Radiotherapy Treatment Machine Research Articles

International audit of Virtual Environment for Radiotherapy Training usage

AbstractIntroductionThe Virtual Environment for Radiotherapy Training (VERT) is a high-fidelity simulation hardware and software resource that replicates the expensive and high-pressure clinical environment of a radiotherapy treatment machine. The simulation allows students to gain confidence with clinical techniques in a safe and unpressured academic environment before clinical placement. The aim of this study was to establish the current and future role of VERT and explore the potential for collaborative resource development and research.MethodsAn anonymous online survey was made available to all users of the software internationally (n=52). A mixture of fixed and open response questions gathered usage data and user feedback.ResultsThe study had a 90% response rate (n=47). Most participants (78·5%) used the resource 1 day/week or less; around 8,000 hours worldwide. It was clear that most participants used the simulation resource to help student to either gain understanding of concepts and techniques or to gain practice with techniques and practical skills. There was good support for collaborative resource development, deployment and evaluation to help VERT users to fully exploit its range of pedagogical uses.ConclusionsThis audit demonstrated high levels of engagement and enthusiasm for collaborative resource development and ongoing research among the radiotherapy simulation community. Adoption of an international Academic Community of Practice for collaborative simulation resource deployment and support may be of significant value and is worthy of further discussion and consideration.

Verification of an irregular field algorithm of a treatment planning system using a locally designed pelvic phantom: A simple design low-cost phantom suitable for quality assurance and control test in radiotherapy

BACKGROUND: Modern radiotherapy treatment machine today comes along side with sophisticated treatment planning systems (TPSs). The accuracy of any TPS depends on the mathematical algorithm it uses and can be well verified using a dedicated phantom. AIMS AND OBJECTIVES: To design a low-cost pelvic phantom and to use the designed phantom to verify whether the accuracy of an Irregular Field Algorithm of a Precise PLAN 2.16 TPS is within ±5% International Commission on Radiation Units and Measurements (ICRU) minimal limit. MATERIALS AND METHODS: Designed pelvic phantom was made of Plexiglas with six tissue equivalent inserts and an ion-chamber port. The mimicked organs for the inserts were: Prostate, bladder, adipose, muscle, rectum, and bone. A Hi-speed computed tomography (CT) simulator was used for acquiring images and CT numbers of the designed pelvic phantom, a Precise PLAN 2.16 TPS was used for image planning, an Elekta-Precise Clinical Linear Accelerator was used for prescription of the planned images and a precalibrated NE 2570/1 farmer-type ion-chamber with an electrometer was used to calculate the mean dose. Data analysis value was done using GraphPad Prism 5.0 statistics software. RESULTS: The maximum percentage deviation with large field sizes of 22 cm × 25 cm for six different inhomogeneous inserts was −3.95%, and bone only homogeneous inserts was 2.38%. The maximum percentage deviation with small field sizes of 5 cm × 5 cm with six different inhomogeneous inserts was −3.57%. The percentage deviation between the solid water phantom and the locally designed pelvic phantom was −3.46%. CONCLUSION: The irregular field algorithm showed an overall accuracy of approximately ±4% with the locally designed pelvic phantom for both large and small field sizes against ±5% ICRU minimal limit. Although there were significant differences in percentage deviation between inhomogeneity and homogeneous insert irrespective of field sizes.

A software tool to automatically assure and report daily treatment deliveries by a cobalt-60 radiation therapy device.

The aims of this study were to develop a method for automatic and immediate verification of treatment delivery after each treatment fraction in order to detect and correct errors, and to develop a comprehensive daily report which includes delivery verification results, daily image‐guided radiation therapy (IGRT) review, and information for weekly physics reviews. After systematically analyzing the requirements for treatment delivery verification and understanding the available information from a commercial MRI‐guided radiotherapy treatment machine, we designed a procedure to use 1) treatment plan files, 2) delivery log files, and 3) beam output information to verify the accuracy and completeness of each daily treatment delivery. The procedure verifies the correctness of delivered treatment plan parameters including beams, beam segments and, for each segment, the beam‐on time and MLC leaf positions. For each beam, composite primary fluence maps are calculated from the MLC leaf positions and segment beam‐on time. Error statistics are calculated on the fluence difference maps between the plan and the delivery. A daily treatment delivery report is designed to include all required information for IGRT and weekly physics reviews including the plan and treatment fraction information, daily beam output information, and the treatment delivery verification results. A computer program was developed to implement the proposed procedure of the automatic delivery verification and daily report generation for an MRI guided radiation therapy system. The program was clinically commissioned. Sensitivity was measured with simulated errors. The final version has been integrated into the commercial version of the treatment delivery system. The method automatically verifies the EBRT treatment deliveries and generates the daily treatment reports. Already in clinical use for over one year, it is useful to facilitate delivery error detection, and to expedite physician daily IGRT review and physicist weekly chart review.PACS number(s): 87.55.km

