Use Of Image-guided Radiotherapy Research Articles

Quality and Safety Considerations in Image Guided Radiation Therapy: An ASTRO Safety White Paper Update

This updated report on image guided radiation therapy (IGRT) is based on a consensus-based white paper previously published by the American Society for Radiation Oncology (ASTRO) addressing patient safety. In the past decade, IGRT technology and procedures have progressed significantly and are now more commonly used. The use of IGRT has now extended beyond high-precision treatments, such as stereotactic radiosurgery and stereotactic body radiation therapy, and into routine clinical practice for many treatment techniques and anatomic sites. Therefore, quality and treatment planning and delivery considerations for these techniques are paramount for patient safety. In 2021, ASTRO convened an interdisciplinary task force to assess the original IGRT white paper and update content where appropriate. Recommendations were created using a consensus-building methodology, and task force members indicated their level of agreement based on a 5-point Likert scale from "strongly agree" to "strongly disagree." A prespecified threshold of ≥75% of raters who selected "strongly agree" or "agree" indicated consensus. The IGRT white paper was published (Pract Radiat Oncol. 2022 Dec) and endorsed by the American Association of Physicists in Medicine (AAPM), American Association of Medical Dosimetrists, and American Society of Radiologic Technologists. Since the first IGRT paper was published by ASTRO in 2013, significant technological advancement has taken place. New and updated considerations in personnel requirements, staffing, education and training, equipment and technological requirements, quality management and assurance, IGRT program management, and safety considerations were reported. A 17-point consensus was reached and recommended in 5 areas surrounding program development, quality assurance, quality management, treatment delivery, and vendor engagement (Table 5, Summary of key recommendations). This IGRT white paper builds on the previous version and uses other guidance documents to primarily focus on processes related to quality and safety. IGRT requires an interdisciplinary team-based approach, staffed by appropriately trained specialists, as well as significant personnel resources, specialized technology, and implementation time. A thorough feasibility analysis of resources is required and should be discussed with all personnel before undertaking new imaging techniques. A comprehensive quality-assurance program must be developed to ensure IGRT is performed safely and effectively. As IGRT technologies continue to improve or emerge, existing practice guidelines should be updated regularly according to the latest AAPM Task Group reports. Patient safety in the application of IGRT is everyone's responsibility, and professional organizations, regulators, vendors, and end-users must demonstrate strong commitments to ensure that the highest levels of safety are achieved.

The use of 18F-FDG PET/CT for radiotherapy treatment planning in non-small cell lung cancer: a mini-review

: In the past decades, the technical achievements in radiotherapy treatment planning and delivery, such as the use of intensity-modulated radiotherapy or the use of image-guided radiotherapy, alongside with the significant developments in molecular imaging and especially the use of positron-emission tomography (PET) have significantly improved radiotherapy treatment precision. In non-small cell lung cancer (NSCLC), the use of 18F-fluoro-desoxy-glucose (18F-FDG) positron-emission tomography/computed tomography (18F-FDG-PET/CT) has a high accuracy for diagnostic workup, staging and response assessment but has been also implemented to optimize target volume concepts in NSCLC with high precision. These advances led, in the recent years, to an increased tumor control and improved outcomes. Especially in the context of emerging systemic treatments, such as immune checkpoint blockades (ICBs), the prevention of unnecessary irradiation of the lymphatic system might be very important. In the past years, several prospective randomized studies have been performed, aiming to optimize, standardize and develop new concepts in the target volume delineation especially in locally advanced NSCLC using different approaches. While the PET-Plan trial used a uniform target volume reduction based on the 18F-FDG-PET/CT signal in the experimental arm, the PET boost trial and the RTOG 1106 used the 18F-FDG-PET/CT information to define an additional boost volume for dose escalation. Within this mini-review, we provide an overview on the role of 18F-FDG-PET/CT, the challenges and the benefits, in radiotherapy of NSCLC.

