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This study used automated data processing techniques to calculate a set of novel treatment plan accuracy metrics, and investigate their usefulness as predictors of quality assurance (QA) success and failure. A small sample of 151 beams from 23 prostate and cranial IMRT treatment plans were used in this study. These plans had been evaluated before treatment using measurements with a diode array system. The TADA software suite was adapted to allow automatic batch calculation of several proposed plan accuracy metrics, including mean field area, small-aperture, off-axis and closed-leaf factors. All of these results were compared to the gamma pass rates from the QA measurements and correlations were investigated. The mean field area factor provided a threshold field size (5 cm2, equivalent to a 2.2 × 2.2 cm2 square field), below which all beams failed the QA tests. The small aperture score provided a useful predictor of plan failure, when averaged over all beams, despite being weakly correlated with gamma pass rates for individual beams. By contrast, the closed leaf and off-axis factors provided information about the geometric arrangement of the beam segments but were not useful for distinguishing between plans that passed and failed QA. This study has provided some simple tests for plan accuracy, which may help minimise time spent on QA assessments of treatments that are unlikely to pass.

Patient specific applicators are needed for vaginal brachytherapy treatments in cases where conventional cylindrical applicators are unsuitable or unusable. These applicators are often produced using a time-consuming and comparatively imprecise moulding method. This proof-of-concept study used Monte Carlo calculations to investigate potential dosimetric effects from creating applicators using several common 3D printing materials. A sample mould was then replicated using a fused deposition modelling (FDM) technique, which allowed catheter channels to be precisely placed with reference to treatment goals, before 3D printing from thermoplastic using a consumer-grade 3D printer. The Monte Carlo results indicated that several FDM filaments caused substantial dose depletions (up to 6%) within the model applicators while having a minor effect (less than 1%) on dose in surrounding tissue. Compared to the sample mould, the 3D printed applicator achieved superior dosimetry in terms of target coverage, while also passing manual tests of smoothness and usability. This study demonstrated an overall process by which 3D printing could replace an imprecise and time-consuming manual process and potentially achieve improved dosimetry in brachytherapy treatments of irregular vaginal anatomy.

In this study, a 3D printing error inspired the development of a novel method for using a sagittally-sliced 3D printed thorax phantom to perform dosimetric verifications of lung radiotherapy treatment methods using a 2D ionization chamber array. A full-size thorax model was designed for 3D printing with multiple tissue densities including lung and bone and printed as a series of 2.4 cm sagittal slices using a Raise 3D Pro dual nozzle printer (Raise 3D Technologies Inc, Irvine, USA). An error introduced midway through printing resulted in one half of the phantom being printed at unrealistically high densities. A method was therefore devised whereby the entire phantom was used to plan two lung treatments, one conventionally fractionated and one hypo-fractionated, which were then verified via measurements using an Octavius 729 ionisation chamber array (PTW-Freiburg GmbH, Freiburg, Germany) in combination with several correctly-printed slices of the phantom. The measurements allowed dose distributions in planes through the target, adjacent to the target and at the location key of organs at risk to be verified, for both treatment plans. This method has the potential to be adapted for use with other phantoms and other dosimetry arrays to allow efficient evaluation of future treatment techniques.

This work examined the suitability of the PAGAT gel dosimeter for use in dose distribution measurements around high-density implants. An assessment of the gels reactivity with various metals was performed and no corrosive effects were observed. An artefact reduction technique was also investigated in order to minimise scattering of the laser light in the optical CT scans. The potential for attenuation and backscatter measurements using this gel dosimeter were examined for a temporary tissue expander's internal magnetic port.

3D printing is a promising solution for the production of bespoke phantoms and phantom components, for radiotherapy dosimetry and quality assurance (QA) purposes. This proof-of-concept study investigated the use of a dual-head printer to deposit two different filaments (polylactic acid (PLA) and StoneFil PLA-concrete (Formfutura BV, Nijmegen, Netherlands)) at several different in-fill densities, to achieve quasi-simultaneous 3D printing of muscle-, lung- and bone-equivalent media. A Raise 3D Pro 3D printer (Raise 3D Technologies Inc, Irvine, USA) was used to print one thoracic and one cranial phantom slab. Analysis using in-house 3D print QA software showed that the two humanoid phantom slabs geometrically matched the stereolithography (STL) files on which they were based, within 0.3 mm, except in one area of the thoracic slab that was affected by thermal warping by up to 3.4 mm. The 3D printed muscle, lung and bone materials in the two humanoid phantom slabs were approximately radiologically-equivalent to human muscle, lung and bone. In particular, the use of StoneFil with a nominally constant in-fill density of 100% resulted in regions that were approximately inner-bone-equivalent, at kV and MV energies. These regions were bounded by walls that were substantially denser than inner bone, although generally not dense enough to be truly cortical-bone-equivalent. This proof-of-concept study demonstrated a method by which multiple tissue-equivalent materials (eg. muscle-, lung- and bone-equivalent media) can be deposited within one 3D print, allowing complex phantom components to be fabricated efficiently in a clinical setting.

