Intrafraction tumor motion during deep inspiration breath hold pancreatic cancer treatment

A systematic review of tumour position reproducibility and stability in breath-hold for radiation therapy of the upper abdomen

Background and purpose

Upper abdominal malignancies are relatively rare, and although surgery is considered the primary treatment option, radiation therapy has an emerging role in the management of liver, pancreas, kidney and adrenal gland tumours. Furthermore, stereotactic radiation therapy for the management of upper abdominal metastases is an expanding clinical indication. Breath-hold is one respiratory motion management strategy used in upper abdominal radiation therapy, and the reproducibility, and stability of breath-hold is critical for overall treatment accuracy.

Materials and methods

A systematic review of the literature was conducted in Medline, Embase and Cochrane databases with keyword and vocabulary terms related to radiation therapy, breath-hold and upper abdominal tumours.

Results

Following screening against the selection criteria, 41 studies were included. Breath-hold reproducibility was the most commonly reported outcome and exhale breath-hold was the most common type. Studies were either prospective or retrospective cohort studies, and the mean sample size was 19 participants. The risk of bias of each included study was assessed, and the mean quality assessment score for included studies was 90 % (77-100 %). Median exhale breath-hold cranio-caudal inter-fraction reproducibility was 0.6 mm, (IQR 0.3-1.6 mm), compared to inspiratory breath-hold 0.0 mm (IQR -0.6-2.97 mm). Stability measurements were ≤3 mm in 71 % of studies, irrespective of breath-hold type.

Discussion

Formulating institutional protocols for best clinical practice regarding breath-hold for upper abdominal tumours is challenging, given the significant variation in practices, interventions and definitions observed in the literature. Further investigation to individualise breath-hold strategies and safety margins is warranted.

Dose-Escalated SBRT for Borderline and Locally Advanced Pancreatic Cancer: Resectability Rate and Pathological Results of a Multicenter Prospective Study

OBJECTIVE

We demonstrated for the first time the safety and feasibility of escalating up to 55 Gy/11 Gy/fr/5fr in borderline (BRPC)/unresectable locally advanced pancreatic cancer (LAPC), using the standard LINAC platform. The aim of the present study is to assess for the first time the impact of this high-dose neoadjuvant stereotactic ablative radiotherapy (SABRT) protocol on tumor resectability and pathological responses.

MATERIALS/METHODS

From June 2017 to December 2022, patients with BRPC/LAPC were treated with neoadjuvant chemotherapy (ChT) and SABRT-escalated doses of SIB at 45 Gy, 50 Gy, and up to 55 Gy (BED ≥ 100). Radiological evaluation was conducted with a CT scan 6-8 weeks post-treatment to determine resectability status based on established criteria (SAR/APA2014). Surgical decisions were made by the multidisciplinary tumor board of the participating institutions. Pathological assessments post-surgery used criteria from the College of American Pathologists (CAP), categorizing resection status as R0 (negative margins), R1 (microscopic tumor margins), and R2 (macroscopic tumor margins). Tumor response was evaluated with the Tumor Response Scoring (TRS) system, as G0 (no viable cancer cells), G1 (single cells or rare small groups), G2 (residual cancer with evident regression), and G3 (extensive residual cancer).

RESULTS

Thirty-three patients (p) were included: 39.4% (13p) BRPC/60.6% (20p) LAPC. After ChT-SABRT, 45.5% (15p) were considered resectable, with 11/13 (84.6%) BRPC and 4/20 (20%) LAPC (p < 0.0001). One patient refused surgery and other patient died of COVID sepsis. Two more patients had disseminated disease at surgery. Among the 11 patients who underwent full surgery, all patients achieved either clean margins R0: 72.7% (8p) or microscopic affected margins R1: 27.3% (3p). TRS scores were G1: 27.3% (3p), G2: 54.5% (6p), and G3: 18.2% (2p). The present follow-up (FUP) was closed on 1 November 2024 (23.55 months, range: 6-71 months). The mean freedom from local progression as the first cause of disease failure was 43.30 ± 3.09 (37.23-49.38), and the median was not reached. The actuarial 1- and 2-year rates for freedom from local relapse as a first cause of disease failure were 92.3% (87.7-93.3%) and 79.7% (79.7-87.7%), respectively.

CONCLUSIONS

Neoadjuvant ChT-SABRT in LAPC improves resectability rates and induces relevant tumor regression. These promising findings should be validated by larger sample sizes and extended follow-up.

A systematic review of the impact of abdominal compression and breath-hold techniques on motion, inter-fraction set-up errors, and intra-fraction errors in patients with hepatobiliary and pancreatic malignancies

BACKGROUND AND PURPOSE

Reducing motion is vital when radiotherapy is used to treat patients with hepatobiliary (HPB) and pancreatic malignancies. Abdominal compression (AC) and breath-hold (BH) techniques aim to minimise respiratory motion, yet their adoption remains limited, and practices vary. This review examines the impact of AC and BH on motion, set-up errors, and patient tolerability in HPB and pancreatic patients.

MATERIALS AND METHODS

This systematic review, conducted using PRISMA and PICOS criteria, includes publications from January 2015 to February 2023. Eligible studies focused on AC and BH interventions in adults with HPB and pancreatic malignancies. Endpoints examined motion, set-up errors, intra-fraction errors, and patient tolerability. Due to study heterogeneity, Synthesis Without Meta-Analysis was used, and a 5 mm threshold assessed the impact of motion mitigation.

