Margin Recipe Research Articles

Modeling and prediction of set‑up errors in breast cancer image‑guided radiotherapy using the Gaussian mixture model.

The aim of the present study was to develop a prediction model for set-up error distribution in breast cancer image-guided radiotherapy (IGRT) using a Gaussian mixture model (GMM). To achieve this, the image-guided set-up errors data of 80 patients with breast cancer were selected, and the GMM was used to develop the set-up errors distribution prediction model. The predicted error center points, covariance and probability were calculated and compared with the planning target volume (PTV) margin formula. A total of 1,200 sets of set-up errors in IGRT for breast cancer were collected. The results of the Gaussian model parameters showed that the set-up errors were mainly in the direction of µ1-µ4 center points. All the raw errors in the lateral, longitudinal and vertical directions were -6.30-4.60, -5.40-1.47 and -2.70-1.70 mm, respectively. According to the probability of each center, the set-up error was most likely to shift in the µ1 direction, reaching 0.53. The set-up errors of the other three centers, µ2, µ3 and µ4, were 0.11, 0.34 and 0.12, respectively. According to the covariance parameters of the GMM, the maximum statistical standard deviation of the set-up errors reached 29.06. In conclusion, the results of the present study demonstrated that the GMM can be used to quantitatively describe and predict the distribution of set-up errors in IGRT for breast cancer, and these findings could be useful as a reference for set-up error control and tumor PTV expansion in breast cancer radiotherapy without routine, daily IGRT.

1578: Pareto-optimal margin recipe for robust treatment of cervical cancer with plan-of-the-day IMPT

1578: Pareto-optimal margin recipe for robust treatment of cervical cancer with plan-of-the-day IMPT

Implementing Plan of the Day for Cervical Cancer: A Comparison of Target Volume Generation Methods

Background and purposeDue to substantial interfraction motion in cervix cancer, Plan-of-the-Day (PotD) adaptive radiotherapy may be of benefit to patients. Implementation is limited by uncertainty over how to generate the planning target volumes (PTVs). We compared published methods on our own patients. Materials and methodsForty patients each had three planning scans with variable bladder filling and daily cone beam CTs (CBCTs) during radiotherapy; 5-11 CBCTs were selected to represent interfraction motion. Clinical target volumes (CTVs) and organs at risk (OARs) were contoured following EMBRACE-II guidelines. A literature search identified 30 adaptive and non-adaptive solutions to PTV generation, which we applied to our patients. PTV sizes and mean coverage of the daily CTV were determined. For 11 patients, the clinically-implemented subjectively-edited plan library was also investigated. ResultsEleven studies assessed 15 PotD strategies against non-adaptive comparators on median 14 patients (range 9-23). Some PotD approaches applied margin recipes to the CTV on each planning scan, some modelled the CTV against bladder volume, and others applied incremental isotropic margins to the CTV with a single planning scan. Generally, coverage improved as PTV size increased. The fixed isotropic margin required to provide 100% coverage of all patients was 44mm, with mean PTV size 3316cc. The PotD strategy with the best coverage was a two-plan library formed by modelling the CTV against bladder volume with extrapolation; it provided 98% mean coverage with 1419cc mean PTV size. A three-plan library consisting of the CTV on each planning scan with 10mm margin provided 96% mean coverage with 1346cc mean PTV size. The clinically-implemented solution which employed subjective extrapolation, had mean 100% coverage and 1282cc PTV size on the 11-patient subset. Coverage provided by the best non-adaptive strategies was not statistically superior to the best PotD strategy (p = 0.13) but PTVs were larger (p = 0.02). ConclusionWe identified a modelled two-plan method, and a simple three-plan method, which both provided excellent coverage with small PTVs compared to non-adaptive strategies.

