Inter- and intrafractional localisation errors in cone-beam CT guided stereotactic radiation therapy of tumours in the liver and lung

Figures & data

Figure 1. The magnitude of the interfractional baseline shift (3D) for each treatment fraction of the patients treated for lung tumours.

Table I. Inter- and intra-fraction PPE for the 15 patients treated for liver tumours.

	LR (mm)	CC (mm)	AP (mm)
Interfraction PPE^1
GM	0.9	0.3	0.8
Σ	1.9	2.7	1.3
σ	2.1	1.5	1.5
intrafraction PPE^1
GM	0.2	0.2	0.2
Σ	0.9	0.5	0.7
σ	0.7	0.7	0.7

Abbreviations: LR = left-right, CC = cranial-caudal, AP = anterior-posterior, PPE = patient positioning error, GM = group mean, Σ = systematic error, Σ = random error.

¹Includes data from 16 individual isocentres. One of the patients was treated using two isocentres.

Table II. Interfraction alignment errors of bony anatomy, tumour, and baseline for the 19 patients treated for lung tumours.

	LR (mm)	CC (mm)	AP (mm)
Bone (PPE)
GM	1.4	0.2	0.0
Σ	2.3	4.5	1.6
σ	1.9	2.8	1.4
Tumour (TPE)^1
GM	1.0	0.3	0.0
Σ	2.5	3.8	2.8
σ	1.7	2.7	2.1
Baseline shift^1
GM	0.3	−0.4	−0.2
Σ	1.1	2.9	2.9
σ	0.8	1.7	1.6

Abbreviations: LR = left-right, CC = cranial-caudal, AP = anterior-posterior, PPE = patient positioning error, TPE = tumour positioning error, GM = group mean, Σ = systematic error, σ = random error.

¹Tumor and baseline data only includes 18 of the 19 lung tumours. In one of the patients the tumour was not identifiable on the CBCT.

Table III. Intrafraction alignment errors of bony anatomy, tumour, and baseline for the 19 patients treated for lung tumours.

	LR (mm)	CC (mm)	AP (mm)
Bone (PPE)
GM	0.3	0.4	0.4
Σ	0.7	0.7	0.6
σ	0.9	1.0	0.8
Tumour (TPE)^1
GM	0.4	0.3	0.5
Σ	0.8	0.8	0.7
σ	0.8	1.7	1.1
Baseline shift^1
GM	0.0	0.0	−0.1
Σ	0.7	0.7	0.6
σ	0.9	1.7	1.2

¹Tumor and baseline data only includes 18 of the 19 lung tumours. In one of the patients the tumour was not identifiable on the CBCT.

Table IV. PTV margins required to account for the determined inter- and intra-fractional systematic and random localisation errors of the patients treated for lung tumors.

	LR PTV (mm)			CC PTV (mm)			AP PTV (mm)
	Water (95%)	Lung (95%)	Lung (80%)	Water (95%)	Lung (95%)	Lung (80%)	Water (95%)	Lung (95%)	Lung (80%)
SBF alone	7.3	6.9	6.7	12.0	11.0	10.4	8.6	8.0	7.6
CBCT, Bones	3.6	3.5	3.4	8.8	8.3	7.9	8.2	7.8	7.6
CBCT, Tumour	2.1	2.0	1.9	2.8	2.4	2.2	2.0	1.8	1.7

Abbreviations: LR = left-right, CC = cranial-caudal, AP = anterior-posterior

Margins are calculated according to Equation 1, assuming all tumours are surrounded by either water density-equivalent tissue or lung tissue. Margins ensuring dose coverage of the CTV with both the 95% and 80% dose level are stated using either SBF coordinates alone, CBCT match on bony anatomy, or CBCT match on the tumour for positioning.

Figure 2. Interfraction mean PPE (3D) as a function of patient BMI. Patients treated without abdominal compression are marked with filled circles and triangles. Upper outliers are marked with arrows (upper fence = 10.6 mm). The correlation is significant when patients treated without compression are included (r_s = 0.44, p = 0.014), but not if they are excluded from the data set (r_s = 0.19, p = 0.37). A straight line is fitted to all of the data points (Pearson correlation coefficient r = 0.56).

Figure 3. Mean interfractional baseline shift (3D) of the lung tumours as a function of the distance between the tumour and the spinal cord as measured on the planning CT (r_s = 0.74, p < 0.001, including both patients treated with and without abdominal compression). A straight line is fitted to the all of the data points (Pearson correlation coefficient r = 0.70).