Low-dose CT protocols for guiding radiofrequency ablation for the treatment of small renal cell carcinomas

Figures & data

Figure 1. Low-dose CT protocols for guiding RFA in a 34-year-old man. (A) Contrast-enhanced axial CT image in the planning phase shows the location, size and number of RCC (white solid arrow) before lesion targeting. A white blank arrow indicates a grid for localising a tumour. (B) Unenhanced axial CT image in the targeting phase shows the direction and location of an electrode (black arrow) that is placed within the tumour. (C) Unenhanced axial CT image for monitoring phase shows the ablation area (arrowheads). No complication occurred following each ablation cycle. A black arrow indicates an electrode. (D) Unenhanced axial CT image for survey phase shows that the tumour size (white solid arrow) and tumour margin (arrowheads) are markedly shrunken. Overall CT image quality shown in (A–D) is not good but acceptable for RFA procedures. (E) Contrast-enhanced axial CT image, which is obtained 51 months after RFA, shows no local tumour progression but a post-ablation scar tissue (white solid arrow).

Figure 2. A photograph of the Proteus RF Electrode. The length of noninsulated electrode (arrowhead) is controlled from 0.5 to 3 cm in the handle (arrow).

Table 1. CTDIvol, DLP and effective dose of each RFA phase per session.

	RFA phases
Radiation dose of CT parameters	Planning	Targeting	Monitoring	Survey	p value
DLP (mGycm)	296.1 (133.4–588.7)	548.4 (183.6–2406.9)	224.0 (81.6–1170.1)	148.0 (37.6–232.5)	<0.0001
CTDI volume (mGy)	13.6 (6.4–31.4)	165.6 (49.5–634.4)	67.9 (22.0–345.0)	10.7 (5.5–13.8)	<0.0001
Effective dose (mSv)	4.4 (2.0–8.8)	8.2 (2.8–36.1)	3.4 (1.2–17.6)	2.2 (0.6–3.5)	<0.0001

Data are presented as median (range).

CTDI: CT dose index; DLP: dose length product.

Table 2. CT parameters of RFA phases.

	RFA phases
CT parameters	Planning	Targeting	Monitoring	Post-survey	p value
Number of scans	2 (1–3)	14 (6–59)	5 (3–25)	1 (1–1)	<0.0001
Scan range (cm)	20.6 (6.4–25.2)	3.3 (3.3–5.0)	3.3 (2.0–4.6)	13.9 (3.3–22.3)	<0.0001
Total tube current (mAs)	886 (331–1768)	4320 (1863–24721)	1800 (801–9218)	1380 (445–1833)	<0.0001
Exposure time (sec)	9.5 (4.1–25.3)	54.0 (21.6–245.6)	20.2 (10.8–92.2)	14.7 (3.6–19.3)	<0.0001

Data are presented as median (range).

Table 3. Subset analysis in terms of RCC size and location.

Subset analysis	Effective dose (mSv)	p value
RCC size (n = 31)
≤ 2 cm (n = 14)	17.2 ± 5.3 (7.8–25.5)	0.0322
> 2 cm (n = 17)	24.6 ± 11.3 (11.8–50.9)
RCC location (n = 31)
Exophytic (n = 15)	19.0 ± 8.5 (11.8–45.8)	0.1998
Endophytic (n = 16)	23.5 ± 10.5 (7.8–50.9)

Data are presented as mean ± standard deviation (range).