Practical implementation of a collapsed cone convolution algorithm for a radiation treatment planning system

A collapsed cone convolution algorithm was applied to a treatment planning system for the calculation of dose distributions. The distribution of beam fluences was determined using a three-source model by considering the source strengths of the primary beam, the beam scattered from the primary collimators, and an extra beam scattered from extra structures in the gantry head of the radiotherapy treatment machine. The distribution of the total energy released per unit mass (TERMA) was calculated from the distribution of the fluence by considering several physical effects such as the emission of poly-energetic photon spectra, the attenuation of the beam fluence in a medium, the horn effect, the beam-softening effect, and beam transmission through collimators or multi-leaf collimators. The distribution of the doses was calculated by using the convolution of the distribution of the TERMA and the poly-energetic kernel. The distribution of the kernel was approximated to several tens of collapsed cone lines to express the energies transferred by the electrons that originated from the interactions between the photons and the medium. The implemented algorithm was validated by comparing the calculated percentage depth doses (PDDs) and dose profiles with the measured PDDs and relevant profiles. In addition, the dose distribution for an irregular-shaped radiation field was verified by comparing the calculated doses with the measured doses obtained via EDR2 film dosimetry and with the calculated doses obtained using a different treatment planning system based on the pencil beam algorithm (Eclipse, Varian, Palo Alto, USA). The majority of the calculated doses for the PDDs, the profiles, and the irregular-shaped field showed good agreement with the measured doses to within a 2% dose difference, except in the build-up regions. The implemented algorithm was proven to be efficient and accurate for clinical purposes in radiation therapy, and it was found to be easily implementable in treatment planning systems.

A new approach to quantify the mechanical and radiation isocentres of radiotherapy treatment machine gantries

In this paper a new method is proposed to quantify and reduce the radiation beam position uncertainty due to the radiotherapy treatment machine gantry deflection. A new tool has been designed and manufactured to provide the means to measure the alignment of the collimator axis and of the beam central axis in space, using the NDI Polaris optical tracking system and Gafchromic® films. The tool can be mounted onto the accessory tray of the linacs from different manufacturers. The approach has been demonstrated with measurements of the mechanical isocentre being performed on ten linacs from three major manufacturers at four clinical sites. Measurements of the radiation isocentre were performed on a single linac. The collimator axis trajectory is modelled using a vector-end effector in order to provide more information than standard mechanical assessment methods. The method uses a mathematical optimization technique to calculate the position of the mechanical isocentre and the ‘size’ of the collimator axes intersection locus. Deviations of the collimator axes from the isocentre are expressed in terms of systematic and random error. The effects of measurement uncertainties are evaluated both via simulations and experimentally. The use of optical tracking and optimization techniques combined with an operator-induced measurement error compensation algorithm leads to a faster measurement of the mechanical isocentre (20 min for 24 angles) and eliminates operator-induced uncertainties. The uncertainty of the measurement of the mechanical isocentre was between 40 µm and 70 µm in terms of standard deviation. For some of the linacs assessed, the mechanical isocentre obtained using a standard approach with an adjustable pointer was displaced by over 1 mm from that found with the proposed method. The radii of the collimator axes intersection locus found with the proposed method were between 0.4 mm and 0.72 mm for the linacs assessed. Film measurement revealed a misalignment of the mechanical isocentre and the radiation isocentre by 0.4 mm. The proposed method potentially enables a reduction of the beam position uncertainty. This may be achieved at the planning stage by compensating for the identified systematic collimator axes deviations which were found to be reproducible. The method also creates a potential for using different setup margins independently for each axis and for each gantry angle, calculated specifically for a given linac.

