Stereotactic Body Radiation Therapy Treatment Research Articles

Scorecards: Quantifying Dosimetric Plan Quality in Pancreatic Ductal Adenocarcinoma Stereotactic Body Radiation Therapy

A scoring mechanism called the scorecard that objectively quantifies the dosimetric plan quality of pancreas stereotactic body radiation therapy treatment plans is introduced. A retrospective analysis of patients with pancreatic ductal adenocarcinoma receiving stereotactic body radiation therapy at our institution between November 2019 and November 2020 was performed. Ten patients were identified. All patients were treated to 36 Gy in 5 fractions, and organs at risk (OARs) were constrained based on Alliance A021501. The scorecard awarded points for OAR doses lower than those cited in Alliance A021501. A team of 3 treatment planners and 2 radiation oncologists, including a physician resident without plan optimization experience, discussed the relative importance of the goals of the treatment plan and added additional metrics for OARs and plan quality indexes to create a more rigorous scoring mechanism. The scorecard for this study consisted of 42 metrics, each with a unique piecewise linear scoring function which is summed to calculate the total score (maximum possible score of 365). The scorecard-guided plan, the planning and optimization for which were done exclusively by the physician resident with no prior plan optimization experience, was compared with the clinical plan, the planning and optimization for which were done by expert dosimetrists, using the Sign test. Scorecard-guided plans had, on average, higher total scores than those clinically delivered for each patient, averaging 280.1 for plans clinically delivered and 311.7 for plans made using the scorecard (P=.003). Additionally, for most metrics, the average score of each metric across all 10 patients was higher for scorecard-guided plans than for clinically delivered plans. The scorecard guided the planner toward higher coverage, conformality, and OAR sparing. A scorecard tool can help clarify the goals of a treatment plan and provide an objective method for comparing the results of different plans. Our study suggests that a completely novice treatment planner can use a scorecard to create treatment plans with enhanced coverage, conformality, and improved OAR sparing, which may have significant effects on both tumor control and toxicity. These tools, including the scorecard used in this study, have been made freely available.

Efficacy of preoxygenation administration in volunteers, in extending the end-expiration breath-hold duration for application to abdominal radiotherapy

End expiration breath hold (EEBH) is the preferred motion management method for abdominal Stereotactic Ablative Body Radiotherapy (SABR) treatments. However, multiple short EEBHs are required to complete a single treatment session. The study aimed to determine the efficacy of preoxygenation with hyperventilation in extending an EEBH duration.We randomised 10 healthy participants into two arms, each included breathing room air and oxygen at a rate of 10 L per minute (l/min) without hyperventilation for four minutes, and normally for four minutes and with hyperventilation for one minute at a rate of 20 breaths/minute for hyperventilation. The type of gas was blinded from the participants for each test. EEBH durations were then recorded, as well as systolic blood pressure, SpO2 and heart rate. A discomfort rating was also recorded after each breath hold.A significant increase in duration of almost 50% was observed between normal breathing of room air and breathing oxygen normally followed by hyperventilation. Vital signs remained consistent between the 4 tests. The tests were well tolerated with 75% of participants recording none or minimal discomfort.Preoxygenation with hyperventilation could be used to increase the EEBH duration for abdominal SABR patients which would assist in the accuracy of these treatments and possibly resulting in a reduction of overall treatment times.

Association of neutrophil-lymphocyte ratio with survival in peripheral early-stage non–small-cell lung cancer after stereotactic body radiation therapy.

e20547 Background: Prior studies have demonstrated that neutrophil-lymphocyte ratio (NLR) can predict overall survival in patients undergoing stereotactic body radiation therapy (SBRT) for multiple types of cancer. The role of neutrophil-lymphocyte ratio (NLR) as a predictor for survival in single fraction SBRT-treated non-small cell lung cancer (NSCLC) patients remains unclear. Methods: A single-institution database of peripheral early-stage NSCLC patients treated with SBRT from February 2007 to May 2022 was queried. Consecutive patients with peripheral early-stage NSCLC (T1-2N0M0) and a complete blood count within six months of the start of SBRT treatment were included. Patients treated with SBRT regimens of more than 3 fractions were excluded as these regimens were reserved for patients with centrally located lesions with higher risk of toxicity which could affect survival. Optimal threshold of neutrophil-lymphocyte ratio (NLR) was defined based on maximally selected rank statistics. Cox multivariable analysis (MVA), Kaplan-Meier, and propensity score matching were performed to evaluate outcomes. Results: A total of 286 patients (164 female [57.3%]; median [IQR] age 76 [69-81] years) were included for analysis with median follow up of 19.7 months. The median NLR was 3.06 ([IQR] 2.21-4.33). There were 15 local failures, 27 nodal failures, and 50 distant failures. On Cox multivariate analysis, as a continuous variable, NLR was shown to be an independent predictor of OS (adjusted hazards ratio [aHR] 1.06, 95% CI 1.02-1.10, p = 0.005; Figure 1) and PFS (aHR 1.05, 95% CI 1.01-1.09, p = 0.013; Figure 1). In addition, NLR was associated with DF (aHR 1.11, 95% CI 1.05-1.18, p < 0.001; Figure 1). Maximally selected rank statistics determined 3.28 as the cutoff point of high NLR versus low NLR. These findings were confirmed upon propensity matching. Conclusions: Pretreatment NLR is an independent predictor for survival outcomes of peripheral early-stage NSCLC patients after SBRT. High NLR is associated with worse overall survival, progression-free survival, and distant metastasis. Pretreatment NLR levels should be tracked on trials for early-stage NSCLC patients.

