Discussion topic:
Choose one of the following questions to research and discuss:
1. Discuss the differences and the advantages/disadvantages of a conventional simulator versus a CT simulator. (Have you ever seen a conventional simulator?)
2.How does slice thickness affect image detail on a CT simulator? What is a typical slice thickness for treatment planning and why?
Discussion post:
Slice thickness can have a significant impact on image detail on a CT simulator. According to a May 2014 study in Clinical and Translational Oncology1 slice thickness has a direct relationship with tumor volume definition. In this study a variety of brain tumor sizes were scanned with slice thickness ranging from 1mm to 10mm. Next a conformity index determined tumor size compared isodoses. The result was the smaller slice thickness had a marked improvement in conformity index for smaller tumors. Larger tumor volume definition was not affected by slice thickness. The study concluded stating “the accuracy of radiotherapy tumor volume definition depends on CT slice thickness.” This study is evidence that the detail offered by smaller slice thickness is significant especially for smaller tumors. This is an important consideration for facilities that perform stereotactic radiosurgery and stereotactic body therapy.1
Where I work at UF Cancer Center we use 2.0mm slices for most treatment planning. As shown by the Clinical and Translational Oncology1 study, 2.0mm slice thickness is optimal for large and small tumor definition. However, stereotactic radiosurgery (SRS) and stereotactic body therapy (SBRT) UF Cancer Center uses 1.5mm slice thickness for increases accuracy in tumor volume definition. Additionally, we use 4-D breathing techniques that utilize a slower pitch for SBRT cases. The 4-D technique shows lung and tumor movement which combined with 1.5mm slice thickness allows for the best possible tumor definition. In cases where patients have irregular breathing patterns instead of a 4-D scan three scans are done also with 1.5mm slice thickness; a regular scan, an inspiration hold scan, and an expiration hold scan.
References
1. Caivano R, Fiorentino P, Pedicini P, et al. The impact of tomography slice thickness on the assessment of stereotactic, 3D conformal and intensity modulated radiotherapy of brain tumors. Clinical and Translational Oncology. 2014;16(5). http://link.springer.com/article/10.1007/s12094-013-1111-4. Accessed on November 29, 2016.
2. Xiao Y, Kry S, Popple R, et al. Flattening filter-free accelerators: a report from the AAPM Therapy Emer ging Technology Assessment Work Group. Journal of Applied Clinical Medical Physics. 2015;16(3). http://www.jacmp.org/index.php/jacmp/article/view/5219/html_276. Accessed September 21, 2016.
Choose one of the following questions to research and discuss:
1. Discuss the differences and the advantages/disadvantages of a conventional simulator versus a CT simulator. (Have you ever seen a conventional simulator?)
2.How does slice thickness affect image detail on a CT simulator? What is a typical slice thickness for treatment planning and why?
Discussion post:
Slice thickness can have a significant impact on image detail on a CT simulator. According to a May 2014 study in Clinical and Translational Oncology1 slice thickness has a direct relationship with tumor volume definition. In this study a variety of brain tumor sizes were scanned with slice thickness ranging from 1mm to 10mm. Next a conformity index determined tumor size compared isodoses. The result was the smaller slice thickness had a marked improvement in conformity index for smaller tumors. Larger tumor volume definition was not affected by slice thickness. The study concluded stating “the accuracy of radiotherapy tumor volume definition depends on CT slice thickness.” This study is evidence that the detail offered by smaller slice thickness is significant especially for smaller tumors. This is an important consideration for facilities that perform stereotactic radiosurgery and stereotactic body therapy.1
Where I work at UF Cancer Center we use 2.0mm slices for most treatment planning. As shown by the Clinical and Translational Oncology1 study, 2.0mm slice thickness is optimal for large and small tumor definition. However, stereotactic radiosurgery (SRS) and stereotactic body therapy (SBRT) UF Cancer Center uses 1.5mm slice thickness for increases accuracy in tumor volume definition. Additionally, we use 4-D breathing techniques that utilize a slower pitch for SBRT cases. The 4-D technique shows lung and tumor movement which combined with 1.5mm slice thickness allows for the best possible tumor definition. In cases where patients have irregular breathing patterns instead of a 4-D scan three scans are done also with 1.5mm slice thickness; a regular scan, an inspiration hold scan, and an expiration hold scan.
References
1. Caivano R, Fiorentino P, Pedicini P, et al. The impact of tomography slice thickness on the assessment of stereotactic, 3D conformal and intensity modulated radiotherapy of brain tumors. Clinical and Translational Oncology. 2014;16(5). http://link.springer.com/article/10.1007/s12094-013-1111-4. Accessed on November 29, 2016.
2. Xiao Y, Kry S, Popple R, et al. Flattening filter-free accelerators: a report from the AAPM Therapy Emer ging Technology Assessment Work Group. Journal of Applied Clinical Medical Physics. 2015;16(3). http://www.jacmp.org/index.php/jacmp/article/view/5219/html_276. Accessed September 21, 2016.