Cardiol Res

Cardiology Research, ISSN 1923-2829 print, 1923-2837 online, Open Access

Article copyright, the authors; Journal compilation copyright, Cardiol Res and Elmer Press Inc

Journal website https://www.cardiologyres.org

Original Article

Volume 14, Number 4, August 2023, pages 279-290

Dosimetric Evaluation of Cardiac Structures on Left Breast Cancer Radiotherapy: Impact of Movement, Dose Calculation Algorithm and Treatment Technique

Figure 1. Effect of radiation on the heart. The physiopathology of radiation damage on the heart is complex and multifactorial, involving damage to the endothelial cells, conduction system, and myocardial cells themselves. The severity of radiation-induced cardiotoxicity depends on a variety of factors, including the dose and duration of radiation exposure, as well as individual patient factors such as age and underlying cardiovascular health.

Figure 2. Example of the set of images acquired for one patient: free breathing CT (left); paCT (middle); and DIBH CT (right). Red contours correspond to the target, while yellow, blue, green and orange contoured substructures in the heart correspond to left and right ventricles and left and right atria, respectively. Blurred heart and cardia substructures can be seen in the central image due to movement. CT: computed tomography; DIBH: deep inspiration breath-hold; paCT: phase-average CT.

Figure 3. Difference between patients’ doses calculated using paCT and FB CT images. Mean dose (left) and D_20cc (right) for each structure. CT: computed tomography; D_20cc: minimum dose to the 20 most irradiated cubic centimeters of volume; FB: free breathing; paCT: phase-average CT.

Figure 4. Difference of mean dose (left) and D_20cc (right) on each structure for the 10 patients, calculated for the DIBH plan vs. the reference plan. DIBH: deep inspiration breath-hold; D_20cc: minimum dose to the 20 most irradiated cubic centimeters of volume.

Figure 5. Difference of mean dose (left) and D_20cc (right) on each structure for the 10 patients, calculated for the extended margin plan vs. the reference plan. D_20cc: minimum dose to the 20 most irradiated cubic centimeters of volume.

Figure 6. Representative DVH of one patient for the heart and cardiac substructures calculated with the three algorithms: PB, CC and MC. DVHs for the target, heart and its substructures. CC: collapsed cone; DVH: dose volume histogram; MC: Monte Carlo; PB: pencil beam.

Figure 7. Mean difference in cGy between patient mean doses calculated for different structures with PB, CC and MC in Monaco. The dose calculated with Monte Carlo is used as a reference. CC: collapsed cone; MC: Monte Carlo; PB: pencil beam.

**Table 1.** Cohort of Patients Along With Their Respective Medical History and Treatment Plan
	Patient 1	Patient 2	Patient 3	Patient 4	Patient 5	Patient 6	Patient 7	Patient 8	Patient 9	Patient 10
AHT: arterial hypertension; BMI: body mass index; DLP: dyslipidemia; DM2: diabetes mellitus type 2; RT: radiotherapy.
Age	45	42	75	49	59	43	69	63	67	61
Previous RT	No	No	Yes	No	No	No	No	No	No	Yes
Total Gy	52.5	50	40	40	40	40	40	40	42.5	66
Fractions	20	20	15	15	15	15	15	15	16	33
Boost	Yes	Yes	No	No	No	No	No	No	No	Yes
Height (cm)	-	165	-	157	154	164	156	163	152	163
Weight (kg)	67	106	66	55	68	60	57	79.5	80	104
BMI	-	38.9	-	22.3	28.6	22.3	23.4	29.9	34.6	39.1
Smoker	Yes	Yes	Yes	Yes	Yes	No	Yes	Yes	No	Yes
DM2	No	Yes	No	No	Yes	No	No	Yes	No	No
AHT	No	No	No	No	Yes	No	Yes	No	Yes	No
DLP	No	Yes	No	No	No	No	No	Yes	No	Yes

Table 1. Cohort of Patients Along With Their Respective Medical History and Treatment Plan

Patient 1

Patient 2

Patient 3

Patient 4

Patient 5

Patient 6

Patient 7

Patient 8

Patient 9

Patient 10

AHT: arterial hypertension; BMI: body mass index; DLP: dyslipidemia; DM2: diabetes mellitus type 2; RT: radiotherapy.

Age

Previous RT

Yes

Total Gy

52.5

42.5

Fractions

Boost

Yes

Height (cm)

165

157

154

164

156

163

152

163

Weight (kg)

106

79.5

104

BMI

38.9

22.3

28.6

22.3

23.4

29.9

34.6

39.1

Smoker

Yes

DM2

Yes

AHT

Yes

DLP

Yes

**Table 2.** Volume and Dose Parameter Values (Mean Dose and D_20cc) for the Heart and Its Substructures on FB and Volume Increments due to Movement
	FB CT volume (cc)	FB CT mean dose (cGy)	FB CT D_20cc (cGy)	paCT volume increment (%)
CT: computed tomography; FB: free breathing; LA: left atrium; LV: left ventricle; RA: right atrium; RV: right ventricle; paCT: phase-average CT.
Heart	679 ± 46	236 ± 29	1,650 ± 430	19.9 ± 8.1
LV	171.4 ± 3.9	381 ± 64	830 ± 200	35 ± 11
RV	106.0 ± 6.8	256 ± 57	293 ± 56	36 ± 14
LA	78 ± 13	74.2 ± 3.3	82.3 ± 4.4	0.8 ± 6.4
RA	67.7 ± 6.2	65.6 ± 3.7	70.1 ± 3.2	42 ± 14