The role of EPID in vivo dosimetry in the risk management of stereotactic lung treatments.

In this work we report our experience with the use of in vivo dosimetry (IVD) in the risk management of stereotactic lung treatments. Acommercial software based on the electronic portal imaging device (EPID) signal was used to reconstruct the actual planning target volume (PTV) dose of stereotactic lung treatments. The study was designed in two phases: i)in the observational phase, the IVD results of 41consecutive patients were reviewed and out-of-tolerance cases were studied for root cause analysis; ii)in the active phase, the IVD results of 52patients were analyzed and corrective actions were taken when needed. Moreover, proactive preventions were further introduced to reduce the risk of future failures. The error occurrence rate was analyzed to evaluate the effectiveness of proactive actions. Atotal of 330fractions were analyzed. In the first phase, 13errors were identified. In the active phase, 12errors were detected, 5of which needed corrective actions; in 4patients the actions taken corrected the error. Several preventions and barriers were introduced to reduce the risk of future failures: the planning checklist was updated, the procedure for vacuum pillows was improved, and use of the respiratory compression belt was optimized. Adecrease in the failure rate was observed, showing the effectiveness of procedural adjustment. The use of IVD allowed the quality of lung stereotactic body radiation therapy (SBRT) treatments to be improved. Patient-specific and procedural corrective actions were successfully taken as part of risk management, leading to an overall improvement in the dosimetric accuracy.

Effects of stereotactic body radiotherapy for clinical outcomes of patients with liver metastasis and hepatocellular carcinoma: A retrospective study.

This retrospective clinical study described the treatment efficacy and safety of stereotactic body radiotherapy (SBRT) for patients of hepatocellular carcinoma (HCC) and liver metastasis tumors. The therapeutic effect and prognosis of patients with liver cancer treated with stereotactic body radiation therapy (SBRT) at the Fudan University Shanghai Cancer Center (Shanghai, China) between July 2011 and December 2020 were retrospectively analyzed. Overall survival (OS), local control (LC) rates and progression-free survival (PFS) were evaluated using Kaplan-Meier analysis and the log-rank test. Local progression was defined as tumor growth after SBRT on dynamic computed tomography follow-up. Treatment-related toxicities were assessed according to the Common Terminology Criteria for Adverse Events version 4. A total of 36 patients with liver cancer were enrolled in the present study. The prescribed dosages (14 Gy in 3 fractions or 16 Gy in 3 fractions) were applied for SBRT treatments. The median follow-up time was 21.4 months. The median OS time was 20.4 [95% confidence interval (CI): 6.6-34.2] months, and the 2-year OS rates for the total population, HCC group and liver metastasis group were 47.5, 73.3 and 34.2%, respectively. The median PFS time was 17.3 (95% CI: 11.8-22.8) months and the 2-year PFS rates for the total population, HCC group and liver metastasis group were 36.3, 44.0 and 31.4%, respectively. The 2-year LC rates for the total population, HCC group and liver metastasis group were 83.4, 85.7 and 81.6%, respectively. The most common grade IV toxicity for the HCC group was liver function impairment (15.4%), followed by thrombocytopenia (7.7%). There were no grade III/IV radiation pneumonia or digestive discomfort. The present study aimed to explore a safe, effective and non-invasive treatment method for liver tumors. At the same time, the innovation of the present study is to find a safe and effective prescription dose of SBRT in the absence of consensus on guidelines.

Online verification of breath-hold reproducibility using kV-triggered imaging for liver stereotactic body radiation therapy.

