Setup error and motion during deep inspiration breath-hold breast radiotherapy measured with continuous portal imaging

Figures & data

Figure 1. (a) The external marker block position for patient group 1 and 2. Field 1 (F1), field 2 (F2) and the u direction are indicated. (b) A schematic drawing of the marker block motion before and during a DIBH, indicating the gating level and gating window. (c) An example of a portal image of field 2. The relative deviation of the chest wall was found by comparison of the pixel intensities in three regions of interest as shown. The u (and v) directions are indicated by arrows.

Table I. Patient characteristics and treatment information for patient groups 1 and 2.

	Group 1	Group 2
Number of patients	27	31
Treatment technique
Whole breast irradiation	17	21
Locoregional treatment after BCS	2	3
Post-mastectomy treatment	8	7
Dose and fractionation
50 Gy/25 fx	22	22
40 Gy/15 fx	5	9
Age (years)
Median (range)	62 (28–69)	65 (44–83)
BMI
Median (range)	26.0 (20.1–37.1)	25.2 (16.2–40.6)^a
Current smoker
Yes/No	1/26	8/23
Astma or COPD
Yes/No	0/27	4/27

BCS: Breast conserving surgery; BMI, body mass index; COPD, chronic obstructive pulmonary disease. ^aBMI missing for one patient.

Figure 2. Cumulative frequencies of (a) absolute inter-fraction setup error, (b) absolute inter-field shift and (c) intra-field motion range for group 1 and 2.

Figure 3. The time resolved setup errors of the chest wall for (a) all imaged fractions and (b) the first treatment fraction for a typical patient. For the first fraction, the figure also shows (c) the external marker block position and (d) the resulting gate signal, which is in “enable state” when the marker block is inside the gating window [- - - -].

Figure 4. Box plots of the patient individual (a) inter-fraction setup error (b) inter-field shift and (c) intra-field motion range. The box indicates the 25th and 75th percentiles, while the extending narrow bars indicate the most extreme data points that are not considered outliers [o].

Figure 5. Three examples of internal chest wall setup error and external marker block position during fractions with large inter-field shifts (a, c) and intra-field motion (b, c). The gating window (---) and resulting binary beam-enable signal (bottom graph) are indicated for each case.

Table II. Gating and imaging characteristics for patient groups 1 and 2.

	Group 1	Group 2
Lateral marker block shift (mm)
Mean (range)	51 (23–74)	3 (−14–14)
Gating level (mm)
Mean (range)	18.7 (13.2–25.7)	15.8 (10.6–22.4)
Gating window
1.6 mm	–	1
1.9–2.1 mm	26	27
2.4–2.6 mm	1	2
3.6 mm	–	1
Gantry angle (°)
Mean (range), Field 1	127 (117–141)	128 (120–135)
Mean (range), Field 2	302 (294–315)	305 (295–312)
Fractions with portal images
Total	199	216
for inter-fraction setup error	199	216
for inter-field shift	198	212
for intra-field motion	199	205

Table III. The inter-fraction setup error (fields 1 + 2), inter-field shift, and intra-field motion for patient group 1 and 2, individually and combined.

	Group 1	Group 2	Group 1 + 2
Inter-fraction setup error (mm)
Group mean error (M)	0.2	− 0.3	− 0.1
Systematic error (Σ)	1.3	1.4	1.4
Random error (σ)	1.9	1.5	1.7
Inter-field shift (mm)
Group mean shift (M)	0.1	− 0.1	0.0
Systematic shift (Σ)	1.2	1.1	1.1
Random shift (σ)	1.7	0.9	1.3
Intra-field motion (mm)
Standard deviation	0.5	0.4	0.5
Range	0.1–6.6	0.0–9.8	0.0–9.8