Planning Target Volume Margin Quantification of Retroperitoneal Tumors Using Robotic Stereotactic Body Radiotherapy with Spine Tracking

Stereotactic body radiotherapy treatment (SBRT) is an effective modality for treating primary and oligometastatic malignant lesions. Appropriate planning target volume (PTV) margins are essential when delivering SBRT to maximize target prescription coverage while minimizing dose to surrounding organs-at-risk. Spine tracking uses boney spinal anatomy as a surrogate for tumor localization during treatment delivery on robotic linear accelerator platforms that employ intrafraction kV x-ray imaging. The aim of this study was to quantify the PTV margin needed when spine tracking was used for tumor localization when treating retroperitoneal metastatic lesions with robotic SBRT. A single institution chart review was performed and identified 16 patients with retroperitoneal tumors treated stereotactically over 19 courses in 103 fractions. Daily cone-beam computed tomography (CBCT) images that were registered based on tumor position at the time of treatment were analyzed. Rigid registrations were re-performed aligning the position of the spine on the CBCT relative to its position on the planning CT. Shifts from the treatment position were recorded and per-patient mean shifts and standard deviations were calculated. Van Herk's margin recipe was used to determine the additional PTV margin required if spine tracking was used instead of soft tissue alignment. Patient tumors were stratified and compared based on proximity to the vertebral column (≤1 cm vs >1 cm) and location within the retroperitoneum (superior vs inferior to the renal artery). Student's t-test was used to compare statistical differences of shifts based on location. The additional margins calculated by van Herk's margin recipe to adequately cover the target volumes within the 95% isodose surface for 90% of the entire patient cohort in the vertical, longitudinal, and lateral directions were 2.7, 2.8, and 2.8 mm, respectively. When tumors were stratified by proximity to the vertebral column, average longitudinal (p<0.001) and total shifts (p<0.001) were statistically significant. Isometric PTV expansions of 3, 4, and 5 mm would have encompassed 55%, 76%, and 86% of the maximum total shifts for lesions >1 cm from the vertebral column versus 94%, 100%, and 100% for lesions ≤1 cm. When stratified by location within the retroperitoneum, isometric PTV expansions of 3, 4, and 5 mm would have encompassed 82%, 94%, and 100% of the maximum total shifts for lesions superior to the renal artery versus 78%, 94%, and 98% for lesions inferior to the renal artery. When treating retroperitoneal tumors with robotic SBRT, a minimum isometric margin expansion between 3 to 5 mm when creating the PTV is recommended if spine tracking is used for intrafraction tumor localization. Target volumes adjacent to the vertebral column may have PTV margins decreased to ≤4 mm without compromising target coverage.

Robustness analysis of CTV and OAR dose in clinical PBS-PT of neuro-oncological tumors: prescription-dose calibration and inter-patient variation with the Dutch proton robustness evaluation protocol.

Objective. The Dutch proton robustness evaluation protocol prescribes the dose of the clinical target volume (CTV) to the voxel-wise minimum (VWmin) dose of 28 scenarios. This results in a consistent but conservative near-minimum CTV dose (D98%,CTV). In this study, we analyzed (i) the correlation between VWmin/voxel-wise maximum (VWmax) metrics and actually delivered dose to the CTV and organs at risk (OARs) under the impact of treatment errors, and (ii) the performance of the protocol before and after its calibration with adequate prescription-dose levels.Approach. Twenty-one neuro-oncological patients were included. Polynomial chaos expansion was applied to perform a probabilistic robustness evaluation using 100,000 complete fractionated treatments per patient. Patient-specific scenario distributions of clinically relevant dosimetric parameters for the CTV and OARs were determined and compared to clinical VWmin and VWmax dose metrics for different scenario subsets used in the robustness evaluation protocol.Main results. The inclusion of more geometrical scenarios leads to a significant increase of the conservativism of the protocol in terms of clinical VWmin and VWmax values for the CTV and OARs. The protocol could be calibrated using VWmin dose evaluation levels of 93.0%-92.3%, depending on the scenario subset selected. Despite this calibration of the protocol, robustness recipes for proton therapy showed remaining differences and an increased sensitivity to geometrical random errors compared to photon-based margin recipes.Significance. The Dutch proton robustness evaluation protocol, combined with the photon-based margin recipe, could be calibrated with a VWmin evaluation dose level of 92.5%. However, it shows limitations in predicting robustness in dose, especially for the near-maximum dose metrics to OARs. Consistent robustness recipes could improve proton treatment planning to calibrate residual differences from photon-based assumptions.