RESULTS

In forty studies, 14 explored AC and 26 BH, with 20 on HPB, 13 on pancreatic, and 7 on mixed cohorts. Six studied pre-treatment, 22 inter/intra-fraction errors, and 12 both. Six AC pre-treatment studies showed > 5 mm motion, and 4 BH and 2 AC studies reported > 5 mm inter-fraction errors. Compression studies commonly investigated the arch and belt, and DIBH was the predominant BH technique. No studies compared AC and BH. There was variation in the techniques, and several studies did not follow standardised error reporting. Patient experience and tolerability were under-reported.

CONCLUSION

The results indicate that AC effectively reduces motion, but its effectiveness may vary between patients. BH can immobilise motion; however, it can be inconsistent between fractions. The review underscores the need for larger, standardised studies and emphasizes the importance of considering the patient's perspective for tailored treatments.

Dose-escalated SBRT for borderline and locally advanced pancreatic cancer. Feasibility, safety and preliminary clinical results of a multicenter study

Background

Pancreatic Stereotactic Body Radiotherapy (SBRT) allows for the administration of a higher biologically effective doses (BED), that would be essential to achieve durable tumor control. Escalating treatment doses need a very accurate tumor positioning and motion control during radiotherapy.The aim of this study to assess the feasibility and safety of a Simultaneous Integrated Boost (SIB) dose-escalated protocol at 45 Gy, 50 Gy and 55 Gy in 5 consecutive daily fractions, in Border Line Resectable Pancreatic Cancer (BRCP) /Locally Advanced Pancreatic Cancer (LAPC) by means of a standard LINAC platform.

Methods

Patients diagnosed of BRPC/LAPC, candidates for neoadjuvant chemotherapy and SBRT, in four university hospitals of the province of Las Palmas (Canary Islands, Spain) were included in this prospective study. Radiotherapy was administered using standard technology (LINACS) with advanced positioning (Lipiodol® and metallic stent used as fiducial markers) and tumor motion control (4D, DBH, Calypso®). There were 3 planned dose-escalated SIB groups, 45 Gy/5f (9 patients) 50 Gy/5f (9 + 9 patients) and 55 Gy/5f (9 patients). The defined primary end points of the study were the safety and feasibility of the proposed treatment protocol. Secondary endpoints included radiological tumor response after SBRT, local control and survival.

Results

From June 2017 to December 2022, sixty-two patients were initially assessed for eligibility in the study in the four participating centers, and 49 were candidates for chemotherapy (CHT). Forty-one were referred to radiotherapy after CHT and 33 finally were treated by escalated-dose SIB, 45 Gy (9 patients) 50 Gy (16 patients), 55 Gy(8 patients). All patients completed the scheduled treatment and no acute or late severe (≥grade3) gastrointestinal toxicity was observed.Local response was analyzed by CT/MRI two months after the end of SBRT. Ten patients (31,25 %) achieved objective response (2/9:45 Gy, 5/15:50 Gy, 3/8:55 Gy). Follow-up was closed as July 2023. Freedom from local progression at 1-2y were 89,3% (95 %CI:83,4-95,2%) and 66 % (95 %CI:54,6-77,4%) respectively. The 1-2y survival rates were 95,7% (95 %CI:91,4-100 % and 48,6% (95 %CI:37,7-59,5%) respectively.

Conclusion

These promising results should be confirmed by further studies with larger sample size and extended follow-up period.

Deep inspiration breath hold real-time tumor-tracking radiation therapy (DBRT) as a novel stereotactic body radiation therapy approach for lung tumors

Radiotherapy with deep inspiration breath hold (DIBH) reduces doses to the lungs and organs at risk. The stability of breath holding and reproducibility of tumor location are higher during expiration than during inspiration; therefore, we developed an irradiation method combining DIBH and real-time tumor-tracking radiotherapy (RTRT) (DBRT). Nine patients were enrolled in this study. Fiducial markers were placed near tumors using bronchoscopy. Treatment planning computed tomography (CT) was performed thrice during DIBH, assisted by spirometer-based device. Each CT scan was fused using fiducial markers. Gross tumor volume (GTV) was contoured for each dataset and summed to create GTVsum; adding a 5-mm margin around GTVsum generated the planning target volume. The prescribed dose was mainly 42 Gy in four fractions. The treatment plan was created using DIBH CT (DBRT-plan), with a similar treatment plan created for expiratory CT for cases for which DBRT could not be performed (conv-plan). Vx defined as the volume of the lung received x Gy, and the mean lung dose, V20, V10, and V5 were evaluated. DBRT was completed in all patients. Mean dose, V20, and V10 were significantly lower in the DBRT-plan than in the conv-plan (all p = 0.003). Mean rates of decrease for mean dose, V20, and V10 were 14.0%, 27.6%, and 19.1%, respectively. No significant difference was observed in V5. We developed DBRT, a stereotactic body radiation therapy performed with the DIBH technique; it combines a spirometer-based breath-hold support system with an RTRT system. All patients who underwent DBRT completed the procedure without any technical or mechanical complications. This is a promising methodology that may significantly reduce lung doses.

Comparison of baseline drifts using three reflector blocks versus using a single reflector block for the calibration of wall-mounted Respiratory Gating for Scanner (RGSC) camera integrated with a CT

BACKGROUND

The calibration of the Respiratory Gating for SCanner (RGSC) system is critical to achieve better and more stable accuracy. The current procedure for a wall-mounted RGSC system has a relatively large residual error.

PURPOSE

To compare the baseline drifts in the image acquisition of DIBH using three reflector blocks versus using a single reflector block in the calibration of a wall-mounted RGSC camera system.

