Is full-automation in radiotherapy treatment planning ready for take off?

Radiotherapy treatment planning is undergoing a transformation with the increasing integration of automation. This transition draws parallels with the aviation industry, which has a long-standing history of addressing challenges and opportunities introduced by automated systems. Both fields witness a shift from manual operations to systems capable of operating independently, raising questions about the risks and evolving role of humans within automated workflows. In response to this shift, a working group assembled during the ESTRO Physics Workshop 2023, reflected on parallels to draw lessons for radiotherapy. A taxonomy is proposed, leveraging insights from aviation, that outlines the observed levels of automation within the context of radiotherapy and their corresponding implications for human involvement. Among the common identified risks associated with automation integration are complacency, overreliance, attention tunneling, data overload, a lack of transparency and training. These risks require mitigation strategies. Such strategies include ensuring role complementarity, introducing checklists and safety requirements for human-automation interaction and using automation for cognitive unload and workflow management. Focusing on already automated processes, such as dose calculation and auto-contouring as examples, we have translated lessons learned from aviation. It remains crucial to strike a balance between automation and human involvement. While automation offers the potential for increased efficiency and accuracy, it must be complemented by human oversight, expertise, and critical decision-making. The irreplaceable value of human judgment remains, particularly in complex clinical situations. Learning from aviation, we identify a need for human factors engineering research in radiation oncology and a continued requirement for proactive incident learning.

Quantitative Assessment of Full-Time Equivalent Effort for Kilovoltage-Cone Beam Computed Tomography Guided Online Adaptive Radiation Therapy for Medical Physicists

PURPOSE

With recent clinical adoption of online adaptive radiation therapy (oART) and the increased workload associated with adaptive radiation therapy (RT), proper staffing for medical physicists is paramount to safe clinical operation. However, there is currently no consensus on the full-time equivalent (FTE) requirements for safe administration of cone beam computed tomography (CBCT)-guided oART. This study aimed to quantitatively assess medical physics workload and staffing needs of a CBCT-guided oART program.

METHODS AND MATERIALS

We conducted a detailed analysis of the CBCT-guided adaptive planning and treatment workflows, encompassing tasks such as patient consultation, treatment planning, plan review, training, quality assurance, and treatment delivery. Using data from machine logs, clinical database queries, and staff surveys, we present a framework for estimating FTE values for different staffing scenarios, considering medical physicists' roles as planners, adaptors, or both.

RESULTS

FTE calculations, based on an example workload of 100 adaptive and 200 nonadaptive patients per year, for 3 staffing scenarios were provided: medical physicists as planners and adaptors (2.9 FTE), medical physicists as planners but not adaptors (2.6 FTE), and medical physicists as adaptors but not planners (1.4 FTE). These findings offer calculation guidance and benchmarks for staffing requirements in CBCT-guided oART programs, emphasizing the need for specific staffing models to accommodate the complexities of adaptive RT.

CONCLUSIONS

This study outlines a framework for calculating FTE requirements for medical physicists in a CBCT-guided oART program. By analyzing the processes for 3 common adaptive RT workflows, this work can provide effective workforce planning and resource allocation estimates. This analysis can be used either before the implementation of an oART program, for program development, or as a review of current practices to ensure operational efficiency and proper staffing levels are maintained.

Unlocking the adaptive advantage: correlation and machine learning classification to identify optimal online adaptive stereotactic partial breast candidates

Objective.Online adaptive radiotherapy (OART) is a promising technique for delivering stereotactic accelerated partial breast irradiation (APBI), as lumpectomy cavities vary in location and size between simulation and treatment. However, OART is resource-intensive, increasing planning and treatment times and decreasing machine throughput compared to the standard of care (SOC). Thus, it is pertinent to identify high-yield OART candidates to best allocate resources.Approach.Reference plans (plans based on simulation anatomy), SOC plans (reference plans recalculated onto daily anatomy), and daily adaptive plans were analyzed for 31 sequential APBI targets, resulting in the analysis of 333 treatment plans. Spearman correlations between 22 reference plan metrics and 10 adaptive benefits, defined as the difference between mean SOC and delivered metrics, were analyzed to select a univariate predictor of OART benefit. A multivariate logistic regression model was then trained to stratify high- and low-benefit candidates.Main results.Adaptively delivered plans showed dosimetric benefit as compared to SOC plans for most plan metrics, although the degree of adaptive benefit varied per patient. The univariate model showed high likelihood for dosimetric adaptive benefit when the reference plan ipsilateral breast V15Gy exceeds 23.5%. Recursive feature elimination identified 5 metrics that predict high-dosimetric-benefit adaptive patients. Using leave-one-out cross validation, the univariate and multivariate models classified targets with 74.2% and 83.9% accuracy, resulting in improvement in per-fraction adaptive benefit between targets identified as high- and low-yield for 7/10 and 8/10 plan metrics, respectively.Significance.This retrospective, exploratory study demonstrated that dosimetric benefit can be predicted using only ipsilateral breast V15Gy on the reference treatment plan, allowing for a simple, interpretable model. Using multivariate logistic regression for adaptive benefit prediction led to increased accuracy at the cost of a more complicated model. This work presents a methodology for clinics wishing to triage OART resource allocation.

