Cone Beam CT Image Guidance Research Articles

About Intelligence (Artificial or Not) – A Discussion with Marcel van Herk

Professor Marcel van Herk is the chair of the radiotherapy physics at the University of Manchester. As a medical physics student he started on the development of a liquid ionization imaging device that later became the Varian PortalVision system for electronic portal imaging. Starting during a Postdoc at Harvard Medical School, USA in 1992, his work incorporated 3D image processing, first CT-MR image registration for treatment planning, later measuring organ motion and other uncertainties in radiotherapy such as delineation variability. Much of this work has been integrated in the Elekta Synergy cone-beam CT image guidance system developed. He also held a part-time teaching role as a Professor at the University of Amsterdam working amongst others at the integration of microscopic optical imaging into radiotherapy treatment planning. His goal is to do research to improve the clinical practice of radiotherapy.

Endovascular steerable and endobronchial precurved guiding sheaths for transbronchial needle delivery under augmented fluoroscopy and cone beam CT image guidance.

BackgroundEndobronchial navigation is performed in a variety of ways, none of which are meeting all the clinicians’ needs required to reach diagnostic success in every patient. We sought to characterize precurved and steerable guiding sheaths (GS) in endobronchial targeting for lung biopsy using cone beam computed tomography (CBCT) based augmented fluoroscopy (AF) image guidance.MethodsFour precurved GS (EdgeTM 45, 90, 180, 180EW, Medtronic) and two steerable GS [6.5 F Destino Twist (DT), Oscor; 6 F Morph, BioCardia] were evaluated alone and in combination with an electromagnetic tracking (EM) guide and biopsy needles in three experimental phases: (I) bench model to assess GS deflection and perform biopsy simulations; (II) ex vivo swine lung comparing 2 steerable and 2 precurved GS; and (III) in vivo male swine lung to deliver a needle (n=2 swine) or to deliver a fiducial marker (n=2 swine) using 2 steerable GS. Ex vivo and in vivo image guidance was performed with either commercial or prototype AF image guidance software (Philips) based on either prior CT or procedural CBCT. Primary outcomes were GS delivery angle (θGS) and needle delivery angle (θN) in bench evaluation and needle delivery error (mm) (mean ± se) for ex vivo and in vivo studies.ResultsThe steerable DT had the largest range of GS delivery angles (θN: 0–114°) with either the 21 G or 19 G biopsy needle in the bench model. In ex vivo swine lung, needle delivery errors were 8.7±0.9 mm (precurved Edge 90), 5.4±1.9 mm (precurved Edge 180), 4.7±1.2 mm (steerable DT), and 5.6±2.4 mm (steerable Morph). In vivo, the needle delivery errors for the steerable GS were 6.0±1.0 mm (DT) and 15±7.0 mm (Morph). In vivo marker coil delivery was successful for both the steerable DT and morph GS. A case report demonstrated successful needle biopsy with the steerable DT.ConclusionsEndobronchial needle delivery with AF guidance is feasible without a bronchoscope with steerable GS providing comparable or improved accuracy compared to precurved GS.

Single Fraction (30 Gy) Stereotactic Body Radiation Treatment of Peripheral Lung Lesions using Flattening Filter Free Volumetric Modulated Arc Therapy (FFF-VMAT): Early Clinical Outcomes