MATERIALS AND METHODS

Varian provides a calibration plate with three rows of calibration points: each row is separated by 15 cm longitudinally and by 10 cm laterally. In Varian's single-block calibration method, the reflector block was first placed on the center point of the calibration plate and aligned with the scanner isocenter. The calibration took a picture of the block, then placed the block on the other eight points sequentially. In the proposed three-block method, we placed three reflector blocks on the center row, with the center block aligned with the isocenter, and we took a picture of the center block by manually blocking the other two blocks in calibration. By moving the couch longitudinally in or out 15 cm, the calibration goes through all nine points. Monte Carlo simulation was done using Matlab to analyze the calibration matrix eigenvalue characteristics.

RESULTS

For a typical scan length of 40 cm of DIBH, the residual baseline drift in simulated DIBH is 0.02 ± 0.03  versus 0.30 ± 0.12 cm for three-block calibration and single-block calibration, respectively. To achieve 0.5 mm tolerance for the eigenvalue, the laser and reflector box should be within ±3 mm uncertainties based on the eigenvalue simulation.

CONCLUSION

Three-block calibration method effectively removes baseline drift caused by couch movement in DIBH/4D CT scan for the wall-mounted camera while the single-block calibration method still has significant residual baseline drift.

Comparison of setup accuracy of optical surface image versus orthogonal x-ray images for VMAT of the left breast using deep-inspiration breath-hold

To compare the setup accuracy of optical surface image (OSI) versus orthogonal x-ray images (2DkV) using cone beam computed tomography (CBCT) as ground truth for radiotherapy of left breast cancer in deep-inspiration breath-hold (DIBH). Ten left breast DIBH patients treated with volumetric modulated arc therapy (VMAT) were studied retrospectively. OSI, 2DkV, and CBCT were acquired weekly at treatment setup. OSI, 2DkV, and CBCT were registered to planning CT or planning DRR based on a breast surface region of interest (ROI), bony anatomy (chestwall and sternum), and both bony anatomy and breast surface, respectively. These registrations provided couch shifts for each imaging system. The setup errors, or the difference in couch shifts between OSI and CBCT were compared to those between 2DkV and CBCT. A second OSI was acquired during last beam delivery to evaluate intrafraction motion. The median absolute setup errors were (0.21, 0.27, 0.23 cm, 0.6°, 1.3°, 1.0°) for OSI, and (0.26, 0.24, 0.18 cm, 0.9°, 1.0°, 0.6°) for 2DkV in vertical, longitudinal and lateral translations, and in rotation, roll and pitch, respectively. None of the setup errors was significantly different between OSI and 2DkV. For both systems, the systematic and random setup errors were ≤0.6 cm and ≤1.5° in all directions. Nevertheless, larger setup errors were observed in some sessions in both systems. There was no correlation between OSI and CBCT whereas there was modest correlation between 2DkV and CBCT. The intrafraction motion in DIBH detected by OSI was small with median absolute translations <0.2 cm, and rotations ≤0.4°. Though OSI showed comparable and small setup errors as 2DkV, it showed no correlation with CBCT. We concluded that to achieve accurate setup for both bony anatomy and breast surface, daily 2DkV can't be omitted following OSI for left breast patients treated with DIBH VMAT.

Surface-Guided Radiotherapy: Can We Move on from the Era of Three-Point Markers to the New Era of Thousands of Points?

The surface-guided radiotherapy (SGRT) technique improves patient positioning with submillimeter accuracy compared with the conventional positioning technique of lasers using three-point tattoos. SGRT provides solutions to considerations that arise from the conventional setup technique, such as variability in tattoo position and the psychological impact of the tattoos. Moreover, SGRT provides monitoring of intrafractional motion.

PURPOSE

This literature review covers the basics of SGRT systems and examines whether SGRT can replace the traditional positioning technique. In addition, it investigates SGRT's potential in reducing positioning times, factors affecting SGRT accuracy, the effectiveness of live monitoring, and the impact on patient dosage.

MATERIALS AND METHODS

This study focused on papers published from 2016 onward that compared SGRT with the traditional positioning technique and investigated factors affecting SGRT accuracy and effectiveness.

RESULTS/CONCLUSIONS

SGRT provides the same or better results regarding patient positioning. The implementation of SGRT can reduce overall treatment time. It is an effective technique for detecting intrafraction patient motion, improving treatment accuracy and precision, and creating a safe and comfortable environment for the patient during treatment.

Dosimetry impact of distinct gating strategies in cine MR image-guided breath-hold pancreatic cancer radiotherapy

PURPOSE

To investigate the dosimetry effects of different gating strategies in cine magnetic resonance imaging (MRI)-guided breath-hold pancreatic cancer radiotherapy.

METHODS

Two cine MRI-based gating strategies were investigated： a tumor contour-based gating strategy at a gating threshold of 0-5% and a tumor displacement-based gating strategy at a gating threshold of 3-5 mm. The cine MRI videos were obtained from 17 pancreatic cancer patients who received MRI-guided radiation therapy. We calculated the tumor displacement in each cine MR frame that satisfied the gating threshold and obtained the proportion of frames with different displacements. We generated IMRT and VMAT plans using a 33 Gy prescription, and motion plans were generated by adding up all isocenter-shift plans corresponding to different tumor displacements. The dose parameters of GTV, PTV, and organs at risk (OAR) were compared between the original and motion plans.

RESULTS

In both gating strategies, the difference was significant in PTV coverage but not in GTV coverage between the original and motion plans. OAR dose parameters deteriorate with increasing gating threshold. The beam duty cycle increased from 19.5±14.3% (median 18.0%) to 60.8±15.6% (61.1%) for gating thresholds from 0% to 5% in tumor contour-based gating and from 51.7±11.5% (49.7%) to 67.3±12.4% (67.1%) for gating thresholds from 3 to 5 mm in tumor displacement-based gating.