Imaging doses from the Elekta Synergy X-ray cone beam CT system

The Elekta Synergy is a radiotherapy treatment machine with integrated kilovoltage (kV) X-ray imaging system capable of producing cone beam CT (CBCT) images of the patient in the treatment position. The aim of this study is to assess the additional imaging dose. Cone beam CT dose index (CBDI) is introduced and measured inside standard CTDI phantoms for several sites (head: 100 kV, 38 mAs, lung: 120 kV, 152 mAs and pelvis: 130 kV, 456 mAs). The measured weighted doses were compared with thermoluminescent dosimeter (TLD) measurements at various locations in a Rando phantom and at patients' surfaces. The measured CBDIs in-air at the isocentre were 9.2 mGy 100 mAs(-1), 7.3 mGy 100 mAs(-1) and 5.3 mGy 100 mAs(-1) for 130 kV, 120 kV and 100 kV, respectively. The body phantom weighted CBDI were 5.5 mGy 100 mAs(-1) and 3.8 mGy 100 mAs(-1 )for 130 kV and 120 kV. The head phantom weighted CBDI was 4.3 mGy 100 mAs(-1) for 100 kV. The weighted doses for the Christie Hospital CBCT imaging techniques were 1.6 mGy, 6 mGy and 22 mGy for the head, lung and pelvis. The measured CBDIs were used to estimate the total effective dose for the Synergy system using the ImPACT CT Patient Dosimetry Calculator. Measured CBCT doses using the Christie Hospital protocols are low for head and lung scans whether compared with electronic portal imaging (EPI), commonly used for treatment verification, or single and multiple slice CT. For the pelvis, doses are similar to EPI but higher than CT. Repeated use of CBCT for treatment verification is likely and hence the total patient dose needs to be carefully considered. It is important to consider further development of low dose CBCT techniques to keep additional doses as low as reasonably practicable.

MO‐D‐230A‐02: An Immersive Virtual Environment for Training of Radiotherapy Students and Developing Clinical Experience

Purpose: Radiotherapy equipment and techniques are rapidly developing and so efficient training is invaluable. However, the demands on clinical systems and the lack of trained personnel make it difficult to achieve. As an alternative approach we have developed virtual reality training tools, fully interactive and operating on a life size scale these can provide valuable experience for students and staff. We designed a study for 42 first year therapist students to investigate the usefulness of our training environment for learning a clinical technique that typically causes problems. Method and Materials: We have created a virtual environment that simulates an actual radiotherapy treatment machine, controlled via an actual handheld control pendant. The study was developed to simulate a “skin apposition” electron beam treatment. A virtual patient, based on the visible human female dataset, complete with rectangular markings for a range of different treatment sites, provided a range of treatment scenarios. At the Hull Immersive Visualization Environment (HIVE) we are able to project our graphics display onto a 5.3 m by 2.5 m ‘Power Wall’ utilizing stereoscopic visualization enabled via LCD shutter glasses. Such immersive interaction techniques (including the use of the Linac hand pendant) add to the user's sense of reality. To provide feedback, we have implemented a ‘scoring algorithm’ to assess how well the user has set up the beam/ patient. Results: The students reported the training environment to be realistic and following its use 93% perceived an improvement in their understanding of this clinical technique and 69% found the control system easy to master. Conclusion: Having implemented such training software and hardware we are beginning to perform academic studies to assess the impact of its use in the educational forum. We wish to understand which areas of multi‐discipline training will benefit from such an approach.

The development and evaluation of a virtual radiotherapy treatment machine using an immersive visualisation environment

Due to the lengthy learning process associated with complicated clinical techniques, undergraduate radiotherapy students can struggle to access sufficient time or patients to gain the level of expertise they require. By developing a hybrid virtual environment with real controls, it was hoped that group learning of these techniques could take place away from the clinical departments. This paper presents initial evaluation of the use of a three-dimensional immersive visualisation environment (IVE) to simulate a working radiotherapy treatment machine. A virtual patient complete with a range of different treatment sites was used to enhance learning and teaching of beam alignment in 3D. Pre- and post-questionnaires were used to evaluate the perceptions of 42-year 1 pre-registration students with regards to the learning that had taken place. 93% of students perceived an improvement in their understanding and confidence in their technical skills as a result of using the IVE. The mean overall improvement was 21.2% ( p < 0.00001), and this was positively correlated to perceived realism of the application. The application was reported to be both realistic and enjoyable. Feedback suggested it has a role to play in development of technical skills and also pre-clinical induction. More work with the application is ongoing to clarify that role and the potential benefits of this technology.

