Between December 2018 to November 2019, a total of 25 patients with 50 CT scans who underwent tangential field radiotherapy for left sided breast cancer with DIBH technique, were eligible for this study as shown in Table I. Median age was 47.6 years with a range extending from 28 years to 69 years. 12 out of 25 women (48%) analysed had Stage III A disease while only 1 woman had Stage I disease. Indication for Adjuvant RT in Stage I was inadequate axillary dissection with other risk factors like young age, high grade and triple negativity. Mean breath hold duration was 19.84 ± 3.84 seconds with a range extending from 15 second to 30 seconds.
Table I: Patient characteristics
CHARACTERISTICS
|
n (%)
|
Median age
|
47.6 years ( Range 28–69years)
|
Menopausal status
Premenopausal
Perimenopausal
Postmenopausal
|
11 ( 44%)
04 ( 14%)
10 ( 40%)
|
Prior fertility treatment
|
3 (12%)
|
Family history
|
4 (16%)
|
AJCC Staging
Stage I
Stage IIA
Stage IIB
Stage IIIA
|
01 (4%)
04 (16%)
08 (32%)
12 (48%)
|
Surgery
MRM + ALND
|
25 (100%)
|
Hormone Status
ER/PR
HER 2 neu
|
17 (68%)
04 (16%)
|
Chemotherapy
|
23 (92%)
|
Mean Breath Holding Duration (seconds)
|
19.82 seconds
|
Dosimetric analysis was done with the help of DVH generated for FB and DIBH plans for each patient. The dose volume parameters for the Heart, LAD, Left lung, both lungs and PTV were compared and recorded using the thus generated DVH as shown in Table II-V. DIBH significantly reduced mean heart doses in comparison with FB. All cardiac volume parameters analysed showed a significant reduction with DIBH as tabulated in Table II.
The relative reduction in average mean heart dose (D mean) with DIBH technique was 1.46Gy or 28.19% ie to more than one-fourth (from 5.18Gy (with FB) to 3.72Gy (with DIBH) (p value < 0.001)). The mean of maximum heart dose ( Dmax) was reduced from 38.63Gy with FB to 37.73Gy with DIBH (corresponding to a 2.3% reduction of maximum heart dose). However this reduction was not statistically significant (p = 0.381).
Table II : Comparison of FB and DIBH - Cardiac dose volume parameters
Comparison of Cardiac dose volume parameters in FB vs DIBH
|
|
V5
(%)
|
V10 (%)
|
V15 (%)
|
V20 (%)
|
V25 (%)
|
V30 (%)
|
Dmean
Gy
|
Dmax
Gy
|
FB
|
Mean
|
16.35
|
10.38
|
8.70
|
7.30
|
6.33
|
5.43
|
5.18
|
38.63
|
STD
|
10.45
|
6.12
|
5.07
|
4.70
|
4.41
|
4.05
|
2.39
|
4.9
|
DIBH
|
Mean
|
13.1
|
6.94
|
5.41
|
4.24
|
3.4
|
2.77
|
3.72
|
37.73
|
STD
|
9.59
|
5.22
|
4.61
|
4.22
|
3.86
|
3.52
|
1.57
|
4.83
|
p value
|
|
0.006
|
0.002
|
< 0.001
|
< 0.001
|
< 0.001
|
< 0.001
|
< 0.001
|
0.381
|
% decrease with DIBH
|
Mean
|
17.74
|
33.14
|
37.82
|
41.92
|
46.29
|
48.99
|
28.19
|
2.33
|
STD
|
8.23
|
14.71
|
9.07
|
10.21
|
12.47
|
13.09
|
34.31
|
1.43
|
FB-Free Breathing, DIBH - Deep Inspiratory Breath Hold, STD – Standard Deviation, V’x’Gy – Volume of Heart receiving ‘x’Gy, D mean –Mean Dose, D max – Maximum Dose
LAD artery is the closest major coronary vessel to tangential breast fields. Because of its small volume, delineating and evaluating the dose to LAD is a difficult task and depends on the physicians expertise. This is further aggravated by setbacks like washout of contrast before acquiring both sets of CT images, presence of motion artefacts and improper slice thickness. Very few studies in the literature have dealt with doses to the LAD and no standard protocols are present for the estimation of LAD doses nor have limiting factors or tolerances been defined. LAD doses in FB and DIBH plans were evaluated by tabulating the Dmean and Dmax doses as shown in Table III. Mean of LAD dose was reduced from 25.94Gy (in FB) to 16.99Gy (in DIBH) with a significant pvalue < 0.001. This corresponds to a relative reduction of 8.95Gy or 34.50% in the mean LAD doses with DIBH technique. The mean maximum LAD (Dmax) was reduced from 39.86Gy with FB to 38.39Gy with DIBH which was statistically significant (p = 0.003). This corresponds to a 3.69% reduction of maximum LAD dose with the use of DIBH technique.
