Quality assurance of conventional non-CT-based internal mammary lymph node irradiation in a prospective Danish Breast Cancer Cooperative Group trial: The DBCG-IMN study

Figures & data

Table I. Overview of the implementation of DBCG-IMN radiotherapy guidelines, non-CT-based techniques for IMN radiotherapy and the transition from simulator-based to 3D-CT-guided dose planning in the DBCG radiotherapy departments.

Radiotherapy Department	DBCG-IMN guidelines implemented	Post-mastectomy		Post-lumpectomy
		Sim to 3D-CT	Sim IMN treatment	Sim to 3D-CT	Sim IMN treatment
Aalborg	January 2003	October 2005	PM Right	October 2005	PL Right T*
Aarhus	January 2003	June 2006	PM Right	Before January 2003	N/A
Flensburg	January 2003	Before January 2003	N/A	Before January 2003	N/A
Herlev	February 2003	October 2007	PM Right	October 2007	PL Right E+ T^†
Odense	January 2003	February 2006	PM Right	May 2005	PL Right T*
Rigshospitalet	January 2004^‡	September 2005	PM Right	N/A	N/A
Vejle	April 2003	March 2009	PM Right	Before January 2003	N/A

IMN, internal mammary lymph nodes; N/A, not applicable; PL right E+ T, Tangential fields combined with a separate IMN electron field; PM Right, three field post-mastectomy radiotherapy with a separate IMN electron field; PL right T, Wide tangential fields with IMN inclusion; Sim to 3D-CT, date of transition from non-CT-based treatment planning to three dimensional CT-guided dose planning; Sim IMN treatment, Preferred RT treatment modality in non-CT-based treatment planning for IMNs.

*Patients referred for PL Right E+ T only in case of anatomy unfit for tangential fields; ^†Although not using fully 3D-CT-based techniques, 5–6 CT slices per patient were used for planning since before January 2003; ^‡Guidelines only implemented for PM patients, as Rigshospitalet used gating for PL patients allowing IMN-RT for all.

Figure 1. Field arrangements in the five radiotherapy techniques. Left: A: Left-sided two field arrangement in post-mastectomy patients (PM Left), B: Right-sided three field arrangement in post-mastectomy patients (PM Right), C: Left-sided standard tangents in post-lumpectomy patients (PL Left), D: Right-sided wide tangents in post-lumpectomy patients (PL Right T) and E: Right-sided electron field combined with tangential fields in post-lumpectomy patients (PL Right E + T). Black: Shielded areas. Light grey: Photon fields. Dark grey: Electron fields. Right: Axial slices: Dashed Lines: Electron field borders, Solid lines: Photon field borders. Dotted lines: Field axis.

Figure 2. Internal mammary node dose coverage in the different techniques. Horizontal lines: Mean. Filled circles: individual patient dose coverage estimates.

Figure 3. Internal mammary node point doses at a point within the internal mammary node clinical target volume contour in the third intercostal space.

Table II. Summary of dose coverage estimates for internal mammary lymph nodes and organs at risk in the five standard DBCG techniques.

CTV/OAR	PM Left	PM Right	PL Left	PL Right T	PL Right E+T
IMN V43.2 Gy (%)	8.0 ± 16.1 (0.0–52.5)	86.9 ± 5.4 (79.0–94.5)^*†	16.2 ± 21.3 (0.0–56.1)	73.4 ± 23.1 (26.0–98.7)^*‡	85.1 ± 4.4 (76.0–90.2)^*†
Heart
MHD (Gy)	1.8 ± 0.4 (1.3–2.5)	3.5 ± 1.3 (1.6–5.8)	3.4 ± 1.2 (1.3–5.1)	0.8 ± 0.2 (0.6–1.2)	2.2 ± 0.9 (1.3–4.3)
V20 Gy (%)	0.1 ± 0.2 (0.0–0.6)	4.7 ± 3.1 (1.0–10.0)	4.2 ± 2.8 (0.0–8.4)	0.0 ± 0.0 (0.0–0.0)	2.3 ± 1.9 (0.9–6.1)
V40 Gy (%)	0.0 ± 0.0 (0.0–0.0)	0.7 ± 0.8 (0.0–2.6)	2.2 ± 1.6 (0.0–4.8)	0.0 ± 0.0 (0.0–0.0)	0.0 ± 0.1 (0.0–0.3)
LADmean (Gy)	3.7 ± 1.3 (2.2–5.4)	1.0 ± 0.9 (0.2–3.4)	21.6 ± 16.0 (3.4–55.9)	0.3 ± 0.1 (0.1–0.5)	0.9 ± 0.8 (0.2–2.9)
Ipsilateral lung
V20 Gy (%)	17.1 ± 4.2 (10.2–23.8)	19.3 ± 2.7 (15.0–22.7)	30.4 ± 11.5 (10.9–49.7)	26.0 ± 9.8 (16.9–43.8)	37.9 ± 5.7 (31.5–47.4)

CTV, clinical target volume; IMN, internal mammary lymph nodes; LADmean, mean dose to the left descending coronary artery; MHD, mean heart dose; V_x, Relative volume V irradiated to a minimum dose x.

Data are shown as mean values ± 1 SD, range in parentheses.

*Significant difference between left-sided and right-sided techniques, p < 0.0001; ^†Unpaired t test with no assumption of equal variance; ^‡Unpaired t-test with assumption of equal variance.