Comparison of cone beam computed tomography (CBCT)-based image guided radiotherapy approaches in the reduction of setup uncertainties during deep inspiration breath-hold radiotherapy (DIBH-RT) for left breast cancer

Advances in radiotherapy has allowed higher cure rates for cancer such as breast and thus, it is important to reduce the possible radiation side effects from exposure to other organs such as the heart. Deep inspiration breath-hold radiotherapy technique (DIBH-RT) significantly reduces cardiac dose during left breast radiotherapy, but the patient setup requires careful adoption of image guidance radiotherapy technique (IGRT) approaches. This study investigates the effectiveness of cone beam computed tomography (CBCT)-based IGRT protocols for patients' inter-fraction set-up correction. Setup error data from two patients’ groups; A and B who had daily CBCT and first 3 fractions + weekly CBCT imaging respectively, were analysed. This constitutes a total of 13 left breast cancer patients treated using DIBH-RT at Advanced Medical Dental Institute (AMDI), Universiti Sains Malaysia (USM), Malaysia. The analysis was performed using MATLAB (MathWorks Inc Natick MA) to calculate the mean setup errors. The population systematic (∑) and random (σ) errors were calculated for non-IGRT, online, and two offline IGRT protocols; no action level (NAL) and extended no action level (eNAL) for each patient group. The corresponding planning target volume (PTV) margin and its percentage reduction for each of the IGRT protocols were established using van Herk margin recipe. The least population systematic setup error and PTV margin were found when using the online protocol (∑X/Y/Z = 0.17/0.22/0.31 mm; PTVX/Y/Z = 0.71/0.92/1.28 mm) followed by eNAL (∑X/Y/Z = 1.32/1.94/1.85 mm; PTVX/Y/Z = 5.75/7.99/8.46 mm), NAL (∑X/Y/Z = 1.45/2.26/1.84 mm; PTVX/Y/Z = 6.27/8.93/8.46 mm) and non-IGRT (∑X/Y/Z = 2.28/3.35/3.10 mm; PTVX/Y/Z = 7.77/10.85/10.93 mm). Up to 90% in PTV margin reduction is achieved with the online protocol. In conclusion, the use of IGRT during DIBH-RT for left breast cancer patients reduces patient set-up error and allows the use of tighter PTV margins. The online IGRT protocol was shown to be more effective in the reduction of errors and the PTV margin followed by eNAL and NAL offline IGRT protocols.

Comprehensive Treatment Uncertainty Analysis and PTV Margin Estimation for Fiducial Tracking in Robotic Liver Stereotactic Body Radiation Therapy.

This study aims to quantify the uncertainties of CyberKnife Synchrony fiducial tracking for liver stereotactic body radiation therapy (SBRT) cases, and evaluate the required planning target volume (PTV) margins. A total of 11 liver tumor patients with a total of 57 fractions, who underwent SBRT with synchronous fiducial tracking, were enrolled for the present study. The correlation/prediction model error, geometric error, and beam targeting error were quantified to determine the patient-level and fraction-level individual composite treatment uncertainties. The composite uncertainties and multiple margin recipes were compared for scenarios with and without rotation correction during treatment. The correlation model error-related uncertainty was 4.3±1.8, 1.4±0.5 and 1.8±0.7 mm in the superior-inferior (SI), left-right, and anterior-posterior directions, respectively. These were the primary contributors among all uncertainty sources. The geometric error significantly increased for treatments without rotation correction. The fraction-level composite uncertainties had a long tail distribution. Furthermore, the generally used 5-mm isotropic margin covered all uncertainties in the left-right and anterior-posterior directions, and only 75% of uncertainties in the SI direction. In order to cover 90% of uncertainties in the SI direction, an 8-mm margin would be needed. For scenarios without rotation correction, additional safety margins should be added, especially in the superior-inferior and anterior-posterior directions. The present study revealed that the correlation model error contributes to most of the uncertainties in the results. Most patients/fractions can be covered by a 5-mm margin. Patients with large treatment uncertainties might need a patient-specific margin.

