Investigating strategies to reduce toxicity in stereotactic ablative radiotherapy for central lung tumors

Figures & data

Figure 1. Representative axial slices (phase 50%) of four central tumors included in this study. Top left para-cardiac, top right hilar, bottom para-mediastinal (non-cardiac). The inner and outer outlines define the gross and planning tumor volumes, respectively.

Table I. Baseline tumor characteristics.

		n	%
T-Stage (7th edition)	T2a	4	40%
	T2b	5	50%
	M1	1	10%
Location	Upper thorax	3	30%
	Lower thorax	7	70%
	Left lung	6	60%
	Right lung	4	40%
Central location	Peri-hilar	5	50%
	Para-cardiac	1	10%
	Para-mediastinal (non-cardiac)	4	40%
Size	Median tumor diameter in mm (range)	52.5 (38–65)
	Median PTV volume in cm^3 (range)	162.1 (110–210)
Movement	Median motion in mm (range)	8.9 (6.1–14.1)

PTV, planning target volume.

Figure 2. Differences in gross tumor volume (GTV) size during breathing relative to phase 50% GTV (above), and the maximum Hausdorff distance between the GTV in each respiratory phase and the GTV 50% (below). Shown in color online.

Figure 3. Illustration of significant variation in size and shape during breathing, with representative axial and coronal slices from patient 3 whose tumor showed the greatest change. CT images on left from phase 50% and on right from phase 0%. Contours from both phases are shown after rigid registration of the CT scans.

Table II. The impact of strategies to account for change in tumor size and shape during breathing.

	ITVFB (cm^3)	ITVT (cm^3)		GTV 50% alone	GTV 50% + 3 mm	GTV 50% + 5 mm	GTV 0% and 50%
Patient 1	111.8	97.7	Size (%)	64.1	91.7	123.2	79.5
			Coverage (%)	64.1	82.6	93.1	79.5
Patient 2	85.8	81.5	Size (%)	72.6	109.6	149.9	81.3
			Coverage (%)	72.6	95.2	99.5	81.3
Patient 3	104.1	101.9	Size (%)	56.8	84.1	113.5	78.5
			Coverage (%)	56.8	76.0	86.8	78.5
Patient 4	89.7	86.4	Size (%)	70.1	107.3	146.9	79.5
			Coverage (%)	70.1	89.1	96.2	79.5
Patient 5	64.9	62.4	Size (%)	69.6	105.8	146.2	89.4
			Coverage (%)	69.6	89.4	97.4	89.4
Patient 6	66.9	52.7	Size (%)	79.9	115.7	156.9	87.7
			Coverage (%)	79.9	96.0	99.8	87.7
Patient 7	53.1	43.8	Size (%)	78.5	118.0	174.2	82.9
			Coverage (%)	78.5	96.3	99.5	82.9
Patient 8	65.3	56.1	Size (%)	70.8	106.1	145.1	80.0
			Coverage (%)	70.8	92.0	97.9	80.0
Patient 9	106.8	96.0	Size (%)	82.0	109.0	138.8	86.0
			Coverage (%)	82.0	96.6	99.8	86.0
Patient 10	117.3	110.4	Size (%)	85.1	109.8	144.3	90.1
			Coverage (%)	85.1	97.9	100.0	90.1

The free-breathing ITV (ITV_FB) is defined by the union of gross tumor volumes (GTVs) from all 10 4DCT phases and represents an ITV that accounts for motion and the changes in tumor size and shape during breathing. The union of GTVs after rigid registration (ITV_T), accounts for variation in tumor size and shape only, assuming motion is perfectly accounted for using a tracking strategy. The size and coverage of the ITV generated using other strategies have been reported relative to ITV_T.