Aims: To investigate variation in tumour breathing motion (TBM) between the planning four-dimensional computed tomograph (4DCT) and treatment itself for primary or secondary lung tumours undergoing stereotactic ablative radiotherapy (SABR).Materials and methods: Sixteen consecutive patients underwent planning 4DCT at least 1 week after implantation of a fiducial marker. The maximal extent of breathing motion of the intra-tumoural fiducial was measured at 4DCT and again at delivery of each SABR fraction on the linac using stereoscopic kilovoltage imaging. Displacements of the fiducial beyond planned limits were measured in three dimensions and represented as vectors. Variation in breathing motion between the planning 4DCT and treatment, and between individual SABR fractions was analysed.Results: Although TBM at treatment exceeded planned tumour motion limits for at least part of the course for all patients, 31% of patients remained consistently within 1 mm, 50% within 2 mm and 69% consistently within 3 mm of planned parameters. However, 19% of patients experienced TBM variation 5 mm or more beyond planned limits for at least one fraction. For all patients, the median displacement vector at treatment beyond the planned motion envelope was 1.0 mm (mean 2.0 mm, range 0-12.7 mm). Variation in TBM at treatment from 4DCT correlated neither with the magnitude of TBM at 4DCT nor with planning target volume size (rs = 0.13, P = 0.62; rs = 0.02, P = 0.94, respectively). Nor was TBM variation related to tumour type or lobar position (P = 0.35, P = 0.06, respectively). Inter-fraction TBM variation was modest, with an average standard deviation of 1.7 mm (0.3-8.7 mm).Conclusions: TBM variation between 4DCT and treatment and between SABR fractions was modest for most patients. However, 19% of patients experienced significant TBM variation that could be clinically relevant for those most severely affected. It seems prudent to carry out on-couch assessment of TBM at each SABR fraction to identify such patients who might benefit from respiratory gating or adaptive radiotherapy to maintain tumour motion within the planned limits. (C) 2015 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

Free-breathing respiratory gated SBRT of surgically inoperable lung cancer has been clinically commissioned. This study was to establish the tumour tracking accuracy under clinical conditions based on an implanted fiducial marker. A VisicoilTM marker embedded in tissue-equivalent material mounted in a phantom (ET Gating PhantomTM Brainlab) driven by a patient's breathing data was treated with the ExacTracTM system. This one-dimensional moving marker represented a tumour motion in superior-inferior (S-I) direction measured through 4DCT study of the same patient. Both GafchromicTM films and the stereoscopic kV images were used for tracking the position of the marker. For tumour motion at magnitudes of 10, 20 and 29 mm and treated with corresponding gate widths of 50%, 33% and 20% of free breathing amplitude, the implanted marker was able to be tracked with a deviation ≤1.53 mm to its planned position.

Most of our radiobiology knowledge comes from studies using high doses of radiation. Current radiation protection is based on epidemiology at high dose exposure. The vast majority of the population are never exposed to high dose radiation. In contrast, with new and emerging diagnostic, industrial and security related procedures, more and more people are exposed to low or very low doses of radiation. It is now clear that the biological responses of cells and organisms after low dose radiation exposure are different to the responses after high dose radiation. Low dose radiation phenomena such as radio-adaptive responses and bystander effects do not strictly conform to the theory behind current radiation risk regulation. The biological mechanisms of adaptive responses and bystander effects have been an active area of study over recent years but still remain to be fully elucidated. Study of the mechanism of such responses after very low dose exposure poses many technical and interpretive challenges. Some of the major outstanding questions related to biological responses to low dose radiation will be addressed, and the approaches that are currently being taken to further our knowledge in these areas will be discussed.