Order From Chaos: The Benefits of Standardized Nomenclature in Radiation Oncology

Although standardization has been shown to improve patient safety and improve the efficiency of workflows, implementation of standards can take considerable effort and requires the engagement of all clinical stakeholders. Engaging team members includes increasing awareness of the proposed benefit of the standard, a clear implementation plan, monitoring for improvements, and open communication to support successful implementation. The benefits of standardization often focus on large institutions to improve research endeavors, yet all clinics can benefit from standardization to increase quality and implement more efficient or automated workflow. The benefits of nomenclature standardization for all team members and institution sizes, including success stories, are discussed with practical implementation guides to facilitate the adoption of standardized nomenclature in radiation oncology.

Prospective Evaluation of Automated Contouring for CT-Based Brachytherapy for Gynecologic Malignancies

Purpose

The use of deep learning to auto-contour organs at risk (OARs) in gynecologic radiation treatment is well established. Yet, there is limited data investigating the prospective use of auto-contouring in clinical practice. In this study, we assess the accuracy and efficiency of auto-contouring OARs for computed tomography-based brachytherapy treatment planning of gynecologic malignancies.

Methods and Materials

An inhouse contouring tool automatically delineated 5 OARs in gynecologic radiation treatment planning: the bladder, small bowel, sigmoid, rectum, and urethra. Accuracy of each auto-contour was evaluated using a 5-point Likert scale: a score of 5 indicated the contour could be used without edits, while a score of 1 indicated the contour was unusable. During scoring, automated contours were edited and subsequently used for treatment planning. Dice similarity coefficient, mean surface distance, 95% Hausdorff distance, Hausdorff distance, and dosimetric changes between original and edited contours were calculated. Contour approval time and total planning time of a prospective auto-contoured (AC) cohort were compared with times from a retrospective manually contoured (MC) cohort.

Results

Thirty AC cases from January 2022 to July 2022 and 31 MC cases from July 2021 to January 2022 were included. The mean (±SD) Likert score for each OAR was the following: bladder 4.77 (±0.58), small bowel 3.96 (±0.91), sigmoid colon 3.92 (±0.81), rectum 4.6 (±0.71), and urethra 4.27 (±0.78). No ACs required major edits. All OARs had a mean Dice similarity coefficient > 0.86, mean surface distance < 0.48 mm, 95% Hausdorff distance < 3.2 mm, and Hausdorff distance < 10.32 mm between original and edited contours. There was no significant difference in dose-volume histogram metrics (D2.0 cc/D0.1 cc) between original and edited contours (P values > .05). The average time to plan approval in the AC cohort was 19% less than the MC cohort. (AC vs MC, 117.0 + 18.0 minutes vs 144.9 ± 64.5 minutes, P = .045).

Conclusions

Automated contouring is useful and accurate in clinical practice. Auto-contouring OARs streamlines radiation treatment workflows and decreases time required to design and approve gynecologic brachytherapy plans.

Improved Dosimetry and Plan Quality for Accelerated Partial Breast Irradiation Using Online Adaptive Radiation Therapy: A Single Institutional Study

Purpose

Accelerated partial breast irradiation (APBI) is an attractive treatment modality for eligible patients as it has been shown to result in similar local control and improved cosmetic outcomes compared with whole breast radiation therapy. The use of online adaptive radiation therapy (OART) for APBI is promising as it allows for a reduction of planning target volume margins because breast motion and lumpectomy cavity volume changes are accounted for in daily imaging. Here we present a retrospective, single-institution evaluation on the adequacy of kV-cone beam computed tomography (CBCT) OART for APBI treatments.

Methods and Materials

Nineteen patients (21 treatment sites) were treated to 30 Gy in 5 fractions between January of 2022 and May of 2023. Time between simulation and treatment, change in gross tumor (ie, lumpectomy cavity) volume, and differences in dose volume histogram metrics with adaption were analyzed. The Wilcoxon paired, nonparametric test was used to test for dose volume histogram metric differences between the scheduled plans (initial plans recalculated on daily CBCT anatomy) and delivered plans, either the scheduled or adapted plan, which was reoptimized using daily anatomy.

Results

Median (interquartile range) time from simulation to first treatment was 26 days (21-32 days). During this same time, median gross tumor volume reduction was 16.0% (7.3%-23.9%) relative to simulation volume. Adaptive treatments took 31.3 minutes (27.4-36.6 minutes) from start of CBCT to treatment session end. At treatment, the adaptive plan was selected for 86% (89/103) of evaluable fractions. In evaluating plan quality, 78% of delivered plans met all target, organs at risk, and conformity metrics evaluated, compared with 34% of scheduled plans.

Conclusions

Use of OART for stereotactic linac-based APBI allowed for safe, high-quality treatments in this cohort of 21 treatment courses. Although treatment delivery times were longer than traditional stereotactic body treatments, there were notable improvements in plan quality for APBI using OART.

Evaluation and correlation of patient movement during online adaptive radiotherapy with CBCT and a surface imaging system

PURPOSE

With the clinical implementation of kV-CBCT-based daily online-adaptive radiotherapy, the ability to monitor, quantify, and correct patient movement during adaptive sessions is paramount. With sessions lasting between 20-45 min, the ability to detect and correct for small movements without restarting the entire session is critical to the adaptive workflow and dosimetric outcome. The purpose of this study was to quantify and evaluate the correlation of observed patient movement with machine logs and a surface imaging (SI) system during adaptive radiation therapy.

METHODS

Treatment machine logs and SGRT registration data log files for 1972 individual sessions were exported and analyzed. For each session, the calculated shifts from a pre-delivery position verification CBCT were extracted from the machine logs and compared to the SGRT registration data log files captured during motion monitoring. The SGRT calculated shifts were compared to the reported shifts of the machine logs for comparison for all patients and eight disease site categories.