Development of a PTV margin for preclinical irradiation of orthotopic pancreatic tumors derived from a well-known recipe for humans

In human radiotherapy a safety margin (PTV margin) is essential for successful irradiation and is usually part of clinical treatment planning. In preclinical radiotherapy research with small animals, most uncertainties and inaccuracies are present as well, but according to the literature a margin is used only scarcely. In addition, there is only little experience about the appropriate size of the margin, which should carefully be investigated and considered, since sparing of organs at risk or normal tissue is affected.Here we estimate the needed margin for preclinical irradiation by adapting a well-known human margin recipe from van Herck et al. to the dimensions and requirements of the specimen on a small animal radiation research platform (SARRP). We adjusted the factors of the described formula to the specific challenges in an orthotopic pancreatic tumor mouse model to establish an appropriate margin concept. The SARRP was used with its image-guidance irradiation possibility for arc irradiation with a field size of 10 × 10 mm2 for 5 fractions. Our goal was to irradiate the clinical target volume (CTV) of at least 90% of our mice with at least 95% of the prescribed dose. By carefully analyzing all relevant factors we gain a CTV to planning target volume (PTV) margin of 1.5 mm for our preclinical setup.The stated safety margin is strongly dependent on the exact setting of the experiment and has to be adjusted for other experimental settings. The few stated values in literature correspond well to our result. Even if using margins in the preclinical setting might be an additional challenge, we think it is crucial to use them to produce reliable results and improve the efficacy of radiotherapy.

In-vivo quality assurance of dynamic tumor tracking (DTT) for liver SABR using EPID images.

To assess dynamic tumor tracking (DTT) target localization uncertainty for in-vivo marker-based stereotactic ablative radiotherapy (SABR) treatments of the liver using electronic-portal-imaging-device (EPID) images. The Planning Target Volume (PTV) margin contribution for DTT is estimated. Phantom and patient EPID images were acquired during non-coplanar 3DCRT-DTT delivered on a Vero4DRT linac. A chain-code algorithm was applied to detect Multileaf Collimator (MLC)-defined radiation field edges. Gold-seed markers were detected using a connected neighbor algorithm. For each EPID image, the absolute differences between the measured center-of-mass (COM) of the markers relative to the aperture-center (Tracking Error, (ET )) was reported in pan, tilt, and 2D-vector directions at the isocenter-plane. An acrylic cube phantom implanted with gold-seed markers was irradiated with non-coplanar 3DCRT-DTT beams and EPID images collected. Patient Study: Eight liver SABR patients were treated with non-coplanar 3DCRT-DTT beams. All patients had three to four implanted gold-markers. In-vivo EPID images were analyzed. Phantom Study: On the 125 EPID images collected, 100% of the markers were identified. The average±SD of ET were 0.24±0.21, 0.47±0.38, and 0.58±0.37mm in pan, tilt and 2D directions, respectively. Patient Study: Of the 1430 EPID patient images acquired, 78% had detectable markers. Over all patients, the average±SD of ET was 0.33±0.41mm in pan, 0.63±0.75mm in tilt and 0.77±0.80mm in 2D directions The random 2D-error, σ, for all patients was 0.79mm and the systematic 2D-error, Σ, was 0.20mm. Using the Van Herk margin formula 1.1mm planning target margin can represent the marker based DTT uncertainty. Marker-based DTT uncertainty can be evaluated in-vivo on a field-by-field basis using EPID images. This information can contribute to PTV margin calculations for DTT.

