ORCID Profile
0000-0002-6546-0695
Current Organisations
Australian National University
,
Canberra Hospital
,
University of New South Wales
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Publisher: Medknow
Date: 2009
Publisher: Wiley
Date: 31-07-2021
Abstract: There is significant potential to analyse and model routinely collected data for radiotherapy patients to provide evidence to support clinical decisions, particularly where clinical trials evidence is limited or non‐existent. However, in practice there are administrative, ethical, technical, logistical and legislative barriers to having coordinated data analysis platforms across radiation oncology centres. A distributed learning network of computer systems is presented, with software tools to extract and report on oncology data and to enable statistical model development. A distributed or federated learning approach keeps data in the local centre, but models are developed from the entire cohort. The feasibility of this approach is demonstrated across six Australian oncology centres, using routinely collected lung cancer data from oncology information systems. The infrastructure was used to validate and develop machine learning for model‐based clinical decision support and for one centre to assess patient eligibility criteria for two major lung cancer radiotherapy clinical trials (RTOG‐9410, RTOG‐0617). External validation of a 2‐year overall survival model for non–small cell lung cancer (NSCLC) gave an AUC of 0.65 and C‐index of 0.62 across the network. For one centre, 65% of Stage III NSCLC patients did not meet eligibility criteria for either of the two practice‐changing clinical trials, and these patients had poorer survival than eligible patients (10.6 m vs. 15.8 m, P = 0.024). Population‐based studies on routine data are possible using a distributed learning approach. This has the potential for decision support models for patients for whom supporting clinical trial evidence is not applicable.
Publisher: Elsevier BV
Date: 03-2019
DOI: 10.1016/J.RADONC.2018.12.015
Abstract: To investigate if a local dose-effect (LDE) relationship for perfusion loss improves the NTCP model fit for SBRT induced radiation pneumonitis (RP) compared to conventional LDEs. Multi-institutional data of 1015 patients treated with SBRT were analyzed. Dose distributions were converted to NTD with α/β = 3 Gy. The Lyman-Kutcher-Burman NTCP model was fitted to the incidence grade ≥2 RP by maximum likelihood estimation with mean lung dose (MLD), equivalent uniform doses (EUD) using three LDE functions (power-law (EUD The median time to grade ≥2 RP was 4.2 months and plateaued after 17 months at 5.4%. A strong dose-effect relationship for RP incidence was observed. The EUD A LDE for perfusion loss provided modest improvement in NTCP model fit for SBRT induced radiation pneumonitis.
Publisher: Elsevier BV
Date: 04-2015
Publisher: British Institute of Radiology
Date: 11-2020
Abstract: Preclinical animal models allow testing and refinement of novel therapeutic strategies. The most common preclinical animal irradiators are fixed source cabinet irradiators, which are vastly inferior to clinical linear accelerators capable of delivering highly conformal and precise treatments. The purpose of this study was to design, manufacture and test an irradiation jig (small animal focal irradiation jig, SARJ) that would enable focal irradiation of subcutaneous tumours in a standard fixed source cabinet irradiator. A lead shielded SARJ was designed to rotate animal holders about the longitudinal axis and slide vertically from the base plate. Radiation dosimetry was undertaken using the built-in ion chamber and GAFChromic RTQA2 and EBT-XD films. Treatment effectiveness was determined by irradiating mice with subcutaneous melanoma lesions using a dose of 36 Gy in three fractions (12 Gy x 3) over three consecutive days. The SARJ was tested for X-ray shielding effectiveness, verification of dose rate, total dose delivered to tumour and dose uniformity. Accurate and uniform delivery of X-ray dose was achieved. X-ray doses were limited to the tumour site when animal holders were rotated around their longitudinal axis to 15 o and 195 o , allowing sequential dose delivery using parallel-opposed tangential beams. Irradiation of subcutaneous melanoma tumour established on the flanks of mice showed regression. SARJ enabled delivery of tangential parallel-opposed radiation beams to subcutaneous tumours in up to five mice simultaneously. SARJ allowed high throughput testing of clinically relevant dose delivery using a standard cabinet-style fixed source irradiator. A custom designed jig has been manufactured to fit into conventional cabinet irradiators and is dosimetrically validated to deliver clinically relevant dose distributions to subcutaneous tumours in mice for preclinical studies.
Publisher: Springer Science and Business Media LLC
Date: 11-05-2016
DOI: 10.1007/S13246-016-0446-X
Abstract: The impact of microscopic disease extension (MDE), extra-CTV tumour islets (TIs), incidental dose and dose conformity on tumour control probability (TCP) is analyzed using insilico simulations in this study. MDE in the region in between GTV and CTV is simulated inclusive of geometric uncertainties (GE) using spherical targets and spherical dose distribution. To study the effect of incidental dose on TIs and the effect of dose-response curve (DRC) on tumour control, islets were randomly distributed and TCP was calculated for various dose levels by rescaling the dose. Further, the impact of dose conformity on required PTV margins is also studied. The required PTV margins are ~2 mm lesser than assuming a uniform clonogen density if an exponential clonogen density fall off in the GTV-CTV is assumed. However, margins are almost equal if GE is higher in both cases. This shows that GE has a profound impact on margins. The effect of TIs showed a bi-phasic relation with increasing dose, indicating that patients with islets not in the beam paths do not benefit from dose escalation. Increasing dose conformity is also found to have considerable effect on TCP loss especially for larger GE. Further, smaller margins in IGRT should be used with caution where uncertainty in CTV definition is of concern.