Table 2. Volume and Dose Parameter Values (Mean Dose and D_20cc) for the Heart and Its Substructures on FB and Volume Increments due to Movement

FB CT volume (cc)

FB CT mean dose (cGy)

FB CT D_20cc (cGy)

paCT volume increment (%)

CT: computed tomography; FB: free breathing; LA: left atrium; LV: left ventricle; RA: right atrium; RV: right ventricle; paCT: phase-average CT.

Heart

679 ± 46

236 ± 29

1,650 ± 430

19.9 ± 8.1

171.4 ± 3.9

381 ± 64

830 ± 200

35 ± 11

106.0 ± 6.8

256 ± 57

293 ± 56

36 ± 14

78 ± 13

74.2 ± 3.3

82.3 ± 4.4

0.8 ± 6.4

67.7 ± 6.2

65.6 ± 3.7

70.1 ± 3.2

42 ± 14

**Table 3.** Comparison of V2 and V5 Values Calculated on FB CT and paCT Image Sets for the Reference Plan
			Heart	LV	RV	LA
As reference, parameter values are also shown as a percentage of the corresponding substructure volume. Right atrium’s parameters were excluded from this table as all values were equal to zero within uncertainties. CT: computed tomography; FB: free breathing; LA: left atrium; LV: left ventricle; RV: right ventricle; paCT: phase-average CT.
FB CT	V2	(cc)	129 ± 17	61.2 ± 7.8	29.5 ± 5.8	0.14 ± 0.11
		(%)	18.9 ± 2.0	36.0 ± 4.8	27.1 ± 4.9	0.22 ± 0.18
	V5	(cc)	46.0 ± 7.6	23.2 ± 4.1	7.8 ± 2.9	0 ± 0
		(%)	6.8 ± 1.0	13.7 ± 2.5	7.1 ± 2.6	0 ± 0
paCT	V2	(cc)	180 ± 25	85 ± 13	40.0 ± 6.0	2.1 ± 1.1
		(%)	22.0 ± 2.3	36.5 ± 4.7	29.3 ± 4.0	3.0 ± 1.5
	V5	(cc)	75 ± 12	37.1 ± 7.1	13.0 ± 4.0	0.24 ± 0.16
		(%)	9.1 ± 1.3	15.8 ± 2.7	9.2 ± 2.6	0.32 ± 0.22

Table 3. Comparison of V2 and V5 Values Calculated on FB CT and paCT Image Sets for the Reference Plan

Heart

As reference, parameter values are also shown as a percentage of the corresponding substructure volume. Right atrium’s parameters were excluded from this table as all values were equal to zero within uncertainties. CT: computed tomography; FB: free breathing; LA: left atrium; LV: left ventricle; RV: right ventricle; paCT: phase-average CT.

FB CT

(cc)

129 ± 17

61.2 ± 7.8

29.5 ± 5.8

0.14 ± 0.11

(%)

18.9 ± 2.0

36.0 ± 4.8

27.1 ± 4.9

0.22 ± 0.18

(cc)

46.0 ± 7.6

23.2 ± 4.1

7.8 ± 2.9

0 ± 0

(%)

6.8 ± 1.0

13.7 ± 2.5

7.1 ± 2.6

0 ± 0

paCT

(cc)

180 ± 25

85 ± 13

40.0 ± 6.0

2.1 ± 1.1

(%)

22.0 ± 2.3

36.5 ± 4.7

29.3 ± 4.0

3.0 ± 1.5

(cc)

75 ± 12

37.1 ± 7.1

13.0 ± 4.0

0.24 ± 0.16

(%)

9.1 ± 1.3

15.8 ± 2.7

9.2 ± 2.6

0.32 ± 0.22

**Table 4.** Comparison of V2 and V5 Values for the Reference, Extended Margin and DIBH Plans
			Heart	LV	RV	LA
As reference, parameter values as a percentage of the corresponding substructure volume are also shown. Right atrium’s parameters were excluded from this table as all values were equal to zero within uncertainties. DIBH: deep inspiration breath-hold; LA: left atrium; LV: left ventricle; RV: right ventricle.
Reference	V2	(cc)	180 ± 25	85 ± 13	40.0 ± 6.0	2.1 ± 1.1
		(%)	22.0 ± 2.3	36.5 ± 4.7	29.3 ± 4.0	3.0 ± 1.5
	V5	(cc)	75 ± 12	37.1 ± 7.1	13.0 ± 4.0	0.24 ± 0.16
		(%)	9.1 ± 1.3	15.8 ± 2.7	9.2 ± 2.6	0.32 ± 0.22
Extended margin	V2	(cc)	152 ± 26	73 ± 13	31.4 ± 7.1	1.44 ± 0.73
		(%)	18.1 ± 2.6	30.8 ± 4.7	21.9 ± 4.3	2.0 ± 1.0
	V5	(cc)	59 ± 13	29.2 ± 6.6	8.9 ± 4.0	0.104 ± 0.074
		(%)	6.9 ± 1.4	12.1 ± 2.6	5.8 ± 2.5	0.14 ± 0.10
DIBH	V2	(cc)	98 ± 24	44 ± 10	15.7 ± 5.2	0.27 ± 0.19
		(%)	14.8 ± 3.5	24.8 ± 5.5	17.1 ± 5.5	0.62 ± 0.48
	V5	(cc)	27.9 ± 8.3	12.4 ± 3.9	2.5 ± 1.4	0 ± 0
		(%)	4.2 ± 1.2	7.0 ± 2.0	2.5 ± 1.4	0 ± 0