We propose the application of optical calorimetry to measure the peak to valley ratio for synchrotron microbeam radiation therapy (MRT). We use a modified Schlieren approach known as reference image topography (RIT) which enables one to obtain a map of the rate of change of the refractive index in a water bath from which the absorbed dose can be determined with sufficient spatial accuracy to determine the peak to valley ratio. We modelled the calorimetric properties of X-rays using a heated wire in a water bath. Our RIT system comprised a light source, a textured reference object and a camera and lens combination. We measured temperature contours and showed a plume rising from the heated wire. The total temperature change in water was 12 degrees C, 500 times greater than the calculated change from a 1 ms exposure on a synchrotron. At 1.0 ms, thermal diffusion will be the major cause of uncertainty in determining the peak to valley ratio, and we calculate thermal diffusion will reduce the measured peak to valley ratio to 76% of its initial value, but the individual microbeams will still resolve. We demonstrate proof of concept for measuring X-ray dose using a modified RIT method.

PURPOSE:In this paper, the authors assess the accuracy of the Brainlab ExacTrac system for frameless intracranial stereotactic treatments in clinical practice. METHODS:They recorded couch angle and image fusion results (comprising lateral, longitudinal, and vertical shifts, and rotation corrections about these axes) for 109 stereotactic radiosurgery and 166 stereotactic radiotherapy patient treatments. Frameless stereotactic treatments involve iterative 6D image fusion corrections applied until the results conform to customizable pass criteria, theirs being 0.7 mm and 0.5° for each axis. The planning CT slice thickness was 1.25 mm. It has been reported in the literature that the CT slices' thickness impacts the accuracy of localization to bony anatomy. The principle of invariance with respect to patient orientation was used to determine spatial accuracy. RESULTS:The data for radiosurgery comprised 927 image pairs, of which 532 passed (pass ratio of 57.4%). The data for radiotherapy comprised 15983 image pairs, of which 10 050 passed (pass ratio of 62.9%). For stereotactic radiotherapy, the combined uncertainty of ExacTrac calibration, image fusion, and intrafraction motion was (95% confidence interval) 0.290-0.302 and 0.306-0.319 mm in the longitudinal and lateral axes, respectively. The combined uncertainty of image fusion and intrafraction motion in the anterior-posterior coordinates was 0.174-0.182 mm. For stereotactic radiosurgery, the equivalent ranges are 0.323-0.393, 0.337-0.409, and 0.231-0.281 mm. The overall spatial accuracy was 1.24 mm for stereotactic radiotherapy (SRT) and 1.35 mm for stereotactic radiosurgery (SRS). CONCLUSIONS:The ExacTrac intracranial frameless stereotactic system spatial accuracy is adequate for clinical practice, and with the same pass criteria, SRT is more accurate than SRS. They now use frameless stereotaxy exclusively at their center.

Despite the highly localized doses that may be delivered via stereotactic radiotherapy, a small dose is nonetheless delivered to out-of-field regions, which may cause detriment to the patient. In this work, a systematic set of dose measurements have been undertaken up to a distance of 45 cm from the isocentre, for stereotactic fields shaped by a BrainLAB mini-multileaf collimator (MMLC) mounted on a Varian 600C linear accelerator. A range of treatment parameters were varied so as to determine the factors of greatest influence and establish relationships with dose. The commercial treatment planning software (TPS) miscalculates the dose to out-of-field regions. Measured dose decreases consistently out to 45 cm, whereas the TPS decreases out to 10-15 cm, at which point the predicted dose is constant. At the 5-10 cm off-axis distance (OAD), measurements indicate doses of about 5-10% of the dose at the isocentre, 1% at 15 cm OAD and 0.1% at 45 cm OAD. There are several observed trends. Greater MMLC field sizes (with static jaw) result in higher out-of-field dose, as do shallower depths. The source-to-surface distance does not greatly influence peripheral dose. However, the results given in this work do indicate that simple treatment arrangements, such as preferable collimator rotation, would in certain cases reduce out-of-field dose by an order of magnitude. Peripheral dose raises questions of treatment optimization, particularly in cases where patients have a long life expectancy in which secondary effects may become manifest, such as in the treatment of paediatric patients or those with a non-malignant primary. For instance, for a 20 Gy hypo-fractionated treatment, dose to out-of-field regions is of the order of cGy-a substantial dose in radiation protection terms.

