Prabhjot Juneja

The first clinical treatment with kilovoltage intrafraction monitoring (KIM): A real-time image guidance method

PURPOSE Kilovoltage intrafraction monitoring (KIM) is a real-time image guidance method that uses widely available radiotherapy technology, i.e., a gantry-mounted x-ray imager. The authors report on the geometric and dosimetric results of the first patient treatment using KIM which occurred on September 16, 2014. METHODS KIM uses current and prior 2D x-ray images to estimate the 3D target position during cancer radiotherapy treatment delivery. KIM software was written to process kilovoltage (kV) images streamed from a standard C-arm linear accelerator with a gantry-mounted kV x-ray imaging system. A 120° pretreatment kV imaging arc was acquired to build the patient-specific 2D to 3D motion correlation. The kV imager was activated during the megavoltage (MV) treatment, a dual arc VMAT prostate treatment, to estimate the 3D prostate position in real-time. All necessary ethics, legal, and regulatory requirements were met for this clinical study. The quality assurance processes were completed and peer reviewed. RESULTS During treatment, a prostate position offset of nearly 3 mm in the posterior direction was observed with KIM. This position offset did not trigger a gating event. After the treatment, the prostate motion was independently measured using kV/MV triangulation, resulting in a mean difference of less than 0.6 mm and standard deviation of less than 0.6 mm in each direction. The accuracy of the marker segmentation was visually assessed during and after treatment and found to be performing well. During treatment, there were no interruptions due to performance of the KIM software. CONCLUSIONS For the first time, KIM has been used for real-time image guidance during cancer radiotherapy. The measured accuracy and precision were both submillimeter for the first treatment fraction. This clinical translational research milestone paves the way for the broad implementation of real-time image guidance to facilitate the detection and correction of geometric and dosimetric errors, and resultant improved clinical outcomes, in cancer radiotherapy.

Real-Time 3D Image Guidance Using a Standard LINAC: Measured Motion, Accuracy, and Precision of the First Prospective Clinical Trial of Kilovoltage Intrafraction Monitoring–Guided Gating for Prostate Cancer Radiation Therapy

PURPOSE Kilovoltage intrafraction monitoring (KIM) is a new real-time 3-dimensional image guidance method. Unlike previous real-time image guidance methods, KIM uses a standard linear accelerator without any additional equipment needed. The first prospective clinical trial of KIM is underway for prostate cancer radiation therapy. In this paper we report on the measured motion accuracy and precision using real-time KIM-guided gating. METHODS AND MATERIALS Imaging and motion information from the first 200 fractions from 6 patient prostate cancer radiation therapy volumetric modulated arc therapy treatments were analyzed. A 3-mm/5-second action threshold was used to trigger a gating event where the beam is paused and the couch position adjusted to realign the prostate to the treatment isocenter. To quantify the in vivo accuracy and precision, KIM was compared with simultaneously acquired kV/MV triangulation for 187 fractions. RESULTS KIM was successfully used in 197 of 200 fractions. Gating events occurred in 29 fractions (14.5%). In these 29 fractions, the percentage of beam-on time, the prostate displacement was >3 mm from the isocenter position, reduced from 73% without KIM to 24% with KIM-guided gating. Displacements >5 mm were reduced from 16% without KIM to 0% with KIM. The KIM accuracy was measured at <0.3 mm in all 3 dimensions. The KIM precision was <0.6 mm in all 3 dimensions. CONCLUSIONS Clinical implementation of real-time KIM image guidance combined with gating for prostate cancer eliminates large prostate displacements during treatment delivery. Both in vivo KIM accuracy and precision are well below 1 mm.

Determining appropriate imaging parameters for kilovoltage intrafraction monitoring: an experimental phantom study.

Kilovoltage intrafraction monitoring (KIM) utilises the kV imager during treatment for real-time tracking of prostate fiducial markers. However, its effectiveness relies on sufficient image quality for the fiducial tracking task. To guide the performance characterisation of KIM under different clinically relevant conditions, the effect of different kV parameters and patient size on image quality, and quantification of MV scatter from the patient to the kV detector panel were investigated in this study. Image quality was determined for a range of kV acquisition frame rates, kV exposure, MV dose rates and patient sizes. Two methods were used to determine image quality; the ratio of kV signal through the patient to the MV scatter from the patient incident on the kilovoltage detector, and the signal-to-noise ratio (SNR). The effect of patient size and frame rate on MV scatter was evaluated in a homogeneous CIRS pelvis phantom and marker segmentation was determined utilising the Rando phantom with embedded markers. MV scatter incident on the detector was shown to be dependent on patient thickness and frame rate. The segmentation code was shown to be successful for all frame rates above 3 Hz for the Rando phantom corresponding to a kV to MV ratio of 0.16 and an SNR of 1.67. For a maximum patient dimension less than 36.4 cm the conservative kV parameters of 5 Hz at 1 mAs can be used to reduce dose while retaining image quality, where the current baseline kV parameters of 10 Hz at 1 mAs is shown to be adequate for marker segmentation up to a patient dimension of 40 cm. In conclusion, the MV scatter component of image quality noise for KIM has been quantified. For most prostate patients, use of KIM with 10 Hz imaging at 1 mAs is adequate however image quality can be maintained and imaging dose reduced by altering existing acquisition parameters.

