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Assessing Dosimetric Improvements in Left-Sided Breast Cancer Patients with IMN Involvement Using VMAT and Deep Inspiration Breath Hold

SK Edgington*, LT Vanbenthuysen, J Pursley, AG Taghian, SM MacDonald, RB Jimenez, DP Gierga, Massachusetts General Hospital and Harvard Medical School, Boston, MA


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: Three-dimensional conformal radiation therapy (3D-CRT) is used for chest wall (CW) patients with internal mammary nodes (IMNs) but it is challenging to maintain target coverage while limiting organ-at-risk (OAR) doses. Volumetric modulated arc therapy (VMAT) may improve plan quality. Deep-inspiration breath-hold (DIBH) can reduce cardiac dose for left-sided patients, but may not be necessary for cardiac sparing if VMAT is used.

Methods: 3D-CRT plans were compared to multicriteria optimization-based VMAT plans for ten left-sided patients with IMN involvement using free-breathing (FB) and DIBH. The CW and IMNs were prescribed to 5040 cGy. DVH data was compared for all four plans per patient and metrics averaged over all patients. Heart blocking was used for 3D-CRT to maintain cardiac dose between FB and DIBH.

Results: For VMAT-DIBH compared to VMAT-FB, cardiac mean and maximum dose was significantly reduced from 404 to 316 cGy and 1768 to 1268 cGy, respectively. Maximum cardiac dose did not change significantly between 3D-FB and VMAT-FB or 3D-DIBH and VMAT-DIBH. In the ipsilateral lung, no significant differences were observed between FB and DIBH, however V5 significantly increased for VMAT-DIBH vs 3D-DIBH (51% vs 45%) but V20 decreased (20% vs 23%). Contralateral breast dose significantly increased for VMAT-DIBH vs 3D-DIBH (850 vs 70 cGy). Minimal differences in CW coverage were observed between FB and DIBH, however VMAT improved CW coverage. DIBH increased IMN coverage (D90) for 3D-CRT from 2530 to 3540 cGy. IMN D90 was significantly higher for both VMAT-DIBH and VMAT-FB (4815 and 4911 cGy) vs 3D-DIBH and 3D-FB but the differences between VMAT-DIBH and VMAT-FB were not significant.

Conclusion: VMAT allowed for improved target coverage, regardless of breathing technique, compared to 3D-CRT, at the expense of higher mean cardiac dose. DIBH reduced cardiac dose for VMAT although VMAT FB doses may still be clinically acceptable.


Breast, Treatment Planning, Treatment Techniques


TH- External beam- photons: treatment planning/virtual clinical studies

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