Customizing Treatment Scheduling Windows with a Time Margin Recipe: A Single-institutional Study.

Rising cancer incidences, complex treatment techniques, and workflows have all impacted the radiotherapy scheduling process. Intelligent appointment scheduling is needed to help radiotherapy users adapt to new practices. We utilized van Herk's safety margin formula to determine the radiotherapy department's treatment scheduling window (TSW). In addition, we examined the influence of in-room imaging on linac occupancy time (LOT). Varian Aria™ software version 15.1 was used to collect retrospective data on LOT, treatment site, intent, techniques, special protocol, and in-room imaging. Treatment scheduling windows varied across treatment sites. The mean TSW using van Herk's formalism was 31.5 min, significantly longer than the current TSW of 15 min (P = 0.036), with the pelvic site having the longest (43.8 min) and the brain site having the shortest (12 min). 28% of patients exceeded the in-practice TSW of 15 min. 46.2% of patients had multiple images per fraction, with the proportion being highest in pelvic patients (33%). Patients treated with palliative intent, intensity-modulated radiotherapy, special protocols (bladder protocol and gating), and multiple in-room images per fraction had significantly higher LOT. High treatment time uncertainty was observed in the pelvic and thorax sites, indicating the impact of in-room imaging frequency and on-couch treatment decisions on overall treatment time and indicating that current treatment practices should be reviewed and modified if necessary. The time margin recipe can customize the treatment scheduling window and improve treatment practices. This formalism can help manage the radiotherapy department's workload and reduce patient wait times.

A margin recipe for the management of intra-fraction target motion in radiotherapy.

Strategies to limit the impact of intra-fraction motion during treatment are common in radiotherapy. Margin recipes, however, are not designed to incorporate these strategies. This work aimed to provide a framework to determine how motion management strategies influence treatment margins. Two models of intra-fraction motion were considered. In model 1 motion was instantaneous, before treatment starts and in model 2 motion was a continuous drift during treatment. Motion management strategies were modelled by truncating the underlying error distribution at cσ, with σ the standard deviation of the distribution and c a free parameter. Using Monte Carlo simulations, we determined how motion management changed the required margin. The analysis was performed for different number of treatment fractions and different standard deviations of the underlying random and systematic errors. The required margin for a continuous drift was found to be well approximated by an average position of the target at ¾ of the drift. Introducing a truncation at cσ, the relative change in the margin was equal to 0.3c. This result held for both models, was independent of σ or the number of fractions and naturally generalizes to the situation with a residual (systematic) error. Treatment margins can be determined when motion management strategies are applied. Moreover, our analysis can be used to study the potential benefit of different motion management strategies. This allows to discuss and determine the most appropriate strategy for margin reduction.

ANALYSIS OF THE CORN TRADING CHAIN AND MARGIN IN OGAN KOMERING ULU REGENCY

This study aims to analyze the banana trading chain and margin in Jayapura District, East OKU Regency, South Sumatra Province. The research was carried out deliberately considering that Jayapura District, East OKU District is the center of bananas in East OKU District. The research was carried out in March 2022. The research method used was a survey method and the sampling method used was a simple random method. The analytical tool used in processing research data is a mathematical method with a margin formula to calculate marketing margin and marketing channel efficiency. Discussion of research results is carried out by descriptive analysis. The results showed that there were 3 banana trading channels in the research location, the processed data showed that the margin for trading at agents was 800 rupiahs and at 2000 rupiahs at retailers. The results also show that the most efficient trade system channel is channel 3 with an efficiency value of 1 percent.