RESULTS

The average (±STD) net displacement of the SGRT shifts were 2.6 ± 3.4 mm, 2.6 ± 3.5 mm, and 3.0 ± 3.2 in the lateral, longitudinal, and vertical directions, respectively. For the treatment machine logs, the average net displacements in the lateral, longitudinal, and vertical directions were 2.7 ± 3.7 mm, 2.6 ± 3.7 mm, and 3.2 ± 3.6 mm. The average difference (Machine-SGRT) was -0.1 ± 1.8 mm, 0.2 ± 2.1 mm, and -0.5 ± 2.5 mm for the lateral, longitudinal, and vertical directions. On average, a movement of 5.8 ± 5.6 mm and 5.3 ± 4.9 mm was calculated prior to delivery for the CBCT and SGRT systems, respectively. The Pearson correlation coefficient between CBCT and SGRT shifts was r = 0.88. The mean and median difference between the treatment machine logs and SGRT log files was less than 1 mm for all sites.

CONCLUSION

Surface imaging should be used to monitor and quantify patient movement during adaptive radiotherapy.

Understanding the Effect of Prescription Isodose in Single-Fraction Stereotactic Radiosurgery on Plan Quality and Clinical Outcomes for Solid Brain Metastases

BACKGROUND AND OBJECTIVES

There is wide variation in treatment planning strategy for central nervous system (CNS) stereotactic radiosurgery. We sought to understand what relationships exist between intratumor maximum dose and local control (LC) or CNS toxicity, and dosimetric effects of constraining hotspots on plan quality of multiple metastases volumetric modulated arc therapy radiosurgery plans.

METHODS

We captured brain metastases from 2015 to 2017 treated with single-isocenter volumetric modulated arc therapy radiosurgery. Included tumors received single-fraction stereotactic radiosurgery, had no previous surgery or radiation, and available follow-up imaging. Our criterion for local failure was 25% increase in tumor diameter on follow-up MRI or pathologic confirmation of tumor recurrence. We defined significant CNS toxicity as Radiation Therapy Oncology Group irreversible Grade 3 or higher. We performed univariate and multivariate analyses evaluating factors affecting LC. We examined 10 stereotactic radiosurgery plans with prescriptions of 18 Gy to all targets originally planned without constraints on the maximum dose within the tumor. We replanned each with a constraint of Dmax 120%. We compared V50%, mean brain dose, and Dmax between plans.

RESULTS

Five hundred and thirty tumors in 116 patients were available for analysis. Median prescription dose was 18 Gy, and median prescription isodose line (IDL) was 73%. Kaplan-Meier estimate of 12-month LC only tumor volume (HR 1.43 [1.22-1.68] P < .001) was predictive of local failure on univariate analysis; prescription IDL and histology were not. In multivariate analysis, tumor volume impacted local failure (HR 1.43 [1.22-1.69] P < .001) but prescription IDL did not (HR 0.95 [0.86-1.05] P = .288). Only a single grade 3 and 2 grade 4 toxicities were observed; tumor volume was predictive of CNS toxicity (HR 1.58 [1.25-2.00]; P < .001), whereas prescription IDL was not (HR 1.01 [0.87-1.17] P = .940).

CONCLUSION

The prescription isodose line had no impact on local tumor control or CNS toxicity. Penalizing radiosurgery hotspots resulted in worse radiosurgery plans with poorer gradient. Limiting maximum dose in gross tumor causes increased collateral exposure to surrounding tissue and should be avoided.

kV-CBCT-Guided Daily Adaptation Improves Target Coverage and Spares Normal Tissue for Accelerated Partial Breast Irradiation

PURPOSE/OBJECTIVE(S)

Linear accelerator based accelerated partial breast irradiation (APBI) in early-stage breast cancer necessitates a reduction in non-target breast tissue to decrease long term toxicity and adverse cosmetic outcome. In particular, lumpectomy cavity seromas may decrease in size and deform in shape during the course of short course APBI. Online adaptive RT (oART) offers considerable prospect for treating mobile targets through pendulous breast anatomy. However, there are limited studies outlining the methods and outcomes of CBCT-based oART for APBI. Here we present a retrospective, single institutional study analyzing the treatment process for patients receiving stereotactic kV-CBCT guided oART APBI.

MATERIALS/METHODS

Fourteen patients were treated to 30 Gy in 5 fractions for a total of 70 fractions. Time between simulation and treatment, change in gross tumor volume (GTV), and differences in DVH metrics with adaption were analyzed. The Wilcoxon paired, non-parametric test was utilized to test for DVH metric differences between the scheduled plans (initial plans recalculated on daily CBCT anatomy) and treated plans, which were either the scheduled or adapted plan (initial plans re-optimized using daily anatomy), depending on the preference of the treating physician or physicist.

RESULTS

Median (inter-quartile range) time from simulation to first treatment was 28 days (21-33 days). During this same time, GTV volume reduced to 72.5% (57.8-87.3%) of the simulation lumpectomy cavity volume. Adaptive treatments required 31.1 min (27.2-37.1 min) from start of CBCT to treatment session end. Table 1 summarizes differences between scheduled and treated plan metrics for 70 fractions, 62 (89%) of which were treated adaptively and 8 (11%) of which were treated using the scheduled plan. Significant improvement in prescription planning target volume coverage (p = 0.003), significant reduction in 5/6 organ-at-risk metrics evaluated (p ≤ 0.003), and significant improvement in conformity index and high dose spillage (p ≤ 0.001) were realized with adaption. Table 1: Scheduled versus treated plan metrics.