The introduction of mini-multi-leaf collimators (MMLC) into radiotherapy has seen the use of smaller field sizes become increasingly important. Small field sizes that tightly conform to precise target regions are sought in radiotherapy to deliver doses with a high therapeutic ratio. MMLCs have made it possible to shrink field sizes in radiotherapy to below half a centimetre. The dosimetry of such fields with conventional dosimeters such as gas-ionisation chambers is not feasible due to limitations caused by the chambers relatively large size compared to the size of the collimated beam. In this work, the dose distribution of radiotherapy beams collimated to such small sizes were examined using polyacrylamide gels dosimeters, Gafchromic films and micro-thermoluminescence dosimeters (micro-TLDs). Dose penumbra widths obtained with gel dosimeters, Gafchormic film and micro-TLDs were generally in agreement with each other, although a wider FWHM of the field was measured with gel in comparison to film. An asymmetric dose distribution between the two axis profiles of a 3×3mm collimated field was observed and can be attributed to an inherent asymmetry of the MMLC.

Purpose: Microbeam radiotherapy (MRT) is a technique that use array parallel thin (<100μm) slices of synchrotron generated x‐ray beam. In this study, we investigated the radio‐sensitizing effects of gold nanoparticles (AuNps) on endothelial cells culture model in combination with irradiation of MRT. Method and Materials: Bovine aortic endothelial cells (BAECs) were cultured as a confluent monolayer on a 2 well chamber slides with 0mM, 0.5 mM and 1.0mM of AuNps. The cells were irradiated with 10 Gy of synchrotron generated x‐ray beam of median energy 150 kVp. Each microbeam is approximately 30 microns wide with a spacing of 200 microns between adjacent microbeams. Gafchromic films were attached to the cells culture slide to verify the dose received by the cells. The experiments were performed on the BL28B2 beamline at the SPring8 Synchrotron Japan. The cells were then fixed at 6, 12 and 24 hours after irradiation and were imaged using phase contrast microscope. Cells viability assays using tryphan blue exclusion method were performed after 24 hours of irradiation. Results: The observations under phase contrast microscopy show all the cells were dead at the area of irradiation. Samples with AuNps clearly showed the path of microbeam which is visible as a straight line compared to the samples without AuNps. There are some neighbouring cells start to migrate to the irradiated area, filling the gap for both samples. The cells viability results showed the dose enhancement effects where only 52% cells survived for 0.5 mMol AuNps and only 18% survive for 1mMol AuNps when irradiated with microbeam. These results were expressed as percentage relative to the control samples. Conclusion: The results demonstrate that the AuNps are effective radiosensitizer that will increase the therapeutic efficacy of MRT.

Aneurysm clips within stereotactic treatment volumes enhance spatial accuracy but perturb the dose distribution. The dose perturbations caused by a standard titanium alloy aneurysm clip (Ti6Al4V) have been measured with Gafchromic® EBT film. The maximum dose perturbation was an increase of 6 % within 0.5 mm of the beam entry surface of the clip, and a decrease of 7 % within 0.5 mm of the beam exit surface of the clip. Results also showed perturbations to film readout due to the presence of micro dust particles on the film affecting optical properties at high spatial resolution (21um) scanning. Special procedures should be used when film is immersed in water, dried and then read at high spatial resolution. We recommend that films should be immersed only in distilled water and tools such as canned air puffs should be used to clean films without scratches.

Purpose: To quantify radiologic image contrast enhancement using gold nanoparticles compared to iodinated contrast media (CM) over the entire diagnostic range of x-ray energies. Method and Materials: A Perspex phantom with 4mm cylindrical wells was used to simulate small portions of vasculature. Each well was loaded with either gold nanoparticle solution or iodinated CM at equal concentration (0.5077 M radiopaque element). The phantom was imaged under full scatter conditions in computed radiography (CR) (40–80 kVp) and computed tomography (CT) (80–140 kVp). Images obtained at low energies (≈ 40 kVp) were validated using diagnostic type gafchromic film (Gafchromic® XRQA). CdTe detector with MCA was used to obtain transmission spectra after x-ray beam at 130 kVp passed through solutions of gold nanoparticles or iodinated CM. Results: CT and CR images were evaluated for contrast enhancement by contrast-to-noise ratio (CNR). Low energy results support previous findings, with gold exhibiting a 60% greater CNR than iodine. Gold nanoparticles also displayed excellent image contrast in CT, producing over two times greater signal than iodinated CM at 140 kVp. Over the x-ray energy range of 70–100 kVp, however, both samples displayed similar contrast values. CdTe attenuation spectra are in accordance with image results where gold nanoparticles show a greater probability of attenuation than iodine for photons below approximately 35 keV and above 80 keV. Conclusion: Data indicates that a solution bearing gold nanoparticles would be an effective alternative to iodinated CM diagnostic radiology particularly at lower and higher ends of x-ray energies used in radiology, such as mammography and CT. Conflict of Interest (only if applicable): Funding provided by NanoVic (Nanotechnology Victoria, Ltc.)