Helical TomoTherapy treatment and delivery systems (Accuray Inc, Sunnyvale, USA) allow off-line adaptation of radiotherapy treatments, with dose calculations that use MV computed tomography (CT) data acquired at treatment. This study aimed to assess the potential dosimetric effects of a gas-filled temporary tissue expander (TTE) on the accuracy of breast radiotherapy dose calculations from both the TomoTherapy treatment planning system (TPS), which uses kV CT data, and the TomoTherapy adaptive radiotherapy (ART) system, which uses MV CT data. A TomoTherapy treatment plan was created and delivered to a 3D-printed rectilinear model of a breast with implanted gas-filled TTE, including a stainless steel CO 2 container, and film measurements of the delivered dose were compared against dose calculations from the TPS and ART systems. The film measurements showed that the TomoTherapy TPS provided comparatively accurate dose calculations in the ~550 cm 2 volume of air that modelled the gas filling of the TTE and within the surrounding tissue-equivalent materials, except in regions where the beam was transmitted through the stainless steel CO 2 container, possibly due to the volume of stainless steel being over-estimated in the kV CT images that were used to generate the treatment plan. The ART system provided more accurate dose calculations than the TPS in regions affected by the stainless steel container, but also over-estimated the dose in the air within the TTE. These results suggest that the TomoTherapy TPS and ART systems could be used to produce reliable dose calculations of breast treatments in the presence of gas-filled TTEs, if kV CT imaging options are chosen to avoid artefacts and minimise the need for density over-rides and if treatment targets that include only clinically relevant tissues, and exclude all TTE components, are used to evaluate and compare the doses calculated by both systems.

The increase in complexity of treatment plans over time through modalities such as intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) has often not been met with an increase in capability of the secondary dose calculation checking systems typically used to verify the treatment planning system. Monte Carlo (MC) codes such as EGSnrc have become easily available and are capable of performing calculations of highly complex radiotherapy treatments. This educational note demonstrates a method for implementing and using a fully automated system for performing and analysing full MC calculations of conformal, IMRT and VMAT radiotherapy plans. Example calculations were based on BEAMnrc/DOSXYZnrc and are performed automatically after either uploading exported plan DICOM data through a Python-based web interface, or exporting DICOM data to a monitored network location. This note demonstrates how completed MC calculations can then be analysed using an automatically generated dose point comparison report, or easily re-imported back into the treatment planning system. Agreement between the TPS and MC calculation was an improvement on agreement between RadCalc and the TPS, with differences ranging from 1.2 to 5.5% between RadCalc and the treatment planning system (TPS), and 0.1–1.7% between MC and TPS. Comparison of the dose-volume histogram (DVH) parameters Dmean, D98%, D2%, and Dmax for the example VMAT plans showed agreement for the mean planning target volume dose within 0.25%, D98% and D2% generally within 1% with the exception of a brain case, and Dmax within 1%. Overall, this note provides a demonstration of a system that has been integrated well into existing clinical workflow, and has been shown to be a valuable additional tool in the secondary checking of treatment plan calculations.

Bolus plays an important role in the radiation therapy of superficial lesions and the application of 3D printing to its design can improve fit and dosimetry. This study quantitatively compares the fits of boluses designed from different imaging modalities. A head phantom was imaged using three systems: a CT simulator, a 3D optical scanner, and an interchangeable lens camera. Nose boluses were designed and 3D printed from each modality. A 3D printed phantom with air gaps of known thicknesses was used to calibrate mean HU to measure air gaps of unknown thickness and assess the fit of each bolus on the head phantom. The bolus created from the optical scanner data resulted in the best fit, with a mean air gap of 0.16 mm. Smoothing of the CT bolus resulted in a more clinically suitable model, comparable to that from the optical scanner method. The bolus produced from the photogrammetry method resulted in air gaps larger than 1 mm in thickness. The use of optical scanner and photogrammetry models have many advantages over the conventional bolus-from-CT method, however workflow should be refined to ensure accuracy if implemented clinically.

Strontium 90 (Sr-90) has been commonly used in the radiation treatment of pterygia of the eye. A radioactive plaque is placed in an applicator onto the surface of the eyeball for a specific length of time to achieve a desired dose. Dose is usually calculated using source activity and decay, as well as the distance from it to the surface of the eye. However, this assumes a flat eye surface. This investigation used 3D printing to produce an anthropomorphic eyeball phantom on which to perform dosimetry measurements for two different applicator sizes. These doses were compared to planar geometry measurements and a dose difference found. While planar geometry measurements are useful for routine quality assurance, measurements of the effects of the curved surface on dose calculations can provide valuable clinical information.

Given the existing literature on the subject, there is obviously a need for specific advice on quality assurance (QA) tolerances for departments using or implementing 3D printed bolus for radiotherapy treatments. With a view to providing initial suggested QA tolerances for 3D printed bolus, this study evaluated the dosimetric effects of changes in bolus geometry and density, for a particularly common and challenging clinical situation: specifically, volumetric modulated arc therapy (VMAT) treatment of the nose. Film-based dose verification measurements demonstrated that both the AAA and the AXB algorithms used by the Varian Eclipse treatment planning system (Varian Medical Systems, Palo Alto, USA) were capable of providing sufficiently accurate dose calculations to allow this planning system to be used to evaluate the effects of bolus errors on dose distributions from VMAT treatments of the nose. Thereafter, the AAA and AXB algorithms were used to calculate the dosimetric effects of applying a range of simulated errors to the design of a virtual bolus, to identify QA tolerances that could be used to avoid clinically significant effects from common printing errors. Results were generally consistent, whether the treatment target was superficial and treated with counter-rotating coplanar arcs or more-penetrating and treated with noncoplanar arcs, and whether the dose was calculated using the AAA algorithm or the AXB algorithm. The results of this study suggest the following QA tolerances are advisable, when 3D printed bolus is fabricated for use in photon VMAT treatments of the nose: bolus relative electron density variation within ±5% (although an action level at ±10% may be permissible); bolus thickness variation within ±1 mm (or 0.5 mm variation on opposite sides); and air gap between bolus and skin ≤5 mm. These tolerances should be investigated for validity with respect to other treatment modalities and anatomical sites. This study provides a set of baselines for future comparisons and a useful method for identifying additional or alternative 3D printed bolus QA tolerances.