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Sutherland B.,Genesis CancerCare Queensland | Middlebrook N.,Genesis CancerCare Queensland | Kairn T.,Genesis CancerCare Queensland | Kairn T.,Queensland University of Technology | Hill B.,Genesis CancerCare Queensland
Australasian Physical and Engineering Sciences in Medicine | Year: 2015

This study assessed the validity of the conversion from percentage depth dose (PDD) to tissue maximum ratio (TMR) using BJR Supplement 25 data for flattened and flattening filter free (FFF) beams. PDD and TMR scans for a variety of field sizes were measured in water using a Sun Nuclear Corporation 3D SCANNER™ on a Varian TrueBeam linear accelerator in 6 MV, 10 MV and 6 MV FFF beams. The BJR Supplement 25 data was used to convert the measured PDDs to TMRs and these were compared with the directly measured TMR data. The TMR plots calculated from PDD were within 1 % for the 10 MV and 6 MV flattened beams, for field sizes 3 cm × 3 cm to 40 cm × 40 cm inclusive, at depths measured beyond the depth of maximum dose. The disagreement between the measured and calculated TMR plots for the 6 MV FFF beam increased with depth and field size to a maximum of 1.7 % for a 40 cm × 40 cm field. The results found in this study indicate that the BJR Supplement 25 data should not be used for field sizes larger than 20 cm × 20 cm at depths greater than 15 cm for the 6 MV FFF beam. It is advised that PDD to TMR conversion for FFF beams should be done with phantom scatter ratios appropriate to FFF beams, or the TMR should be directly measured if required. © 2015, Australasian College of Physical Scientists and Engineers in Medicine. Source

Kairn T.,Genesis CancerCare Queensland | Kairn T.,Queensland University of Technology | Ibrahim S.,Princess Alexandra Hospital | Inness E.,Princess Alexandra Hospital | And 2 more authors.
IFMBE Proceedings | Year: 2015

This study investigated a potential source of inaccuracy for diode measurements in modulated beams; the effect of diode housing asymmetry on measurement results. The possible effects of diode housing asymmetry on the measurement of steep dose gradients were evaluated by measuring 5×5 cm2 beam profiles, with three cylindrical diodes and two commonly used ionization chambers, with each dosimeter positioned in a 3D scanning water tank with its stem perpendicular to the beam axis (horizontal) and parallel to the direction of scanning. The resulting profiles were used to compare the penumbrae measured with the diode stem pointing into (equivalent to a “stem-first” setup) and out of the field (equivalent to a “stem-last” setup) in order to evaluate the effects of dosimeter alignment and thereby identify the effects of dosimeter asymmetry. The stem-first and stem-last orientations resulted in differences of up to 0.2 mm in the measured 20-80% penumbra widths and differences of up to 0.4 mm in the offaxis position of the 90% isodose. These differences, which are smaller than previously reported for older model dosimeters, were apparent in the profile results for both diodes and smallvolume ionization chambers. As an extension to this study, the practical use of all five dosimeters was exemplified by measuring point doses in IMRT test beams. These measurements showed good agreement (within 2%) between the diodes and the small volume ionization chamber, with all of these dosimeters being able to identify a region 3% under-dosage which was not identified by a larger volume (6 mm diameter) ionization chamber. The results of this work should help to remove some of the barriers to the use of diodes for modulated radiotherapy dosimetry in the future. © Springer International Publishing Switzerland 2015. Source

Kairn T.,Genesis CancerCare Queensland | Kairn T.,Queensland University of Technology | Crowe S.B.,Queensland University of Technology | Markwell T.,Materials Radiation Oncology
IFMBE Proceedings | Year: 2015

