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Comparative Motion and Dosimetric Analysis of Organs at Risk near Pancreatic Tumors Treated with Stereotactic Body Radiation Therapy with and without Abdominal Compression using 4DCT Datasets

Karakas, Zeynep N
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1463151135

Abstract Details

2016, Master of Science, University of Toledo, Physics.
Abdominal compression (AC) may be used to control tumor motion during radiation therapy treatments for patients with tumors near the diaphragm. Inadvertently treating with AC using plans designed without AC, or vice versa, may result in differences in planned dose to normal tissue and target coverage. Consequences may be greatest for cases involving tumors undergoing hypofractionated, high-dose radiation treatments near radiosensitive organs directly beneath the AC belt, like pancreatic tumors treated with stereotactic body radiation therapy (SBRT). Researchers speculate that using AC in SBRT for pancreatic tumors may worsen dosimetry to surrounding organs at risk (OARs), including stomach and bowel, but publications on the use of AC during SBRT treatments of the pancreas are limited. The purpose of this study is to quantify the effects of AC on the motion and dose to OARs near pancreatic tumors with SBRT-level dose prescriptions. Motion was analyzed by measuring the deviation of the centroid of OAR contours at maximum expiration (0%) and maximum inspiration (50%) for with and without AC. The dosimetric effects of AC were investigated by examining dose to OARs for two particular scenarios: treating (1) with AC and (2) without AC, when planned otherwise. Six patients with pancreatic tumors and SBRT-level dose prescriptions (either 30 Gy or 40 Gy delivered in 5 fractions) were retrospectively evaluated in this study. Of these patients, 5 were planned with conformal arcs and 1 with IMRT. All patients had two plans and two 4D computed tomography (4DCT) datasets, one with AC and one without AC. Plans were normalized so that 95% of the PTV received 100% prescription dose; the same total MUs and MU/beam were used in both (with and without) AC plans for each patient. Four OARs—proximal and distal kidney, stomach and liver—were segmented on the 0% and 50% phases of with and without AC 4DCT datasets. Planning organ at risk (PRV) volumes were created by combining 0% and 50% contours to account for intrafractional organ motion, and were used in comparative dose analysis. Two-tailed paired t-test was used to compare motion and dose between with and without AC CTs, with differences of p<0.05 considered significant. Differences in the motion of OARs between with AC and without AC were insignificant except for liver, which was found to be significantly smaller along the superior-inferior direction with AC than without AC (7 mm vs. 10 mm, p=0.043). However, vector motion (along the lateral, anterior-posterior, and superior-inferior planes) was insignificant for all OARs. As expected, the maximum and mean dose to PRVs for both scenarios did not change for most organs except for liver, which was found to be statistically smaller with AC than without AC (Dmax=80 cGy vs. 104 cGy, p=0.045 and Dmean=1125 cGy vs. 1432 cGy, p=0.015). Also, target coverage was different between with and without AC; the 100% prescription dose to the PTV was significantly smaller with AC for both scenarios, but coverage by the 95% isodose line was relatively unchanged. All these findings were deemed to be independent of OAR volumes between with and without AC, since differences in contour volumes were marginal, and only account for intrafractional motion in 4DCT datasets used for analysis.
David Pearson (Committee Chair)
E Ishmael Parsai (Committee Member)
Diana Shvydka (Committee Member)
57 p.
Medical Imaging; Physics; Radiation
abdominal compression; pancreatic cancer; stereotactic body radiation therapy; SBRT; radiation therapy; medical physics; radiation physics; tumor motion control; 4DCT

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Citations

  • Karakas, Z. N. (2016). Comparative Motion and Dosimetric Analysis of Organs at Risk near Pancreatic Tumors Treated with Stereotactic Body Radiation Therapy with and without Abdominal Compression using 4DCT Datasets [Master's thesis, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1463151135

    APA Style (7th edition)

  • Karakas, Zeynep. Comparative Motion and Dosimetric Analysis of Organs at Risk near Pancreatic Tumors Treated with Stereotactic Body Radiation Therapy with and without Abdominal Compression using 4DCT Datasets. 2016. University of Toledo, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1463151135.

    MLA Style (8th edition)

  • Karakas, Zeynep. "Comparative Motion and Dosimetric Analysis of Organs at Risk near Pancreatic Tumors Treated with Stereotactic Body Radiation Therapy with and without Abdominal Compression using 4DCT Datasets." Master's thesis, University of Toledo, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1463151135

    Chicago Manual of Style (17th edition)

toledo1463151135
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© 2016, all rights reserved.
This open access ETD is published by University of Toledo and OhioLINK.