To introduce a new technique for online breath-hold verification for liver stereotactic body radiation therapy (SBRT) based on kilovoltage-triggered imaging and liver dome positions. Twenty-five liver SBRT patients treated with deep inspiration breath-hold were included in this IRB-approved study. To verify the breath-hold reproducibility during treatment, a KV-triggered image was acquired at the beginning of each breath-hold. The liver dome position was visually compared with the expected upper/lower liver boundaries created by expanding/contracting the liver contour 5 mm in the superior-inferior direction. If the liver dome was within the boundaries, delivery continued; otherwise, beam was held manually, and the patient was instructed to take another breath-hold until the liver dome fell within boundaries. The liver dome was delineated on each triggered image. The mean distance between the delineated liver dome to the projected planning liver contour was defined as liver dome position error edome . The mean and maximum edome of each patient were compared between no breath-hold verification (all triggered images) and with online breath-hold verification (triggered images without beam-hold). Seven hundred thirteen breath-hold triggered images from 92 fractions were analyzed. For each patient, an average of 1.5 breath-holds (range 0-7 for all patients) resulted in beam-hold, accounting for 5% (0-18%) of all breath-holds; online breath-hold verification reduced the mean edome from 3.1 mm (1.3-6.1 mm) to 2.7 mm (1.2-5.2 mm) and the maximum edome from 8.6 mm (3.0-18.0 mm) to 6.7 mm (3.0-9.0 mm). The percentage of breath-holds with edome >5 mm was reduced from 15% (0-42%) without breath-hold verification to 11% (0-35%) with online breath-hold verification. online breath-hold verification eliminated breath-holds with edome >10 mm, which happened in 3% (0-17%) of all breath-holds. It is clinically feasible to monitor the reproducibility of each breath-hold during liver SBRT treatment using triggered images and liver dome. Online breath-hold verification improves the treatment accuracy for liver SBRT.

Evaluation of commercial devices for patient specific QA of stereotactic radiotherapy plans.

Stereotactic radiotherapy (SRT) methods have become common for the treatment of small tumors in various parts of the body. Small field dosimetry has a unique set of challenges when it comes to the pre-treatment validation of a radiotherapy plan that involves film dosimetry or high-resolution detectors. Comparison of commercial quality assurance (QA) devices to the film dosimetry method for pre-treatment evaluation of stereotactic radiosurgery (SRS), fractionated SRT, and stereotactic body radiation therapy treatment plans have been evaluated in this study. Forty stereotactic QA plans were measured using EBT-XD film, IBA Matrixx Resolution, SNC ArcCHECK, Varian aS1200 EPID, SNC SRS MapCHECK, and IBA myQA SRS. The results of the commercial devices are compared to the EBT-XD film dosimetry results for each gamma criteria. Treatment plan characteristics such as modulation factor and target volume were investigated for correlation with the passing rates. It was found that all detectors have greater than 95% passing rates at 3%/3mm. Passing rates decrease rapidly for ArcCHECK and the Matrixx as criteria became more strict. In contrast, EBT-XD film, SNC SRS MapCHECK, and IBA myQA SRS passing rates do not decline as rapidly when compared to Matrix Resolution, ArcCHECK, and the EPID. EBT-XD film, SNC SRS MapCHECK, and IBA myQA SRS maintain greater than 90% passing rate at 2%/1mm and greater than 80% at 1%/1mm. Additionally, the ability of these devices to detect changes in dose distribution due to MLC positioning errors was investigated. Ten VMAT SBRT/SRS treatment plans were created with 6MV FFF or 10MV FFF beam energies using Eclipse 15.6. A MATLAB script was used to create two MLC positioning error scenarios from the original treatment plan. It was found that errors in MLC positioning were most reliably detected at 2%/1mm for high-resolution detectors and that lower-resolution detectors did not consistently detect MLC positioning errors.

PO-01-050 STRUCTURAL CARDIAC CHANGES DETECTED BY MRI AFTER STEREOTACTIC BODY RADIOTHERAPY FOR TARGETS IN CLOSE PROXIMITY TO THE HEART

Stereotactic body radiation therapy (SBRT) has become a standard of care for inoperable early-stage non-small cell lung cancer and in case of pulmonary oligometastases. Recent studies indicate that incidental irradiation of the heart may be associated with an increased risk of non-cancer-related deaths. This study aims to assess and examine structural cardiac changes following peri- and myocardial SBRT using a systematic cardiac follow-up protocol including cardiac magnetic resonance (CMR) imaging. For 1485 patients treated with local-ablative SBRT from January 2014 to February 2022 at our institution, the distance between the planning target volume (PTV) and the heart was measured. Forty-eight out of 134 patients treated in close proximity (<2cm) to the heart were alive at follow-up. Of those, 20 were randomly invited to undergo a structured cardiac follow-up protocol including CMR. Ten patients consented to participate and underwent a structural follow-up protocol. Registration of CMR image data and the SBRT treatment plan was performed to examine a possible correlation between the dose delivered to the myocardium and structural cardiac changes assessed by CMR. Among the 10 participating patients, the most common primary tumors were non-small cell lung cancer (n=3) and small-cell lung cancer (n=2) (Table 1). Five patients presented with pre-SBRT cardiovascular comorbidities. Seven patients received SBRT for pulmonary or vertebral metastases and three patients for primary lung cancer with a median dose of 42.5 Gy (30.0-48.0 Gy) in 3-10 fractions. The mean heart dose (Dmean) and maximum heart dose (Dmax) were 4.9 Gy (0.7-8.4 Gy) and 36.2 Gy (8.3 – 64.1 Gy), respectively. On CMR, five patients showed myocardial alterations, such as late gadolinium enhancement and edema after a median follow-up time of 5.6 years (0.1-6.3 years) as shown in Figure 1. In patients with structural changes of the myocardium the median distance between the treated lesion and myocardium with 0.0 (0.0-1.08) cm vs. 1.4 (0.41-2.0) cm was significantly lower (p=0.015). Additionally, patients with structural changes on CMR showed significantly higher Dmax (135.4 Gy vs. 25.4 Gy, p=0.009), Dmean (4.4 Gy vs. 3.4 Gy, p=0.05). In this pilot study, patients treated with SBRT for pulmonary targets with PTV overlapping the heart showed structural changes of the myocardium in CMR. The presence of structural changes correlates with higher heart doses.

