PV QA 3 - Poster Viewing Q&A 3
Purpose/Objective(s): This study aims at proving that voluntary Deep Inspiration Breath- Holding (vDIBH) technique lowers radiation exposure to the heart and Left Anterior Descending Artery (LAD) without compromising coverage of left breast or chest wall. Irradiation of a substantial volume of the heart to a sufficiently high dose can damage virtually any component of the heart which can cause significant morbidity or mortality.
Materials/Methods: Sixty-six women with left sided breast cancer requiring post-operative radiotherapy and fulfilling inclusion criteria were accrued from radiotherapy department at a single institution from November 2015 to December 2016. Inclusion criteria comprised patients with non-metastatic left breast cancer who are candidates for post-operative radiotherapy and can hold their breaths for longer than 20 seconds. Informed consent was obtained from all patients who were then coached on proper method of breath holding. 2 sets of CT simulations were done during free breathing and DIBH techniques. The average time for which the patients were asked to hold their breath was between 18 and 23 seconds. Both CT image data serials were then transferred to the treatment planning system where target volume and organs at risk (left lung, heart, and contralateral breast) were delineated according to RTOG protocols. LAD arteries were contoured according to the University of Michigan cardiac atlas. 3D-conformal planning using hypofractionated dose of 40Gy/15 fractions was done in all cases. Dose-Volume Histograms were used to compare between both techniques regarding doses to critical organs at risk (mean heart dose, V10-heart, V20-heart, V25-heart, LAD artery, contralateral breast, and lungs), and planning target volume (PTV). Acceptance was based on RTOG 1005 and University of Michigan protocols.
Results: Using vDIBH technique, all patients had lower heart and LAD artery doses. In the free breathing serials, mean heart doses ranged from 99 cGy to 613 cGy with the average being 330 cGy. Based on RTOG 1005 protocol, 3 patients had an unacceptable mean heart dose of more than 500 cGy, while 14 patients had a less than ideal mean heart dose between 400 and 500 cGy. Utilizing vDIBH technique, mean heart doses ranged from 74 cGy to 407 cGy with the average being 210 cGy. This represents a statistically significant difference (p-value <0.001). Patients who received internal mammary nodal irradiation, with wide tangential fields, showed statistically significant lower doses regarding heart and LAD artery between both techniques (p-value <0.05).
Conclusion: vDIBH technique was associated with lower radiation dose to the heart, LAD artery and ipsilateral lung without compromising coverage of the breast or chest wall.
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