Heart sparing breast cancer radiotherapy using continuous positive airway pressure (CPAP) and conventional supine tangential fields: an alternative method for patients with limited accessibility to advanced radiotherapy techniques

Figures & data

Figure 1. Physical changes in the thorax with continuous positive airway pressure (CPAP) compared to free-breathing in patients with different cardiac–thoracic anatomy. Digitally reconstructed radiographs (top) and axial images (bottom) from computed tomography simulation scans representative thoracic changes with free-breathing and after 30 min of CPAP breathing under the individual maximum tolerable air pressure (between 6 and 15 cmH₂O with 0.21 of fraction of inspired oxygen with the use of a mask interface) in patients with different cardiac–thoracic anatomy (CTA). Unfavorable CTA was defined per Taylor et al.,⁵ the maximum distance >1 cm between the heart contour and the posterior edge of the tangent field as measured on computed tomography simulation with FB. Chest wall deformity with pectus excavatum was considered as challenging CTA. If the patient did not meet the two descriptions stated above, the patient was categorized as favorable CTA. Panel A, B, and C shows patient with favorable-, unfavorable-, and challenging CTA, respectively (Supplementary Figures S1 A and B with favorable- and challenging CTA, respectively).

Table 1. Physical changes in the thorax with continuous positive airway pressure compared to free-breathing in patients with different cardiac–thoracic anatomy.

	Favorable CTA		Unfavorable CTA		Challenging CTA
	FB	CPAP	FB	CPAP	FB	CPAP
Lung
Volume (cm^3)
Right	1981	2432	1390	1776	142	2391
% change	+23%		+28%		+68%
Left	1676	2113	1190	1552	1465	1929
% change	+26%		+30%		+32%
Total	3656	4545	2580	3328	2886	4320
% change	+24%		+29%		+50%
Heart
Distance (cm) from sternal notch	7.7	8.2	5.2	6.2	8	9.2
% change	+7%		+18%		+15%
Volume (cm^3) in left-sided tangent field	2.2	0.01	35.5	2.8	19	1.2
% change	−99%		−92%		−94%
Liver
Distance (cm) from sternal notch	17	19.5	8	11.7	9	11
% change	+15%		+47%		+22%
Volume (cm^3) in right-sided tangent field	20.1	3.3	209.8	136.1	60.5	54.4
% change	−84%		−35%		−10%

CTA: cardiac–thoracic anatomy; FB: free-breathing; CPAP: continuous positive airway pressure (30 min under the individual maximum tolerable air pressure (between 6 and 15 cmH₂O with 0.21 of fraction of inspired oxygen with the use of a mask interface).

Unfavorable CTA was defined per Taylor et al.,⁵ the maximum distance >1 cm between the heart contour and the posterior edge of the tangent field as measured on computed tomography simulation with FB. Chest wall deformity with pectus excavatum was considered as challenging CTA. If the patient did not meet the two descriptions stated above, the patient was categorized as favorable CTA. % change was calculated by (parameter with FB – parameter with CPAP)/parameter with FB.

Table 2. Continuous positive airway pressure effects on radiation doses to organs at risks compared to free-breathing in patients with different cardiac–thoracic anatomy.

	Favorable CTA		Unfavorable CTA		Challenging CTA
	FB	CPAP	FB	CPAP	FB	CPAP
Lung
Ipsilateral-lung in left-sided RT plan	without IMN RT		with IMN RT
Dmean	9.7 Gy	9.1 Gy	18.8 Gy	17.7 Gy	23.9 Gy	18 Gy
% change	−6%		−6%		−25%
V20 (%)	17	16	39	36	48	36
% change	−9%		−8%		−26%
Ipsilateral-lung in right-sided RT plan	without IMN RT		without IMR RT
Dmean	10.1 Gy	8.7 Gy	10.1 Gy	8.2 Gy	11.0 Gy	9.8 Gy
% change	−14%		−19%		−11%
V20 (%)	17.8	14.2	18.5	14.2	19.5	17.7
% change	−20%		−23%		−9%
Heart
In left-sided RT plan	without IMR RT		with IMN RT
Dmean	2.6 Gy	2 Gy	11.3 Gy	2.9 Gy	4.8 Gy	0.9 Gy
% change	−23%		−74%		−81%
V25 (%)	1.9	0.3	18.9	2.3	6.8	0.0
% change	−84%		−88%		−100%
Liver
In right-RT plan
Dmax	19.2 Gy	9.3 Gy	52.6 Gy	23.5 Gy	51.1 Gy	51.9 Gy
% change	−52%		−55%		+2%

RT: radiotherapy; FB: free-breathing; CPAP: continuous positive airway pressure (30 min under the individual maximum tolerable air pressure (between 6 and 15 cmH₂O with 0.21 of fraction of inspired oxygen with the use of a mask interface); CTA: cardiac–thoracic anatomy; IMN: internal mammary node; D_mean: mean radiation dose; D_max: maximum radiation dose; V20 and V25: volume receiving at least 20 and 25 Gy, respectively.

Unfavorable CTA was defined per Taylor et al.,⁵ the maximum distance >1 cm between the heart contour and the posterior edge of the tangent field as measured on computed tomography simulation with FB. Chest wall deformity with pectus excavatum was considered as challenging CTA. If the patient did not meet the two descriptions stated above, the patient was categorized as favorable CTA. % change was calculated by (parameter with FB – parameter with CPAP)/parameter with FB.