Quality and Safety Considerations in Image Guided Radiation Therapy: An ASTRO Safety White Paper Update

PurposeThis updated report on image guided radiation therapy (IGRT) is part of a series of consensus-based white papers previously published by the American Society for Radiation Oncology addressing patient safety. Since the first white papers were published, IGRT technology and procedures have progressed significantly such that these procedures are now more commonly used. The use of IGRT has now extended beyond high-precision treatments, such as stereotactic radiosurgery and stereotactic body radiation therapy, and into routine clinical practice for many treatment techniques and anatomic sites. Therefore, quality and patient safety considerations for these techniques remain an important area of focus. Methods and MaterialsThe American Society for Radiation Oncology convened an interdisciplinary task force to assess the original IGRT white paper and update content where appropriate. Recommendations were created using a consensus-building methodology, and task force members indicated their level of agreement based on a 5-point Likert scale from “strongly agree” to “strongly disagree.” A prespecified threshold of ≥75% of raters who selected “strongly agree” or “agree” indicated consensus. SummaryThis IGRT white paper builds on the previous version and uses other guidance documents to primarily focus on processes related to quality and safety. IGRT requires an interdisciplinary team-based approach, staffed by appropriately trained specialists, as well as significant personnel resources, specialized technology, and implementation time. A thorough feasibility analysis of resources is required to achieve the clinical and technical goals and should be discussed with all personnel before undertaking new imaging techniques. A comprehensive quality-assurance program must be developed, using established guidance, to ensure IGRT is performed in a safe and effective manner. As IGRT technologies continue to improve or emerge, existing practice guidelines should be reviewed or updated regularly according to the latest American Association of Physicists in Medicine Task Group reports or guidelines. Patient safety in the application of IGRT is everyone's responsibility, and professional organizations, regulators, vendors, and end-users must demonstrate a clear commitment to working together to ensure the highest levels of safety.

Cost of Care Related to Treatment of Bone Metastases: Real World Data from a National Health Insurance Provider

<h3>Purpose/Objective(s)</h3> Bone metastases are a common occurrence in patients with advanced stage malignancy, often impacting quality of life. Radiation has been, and remains, a highly effective modality for the treatment of symptomatic bone metastases. Various radiation fractionation schemes and techniques exist and are used across the United States in these patients. The cost of care presumably varies significantly based on those factors (technique and number of fractions). We accessed payer claims data from a health insurance provider in Pennsylvania, Delaware, and West Virginia to help determine the actual cost of care for patients with bone metastases treated with radiation. <h3>Materials/Methods</h3> This study was a secondary data analysis of medical claims data using a retrospective design among insured members in Pennsylvania, Delaware, and West Virginia with an ICD-10 code of C79.51 and history of radiation therapy billed under that code from 1/1/2016 to 9/30/2021. Patients were grouped by age, sex, and geographical region. Number of claims and total cost of care were tabulated by year. We also examined which radiation technique was used (intensity modulated radiation therapy (IMRT) vs. 3D conformal radiotherapy (3D CRT) vs. complex isodose plan) based on CPT codes. Lastly, we looked at the use of image guided radiation therapy (IGRT) over that same time period, again using CPT codes. <h3>Results</h3> We identified 29,201 patients treated with radiation for diagnosis code C79.51 between 2016 and 2021. The median number of claims per year was 4,866 (2,744-6,000). Fifty-one percent of patients were male (13,676). The majority of patients (79%) resided in Pennsylvania. The median total cost of care related to ICD-10 C79.51 was $181,918,217 ($163,672,315-$183,565,407). The median number of claims for those years was 95,024 (89,870-101,449). The number of claims per patient varied from 2.3-5.0 and 3.5-10.2 for isodose complex treatment and IMRT, respectively. Most patients were treated using isodose complex technique or 3D CRT (combined 80-90%) with a relatively even split. The use of IMRT remained relatively stable over the timeframe (5-15%). The use of IGRT increased over time, with highest number of claims for IGRT being 2020 (458 claims) (median 266, range: 183-458). The median cost per year for all care related to ICD10 C79.51 was $10,887,581, $7,274,264, and $1,902,141 for patients treated with 3D CRT, IMRT, and isodose complex, respectively. <h3>Conclusion</h3> Radiation remains a widely used technique for the palliation of bone metastases. The cost of care related to its use are significant. The use of IGRT increased over time, with no obvious impact on overall cost of care. The use of IMRT remained low for bone metastases, with an associated increase in cost of care. The overall cost of care remained lowest for those patients treated with isodose complex treatment.

