Engineering topics

Mathai, Mathew

Publications and source records attributed to Mathai, Mathew.

4 records

DOE OSTI2013

Clinical Response of Pelvic and Para-aortic Lymphadenopathy to a Radiation Boost in the Definitive Management of Locally Advanced Cervical Cancer

Purpose: Optimal treatment with radiation for metastatic lymphadenopathy in locally advanced cervical cancer remains controversial. We investigated the clinical dose response threshold for pelvic and para-aortic lymph node boost using radiographic imaging and clinical outcomes. Methods and Materials: Between 2007 and 2011, 68 patients were treated for locally advanced cervical cancer; 40 patients had clinically involved pelvic and/or para-aortic lymph nodes. Computed tomography (CT) or 18F-labeled fluorodeoxyglucose-positron emission tomography scans obtained pre- and postchemoradiation for 18 patients were reviewed to assess therapeutic radiographic response of individual lymph nodes. External beam boost doses to involved nodes were compared to treatment response, assessed by change in size of lymph nodes by short axis and change in standard uptake value (SUV). Patterns of failure, time to recurrence, overall survival (OS), and disease-free survival (DFS) were determined. Results: Sixty-four lymph nodes suspicious for metastatic involvement were identified. Radiation boost doses ranged from 0 to 15 Gy, with a mean total dose of 52.3 Gy. Pelvic lymph nodes were treated with a slightly higher dose than para-aortic lymph nodes: mean 55.3 Gy versus 51.7 Gy, respectively. There was no correlation between dose delivered and change in size of lymph nodes along the short axis. All lymph nodes underwent a decrease in SUV with a complete resolution of abnormal uptake observed in 68%. Decrease in SUV was significantly greater for lymph nodes treated with ≥54 Gy compared to those treated with <54 Gy (P=.006). Median follow-up was 18.7 months. At 2 years, OS and DFS for the entire cohort were 78% and 50%, respectively. Locoregional control at 2 years was 84%. Conclusions: A biologic response, as measured by the change in SUV for metastatic lymph nodes, was observed at a dose threshold of 54 Gy. We recommend that involved lymph nodes be treated to this minimum dose.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2012

Failure Mode and Effect Analysis for Delivery of Lung Stereotactic Body Radiation Therapy

Purpose: To improve the quality and safety of our practice of stereotactic body radiation therapy (SBRT), we analyzed the process following the failure mode and effects analysis (FMEA) method. Methods: The FMEA was performed by a multidisciplinary team. For each step in the SBRT delivery process, a potential failure occurrence was derived and three factors were assessed: the probability of each occurrence, the severity if the event occurs, and the probability of detection by the treatment team. A rank of 1 to 10 was assigned to each factor, and then the multiplied ranks yielded the relative risks (risk priority numbers). The failure modes with the highest risk priority numbers were then considered to implement process improvement measures. Results: A total of 28 occurrences were derived, of which nine events scored with significantly high risk priority numbers. The risk priority numbers of the highest ranked events ranged from 20 to 80. These included transcription errors of the stereotactic coordinates and machine failures. Conclusion: Several areas of our SBRT delivery were reconsidered in terms of process improvement, and safety measures, including treatment checklists and a surgical time-out, were added for our practice of gantry-based image-guided SBRT. This study serves as a guide for other users of SBRT to perform FMEA of their own practice.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2012

Solution-Processable Transparent Conductive Hole Injection Electrode for OLED SSL

An interconnected network of silver nanowires has been used as transparent anode in OLED devices. This layer was deposited by spin-coating and slot-die coating from an aqueous nanowire suspension. The sheet resistance of the film was 10ohms/sq with a transmission (including the glass substrate) of higher than 85%. The first phase of the project focused on the implementation of this nanowire layer with a hole-injection-layer (HIL) which has been developed at Plextronics and has been shown to provide good stability and efficiency in conventional OLED devices. We modified the HIL solution such that it coated reasonably well with suitable surface morphology so that actual devices can be manufactured. During the second phase we investigated the hole-injection and stability of hole-onlydevices. We determined that the use of the nanowire network as anode does not introduce an additional degradation mechanism since the observed device characteristics did not differ from those made with ITO anode. We then proceeded to make actual OLED devices with this nanowire / HIL stack and achieved device characteristics similar state-of-the-art OLED devices with a single junction. In order to gain traction with potential OLED manufacturers, we decided to contract Novaled to prepare large-area demonstrators for us. For these devices, we used an allevaporated stack, i.e. we did use Novaled's HIL material instead of Plextronics. We successfully fabricated demonstrators with an area of 25cm2 with a double or triple junction stack. Minor stack optimizations were necessary to achieve efficacies and lifetime equivalent with ITO devices made with the same devices stack. Due to the reduced microcavity effect, the color of the emitted light is significantly more stable with respect to the viewing angle compared to ITO devices. This fact in conjunction with the promise of lower production cost due to the elimination of the ITO sputtering process and the direct patterning of the anode layer are the obvious advantages of this technology. The project has shown that this nanowire technology is a viable option to achieve OLED devices with good lifetime and efficiency and we are currently working with manufacturers to utilize this technology in a production setting.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2012

Addition of a third field significantly increases dose to the brachial plexus for patients undergoing tangential whole-breast therapy after lumpectomy

Our goal was to evaluate brachial plexus (BP) dose with and without the use of supraclavicular (SCL) irradiation in patients undergoing breast-conserving therapy with whole-breast radiation therapy (RT) after lumpectomy. Using the standardized Radiation Therapy Oncology Group (RTOG)-endorsed guidelines delineation, we contoured the BP for 10 postlumpectomy breast cancer patients. The radiation dose to the whole breast was 50.4 Gy using tangential fields in 1.8-Gy fractions, followed by a conedown to the operative bed using electrons (10 Gy). The prescription dose to the SCL field was 50.4 Gy, delivered to 3-cm depth. The mean BP volume was 14.5 {+-} 1.5 cm{sup 3}. With tangential fields alone, the median mean dose to the BP was 0.57 Gy, the median maximum dose was 1.93 Gy, and the irradiated volume of the BP receiving 40, 45, and 50 Gy was 0%. When the third (SCL field) was added, the dose to the BP was significantly increased (P = .01): the median mean dose to the BP was 40.60 Gy, and the median maximum dose was 52.22 Gy. With 3-field RT, the median irradiated volume of the BP receiving 40, 45, and 50 Gy was 83.5%, 68.5%, and 24.6%, respectively. The addition of the SCL field significantly increases dose to the BP. The possibility of increasing the risk of BP morbidity should be considered in the context of clinical decision making.

61 RADIATION PROTECTION AND DOSIMETRY↗