Purpose: We present the first clinical implementation of a real-time six-degree of freedom (6DoF) Kilovoltage Intrafraction Monitoring (KIM) system which tracks the cancer target translational and rotational motions during treatment. The method was applied to measure and correct for target motion during stereotactic body radiotherapy (SBRT) for prostate cancer. The 6 DoF KIM system has sub-millimetre accuracy and precision in all three translational axes, and less than 1° accuracy and 4° precision in all three rotational axes.

A virtual EPID standard phantom audit (VESPA) has been implemented for remote auditing in support of facility credentialing for clinical trials using IMRT and VMAT. VESPA is based on published methods and a clinically established IMRT QA procedure, here extended to multi-vendor equipment. Facilities are provided with comprehensive instructions and CT datasets to create treatment plans. They deliver the treatment directly to their EPID without any phantom or couch in the beam. In addition, they deliver a set of simple calibration fields per instructions. Collected EPID images are uploaded electronically. In the analysis, the dose is projected back into a virtual cylindrical phantom. 3D gamma analysis is performed. 2D dose planes and linear dose profiles are provided and can be considered when needed for clarification. In addition, using a virtual flat-phantom, 2D field-by-field or arc-by-arc gamma analyses are performed. Pilot facilities covering a range of planning and delivery systems have performed data acquisition and upload successfully. Advantages of VESPA are (1) fast turnaround mainly driven by the facility's capability of providing the requested EPID images, (2) the possibility for facilities performing the audit in parallel, as there is no need to wait for a phantom, (3) simple and efficient credentialing for international facilities, (4) a large set of data points, and (5) a reduced impact on resources and environment as there is no need to transport heavy phantoms or audit staff. Limitations of the current implementation of VESPA for trials credentialing are that it does not provide absolute dosimetry, therefore a Level I audit is still required, and that it relies on correctly delivered open calibration fields, which are used for system calibration. The implemented EPID based IMRT and VMAT audit system promises to dramatically improve credentialing efficiency for clinical trials and wider applications.

Background and Purpose: Electronic portal imaging devices (EPIDs) can be used to reconstruct dose inside a virtual phantom. This work aims to study the feasibility of using this method for remote dosimetry auditing of clinical trials. Materials and Methods: Six centres participated in an intensity modulated radiotherapy (IMRT) pilot study of this new audit approach. Each centre produced a head and neck (HN) and post-prostatectomy (PP) trial plan and transferred the plans to virtual phantoms to calculate a reference dose distribution. They acquired in-air images of the treatment fields along with calibration images using their EPID. These data were sent to the central site where the images were converted to 2D field-byfield doses in a flat virtual water phantom and to 3D combined field doses in a cylindrical virtual phantom for comparison with corresponding reference dose distributions. Additional test images were used to assess the accuracy of the method when using different EPIDs. Results: Field-by-field 2D analysis yielded mean gamma pass-rates of 99.6% (± 0.3%) and 99.6% (± 0.6%) for HN and PP plans respectively (3%/3 mm, doses greater than 10% global max). 3D combined field analysis gave mean pass-rates of 97.9% (± 2.6%) and 97.9% (± 1.8%) for the HN and PP plans. Dosimetry tests revealed some field size limitations of the EPIDs. Conclusions: The remote auditing methodology using EPIDs is feasible and potentially an inexpensive method.

BackgroundMOSFET dosimetry is a method that has been used to measure in-vivo doses during brachytherapy treatments and during linac based radiotherapy treatment. Rectal displacement devices (RDDs) allow for safe dose escalation for prostate cancer treatment. This study used dual MOSkin detectors to assess real-time in vivo rectal wall dose in patients with an RDD in place during a high dose prostate stereotactic body radiation therapy (SBRT) boost trial.MethodsThe PROMETHEUS study commenced in 2014 and provides a prostate SBRT boost dose with a RDD in place. Twelve patients received two boost fractions of 9.5–10 Gy each delivered to the prostate with a dual arc volumetric modulated arc therapy (VMAT) technique. Two MOSkins in a face-to-face arrangement (dual MOSkin) were used to decrease angular dependence. A dual MOSkin was attached to the anterior surface of the Rectafix and read out at 1 Hz during each treatment. The planned dose at each measurement point was exported from the planning system and compared with the measured dose. The root mean square error normalised to the total planned dose was calculated for each measurement point and treatment arc for the entire course of treatment.ResultsThe average difference between the measured and planned doses over the whole course of treatment for all arcs measured was 9.7% with a standard deviation of 3.6%. The cumulative MOSkin reading was lower than the total planned dose for 64% of the arcs measured. The average difference between the final measured and final planned doses for all arcs measured was 3.4% of the final planned dose, with a standard deviation of 10.3%.ConclusionsMOSkin detectors were an effective tool for measuring dose delivered to the anterior rectal wall in real time during prostate SBRT boost treatments for the purpose of both ensuring the rectal doses remain within acceptable limits during the treatment and for the verification of final rectal doses.

BackgroundKilovoltage Intrafraction Monitoring (KIM) is a method which determines the three‐dimensional position of the prostate from two‐dimensional kilovoltage (kV) projections taken during linac based radiotherapy treatment with real‐time feedback. Rectal displacement devices (RDDs) allow for improved rectal dosimetry during prostate cancer treatment. This study used KIM to perform a preliminary investigation of prostate intrafraction motion observed in patients with an RDD in place.MethodsTen patients with intermediate to high‐risk prostate cancer were treated with a Rectafix RDD in place during two boost fractions of 9.5–10 Gy delivered using volumetric modulated arc therapy (VMAT) on Clinac iX and Truebeam linacs. Two‐dimensional kV projections were acquired during treatment. KIM software was used following treatment to determine the displacement of the prostate over time. The displacement results were analyzed to determine the percentage of treatment time the prostate spent within 1 mm, between 1 and 2 mm, between 2 and 3 mm and greater than 3 mm from its initial position.Results KIM successfully measured displacement for 19 prostate stereotactic boost fractions. The prostate was within 1 mm of its initial position for 84.8%, 1–2 mm for 14%, 2–3 mm 1.2% and ≥3 mm only 0.4% of the treatment time.ConclusionsIn this preliminary study using KIM, KIM was successfully used to measure prostate intrafraction motion, which was found to be small in the presence of a rectal displacement device.Trial registrationThe Hunter New England Human Research Ethics Committee reference number is 14/08/20/3.01.