Evaluating the Inter-Reviewer Reliability and Evidentiary Grounds for Third-Party Peer-to-Peer Mandated Downgrading of Radiation Therapy Prescriptions

<h3>Purpose/Objective(s)</h3> Health plans employ utilization management strategies to control access to certain treatments in a bid to cut health care spending, frequently requiring prior authorization (PA) and subsequent peer-to-peer (P2P) discussion if the prescribed studies or treatments are not initially approved. In theory, P2P reviewers should follow current, evidence-based clinical guidelines and have knowledge of novel treatments to optimize patient care. We examine P2P determinations to downgrade prescriptions (Rx) of radiotherapy (RT) and evaluate both the evidentiary basis and internal consistency of these decisions, as applied to patients at a large academic radiation medicine department. <h3>Materials/Methods</h3> De-identified departmental billing records from 1/12/21 to 8/12/21 were used to query cases in which an Rx for RT was denied PA and ultimately downgraded on P2P in terms of RT technique, fraction number, or use of image-guided radiation therapy (IGRT). These were cross-identified with patient charts in an IRB-approved electronic medical record, and clinical details reviewed. The P2P record was searched for pair matches for each downgraded Rx (i.e., anatomic site, modality, fractionation), such that the match was approved unaltered. PubMed searches were performed for literature supporting the initial Rx in terms of control, survival, or toxicity outcomes. <h3>Results</h3> 1620 Rx were prescribed during the analyzed period, of which 697 cases were referred for PA. 123 (17.6%) of the latter were denied and referred to P2P. 31 of the 123 (25.2%) resulted in a downgraded Rx, of which 13 (41.9%) were for curative treatment, 8 (25.8%) for treatment of oligometastatic disease (OMD), and 10 (32.3%) for non-OMD palliative treatment. No Rx were downgraded for fraction number. 15 downgraded Rx (48.4%) were pair-matched with Rx that were approved unaltered on P2P. 3 (9.6%) downgraded Rx were matched with approved Rx for higher grade modality (e.g., IMRT over 3DCRT) for equivalent indications. 18 of 31 downgraded Rx (58.1%) were matched with approvals for identical or upgraded Rx, including 10 curative cases, 7 OMD cases, and 2 of 5 cases in which IGRT alone was excluded on P2P. For 17 downgraded Rx (54.8%), literature in support of the original Rx was identified, including at minimum a phase II study, a meta-analysis of > 1000 subjects, or a retrospective review with between 86 and 202 subjects. Multiple phase II studies supported all Rx for OMD that were downgraded. <h3>Conclusion</h3> Our analysis shows that more than half of treatment downgrades resulting from the P2P process can be matched with P2P approvals of the same or upgraded treatment for the same indication. We further show that published evidence could have upheld the initial prescriptions in more than half of P2P downgrades. These results suggest a high degree of inter-reviewer variability and inconsistent fidelity to evidence-based management in P2P decisions to downgrade RT Rx. Multi-institutional quality review of ultimate P2P dispositions is warranted.

Optimization of brain tumours irradiation determining the set-up margin

The aim of this work was to evaluate whether the excising margin of the clinical tumor volume and planning target volume correspond with calculated radiation margin based on systematic errors, and definition of radiation margins of individual brain lobes. This research was a retrospective cross-sectional study. We checked the systematic errors and calculated their average and the size of radiation margins. The average systematic errors were calculated in four directions: lateral, longitudinal, vertical, and rotation. The largest average systematic error was calculated in the lateral direction in the cerebellar area, and the error was also statistically significant(p &lt; 0.05). In rotational direction we notice the statistically significant difference in frontal lopbe (p = 0.037), and cerebellar area (p = 0.002). The largest safety margin, as measured by the apverage systematic errors, is requirped for irradiation of the cerebellum. The safety margin size of 6.94 mm was calculated according to the formula of Van Herk. However, the smallest safety margin can be used for irradiation of the occipital lobe of the brain, namely 4.85 mm. The linear regression results that only cerebellar lesions affect lateral displacements. Based on our calculation of the mean systematic errors, we estimate that the clinical target volume - planning target volume safety margin can't be reduced further from the current 5 mm to a size of 3 mm without the use of image guided radiotherapy.

Image-guided Adaptive Radiotherapy for Bladder Cancer

Technological advancement has facilitated patient-specific radiotherapy in bladder cancer. This has been made possible by developments in image-guided radiotherapy (IGRT). Particularly transformative has been the integration of volumetric imaging into the workflow. The ability to visualise the bladder target using cone beam computed tomography and magnetic resonance imaging initially assisted with determining the magnitude of inter- and intra-fraction target change. It has led to greater confidence in ascertaining true anatomy at each fraction. The increased certainty of dose delivered to the bladder has permitted the safe reduction of planning target volume margins. IGRT has therefore improved target coverage with a reduction in integral dose to the surrounding tissue. Use of IGRT to feed back into plan and dose delivery optimisation according to the anatomy of the day has enabled adaptive radiotherapy bladder solutions. Here we undertake a review of the stepwise developments underpinning IGRT and adaptive radiotherapy strategies for external beam bladder cancer radiotherapy. We present the evidence in accordance with the framework for systematic clinical evaluation of technical innovations in radiation oncology (R-IDEAL).

