Abstract
BackgroundThe aim of this study was to compare dose-volume histogram (DVH) with dose-mass histogram (DMH) parameters for treatment of left-sided breast cancer in deep inspiration breath-hold (DIBH) and free breathing (FB). Additionally, lung expansion and anatomical factors were analyzed and correlated to dose differences.MethodsFor 31 patients 3D conformal radiation therapy plans were retrospectively calculated on FB and DIBH CTs in the treatment planning system. The calculated doses, structures and CT data were transferred into MATLAB and DVHs and DMHs were calculated. Mean doses (Dmean), volumes and masses receiving certain doses (Vx, Mx) were determined for the left lung and the heart. Additionally, expansion of the left lung was evaluated using deformable image registration. Differences in DVH and DMH dose parameters between FB and DIBH were statistically analyzed and correlated to lung expansion and anatomical factors.ResultsDIBH reduced Dmean (DVH) and relative V20 (V20 [%]) of the left lung in all patients, on average by − 19 ± 9% (mean ± standard deviation) and − 24 ± 10%. Dmean (DMH) and M20 [%] were also significantly reduced (− 12 ± 11%, − 16 ± 13%), however 4 patients had higher DMH values in DIBH than in FB. Linear regression showed good correlations between DVH and DMH parameters, e.g. a dosimetric benefit smaller than 8.4% for Dmean (DVH) in DIBH indicated more irradiated lung mass in DIBH than in FB. The mean expansion of the left lung between FB and DIBH was 1.5 ± 2.4 mm (left), 16.0 ± 4.0 mm (anterior) and 12.2 ± 4.6 mm (caudal). No significant correlations were found between expansions and differences in Dmean for the left lung. The heart dose in DIBH was reduced in all patients by 53% (Dmean) and this dosimetric benefit correlated to lung expansion in anterior.ConclusionsTreatment of left-sided breast cancer in DIBH reduced dose to the heart and in most cases the lung dose, relative irradiated lung volume and lung mass. A mass related dosimetric benefit in DIBH can be achieved as long as the volume related benefit is about ≥8–9%. The lung expansion (breathing pattern) showed no impact on lung dose, but on heart dose. A stronger chest breathing (anterior expansion) for DIBH seems to be more beneficial than abdominal breathing.
Highlights
Radiation therapy is well-established in the treatment of breast cancer reducing the rate of locoregional recurrence and improving survival rate [1, 2]
The total lung mass showed a good accordance between free breathing (FB) and deep inspiration breath-hold (DIBH), whereas the mean lung density decreased from 0.31 ± 0.05 g/cm3 (FB) to 0.17 ± 0.03 g/cm3 (DIBH) (Table 1)
Irradiation in DIBH resulted in a significant reduction of mean dose (Dmean) to the left lung of the dose-volume histogram (DVH) from 10.0 ± 1.7 Gy (FB) to 8.1 ± 1.6 Gy (DIBH) (p < 0.01, Table 1)
Summary
Radiation therapy is well-established in the treatment of breast cancer reducing the rate of locoregional recurrence and improving survival rate [1, 2]. To reduce the risk of short or long term side-effects several techniques are available (e.g. intensity-modulated radiation therapy, treatment in prone position or respiration correlated irradiation) which provide improved dose sparing to the heart and the lung. A promising technique is gated irradiation during deep inspiration breath-hold (DIBH) [12,13,14,15,16,17,18,19,20,21,22,23,24,25,26] This technique was investigated by several studies with diverse endpoints, mostly focused on reducing dose to the heart and heart substructures like the left anterior descending coronary artery (LAD) in left sided breast cancer treatment. Lung expansion and anatomical factors were analyzed and correlated to dose differences
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