HOW TO REDUCE TURNOVER INTENTION OF YOUNG PROGRAMMERS WITH TRANSFORMATIONAL LEADERSHIP MEDIATED THROUGH ORGANIZATIONAL COMMITMENT

This study aims to analyze the banana trading chain and margin in Jayapura District, East OKU Regency, South Sumatra Province. The research was carried out deliberately considering that Jayapura District, East OKU District is the center of bananas in East OKU District. The research was carried out in March 2022. The research method used was a survey method and the sampling method used was a simple random method. The analytical tool used in processing research data is a mathematical method with a margin formula to calculate marketing margin and marketing channel efficiency. Discussion of research results is carried out by descriptive analysis. The results showed that there were 3 banana trading channels in the research location, the processed data showed that the margin for trading at agents was 800 rupiahs and at 2000 rupiahs at retailers. The results also show that the most efficient trade system channel is channel 3 with an efficiency value of 1 percent.

ANALYSIS OF THE BANANA TRADING CHAIN AND MARGIN IN JAYAPURA SUB-DISTRICT, EAST OKU DISTRICT

This study aims to analyze the banana trading chain and margin in Jayapura District, East OKU Regency, South Sumatra Province. The research was carried out deliberately considering that Jayapura District, East OKU District is the center of bananas in East OKU District. The research was carried out in March 2022. The research method used was a survey method and the sampling method used was a simple random method. The analytical tool used in processing research data is a mathematical method with a margin formula to calculate marketing margin and marketing channel efficiency. Discussion of research results is carried out by descriptive analysis. The results showed that there were 3 banana trading channels in the research location, the processed data showed that the margin for trading at agents was 800 rupiahs and at 2000 rupiahs at retailers. The results also show that the most efficient trade system channel is channel 3 with an efficiency value of 1 percent

Evaluation of internal margins for prostate for step and shoot intensity-modulated radiation therapy and volumetric modulated arc therapy using different margin formulas.

PurposeThis feasibility study evaluated the intra‐fractional prostate motion using an ultrasound image‐guided system during step and shoot intensity‐modulated radiation therapy (SS‐IMRT) and volumetric modulated arc therapy (VMAT). Moreover, the internal margins (IMs) using different margin formulas were calculated.MethodsFourteen consecutive patients with prostate cancer who underwent SS‐IMRT (n = 5) or VMAT (n = 9) between March 2019 and April 2020 were considered. The intra‐fractional prostate motion was observed in the superior–inferior (SI), anterior–posterior (AP), and left–right (LR) directions. The displacement of the prostate was defined as the displacement from the initial position at the scanning start time, which was evaluated using the mean ± standard deviation (SD). IMs were calculated using the van Herk and restricted maximum likelihood (REML) formulas for SS‐IMRT and VMAT.ResultsFor SS‐IMRT, the maximum displacements of the prostate motion were 0.17 ± 0.18, 0.56 ± 0.86, and 0.18 ± 0.59 mm in the SI, AP, and LR directions, respectively. For VMAT, the maximum displacements of the prostate motion were 0.19 ± 0.64, 0.22 ± 0.35, and 0.14 ± 0.37 mm in the SI, AP, and LR directions, respectively. The IMs obtained for SS‐IMRT and VMAT were within 2.3 mm and 1.2 mm using the van Herk formula and within 1.2 mm and 0.8 mm using the REML formula.ConclusionsThis feasibility study confirmed that intra‐fractional prostate motion was observed with SS‐IMRT and VMAT using different margin formulas. The IMs should be determined according to each irradiation technique using the REML margin.

Towards mid-position based Stereotactic Body Radiation Therapy using online magnetic resonance imaging guidance for central lung tumours.