PO-01-026 STEREOTACTIC CARDIAC RADIOTHERAPY FOR RECURRENT VENTRICULAR TACHYCARDIA IN PRESENCE OF WIRELESS LEFT VENTRICULAR ENDOCARDIAL STIMULATION SYSTEM

Cardiac stereotactic body radiotherapy (SBRT) is a novel therapy for refractory ventricular tachycardia (VT). However, there remain knowledge gaps due to limited experience. The wireless stimulation endocardial cardiac resynchronization therapy (WiSE CRT) is a promising method of left ventricular (LV) resynchronization using a receiver electrode implanted in LV and a transmitter implanted in the intercostal space that is connected to a subcutaneous battery. The safety of cardiac SBRT in the presence of WiSE CRT has not been reported. We present a case of successful cardiac SBRT for recurrent VT from the LV apex delivered safely in a patient with WiSE CRT. N/A An 83-year-old man had a history of ischemic cardiomyopathy with LV apical infarct, LV ejection fraction 20%, NYHA Class III, underlying left bundle branch block status post CRT-D placement, severe coronary artery disease, paroxysmal atrial fibrillation, chronic kidney disease stage III, hyperlipidemia and orthostatic hypotension. He had initially presented with appropriate defibrillator discharges due to paroxysmal VT. He underwent catheter ablation of VT originating from the LV apex. The procedure was complicated by pericardial effusion requiring emergent pericardiocentesis. He was discharged on amiodarone but this had to be discontinued due to adverse effects. He had recurrence of VT and defibrillator shock and mexiletine was started. He started experiencing worsening heart failure symptoms. CRT-D interrogation revealed recurrent episodes of VT terminated by antitachycardia pacing and LV lead malfunction with high impedance and elevated capture threshold with loss of LV pacing. He underwent WiSE CRT system implant and the transvenous LV lead was turned off. Subsequently he had multiple admissions for VT storm requiring device therapies despite antiarrhythmic medication changes including sotalol and mexiletine. Therefore, he underwent cardiac SBRT targeting the LV apical substrate with 25 Gy dose delivered in a single fraction. SBRT treatment plan was created by contouring the components of the Wise CRT system and limiting dose to them <10 Gy (Figure). He has been weaned off antiarrhythmic drugs and has had no recurrent VT for 2.5 months since SBRT. Wise CRT function and battery status remained stable with no detrimental effects based on device interrogation till 2.5 months post SBRT. With careful treatment planning, cardiac SBRT can be delivered safely in the presence of WiSE CRT.

The use of a thin guide-wire for urethral definition in prostate SBRT treatments with Cyberknife.

To study and analyze the effect of the use of a thin guide-wire instead of a Foley catheter for urethral definition in prostate stereotactic body radiation therapy (SBRT) treatments and to compare treatment parameters in both situations. Thirty-seven prostate SBRT patients were employed in this study. A Foley catheter was employed in nine of them, and a guide-wire was employed in the other 28 patients. For each of the 28 patients in which the guide-wire was employed, a comparison between urethral positions in both situations was performed, allowing for a margin definition of the urethra when a Foley catheter was employed. Displacements of the prostate during treatment were obtained, allowing for an analysis of prostate positions in both situations. Also, different treatment parameters such as the number of treatment interruptions, couch movements performed, and x-rays needed were gathered. Large differences between urethral positions can be found in the anterior-posterior (AP) directions compared to those in the lateral (LAT) direction. Differences are also larger in areas closer to the base of the prostate, where margins applied in the case of using a Foley catheter are 16mm with a mean displacement of 6mm in the posterior direction. No differences in the treatment parameters were found during treatment in both situations. The difference found in absolute prostate pitch rotations suggests that the Foley catheter provokes a shift of the prostate position, which does not occur when employing the guide-wire. Foley catheters shift the urethral position, making them a wrong surrogate of the urethra when no catheters are present. The margins needed to assess uncertainties introduced by the use of a Foley catheter are larger than those usually applied. The use of a Foley catheter did not present any additional difficulty during treatment delivery in terms of images employed or interruptions produced.

