Benefit of Deep Inspiratory Breath Hold for Right Breast Cancer When Regional Lymph Nodes Are Irradiated.

BACKGROUND: Although deep inspiratory breath-hold (DIBH) is routinely used for left-sided breast cancers, its benefits for right-sided breast cancer (rBC) have yet to be established. We compared free-breathing (FB) and DIBH treatment plans for a cohort of rBC undergoing regional nodal irradiation (RNI) to determine its potential benefits. METHODS AND MATERIALS: rBC patients considered for RNI (internal mammary nodal chains, supraclavicular field, with or without axilla) from October 2017 to May 2020 were included in this analysis. For each patient, FB versus DIBH plans were generated and dose volume histograms evaluated the following parameters: mean lung dose, ipsilateral lung V20/V5 (volumes of lung receiving 20 Gy and 5 Gy, respectively); mean heart dose and heart V5 (volumes of heart receiving 5 Gy); liver V20 absolute /V30 absolute (absolute volume of liver receiving 20 Gy and 30 Gy, respectively), liver Dmax, and total liver volume irradiated (TVIliver). The dosimetric parameters were compared using Wilcoxon signed-rank testing. RESULTS: Fifty-four patients were eligible for analysis, comparing 108 FB and DIBH plans. DIBH significantly decreased all lung and liver parameters: mean lung dose (19.7 Gy-16.2 Gy, P < .001), lung V20 (40.7%-31.7%, P < .001), lung V5 (61.2%-54.5%, P < .001), TVIliver (1446 cc vs 1264 cc; P = .006) liver Dmax (50.2 Gy vs 48.9 Gy; P = .023), liver V20 (78.8-23.9 cc, P < .001), and liver V30 (58.1-14.6 cc, P < .001) compared with FB. DIBH use did not significantly improve heart parameters, although the V5Heart trended on significance (1.25-0.6, P = .067). CONCLUSIONS: This is the largest cohort to date analyzing DIBH for RNI-rBC. Our findings demonstrate significant improvement in all lung and liver parameters with DIBH, supporting its routine consideration for rBC patients undergoing comprehensive RNI.

Standard Tangential Radiation Fields Do Not Provide Incidental Coverage to the Internal Mammary Nodes.

PURPOSE: The purpose of the study was to evaluate the incidental dose delivered to the internal mammary nodes (IMNs) in patients treated with tangential 3-dimensional conformal radiation therapy and to identify potential parameters that may affect the IMN mean dose. METHODS AND MATERIALS: The study cohort consisted of 362 consecutively treated patients with breast cancer in our center between January 2015 and July 2017 who had received adjuvant whole-breast radiation therapy or postmastectomy radiation with or without a supraclavicular ± axillary field and without intentional inclusion of the IMN chain. The clinical target volume (CTV) for the IMNs was contoured per the Radiation Therapy Oncology Group 3509/3510 protocol and was then divided into 3 subregions: upper, mid, and lower thirds. The planning target volume for the IMNs was generated by adding 5 mm to the CTV. The primary endpoint was to assess the V40 (volume receiving 40 Gy) to the IMN planning target volume and its potential influencing parameters using a linear regression model. RESULTS: The mean (±standard deviation) dose to the CTV IMN chain was 36% ± 28.7%. The Kruskal-Wallis test demonstrated significant differences in the median dose delivered to each level: upper third (7.2%), mid third (21.5%), and lower third (41.7%) (P < .001). The mean V40 IMN planning target volume was 14.2% (standard deviation, 18.7%). Presternal fat thickness (regression coefficient [RC] = -16.4; P < .001), postmastectomy radiation (RC = 24; P < .001), reconstruction after mastectomy (RC = -22.4; P < .001), and the addition of a supraclavicular field (RC = 8.8; P = .03) were all significantly associated with IMN mean dose. CONCLUSIONS: For patients receiving standard breast/chest wall tangential radiation fields, the IMN chain is not incidentally covered with therapeutic doses in the vast majority of cases. Therefore, if regional nodal radiation is intended to include the IMNs, contouring and careful plan review are necessary to ensure adequate therapeutic coverage.