Background and purpose: Central lung tumours can be treated by magnetic resonance (MR)-guided radiotherapy. Complications might be reduced by decreasing the Planning Target Volume (PTV) using mid-position (midP)-based planning instead of Internal Target Volume (ITV)-based planning. In this study, we aimed to verify a method to automatically derive patient-specific PTV margins for midP-based planning, and show dosimetric robustness of midP-based planning for a 1.5T MR-linac.Materials and methods: Central(n = 12) and peripheral(n = 4) central lung tumour cases who received 8x7.5 Gy were included. A midP-image was reconstructed from ten phases of the 4D-Computed Tomography using deformable image registration. The Gross Tumor Volume (GTV) was delineated on the midP-image and the PTV margin was automatically calculated based on van Herk’s margin recipe, treating the standard deviation of all Deformation Vector Fields, within the GTV, as random error component. Dosimetric robustness of midP-based planning for MR-linac using automatically derived margins was verified by 4D dose-accumulation. MidP-based plans were compared to ITV-based plans. Automatically derived margins were verified with manually derived margins.Results: The mean D95% target coverage in GTV + 2 mm was 59.9 Gy and 62.0 Gy for midP- and ITV-based central lung plans, respectively. The mean lung dose was significantly lower for midP-based treatment plans (difference:-0.3 Gy; ). Automatically derived margins agreed within one millimeter with manually derived margins.Conclusions: This retrospective study indicates that mid-position-based treatment plans for central lung Stereotactic Body Radiation Therapy yield lower OAR doses compared to ITV-based treatment plans on the MR-linac. Patient-specific GTV-to-PTV margins can be derived automatically and result in clinically acceptable target coverage.

Assessment of planning target volume margins in 1.5 T magnetic resonance‐guided stereotactic body radiation therapy for localized prostate cancer

AbstractObjectiveWe aimed to determine the planning target volume margins applicable to magnetic resonance‐guided stereotactic body radiation therapy (MRgSBRT) of localized prostate cancer on a 1.5 T MR‐Linac.MethodsA total of 10 patients with low‐ to intermediate‐risk prostate cancer were retrospectively enrolled. All patients received five‐fraction MRgSBRT treatments, and underwent daily endorectal ballooning and bladder control. Five patients were implanted with the hydrogel rectal spacer. Three MR scans at each fraction were acquired to evaluate the intrafractional prostate motion. The required planning target volume margin was determined using the van Herk margin recipe based on direct MR‐MR prostate registration. The set‐up margin for localization using bony anatomy was also estimated.ResultsThe mean and standard deviation of translational displacement in left‐right (LR), superior‐inferior (SI), and anterior‐posterior (AP) directions were –0.3 ± 0.7, 2.0 ± 1.5, and 1.4 ± 1.1 mm, respectively. Planning target volume margins over the MRgSBRT fraction duration were 2.8 (LR), 5.3 (SI), and 3.9 mm (AP). Set‐up margins were estimated to 2.6 (LR), 3.3 (SI), and 3.3 mm (AP). Prostate motion increased considerably with treatment duration. Adapt‐to‐position had smaller intrafractional motions than adapt‐to‐shape. The rectal spacer insignificantly (p &gt; 0.1) reduced the prostate motion in SI and AP.ConclusionOnline workflow efficiency enhancement and intrafractional motion monitoring are vital for planning target volume margin reduction and precision enhancement in MRgSBRT.

Scalability analysis of machine learning QoT estimators for a cloud-native SDN controller on a WDM over SDM network

Maintaining a good quality of transmission (QoT) in optical transport networks is key to maintaining the service level agreement between the user and the service provider. QoT prediction techniques have been used to assure the quality of new lightpaths as well as that of the previously provisioned ones. Traditionally, two different approaches have been used: analytical methods, which take into account most physical impairments that are accurate but complex, and high margin formulas, which require much less computational resources at the cost of high margins. With the recent progress of machine learning (ML) together with software defined networking (SDN), ML has been considered as another option that could be both accurate and that does not consume as many resources as analytical methods. SDN architectures are difficult to scale because they are usually centralized; this is even worse with QoT predictors using ML. In this paper, a solution to this issue is presented using a cloud-native architecture, and its scalability is evaluated using three different ML QoT predictors and experimentally validated in a real wavelength-division multiplexing (WDM) over spatial-division multiplexing (SDM) testbed.

