Browsing by Subject "Radiosurgery"
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Item A Comprehensive Patient Education Video for Radiosurgery of the Central Nervous System(2009-06-17) Fels, Thomas Jeffery; Calver, Lewis E.The purpose of this thesis project was to produce a comprehensive patient education video describing the concept of radiosurgery and the terms associated with its use. This video will be viewed by patients recently diagnosed with a brain or spinal disorder who are contemplating radiosurgery, specifically the use of the Gamma Knife(r) or the CyberKnife(r). Much of the information presented online does not provide a comprehensive overview of all of the potential risks involved in radiosurgery and damage to healthy tissue that may occur. By viewing this program that includes 3D and 2D animation, illustration, and written description, the patient will be informed of what is involved in radiosurgery including the possible strengths and weaknesses of radiosurgery. This video was designed to help the patients better understand the process of radiosurgery and how it may affect their life. This will assist doctors with consistent information that may be difficult to portray verbally to each patient. Consistent information in the form of a video can supplement communication between patient and physician. The patients may then be able to make informed decisions on whether they would like to use this technology in their radiation therapy.Item Moving Phantom Study of Stereotactic Body Radiation Therapy for Lung Cancer(2011-02-01) Huang, Long; Papiez, LechTo assess the accuracy of current stereotactic body radiation therapy (SBRT) lung treatment methodologies, we performed a systematic evaluation using phantoms that simulated motions from real patients (irregular motions) as well as sinusoidal motions (regular motions). The irregular patterns investigated in this study were of two types: small range irregular breathing motions (=10mm) and large range irregular breathing motions (=20mm). Four-dimensional computed tomography (4DCT) and cone beam computed tomography (CBCT) are important methodologies for SBRT, but previously have only been used to evaluate regular patterns. For targets moving regularly or irregularly within a small range (7.0 ± 1.8 mm, n = 6), we observed good agreement between the measured and computed dose distributions. However, for targets moving irregularly with a larger range (20.8 ± 2.6 mm, n = 4), the measured isodose lines were found to be shifted relative to the planned distribution, resulting in an underdosing (over 20%) in a portion of the PTV. In this underdosed volume, 1-2% of the PTV is underdosed by over 18 Gy, causing a 35-40% drop in the local control rate. We further observed that the discrepancy between the planned and measured dose distribution was due to the inaccurate representation of the irregular target motion in the maximum intensity projection (MIP) images generated from 4DCT, which could not be corrected by CBCT. A method of Extended Distance Virtual Isocenter (EDVI) was developed to lower the toxicity of healthy tissues. In all, caution should be used when planning from 4DCT images in the presence of large and irregular target motion. The inaccuracy inherent in 4DCT MIP and CBCT images can be mitigated through the application of methodologies to reduce respiratory motion, such as abdominal compression, and through the use of volumetric image guidance to assure precise targeting with minimal shifts.Item Parameters that Predict for High Grade Rectal Toxicity in Prostate Cancer Patients Undergoing Stereotactic Body Radiation Therapy- Analysis of Phase I/II at UT Southwestern(2013-01-22) Straka, Christopher; Kim, D. Nathan; Pistenmaa, David; Lotan, Yair; Xie, Xian-Jin; Timmerman, RobertINTRODUCTION: Conventional radiation therapy (CRT) is a well-accepted option for PCa treatment with high disease control rate, and low (< 3-5%) risk of rectal toxicity. SBRT, unlike CRT, delivers higher doses of radiation in 1-5 fractions, reducing treatment time significantly (from 8-9 weeks to ~ 2 weeks). Benefits of SBRT include improved patient convenience, significant healthcare cost reduction, and it has strong biologic rationale. A dose escalation phase I study (Boike et. al, JCO 2011) established 45-50 Gy in 5 treatments as effective and safe. Phase II study at 50 Gy was recently completed. Interim analysis unexpectedly revealed a significant number of grade 3+ delayed rectal events. We performed a rigorous analysis to determine potential etiology and methods to avoid occurrence of such rectal events. METHODS: Clinical parameters evaluated include tumor stage, Gleason grade, prostate volume, comorbid conditions (diabetes, smoking history, immunosuppression), race, age, and baseline bowel function score. Treatment planning parameters collected and evaluated included rectal wall volume receiving high doses of radiation, target volume size, rectal wall size, and degree of circumferential radiation to the rectal wall. Uni/multivariate analysis and correlative studies were conducted. RESULTS: 59 low/intermediate risk Pca patients were enrolled in this phase I/II study at UTSW. Median follow-up for all patients is 25.5 months. Tumor control rate is 99% to date. No patients experienced high grade rectal toxicity at 45 and 47.5 Gy, but at 50 Gy 10.8% experienced ≥ grade 3 rectal toxicity. Significant parameters were rectal volume receiving 50 Gy, HR of 2.67 (1.25, 5.71), p=.0113; rectal circumference irradiated by 24 Gy, 39 Gy and 50 Gy, HR of 1.1 (1.01,1.2) (p=.03), 1.2 (1.01, 1.38) (p=.04), and 1.22 (1.01, 1.47) (p=.04) respectively; and possibly diabetes HR 6.86 (0.83, 56.8) (p=.074). All 4 patients with grade 3+ rectal toxicity had > 3.5 cm3 rectal wall irradiated by 50 Gy. All patients without rectal toxicity had < 3.5 cm3 rectal wall irradiated by 50 Gy. DISCUSSION: We have determined the absolute threshold dose volume constraint to avoid rectal toxicity for SBRT of Pca. These findings contribute significantly to the radiobiology of bowel tolerance. If anatomy does not permit safe rectal dose constraints, dose reduced SBRT or alternatively CRT should be considered. When rectal constraints are met, or when 45-47.5 Gy prescription dose is used, SBRT seems to be a potent, safe, convenient and cost effective treatment for patients with low/intermediate risk PCa.Item [UT Southwestern Medical Center News](2006-09-08) Heinzl, Toni