Decision Regret among Patients with Early-stage Lung Cancer Undergoing Radiation Therapy or Surgical Resection

AimsClinical equipoise exists regarding early-stage lung cancer treatment among patients as trials comparing stereotactic body radiation therapy (SBRT) and surgical resection are unavailable. Given the potential differences in treatment effectiveness and side-effects, we sought to determine the associations between treatment type, decision regret and depression. Materials and methodsA multicentre, prospective study of patients with stage IA–IIA non-small cell lung cancer (NSCLC) with planned treatment with SBRT or surgical resection was conducted. Decision regret and depression were measured using the Decision Regret Scale (DRS) and Patient Health Questionnaire-4 (PHQ-4) at 3, 6 and 12 months post-treatment, respectively. Mixed linear regression modelling examined associations between treatment and decision regret adjusting for patient sociodemographics. ResultsAmong 211 study participants with early-stage lung cancer, 128 (61%) patients received SBRT and 83 (39%) received surgical resection. The mean age was 73 years (standard deviation = 8); 57% were female; 79% were White non-Hispanic. In the entire cohort at 3 months post-treatment, 72 (34%) and 57 (27%) patients had mild and severe decision regret, respectively. Among patients who received SBRT or surgery, 71% and 46% of patients experienced at least mild decision regret at 3 months, respectively. DRS scores increased at 6 months and decreased slightly at 12 months of follow-up in both groups. Higher DRS scores were associated with SBRT treatment (adjusted mean difference = 4.18, 95% confidence interval 0.82 to 7.54) and depression (adjusted mean difference = 3.49, 95% confidence interval 0.52 to 6.47). Neither patient satisfaction with their provider nor decision-making role concordance was associated with DRS scores. ConclusionsMost early-stage lung cancer patients experienced at least mild decision regret, which was associated with SBRT treatment and depression symptoms. Findings suggest patients with early-stage lung cancer may not be receiving optimal treatment decision-making support. Therefore, opportunities for improved patient–clinician communication probably exist.

Stereotactic body radiation therapy (SBRT) following Yttrium-90 (90Y) selective internal radiation therapy (SIRT): a feasibility planning study using 90Y delivered dose

Objective. 90Y selective internal radiation therapy (SIRT) treatment of hepatocellular carcinoma (HCC) can potentially underdose lesions, as identified on post-therapy PET/CT imaging. This study introduces a methodology and explores the feasibility for selectively treating SIRT-underdosed HCC lesions, or lesion subvolumes, with stereotactic body radiation therapy (SBRT) following post-SIRT dosimetry. Approach. We retrospectively analyzed post-treatment PET/CT images of 20 HCC patients after 90Y SIRT. Predicted tumor response from SIRT was quantified based on personalized post-therapy dosimetry and corresponding response models. Predicted non-responding tumor regions were then targeted with a hypothetical SBRT boost plan using a framework for selecting eligible tumors and tumor subregions. SBRT boost plans were compared to SBRT plans targeting all tumors irrespective of SIRT dose with the same prescription and organ-at-risk (OAR) objectives. The potential benefit of SIRT followed by a SBRT was evaluated based on OAR dose and predicted toxicity compared to the independent SBRT treatment. Main results. Following SIRT, 14/20 patients had at least one predicted non-responding tumor considered eligible for a SBRT boost. When comparing SBRT plans, 10/14 (71%) SBRTboost and 12/20 (60%) SBRTalone plans were within OAR dose constraints. For three patients, SBRTboost plans were within OAR constraints while SBRTalone plans were not. Across the 14 eligible patients, SBRTboost plans had significantly less dose to the healthy liver (decrease in mean dose was on average ± standard deviation, 2.09 Gy ± 1.99 Gy, ) and reduced the overall targeted PTV volume (39% ± 21%) compared with SBRTalone. Significance. A clinical methodology for treating HCC using a synergized SIRT and SBRT approach is presented, demonstrating that it could reduce normal tissue toxicity risk in a majority of our retrospectively evaluated cases. Selectively targeting SIRT underdosed HCC lesions, or lesion subvolumes, with SBRT could improve tumor control and patient outcomes post-SIRT and allow SIRT to function as a target debulking tool for cases when SBRT is not independently feasible.

Inter- and intrafraction dose variations in robotic stereotactic body radiation therapy (SBRT) for perihilar cholangiocarcinoma in the prospective phase I STRONG trial.

