Individualized threshold for tumor segmentation in <sup>18</sup>F-FDG PET/CT imaging: The key for response evaluation of neoadjuvant chemoradiation therapy in patients with rectal cancer?

Fagundes, Theara C.; Mafra, Arnoldo; Silva, Rodrigo G.; Castro, Ana C. G.; Silva, Luciana C.; Aguiar, Priscilla T.; Silva, Josiane A.; P. Junior, Eduardo; Machado, Alexei M.; Mamede, Marcelo

doi:10.1590/1806-9282.64.02.119

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ORIGINAL ARTICLES • Rev. Assoc. Med. Bras. 64 (2) • Feb 2018 • https://doi.org/10.1590/1806-9282.64.02.119 copy

Individualized threshold for tumor segmentation in ¹⁸F-FDG PET/CT imaging: The key for response evaluation of neoadjuvant chemoradiation therapy in patients with rectal cancer?

Individualização na segmentação tumoral de imagens de ¹⁸F-FDG PET/CT: a chave para avaliação de resposta terapêutica neoadjuvante em pacientes com câncer retal?

Authorship SCIMAGO INSTITUTIONS RANKINGS

Summary

Introduction:

The standard treatment for locally advanced rectal cancer (RC) consists of neoadjuvant chemoradiation followed by radical surgery. Regardless the extensive use of SUV_max in ¹⁸F-FDG PET tumor uptake as representation of tumor glycolytic consumption, there is a trend to apply metabolic volume instead. Thus, the aim of the present study was to evaluate a noninvasive method for tumor segmentation using the ¹⁸F-FDG PET imaging in order to predict response to neoadjuvant chemoradiation therapy in patients with rectal cancer.

Method:

The sample consisted of stage II and III rectal cancer patients undergoing ¹⁸F-FDG PET/CT examination before and eight weeks after neoadjuvant therapy. An individualized tumor segmentation methodology was applied to generate tumor volumes (SUV_2SD) and compare with standard SUVmax and fixed threshold (SUV_40%, SUV_50% and SUV_60%) pre- and post-therapy. Therapeutic response was assessed in the resected specimens using Dworak's protocol recommendations. Several variables were generated and compared with the histopathological results.

Results:

Seventeen (17) patients were included and analyzed. Significant differences were observed between responders (Dworak 3 and 4) and non-responders for SUV_max-2 (p<0.01), SUV_2SD-2 (p<0.05), SUV_40%-2 (p<0.05), SUV5_0%-2 (p<0.05) and SUV_60%-2 (p<0.05). ROC analyses showed significant areas under the curve (p<0.01) for the proposed methodology with sensitivity and specificity varying from 60% to 83% and 73% to 82%, respectively.

Conclusion:

The present study confirmed the predictive power of the variables using a noninvasive individualized methodology for tumor segmentation based on ¹⁸F-FDG PET/CT imaging for response evaluation in patients with rectal cancer after neoadjuvant chemoradiation therapy.

Keywords:
Rectal Neoplasms; Neoadjuvant Therapy; Fluorodeoxyglucose F18; Positron-Emission Tomography

		2SD			40%			50%			60%
Pre-therapy
	SUV_max-1	Vol_2SD-1	SUV_2SD-1	TLG_2SD-1	Vol_40%-1	SUV_40%-1	TLG_40%-1	Vol_50%-1	SUV_50%-1	TLG_50%-1	Vol_60%-1	SUV_60%-1	TLG_60%-1
Mean	24.0	81.5	7.3	681.7	23.4	12.7	344.3	13.7	15.1	232.5	7.1	16.9	133.2
Median	23.7	62.1	7.0	376.3	15.7	10.3	146.0	10.1	15.5	125.6	5.0	16.8	66.1
SD	8.9	72.5	2.3	797.8	21.7	5.6	430.0	13.4	5.6	284.9	7.6	6.2	165.2
Post-therapy
	SUV_max-2	Vol_2SD-2	SUV_2SD-2	TLG_2SD-2	Vol_40%-2	SUV_40%-2	TLG_40%-2	Vol_50%-2	SUV_50%-2	TLG_50%-2	Vol_60%-2	SUV_60%-2	TLG_60%-2
Mean	8.9	14.3	4.1	63.8	7.7	5.3	41.9	4.4	6.1	28.3	2.4	7.0	17.4
Median	8.1	9.6	3.7	39.5	4.9	4.5	23.0	2.6	5.1	13.5	1.2	5.8	7.1
SD	3.6	15.2	1.1	85.2	6.8	2.1	52.5	4.5	2.3	40.8	2.8	2.6	27.7

Patient	%ΔSUV_max	2SD			40%			50%			60%
Patient	%ΔSUV_max	%ΔVOl_2SD	%ΔSUV_2SD	%ΔTLG_2SD	%ΔVol_40%	%ΔSUV_40%	%ΔTLG_40%	%ΔVol_50%	%ΔSUV_50%	%ΔTLG_50%	%ΔVol_60%	%ΔSUV_60%	%ΔTLG_60%
Mean	61.3	78.0	44.4	85.6	52.6	44.6	72.1	55.7	60.6	79.2	54.3	59.7	77.8
Median	63.3	82.9	40.3	93.3	59.6	60.7	88.5	72.1	56.8	91.7	70.2	56.8	90.7
SD	14.5	19.9	22.7	14.5	43.7	75.3	35.9	41.6	17.7	22.8	47.6	17.7	26.5

Variable	AUC	p-value	Cutoff value	Sensitivity (%)	Specificity (%)
SUV_max-2	0.894	0.0001	<7.9	83.3	72.7
SUV_2SD-1	0.750	0.055	<6.2	83.3	72.7
SUV_2SD-2	0.818	0.0034	<3.3	60.0	81.8
SUV_40%-2	0.855	0.001	<4.5	100.0	63.6
SUV_50%-2	0.864	0.0004	<5.2	100.0	63.6
SUV_60%-2	0.864	0.0004	<6.0	100.0	63.6
%ΔSUV_40%	0.758	0.037	>68.8%	66.7	81.8
%ΔSUV_50%	0.758	0.037	>67.4%	66.7	81.8

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[1] *Correspondence: Departamento de Anatomia e Imagem, Faculdade de Medicina, UFMG, Address: Av. Prof. Alfredo Balena, 190, sala 175, Belo Horizonte, MG - Brasil, Postal code: 30130-100. mamede.mm@gmail.com

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Individualized threshold for tumor segmentation in 18F-FDG PET/CT imaging: The key for response evaluation of neoadjuvant chemoradiation therapy in patients with rectal cancer?

Individualização na segmentação tumoral de imagens de 18F-FDG PET/CT: a chave para avaliação de resposta terapêutica neoadjuvante em pacientes com câncer retal?

Summary

Introduction:

Method:

Results:

Conclusion:

Individualized threshold for tumor segmentation in ¹⁸F-FDG PET/CT imaging: The key for response evaluation of neoadjuvant chemoradiation therapy in patients with rectal cancer?

Individualização na segmentação tumoral de imagens de ¹⁸F-FDG PET/CT: a chave para avaliação de resposta terapêutica neoadjuvante em pacientes com câncer retal?