Surface-guided radiation therapy for breast cancer: more precise positioning.

Hypofractionated radiation therapy for breast cancer requires highly precise delivery through the use of image-guided radiotherapy (IGRT). Surface-guided radiation therapy (SGRT) is being increasingly used for patient positioning in breast radiotherapy. We aimed to assess the role of SGRT for verification of breast radiotherapy and the tumour bed. Prospective study of 252 patients with early stage breast cancer. A total of 1170 determinations of daily positioning were performed. Breast surface positioning was determined with SGRT (AlignRT) and correlated with the surgical clips in the tumour bed, verified by IGRT (ExacTrac). SGRT improved surface matching by a mean of 5.3 points compared to conventional skin markers (98.0 vs. 92.7), a statistically significant difference (p < 0.01, Wilcoxon Test). For surface matching values > 95%, ≥ 3 clips coincided in 99.7% of the determinations and all markers coincided in 92.5%. For surface matching rates > 90%, the location of ≥ 3 clips coincided in 99.55% of determinations. SGRT improves patient positioning accuracy compared to skin markers. Optimal breast SGRT can accurately verify the localisation of the tumour bed, ensuring matching with ≥ 3 surgical clips. SGRT can eliminate unwanted radiation from IGRT verification systems.

What is the Optimal Dose, Fractionation and Volume for Bladder Radiotherapy?

External beam radiotherapy (EBRT), as part of a trimodality approach, is an attractive bladder-preserving alternative to radical cystectomy. Several EBRT regimens with different treatment volumes have been described with similar tumour control and, so far, clear recommendations on the optimal radiotherapy regimen and treatment volume are lacking. The current review summarises EBRT literature on dose prescription, fractionation as well as treatment volume in order to guide clinicians in their daily practice when treating patients with muscle-invasive bladder cancer. Taking into account literature on repopulation, continuous-course radiotherapy can be used safely in daily practice where a split-course should only be reserved for those patients who are fit enough to undergo a radical cystectomy in case of a poor early response. A recent meta-analysis has proven that hypofractionated radiotherapy is superior to conventional radiotherapy with regards to invasive locoregional control with similar toxicity profiles. In the absence of node-positive disease, the target volume can be restricted to the bladder. In order to compensate for organ motion, very large margins need to be applied in the absence of image-guided radiotherapy (IGRT). Therefore, the use of IGRT or an adaptive approach is recommended. Based on the available literature, one can conclude that moderate hypofractionated radiotherapy to a dose of 55 Gy in 20 fractions to the bladder only, delivered with IGRT, can be considered standard of care for patients with node-negative invasive bladder cancer.

Outcomes of patients with nasopharyngeal carcinoma treated with intensity-modulated radiotherapy.

Nasopharyngeal cancer shows a good response to intensity-modulated radiotherapy. However, there is no clear evidence for the benefits of routine use of image-guided radiotherapy. The purpose of this study was to perform a retrospective investigation of the treatment outcomes, treatment-related complications and prognostic factors for nasopharyngeal cancer treated with intensity-modulated radiotherapy and image-guided radiotherapy techniques. Retrospective analysis was performed on 326 consecutive nasopharyngeal cancer patients treated between 2004 and 2015. Potentially significant patient-related and treatment-related variables were analyzed. Radiation-related complications were recorded. The 5-year overall survival and disease-free survival rates of these patients were 77.9% and 70.5%, respectively. Age, AJCC (American Joint Committee on Cancer) stage, retropharyngeal lymphadenopathy, treatment interruption and body mass index were independent prognostic factors for overall survival. Age, AJCC stage, retropharyngeal lymphadenopathy, image-guided radiotherapy and body mass index were independent prognostic factors for disease-free survival. In conclusion, intensity-modulated radiotherapy significantly improves the treatment outcomes of nasopharyngeal cancer. With the aid of image-guided radiotherapy, the advantage of intensity-modulated radiotherapy might be further amplified.