The Digital Imaging and Communications in Medicine (DICOM) standard1 is meant to allow communication of medical images between equipment provided by different vendors, but when two applications do not interact correctly in a multi-vendor environment it is often first necessary to demonstrate non-compliance of either the sender or the receiver before a resolution to the problem can be progressed. Sometimes the only way to do this is to monitor the network communication between the two applications to find out which one is not complying with the DICOM standard. Packet sniffing is a technique of network traffic analysis by passive observation of all information transiting a point on the network, regardless of the specified sender or receiver. DICOM packet sniffing traps and interprets the network communication between two DICOM applications to determine which is non compliant. This is illustrated with reference to three examples, a radiotherapy planning system unable to receive CT data from a particular CT scanner, a radiotherapy simulator unable to print correctly on a DICOM printer, and a PACS unable to respond when queried about what images it has in its archive by a radiotherapy treatment planning system. Additionally in this work it has been proven that it is feasible to extract DICOM images from the intercepted network data. This process can be applied to determine the cause of a DICOM image being rendered differently by the sender and the receiver.

Some radiotherapy patients are treated with titanium surgical aneurysm clips in the radiation field. This is of particular importance for stereotactic radiosurgery brain treatments, where the length of the blade of the clip may be comparable to the size of the radiation field. This study seeks to determine the extent of the dosimetric effects caused by surgical clips in stereotactic radiosurgery, using polyacrylamide gel phantoms and EBT type Gafchromic films. Using gel phantoms scanned with magnetic resonance imaging scanner, dose enhancement of around 20% was noted at distances less than 2 mm away from the clip surface. Gafchromic films showed about 6% variations in the dose up to few millimeters from the clip. These experimental results confirmed results predicted by Monte Carlo simulation techniques for higher density material surgical clips such as lead and platinum. Moreover, these experimental measurements clearly indicate dose reduction due to radiation attenuation behind the clip of about 4%.

Purpose: To investigate the radiosensitization of superficial kilovoltage range of x‐ray energy and megavoltage electron beams due to the presence of gold nanoparticles (AuNps) using cell survival curves and normoxic polyacrymide gel (nPAG). Method and Materials: Bovine aortic endothelial cells (BAECs) with and without AuNps were irradiated with kilovoltage superficial x‐ray beams and megavoltage electron beams. Cell survival at various concentrations of AuNps (0.25mMol–1mMol) was measured using colorimetric assay. Level of dose enhancement for x‐ray and electron beams was also quantified using AuNps doped nPAG. Results: AuNps enhanced the cells killing up to 21 fold for 1mMol of AuNps irradiated with 80 kVp x‐ray beams. Maximum dose enhancement factor (DEF) of 4.63 was measured for 12 MeV electron beams in the presence of 1mMol AuNps. 80 kVp which represents effective beam energy of around 40 keV was the optimum energy found that yield highest enhancement ratio. Measurements using AuNps doped nPAG also exhibit higher polymerization resulting from increased photoelectric interactions, Auger electrons and characteristic x‐ray generation. The experimental dose enhancements obtained were also in agreement with theoretical calculation and those previously documented for iodine atoms. Conclusion: Both experiments with cell culture and nPAG confirm that AuNps are able to enhance the radiation dose for x‐ray and electron superficial therapy. Lower doses from external sources are required to produce the same radiation effect with AuNps compared without application of AuNps. This will lead to improvement in superficial radiotherapy techniques of both x‐ray and electron. The use of this technique with microbeam radiotherapy technique and kilovoltage type intraoperative radiotherapy techniques are now under investigation in our group.

