Feasibility of single time point dosimetry during 177Lu-PSMA-617 treatments of prostate cancer
(2022) MSFT01 20222Medical Physics Programme
- Abstract
- Introduction: Standard dosimetry methods for radionuclide therapies re- quire imaging at multiple time points post injection. An alternative method has been presented in the literature that uses previously acquired pharma- cokinetic data to create so-called dose factors. Multiplying the dose factors with an activity concentration (Bq/ml) taken from a single time point mea- surement results in an estimated absorbed dose (Gy). The dose factors were presented for 177Lu-PSMA-617 therapies for patients with metastatic cas- trate resistant prostate cancers. Before the new method (1-point method) is applied for clinical use it needs careful validation by comparing it to the standard dosimetry method (2-point method). In this study dosimetry was... (More)
- Introduction: Standard dosimetry methods for radionuclide therapies re- quire imaging at multiple time points post injection. An alternative method has been presented in the literature that uses previously acquired pharma- cokinetic data to create so-called dose factors. Multiplying the dose factors with an activity concentration (Bq/ml) taken from a single time point mea- surement results in an estimated absorbed dose (Gy). The dose factors were presented for 177Lu-PSMA-617 therapies for patients with metastatic cas- trate resistant prostate cancers. Before the new method (1-point method) is applied for clinical use it needs careful validation by comparing it to the standard dosimetry method (2-point method). In this study dosimetry was performed on kidneys, salivary glands and tumors. The resulting absorbed doses were compared between methods to evaluate the applicability of the 1-point method.
Method: Dosimetry was performed on 5 patients, using SPECT/CT images acquired 24 and 96 h post injection. Images were reconstructed with OSEM, using attenuation correction, resolution recovery and model based scatter correction (ESSE). Partial volume correction was performed by convolving the VOI with a Gaussian point spread function and determining the ratio of VOI counts with and without effects of limited spatial resolution. Two dosimetry methods were used, the 2-point method that incorporated images from both imaging time points and the 1-point method. Absorbed doses using the 1-point method were calculated for the two different imaging time points separately. Salivary glands and kidneys were delineated manually, tumor delineation was made using an automated method based on differ- ence of Gaussians. Tumors were categorised into soft tissue and bone lesions based on their mean density and corresponding coefficient of variation, using support vector machines for classification.
Results: Mean absorbed dose (standard deviation) per injected activity to kidneys was 0.56 +- 0.14 (2-point method), 0.59 +- 0.11 (1-point method 24h-image) and 0.44+-0.16 (1-point method 96h-image) Gy/GBq, to sub- mandibular glands it was 0.36 +- 0.15 (2-point method), 0.34 +- 0.14 (1-point method 24h-image), 0.23 +- 0.12 (1-point method 96h-image) Gy/GBq, and for parotid glands 0.31 +- 0.15 (2-point method), 0.32 +- 0.13 (1-point method 24h-image) and 0.19 +-0.14 (1-point method 96h-image) Gy/GBq. Categori- sation of tumor type using support vector machines on test data correctly categorised 50 out of 51 tumors.
Conclusion: The 1-point method for performing dosimetry was deemed sufficiently accurate based on the low mean difference in absorbed dose com- pared to the 2-point method. This applies to images taken 24 h post in- jection, imaging at 96 hours resulted in poor agreement with the 2-point method. (Less) - Popular Abstract (Swedish)
- Prostatacancer innebär att det har bildats en elakartad tumör i prostatan. Till en början växer cancern enbart i prostatakörteln. I detta fall har pa- tienten goda möjligheter till att bli botad. Om cancern sprider sig utanför prostatan så minskar möjligheten att bota cancern. Då brukar behandling gå ut på att minska symptom och bromsa spridningen, så kallad palliativ behandling. Radionuklidterapi kan användas som palliativ behandling för prostatacancer. Dessa behandlingar innebär att man tillför ett radioaktivt läkemedel till patienten. Ett radioaktivt läkemedel speciellt anpassat för be- handling av spridd prostatacancer är 177Lu-PSMA-617. PSMA-617 är ett läkemedel som ackumuleras i prostata och prostatacancerceller. 177Lu är ett... (More)
- Prostatacancer innebär att det har bildats en elakartad tumör i prostatan. Till en början växer cancern enbart i prostatakörteln. I detta fall har pa- tienten goda möjligheter till att bli botad. Om cancern sprider sig utanför prostatan så minskar möjligheten att bota cancern. Då brukar behandling gå ut på att minska symptom och bromsa spridningen, så kallad palliativ behandling. Radionuklidterapi kan användas som palliativ behandling för prostatacancer. Dessa behandlingar innebär att man tillför ett radioaktivt läkemedel till patienten. Ett radioaktivt läkemedel speciellt anpassat för be- handling av spridd prostatacancer är 177Lu-PSMA-617. PSMA-617 är ett läkemedel som ackumuleras i prostata och prostatacancerceller. 177Lu är ett radioaktivt ämne som emitterar så kallade beta-partiklar när den sönder- faller. Dessa beta-partiklar kan orsaka biologisk skada på vävnader. Genom att kemiskt koppla ihop 177Lu med PSMA-617 så skapas ett radioaktivt läkemedel. PSMA-617:s uppgift är att se till att det radioaktiva läkemedlet ackumuleras på prostatacancerceller där 177Lu i sin tur gör biologisk skada på dessa celler.