CONCLUSION

APBI using oART decreased most organs at risk DVH metrics, improved plan quality metrics, and increased target coverage, justifying the use of kV-CBCT-guided oART for APBI.

Commissioning and clinical evaluation of the IDENTIFYTM surface imaging system for frameless stereotactic radiosurgery

PURPOSE

To commission and assess the clinical performance of a new commercial surface imaging (SI) system by analyzing intra-fraction motion from the initial cohort of patients treated with frameless stereotactic radiosurgery (fSRS).

METHODS

The IDENTIFYTM SI system was commissioned for clinical use on an Edge (Varian Medical Systems, Palo Alto, CA) linear accelerator. All patients who received intracranial radiotherapy with HyperArcTM (Varian Medical Systems, Palo Alto, CA) were immobilized with the EncompassTM (Qfix, Avondale, PA) thermoplastic mask and monitored for intra-fraction motion with SI. IDENTIFYTM log files were correlated with trajectory log files to correlate treatment parameters with SI-reported offsets. IDENTIFYTM reported offsets were correlated with gantry and couch angles to assess system performance for obstructed and clear camera field of view. Data were stratified by race to evaluate performance differences due to skin tone.

RESULTS

All commissioning data were found to meet recommended tolerances. IDENTIFYTM was used to monitor intra-fraction motion on 1164 fractions from 386 patients. The median magnitude of translational SI reported offsets at the end of treatment was 0.27 mm. SI reported offsets were shown to increase when camera pods are blocked by the gantry with larger increases seen at non-zero couch angles. With camera obstruction, the median magnitude of the SI reported offset was 0.50 and 0.80 mm for White and Black patients, respectively.

CONCLUSIONS

IDENTIFYTM performance during fSRS is comparable to other commercially available SI systems where offsets are shown to increase at non-zero couch angles and during camera pod blockage.

Frameless LINAC-Based Stereotactic Radiosurgery is Safe and Effective for Essential and Parkinsonian Tremor

PURPOSE/OBJECTIVE(S)

Stereotactic radiosurgery (SRS) to the thalamus is an ablative technique used for treatment of refractory tremor of essential or Parkinsonian origin. Because of the high dose, small target, and required precision, framed SRS on the Gamma Knife has been the historical platform of choice. We tested our recently developed technique to emulate GK dose distributions on a multi-leaf collimator (MLC)-equipped linear accelerator (LINAC) without cumbersome, inefficient cones in a prospective trial of safety and efficacy.

MATERIALS/METHODS

We quantified pre-treatment contralateral tremor according to FTM scoring system. We obtained MPRAGE, FGATIR, DTI, and RS-fMRI sequences. We identified the VIM via classical stereotactic reference location and connectomically, and then targeted it to 135 Gy dmax in a manner dosimetrically roughly equivalent to 4 mm GK shot. We adjusted each target such that the 25 Gy isodose line did not overlap the posterior limb of the capsule. We immobilized patients in a highly rigid thermoplastic mask and delivered treatment on an Edge™ LINAC with HDMLC. Intrafraction optical surface monitoring (OSMS) ensured patient immobility. We surveilled post-treatment imaging and recorded tremor scoring, QOL outcomes, and adverse events.

RESULTS

We accrued 42 patients (16 female, 26 males; median age 72.5) over 36 months. 38 had essential tremor, 4 had tremor-dominant Parkinson's; 2 withdrew prior to treatment. Ten patients were on therapeutic anti-coagulation, and were not required to discontinue. At time of submission 39 patients had follow-up ≥ 6 months. 35/39 (89.7%) exhibited clinically meaningful tremor reduction. Mean limb tremor reduction among responders was 43.5% (range: 9 - 100%). Time to patient-reported tremor improvement was 0.3 to 15 months. One patient experienced Gr 3, and 4 patients experienced Gr 1-2 toxicity.

CONCLUSION

MLC-based SRS thalamotomy is safe and effective for refractory tremor treatment. Multidisciplinary management is key for proper patient selection, treatment, and monitoring. Our outcomes appear congruent to historical GK controls as well as more modern MRgFUS outcomes.

Operational Ontology for Radiation Oncology (OORO): A Professional Society-Based, Multi-Stakeholder Consensus Driven Informatics Standard Supporting Clinical and Research Use of Real-World Data

PURPOSE/OBJECTIVE(S)

There is a critical need for large-scale, multi-institutional "real-world" data to evaluate patient, diagnosis and treatment factors affecting oncology patient outcomes. However, lack of data standardization undermines the potential for automated learning from the vast amount of information routinely archived in electronic health records (EHRs), Radiation Oncology Information Systems and other cancer care databases. As next step to promote data standardization beyond the American Association of Physicists in Medicine (AAPM)'s TG-263 guidance for radiotherapy (RT) nomenclature, the AAPM's Big Data Subcommittee (BDSC) has led an international RT professional society collaboration to develop the Operational Ontology for Radiation Oncology (OORO).

MATERIALS/METHODS

Initiated July 2019 to explore issues that typically compromise formation of large inter- and intra- institutional databases from EHRs, the AAPM's BDSC membership includes representatives from the AAPM, American Society of Radiation Oncology (ASTRO), Canadian Organization of Medical Physicists (COMP), Canadian Association of Radiation Oncology (CARO), European Society of Therapeutic Radiation Oncology (ESTRO) and clinical trials experts from NRG Oncology. Multiple external stakeholders were engaged, including government agencies, vendors and RT community members through the iterative and consensus-driven approach to OORO development.