TraceIT: A prospective pilot study of a temporary intravesical fiducial marker for bladder cancer radiation therapy.

457 Background: Precision image-guided radiotherapy (RT) for patients (pts) with muscle-invasive bladder cancer (MIBC) is limited by daily anatomic variation and difficulty visualizing the tumor bed. We hypothesized that TraceIT, a radiopaque resorbable hydrogel, can be injected around the tumor bed to improve image guidance. We present the results of our pilot trial (NCT03125226) evaluating safety/feasibility of TraceIT in pts undergoing definitive RT. Methods: Eligibility included MIBC with plan to receive definitive RT +/- chemo. Fifteen patients were available for analysis (11 enrolled on trial from 2017-2018, plus an additional 4 received TraceIT off study). TraceIT was injected around the circumference of the tumor bed during pre-radiation maximal re-transurethral resection of bladder tumor (TURBT) for all pts, and again during the mid-radiation TURBT to improve visibility in n = 8 pts. The primary endpoint was assessment of interfraction motion on daily cone-beam CT (CBCTs) based on alignment to fiducial vs standard-of-care pelvic bone anatomy. Van Herk (VH) margin equation was used to determine the planning target volume margin optimized for the clinical target volume receiving at least 95%-prescription dose in 90% of pts. Recurrence rates and survival were estimated by Kaplan Meier. Toxicity was measured by CTCAE v4.03. Results: Patients underwent RT to a median total dose of 63.5 Gy (range 35.75-66.6), typically to an initial small pelvis field follow by a tumor boost. 14/15 received chemo with RT. Median TraceIT volume was 0.5cc (range 0.3-0.75) per injection site for 4 (range 4-6) sites per patient for total volume of 2cc (range 2-3). All pts demonstrated 100% visibility of TraceIT on initial simulation CT and day 1 CBCT. TraceIT visibility declined slightly over time, with 91.5% of patients having visible TraceIT by the end of the initial RT phase (usually week 5) and 82.5% by end of the boost phase. For the initial phase, alignment to fiducials over bone anatomy allowed for reduced VH margins (0.67cm vs 1.56cm). For the boost phase, the VH margin was similar between fiducial and bone alignment (1.01cm vs 0.96cm). There have been no acute or late complications from TraceIT placement. There were no grade grade (G) 4/5 toxicities; three pts had acute G 3 events, and three pts experienced late G 3 toxicity: two related to hematuria and one from ureteral stenosis. There were no late G≥2 GI toxicities. No patients have undergone cystectomy. At a median follow-up of 22 months, 2-yr OS was 79.1% and 2-yr PFS was 75.4%. Conclusions: TraceIT is safe and feasible for use in image-guided RT. TraceIT can increase the precision of RT by facilitating accurate target delineation of the bladder tumor bed and daily motion management which may allow for smaller radiation treatment margins to be used to reduce toxicity and to potentially facilitate safe dose escalation to tumor, which can improve tumor control. Clinical trial information: NCT03125226.

ACR-ASTRO Practice Parameter for Image-guided Radiation Therapy (IGRT).

The American College of Radiology (ACR) and the American Society for Radiation Oncology (ASTRO) have jointly developed the following practice parameter for image-guided radiation therapy (IGRT). IGRT is radiation therapy that employs imaging to maximize accuracy and precision throughout the entire process of treatment delivery with the goal of optimizing accuracy and reliability of radiation therapy to the target, while minimizing dose to normal tissues. The ACR-ASTRO Practice Parameter for IGRT was revised according to the process described on the ACR website ("The Process for Developing ACR Practice Parameters and Technical Standards," www.acr.org/ClinicalResources/Practice-Parametersand-Technical-Standards) by the Committee on Practice Parameters of the ACR Commission on Radiation Oncology in collaboration with the ASTRO. Both societies then reviewed and approved the document. This practice parameter is developed to serve as a tool in the appropriate application of IGRT in the care of patients with conditions where radiation therapy is indicated. It addresses clinical implementation of IGRT including personnel qualifications, quality assurance standards, indications, and suggested documentation. This practice parameter is a tool to guide clinical use of IGRT and does not make recommendations on site-specific IGRT directives. It focuses on the best practices and principles to consider when using IGRT effectively, especially with the significant increase in imaging data that is now available with IGRT. The clinical benefit and medical necessity of the imaging modality and frequency of IGRT should be assessed for each patient.

