CT-planned internal mammary node radiotherapy in the DBCG-IMN study: Benefit versus potentially harmful effects

Figures & data

Figure 1. Random sampling of patients stratified on type and laterality of operation was carried out in four departments. Dose distributions were recalculated with various methods as indicated. AAA, anisotropic analytical algorithm; CCA, enhanced collapsed cone algorithm; FMU, fixed monitor units; PB, pencil beam algorithm; S. size, sample size.

Table I. Estimates of doses to internal mammary nodes and organs at risk in 68 original treatment plans.

CTV/OAR	Left (n = 30)	Right (n = 38)	Estimated difference†
IMN V90% (%)	35.2 ± 27.7	73.2 ± 26.9	38.0 (5.5; 70.5)*
Heart
MHD (Gy)	4.0 ± 2.0	1.1 ± 0.4	−2.9 (−4.0; −1.7)*
V20Gy (%)	5.6 ± 4.3	0.1 ± 0.4	−5.4 (−8.5; −2.3)*
V40Gy (%)	2.4 ± 2.8	< 0.1 ± < 0.1	−2.3 (−4.1; −0.6)*
LADCADmax (Gy)	39.6 ± 11.9	1.2 ± 0.4	−38.4 (−48.5; −28.4)*
Ipsilateral lung
V20Gy (%)	25.9 ± 6.0	31.4 ± 4.6	5.4 (1.4; 9.5)*

CTV, clinical target volume; IMN, internal mammary lymph nodes; LADCADmax, maximal dose to the left anterior descending coronary artery; MHD, mean heart dose; OAR, organ at risk; V_x, relative volume V irradiated to a minimum dose or proportion of a prescribed dose x.

Data are shown as mean values ± 1 SD, 95% confidence interval in parenthesis.

^†Estimates calculated using linear regression with robust standard errors, as sampling was clustered on radiotherapy centers.

*p < 0.05.

Table II. Left-side average estimates of dose coverage for internal mammary nodes and organs at risk with and without internal mammary node radiotherapy.

CTV/OAR	Plan 1 (n = 6)	Plan 2 (n = 6)	Difference plan 1 to plan 2	Plan 3 (n = 6)	Difference plan 1 to plan 3
IMN V90% (%)	29.0 ± 40.4	93.3 ± 5.1	64.3 (26.3; 102.0)*	74.9 ± 25.8	45.9 (18.6; 73.2)*
Heart
MHD (Gy)	2.6 ± 1.7	7.5 ± 4.7	4.8 (0.9; 8.7)*	4.8 ± 1.8	2.1 (0.5; 3.7)*
V20Gy (%)	2.3 ± 2.4	11.2 ± 11.6	8.9 (−1.0; 18.9)	7.2 ± 3.7	4.8 (1.5; 8.1)*
V40Gy (%)	0.6 ± 0.7	6.9 ± 2.4	6.2 (0.2; 12.3)*	3.1 ± 0.7	2.5 (0.8; 4.1)*
LADCADmax (Gy)	27.5 ± 18.9	44.8 ± 1.6	17.3 (−0.3; 34.9)	44.2 ± 3.5	16.7 (−1.1; 34.5)
Ipsilateral lung
V20Gy (%)	24.6 ± 4.5	34.8 ± 5.6	10.2 (2.1; 18.3)*	31.0 ± 2.6	6.4 (2.6; 10.1)*

Plan 1 is the original treatment plan with no intent of IMN treatment. Plan 2 is a simulated plan in which the IMN are treated and the coverage of the IMN CTV has first priority. Plan 3 is a simulated plan in which the IMN are treated and the dose constraints for heart and lungs are prioritized over IMN coverage – three of the patients had a plan 3 identical to plan 2.

CTV, clinical target volume; IMN, internal mammary lymph nodes; LADCADmax, maximal dose to the left anterior descending coronary artery; MHD, mean heart dose; OAR, organ at risk; V_x, relative volume V irradiated to a minimum dose or proportion of a prescribed dose x.

Data are shown as mean values ± 1 SD, 95% confidence interval in parentheses.

*Paired t-test, p < 0.05.

Table III. Dose estimates resulting from three different calculation methods.

CTV/OAR	Pencil beam		PB to AAA		PB to AAA with FMU		Difference AAA vs. AAA with FMU
	Left (n = 5)	Right (n = 6)	Left (n = 5)	Right (n = 6)	Left (n = 5)	Right (n = 6)	Left (n = 5)	Right (n = 6)
IMN V90% (%)	16.53 ± 26.90	85.30 ± 12.78	8.67 ± 6.91*	3.17 ± 1.92*	7.14 ± 5.96	1.70 ± 1.85	−1.53 (−2.76; −0.30)*	−1.47 (−2.14; −0.80)*
Heart
MHD (Gy)	2.87 ± 1.17	1.12 ± 0.49	−0.36 ± 0.14*	−0.36 ± 0.29*	−0.42 ± 0.16*	−0.38 ± 0.30*	−0.06 (−0.14; 0.01)	−0.02 (−0.04; <−0.01)*
V20Gy (%)	2.14 ± 2.47	0.08 ± 0.19	0.22 ± 0.21	0.01 ± 0.04	0.17 ± 0.19	0.01 ± 0.03	−0.05 (−0.10; −0.01)	−0.01 (−0.02; 0.01)
V40Gy (%)	0.67 ± 1.09	0.01 ± 0.01	0.40 ± 0.45	0.02 ± 0.06	0.28 ± 0.31	0.02 ± 0.04	−0.12 (−0.29; 0.06)	−0.01 (−0.03; 0.01)
LADCADmax (Gy)	34.07 ± 14.23	1.24 ± 0.59	1.26 ± 2.05	−0.42 ± 0.35*	0.30 ± 2.06	−0.43 ± 0.35*	−0.96 (−1.22; −0.70)	−0.01 (−0.02; < 0.01)
Ipsilateral lung
V20Gy (%)	22.73 ± 6.23	31.30 ± 1.98	0.56 ± 0.31*	1.21 ± 0.28*	1.23 ± 1.05	1.08 ± 0.26*	0.67 (−0.92; 2.26)	−0.13 (−0.38; 0.12)

In 11 patients, 6 with right-sided and 5 with left-sided breast cancer, the original PB plan was recalculated using AAA with or without fixed monitor units. The resulting changes in dose estimates and the differences between the two recalculation methods are summarized.

AAA, anisotropic analytical algorithm; CTV, clinical target volume; FMU, fixed monitor units; IMN, internal mammary lymph nodes; LADCADmax, maximal dose to the left anterior descending coronary artery; MHD, mean heart dose; OAR, organ at risk; PB, pencil beam algorithm; V_x, relative volume V irradiated to a minimum dose or proportion of a prescribed dose x.

Data are shown as mean values ± 1 SD, 95% confidence interval in parentheses.

*Paired t-test, p < 0.05.