RESULTS

The OORO includes 42 key elements, 359 attributes, 144 value sets, and 155 relationships, ranked for priority of implementation based on clinical significance, likelihood of availability in EHRs, or ability to modify routine clinical processes to permit aggregation. The initial version of OORO includes many disease-site independent concepts common for all cancer patients and a smaller set specific for prostate cancer. The OORO development methodology is currently being applied/adapted to include additional disease site-specific concepts beginning with head and neck cancers.

CONCLUSION

The first of its kind in radiation oncology, the OORO is a professional society-based, multi-stakeholder, consensus driven informatics standard. The iterative and collaborative approach to ontology development and refinement aims to ensure that OORO serves as a « living » guidance document, facilitating incremental expansion of data elements over time, as disease site-specific standards are set and RT concepts evolve. Supporting construction of comprehensive "real-world" datasets and application of advanced analytic techniques, including artificial intelligence (AI), OORO holds the potential to revolutionize patient management and improve outcomes.

A roadmap for implementation of kV-CBCT online adaptive radiation therapy and initial first year experiences

PURPOSE

Online Adaptive Radiation Therapy (oART) follows a different treatment paradigm than conventional radiotherapy, and because of this, the resources, implementation, and workflows needed are unique. The purpose of this report is to outline our institution's experience establishing, organizing, and implementing an oART program using the Ethos therapy system.

METHODS

We include resources used, operational models utilized, program creation timelines, and our institutional experiences with the implementation and operation of an oART program. Additionally, we provide a detailed summary of our first year's clinical experience where we delivered over 1000 daily adaptive fractions. For all treatments, the different stages of online adaption, primary patient set-up, initial kV-CBCT acquisition, contouring review and edit of influencer structures, target review and edits, plan evaluation and selection, Mobius3D 2nd check and adaptive QA, 2nd kV-CBCT for positional verification, treatment delivery, and patient leaving the room, were analyzed.

RESULTS

We retrospectively analyzed data from 97 patients treated from August 2021-August 2022. One thousand six hundred seventy seven individual fractions were treated and analyzed, 632(38%) were non-adaptive and 1045(62%) were adaptive. Seventy four of the 97 patients (76%) were treated with standard fractionation and 23 (24%) received stereotactic treatments. For the adaptive treatments, the generated adaptive plan was selected in 92% of treatments. On average(±std), adaptive sessions took 34.52 ± 11.42 min from start to finish. The entire adaptive process (from start of contour generation to verification CBCT), performed by the physicist (and physician on select days), was 19.84 ± 8.21 min.

CONCLUSION

We present our institution's experience commissioning an oART program using the Ethos therapy system. It took us 12 months from project inception to the treatment of our first patient and 12 months to treat 1000 adaptive fractions. Retrospective analysis of delivered fractions showed that the average overall treatment time was approximately 35 min and the average time for the adaptive component of treatment was approximately 20 min.

Dose prescription and reporting in stereotactic body radiotherapy: A multi-institutional study

BACKGROUND AND PURPOSE

Radiation dose prescriptions are foundational for optimizing treatment efficacy and limiting treatment-related toxicity. We sought to assess the lack of standardization of SBRT dose prescriptions across institutions.

MATERIALS & METHODS

Dosimetric data from 1298 patients from 9 academic institutions treated with IMRT and VMAT were collected. Dose parameters D100, D98, D95, D50, and D2 were used to assess dosimetric variability.

RESULTS

Disease sites included lung (48.3 %) followed by liver (29.7 %), prostate (7.5 %), spine (6.8 %), brain (4.1 %), and pancreas (2.5 %). The PTV volume in lung varied widely with bimodality into two main groups (22.0-28.7 cm3) and (48.0-67.1 cm3). A hot spot ranging from 120-150 % was noted in nearly half of the patients, with significant variation across institutions. A D50 ≥ 110 % was found in nearly half of the institutions. There was significant dosimetric variation across institutions.

CONCLUSIONS

The SBRT prescriptions in the literature or in treatment guidelines currently lack nuance and hence there is significant variation in dose prescriptions across academic institutions. These findings add greater importance to the identification of dose parameters associated with improved clinical outcome comparisons as we move towards more hypofractionated treatments. There is a need for standardized reporting to help institutions in adapting treatment protocols based on the outcome of clinical trials. Dosimetric parameters are subsequently needed for uniformity and thereby standardizing planning guidelines to maximize efficacy, mitigate toxicity, and reduce treatment disparities are urgently needed.

A focused review of statistical practices for relating radiation dose-volume exposure and toxicity

PURPOSE

Relating dose-volume histogram (DVH) information to patient outcomes is critical for outcomes research in radiation oncology, but this is statistically challenging. We performed this focused review of DVH toxicity studies to characterize current statistical approaches and determine the need for updated reporting recommendations.

METHODS AND MATERIALS

We performed a focused MEDLINE search to identify studies published in 5 radiation oncology specialty journals that associated dosimetry with toxicity outcomes in humans receiving radiotherapy between 2015 and 2021. Elements abstracted from each manuscript included the study outcome, organs-at-risk (OARs) considered, DVH parameters analyzed, summary of the analytic approach, use of multivariable statistics, goodness-of-fit reporting, completeness of model reporting, assessment of multicollinearity, adjustment for multiple comparisons, and methods for dichotomizing variables. Each study was also assessed for sufficient reporting to allow for replication of results.