Bony-based and prostate-based image guidance for lo-calized prostate cancer radiotherapy

An important modality for the treatment of prostate cancer is teletherapy. The use of image-guided radiotherapy (IGRT) is a valuable tool in this treatment. This study retrospectively compared how repositioning the patient based on bone structure (B-ISO) and the prostate itself (P-ISO) affected the volumetric dose in the rectum, bladder, and clinical treatment volume (CTV). Additionally, the probability of normal tissue complication (NTCP) for the rectum was computed. We evaluated 155 cone-beam computed tomography (CBCT) from 8 patients. The treatment plans used beam modulation techniques. The planning target volume (PTV) margin adopted in both scenarios was 1 cm. The organs of interest were outlined over each CBCT and then treatment plans were applied so that the absorbed dose could be computed. NTCP values were calculated for the rectum. Analyzing dose-volume metrics published by the Quantitative Analysis of Normal Tissue Effects in the Clinic (QUANTEC), there was no significant difference between the two repositioning strategies for the rectum and bladder. There was a slight degradation in CTV coverage for the B-ISO strategy, but still with adequate coverage. Analysis of the uniform equivalent dose (EUD) and NTCP for the rectum showed little sensitivity to the strategy used. The present study showed that the use of CBCT in radiotherapy for prostate cancer treatment did not significantly improve volumetric doses for the rectum, bladder, and CTV, as well as NTCP for the rectum.

Observer uncertainties of soft tissue-based patient positioning in IGRT.

PurposeThere remain uncertainties due to inter‐ and intraobserver variability in soft‐tissue‐based patient positioning even with the use of image‐guided radiation therapy (IGRT). This study aimed to reveal observer uncertainties of soft‐tissue‐based patient positioning on cone‐beam computed tomography (CBCT) images for prostate cancer IGRT.MethodsTwenty‐six patients (7–8 fractions/patient, total number of 204 fractions) who underwent IGRT for prostate cancer were selected. Six radiation therapists retrospectively measured prostate cancer location errors (PCLEs) of soft‐tissue‐based patient positioning between planning CT (pCT) and pretreatment CBCT (pre‐CBCT) images after automatic bone‐based registration. Observer uncertainties were evaluated based on residual errors, which denoted the differences between soft‐tissue and reference positioning errors. Reference positioning errors were obtained as PCLEs of contour‐based patient positioning between pCT and pre‐CBCT images. Intraobserver variations were obtained from the difference between the first and second soft‐tissue‐based patient positioning repeated by the same observer for each fraction. Systematic and random errors of inter‐ and intraobserver variations were calculated in anterior–posterior (AP), superior–inferior (SI), and left–right (LR) directions. Finally, clinical target volume (CTV)‐to‐planning target volume (PTV) margins were obtained from systematic and random errors of inter‐ and intraobserver variations in AP, SI, and LR directions.ResultsInterobserver variations in AP, SI, and LR directions were 0.9, 0.9, and 0.5 mm, respectively, for the systematic error, and 1.8, 2.2, and 1.1 mm, respectively, for random error. Intraobserver variations were <0.2 mm in all directions. CTV‐to‐PTV margins in AP, SI, and LR directions were 3.5, 3.8, and 2.1 mm, respectively.ConclusionIntraobserver variability was sufficiently small and would be negligible. However, uncertainties due to interobserver variability for soft‐tissue‐based patient positioning using CBCT images should be considered in CTV‐to‐PTV margins.

ESTRO ACROP consensus guideline on the use of image guided radiation therapy for localized prostate cancer

Use of image-guided radiation therapy (IGRT) helps to account for daily prostate position changes during radiation therapy for prostate cancer. However, guidelines for the use of IGRT are scarce.An ESTRO panel consisting of leading radiation oncologists and medical physicists was assembled to review the literature and formulate a consensus guideline of methods and procedure for IGRT in prostate cases. Advanced methods and procedures are also described which the committee judged relevant to further improve clinical practice. Moreover, ranges for margins for the three most popular IGRT scenarios have been suggested as examples.

Technical note: improved positioning protocol for patient setup accuracy in conventional radiotherapy for lung cancer.

