Advanced

Quantification of I-131 Activity from Gamma Camera Images of Thyroid Cancer Patients

Westerbergh, Frida (2019) MSFT01 20191
Medical Physics Programme
Abstract
BACKGROUND:
Radioiodine (131I) has been used in thyroid cancer treatments for many years,
and has demonstrated good results with regards to disease management.
Radioiodine therapy is however partially empirical, as not very much is known
concerning radiation dosimetry. At Skåne University Hospital, the number of
treatments has been growing steadily over the past couple of years, resulting in
an increased demand for dosimetry. The aim of this thesis was to develop a
method for patient-specific 131I activity quantifications, and thereby provide a
foundation for patient-specific dosimetry at Skåne University Hospital.

METHOD: Planar measurements were performed to evaluate the degradation from
penetration and scatter, and assess... (More)
BACKGROUND:
Radioiodine (131I) has been used in thyroid cancer treatments for many years,
and has demonstrated good results with regards to disease management.
Radioiodine therapy is however partially empirical, as not very much is known
concerning radiation dosimetry. At Skåne University Hospital, the number of
treatments has been growing steadily over the past couple of years, resulting in
an increased demand for dosimetry. The aim of this thesis was to develop a
method for patient-specific 131I activity quantifications, and thereby provide a
foundation for patient-specific dosimetry at Skåne University Hospital.

METHOD: Planar measurements were performed to evaluate the degradation from
penetration and scatter, and assess the effectiveness of two different window
based scatter corrections (namely a DEW and a TEW correction). Calibration
factors were established for planar and SPECT acquisitions, and the NEMA
Body Phantom was used to study partial volume effects. Lastly, an
anthropomorphic phantom study was carried through to test the quantification
method and thereby assess potential quantification errors in patient imaging.

RESULTS: For spherical structures, quantifications errors of up to 40% were obtained for
planar images, while SPECT quantification errors were generally below 10%.
For non-spherical structures, the error was significantly increased. In the planar
studies of scatter and penetration, a TEW scatter correction was shown to be
most effective. However, in quantifications, the scatter correction appeared to
have little impact on the accuracy of the results. Instead, the quantification error
seem to majorly depend on size and shape of the lesion, as well as the overall
attenuation properties of the examined object.

CONCLUSIONS: With the developed method, accurate SPECT quantifications are feasible.
However, a varying patient geometry can potentially induce significant errors,
as a window based scatter correction alone cannot compensate for large
variations in the level of attenuation. Hence, the accuracy of the calibration is
crucial. Object shape effects appear to be significant, as applying a sphere-based
recovery coefficient to a non-spherical structure will not recover all of the
activity, and errors remain large. Planar quantifications are generally associated
with large errors, and accurate planar quantifications would be difficult to
achieve in patient imaging.

Additional work is needed to improve the accuracy of the method. Nonspherical
recovery coefficient needs to be established, and effects of variations
in patient geometry and 131I uptake should be examined more thoroughly.
Furthermore, the reconstruction protocol should be optimized. In order for
dosimetry to be performed, methods of mass determination would need to be
explored. Also, methods of determining the effective half-life would need
assessment. (Less)
Popular Abstract (Swedish)
Jod är ett grundämne som är livsnödvändigt för människan. Det finns att hitta i bland annat fisk, skaldjur
ägg och mejeriprodukter. Många av oss har även jodberikat salt på middagsbordet. En del av det jod vi får
i oss via kosten kommer att ansamlas i sköldkörteln - ett organ som sitter under struphuvudet, på halsens
nedre del. Sköldkörteln har i uppgift att producera hormoner. Dessa hormoner utsöndras i blodet, och tas
upp av kroppens alla vävnader, där de hjälper cellerna att reglera sin ämnesomsättning. Sköldkörteln
påverkar därmed många av kroppens viktiga funktioner. För att produktionen av sköldkörtelhormoner skall
fungera normalt krävs jod.

Det jod som finns i vårt hushållssalt har en syster – det radioaktiva jodet. Kroppen... (More)
Jod är ett grundämne som är livsnödvändigt för människan. Det finns att hitta i bland annat fisk, skaldjur
ägg och mejeriprodukter. Många av oss har även jodberikat salt på middagsbordet. En del av det jod vi får
i oss via kosten kommer att ansamlas i sköldkörteln - ett organ som sitter under struphuvudet, på halsens
nedre del. Sköldkörteln har i uppgift att producera hormoner. Dessa hormoner utsöndras i blodet, och tas
upp av kroppens alla vävnader, där de hjälper cellerna att reglera sin ämnesomsättning. Sköldkörteln
påverkar därmed många av kroppens viktiga funktioner. För att produktionen av sköldkörtelhormoner skall
fungera normalt krävs jod.