RESULTS

The MEDLINE search returned 2,300 studies for review and 325 met the inclusion criteria for the analysis. DVH variables were dichotomized using cut points in 154 (47.4%) studies. Logistic regression (55.4% of studies) was the most common statistical method used to relate DVH to toxicity outcomes, followed by Cox regression (20.6%) and linear regression (12.0%). Multivariable statistical tests were performed in 226 (69.5%) studies; of these, the possibility of multicollinearity was addressed in 47.8% and model goodness-of-fit were reported in 32.6%. The threshold for statistical significance was adjusted to account for multiple comparisons in 41 of 196 (17.1%) studies that included multiple statistical comparisons. Twenty-eight (8.6%) studies were classified as missing details necessary to reproduce the study results.

CONCLUSIONS

Current practices of statistical reporting in DVH outcomes suggest that studies may be vulnerable to threats against internal and external validity. Recommendations for reporting are provided herein to guard against such threats and to promote cohesiveness among radiation oncology outcomes researchers.

Leveraging intelligent optimization for automated, cardiac-sparing accelerated partial breast treatment planning

Background

Accelerated partial breast irradiation (APBI) yields similar rates of recurrence and cosmetic outcomes as compared to whole breast radiation therapy (RT) when patients and treatment techniques are appropriately selected. APBI combined with stereotactic body radiation therapy (SBRT) is a promising technique for precisely delivering high levels of radiation while avoiding uninvolved breast tissue. Here we investigate the feasibility of automatically generating high quality APBI plans in the Ethos adaptive workspace with a specific emphasis on sparing the heart.

Methods

Nine patients (10 target volumes) were utilized to iteratively tune an Ethos APBI planning template for automatic plan generation. Twenty patients previously treated on a TrueBeam Edge accelerator were then automatically replanned using this template without manual intervention or reoptimization. The unbiased validation cohort Ethos plans were benchmarked via adherence to planning objectives, a comparison of DVH and quality indices against the clinical Edge plans, and qualitative reviews by two board-certified radiation oncologists.

Results

85% (17/20) of automated validation cohort plans met all planning objectives; three plans did not achieve the contralateral lung V1.5Gy objective, but all other objectives were achieved. Compared to the Eclipse generated plans, the proposed Ethos template generated plans with greater evaluation planning target volume (PTV_Eval) V100% coverage (p = 0.01), significantly decreased heart V1.5Gy (p< 0.001), and increased contralateral breast V5Gy, skin D0.01cc, and RTOG conformity index (p = 0.03, p = 0.03, and p = 0.01, respectively). However, only the reduction in heart dose was significant after correcting for multiple testing. Physicist-selected plans were deemed clinically acceptable without modification for 75% and 90% of plans by physicians A and B, respectively. Physicians A and B scored at least one automatically generated plan as clinically acceptable for 100% and 95% of planning intents, respectively.

Conclusions

Standard left- and right-sided planning templates automatically generated APBI plans of comparable quality to manually generated plans treated on a stereotactic linear accelerator, with a significant reduction in heart dose compared to Eclipse generated plans. The methods presented in this work elucidate an approach for generating automated, cardiac-sparing APBI treatment plans for daily adaptive RT with high efficiency.

Connectomic Basis for Tremor Control in Stereotactic Radiosurgical Thalamotomy

BACKGROUND AND PURPOSE

Given the increased use of stereotactic radiosurgical thalamotomy and other ablative therapies for tremor, new biomarkers are needed to improve outcomes. Using resting-state fMRI and MR tractography, we hypothesized that a "connectome fingerprint" can predict tremor outcomes and potentially serve as a targeting biomarker for stereotactic radiosurgical thalamotomy.

MATERIALS AND METHODS

We evaluated 27 patients who underwent unilateral stereotactic radiosurgical thalamotomy for essential tremor or tremor-predominant Parkinson disease. Percentage postoperative improvement in the contralateral limb Fahn-Tolosa-Marin Clinical Tremor Rating Scale (TRS) was the primary end point. Connectome-style resting-state fMRI and MR tractography were performed before stereotactic radiosurgery. Using the final lesion volume as a seed, "connectivity fingerprints" representing ideal connectivity maps were generated as whole-brain R-maps using a voxelwise nonparametric Spearman correlation. A leave-one-out cross-validation was performed using the generated R-maps.

RESULTS

The mean improvement in the contralateral tremor score was 55.1% (SD, 38.9%) at a mean follow-up of 10.0 (SD, 5.0) months. Structural connectivity correlated with contralateral TRS improvement (r = 0.52; P  = .006) and explained 27.0% of the variance in outcome. Functional connectivity correlated with contralateral TRS improvement (r = 0.50; P  = .008) and explained 25.0% of the variance in outcome. Nodes most correlated with tremor improvement corresponded to areas of known network dysfunction in tremor, including the cerebello-thalamo-cortical pathway and the primary and extrastriate visual cortices.

CONCLUSIONS

Stereotactic radiosurgical targets with a distinct connectivity profile predict improvement in tremor after treatment. Such connectomic fingerprints show promise for developing patient-specific biomarkers to guide therapy with stereotactic radiosurgical thalamotomy.