Table III: Comparison of FB and DIBH - LAD dose parameters
Comparison of LAD dose parameters in FB vs DIBH
|
|
Dmean
Gy
|
Dmax
Gy
|
FB
|
Mean
|
25.94
|
39.86
|
STD
|
8.17
|
1.78
|
DIBH
|
Mean
|
16.99
|
38.39
|
STD
|
9.39
|
2.56
|
p value
|
|
< 0.001
|
0.003
|
% decrease with DIBH
|
Mean
|
34.50
|
3.69
|
STD
|
14.93
|
43.82
|
FB – Free Breathing, DIBH - Deep Inspiratory Breath Hold, STD – Standard Deviation, D mean –Mean Dose, D max – Maximum Dose
The maximal heart distance (MHD) is the width of heart in the tangent fields at its maximal level as shown in Fig III (Brady et al. 2019). Smaller maximum heart distance (MHD) was observed in DIBH scan when compared to FB scans.The mean MHD in FB and DIBH scans were 2.168cm and 1.224cm respectively. The maximum heart distance was thus reduced to almost half (43.54%) in DIBH technique, with a significant p value < 0.001.
There was a significant reduction in the ipsilateral mean lung doses (Dmean) and other lung volume parameters with DIBH technique when compare to FB technique as shown in Table IV. Even combined lung parameters like V20Gy and Mean Lung Dose (MLD) was significantly reduced as tabulated in Table V. CT scans using DIBH showed a significant larger total lung volume(TLV). The TLV was 2011.01cc in FB scan and 3123.38cc in DIBH scan. The mean increase in the Total Lung Volume was 55.31% (p < 0.001).
Table IV: Comparison of FB and DIBH - Lung dose volume parameters
Comparison of Ipsilateral lung dose volume parameters in FB vs DIBH
|
|
V5
(%)
|
V10 (%)
|
V15 (%)
|
V20 (%)
|
V25 (%)
|
V30 (%)
|
Dmean
Gy
|
Dmax
Gy
|
FB
|
Mean
|
44.51
|
30.56
|
25.74
|
22.81
|
20.02
|
17.31
|
10.77
|
41.1
|
STD
|
10.47
|
7.51
|
6.64
|
6.51
|
6.77
|
6.69
|
2.45
|
1.12
|
DIBH
|
Mean
|
34.25
|
22.56
|
19.43
|
17.36
|
15.41
|
13.34
|
8.72
|
41.34
|
STD
|
8.40
|
7.21
|
7.14
|
6.89
|
6.32
|
5.99
|
2.63
|
0.89
|
p value
|
|
< 0.001
|
< 0.001
|
< 0.001
|
< 0.001
|
< 0.001
|
< 0.001
|
< 0.001
|
0.219
|
% decrease with DIBH
|
Mean
|
23.05
|
26.18
|
24.51
|
23.89
|
23.03
|
22.94
|
19.03
|
0.59
|
STD
|
19.77
|
3.99
|
7.53
|
5.84
|
6.65
|
10.46
|
7.35
|
20.54
|
FB – Free Breathing, DIBH - Deep Inspiratory Breath Hold, STD – Standard Deviation, V’x’Gy – Volume of Left Lung receiving ‘x’Gy, D mean – Mean Dose, D max – Maximum Dose |
Table V: Comparison of FB and DIBH - Combined Lung dose parameters
Comparison of Combined lung dose volume parameters in FB vs DIBH
|
|
V20Gy
%
|
MLD
Gy
|
TLV
cc
|
FB
|
Mean
|
10.47
|
5.424
|
2011.01
|
STD
|
2.86
|
1.15
|
550.89
|
DIBH
|
Mean
|
8.19
|
4
|
3123.38
|
STD
|
2.72
|
1.08
|
719.27
|
p(*)
|
|
< 0.001
|
< 0.001
|
< 0.001
|
% decrease with DIBH
|
Mean
|
21.78
|
26.25
|
55.31
|
STD
|
4.89
|
6.09
|
30.57
|
FB – Free Breathing, DIBH - Deep Inspiratory Breath Hold, STD – Standard Deviation, MLD – Mean Lung Dose, V20Gy - Volume of Both lungs receiving 20Gy, TLV – Total Lung Volume.
In PTV, Dmean, Dmax and V95% ie % volume of PTV receiving more than 95% of prescribed dose was analyzed. There was no significant difference in the Breast PTV target dose coverage parameters in both the plan in terms of Dmean, Dmax. But V95% values were significantly better with DIBH plans.