Time filter

Source Type

Arumugam S.,Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute | Xing A.,Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute | Young T.,Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute | Holloway L.,Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute | And 3 more authors.
Physica Medica | Year: 2015

Purpose: To study the sensitivity of an ArcCHECK dosimeter in detecting delivery errors during the delivery of Volumetric Modulated Arc Therapy (VMAT). Methods: Three types of errors in Multi Leaf Collimator (MLC) position and dose delivery were simulated separately in the delivery of five prostate and five head and neck (H&N) VMAT plans: (i) Gantry independent: a systematic shift in MLC position and variation in output to the whole arc; (ii) Gantry dependent: sag in MLC position and output variation as a function of gantry angle; (iii) Control point specific MLC and output errors introduced to only a specific number of Control Points (CP). The difference in local and global gamma (γ) pass rate between the no-error and error-simulated measurements with 2%/2 mm and 3%/3 mm tolerances was calculated to assess the sensitivity of ArcCHECK. The clinical impact of these errors was also calculated. Results: ArcCHECK was able to detect a minimum 3 mm MLC error and 3% output error for Gantry independent errors using either local or global gamma with 2%/2 mm tolerance. For the Gantry dependent error scenario a minimum 3 mm MLC error and 3% dose error was identifiable by ArcCHECK using either global or local gamma with 2%/2 mm tolerance. In errors introduced to specific CPs a MLC error of 10 mm and dose error of 100% introduced to 4CPs were detected by ArcCHECK. Conclusion: ArcCHECK used with either local or global gamma analysis and 2%/2 mm criteria can be confidently used in the clinic to detect errors above the stated error values. © 2015 Associazione Italiana di Fisica Medica.


Arumugam S.,Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute | Arumugam S.,University of New South Wales | Xing A.,Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute | Xing A.,University of New South Wales | And 7 more authors.
Physica Medica | Year: 2016

Aim To study the sensitivity of three commercial dosimetric systems, Delta4, Multicube and Octavius4D, in detecting Volumetric Modulated Arc Therapy (VMAT) delivery errors. Methods Fourteen prostate and head and neck (H&N) VMAT plans were considered for this study. Three types of errors were introduced into the original plans: gantry angle independent and dependent MLC errors, and gantry angle dependent dose errors. The dose matrix measured by each detector system for the no-error and error introduced delivery were compared with the reference Treatment Planning System (TPS) calculated dose matrix for no-error plans using gamma (γ) analysis with 2%/2 mm tolerance criteria. The ability of the detector system in identifying the minimum error in each scenario was assessed by analysing the gamma pass rates of no error delivery and error delivery using a Wilcoxon signed-rank test. The relative sensitivity of the system was assessed by determining the slope of the gamma pass line for studied error magnitude in each error scenario. Results In the gantry angle independent and dependent MLC error scenario the Delta4, Multicube and Octavius4D systems detected a minimum 2 mm error. In the gantry angle dependent dose error scenario all studied systems detected a minimum 3% and 2% error in prostate and H&N plans respectively. In the studied detector systems Multicube showed relatively less sensitivity to the errors in the majority of error scenarios. Conclusion The studied systems identified the same magnitude of minimum errors in all considered error scenarios. © 2016 Associazione Italiana di Fisica Medica


PubMed | Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute, University of New South Wales and Liverpool and Macarthur Cancer Therapy Centres
Type: Journal Article | Journal: Medical physics | Year: 2016