Using fiducial-marker-based robotic respiratory tumor tracking, we treated perihilar cholangiocarcinoma patients in the STRONG trial with 15 daily fractions of 4 Gy. For each of the included patients, in-room diagnostic-quality repeat CTs (rCT) were acquired pre- and post-dose delivery in 6 treatment fractions to analyze inter- and intrafraction dose variations. Planning CTs (pCTs) and rCTs were acquired in expiration breath-hold. Analogous to treatment, spine and fiducials were used to register rCTs with pCTs. In each rCT, all OARs were contoured, and the target was rigidly copied from the pCT based on grey values. The rCTs acquired were used to calculate the doses to be delivered through the treatment-unit settings. On average, target doses in rCTs and pCTs were similar. However, due to target displacements relative to the fiducials in rCTs, 10% of the rCTs showed PTV coverage losses of >10%. Although target coverages had been planned below desired values in order to protect OARs, many pre-rCTs contained OAR constraint violations: 44.4% for the 6 major constraints. Most OAR dose differences between pre- and post-rCTs were not statistically significant. The dose deviations observed in repeat CTs represent opportunities for more advanced adaptive approaches to enhancing SBRT treatment quality.

Evaluation of deep learning based implanted fiducial markers tracking in pancreatic cancer patients

Real-time target position verification during pancreas stereotactic body radiation therapy (SBRT) is important for the detection of unplanned tumour motions. Fast and accurate fiducial marker segmentation is a Requirement of real-time marker-based verification. Deep learning (DL) segmentation techniques are ideal because they don’t require additional learning imaging or prior marker information (e.g., shape, orientation). In this study, we evaluated three DL frameworks for marker tracking applied to pancreatic cancer patient data. The DL frameworks evaluated were (1) a convolutional neural network (CNN) classifier with sliding window, (2) a pretrained you-only-look-once (YOLO) version-4 architecture, and (3) a hybrid CNN-YOLO. Intrafraction kV images collected during pancreas SBRT treatments were used as training data (44 fractions, 2017 frames). All patients had 1-4 implanted fiducial markers. Each model was evaluated on unseen kV images (42 fractions, 2517 frames). The ground truth was calculated from manual segmentation and triangulation of markers in orthogonal paired kV/MV images. The sensitivity, specificity, and area under the precision-recall curve (AUC) were calculated. In addition, the mean-absolute-error (MAE), root-mean-square-error (RMSE) and standard-error-of-mean (SEM) were calculated for the centroid of the markers predicted by the models, relative to the ground truth. The sensitivity and specificity of the CNN model were 99.41% and 99.69%, respectively. The AUC was 0.9998. The average precision of the YOLO model for different values of recall was 96.49%. The MAE of the three models in the left-right, superior-inferior, and anterior-posterior directions were under 0.88 ± 0.11 mm, and the RMSE were under 1.09 ± 0.12 mm. The detection times per frame on a GPU were 48.3, 22.9, and 17.1 milliseconds for the CNN, YOLO, and CNN-YOLO, respectively. The results demonstrate submillimeter accuracy of marker position predicted by DL models compared to the ground truth. The marker detection time was fast enough to meet the requirements for real-time application.

Precise dosimetric comparison between GAMOS and the collapsed cone convolution algorithm of 4D DOSE accumulated in lung SBRT treatments

BackgroundIt is widely accepted that Monte Carlo dose calculations offers a higher precision that the commercially available dose calculation algorithms. This advantage may be especially relevant for lung Stereotactic Body Radiation Therapy (SBRT), as this is a precise technique applied to an area of big inhomogeneity. PurposeWe conducted a comparative study to reveal the differences between the doses calculated using the Collapsed Cone Convolution algorithm and the GAMOS/Geant4 Monte Carlo calculation for lung cancer patients treated with Stereotactic Body Radiation Therapy on an Elekta Versa HD linac. MethodsFor this study a set of ten patient treatments carried out at the Clínica Universidad de Navarra was selected. Theanalysis is based on the comparison of several dosimetric quantities for the Gross Tumor Volume (GTV) and several OrgansAt Risk (OARs), and also a gamma index calculation with distance-to-agreement set to 2 mm and dose difference to 3%, as recommended by ICRU to assess clinical impact. In order to guarantee a small uncertainty in the Monte Carlo calculation of the dosimetric quantities, we studied in detail the validity of different methods that may be used to determine this uncertainty.To compensate for lung movements, a 4D-Cone-beam Computed Tomography (CBCT) was acquired before treatment, whichallowed us to identify eight respiratory phases using a temporal binning. Using commercial MIM software®, we performed a deformable image registration between the eight CT respiration phases to construct the 4D doses. The same procedure was applied for the Treatment Planning System (TPS) dose files and for the Monte Carlo dose files. ResultsThe differences between the two algorithms reveal the known weaknesses of the Collapsed Cone Convolution (CCC) algorithm for the calculation of lateral doses and in regions of large density change. The comparison between the two algorithms for individual phase doses shows differences up to 5% of the GTV D95 or 3–4 Gy in some OARs, which may have a clinical impact. Nevertheless these differences are reduced for the 4D dose in most quantities under study. ConclusionsComparing the dose calculated with a Collapsed Cone Convolution algorithm with GAMOS/Geant4 for ten patients and eight respiratory phases, we found some differences that could have a clinical impact. When combining the eight temporal phases into a 4D dose using the MIM Deformable Image Registration software, the differences diminished substantially.Our statistical analysis concludes that dose uncertainty in the voxels with a maximum dose below a given percentage guarantees uncertainty in the dosimetric quantities below that figure.

