Feasibility of CT quantification of intratumoural 166Ho-microspheres

European Radiology Experimental

Table 4 Ho recovery in patients single-photon emission computed tomography (SPECT) and computed tomography (CT)

Patient	Tumour volume	Injected Ho		SPECT recovery		CT recovery		Volume of voxels with HU > 100
	cm³	MBq	mg	MBq	%	mg	%	cm³	%
1	44.6	366.7	36.5	309.2	84.3	32.4	88.8	2.7	6.1
2 left	5.6	53.9	13.7	9.6	17.8	2.3	16.5	0.5	8.0
2 right	6.1	63.8	16.2	16.9	26.5	3.8	23.5	0.6	9.3
3	3.9	17.6	3.1	8.5	48.3	1.5	48.6	0.9	23.1

Three patients with recurrent head and neck cancer were treated with radioactive ¹⁶⁶Ho-microspheres and underwent SPECT/CT imaging. Patient 2 was treated on both sides of the neck. Base on the injected activity, the corresponding amount of mg Ho was calculated. Injected activity compared to SPECT recovery was 17.8–84.3%. CT recovery was in line with SPECT imaging ranging from 16.5 to 88.8%. Tumour volume was 3.9–44.6 cm³ based on the > 100 HU threshold; from 6.1 to 23.1% of tumour volume was filled with ¹⁶⁶Ho-microspheres