Laura Tyburski

William Beaumont Army Medical Center, El Paso, Texas, United States

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Publications (4)17.03 Total impact

  • No preview · Article · Oct 2005 · International Journal of Radiation OncologyBiologyPhysics
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    ABSTRACT: We present our ongoing clinical experience utilizing 3D conformal radiation therapy (3D-CRT) to deliver partial-breast irradiation (PBI) in patients with early-stage breast cancer treated with breast-conserving therapy. Thirty-one patients referred for postoperative radiation therapy after lumpectomy were treated with PBI using our previously reported 3D-CRT technique. Ninety-four percent of patients had surgical clips outlining the lumpectomy cavity (mean: 6 clips). The clinical target volume (CTV) consisted of the lumpectomy cavity plus a 10-mm margin in 9 patients and 15-mm margin in 22 (median: 15 mm). The planning target volume consisted of the CTV plus a 10-mm margin for breathing motion and treatment setup uncertainties. The prescribed dose (PD) was 34 or 38.5 Gy (6 patients and 25 patients, respectively) in 10 fractions b.i.d. separated by 6 h and delivered in 5 consecutive days. Patients were treated in the supine position with 3-5 beams (mean: 4) designed to irradiate the CTV with <10% inhomogeneity and a comparable or lower dose to the heart, lung, and contralateral breast compared with standard whole-breast tangents. The median follow-up duration is 10 months (range: 1-30 months). Four patients have been followed >2 years, 6 >1.5 years, and 5 >1 year. The remaining 16 patients have been followed <12 months. No skin changes greater than Grade 1 erythema were noted during treatment. At the initial 4-8-week follow-up visit, 19 patients (61%) experienced Grade 1 toxicity and 3 patients (10%) Grade 2 toxicity. No Grade 3 toxicities were observed. The remaining 9 patients (29%) had no observable radiation effects. Cosmetic results were rated as good/excellent in all evaluable patients at 6 months (n = 3), 12 months (n = 5), 18 months (n = 6), and in the 4 evaluable patients at >2 years after treatment. The mean coverage of the CTV by the 100% isodose line (IDL) was 98% (range: 54-100%, median: 100%) and by the 95% IDL, 100% (range: 99-100%). The mean coverage of the planning target volume by the 95% IDL was 100% (range: 97-100%). The mean percentage of the breast receiving 100% of the PD was 23% (range: 14-39%). The mean percentage of the breast receiving 50% of the PD was 47% (range: 34-60%). Utilizing 3D-CRT to deliver PBI is technically feasible, and acute toxicity to date has been minimal. Additional follow-up will be needed to assess the long-term effects of these larger fraction sizes on normal-tissue sequelae and the impact of this fractionation schedule on treatment efficacy.
    No preview · Article · Jan 2004 · International Journal of Radiation OncologyBiologyPhysics
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    ABSTRACT: To improve the efficacy of dose delivery and dose escalation for external beam radiotherapy of prostate cancer, an off-line strategy for constructing a patient-specific planning target volume is developed in the adaptive radiotherapy process using image feedback of target location and patient setup position. We hypothesize that a patient-specific confidence-limited planning target volume (cl-PTV), constructed using an initial sequence of daily measurements of internal target motion and patient setup error, exists and ensures that the clinical target volume (CTV) in the prostate cancer patient receives the prescribed dose within a predefined dose tolerance. A patient-specific bounding volume to correct for target location and compensate for target random motion was first constructed using the convex hull of the first k days of CT measurements. The bounding volume and the initial days of CT measurements were minimized based on a predefined dosimetric criterion. The hypothesis was tested using multiple daily CT images by mimicking the actual treatment of both conventional 4-field-box and intensity-modulated radiotherapy (IMRT) on each of 30 patients with prostate cancer. For each patient, a patient-specific setup margin was also applied to the bounding volume to form the final cl-PTV. This margin was determined using the random setup error predicted from the initial days of portal imaging measurements and the residuals after correcting for the systematic setup error. The bounding volume constructed using daily CT measurements in the first week of treatment are adequate for the conventional beam delivery to achieve maximum dose reduction in the CTV of 2% or less of the prescription dose, for at least 80% of patients (p = 0.08), and 4.5% or less for 95% of patients (p = 0.1). However, for IMRT delivery, 2 weeks of daily CT measurements are required to achieve a similar level of the dosimetric criterion, otherwise the maximum dose reduction of 7%, on average, in the CTV is expected. Furthermore, the patient-specific setup margin required for the IMRT treatment is at least twice larger than that for the conventional treatment, to maintain the same dosimetric criterion. As compared to the conventional PTV, the volume of cl-PTV is significantly reduced, while maintaining the same dosimetric criterion. The cl-PTV for prostate treatment can be constructed within the first week of treatment using the feedback of imaging measurements. The cl-PTV has the capability to exclude the systematic variation and compensate for the patient-specific random variation on target location and patient setup position. This implies that in the current off-line image feedback adaptive treatment process, a single plan modification can be performed within the second week of treatment to improve the efficacy of dose delivery and dose escalation for external beam therapy of prostate cancer.
    No preview · Article · Sep 2000 · International Journal of Radiation OncologyBiologyPhysics
  • D. M. Lockman · D. Yan · D. Brabbins · L. Tyburski · A. Martinez

    No preview · Article · Dec 1999 · International Journal of Radiation OncologyBiologyPhysics