CONCLUSION

In tumor contour-based gating strategy, the dose delivery accuracy deteriorates while the dose delivery efficiency improves with increasing gating thresholds. To ensure treatment efficiency, the gating threshold might be no less than 3%. A threshold up to 5% may be acceptable in terms of the GTV coverage. The displacement-based gating strategy may serve as a potential alternative to the tumor contour based gating strategy, in which the gating threshold of approximately 4 mm might be a good choice for reasonably balancing the dose delivery accuracy and efficiency.

ESTRO-ACROP guideline: Recommendations on implementation of breath-hold techniques in radiotherapy

The use of breath-hold techniques in radiotherapy, such as deep-inspiration breath hold, is increasing although guidelines for clinical implementation are lacking. In these recommendations, we aim to provide an overview of available technical solutions and guidance for best practice in the implementation phase. We will discuss specific challenges in different tumour sites including factors such as staff training and patient coaching, accuracy, and reproducibility. In addition, we aim to highlight the need for further research in specific patient groups. This report also reviews considerations for equipment, staff training and patient coaching, as well as image guidance for breath-hold treatments. Dedicated sections for specific indications, namely breast cancer, thoracic and abdominal tumours are also included.

Evaluation of the four-dimensional motion of lung tumors during end-exhalation breath-hold conditions using volumetric cine computed tomography images

BACKGROUND AND PURPOSE

This study was performed to evaluate the four-dimensional motion of lung tumors during end-exhalation (EE) breath-holding (BH) using cine computed tomography (CT) and investigate the correlation between tumor and surrogate marker motions.

MATERIALS AND METHODS

This study included 28 patients who underwent stereotactic body radiation therapy at our institution and were capable of 15-20 s of EE BH within a ±1.5-mm gating window with external markers. During EE BH with cine CT, 21 s of continuous data were acquired using 320-row multislice CT. Displacements in the tumor position during EE BH were assessed in the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions. Pearson's correlation coefficient (r) between tumor motions during EE BH and diaphragm/external marker motions was also determined.

RESULTS

The mean absolute maximum displacements of the tumor position during EE BH were 1.3 (range: 0.2-4.0), 1.9 (range: 0.3-12.0), and 1.3 (range: 0.1-7.2) mm in the LR, AP, and SI directions, respectively. The displacement of the tumor position in the AP direction was weakly correlated (|r| < 0.4) with the external marker and diaphragm displacements in many cases (proportions of 50% and 46%, respectively).

CONCLUSION

We found some cases showing substantial displacement in lung tumor positions during EE BH, especially in the AP direction. Because these tumor position displacements did not correlate with surrogate markers and were difficult to detect, we recommend pretreatment evaluation of the four-dimensional motions of tumors during BH using cine CT.

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

Purpose

To determine the dosimetric limitations of daily online adaptive pancreas stereotactic body radiation treatment by using an automated dose escalation approach.

Methods and Materials

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.

Results

The median D_95% 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 D_95%, 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.

Conclusions

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.

Implementation of triggered kilovoltage imaging for stereotactic radiotherapy of the spine for patients with spinal fixation hardware

Background and purpose

Mitigation of intrafraction motion (IM) is valuable in stereotactic radiotherapy (SRT) radiotherapy where submillimeter accuracy is desired. The purpose of this study was to investigate the application of triggered kilovoltage (kV) imaging for spine SRT patients with hardware by correlating kV imaging with patient motion and summarizing implications of tolerance for IM based on calculated dose.

Materials and methods

Ten plans (33 fractions) were studied, correlating kV imaging during treatment with pre- and post-treatment cone beam computed tomography (CBCT). Images were taken at 20-degree gantry angle intervals during the arc-based treatment. The contour of the hardware with a 1 mm expansion was displayed at the treatment console to manually pause treatment delivery if the hardware was visually detected outside the contour. The treatment CBCTs were compared using retrospective image registration to assess the validity of contour-based method for pausing treatment. Finally, plans were generated to estimate dose volume objective differences in case of 1 mm deviation.

Results

When kV imaging during treatment was used with the 1 mm contour, 100 % of the post-treatment CBCTs reported consistent results. One patient in the cohort exhibited motion greater than 1 mm during treatment which allowed intervention and re-setup during treatment. The average translational motion was 0.35 mm. Treatment plan comparison at 1 mm deviation showed little differences in calculated dose for the target and cord.

Conclusions

Utilizing kV imaging during treatment is an effective method of assessing IM for SRT spine patients with hardware without increasing treatment time.

Dosimetric impact of intrafraction motion under abdominal compression during MR-guided SBRT for (Peri-) pancreatic tumors

Objective. Intrafraction motion is a major concern for the safety and effectiveness of high dose stereotactic body radiotherapy (SBRT) in the upper abdomen. In this study, the impact of the intrafraction motion on the delivered dose was assessed in a patient group that underwent MR-guided radiotherapy for upper abdominal malignancies with an abdominal corset. Approach. Fast online 2D cine MRI was used to extract tumor motion during beam-on time. These tumor motion profiles were combined with linac log files to reconstruct the delivered dose in 89 fractions of MR-guided SBRT in twenty patients. Aside the measured tumor motion, motion profiles were also simulated for a wide range of respiratory amplitudes and drifts, and their subsequent dosimetric impact was calculated in every fraction. Main results. The average (SD) D 99% of the gross tumor volume (GTV), relative to the planned D 99%, was 0.98 (0.03). The average (SD) relative D 0.5cc of the duodenum, small bowel and stomach was 0.99 (0.03), 1.00 (0.03), and 0.97 (0.05), respectively. No correlation of respiratory amplitude with dosimetric impact was observed. Fractions with larger baseline drifts generally led to a larger uncertainty of dosimetric impact on the GTV and organs at risk (OAR). The simulations yielded that the delivered dose is highly dependent on the direction of on baseline drift. Especially in anatomies where the OARs are closely abutting the GTV, even modest LR or AP drifts can lead to substantial deviations from the planned dose. Significance. The vast majority of the fractions was only modestly impacted by intrafraction motion, increasing our confidence that MR-guided SBRT with abdominal compression can be safely executed for patients with abdominal tumors, without the use of gating or tracking strategies.