Det jod som finns i vårt hushållssalt har en syster – det radioaktiva jodet. Kroppen ser ingen skillnad på
dessa två. Om radioaktivt jod tillförs kroppen kommer detta omsättas på samma sätt som vanligt jod, men
med en viktig skillnad – det strålar! Denna egenskap utnyttjar man för att behandla sjukdomar i sköldkörteln,
däribland sköldkörtelcancer. Radioaktivt jod tas upp av cancercellerna, vilka därmed strålas sönder. Vidare
kan man, genom att detektera strålningen i en så kallad gammakamera, avbilda jodets fördelning i kroppen,
och på så sätt få en bild av sjukdomens utbredning.

Vid bildtagning med gammakameran genereras tvådimensionella bilder av det radioaktiva läkemedlet i
patienten. Vidare kan man genom att låta kameran rotera runt patienten kan man även framkalla
tredimensionella bilder – en metod som kallas Single Photon Emssion Computed Tomography (SPECT).
Syftet med detta examensarbete är att, utifrån nuklearmedicinska bilder av patienter som genomgått terapi
med radioaktivt jod, utveckla en metod för att bestämma mängden jod som tagits upp av en cancertumör.
För att göra detta krävs vetskap om de processer som äger rum, från dess att strålningen skickas ut, till dess
att den färdiga bilden har framställts. Vidare måste man ha metoder för att kompensera för den försämring
i bildkvalité som vissa av dessa processer kan föra med sig. Detta arbete fokuserar på just detta; hur gör man
för att kvantifiera mängden jod i en tumör, och hur skall man förhålla sig till de faktorer som försvårar
beräkningarna?

Det långsiktiga målet med arbetet är att göra det möjligt att bestämma vilken stråldos en patient erhåller i
samband med en cancerbehandling med radioaktivt jod, och därigenom potentiellt lägga grunden för en
förbättrad framtida behandling. (Less)
Please use this url to cite or link to this publication:
author
Westerbergh, Frida
supervisor
organization
course
MSFT01 20191
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
8995831
date added to LUP
2019-09-27 09:06:02
date last changed
2019-09-27 09:06:02
@misc{8995831,
  abstract     = {BACKGROUND:
Radioiodine (131I) has been used in thyroid cancer treatments for many years,
and has demonstrated good results with regards to disease management.
Radioiodine therapy is however partially empirical, as not very much is known
concerning radiation dosimetry. At Skåne University Hospital, the number of
treatments has been growing steadily over the past couple of years, resulting in
an increased demand for dosimetry. The aim of this thesis was to develop a
method for patient-specific 131I activity quantifications, and thereby provide a
foundation for patient-specific dosimetry at Skåne University Hospital.

METHOD: Planar measurements were performed to evaluate the degradation from
penetration and scatter, and assess the effectiveness of two different window
based scatter corrections (namely a DEW and a TEW correction). Calibration
factors were established for planar and SPECT acquisitions, and the NEMA
Body Phantom was used to study partial volume effects. Lastly, an
anthropomorphic phantom study was carried through to test the quantification
method and thereby assess potential quantification errors in patient imaging.

RESULTS: For spherical structures, quantifications errors of up to 40% were obtained for
planar images, while SPECT quantification errors were generally below 10%.
For non-spherical structures, the error was significantly increased. In the planar
studies of scatter and penetration, a TEW scatter correction was shown to be
most effective. However, in quantifications, the scatter correction appeared to
have little impact on the accuracy of the results. Instead, the quantification error
seem to majorly depend on size and shape of the lesion, as well as the overall
attenuation properties of the examined object.

CONCLUSIONS: With the developed method, accurate SPECT quantifications are feasible.
However, a varying patient geometry can potentially induce significant errors,
as a window based scatter correction alone cannot compensate for large
variations in the level of attenuation. Hence, the accuracy of the calibration is
crucial. Object shape effects appear to be significant, as applying a sphere-based
recovery coefficient to a non-spherical structure will not recover all of the
activity, and errors remain large. Planar quantifications are generally associated
with large errors, and accurate planar quantifications would be difficult to
achieve in patient imaging.

Additional work is needed to improve the accuracy of the method. Nonspherical
recovery coefficient needs to be established, and effects of variations
in patient geometry and 131I uptake should be examined more thoroughly.
Furthermore, the reconstruction protocol should be optimized. In order for
dosimetry to be performed, methods of mass determination would need to be
explored. Also, methods of determining the effective half-life would need
assessment.},
  author       = {Westerbergh, Frida},
  language     = {eng},
  note         = {Student Paper},
  title        = {Quantification of I-131 Activity from Gamma Camera Images of Thyroid Cancer Patients},
  year         = {2019},
}