Modeling the target dose fall-off in IMRT and VMAT planning techniques for cervical SBRT
- Department of Radiation Oncology, School of Medicine, Cancer Therapy & Research Center, The University of Texas Health Science Center San Antonio, San Antonio, TX 78229 (United States)
There has been growing interest in the use of stereotactic body radiotherapy (SBRT) technique for the treatment of cervical cancer. The purpose of this study was to characterize dose distributions as well as model the target dose fall-off for intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) delivery techniques using 6 and 10 MV photon beam energies. Fifteen (n = 15) patients with non-bulky cervical tumors were planned in Pinnacle{sup 3} with a Varian Novalis Tx (HD120 MLC) using 6 and 10 MV photons with the following techniques: (1) IMRT with 10 non-coplanar beams (2) dual, coplanar 358° VMAT arcs (4° spacing), and (3) triple, non-coplanar VMAT arcs. Treatment volumes and dose prescriptions were segmented according to University of Texas Southwestern (UTSW) Phase II study. All plans were normalized such that 98% of the planning target volume (PTV) received 28 Gy (4 fractions). For the PTV, the following metrics were evaluated: homogeneity index, conformity index, D{sub 2cc}, D{sub mean}, D{sub max}, and dose fall-off parameters. For the organs at risk (OARs), D{sub 2cc}, D{sub 15cc}, D{sub 0.01cc}, V{sub 20}, V{sub 40}, V{sub 50}, V{sub 60}, and V{sub 80} were evaluated for the bladder, bowel, femoral heads, rectum, and sigmoid. Statistical differences were evaluated using a Friedman test with a significance level of 0.05. To model dose fall-off, expanding 2-mm-thick concentric rings were created around the PTV, and doses were recorded. Statistically significant differences (p 3-arc, as compared with IMRT. VMAT{sub 3-arc} improved the bladder V{sub 40}, V{sub 50}, and V{sub 60}, and the bowel V{sub 20} and V{sub 50}. All fitted regressions had an R{sup 2} ≥ 0.98. For cervical SBRT plans, a VMAT{sub 3-arc} approach offers a steeper dose fall-off outside of the target volume. Faster dose fall-off was observed in smaller targets as opposed to medium and large targets, denoting that OAR sparing is dependent on target size. These improvements are further pronounced with the use of 10-MV photons.
- OSTI ID:
- 22824177
- Journal Information:
- Medical Dosimetry, Vol. 43, Issue 1; Other Information: Copyright (c) 2017 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0958-3947
- Country of Publication:
- United States
- Language:
- English
Similar Records
Circumferential or sectored beam arrangements for stereotactic body radiation therapy (SBRT) of primary lung tumors: Effect on target and normal-structure dose-volume metrics
Optimal Patient Positioning (Prone Versus Supine) for VMAT in Gynecologic Cancer: A Dosimetric Study on the Effect of Different Margins