Reproducibility of chestwall and heart position using surface-guided versus RPM-guided DIBH radiotherapy for left breast cancer

This study compared the reproducibility of chestwall and heart position using surface-guided versus RPM (real-time position management)-guided deep inspiration breath hold (DIBH) radiotherapy for left sided breast cancer. Forty DIBH patients under either surface-guided radiotherapy (SGRT) or RPM guidance were studied. For patients treated with tangential fields, reproducibility was measured as the displacements in central lung distance (CLD) and heart shadow to field edge distance (HFD) between pretreatment MV (megavoltage) images and planning DRRs (digitally reconstructed radiographs). For patients treated with volumetric modulated arc therapy (VMAT), sternum to isocenter (ISO) distance (StID), spine to rib edge distance (SpRD), and heart shadow to central axis (CAX) distance (HCD) between pretreatment kV images and planning DRRs were measured. These displacements were compared between SGRT and RPM-guided DIBH. In tangential patients, the mean absolute displacements of SGRT versus RPM guidance were 0.19 versus 0.23 cm in CLD, and 0.33 versus 0.62 cm in HFD. With respect to planning DRR, heart appeared closer to the field edge by 0.04 cm with surface imaging versus 0.62 cm with RPM. In VMAT patients, the displacements of surface imaging versus RPM guidance were 0.21 versus 0.15 cm in StID, 0.24 versus 0.19 cm in SpRD, and 0.72 versus 0.41 cm in HCD. Heart appeared 0.41 cm further away from CAX with surface imaging, whereas 0.10 cm closer to field CAX with RPM. None of the differences between surface imaging and RPM guidance was statistically significant. In conclusion, the displacements of chestwall were small and were comparable with SGRT- or RPM-guided DIBH. The position deviations of heart were larger than those of chestwall with SGRT or RPM. Although none of the differences between SGRT and RPM guidance were statistically significant, there was a trend that the position deviations of heart were smaller and more favorable with SGRT than with RPM guidance in tangential patients.

Evidence-based region of interest (ROI) definition for surface-guided radiotherapy (SGRT) of abdominal cancers using deep-inspiration breath-hold (DIBH)

To define and evaluate the appropriate abdominal region of interest (ROI) as a surrogate of diaphragm positioning in deep-inspiration breath-hold (DIBH) for surface-guided radiotherapy (SGRT) of abdominal cancers using 3D optical surface imaging (OSI). Six potential abdominal ROIs were evaluated to calculate their correlations with the diaphragm position using 4DCT images of 20 abdominal patients. Twelve points of interest (POIs) were defined (six on the central soft tissue and six on the bilateral ribs) at three superior-inferior levels, and different sub-groups represented different ROIs. ROI-1 was the largest, containing all 12 POIs from the xiphoid to the umbilicus and between the lateral body midlines while ROI-2 had only eight inferior POIs, ROI-3 had six lateral POIs, and ROI-4 had four superior-lateral POIs over the ribs, ROI-5 contained six central and two most inferior-lateral POIs and ROI-6 contained six central and four inferior-lateral POIs. Internally, the right diaphragm dome was used to represent its positions in 4DCT (0% and 50% within the cycle). The Pearson correlation coefficients were calculated between the diaphragm dome and all 12 external POIs individually or grouped as six ROIs. The quality of the abdominal ROIs was evaluated as potential internal surrogates and, therefore, potential ROIs for SGRT DIBH setup. The four most inferior POIs show the highest mean correlation (r = 0.75) with diaphragmatic motion, and the correlation decreases as POIs move superiorly. The mean correlations are the highest for ROIs with little or no rib support: r = 0.67 for ROI-2, r = 0.64 for ROI-5, and r = 0.63 for ROI-6, while lower for ROIs with rib support: ROI-1 has r = 0.60, ROI-3 has r = 0.50, and ROI-4 has only r = 0.28. This study demonstrates that the rectangular/triangular soft-tissue ROI (with little rib support) is an optimal surrogate for body positioning and diaphragmatic motion, even when treating tumors under the rib cage. This evidence-based ROI definition should be utilized when treating abdominal cancers with free-breathing (FB) and/or DIBH setup.

Automatic stent recognition using perceptual attention U-net for quantitative intrafraction motion monitoring in pancreatic cancer radiotherapy

PURPOSE

Stent has often been used as an internal surrogate to monitor intrafraction tumor motion during pancreatic cancer radiotherapy. Based on the stent contours generated from planning CT images, the current intrafraction motion review (IMR) system on Varian TrueBeam only provides a tool to verify the stent motion visually but lacks quantitative information. The purpose of this study is to develop an automatic stent recognition method for quantitative intrafraction tumor motion monitoring in pancreatic cancer treatment.

METHODS

A total of 535 IMR images from 14 pancreatic cancer patients were retrospectively selected in this study, with the manual contour of the stent on each image serving as the ground truth. We developed a deep learning-based approach that integrates two mechanisms that focus on the features of the segmentation target. The objective attention modeling was integrated into the U-net framework to deal with the optimization difficulties when training a deep network with 2D IMR images and limited training data. A perceptual loss was combined with the binary cross-entropy loss and a Dice loss for supervision. The deep neural network was trained to capture more contextual information to predict binary stent masks. A random-split test was performed, with images of ten patients (71%, 380 images) randomly selected for training, whereas the rest of four patients (29%, 155 images) were used for testing. Sevenfold cross-validation of the proposed PAUnet on the 14 patients was performed for further evaluation.