Ramifications of Setup Margin Use During Frameless Stereotactic Radiosurgery/Therapy With Gamma Knife Icon Cone-Beam Computed Tomography (CBCT): A Dosimetric Study.

ObjectiveThe objective is to explore the possibility of optimal/rational application of setup margin during treatment planning for frameless stereotactic Gamma Knife radiosurgery/therapy.MethodsUncertainty measurements for frameless Gamma Knife Icon treatment were used to calculate the necessary setup margin via four different published recipes and these margins were subsequently applied to treatment plans of 30 previously treated patients and replans were generated meeting comparable plan quality metrics. All plans were then analyzed based on the ability to maintain normal tissue dose tolerances and the relative increase in target dose coverage probability using a pass/fail scoring system based on published normal tissue dose constraints and an in-house developed optimal scoring method.ResultsGross tumor volume/planning target volume (GTV/PTV) size strongly correlated with both meeting normal tissue tolerances and optimal scores for single fraction plans corroborating published clinical outcomes. The Van Herk Margin Formula (VHMF) and Parker margin formulae were indicated as good candidates for high probabilities of both meeting normal tissue goals and high optimal scores which generally translated to just over 1 mm in GTV to PTV margin.ConclusionFor single fraction treatment, GTV size is highly significant in predicting failure to meet normal tissue goals whereas whether setup margin was used was not a significant predictor. Setup margin can rationally be applied when fraction number is dictated by clinically indicated metrics regarding GTV size of greater or less than 4 cc. 1 mm is a reasonable practical application of margin added to GTV to ensure physical prescription dose target coverage for most cases when clinically desired based on disease type and intended outcome.

A Prospective Study of a Resorbable Intravesical Fiducial Marker for Bladder Cancer Radiation Therapy

PurposeWe conducted a prospective pilot study to evaluate safety and feasibility of TraceIT, a resorbable radiopaque hydrogel, to improve image guidance for bladder cancer radiation therapy (RT). Methods and MaterialsPatients with muscle invasive bladder cancer receiving definitive RT were eligible. TraceIT was injected intravesically around the tumor bed during maximal transurethral resection of bladder tumor. The primary endpoint was the difference between radiation treatment planning margin on daily cone beam computed tomography based on alignment to TraceIT versus standard-of-care pelvic bone anatomy. The Van Herk margin formula was used to determine the optimal planning target volume margin. TraceIT visibility, recurrence rates, and survival were estimated by Kaplan-Meier method. Toxicity was measured by Common Terminology Criteria for Adverse Events version 4.03. ResultsThe trial was fully accrued and 15 patients were analyzed. TraceIT was injected in 4 sites/patient (range, 4-6). Overall, 94% (95% confidence interval [CI], 90%-98%) of injection sites were radiographically visible at RT initiation versus 71% (95% CI, 62%-81%) at RT completion. The median duration of radiographic visibility for injection sites was 106 days (95% CI, 104-113). Most patients were treated with a standard split-course approach with initial pelvic radiation fields, then midcourse repeat transurethral resection of bladder tumor followed by bladder tumor bed boost fields, and 14/15 received concurrent chemotherapy. Alignment to fiducials could allow for reduced planning target volume margins (0.67 vs 1.56 cm) for the initial phase of RT, but not for the boost (1.01 vs 0.96 cm). This allowed for improved target coverage (D95% 80%-83% to 91%-94%) for 2 patients retrospectively planned with both volumetric-modulated arc therapy and 3-dimensional conformal RT. At median follow-up of 22 months, no acute or late complications attributable to TraceIT placement occurred. No patients required salvage cystectomy. ConclusionsTraceIT intravesical fiducial placement is safe and feasible and may facilitate tumor bed delineation and targeting in patients undergoing RT for localized muscle invasive bladder cancer. Improved image guided treatment may facilitate strategies to improve local control and minimize toxicity.