This study used the specific example of 3D printing with acrylonitrile butadiene styrene (ABS) as a means to investigate the potential usefulness of benchtop rapid prototyping as a technique for producing patient specific phantoms for radiotherapy dosimetry. Three small cylinders and one model of a human lung were produced via in-house 3D printing with ABS, using 90%, 50%, 30% and 10% ABS infill densities. These phantom samples were evaluated in terms of their geometric accuracy, tissue equivalence and radiation hardness, when irradiated using a range of clinical radiotherapy beams. The measured dimensions of the small cylindrical phantoms all matched their planned dimensions, within 1mm. The lung phantom was less accurately matched to the lung geometry on which it was based, due to simplifications introduced during the phantom design process. The mass densities, electron densities and linear attenuation coefficients identified using CT data, as well as the results of film measurements made using megavoltage photon and electron beams, indicated that phantoms printed with ABS, using infill densities of 30% or more, are potentially useful as lung- and tissue-equivalent phantoms for patient-specific radiotherapy dosimetry. All cylindrical 3D printed phantom samples were found to be unaffected by prolonged radiation and to accurately match their design specifications. However, care should be taken to avoid oversimplifying anatomical structures when printing more complex phantoms. © Springer International Publishing Switzerland 2015. Source

Tromp D.,Gold Coast University Hospital | Tromp D.,Griffith University | Christie D.R.H.,Genesis CancerCare Queensland | Christie D.R.H.,Bond University
Clinical Oncology | Year: 2015

Aims: Inflammatory bowel disease has traditionally been considered a relative contraindication for radiotherapy due to a perceived increased risk of disease exacerbation and bowel toxicity. The aim of this review was to evaluate the current literature regarding rates of radiotherapy-induced acute and late bowel toxicity in patients with inflammatory bowel disease and to compare these data with those of patients without the disease. Materials and methods: An Ovid Medline search was conducted to identify original articles pertaining to the review question. Using the PRISMA convention a total of 442 articles screened, resulting 8 articles which were suitable for inclusion in the review. Results: In general, the grading of toxicity was scored using either the Radiation Therapy Oncology Group or Common Terminology Criteria for Adverse Events scoring systems. It was found that acute bowel toxicity of ≥ grade 3 occurred in 20% of patients receiving external beam radiotherapy (EBRT) and in 7% of patients receiving brachytherapy. Late bowel toxicity ≥ grade 3 occurred in 15% of EBRT patients and in 5% of patients receiving brachytherapy. Brachytherapy was shown to have similar rates of toxicity and EBRT produced a moderate increase in both acute and late toxicity when compared with individuals without inflammatory bowel disease. Conclusion: In view of these results, we suggest that brachytherapy should be considered as a suitable treatment option for treating pelvic malignancy in patients with inflammatory bowel disease, whereas EBRT should be used with caution. © 2015 The Royal College of Radiologists. Source

Kairn T.,Genesis CancerCare Queensland | Kairn T.,Queensland University of Technology | Charles P.H.,Queensland University of Technology | Cranmer-Sargison G.,Saskatchewan Cancer Agency | And 5 more authors.
Australasian Physical and Engineering Sciences in Medicine | Year: 2015

There have been substantial advances in small field dosimetry techniques and technologies, over the last decade, which have dramatically improved the achievable accuracy of small field dose measurements. This educational note aims to help radiation oncology medical physicists to apply some of these advances in clinical practice. The evaluation of a set of small field output factors (total scatter factors) is used to exemplify a detailed measurement and simulation procedure and as a basis for discussing the possible effects of simplifying that procedure. Field output factors were measured with an unshielded diode and a micro-ionisation chamber, at the centre of a set of square fields defined by a micro-multileaf collimator. Nominal field sizes investigated ranged from 6 9 6 to 98 9 98 mm2. Diode measurements in fields smaller than 30 mm across were corrected using response factors calculated using Monte Carlo simulations of the diode geometry and daisy-chained to match micro-chamber measurements at intermediate field sizes. Diode measurements in fields smaller than 15 mm across were repeated twelve times over three separate measurement sessions, to evaluate the reproducibility of the radiation field size and its correspondence with the nominal field size. The five readings that contributed to each measurement on each day varied by up to 0.26 %, for the ‘‘very small’’ fields smaller than 15 mm, and 0.18 % for the fields larger than 15 mm. The diode response factors calculated for the unshielded diode agreed with previously published results, within uncertainties. The measured dimensions of the very small fields differed by up to 0.3 mm, across the different measurement sessions, contributing an uncertainty of up to 1.2 % to the very small field output factors. The overall uncertainties in the field output factors were 1.8 % for the very small fields and 1.1 % for the fields larger than 15 mm across. Recommended steps for acquiring small field output factor measurements for use in radiotherapy treatment planning system beam configuration data are provided. © Australasian College of Physical Scientists and Engineers in Medicine 2015. Source

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