RESULTS

Our stent segmentation results were compared with the manually segmented contours. For the random-split test, the trained model achieved a mean (±standard deviation) stent Dice similarity coefficient (DSC), 95% Hausdorff distance (HD95), the center-of-mass distance (CMD), and volume difference V o l d i f f $Vo{l_{diff}}$ were 0.96 (±0.01), 1.01 (±0.55) mm, 0.66 (±0.46) mm, and 3.07% (±2.37%), respectively. The sevenfold cross-validation of the proposed PAUnet had the mean (±standard deviation) of 0.96 (±0.02), 0.72 (±0.49) mm, 0.85 (±0.96) mm, and 3.47% (±3.27%) for the DSC, HD95, CMD, and V o l d i f f $Vo{l_{diff}}$ .

CONCLUSION

We developed a novel deep learning-based approach to automatically segment the stent from IMR images, demonstrated its clinical feasibility, and validated its accuracy compared to manual segmentation. The proposed technique could be a useful tool for quantitative intrafraction motion monitoring in pancreatic cancer radiotherapy.

Intrafractional accuracy and efficiency of a surface imaging system for deep inspiration breath hold during ablative gastrointestinal cancer treatment

PURPOSE

Beam gating with deep inspiration breath hold (DIBH) usually depends on some external surrogate to infer internal target movement, and the exact internal movement is unknown. In this study, we tracked internal targets and characterized residual motion during DIBH treatment, guided by a surface imaging system, for gastrointestinal cancer. We also report statistics on treatment time.

METHODS AND MATERIALS

We included 14 gastrointestinal cancer patients treated with surface imaging-guided DIBH volumetrically modulated arc therapy, each with at least one radiopaque marker implanted near or within the target. They were treated in 25, 15, or 10 fractions. Thirteen patients received treatment for pancreatic cancer, and one underwent separate treatments for two liver metastases. The surface imaging system monitored a three-dimensional surface with ± 3 mm translation and ± 3° rotation threshold. During delivery, a kilovolt image was automatically taken every 20° or 40° gantry rotation, and the internal marker was identified from the image. The displacement and residual motion of the markers were calculated. To analyze the treatment efficiency, the treatment time of each fraction was obtained from the imaging and treatment timestamps in the record and verify system.

RESULTS

Although the external surface was monitored and limited to ± 3 mm and ± 3°, significant residual internal target movement was observed in some patients. The range of residual motion was 3-21 mm. The average displacement for this cohort was 0-3 mm. In 19% of the analyzed images, the magnitude of the instantaneous displacement was > 5 mm. The mean treatment time was 17 min with a standard deviation of 4 min.

CONCLUSIONS

Precaution is needed when applying surface image guidance for gastrointestinal cancer treatment. Using it as a solo DIBH technique is discouraged when the correlation between internal anatomy and patient surface is limited. Real-time radiographic verification is critical for safe treatments.

A uniform and versatile surface‐guided radiotherapy procedure and workflow for high‐quality breast deep‐inspiration breath‐hold treatment in a multi‐center institution

Purpose

We share our experiences on uniformly implementing an effective and efficient SGRT procedure with a new clinical workflow for treating breast patients in deep‐inspiration breath‐hold (DIBH) among 9 clinical centers using 26 optical surface imaging (OSI) systems.

Methods

Our procedures have five major components: (1) acquiring both free‐breathing (FB) and DIBH computed tomography (CT) at simulation to quantify the rise of the anterior surface, (2) defining uniformly a large region of interest (ROI) to accommodate large variations in patient anatomy and treatment techniques, (3) performing two‐step setup in FB by first aligning the arm and chin to minimize breast deformation and reproduce local lymphnode positions and then aligning the ROI, (4) aligning the vertical shift precisely from FB to DIBH, and (5) capturing a new on‐site reference image at DIBH to separate residual setup errors from the DIBH motion monitoring uncertainties. Moreover, a new clinical workflow was developed for patient data preparation using 4 OSI offline workstations without interruption of SGRT treatment at 22 OSI online workstations. This procedure/workflow is suitable for all photon planning techniques, including 2‐field, 3‐field, 4‐field, partial breast irradiation (PBI), and volumetric‐modulated arc therapy (VMAT) with or without bolus.

Results

Since 2019, we have developed and applied the uniform breast SGRT DIBH procedure with optimized clinical workflow and ensured treatment accuracy among the nine clinics within our institution. About 150 breast DIBH patients are treated daily and two major upgrades are achieved smoothly throughout our institution, owing to the uniform and versatile procedure, adequate staff training, and efficient workflow with effective clinical supports and backup strategies.

Conclusion

The uniform and versatile breast SGRT DIBH procedure and workflow have been developed to ensure smooth and optimal clinical operations, simplify clinical staff training and clinical troubleshooting, and allow high‐quality SGRT delivery in a busy multi‐center institution.

Inter- and intrafraction motion assessment and accumulated dose quantification of upper gastrointestinal organs during magnetic resonance-guided ablative radiation therapy of pancreas patients

Background and purpose

Stereotactic body radiation therapy (SBRT) of locally advanced pancreatic cancer (LAPC) is challenging due to significant motion of gastrointestinal (GI) organs. The goal of our study was to quantify inter and intrafraction deformations and dose accumulation of upper GI organs in LAPC patients.

