Impact of internal mammary chain irradiation on heart subvolumes doses in breast cancer radiotherapy
PO-1891
Abstract
Impact of internal mammary chain irradiation on heart subvolumes doses in breast cancer radiotherapy
Authors: Zeineb Naimi1, Emna Bennour2, Henda Neji3, Meriem El Bessi1, Raouia Ben Amor1, Mariem Bohli1, Jamel Yahyaoui1, Lotfi Kochbati1
1Abderrahmen Mami Hospital Ariana, Radiation Oncology Department, Ariana, Tunisia; 2Abderrahmen Mami Hospital Ariana, Cardiology Department, Ariana, Tunisia; 3Abderrahmen Mami Hospital Ariana, Radiology Department, Ariana, Tunisia
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Purpose or Objective
The aim of
this study was to analyse the impact of internal mammary chain (IMC)
irradiation on coronary arteries and cardiac subvolumes exposure in breast
cancer (BC) RT.
Material and Methods
One-hundred
and twenty-five patients planned for adjuvant breast cancer RT with indication
of IMC irradiation were evaluated: 75 patients with left-sided BC and 50 patients with
right-sided BC. All patients were treated with hypofractionated 3D conformal RT,
by tangential fields +/- supraclavicular field, using a mono-isocentric
technique. The prescription dose was 40 Gy delivered in 15 fractions +/- an
additional boost of 13.35 Gy. Cardiac subvolumes were contoured based on the
Duane’s cardiac contouring atlas. For each patient, DVHs for coronary arteries
and cardiac chambers were generated with and without including IMC in the
tangential fields. DVHs were statistically compared and the contribution of IMC
irradiation to cardiac substructures mean and maximum doses was assessed.
Results
RT
was delivered to the chest wall in 58% and to the remaining breast in 42% of
patients. Higher doses to the heart and cardiac subvolumes were reported in the
left-sided BC RT when compared to the right-sided BC RT (p<0.01). Regardless
of BC laterality, IMC RT was strongly correlated with MHD, Dmean and Dmax to
coronary arteries and cardiac chambers with Pearson coefficients ranging
between 0.73 and 0.86. The MHD was significantly higher with IMC irradiation
with mean values of 3.83 Gy vs 2.49 Gy (p<0.01) in the left-sided BC group,
and 1.56 Gy vs 0.83 Gy (p=0.02) in the right-sided BC group. IMC RT contributed
to significant increase in Dmean and Dmax to all cardiac chambers and coronary
arteries in both left and right-sided BC RT. The greatest contribution of IMC
RT to cardiac subvolumes doses was found for the left-anterior descending
artery (LAD)/left ventricle (LV) in the left-sided BC RT and for the right
coronary artery (RCA) /right atrium (RA) in the right-sided BC RT. IMC RT yielded,
on average, 23% increase in Dmax LAD and 29.5% in Dmean LV. For the right-sided
BC RT, IMC RT increased on average the Dmax RCA by 17% and Dmean RA by 24.6%.
Conclusion
IMC
RT was related to higher exposure of coronary arteries and cardiac chambers in
both right and left-sided BC RT. The exclusive contribution of IMC RT to heart
subvolumes doses was not negligible, which may translate into an excessive risk
of late cardiovascular morbidity. Heart sparing techniques should be considered
when IMC RT is indicated.