Plan quality analysis of stereotactic ablative body radiotherapy treatment planning in liver tumor.

Stereotactic ablative body radiotherapy (SABR) in the liver, RTOG-1112 guides the treatment modalities including the dose constraints for this technique but not the plan parameters. This study is not only analyzing the plan quality by utilizing the plan parameters and indexes but also compares treatment modalities from the protocol implementation. Twenty-five patients treated in the period from February 2020 to September 2022 were recruited in this analysis. Two planners randomly selected the patients and modalities. The modalities employed were Volumetric-Modulated Arc Therapy (VMAT) and Helical Tomotherapy (HT). Various parameters and indexes were used to access not only the plan quality but also to compare each modality. The parameters and indexes studied were the homogeneity index (HI), conformity index (CI), gradient distance (GD), and the dose received by the organs at risk. The data reveals that the mean volume of PTV is 60.8±53.9 cc where these targets exhibit no significant difference between each modality. The HI shows a consistent value for both modalities. Between each modality, the CI value shows less deviation, but the HT shows slightly higher performance than VMAT. The value of GD is 1.5±0.3cm where the HT provides a shorter distance compared to VMAT as well. The parameters and indexes should be utilized for the plan evaluation although in the guidelines this was not required. Various modalities were employed for treatment. Both can achieve the treatment criteria with slightly low performance of VMAT.

The effect of integrating knowledge-based planning with multicriteria optimization in treatment planning for prostate SBRT.

Knowledge-based planning (KBP) and multicriteria optimization (MCO) are two powerful tools to assist treatment planners in achieving optimal target coverage and organ-at-risk (OAR) sparing. The purpose of this work is to investigate if integrating MCO with conventional KBP can further improve treatment plan quality for prostate cancer stereotactic body radiation therapy (SBRT). A two-phase study was designed to investigate the impact of MCO and KBP in prostate SBRT treatment planning. The first phase involved the creation of a KBP model based on thirty clinical SBRT plans, generated by manual optimization (KBP_M). A ten-patient validation cohort was used to compare manual, MCO, and KBP_M optimization techniques. The next phase involved replanning the original model cohort with additional tradeoff optimization via MCO to create a second model, KBP_MCO. Plans were then generated using linear integration (KBP_M+MCO), non-linear integration (KBP_MCO), and a combination of integration methods (KBP_MCO+MCO). All plans were analyzed for planning target volume (PTV) coverage, OAR constraints, and plan quality metrics. Comparisons were generated to evaluate plan and model quality. Phase 1 highlighted the necessity of KBP and MCO in treatment planning, as both optimization methods improved plan quality metrics (Conformity and Heterogeneity Indices) and reduced mean rectal dose by 2Gy, as compared to manual planning. Integrating MCO with KBP did not further improve plan quality, as little significance was seen over KBP or MCO alone. Principal component score (PCS) fitting showed KBP_MCO improved bladder and rectum estimated and modeled dose correlation by 5% and 22%, respectively; however, model improvements did not significantly impact plan quality. KBP and MCO have shown to reduce OAR dose while maintaining desired PTV coverage in this study. Further integration of KBP and MCO did not show marked improvements in treatment plan quality while requiring increased time in model generation and optimization time.

Clinical Outcome in Patients With Early-Stage Small Cell Lung Cancer Treated With Surgery or Radiation in the Absence of Prophylactic Cranial Irradiation: A Single-Center Retrospective Study

As screening chest computed tomography for patients at high risk for cancer has become more widely accepted, increasing numbers of patients with early-stage small cell lung cancer (SCLC) are being diagnosed. Although surgery is an accepted option for patients with early-stage SCLC, for patients who decline or cannot undergo surgery, stereotactic body radiation treatment (SBRT) is an alternative. Although prophylactic cranial irradiation (PCI) improves survival in patients with limited-stage SCLC, PCI for early-stage SCLC (stage T1-T2) has not been explored. This study defines survival and recurrence patterns in patients with early-stage SCLC who were treated with surgery or SBRT in the absence of PCI. In this single-institution retrospective study, 14 patients diagnosed with early-stage SCLC (stage T1-T2) between July 2015 and May 2021 at a single tertiary care hospital were treated with SBRT or surgery with no PCI. Primary outcomes were locoregional cancer recurrence, distant recurrence, recurrence-free survival, and overall survival. The secondary outcome was development of brain metastasis. Analyses included Cox regression, Kaplan-Meier survival, and log-rank tests. A total of 14 patients (5 women and 9 men) were included in the study: 9 with stage T1 and 5 with stage T2 SCLC. Six patients (43%) received SBRT and 8 (57%) had surgical treatment. All patients except 1 received adjuvant chemotherapy. Median follow-up was 14.3 months (range, 2.4-64.4 months), and the median age at diagnosis was 71.5 years (range, 54-81 years). Cox regression and log-rank tests showed no significant differences in any outcomes between the surgery and SBRT groups, and no patients developed brain metastases during the study period. Data are lacking regarding the benefit of PCI in early-stage SCLC. Although the sample size in this study was too small to draw any conclusions, the findings add to the ongoing dialogue regarding the importance of PCI in this patient population. No difference was identified in survival and cancer recurrence in patients who received either surgery or SBRT in the absence of PCI.