Do we need patient-specific QA for adaptively generated plans? Retrospective evaluation of delivered online adaptive treatment plans on Varian Ethos

BACKGROUND

The clinical introduction of dedicated treatment units for online adaptive radiation therapy (OART) has led to widespread adoption of daily adaptive radiotherapy. OART allows for rapid generation of treatment plans using daily patient anatomy, potentially leading to reduction of treatment margins and increased normal tissue sparing. However, the OART workflow does not allow for measurement of patient-specific quality assurance (PSQA) during treatment delivery sessions and instead relies on secondary dose calculations for verification of adapted plans. It remains unknown if independent dose verification is a sufficient surrogate for PSQA measurements.

PURPOSE

To evaluate the plan quality of previously treated adaptive plans through multiple standard PSQA measurements.

METHODS

This IRB-approved retrospective study included sixteen patients previously treated with OART at our institution. PSQA measurements were performed for each patient's scheduled and adaptive plans: five adaptive plans were randomly selected to perform ion chamber measurements and two adaptive plans were randomly selected for ArcCHECK measurements. The same ArcCHECK 3D dose distribution was also sent to Mobius3D to evaluate the second-check dosimetry system.

RESULTS

All (n = 96) ion chamber measurements agreed with the planned dose within 3% with a mean of 1.4% (± 0.7%). All (n = 48) plans passed ArcCHECK measurements using a 95% gamma passing threshold and 3%/2 mm criteria with a mean of 99.1% (± 0.7%). All (n = 48) plans passed Mobius3D second-check performed with 95% gamma passing threshold and 5%/3 mm criteria with a mean of 99.0% (± 0.2%).

CONCLUSION

Plan measurement for PSQA may not be necessary for every online-adaptive treatment verification. We recommend the establishment of a periodic PSQA check to better understand trends in passing rates for delivered adaptive treatments.

Analysis of a surface imaging system using a six degree-of-freedom couch

Purpose

To validate surface imaging (SI)‐reported offsets using a six degree‐of‐freedom couch and an anthropomorphic phantom for commissioning and routine quality assurance of an SI system used for stereotactic radiosurgery (SRS).

Methods

An anthropomorphic phantom with a radiopaque ball bearing (BB) placed either anterior, midline, or posterior, was tracked with SI with a typical SRS region of interest. Couch motion in all six degrees of freedom was programmed and delivered on a linac. SI system logs were synchronized with linac trajectory logs. Ten random couch positions were selected at couch 0°, 45°, 90°, 270°, 315° with megavolt (MV) images taken to account for couch walkout. The SI residual error (ε), the difference between SI reported offset and MV or trajectory log position, was calculated. Residual errors were measured with and without one SI pod blocked.

Results

The median [range] of magnitude of translational ε was 0.13 [0.07, 0.21], 0.16 [0.11, 0.26], 0.61 [0.50, 0.68], 0.49 [0.42, 0.55], 0.55 [0.38, 0.72] mm for couch rotations of 0°, 45°, 90°, 270°, 315°, respectively, for the midline BB and no pod blocked. The range of all translational ε from all couch angles (with and without pod block) at different BB positions is [0.05, 0.96] mm. The absolute range of difference when changing BB position when no pod is blocked in median translational ε is [0.01, 0.40] mm with the maximum at BB posterior. The absolute range of difference when not changing BB positions with and without pod block in median translational ε is [0.01, 0.37] mm with the maximum at BB posterior and couch 315°.

Conclusion

SI system and linac trajectory log analysis can be used to assess SI system performance with automated couch motion to validate SI accuracy.

Commissioning a multileaf collimator virtual cone for the stereotactic radiosurgery of trigeminal neuralgia

A multileaf collimator (MLC), virtual‐cone treatment technique has been commissioned for trigeminal neuralgia (TGN) at Tri‐Cities Cancer Center (TCCC). This novel technique was initially developed at the University of Alabama in Birmingham (UAB); it is designed to produce a spherical dose profile similar to a fixed, 5‐mm conical collimator distribution. Treatment is delivered with a 10‐MV flattening‐filter‐free (FFF) beam using a high‐definition MLC on a Varian Edge linear accelerator. Absolute dose output and profile measurements were performed in a 20 × 20 × 14 cm³ solid‐water phantom using an Exradin W2 scintillation detector and Gafchromic EBT3 film. Dose output constancy for the virtual cone was evaluated over 6 months using an Exradin A11 parallel plate chamber. The photo‐neutron dose generated by these treatments was assessed at distances of 50 and 100 cm from isocenter using a Ludlum Model 30–7 Series Neutron Meter. TGN treatments at TCCC have been previously delivered at 6‐MV FFF using a 5‐mm stereotactic cone. To assess the dosimetric impact of using a virtual cone, eight patients previously treated for TGN with a 5‐mm cone were re‐planned using a virtual cone. Seven patients have now been treated for TGN using a virtual cone at TCCC. Patient‐specific quality assurance was performed for each patient using Gafchromic EBT‐XD film inside a Standard Imaging Stereotactic Dose Verification Phantom. The commissioning results demonstrate that the virtual‐cone dosimetry, first described at UAB, is reproducible on a second Edge linear accelerator at an independent clinical site. The virtual cone is a credible alternative to a physical, stereotactic cone for the treatment of TGN at TCCC.