Electron or x-ray energies above the threshold for photonuclear activation of certain elements (such as oxygen and copper) can be achieved in some of the high energy beams used today in radiotherapy. Neutrons and gamma radiations are produced in such reactions. These secondary radiations, beside their implications on the treatment, they have potential to be used for quality testing of the radiation beam and can also be imaged with a PET scanner and hence employed for testing such imaging modalities. In this work applications and implications of such secondary radiations in radiotherapy is investigated through oxygen that is in the water molecules inside gel dosimeters and copper in its solid and solution format.

Dose measurements at small fields (around 1×1 cm) in radiotherapy is increasingly becoming important by the introduction of new technologies such as IMRT and it is a challenging task at the same time. Most if not all of the known dosimeters fail to measure the dose reliably at such small fields. Gel dosimeters are tissue equivalent and they are used as phantom and dosimeters at the same time. Their dose resolution is limited by the pixel sizes of the imaging modality used for their scanning, in this case an MRI scanner. Therefore reducing the pixel size increases the dose resolution since the contrast is very high in MRI images. In using normal scanners pixel sizes of around one millimeter at reasonable scanning times is usually obtained. In this work a small core and strong magnetic field scanners are employed which produces pixels of the order of 30 micrometers rendering them as micro-dosimeters.

Imaging with F-18 fluorodeoxyglucose positron emission tomography (PET) significantly improves lung cancer staging, especially when PET and CT information are combined. We describe a method for obtaining CT and PET images at separate acquisitions, which allows coregistration and incorporation of PET information into the radiotherapy (RT) planning process for non-small-cell lung cancer. The influence of PET information on RT planning was analysed for 10 consecutive patients. Computed tomography and PET images were acquired with the patient in an immobilization device, in the treatment position. Using specially written software, PET and CT data were coregistered using fiducial markers and imported into our RT planning system (Cadplan version 6). Treatment plans were prepared with and without access to PET/CT coregistered images and then compared. PET influenced the treatment plan in all cases. in three cases, geographic misses (gross tumour outside planning target volume) would have occurred had PET not been used. in a further three cases, better planning target volume marginal coverage was achieved with PET. In four patients, three with atelectasis, there were significant reductions in V20 (percentage of the total lung volume receiving 20 Gy or more). Use of coregistered PET/CT images significantly altered treatment plans in a majority of cases. This method could be used in routine practice at centres without access to a combined PET/CT scanner.

Small field sizes are increasingly becoming important in radiotherapy particularly since the introduction of intensity-modulated radiation therapy (IMRT) techniques. It is normally a challenging task to reliably measure the delivered dose and to determine its distribution in a medium for such small fields using conventional-type dosimeters such as gas ionisation chambers. Recently, attempts have been made to use films, but they are not tissue equivalent, they measure the dose only in two dimensions and they are not as responsive to radiations. In the present work, polyacrylamide gel (PAG) dosimeters are employed to measure the dose and its distribution in three dimensions for very small field sizes, such as those typically used in stereotactic radiosurgery. Field sizes of 6 x 6 and 18 x 18 mm in width are investigated. The results show an agreement with radiochromic film and ionisation diode measurements, with some variation in measured doses near the edge of the field, where the gel data decreases more rapidly than the other methods.

This paper is motivated by a clinical requirement to utilise ictal SPECT images for target localisation in stereotactic radiosurgery treatment planning using the xknife system which only supports CT and MRI images. To achieve this, the SPECT images were converted from raw (pixel data only) format into a part 10 compliant DICOM CT fileset. The minimum requirements for the recasting of a raw format image as DICOM CT or MRI data set are described in detail. The method can be applied to the importation of raw format images into any radiotherapy treatment planning system that supports CT or MRI import. It is demonstrated that the combination of the low spatial resolution SPECT images, depicting functional information, with high spatial resolution MRI images, which show the structural information, is suitable for stereotactic radiosurgery treatment planning.