Materials and methods

Five LAPC patients undergoing five-fraction magnetic resonance-guided radiation therapy (MRgRT) using abdominal compression and daily online plan adaptation to 50 Gy were analyzed. A pre-treatment, verification, and post-treatment MR imaging (MRI) for each of the five fractions (75 total) were used to calculate intra and interfraction motion. The MRIs were registered using Large Deformation Diffeomorphic Metric Mapping (LDDMM) deformable image registration (DIR) method and total dose delivered to stomach_duodenum, small bowel (SB) and large bowel (LB) were accumulated. Deformations were quantified using gradient magnitude and Jacobian integral of the Deformation Vector Fields (DVF). Registration DVFs were geometrically assessed using Dice and 95th percentile Hausdorff distance (HD95) between the deformed and physician’s contours. Accumulated doses were then calculated from the DVFs.

Results

Median Dice and HD95 were: Stomach_duodenum (0.9, 1.0 mm), SB (0.9, 3.6 mm), and LB (0.9, 2.0 mm). Median (max) interfraction deformation for stomach_duodenum, SB and LB was 6.4 (25.8) mm, 7.9 (40.5) mm and 7.6 (35.9) mm. Median intrafraction deformation was 5.5 (22.6) mm, 8.2 (37.8) mm and 7.2 (26.5) mm. Accumulated doses for two patients exceeded institutional constraints for stomach_duodenum, one of whom experienced Grade1 acute and late abdominal toxicity.

Conclusion

LDDMM method indicates feasibility to measure large GI motion and accumulate dose. Further validation on larger cohort will allow quantitative dose accumulation to more reliably optimize online MRgRT.

Triggered kV Imaging During Spine SBRT for Intrafraction Motion Management

Purpose: To monitor intrafraction motion during spine stereotactic body radiotherapy(SBRT) treatment delivery with readily available technology, we implemented triggered kV imaging using the on-board imager(OBI) of a modern medical linear accelerator with an advanced imaging package. Methods: Triggered kV imaging for intrafraction motion management was tested with an anthropomorphic phantom and simulated spine SBRT treatments to the thoracic and lumbar spine. The vertebral bodies and spinous processes were contoured as the image guided radiotherapy(IGRT) structures specific to this technique. Upon each triggered kV image acquisition, 2D projections of the IGRT structures were automatically calculated and updated at arbitrary angles for display on the kV images. Various shifts/rotations were introduced in x, y, z, pitch, and yaw. Gantry-angle-based triggering was set to acquire kV images every 45°. A group of physicists/physicians(n = 10) participated in a survey to evaluate clinical efficiency and accuracy of clinical decisions on images containing various phantom shifts. This method was implemented clinically for treatment of 42 patients(94 fractions) with 15 second time-based triggering. Result: Phantom images revealed that IGRT structure accuracy and therefore utility of projected contours during triggered imaging improved with smaller CT slice thickness. Contouring vertebra superior and inferior to the treatment site was necessary to detect clinically relevant phantom rotation. From the survey, detectability was proportional to the shift size in all shift directions and inversely related to the CT slice thickness. Clinical implementation helped evaluate robustness of patient immobilization. Based on visual inspection of projected IGRT contours on planar kV images, appreciable intrafraction motion was detected in eleven fractions(11.7%). Discussion: Feasibility of triggered imaging for spine SBRT intrafraction motion management has been demonstrated in phantom experiments and implementation for patient treatments. This technique allows efficient, non-invasive monitoring of patient position using the OBI and patient anatomy as a direct visual guide.

An Evaluation of Total Internal Motions of Locally Advanced Pancreatic Cancer during SABR Using Calypso® Extracranial Tracking, and Its Possible Clinical Impact on Motion Management

(1) Background: the aims of this study were to determine the total extent of pancreatic cancer’s internal motions, using Calypso^® extracranial tracking, and to indicate possible clinical advantages of continuous intrafractional fiducial-based tumor motion tracking during SABR. (2) Methods: thirty-four patients were treated with SABR for LAPC using Calypso^® for motion management. Planning MSCTs in FB and DBH, and 4D-CTs were performed. Using data from Calypso^® and 4D-CTs, the movements of the lesions in the CC, AP and LR directions, as well as the volumes of the 4D-CT-based ITV and the volumes of the Calypso^®-based ITV were compared. (3) Results: significantly larger medians of tumor excursions were found with Calypso^® than with 4D-CT: CC: 29 mm (p < 0.001); AP: 14 mm (p < 0.001) and LR: 11 mm (p < 0.039). The median volume of the Calypso^®-based ITV was significantly larger than that of the 4D-CT based ITV (p < 0.001). (4) Conclusion: beside known respiratory-induced internal motions, pancreatic cancer seems to have significant additional motions which should be considered during respiratory motion management. Only direct and continuous intrafractional fiducial-based motion tracking seems to provide complete coverage of the target lesion with the prescribed isodose, which could allow for safe tumor dose escalation.

The first real-time intrafraction target position monitoring in pancreas SBRT on an Elekta linear accelerator

To perform implanted fiducial based real-time target position monitoring in pancreas stereotactic body radiotherapy (SBRT) using the x-ray imaging system available in a Elekta linear accelerator. An in-house system was developed and clinically utilised for real-time target position monitoring of pancreas SBRT delivery. The developed system was used for the target position monitoring of a pancreas cancer patient treated in free breathing treatment within the study entitled 'Mfolfirinox And STEreotactic Radiotherapy for Patients with Locally Advanced paNcreas cancer (MASTERPLAN): a feasibility study' (ACTRN 12617001642370) consisting of five treatment fractions. The clinical efficacy of the system was studied by performing a retrospective cumulative dose assessment of delivered dose using observed position deviations. The developed system identified two events of baseline shifts in target position that exceeded the accepted tolerance level of ± 3 mm from reference planned position. The retrospective dose assessment study showed that if the position deviations were not detected and corrected for, the maximum dose to duodenum would have increased from 34.6 to 38.8 Gy. The first real-time position monitoring in pancreas SBRT on an Elekta linear accelerator was successfully performed. The developed system was shown to improve the safety and accuracy of SBRT delivery.