Table 4. Comparison of V2 and V5 Values for the Reference, Extended Margin and DIBH Plans

Heart

As reference, parameter values as a percentage of the corresponding substructure volume are also shown. Right atrium’s parameters were excluded from this table as all values were equal to zero within uncertainties. DIBH: deep inspiration breath-hold; LA: left atrium; LV: left ventricle; RV: right ventricle.

Reference

(cc)

180 ± 25

85 ± 13

40.0 ± 6.0

2.1 ± 1.1

(%)

22.0 ± 2.3

36.5 ± 4.7

29.3 ± 4.0

3.0 ± 1.5

(cc)

75 ± 12

37.1 ± 7.1

13.0 ± 4.0

0.24 ± 0.16

(%)

9.1 ± 1.3

15.8 ± 2.7

9.2 ± 2.6

0.32 ± 0.22

Extended margin

(cc)

152 ± 26

73 ± 13

31.4 ± 7.1

1.44 ± 0.73

(%)

18.1 ± 2.6

30.8 ± 4.7

21.9 ± 4.3

2.0 ± 1.0

(cc)

59 ± 13

29.2 ± 6.6

8.9 ± 4.0

0.104 ± 0.074

(%)

6.9 ± 1.4

12.1 ± 2.6

5.8 ± 2.5

0.14 ± 0.10

DIBH

(cc)

98 ± 24

44 ± 10

15.7 ± 5.2

0.27 ± 0.19

(%)

14.8 ± 3.5

24.8 ± 5.5

17.1 ± 5.5

0.62 ± 0.48

(cc)

27.9 ± 8.3

12.4 ± 3.9

2.5 ± 1.4

0 ± 0

(%)

4.2 ± 1.2

7.0 ± 2.0

2.5 ± 1.4

0 ± 0

**Table 5.** Mean Dose to the Target Calculated With the Different Algorithms, and Their Difference in Percentage in Respect to MC
	Mean dose to the target (cGy)	Comparison to MC (%)
CC: collapsed cone; MC: Monte Carlo; PB: pencil beam.
MC	4558,67	0
PB	4490,21	-1,35
CC	4565,27	0,21

Table 5. Mean Dose to the Target Calculated With the Different Algorithms, and Their Difference in Percentage in Respect to MC

Mean dose to the target (cGy)

Comparison to MC (%)

CC: collapsed cone; MC: Monte Carlo; PB: pencil beam.

4558,67

4490,21

-1,35

4565,27

0,21

**Table 6.** Mean EQD2 and Mean Relative Increase of Ischemic Heart Disease Risk Corresponding to the Dosimetric Scenarios Analyzed: Conventional (Reference) Treatment Calculated on FB CT or paCT, Extended Margin and DIBH Plans
	Mean EQD2 (Gy)	Relative risk increment (%)
The reported risk uncertainties only consider dose variations within the cohort. CT: computed tomography; DIBH: deep inspiration breath-hold; EQD2: equivalent dose in 2 Gy fractions; FB: free breathing; paCT: phase-average CT.
Base plan (FB CT)	1.75 ± 0.30	14.7 ± 2.5
Reference (paCT)	2.46 ± 0.43	20.7 ± 3.6
Extended margin	1.88 ± 0.37	15.8 ± 3.1
DIBH	1.17 ± 0.24	9.8 ± 2.0

Table 6. Mean EQD2 and Mean Relative Increase of Ischemic Heart Disease Risk Corresponding to the Dosimetric Scenarios Analyzed: Conventional (Reference) Treatment Calculated on FB CT or paCT, Extended Margin and DIBH Plans

Mean EQD2 (Gy)

Relative risk increment (%)

The reported risk uncertainties only consider dose variations within the cohort. CT: computed tomography; DIBH: deep inspiration breath-hold; EQD2: equivalent dose in 2 Gy fractions; FB: free breathing; paCT: phase-average CT.

Base plan (FB CT)

1.75 ± 0.30

14.7 ± 2.5

Reference (paCT)

2.46 ± 0.43

20.7 ± 3.6

Extended margin

1.88 ± 0.37

15.8 ± 3.1

DIBH

1.17 ± 0.24

9.8 ± 2.0