Feasibility of using ultrasound for real‐time tracking during radiotherapy

This study was designed to examine the feasibility of utilizing transabdominal ultrasound for real-time monitoring of target motion during a radiotherapy fraction. A clinical Acuson 128/XP ultrasound scanner was used to image various stationary and moving phantoms while an Elekta SL25 linear accelerator radiotherapy treatment machine was operating. The ultrasound transducer was positioned to image from the outer edge of the treatment field at all times. Images were acquired to videotape and analyzed using in-house motion tracking algorithms to determine the effect of the SL25 on the quality of the displacement measurements. To determine the effect on the dosimetry of the presence of the transducer, dose distributions were examined using thermoluminescent dosimeters loaded into an Alderson Rando phantom and exposed to a 10 x 10 cm2 treatment field with and without the ultrasound transducer mounted 2.5 cm outside the field edge. The ultrasound images acquired a periodic noise that was shown to occur at the pulsing frequency of the treatment machine. Images of moving tissue were analyzed and the standard deviation on the displacement estimates within the tissue was identical with the SL25 on and off. This implies that the periodic noise did not significantly degrade the precision of the tracking algorithm (which was better than 0.01 mm). The presence of the transducer at the surface of the phantom presented only a 2.6% change to the dose distribution to the volume of the phantom. The feasibility of ultrasonic motion tracking during radiotherapy treatment is demonstrated. This presents the possibility of developing a noninvasive, real-time and low-cost method of tracking target motion during a treatment fraction.

TRAJECTORY CONTROL FOR A NEW TOTAL SKIN ELECTRON TREATMENT MACHINE

The paper focuses attention on the development of a control system for a new radiotherapy treatment machine that makes use of a betatron to deliver electron beams over the whole surface of a patient. The betatron moves above a patient at a fixed distance from the patient support system. This paper presents a method to predict the betatron trajectory, in terms of speed and position, according to variation in the patient's geometry and is concerned with a simulation study of a PID control strategy implemented to control the speed of the betatron.

A philosophical approach to treatment machine maintenance and breakdown.

Planned preventative maintenance (PPM), quality control (QC) checks and breakdown all contribute to the down-time of a radiotherapy treatment machine. Low levels of machine availability are unacceptable both clinically and financially. Clinical data demonstrate that, for many tumours, interruptions to treatment will result in reduced local control. Reductions to the gaps in treatment can be achieved by patient interchange between machines. Maintaining the maximum possible machine availability will reduce the potential for errors associated with the transfer of patients between machines, and reduce the cost of treatment. Practices for routine PPM and QC vary between hospitals. In this report, a rationale for breakdown and maintenance will be described. Based on the faults experienced on a Philips SL 75-5 and a Philips SL25 over a period of 3 years, the workload associated with routine maintenance and quality control are presented and the additional work associated with breakdown discussed. Faults have been categorized on a scale between catastrophe and maintainability. A demonstration of how this analysis can be used to assess the cost-benefits of proposed changes in working patterns by the extension or reduction of maintenance periods is provided. The results indicated that no gain would be made in changing from a 1-day to a 2-day per month PPM schedule.

Editors' note

Radiotherapy treatment planning involves the calculation of absorbed dose to the target volume to be treated. These calculations may be performed manually by superimposing isodose charts from the radiotherapy treatment machine. As anyone who has performed a manual treatment plan will testify, this is not an intellectually stimulating task. The process does not lend itself to the production of accurate and reproducible radiotherapy treatments. Moreover, at the time the paper was written it was common practice not to perform individual treatment plans on all patients because of the time-consuming nature of manual treatment planning.

Computer assisted set-up of a linear accelerator

The term computer assisted set-up, as used by the author, refers to that technique which enables a computer to adjust the field defining parameters of a radiotherapy treatment machine. With due regard to safety and provided that the patient does not significantly change position after the initial set-up, the computer may take control of the machine to change the parameters for subsequent fields of a multiple field treatment. To this end, a system has been developed that allows a microcomputer to control a 6 MV linear accelerator.