Hypofractionated radiation leads to more rapid bleeding cessation in women with vaginal bleeding secondary to gynecologic malignancy

Background

Vaginal bleeding (VB) is common in women with gynecologic (GYN) malignancies. Radiation therapy (RT) is used for the definitive treatment of GYN cancers and palliation of bleeding. The historical dogma is that high dose-per-fraction radiation leads to more rapid bleeding cessation, yet there is scant data supporting this claim. We sought to examine the effect of RT fraction size on VB via retrospective analysis of patients receiving hypofractionated radiation (HFRT) compared to conventionally fractionated radiation (CFRT) for control of bleeding secondary to GYN malignancies.

Methods

We identified patients receiving external beam RT for continuous VB from GYN malignancy treated in our department from 2012 to 2020. RT was classified as HFRT (> 2.0 Gy/fx) or CFRT (1.8–2.0 Gy/fx). Demographic information, disease characteristics, and treatment details were collected. The primary endpoint was days from RT initiation until bleeding resolution. Characteristics between groups were compared via Fisher’s exact test. Time to bleeding cessation was assessed via Kaplan–Meier and log-rank test. Univariable and multivariable Cox-proportional hazards were used to identify factors associated with bleeding cessation.

Results

We identified 43 patients meeting inclusion criteria with 26 and 17 patients receiving CFRT and HFRT, respectively. Comparison of baseline characteristics revealed patients receiving HFRT were older (p = 0.001), more likely to be post-menopausal (p = 0.002), and less likely to receive concurrent chemotherapy (p = 0.004). Time to bleeding cessation was significantly shorter for patients receiving HFRT (log-rank p < 0.001) with median time to bleeding cessation of 5 days (HFRT) versus 16 days (CFRT). Stratification by dose-per-fraction revealed a dose–response effect with more rapid bleeding cessation with increased dose-per-fraction. While HFRT, age, recurrent disease, prior pelvic RT, and prior systemic therapy were associated with time to bleeding cessation on univariable analysis, HFRT was the only factor significantly associated with time to bleeding cessation in the final multivariable model (HR 3.26, p = 0.008).

Conclusions

Patients with continuous VB from GYN tumors receiving HFRT experienced more rapid bleeding cessation than those receiving CFRT. For patients with severe VB, initiation of HFRT to control malignancy related bleeding quickly may be warranted.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13014-022-01995-7.

Evaluation of a two-dimensional diode array for patient-specific quality assurance of HyperArc

PURPOSE

To evaluate a two-dimensional diode array for patient-specific quality assurance of VMAT stereotactic radiosurgery (SRS) plans.

METHODS

The diode array, an SRS MapCHECK (SRSMC), was composed of a 77 mm ×77 mm face-centered array having a spacing of 2.47 mm. Sixty SRS plans were selected from our clinical database, 30 for treatment of a single target and 30 for multiple targets. The target sizes ranged from 2.4 mm to 44.7 mm equivalent diameter (median 8.7 mm). The plans were delivered to the diode array. For multiple target plans, two measurements were obtained at two locations, one corresponding to the largest target and the other to the smallest target. Gamma using a 3%/1 mm criteria and the dose to the center diode were compared with radiochromic film (RCF). Dose to selected regions of the detector electronics was calculated.

RESULTS

The mean difference between the center diode and RCF was -1.2%. For a threshold of at least 95% of detectors/pixels having gamma < 1 for a 3%/1 mm criteria, SRSMC and RCF gave consistent results for 79 of the 90 measurements. For plans with an arc having a patient support angle of 90° or 270°, the median dose to the electronics was 0.65% of the prescription dose.

CONCLUSIONS

SRSMC is an efficient tool for accurate patient-specific quality assurance of VMAT single and multiple target radiosurgery, yielding similar clinical decisions as radiochromic film.

Code Wisely: Risk assessment and mitigation for custom clinical software

Purpose

The task of software development has become an increasing part of the medical physicist's role. Many physicists who are untrained in the best practices of software development have begun creating scripts for clinical use. There is an increasing need for guidance for both developers and medical physicists to code wisely in the clinic.

Materials and Methods

We created a novel model for assessing risk for custom clinical software analogous to failure modes and effects analysis and propose minimum best practices that should be followed to mitigate the risks. Using this risk model, we integrated a literature review and institutional experience to form a practical guide for risk mitigation.

Results

Using this new risk assessment model, we outlined several risk mitigation techniques including unit testing, code review, source control, end‐user testing, and commissioning from the literature while sharing our institutional guidelines for evaluating software for risk and implementing these strategies.

Conclusion

We found very little literature for custom software development guidelines targeted at medical physicists. We have shared our institutional experience and guidelines to help facilitate safe software development for the evolving role of the medical physicist.

A Low-Cost Method to Assess the Performance of Surface Guidance Imaging Systems at Non-Zero Couch Angles

A procedure is presented to assess performance at non-zero couch angles and perform routine quality assurance (QA) on surface-guided radiotherapy (SGRT) imaging systems used for stereotactic radiosurgery (SRS). A low-cost anthropomorphic phantom was used to assess the system under patient-like conditions. The phantom is embedded with a tungsten ball bearing (BB) to facilitate the use of surface imaging (SI) with concurrent megavoltage (MV) imaging to cross-compare and validate SI-reported offsets. Data analysis is done via in-house software that utilized the SGRT system’s log files for automated analysis. This procedure enables users to assess and inter-compare MV-reported offsets with their SGRT system. The analysis provides SGRT system residual error so that users are aware of inherent offsets present in addition to increases in translational offsets due to couch walkout. The procedure was validated with two commercial SGRT systems. The procedure can be used with any surface imaging system and linear accelerator system.