in group I vs. 7 patients in group II p = 0.64. Three patients were treated to the right side in each group (2 after mastectomy and 1 after lumpectomy). There was no difference in the maximum separation between the two groups, p = 0.23. The mean dose for the target volumes and normal tissues that were improved with delineation of the target volumes are listed in Table. There was a trend towards improvement in SCV coverage and breast coverage. There was no difference between coverage of the chest wall (p = 0.42), IMN (p = 0.34), axillary level 1 (0.08), axillary level 2 (p = 0.11), axillary level 3 (p = 0.13), ipsilateral lung V20 (p = 0.47), and ipsilateral lung V30 (p = 0.07). Our analysis reveals that contouring the RTOG target volumes prior to treatment planning can help construct plans that will improve coverage to these regions without increasing dose to the surrounding normal tissues.Poster Viewing Abstract 3567; TableMean coverage of target volumes and surrounding organs at riskStructureGroup 1 (mean)Group II (mean)p-valueBreast V9596.9%98.7%0.05SCV74.9%88.5%0.05Heart V2015.5%8%0.03Contralateral breast V54.3%1.5%0.04 Open table in a new tab