Therapy of thyroid cancer and benign thyroid disease using iodine- 131: assessment of the exposure of the family members a]er patents discharge Maria João Carapinha 1,2, António Barata Tavares 2, Pedro Vaz 3 (1) Área cienafica de Medicina Nuclear, Departamento das Ciências e Tecnologias das Radiações e Biossinais da Saúde, Escola Superior de Tecnologia da Saúde de Lisboa - InsTtuto Politécnico de Lisboa, Portugal. (2) Escola Nacional de Saúde Pública - Universidade Nova de Lisboa, Portugal. (3) Unidade de Protecção e Segurança Radiológica, IST/ITN, InsTtuto Superior Técnico, Universidade Técnica de Lisboa, Portugal.
The Basic Safety Standards DirecTve (96/29/EURATOM) states that dose limits for members of the public do not apply to "exposures of individuals, who are knowingly and willingly helping, other than as part of their occupaton, in the support and comfort of inpatents or outpatents undergoing medical diagnosis or treatment" (ArTcle 6.4(b)) (1). However, other basic principles such as jus$fica$on of practces and op$miza$on of radiological protecton do apply. (1). Europeia C. Protecção contra as radiações ionizantes 97. Direcção- Geral do Ambiente, da Segurança Nuclear e da Protecção Civil; 1999.
The radioiodine therapy has been used in the treatment of thyroid cancer and benign thyroid disease. For family members the major source of radiaton dose is from external exposure, though due to their proximity to the patent there is also potental for exposure via internal contaminaton as a result of excreted or exhaled radioiodine. For therapeutc procedures, exposure levels may be high and restrictons may have to be applied in order to limit the dose. In Portugal patents are treated as outpatents when the administered actvity is less than 740 MBq (2). (2). Decreto- lei nº 180/2002, 182 (2002).
Before discharging an inpatent from a hospital, the medical practtoner must ensure that the residual actvity does not exceed pre- set levels. This can be done by dose measurements performed at 1 meter distance from the standing patent (1). Standard measurement protocols should be defined for this purpose (1). The decision to discharge the patent must be based on the region measurement with the highest exposure rate. In case of hyperthyroidism usually is the thyroid area, but for large thyroid cancer with metastases might be located at another region of the body (1). (1). Europeia C. Protecção contra as radiações ionizantes 97. Direcção- Geral do Ambiente, da Segurança Nuclear e da Protecção Civil; 1999.
Table 1 - Proposed Dose Constraints [msv] for family and close friends per treatment with 131 I (1).. Group of persons Dose constraint (msv) Children (including unborn children *) 1 Adults up to about 60 years old 5** Adults 60+ years old 15 * Unborn children includes embryos and fetuses. ** These levels are not expected to be applied to family and close friends comfortng very ill inpatents, such as mothers taking care of hospitalized children. (1). Europeia C. Protecção contra as radiações ionizantes 97. Direcção- Geral do Ambiente, da Segurança Nuclear e da Protecção Civil; 1999.
! Evaluate the dose received by the members of the family of patents undergoing iodine- 131 ( 131 I) treatments for thyroid cancer (TC) therapy and benign thyroid disease (BTD), a]er they are discharged.
An observatonal study with convenience sampling was performed; Measurements were carried out in 29 family members (FMs) of 21 pa$ents: Group 1 Included 22 FMs (17 adults and 5 children) of patents treated for TC with an average actvity of 3102MBq (range 2405 5920MBq); Group 2 Included 7 FMs (4 adults and 3 children) of patents undergoing radioiodine therapy for BTD, with an average actvity of 366.3MBq (range 281.2 555MBq). Personal dose equivalent HP(10) was determined for patents FMs using a whole body thermoluminescent dosimeters (TLDs), during 14 days.
! Thyroid cancer therapy è Hospitalisa$on of the pa$ent Fig. 1. Room for 131 I therapeutc. Fonte: hwp://www.radioatvos131.com.br/blog/wp- content/uploads/ 2009/07/iodo5.jpg Fig. 2. Measure the residual actvity. Fonte: hwp://www.bbc.co.uk/bitesize/ standard/physics/health_physics/ nuclear_radiaton/revision/7/ Fig. 3. ScinTgraphy with 131 I. Fonte: hwp://www.hsr.com.br/medicinanuclear/pesquisaiodo.aspx?unidade=9&menu=1! Benign thyroid disease è Treated as outpa$ents
All patents were informed about the necessary cautons and all partcipants signed a declaraton of consent to partcipate in this study. Data were statstcally treated with ANOVA and a Pearson's CorrelaTon.
40 35 Residual ac$vity (µsv/h) 30 25 20 15 10 5 0 0 1000 2000 3000 4000 5000 6000 7000 Ac$vity administered to the pa$ent (MBq) Fig. 4. AcTvity administered to the patent (MBq) and your residual actvity (µsv/h).
0.9 0.8 0.7 0.6 0.5 Min Max Median 0.9 0.8 0.7 0.6 Hp(10) 0.4 0.3 0.2 0.1 Hp(10) 0.5 0.4 0.3 0 Benign thyroid disease Thyroid cancer Benign thyroid disease Thyroid cancer Benign thyroid disease Thyroid cancer 0.2 0.1 10 11 59 60 FMs aged (years) 0 0 20 40 60 80 100 Age (years) Fig. 5. and 6. Personal dose equivalent HP(10) in the FMs.
All the average value of the HP(10) received by the 29 FMs was 0.13mSv (range 0.00-0.85mSv) which is below the Portuguese limit of 5mSv for adult carers of patents undergoing 131 I treatments. The average value of the personal HP(10) for group 1 was 0.12±0.10mSv whereas for group 2 was 0.34±0.24mSv which indicates a statcally significant difference (p=0.002) for Hp(10) values between the two groups. A moderate associaton (R=0.401) was confirmed between the actvity administered to the patent and the HP(10) dose values received by FMs. Only 16.1% of the dose Hp(10) received by FMs depends on the patent's administered actvity.
FMs of BTD patents received higher doses when compared with FMs of TC patents. The doses received by the FMs do not depend exclusively on the actvity administered to the patents. It s suggested the review of the guidelines for patents undergoing therapy with 131 I.
! The authors would like to thank all those involved in this research, including patents, their families and all the staff of the insttutons: Serviço de Medicina Nuclear dos Hospitais da Universidade de Coimbra Medical Consult
Therapy of thyroid cancer and benign thyroid disease using iodine- 131: assessment of the exposure of the family members a]er patents discharge Corresponding author: maria.carapinha@estesl.ipl.pt