This study aimed to investigate an improved setup protocol for maintaining patient setup accuracy, with minimal or no use of image-guided radiation therapy in conventional radiotherapy for lung cancer. A coordinate value for the treatment couch in the anterior-posterior (AP) direction was obtained from the first fraction using bony anatomy image guidance. The coordinate value was invariably used for patient positioning in the second and subsequent treatment fractions. The errors of 2410 setup image sets (anterior and lateral) from 105 patients with lung cancer were analyzed. The systematic and random patient positioning errors in the AP direction were 0.6 ± 1.0mm. Such errors accounted for 97% of all fractions within ± 2mm. The protocol resulted in minimal patient setup errors in the AP direction using only one image for guidance; therefore, it may be applied to conventional radiotherapy for lung cancer in case of insufficient image guidance.

The advanced radiotherapy network (ART-NET) UK lung stereotactic ablative radiotherapy survey: national provision and a focus on image guidance.

Stereotactic ablative radiotherapy (SABR) has become the standard of care for suitable patients with peripherally located early stage non-small cell lung cancer. Lung SABR requires strict image-guided radiotherapy (IGRT) protocols to ensure its safe delivery. The aim of this survey was to provide an assessment of current lung SABR practice in the UK. An online semi-structured survey containing a maximum of 32 questions regarding lung SABR, focussing on treatment image verification processes was piloted, developed and disseminated to the radiotherapy managers of 62 National Health Service centres across the UK. The survey had a 100% complete response from NHS centres. 36 centres (58%) currently deliver lung SABR, with half treating fewer than 50 patients per year. Six centres deliver SABR despite not being commissioned by the NHS to provide this service. There is wide variation in the use of IGRT. Eight different permutations of cone beam CT order within the workflow were reported. Almost half of lung centres (17/36, 47%) believe there is a need to update national image guidance associated with lung SABR, such as the use of 'day zero', mid treatment and post treatment cone beam CTs. Our results demonstrate wide variation in IGRT for lung SABR. There is an opportunity to develop existing IGRT workflows and the optimal approach to image guidance. Further work is required to investigate lung SABR provision and potential barriers to its implementation. This survey represents the most comprehensive and accurate assessment of lung SABR practice in the UK since the 2014 SABR consortium survey.

Precision of Two Low-Dose Abdomen/Pelvis CBCT Protocols for Alignment to Bone and Soft Tissue in Pediatric Patients Receiving Image-Guided Radiation Therapy

Recommendations for low-dose cone-beam computed tomography (LD-CBCT) protocols for pediatric image-guided radiation therapy (IGRT) are lacking. We aim to evaluate the precision of two LD-CBCT protocols to align to bone and soft tissue landmarks for pediatric patients receiving IGRT to the abdomen and pelvis (A/P). 858 CBCTs from 46 pediatric patients who received IGRT to the A/P starting January 2015 –December 2017 were reviewed. Image quality of CBCTs over this time guided the development of two significantly dose-reduced protocols, LD-CBCT1 (180º rotation, 120 kV, 63 mAs total, 315 frames, S20 collimator) and LD-CBCT2 (180º rotation, 100 kV, 31.5 mAs total, 315 frames, S20 collimator). Eight patients with at least 1 CBCT from both protocols during the course of IGRT were selected for a simulation study, and a representative LD-CBCT1 and LD-CBCT2 scan was registered to the simulation CT (sim-CT) separately aligning to bone and soft tissue. To simulate the process of correcting a setup error to a bone and soft tissue landmark using each protocol, 18 blinded random offsets (max translation 10 mm any x/y/z direction) were applied to each LD-CBCT1 and LD-CBCT2 from a starting registration to bone and a soft tissue structure. Each of the resultant 504 simulated set-up errors was then blindly corrected using rigid registration by a radiation oncologist. The vector magnitude difference (VM= √(x2 + y2 + z2)) between the random offset and final registration attempt was calculated, adjusting for any systematic error in the initial sim-CT↔LD-CBCT1/2 registration. A one-sided paired T-test was used to evaluate if LD-CBCT1, delivering higher dose, was superior to the lower dose LD-CBCT2 for bone and soft tissue alignment.. Age and patient size (using abdominal area) ranges of the eight sample patients with representative LD-CBCT1 and LD-CBCT2 scans were 1-5-9.2 years and 516-954 cm2, respectively. Comparing 288 registrations to a bone landmark across 8 patients, there was no difference in the vector magnitude of the offsets using LD-CBCT 1 (mean [̄x̄], 0.73 mm; standard deviation [σ], 0.39 mm) and LD-CBCT2 (̄x̄, 0.74 mm; σ, 0.40 mm) (p=0.425). Comparing 216 registrations to a soft tissue landmark across 6 patients, alignment using LD-CBCT2 (̄x̄, 1.55 mm; σ, 1.08 mm) resulted in larger differences in the vector magnitude of the offsets compared to LD-CBCT1 (̄x̄, 1.37 mm; σ, 0.74 mm) (p=0.049). Given the particular importance of reducing dose to normal tissue in pediatric patients and the increasing use of IGRT, clinics treating pediatric patients should consider a protocol mirroring LD-CBCT2 validated in this study for A/P IGRT aligned to bone. Delivering higher dose, LD-CBCT1 was slightly superior to LD-CBCT2 for soft tissue alignment, but further investigation is needed given that this study design evaluated the utility in alignment to a kidney structure as the representative soft tissue structure.

