SU-E-J-193: Gamma Knife Perfexion End-To-End Testing with a Commercial Stereotactic Phantom.

PURPOSE: To investigate the use of the Lucy ® Stereotactic Phantom (Standard Imaging, Inc.) for Gamma Knife Perfexion radiosurgery quality assurance of the imaging, treatment planning, and dose delivery processes. End-to-end testing of the Perfexion and Gamma Plan version 10.1 has not been previously examined in literature. METHODS: The phantom was imaged using both the CT and T1- and T2-weighted MR sequences used for treatment planning. For imaging, the isocentric volume insert and fiducial markers were positioned within the phantom. Scans were transferred to the Gamma Plan treatment planning system and were evaluated for geometric and fusion accuracy. A plan was created to deliver 12Gy to the 50% isodose line to the 5.25cm3 volume. During dose delivery, Gafchromic EBT2 film was positioned in the film insert to replicate the position of the target volume. Dose results were analyzed using RIT software (Radiologic Imaging Technology, Inc.). RESULTS: Image fusion integrity was inspected by overlaying the MR and CT markers (5 fiducial markers spaced 5mm apart) and visually examining the resulting volume insert overlap between the three scans. Geometric accuracy was evaluated by contouring three volumes using Gamma Plan contouring tools. Agreement within 1.1%, 6.7% and 12.2% of the actual volumes was seen with the T1-weighted, T2-weighted, and CT images, respectively. The volume-based acquisition and 1mm slice thickness of the T1-weighted sequence resulted in the most accurate measurement. Geometric measurements along two dimensions showed acceptable accuracy for all imaging modalities within 1.6%. Dosimetry results agreed well with the planned dose. The EBT2 film was calibrated for absolute dose measurements using a dose calibration curve for 0.1-30 Gy and the calibration curve was verified to have <3% error above 1Gy. CONCLUSIONS: The Lucy phantom allows for comprehensive quality assurance testing of the Gamma Knife Perfexion radiosurgery process.

SU-E-T-226: Clinical Implementation of a Gravity-Oriented Wedge for Total Body Irradiation.

PURPOSE: To describe a TBI technique designed within the limits of a small-room geometry and its clinical implementation. METHODS: Following construction of the universal treatment devices, including the double-wedge, beam spoiler table, and patient support table, commissioning consists of measurements to determine the output, tissue-phantom ratio, effective source distance, and off-axis factor. Dose is calculated by applying these factors per patient-specific measurements to arbitrary point in the patient. Typically, ten calculation points are located at mid-separation along the mid-sagittal plane from the head to the ankles. When areas of unacceptably high dose are calculated, custom compensators are constructed from 5-mm sheets of PMMA and placed over the patient on top of the beam spoiler table. The typical dose homogeneity of the planning calculations is within 2% of the prescribed dose. RESULTS: To verify the accuracy of the technique, an anthropomorphic phantom was simulated and treated. In total, 128 thermoluminescent dosimeters (TLDs) were irradiated within the phantom. Concentrations of TLDs were located in the planes of selected calculation points, i.e. the head, neck, sternum, lung, umbilicus, and pelvis. Results showed the average dose to these locations differed from the intended dose by -3.5%, 3.4%, 2.6%, 9.5%, 2.8%, and 0.5%, respectively. Due to its heterogeneous material, a higher discrepancy in the lung dose was anticipated. To demonstrate the dosimetric size of the radiation field, ionization chamber measurements were taken on one lateral side of the treatment area at a constant depth of 5 cm. A few measurements on the contralateral side were within 1 %, verifying the field's lateral symmetry. The approximate treatment area for the current technique is approximately 180×50 cm. CONCLUSIONS: We have demonstrated a small-room technique capable of meeting the dosimetric goal of TBI. To improve the dosimetric characteristics, new universal treatment devices are currently being designed and constructed.

Clinical implementation of the AAPM Task Group 36 recommendations on fetal dose from radiotherapy with photon beams: a head and neck irradiation case report.

We present the results of our efforts in estimating and diminishing the fetal dose expected when a 29-year-old patient, 22 weeks pregnant, received external beam radiation therapy for a squamous cell carcinoma of the tongue. We explain our use of the information contained, and recommendations made, in the Report of the American Association of Physicists in Medicine Radiation Therapy Committee Task Group 36 [Med. Phys. 22, 63-82 (1995)]. We also explain our dose estimation, describe our validation measurements, and demonstrate the effectiveness of supplemental shielding. Consequently, this case report will serve as a guide to radiation oncologists and medical physicists who may encounter similar cases.

A clinical and immunologic study of blood transfusion and postoperative bacterial infection in spinal surgery.

Allogeneic blood transfusion has been implicated as an independent risk factor for postoperative bacterial infection in clinical and animal studies. The association among transfusion, quantitative immunologic factors, and infection was examined in 102 patients undergoing 109 spinal fusion procedures. In 60 procedures, patients received autologous blood only; in 24 procedures, they received at least 1 unit of allogeneic blood, and in 25 procedures, they received no transfusions. Twenty-two patients developed bacterial infections, in 8 cases while in hospital and in 14 cases after discharge. Univariate analysis revealed that patients who received any allogeneic blood and those who received no allogeneic blood differed significantly in the rate of hospital-acquired infection (20.8 vs. 3.5%), length of stay (12.3 vs. 9.7 days), days of fever greater than or equal to 38 degrees C (4.0 vs. 2.9), days on antibiotics (3.9 vs. 2.5), duration of surgery (309 vs. 231 min), blood loss (1343 vs. 887 mL), surgeon, and postoperative drop in natural killer (NK) cells (-174 vs. -42/microL). Multivariate logistic and linear regressions revealed that the number of allogeneic units transfused was the only significant predictor of in-hospital infection (p = 0.016) or days on antibiotics and length of stay. None of the clinical, surgical, or transfusion variables was significantly associated with posthospital infection, although a significantly greater drop in NK cells had occurred in patients who developed infection (p = 0.0035). These data strongly implicate allogeneic transfusion as a risk factor for in-hospital postoperative bacterial infection.(ABSTRACT TRUNCATED AT 250 WORDS)