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. 2016 May-Jun;49(3):150-7.
doi: 10.1590/0100-3984.2015.0079.

Estimating (131)I biokinetics and radiation doses to the red marrow and whole body in thyroid cancer patients: probe detection versus image quantification

José Willegaignon  1 , Rogério Alexandre Pelissoni  2 , Beatriz Christine de Godoy Diniz Lima  2 , Marcelo Tatit Sapienza  3 , George Barberio Coura-Filho  4 , Marcelo Araújo Queiroz  5 , Carlos Alberto Buchpiguel  6
Affiliations

Estimating (131)I biokinetics and radiation doses to the red marrow and whole body in thyroid cancer patients: probe detection versus image quantification

José Willegaignon et al. Radiol Bras. 2016 May-Jun.

Abstract
in English, Portuguese

Objective: To compare the probe detection method with the image quantification method when estimating (131)I biokinetics and radiation doses to the red marrow and whole body in the treatment of thyroid cancer patients.

Materials and methods: Fourteen patients with metastatic thyroid cancer, without metastatic bone involvement, were submitted to therapy planning in order to tailor the therapeutic amount of (131)I to each individual. Whole-body scans and probe measurements were performed at 4, 24, 48, 72, and 96 h after (131)I administration in order to estimate the effective half-life (Teff) and residence time of (131)I in the body.

Results: The mean values for Teff and residence time, respectively, were 19 ± 9 h and 28 ± 12 h for probe detection, compared with 20 ± 13 h and 29 ± 18 h for image quantification. The average dose to the red marrow and whole body, respectively, was 0.061 ± 0.041 mGy/MBq and 0.073 ± 0.040 mGy/MBq for probe detection, compared with 0.066 ± 0.055 mGy/MBq and 0.078 ± 0.056 mGy/MBq for image quantification. Statistical analysis proved that there were no significant differences between the two methods for estimating the Teff (p = 0.801), residence time (p = 0.801), dose to the red marrow (p = 0.708), and dose to the whole body (p = 0.811), even when we considered an optimized approach for calculating doses only at 4 h and 96 h after (131)I administration (p > 0.914).

Conclusion: There is full agreement as to the feasibility of using probe detection and image quantification when estimating (131)I biokinetics and red-marrow/whole-body doses. However, because the probe detection method is inefficacious in identifying tumor sites and critical organs during radionuclide therapy and therefore liable to skew adjustment of the amount of (131)I to be administered to patients under such therapy, it should be used with caution.

Objetivo: Comparar o desempenho dos métodos de detecção de sonda e quantificação de imagens na estimativa da biocinética do radioisótopo 131I e das doses de radiação na medula óssea vermelha e no corpo inteiro durante a radioiodoterapia em pacientes com câncer de tireoide.

Materiais e métodos: Catorze pacientes portadores de câncer metastático de tireoide, sem acometimento ósseo, foram submetidos ao planejamento terapêutico visando estabelecer a melhor atividade de 131I a ser empregada na radioiodoterapia. Imagens cintilográficas e captações de corpo inteiro foram adquiridas 4, 24, 48, 72 e 96 h após a administração de atividades traçadoras de 131I, visando estimar a meia-vida efetiva (T1/2ef) e o tempo de residência do 131I no organismo dos pacientes.

Resultados: Os valores médios de T1/2ef e tempo de residência foram, respectivamente, 19 ± 9 h e 28 ± 12 h pelo método de detecção de sonda e 20 ± 13 h e 29 ± 18 h pela quantificação de imagens. As doses médias na medula óssea vermelha e no corpo inteiro foram, respectivamente, 0,061 ± 0,041 mGy/MBq e 0,073 ± 0,040 mGy/MBq pelo método de detecção de sonda e 0,066 ± 0,055 mGy/MBq e 0,078 ± 0,056 mGy/MBq pela quantificação de imagens. A análise estatística demonstrou que os dois métodos apresentam desempenho semelhante no tocante à estimativa de T1/2ef (p = 0,801), tempo de residência (p = 0,801) e doses, tanto na medula óssea vermelha (p = 0,708) como no corpo inteiro (p = 0,811), mesmo com métodos otimizados de dosimetria que levam em consideração somente dois pontos de medida (4 h e 96 h) após a administração de 131I (p > 0,914).

Conclusão: Existe excelente concordância entre o método de detecção de sonda e a quantificação de imagens quanto à estimativa da biocinética do 131I e das doses absorvidas de radiação. Contudo, o método de detecção de sonda deve ser usado com cuidado por ser incapaz de identificar regiões metastáticas e órgãos críticos durante a terapia com radionuclídeos, podendo distorcer ajustes da atividade de 131I a ser administrada durante a radioiodoterapia.

Keywords: Dosimetry; Iodine radioisotopes/therapeutic use; Radioisotopes/pharmacokinetics; Radiotherapy; Thyroid neoplasms.

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Figures

Figure 1
Figure 1
Schematic arrangement for measuring radiometric data acquired with the probe detection method.
Figure 2
Figure 2
Schematic arrangement for measuring radiometric data acquired with the image quantification method
Figure 3
Figure 3
Correlations between effective half-lives calculated from radiometric data acquired with the probe detection and image quantification methods.
Figure 4
Figure 4
Correlations between residence times calculated from radiometric data acquired with the probe detection and image quantification methods.
Figure 5
Figure 5
Correlations between radiation doses to the red marrow, as calculated from radiometric data acquired with the probe detection and image quantification methods.
Figure 6
Figure 6
Correlations between radiation doses to the whole body, as calculated from radiometric data acquired with the probe detection and image quantification methods.
Figure 7
Figure 7
Correlations between radiation doses to the red marrow and radiation doses to the whole body when only radiometric data acquired with probe detection were considered.
Figure 8
Figure 8
Correlations between radiation doses to the red marrow and radiation doses to the whole body when only radiometric data acquired with image quantification were considered.
Figure 9
Figure 9
Correlations between radiation doses to the red marrow calculated by considering measurements obtained at five time points (4, 24, 48, 72, and 96 h) and those calculated by considering measurements obtained at only two (4 h and 96 h), using only radiometric data acquired with the probe detection method.
Figure 10
Figure 10
Correlations between radiation doses to the whole body calculated by considering measurements obtained at five time points (4, 24, 48, 72, and 96 h) and those calculated by considering measurements obtained at only two (4 h and 96 h), using only radiometric data acquired with the probe detection method.
Figure 11
Figure 11
Correlations between radiation doses to the red marrow calculated by considering measurements obtained at five time points (4, 24, 48, 72, and 96 h) and those calculated by considering measurements obtained at only two (4h and 96 h), using only radiometric data acquired with the image quantification method.
Figure 12
Figure 12
Correlations between radiation doses to the whole body calculated by considering measurements obtained at five time points (4, 24, 48, 72, and 96 h) and those calculated by considering measurements obtained at only two (4 h and 96 h), using only radiometric data acquired with the image quantification method.
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