Accurate positioning of the target volume during treatment is paramount for stereotactic body radiation therapy (SBRT). In this work, the authors present the development of an in-house software tool to verify target position with an Elekta-Synergy linear accelerator using kV planar images acquired during treatment delivery.In-house software, SeedTracker, was developed in matlab to perform the following three functions: 1. predict intended seed positions in a planar view perpendicular to any gantry angle, simulating a portal imaging device, from the 3D seed co-ordinates derived from the treatment planning system; 2. autosegment seed positions in kV planar images; and 3. report the position shift based on the seed positions in the projection images. The performance of SeedTracker was verified using a CIRS humanoid phantom (CIRS, VA, USA) implanted with three Civco gold seed markers (Civco, IA, USA) in the prostate. The true positive rate of autosegmentation (TPRseg) and the accuracy of the software in alerting the user when the isocenter position was outside the tolerance (TPRtrig) were studied. Two-dimensional and 3D static position offsets introduced to the humanoid phantom and 3D dynamic offsets introduced to a gel phantom containing gold seeds were used for evaluation of the system.SeedTracker showed a TPRseg of 100% in the humanoid phantom for projection images acquired at all angles except in the ranges of 80-100 and 260-280 where seeds are obscured by anatomy. This resulted in a TPRtrig of 88% over the entire treatment range for considered 3D static offsets introduced to the phantom. For 2D static offsets where the position offsets were only introduced in the anterior-posterior and lateral directions, the TPRtrig of SeedTracker was limited by both seed detectability and positional offset. SeedTracker showed a false positive trigger in the projection angle range between 130-170 and 310-350 (a maximum of 24% of treatment time) due to limited information that can be derived from monoscopic images. The system accurately determined the dynamic trajectory of the isocenter position in the superior and inferior direction for the studied dynamic offset scenarios based on the seed position in monoscopic images.The developed software has been shown to accurately autosegment the seed positions in kV planar images except for two 20 arcs where seeds are obscured by anatomical structures. The isocenter trajectories determined by the system, based on the monoscopic images, provide useful information for monitoring the prostate position. The developed system has potential application for monitoring prostate position during treatment delivery in linear accelerator based SBRT.


Begg J.,RMIT University | Begg J.,Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute | Taylor M.L.,RMIT University | Holloway L.,Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute | And 6 more authors.
Australasian Physical and Engineering Sciences in Medicine | Year: 2014

Temporally varying light intensity during acquisition of projection images in an optical CT scanner can potentially be misinterpreted as physical properties of the sample. This work investigated the impact of LED light source intensity instability on measured attenuation coefficients. Different scenarios were investigated by conducting one or both of the reference and data scans in a ‘cold’ scanner, where the light source intensity had not yet stabilised. Uniform samples were scanned to assess the impact on measured uniformity. The orange (590 nm) light source decreased in intensity by 29 % over the first 2 h, while the red (633 nm) decreased by 9 %. The rates of change of intensity at 2 h were 0.1 and 0.03 % respectively over a 5 min period—corresponding to the scan duration. The normalisation function of the reconstruction software does not fully account for the intensity differences and discrepancies remain. Attenuation coefficient inaccuracies of up to 8 % were observed for data reconstructed from projection images acquired with a cold scanner. Increased noise was observed for most cases where one or both of the scans was acquired without sufficient warm-up. The decrease in accuracy and increase in noise were most apparent for data reconstructed from reference and data scans acquired with a cold scanner on different days. © 2014, Australasian College of Physical Scientists and Engineers in Medicine.


PubMed | Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute, University of Sydney, University of New South Wales and Maastricht University
Type: Journal Article | Journal: Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology | Year: 2014

A rapid learning approach has been proposed to extract and apply knowledge from routine care data rather than solely relying on clinical trial evidence. To validate this in practice we deployed a previously developed decision support system (DSS) in a typical, busy clinic for non-small cell lung cancer (NSCLC) patients.Gender, age, performance status, lung function, lymph node status, tumor volume and survival were extracted without review from clinical data sources for lung cancer patients. With these data the DSS was tested to predict overall survival.3919 lung cancer patients were identified with 159 eligible for inclusion, due to ineligible histology or stage, non-radical dose, missing tumor volume or survival. The DSS successfully identified a good prognosis group and a medium/poor prognosis group (2 year OS 69% vs. 27/30%, p<0.001). Stage was less discriminatory (2 year OS 47% for stage I-II vs. 36% for stage IIIA-IIIB, p=0.12) with most good prognosis patients having higher stage disease. The DSS predicted a large absolute overall survival benefit (40%) for a radical dose compared to a non-radical dose in patients with a good prognosis, while no survival benefit of radical radiotherapy was predicted for patients with a poor prognosis.A rapid learning environment is possible with the quality of clinical data sufficient to validate a DSS. It uses patient and tumor features to identify prognostic groups in whom therapy can be individualized based on predicted outcomes. Especially the survival benefit of a radical versus non-radical dose predicted by the DSS for various prognostic groups has clinical relevance, but needs to be prospectively validated.