Accuracy and efficiency of respiratory gating comparable to deep inspiration breath hold for pancreatic cancer treatment

Purpose

Deep inspiration breath hold (DIBH) and respiratory gating (RG) are widely used to reduce movement of target and healthy organs caused by breathing during irradiation. We hypothesized that accuracy and efficiency comparable to DIBH can be achieved with RG for pancreas treatment.

Methods and Materials

Twenty consecutive patients with pancreatic cancer treated with DIBH (eight) or RG (twelve) volumetric modulated arc therapy during 2017–2019 were included in this study, with radiopaque markers implanted near or in the targets. Seventeen patients received 25 fractions, while the other three received 15 fractions. Only patients who could not tolerate DIBH received RG treatment. While both techniques relied on respiratory signals from external markers, internal target motions were monitored with kV X‐ray imaging during treatment. A 3‐mm external gating window was used for DIBH treatment; RG treatment was centered on end‐expiration with a duty cycle of 40%, corresponding to an external gating window of 2–3 mm. During dose delivery, kV images were automatically taken every 20^◦ or 40^◦ gantry rotation, from which internal markers were identified. The marker displacement from their initial positions and the residual motion amplitudes were calculated. For the analysis of treatment efficiency, the treatment time of every session was calculated from the motion management waveform files recorded at the treatment console.

Results

Within one fraction, the displacement was 0–5 mm for DIBH and 0–6 mm for RG. The average magnitude of displacement for each patient during the entire course of treatment ranged 0–3 mm for both techniques. No statistically significant difference in displacement or residual motion was observed between the two techniques. The average treatment time was 15 min for DIBH and 17 min for RG, with no statistical significance.

Conclusions

The accuracy and efficiency were comparable between RG and DIBH treatment for pancreas irradiation. RG is a feasible alternative strategy to DIBH.

Positional repeatability and variation in internal and external markers during volumetric-modulated arc therapy under end-exhalation breath-hold conditions for pancreatic cancer patients

The purpose of this study was to assess the positional repeatability of internal and external markers among multiple breath-hold (BH) sessions and evaluate the positional variation of these markers within BH sessions for volumetric-modulated arc therapy (VMAT) for pancreatic cancer patients. A total of 13 consecutive pancreatic cancer patients with an internal marker were enrolled. Single full-arc coplanar VMAT was delivered under end-exhalation BH conditions while monitoring the internal marker with kilovoltage (kV) X-ray fluoroscopy. Positional repeatability of the internal and external markers was determined by the difference between the reference and zero position in all BH sessions, and positional variation was defined by the displacement from the reference position in each BH session during megavolt beam delivery. The overall positional repeatability was 0.6 ± 1.5 mm in the X-axis for the centroid of the internal marker (CoIM), -0.1 ± 2.2 mm in the Y-axis for the CoIM, and 0.8 ± 2.2 mm for the external marker. The frequency of an internal marker position appearing > 2 mm from the reference position in the Y-axis, despite the external marker position being ≤2 mm from the reference position, ranged from 0.0 to 39.9% for each patient. Meanwhile, the proportion of sessions with positional variation ≤2 mm was 93.2 and 98.7% for the CoIM and external marker, respectively. External marker motion can be used as a surrogate for pancreatic tumor motion during BH-VMAT delivery; however, margins of ~5 mm were required to ensure positional repeatability.

Setup Management for Stereotactic Body Radiation Therapy of Patients With Pancreatic Cancer Treated via the Breath-Hold Technique

PURPOSE

Active Breathing Coordinator (Elekta AB, Crawley, UK) is a motion management strategy for radiation treatment. During setup, aligning the patient to the bony spine alone does not necessarily lead to an accurate alignment to soft tissue targets, and further adjustment is necessary. Determining a safe range of values for such adjustments is an important quality assurance measure and was the purpose of this study, with focus on stereotactic body radiation therapy in patients with pancreatic cancer.

METHODS AND MATERIALS

The retrospective study included 19 previously treated patients. For each fraction, a free-breathing cone beam computed tomography scan was registered to a reference breath-hold computed tomography for alignment to the spine. Two perpendicular breath-hold kV projection images were then acquired and compared with corresponding reference digitally reconstructed radiographs for additional alignment with a surrogate fiducial marker. By comparing the breath-hold kV projection images from subsequent treatment fractions with those from the first fraction, we derived the 3-dimensional variability of the fiducial position with respect to the reference image.

RESULTS

We observed intrafraction setup error to be within 2.0 mm. For interfraction, we observed average reproducibility of 1.7 ± 0.8 mm, 2.0 ± 1.4 mm, and 3.2 ± 2.5 mm in the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions, respectively. The average excursion values from free breathing spine to breath-hold fiducial alignment were 1.5 ± 1.4 mm, 2.0 ± 1.9 mm, and 3.0 ± 2.0 mm in the LR, AP and SI directions, respectively. The observed ranges of average excursions among all patients were 0.2 to 5.1 mm, 0.1 to 5. 9 mm, and 0.6 to 7.8 mm in the LR, AP, and SI directions, respectively.

CONCLUSIONS

This study demonstrates that intrafraction targeting errors can be within 2 mm, and interfraction shifts from free-breathing spine to Active Breathing Coordinator breath-hold target can be as high as 8 mm. Values that deviate significantly would need further investigation to rule out factors such as local progression, bowel gas, or fiducial shift before treatment.