Dose Escalation for Pancreas SBRT: Potential and Limitations of using Daily Online Adaptive Radiation Therapy and an Iterative Isotoxicity Automated Planning Approach

To determine the dosimetric limitations of daily online adaptive pancreas stereotactic body radiation treatment by using an automated dose escalation approach. We collected 108 planning and daily computed tomography (CT) scans from 18 patients (18 patients×6 CT scans) who received 5-fraction pancreas stereotactic body radiation treatment at MD Anderson Cancer Center. Dose metrics from the original non-dose-escalated clinical plan (non-DE), the dose-escalated plan created on the original planning CT (DE-ORI), and the dose-escalated plan created on daily adaptive radiation therapy CT (DE-ART) were analyzed. We developed a dose-escalation planning algorithm within the radiation treatment planning system to automate the dose-escalation planning process for efficiency and consistency. In this algorithm, the prescription dose of the dose-escalation plan was escalated before violating any organ-at-risk (OAR) dose constraint. Dose metrics for 3 targets (gross target volume [GTV], tumor vessel interface [TVI], and dose-escalated planning target volume [DE-PTV]) and 9 OARs (duodenum, large bowel, small bowel, stomach, spinal cord, kidneys, liver, and skin) for the 3 plans were compared. Furthermore, we evaluated the effectiveness of the online adaptive dose-escalation planning process by quantifying the effect of the interfractional dose distribution variations among the DE-ART plans. The median D95% dose to the GTV/TVI/DE-PTV was 33.1/36.2/32.4 Gy, 48.5/50.9/40.4 Gy, and 53.7/58.2/44.8 Gy for non-DE, DE-ORI, and DE-ART, respectively. Most OAR dose constraints were not violated for the non-DE and DE-ART plans, while OAR constraints were violated for the majority of the DE-ORI patients due to interfractional motion and lack of adaptation. The maximum difference per fraction in D95%, due to interfractional motion, was 2.5 ± 2.7 Gy, 3.0 ± 2.9 Gy, and 2.0 ± 1.8 Gy for the TVI, GTV, and DE-PTV, respectively. Most patients require daily adaptation of the radiation planning process to maximally escalate delivered dose to the pancreatic tumor without exceeding OAR constraints. Using our automated approach, patients can receive higher target dose than standard of care without violating OAR constraints.

Mitigation of Intensity Modulated Radiation Therapy and Stereotactic Body Radiation Therapy Treatment Planning Errors on the Novel RefleXion X1 System Using Failure Mode and Effect Analysis Within Six Sigma Framework

The aim of this study was to apply the Six Sigma methodology and failure mode and effect analysis (FMEA) to mitigate errors in intensity modulated radiation therapy (IMRT) and stereotactic body radiation therapy (SBRT) treatment planning with the first clinical installation of RefleXion X1. The Six Sigma approach consisted of 5 phases: define, measure, analyze, improve, and control. The define, measure, and analyze phases consisted of process mapping and an FMEA of IMRT and SBRT treatment planning on the X1. The multidisciplinary team outlined the workflow process and identified and ranked the failure modes associated with the plan check items using the American Association of Physicists in Medicine Task Group 100 recommendations. Items with the highest average risk priority numbers (RPNs) and severity ≥7 were prioritized for automation using the Eclipse Scripting Application Programming Interface (ESAPI). The "improve" phase consisted of developing ESAPI scripts before the clinical launch of X1 to improve efficiency and safety. In the "control" phase, the FMEA ranking was re-evaluated 1 year after clinical launch. Overall, 100 plan check items were identified in which the RPN values ranged from 10.2 to 429.0. Fifty of these items (50%) were suitable for automation within ESAPI. Of the 10 highest-risk items, 8 were suitable for automation. Based on the results of the FMEA, 2 scripts were developed: Planning Assistant, used by the planner during preparation for planning, and Automated Plan Check, used by the planner and the plan checker during plan preparation for treatment. After 12 months of clinical use of the X1 and developed scripts, only 3 errors were reported. The average prescript RPN was 138.0, compared with the average postscript RPN of 47.8 (P < .05), signifying a safer process. Implementing new technology in the clinic can be an error-prone process in which the likelihood of errors increases with increasing pressure to implement the technology quickly. To limit errors in clinical implementation of the novel RefleXion X1 system, the Six Sigma method was used to identify failure modes, establish quality control checks, and re-evaluate these checks 1 year after clinical implementation.