PubMed | Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute
Type: Journal Article | Journal: Medical physics | Year: 2013

The delivery of volumetric modulated arc therapy (VMAT) is more complex than other conformal radiotherapy techniques. In this work, the authors present the feasibility of performing routine verification of VMAT delivery using a dose matrix measured by a gantry mounted 2D ion chamber array and corresponding dose matrix calculated by an inhouse developed algorithm.Pinnacle, v9.0, treatment planning system (TPS) was used in this study to generate VMAT plans for a 6 MV photon beam from an Elekta-Synergy linear accelerator. An algorithm was developed and implemented with inhouse computer code to calculate the dose matrix resulting from a VMAT arc in a plane perpendicular to the beam at isocenter. The algorithm was validated using measurement of standard patterns and clinical VMAT plans with a 2D ion chamber array. The clinical VMAT plans were also validated using ArcCHECK measurements. The measured and calculated dose matrices were compared using gamma () analysis with 3%/3 mm criteria and tolerance of 1.The dose matrix comparison of standard patterns has shown excellent agreement with the mean pass rate 97.7 ( = 0.4)%. The validation of clinical VMAT plans using the dose matrix predicted by the algorithm and the corresponding measured dose matrices also showed good agreement with the mean pass rate of 97.6 ( = 1.6)%. The validation of clinical VMAT plans using ArcCHECK measurements showed a mean pass rate of 95.6 ( = 1.8)%.The developed algorithm was shown to accurately predict the dose matrix, in a plane perpendicular to the beam, by considering all possible leaf trajectories in a VMAT delivery. This enables the verification of VMAT delivery using a 2D array detector mounted on a treatment head.


PubMed | Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute and University of New South Wales
Type: Journal Article | Journal: Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB) | Year: 2015

To study the sensitivity of an ArcCHECK dosimeter in detecting delivery errors during the delivery of Volumetric Modulated Arc Therapy (VMAT).Three types of errors in Multi Leaf Collimator (MLC) position and dose delivery were simulated separately in the delivery of five prostate and five head and neck (H&N) VMAT plans: (i) Gantry independent: a systematic shift in MLC position and variation in output to the whole arc; (ii) Gantry dependent: sag in MLC position and output variation as a function of gantry angle; (iii) Control point specific MLC and output errors introduced to only a specific number of Control Points (CP). The difference in local and global gamma () pass rate between the no-error and error-simulated measurements with 2%/2mm and 3%/3mm tolerances was calculated to assess the sensitivity of ArcCHECK. The clinical impact of these errors was also calculated.ArcCHECK was able to detect a minimum 3mm MLC error and 3% output error for Gantry independent errors using either local or global gamma with 2%/2mm tolerance. For the Gantry dependent error scenario a minimum 3mm MLC error and 3% dose error was identifiable by ArcCHECK using either global or local gamma with 2%/2mm tolerance. In errors introduced to specific CPs a MLC error of 10mm and dose error of 100% introduced to 4CPs were detected by ArcCHECK.ArcCHECK used with either local or global gamma analysis and 2%/2mm criteria can be confidently used in the clinic to detect errors above the stated error values.

Loading Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute collaborators
Loading Liverpool and Macarthur Cancer Therapy Centres and Ingham Institute collaborators