Kilovoltage intrafraction monitoring for real-time image guided adaptive radiotherapy reduces total dose for lung SABR

This study presents estimation of typical kV fluoroscopic imaging doses for image-guided real-time adaptive radiotherapy. For a cohort of 10 lung SABR patients the estimated imaging dose to ipsi-lateral lung with real-time adaptation is 9.9-15.1cGy, which is less than the extra lung dose from treatment with potentially larger ITV-based PTV approach.

Interprofessional education: evaluation of a radiation therapy and medical physics student simulation workshop

Interprofessional education (IPE) involves two or more professions engaged in learning with, from and about each other. An initiative was undertaken to explore IPE for radiation therapy (RT) and medical physics (MP) students through a newly developed workshop based around simulated learning. The aims of this study were to explore RT and MP students’ perceptions of working as part of a collaborative team and of their own and the other groups professional roles. Student perceptions of the simulation education tool, the virtual environment for radiotherapy training (VERT) system, were also investigated.

Successful implementation of Virtual Environment for Radiotherapy Training (VERT) in Medical Physics education: The University of Sydney's initial experience and recommendations

This report outlines the University of Sydney’s initial experience with the Virtual Environment for Radiotherapy Training (VERT) system in the Master of Medical Physics program. VERT is a commercially available system, simulating linear accelerators, patient computed tomography (CT) sets, plans and treatment delivery. It was purpose built for radiation therapy (RT) education and offers learners the opportunity to gain knowledge and skills within an interactive, risk-free environment. The integration of VERT into the RT physics module of the Master of Medical Physics program was intended to enhance student knowledge and skills relevant to the curriculum’s learning objectives, and to alleviate some of the burden associated with student access to clinical equipment. Three VERT practical sessions were implemented: “RT treatment planning systems”, “(CT) Anatomy for physicists” and “Linear accelerator measurements”. Our experience and student evaluations were positive and demonstrated the viability of VERT for medical physics (MP) student education. We anticipate that integration of VERT into MP teaching is a valuable addition to traditional methods and can aid MP students’ understanding and readiness for practice. Additional evaluations should be conducted to ascertain VERT’s role in delivering efficient quantity and quality of MP education, and its potential in alleviating burdens placed on clinical departments.

Does breast composition influence late adverse effects in breast radiotherapy

BACKGROUND Large breast size is associated with increased risk of late adverse effects after surgery and radiotherapy for early breast cancer. It is hypothesised that effects of radiotherapy on adipose tissue are responsible for some of the effects seen. In this study, the association of breast composition with late effects was investigated along with other breast features such as fibroglandular tissue distribution, seroma and scar. METHODS The patient dataset comprised of 18 cases with changes in breast appearance at 2 years follow-up post-radiotherapy and 36 controls with no changes, from patients entered into the FAST-Pilot and UK FAST trials at The Royal Marsden. Breast composition, fibroglandular tissue distribution, seroma and scar were assessed on planning CT scan images and compared using univariate analysis. The association of all features with late-adverse effect was tested using logistic regression (adjusting for confounding factors) and matched analysis was performed using conditional logistic regression. RESULTS In univariate analyses, no statistically significant differences were found between cases and controls in terms of breast features studied. A statistically significant association (p < 0.05) between amount of seroma and change in photographic breast appearance was found in unmatched and matched logistic regression analyses with odds ratio (95% CI) of 3.44 (1.28-9.21) and 2.57 (1.05-6.25), respectively. CONCLUSIONS A significant association was found between seroma and late-adverse effects after radiotherapy although no significant associations were noted with breast composition in this study. Therefore, the cause for large breast size as a risk factor for late effects after surgery and optimally planned radiotherapy remains unresolved.

