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Nelson V.K.,Liverpool and Macarthur Cancer Therapy Centres | Hill R.F.,Royal Prince Alfred Hospital | Hill R.F.,University of Sydney
Radiation Measurements | Year: 2011

Backscatter factors (BSF) are used for calculation of absorbed dose in water from kilovoltage x-ray beams through the measurements using air-kerma based dosimetry protocols. The determination of backscatter factors has usually been performed using Monte Carlo calculations. The experimental measurement of BSFs requires that a dosimeter causes minimal perturbation to the x-ray fluence. In this work, we present the results of measuring BSFs using two different thermoluminescent dosimeters (TLDs). These were LiF:Mg,Ti (TLD100) and LiF:Mg,Cu,P (TLD100H) for x-ray beams with energies ranging from 75 to 300 kVp. We also calculated the BSFs for these x-ray beams using the EGSnrc Monte Carlo code and compared our results with published BSFs. With the exception of the 180 kVp x-ray beam (HVL 0.85 mm Cu), the BSFs measured with both materials agree to within 5% of the BSFs published in IPEMB and AAPM protocols and calculated by Monte Carlo simulations. From these results, we propose that BSFs can be readily determined using measurements with TLD100 and TLD100H chips for comparison with published BSFs. © 2011 Elsevier Ltd. All rights reserved.

Lehman M.,Princess Alexandra Hospital | Hayden A.J.,Westmead Cancer Care Center | Martin J.M.,Calvary Materials Newcastle Hospital | Christie D.,Premion | And 4 more authors.
Journal of Medical Imaging and Radiation Oncology | Year: 2014

Australian and New Zealand radiation oncologists with an interest in uro-oncology were invited to participate in a pattern-of-practice survey dealing with the management of intact high-risk prostate cancer. Responses from 46 practitioners (representing 73% of all potential respondents) revealed that high-dose radiation therapy is the standard of care. However, there is variability in practice with regard to the methods used to achieve dose escalation, the use of whole-pelvic radiation therapy and the optimal duration of androgen deprivation therapy employed. A review of the literature outlining the current body of knowledge and the planned and ongoing studies in intact high-risk prostate cancer is presented. © 2013 The Authors. Journal of Medical Imaging and Radiation Oncology published by Wiley Publishing Asia Pty Ltd on behalf of Royal Australian and New Zealand College of Radiologists.

Lehman M.,Princess Alexandra Hospital | Sidhom M.,Liverpool and Macarthur Cancer Therapy Centres | Kneebone A.B.,Northern Sydney Cancer Center | Hayden A.J.,Westmead Cancer Care Center | And 4 more authors.
Journal of Medical Imaging and Radiation Oncology | Year: 2014

Australian and New Zealand radiation oncologists with an interest in uro-oncology were invited to undertake a pattern of practice survey dealing with issues encountered in the management of high-risk prostate cancer in the post-prostatectomy setting. Responses from practitioners revealed a lack of consensus regarding the optimal timing of radiation therapy the use of whole pelvic radiation therapy and the use of androgen deprivation therapy. A review of the literature outlining the current body of knowledge and the clinical studies that will inform future practice is presented. © 2013 The Royal Australian and New Zealand College of Radiologists.

Gustafsson H.,University of Sydney | Vial P.,Northern Sydney Cancer Center | Kuncic Z.,Liverpool and Macarthur Cancer Therapy Centres | Baldock C.,University of Newcastle | And 2 more authors.
Medical Physics | Year: 2011

Purpose: Electronic portal imaging devices (EPIDs) are high resolution systems that produce electronic dose maps with minimal time required for equipment setup, and therefore potentially present a time-saving alternative for intensity modulated radiation therapy (IMRT) pretreatment verification. A modified commercial EPID was investigated operated with an opaque sheet blocking the optical signal produced in the phosphor layer as a precursor to a switched mode dual dosimetry-imaging EPID system. The purpose of this study was to investigate the feasibility of using this system for direct dose to water dosimetry for pretreatment IMRT verification. Methods: A Varian amorphous silicon EPID was modified by placing an opaque sheet between the Gd 2S 2O:Tb phosphor layer and the photodiode array to block the optical photons. The EPID was thus converted to a direct-detecting system (dEPID), in which the high energy radiation deposits energy directly in the photodiode array. The copper build-up was replaced with d max solid water. Sixty-one IMRT beams of varying complexity were delivered to the EPID, to EDR2 dosimetric film and to a 2D ion chamber array (MapCheck). EPID data was compared to film and MapCheck data using gamma analysis with 3%, 3mm pass criteria. Results: The fraction of points that passed the gamma test was on average 98.1 and 98.6, for the EPID versus film and EPID versus MapCheck comparisons, respectively. In the case of comparison with film, the majority of observed discrepancies were associated with problems related to film sensitivity or processing. Conclusions: The very close agreement between EPID and both film and MapCheck data demonstrates that the modified EPID is suitable for direct dose to water measurement for pretreatment IMRT verification. These results suggest a reconfigured EPID could be an efficient and accurate dosimeter. Alternatively, optical switching methods could be developed to produce a dual-mode EPID with both dosimetry and imaging capabilities. © 2011 American Association of Physicists in Medicine.

Jameson M.G.,Liverpool and Macarthur Cancer Therapy Centres | Jameson M.G.,University of Wollongong | Jameson M.G.,Ingham Institute of Applied Medical Research | Kumar S.,Liverpool and Macarthur Cancer Therapy Centres | And 11 more authors.
Radiotherapy and Oncology | Year: 2014

Background and purpose Contouring variation is a well know uncertainty in modern radiotherapy. This study investigates the relationship between contouring variation, tumor control probability (TCP) and equivalent uniform dose (EUD) for conformal non-small cell lung cancer (NSCLC) radiotherapy. Material and methods Seven patients were retrospectively recruited to the study and multiple PTV contours were generated based on CT and PET imaging by three observers. Plans were created for each PTV volume. Volumes were analyzed geometrically using volume, location, dimension and conformity index (CI). Radiobiological plan analysis consisted of two TCP models and EUD. Spearman's correlation coefficient (ρ) was used to quantify the association between geometric variation and radiobiological metrics. Results The variation in CI and TCP for the study was 0.66-0.90% and 0.19-0.68%. Changes in lateral dimension and volume were significantly correlated with TCP and EUD with an average ρ of -0.49 and 0.43 (p < 0.01) respectively. Conclusions TCP and geometric contour variation show significant correlation. This correlation was most significant for changes in lateral dimensions of PTV volumes. This association may be used in the assessment of contouring protocol violations in multicenter clinical trials and aid in the design of future contouring studies. © 2014 Elsevier Ireland Ltd. All rights reserved.

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