Publisher: Elsevier BV
Date: 2014
Publisher: Wiley
Date: 20-03-2013
DOI: 10.1118/1.4795131
Abstract: Geometric uncertainties are inevitable in radiotherapy. To account for these uncertainties, a margin is added to the clinical target volume (CTV) to create the planning target volume (PTV), and its size is critical for obtaining an optimal treatment plan. Dose-based (i.e., physical) margin recipes have been published and widely used, but it is important to consider fractionation and the radiobiological characteristics of the tumor when deriving margins. Hence a tumor control probability (TCP)-based margin is arguably more appropriate. Margins required for ≤ 1% loss in mean population TCP (relative to a static tumor) for varying numbers of fractions, varying slope of the dose-response curve (γ50) and varying degrees of dose distribution conformity are investigated for spherical and four-field (4F)-brick dose distributions. To simulate geometric uncertainties, systematic (Σ) and random (σ) tumor displacements were s led from Gaussian distributions and applied to each fraction for a spherical CTV. Interfraction tumor motion was simulated and the dose accumulated from fraction to fraction on a voxel-by-voxel basis to calculate TCP. PTV margins derived from this work for various fraction numbers and dose-response slopes (γ50) for different degrees of geometric uncertainties are compared with margins calculated using published physical-dose- and TCP-based recipes. Larger margins are required for a decrease in the number of fractions and for an increase in γ50 for both spherical and 4F-brick dose distributions. However, the margins can be close to zero for the 4F-brick distribution for small geometric uncertainties (Σ = 1, σ = 1 mm) irrespective of the number of fractions and the magnitude of γ50 due to the higher "incidental" dose outside the tumor. For Σ = 1 mm and σ = 3 mm, physical-dose-based recipes underestimate the margin only for the combination of hypofractionated treatments and tumors with a high γ50. For all other situations TCP-based margins are smaller than physical-dose-based recipes. Margins depend on the number of fractions and γ50 in addition to Σ and σ. Dose conformity should also be considered since the required margin increases with increasing dose conformity. Ideally margins should be anisotropic and in idualized, taking into account γ50, number of fractions, and the dose distribution, as well as estimates of Σ and σ. No single "recipe" can adequately account for all these variables.
Publisher: Wiley
Date: 06-2009
DOI: 10.1118/1.3182288
Publisher: Wiley
Date: 06-2009
DOI: 10.1118/1.3182013
Publisher: Springer Science and Business Media LLC
Date: 06-02-2019
DOI: 10.1007/S13246-019-00731-Y
Abstract: Cranio-spinal irradiation (CSI) is widely used for treating medulloblastoma cases in children. Radiation-induced second malignancy is of grave concern especially in children due to their long-life expectancy and higher radiosensitivity of tissues at young age. Several techniques can be employed for CSI including 3DCRT, IMRT, VMAT and tomotherapy. However, these techniques are associated with higher risk of second malignancy due to the physical characteristics of photon irradiation which deliver moderately higher doses to normal tissues. On the other hand, proton beam therapy delivers substantially lesser dose to normal tissues due to the sharp dose fall off beyond Bragg peak compared to photon therapy. The aim of this work is to quantify the relative decrease in the risk with proton therapy compared to other photon treatments for CSI. Ten anonymized patient DICOM datasets treated previously were selected for this study. 3DCRT, IMRT, VMAT, tomotherapy and proton therapy with pencil beam scanning (PBS) plans were generated. The prescription dose was 36 Gy in 20 fractions. PBS was chosen due to substantially lesser neutron dose compared to passive scattering. The age of the patients ranged from 3 to 12 with a median age of eight with six male and four female patients. Commonly used linear and a mechanistic doseresponse models (DRM) were used for the analyses. Dose-volume histograms (DVH) were calculated for critical structures to calculate organ equivalent doses (OED) to obtain excess absolute risk (EAR), life-time attributable risk (LAR) and other risk relevant parameters. A α' value of 0.018 Gy
Publisher: British Institute of Radiology
Date: 2015
DOI: 10.1259/BJR.20140372
Publisher: Elsevier BV
Date: 11-2008
Publisher: Elsevier BV
Date: 11-2008
Publisher: Medknow
Date: 2016
Publisher: Elsevier BV
Date: 05-2017
Publisher: Elsevier BV
Date: 05-2011
Publisher: Medknow
Date: 2017
Publisher: Elsevier BV
Date: 03-2013
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Jothybasu Selvaraj.