Adaptive radiotherapy for bladder cancer using deformable image registration of empty and full bladder

A common objective of various adaptive radiotherapy (ART) strategies for bladder cancer is to reduce irradiation of normal tissue, thereby reduce the risk of radiation induced toxicity, and maintain or improve the target coverage. Bladder radiotherapy, typically involves generous margins (up to 20 mm) for bladder planning target volume (PTV).

TH‐AB‐303‐09: Gated Prostate Radiotherapy: Accuracy and Dosimetric Results From First Clinical Study with Kilovoltage Intrafraction Monitoring

Purpose: The purpose of this study is to investigate the localisation accuracy and dosimetric impact of a new real-time IGRT system, kilovoltage intrafraction monitoring (KIM), in a gated prostate cancer radiotherapy clinical trial. Methods: KIM uses kV fluoroscopy to monitor, in real-time, the 3D position of radio-opaque markers implanted into the prostate target. The real-time target position is used to guide the treatment: if the prostate moves outside the tolerance (displacement exceeding 3mm for 5 seconds) the beam is paused and the patient is repositioned. Localisation accuracy is calculated offline by comparing using triangulation when markers are visible in both kV and MV images (ground truth) with the KIM determined positions. Dosimetric accuracy is calculated for fractions with gating events by comparing reconstructed delivered dose (with or without simulated gating events) against planned doses. Results: Seven patients have been recruited to the KIM study, with 4 patients completed treatment. Localisation accuracy of KIM from the 126 fractions to date is 0.1±0.5, 0.3±0.3, and −0.5±0.4 mm in the LR, SI and AP directions, respectively. Prostate gating and couch shift correction was applied in 15 fractions, which reduced the mean prostate position error from 3.9±1.4 mm (simulated no gating) to 2.0±1.2 mm. Delivered target doses (PTV D95%) were closer to planned with gating −1.4% compared to simulated no gating 3.2%. Delivered OAR doses were also closer to planned with gating compared to simulated no gating, mean (range) differences were respectively: rectum V65% −3.5 (−9.4, 5.7) & −5.0 (−11.2,18.7); and bladder V65% 3.2 (−0.9, 25.3) & 4.7 (−1.0, 30.5). Conclusion: KIM gating for prostate radiotherapy has been clinically implemented with sub-millimeter accuracy and improved agreement between the planned and delivered dose distributions. The KIM technology has wide-scale applicability as it is implemented on a standard linear accelerator with little modification. Varian Collaborative Research Agreement; Cancer Australia; NHMRC Australia

TU-A-12A-06: Intra-Observer Variability in Delineation of Target Volumes in Breast Radiotherapy and Its Effect On Accuracy of Deformation Measurements

PURPOSE In breast radiotherapy, the target volume may change during treatment and need adaptation of the treatment plan. This is possible for both tumour bed (TB) and whole breast (WB) target volumes. Delineation of the target (to detect changes) is also subject to uncertainty due to intra- and inter-observer variability. This work measured the uncertainty, due to intraobserver variability, in the quantification of tissue deformation. METHODS Datasets consisting of paired prone and supine CT scans of three patients were used. Significant deformation in target volumes is expected between prone and supine patient positions. The selected cases had 1) no seroma, 2) some seroma, and 3) large seroma. The TB and WB were outlined on each dataset three times by one clinician. Delineation variability was defined as the standard deviations of the distances between observer outlines. For each target volume and each case, tissue deformation between prone and supine delineations was quantified using the Dice similarity coefficient (DSC) and the average surface distance (ASD). The uncertainty in the tissue deformation (due to delineation variability) was quantified by measuring the ranges of DSC and ASD using all combinations of pairs of outlines (9 pairs). RESULTS For the TB, the range of delineation variability was 0.44-1.16 mm. The deformation, DSC and ASD, (and uncertainty in measurement) of the TB between prone and supine position of the cases were: 1) 0.21 (0.17-0.28) and 12.4 mm (11.8-13 mm); 2) 0.54 (0.51-0.57) and 3.3 mm (3.1-3.5 mm); 3) 0.62 (0.61-0.64) and 4.9 mm (4.6-5.2 mm). WB deformation measurements were subject to less uncertainty due to delineation variability than TB deformation measurements. CONCLUSION For the first time, the uncertainty, due to observer variability, in the measurement of the deformation of breast target volumes was investigated. Deformations in these ranges would be difficult to detect. This work was supported in part by Cancer Research-UK under Programme Grant C46/A10588 and in part by the National Institute for Health Research (NIHR) through funding of the biomedical research imaging centre. P. Juneja is supported by the EPSRC Platform Grant EP/H046526/1.