Use of a laser‐guided collimation system to perform direct kilovoltage x‐ray spectra measurements on a linear accelerator onboard imager

The increased use of image-guided radiation therapy (IGRT) has led to increased use of kV on board imaging (OBI) devices. At present, directly measured OBI beam quality data have only been reported in terms of half-value layers (HVL). However, the HVL metric alone does not give the full OBI energy spectra as needed for accurate beam modeling. Although direct kV spectrometer devices exist they typically suffer from detector pile-up when used with OBI sources. We therefore present, for the first time, a novel laser-guided collimation system that allows direct measurement of the full energy spectrum for clinical OBI systems. Several clinically relevant spectra (80, 100, and 125 kVp), with and without the half bow-tie filter, were measured using a thermoelectric cooled cadmium telluride (CdTe) detector paired with a multichannel analyzer. To prevent detector saturation, the photon flux at the detector was reduced by use of an in-house designed laser-guided collimation system. After applying energy bin corrections, direct spectroscopic measurements were compared to Monte Carlo (MC) simulated spectra in order to verify accuracy of collected data. Both percent depth dose (PDD) curves and digitally reconstructed radiographs (DRR) were compared using the measured vs MC spectra. Measured and MC spectra agree with RMSD between 1.96% and 3.29%. PDD curves generated from the measured and MC spectra were found to match except for in the small buildup region, with an overall match for the six beams ranging between 0.3% and 2.7% RMSD. DRRs matched well with a maximum difference in contrast of 1.1% and RMSD of 0.46% contrast for various materials in DRRs. The use of a laser-guided collimation system provided a method for quickly obtaining highly accurate kV spectrum data from OBI sources. For kV dose or DRR calculation, it was found that both spectra produced similar results.

Image guidance and positioning accuracy in clinical practice: influence of positioning errors and imaging dose on the real dose distribution for head and neck cancer treatment

BackgroundModern radiotherapy offers the possibility of highly accurate tumor treatment. To benefit from this precision at its best, regular positioning verification is necessary. By the use of image-guided radiotherapy and the application of safety margins the influence of positioning inaccuracies can be counteracted. In this study the effect of additional imaging dose by set-up verification is compared with the effect of dose smearing by positioning inaccuracies for a collective of head-and-neck cancer patients.MethodsThis study is based on treatment plans of 40 head-and-neck cancer patients. To evaluate the imaging dose several image guidance scenarios with different energies, techniques and frequencies were simulated and added to the original plan. The influence of the positioning inaccuracies was assessed by the use of real applied table shifts for positioning. The isocenters were shifted back appropriately to these values to simulate that no positioning correction had been performed. For the single fractions the shifted plans were summed considering three different scenarios: The summation of only shifted plans, the consideration of the original plan for the fractions with set-up verification, and the addition of the extra imaging dose to the latter. For both effects (additional imaging dose and dose smearing), plans were analyzed and compared considering target coverage, sparing of organs at risk (OAR) and normal tissue complication probability (NTCP).ResultsDaily verification of the patient positioning using 3D imaging with MV energies result in non-negligible high doses. kV imaging has only marginal influence on plan quality, primarily related to sparing of organs at risk, even with daily 3D imaging. For this collective, sparing of organs at risk and NTCP are worse due to potential positioning errors.ConclusionRegular set-up verification is essential for precise radiation treatment. Relating to the additional dose, the use of kV modalities is uncritical for any frequency and technique. Dose smearing due to positioning errors for this collective mainly resulted in a decrease of OAR sparing. Target coverage also suffered from the positioning inaccuracies, especially for individual patients. Taking into account both examined effects the relevance of an extensive IGRT is clearly present, even at the expense of additional imaging dose and time expenditure.