Absorberad dos är ett mått på hur mycket energi som deponerats per massen- het. Denna storhet går att koppla till den radiobiologiska effekt som orsakas av strålning. Målet med radionuklidbehandlingar är att skada cancerceller, dock så kan även friska vävnader ta skada. Det kan vara fördelaktigt att få en uppfattning av mängden absorberad dos olika friska vävnader har fått under behandlingar. Därför att om man vet mängden absorberad dos ett or- gan tolererar innan det skadas kan man planera behandlingar utifrån detta. För att beräkna den absorberad dosen till ett organ så krävs det att man vet mängden radioaktivt läkemedel som befinner sig i organet samt hur det ut- söndras. Man kan med speciella kameror ta bilder för att se fördelningen av det radioaktiva läkemedlet. Detta kallas single-photon emission computed tomography (SPECT). Dessa bilder är underlag för att beräkna den ab- sorberade dosen. Den nuvarande metoden kräver att man tar flera SPECT bilder, gärna med några dagar mellan bildtagningarna.
En nyligen publicerad artikel beskriver en metod för förenklad dosimetri där det räcker med ett bildtagningstillfälle för att beräkna absorberad dos. Målet med detta arbete var att testa och evaluera den nya metoden. Detta gjordes genom att jämföra absorberade doser beräknade med den nya och den nuvarande metoden. Dosimetri utfördes på spottkörtlar, njurar och tumörer för fem patienter som behandlats med 177Lu-PSMA-617.
Resultatet visade att den nya metoden för att beräkna absorberad dos är genomförbar. Denna slutsats baserades på att det var en liten skillnad i absorberad dos mellan de två metoderna. Detta tyder på att man kan införa den nya metoden utan att påverka de resulterande absorberade doserna på ett markant sätt. Fördelen är att den nya metoden är mindre resurskrävande för klinik och patient. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9076001
- author
- Nilsson, Elias
- supervisor
- organization
- course
- MSFT01 20222
- year
- 2022
- type
- H2 - Master's Degree (Two Years)
- subject
- language
- English
- id
- 9076001
- date added to LUP
- 2022-02-25 10:46:53
- date last changed
- 2022-02-25 10:46:53
@misc{9076001,
abstract = {{Introduction: Standard dosimetry methods for radionuclide therapies re- quire imaging at multiple time points post injection. An alternative method has been presented in the literature that uses previously acquired pharma- cokinetic data to create so-called dose factors. Multiplying the dose factors with an activity concentration (Bq/ml) taken from a single time point mea- surement results in an estimated absorbed dose (Gy). The dose factors were presented for 177Lu-PSMA-617 therapies for patients with metastatic cas- trate resistant prostate cancers. Before the new method (1-point method) is applied for clinical use it needs careful validation by comparing it to the standard dosimetry method (2-point method). In this study dosimetry was performed on kidneys, salivary glands and tumors. The resulting absorbed doses were compared between methods to evaluate the applicability of the 1-point method.
Method: Dosimetry was performed on 5 patients, using SPECT/CT images acquired 24 and 96 h post injection. Images were reconstructed with OSEM, using attenuation correction, resolution recovery and model based scatter correction (ESSE). Partial volume correction was performed by convolving the VOI with a Gaussian point spread function and determining the ratio of VOI counts with and without effects of limited spatial resolution. Two dosimetry methods were used, the 2-point method that incorporated images from both imaging time points and the 1-point method. Absorbed doses using the 1-point method were calculated for the two different imaging time points separately. Salivary glands and kidneys were delineated manually, tumor delineation was made using an automated method based on differ- ence of Gaussians. Tumors were categorised into soft tissue and bone lesions based on their mean density and corresponding coefficient of variation, using support vector machines for classification.
Results: Mean absorbed dose (standard deviation) per injected activity to kidneys was 0.56 +- 0.14 (2-point method), 0.59 +- 0.11 (1-point method 24h-image) and 0.44+-0.16 (1-point method 96h-image) Gy/GBq, to sub- mandibular glands it was 0.36 +- 0.15 (2-point method), 0.34 +- 0.14 (1-point method 24h-image), 0.23 +- 0.12 (1-point method 96h-image) Gy/GBq, and for parotid glands 0.31 +- 0.15 (2-point method), 0.32 +- 0.13 (1-point method 24h-image) and 0.19 +-0.14 (1-point method 96h-image) Gy/GBq. Categori- sation of tumor type using support vector machines on test data correctly categorised 50 out of 51 tumors.
Conclusion: The 1-point method for performing dosimetry was deemed sufficiently accurate based on the low mean difference in absorbed dose com- pared to the 2-point method. This applies to images taken 24 h post in- jection, imaging at 96 hours resulted in poor agreement with the 2-point method.}},
author = {{Nilsson, Elias}},
language = {{eng}},
note = {{Student Paper}},
title = {{Feasibility of single time point dosimetry during 177Lu-PSMA-617 treatments of prostate cancer}},
year = {{2022}},
}