2043 - Benefit of Deep Inspiration Breath Hold Technique for VMAT Right-Sided Post-Mastectomy Nodal Irradiation

Purpose/Objective(s): Deep inspiration breath hold (DIBH) is commonly used in left-sided breast cancer radiotherapy to reduce cardiac and pulmonary dose and hence toxicity. The emerging use of volumetric modulated arc therapy (VMAT) technique for breast radiotherapy for improved dose conformity, potentially alters the effectiveness of DIBH. The benefit of DIBH in right sided breast radiotherapy including regional nodal irradiation (RNI) when using VMAT remains underexplored. This study aims to investigate the potential dosimetric benefits of DIBH compared to free breathing (FB) in right-sided breast radiotherapy (including RNI) when using VMAT.

Materials/Methods: Retrospective dosimetric analysis was conducted on 20 right sided post-mastectomy breast cancer (including RNI) patients, with and without implants (autologous or otherwise). All patients had both DIBH and FB planning computed tomography (pCT) scans done on the same day, leading to 40 pCT scans. Clinical target volumes of the right chest wall, axilla levels II, III, supraclavicular fossa, and internal mammary chain were delineated, and expanded by 5mm to create planning target volumes. VMAT plans were generated to a prescription dose of 40.05Gy in 15 fractions, adhering to institutional organs at risk (OAR) dose constraints. The dose to OARs underwent dosimetric comparisons using Wilcoxon signed-rank test or paired t-test, reported as median or mean as appropriate, with normality testing to assess data distribution. Dose metrics were evaluated (where Vx values defined as % volume of the organ receiving XGy and Dx values defined as maximum dose that X% the organ is receiving) for right lung (V17Gy and V5Gy), left lung (V5Gy), heart (D2% and mean dose), left breast (D10%), spinal canal (D0.03cc), esophagus (D1cc), and right humeral head (D5cc).

Results: For the 20 patients, DIBH significantly reduced right lung dose compared to FB, with a decrease in V17Gy (23.04% vs 27.07%, p<0.0001) and V5Gy (51.01% vs 57.27%, p<0.0001). Heart dose was also significantly reduced, with a decrease in maximum D2% (6.664Gy vs 10.01Gy, p=0.0001) and mean (1.82Gy vs 2.59Gy, p < 0.0001) in DIBH compared to FB. A significant reduction in contralateral breast dose was observed, with a decrease in D10% (2.68Gy vs 3.17Gy, p=0.0021) for DIBH compared to FB. Smaller reductions were observed in DIBH compared to FB for esophagus (9.03Gy vs 9.48Gy, p = 0.0446), left lung (2.18% vs 2.17%, p=0.0594), right humeral head (18.73Gy vs 19.31Gy, p=0.1559) and spinal canal (11.16Gy vs 11.89Gy, p=0.1354), though these were not statistically significant.

Conclusion: DIBH significantly reduces lung, heart and contralateral breast dose in right sided breast cancer patients receiving post-mastectomy chest wall radiotherapy, including RNI. These findings suggest that DIBH should be routinely considered for this patient cohort to minimize radiation exposure to these critical organs.