To present early clinical outcomes utilizing stereotactic body radiation therapy (SBRT) to mid lung or peripheral lung lesions, delivering a dose of 30 Gy in a single fraction with flattening filter free volumetric modulated arc therapy (FFF-VMAT). Twenty-four lesions were identified from twenty-three patients with either early stage non-small cell lung cancer (lesions n = 17) or isolated, limited, thoracic progression from a known metastatic cancer diagnosis (lesions n = 2 head and neck, n = 2 rectal, n = 3 lung). Patients were prescribed a single dose of 30 Gy, delivered using FFF VMAT with noncoplanar 6MV beams and cone beam CT image guidance. Four-dimensional (4D) CT based treatment plans were generated using an advanced Acuros-based dose calculation engine for heterogeneity corrections. Plan quality and delivery efficiency were reported. Outcomes evaluated include local control, radiation-induced pneumonitis, and rib toxicity. Median follow-up time was 9 months (range: 1 to 38 months). Mean planning target volume (PTV) was 17.6 ± 13.9 cc. All plans met RTOG requirements for target coverage and dose to organs at risk (OAR). Average values of the conformity index, gradient index, maximum dose at 2 cm away from the PTV, normal lung V20Gy, and normal lung V10Gy were 1.06 ± 0.1, 5.4 ± 1.4, 49.5 ± 4.5%, 0.8 ± 0.5% and 3.2 ± 1.9 %, respectively. All OAR doses were well below RTOG compliance criteria. Average beam on time was 6.6 ± 1.3 min. Four patients were lost to follow up. One patient has initial post-treatment imaging pending. During the follow up period, all patients demonstrated local control of the treated lesion. Six patients developed new distant metastases, 4 of whom had prior stage 4 disease. All patients developed asymptomatic radiographic changes surrounding the treated lesion, though there were no reports of grade 2+ pneumonitis or chest wall pain and no radiographic evidence of rib fracture. Stereotactic delivery of 30 Gy in a single fraction using cone-beam CT image guidance with a non-coplanar FFF-VMAT plan is a fast, safe, and effective treatment modality for managing small mid-lung or peripherally located lung lesions. Local control is excellent and no symptomatic adverse events were noted over the follow up period. This is a promising strategy for rapidly delivering a meaningful oncologic dose to patients unable to tolerate a multi-fraction regimen due to discomfort, medical comorbidities, or socio-economic barriers hindering treatment compliance. Longer clinical follow up in a larger patient cohort is ongoing to further validate these outcomes.

Moderately hypofractionated radiotherapy for localized prostate cancer: updated long-term outcome and toxicity analysis

PurposeEvaluation of long-term outcome and toxicity of moderately hypofractionated radiotherapy using intensity-modulated radiotherapy (IMRT) with simultaneous integrated boost treatment planning and cone beam CT-based image guidance for localized prostate cancer.MethodsBetween 2005 and 2015, 346 consecutive patients with localized prostate cancer received primary radiotherapy using cone beam CT-based image-guided intensity-modulated radiotherapy (IG-IMRT) and volumetric modulated arc therapy (IG-VMAT) with a simultaneous integrated boost (SIB). Total doses of 73.9 Gy (n = 44) and 76.2 Gy (n = 302) to the high-dose PTV were delivered in 32 and 33 fractions, respectively. The low-dose PTV received a dose (D95) of 60.06 Gy in single doses of 1.82 Gy. The pelvic lymph nodes were treated in 91 high-risk patients to 45.5 Gy (D95).ResultsMedian follow-up was 61.8 months. The 5‑year biochemical relapse-free survival (bRFS) was 85.4% for all patients and 93.3, 87.4, and 79.4% for low-, intermediate-, and high-risk disease, respectively. The 5‑year prostate cancer-specific survival (PSS) was 94.8% for all patients and 98.7, 98.9, 89.3% for low-, intermediate-, and high-risk disease, respectively. The 5‑year and 10-year overall survival rates were 83.8 and 66.3% and the 5‑year and 10-year freedom from distant metastasis rates were 92.2 and 88.0%, respectively. Cumulative 5‑year late GU toxicity and late GI toxicity grade ≥2 was observed in 26.3 and 12.1% of the patients, respectively. Cumulative 5‑year late grade 3 GU/GI toxicity occurred in 4.0/1.2%.ConclusionModerately hypofractionated radiotherapy using SIB treatment planning and cone beam CT image guidance resulted in high biochemical control and survival with low rates of late toxicity.

Cone-Beam CT Image Guidance With and Without Electromagnetic Navigation Bronchoscopy for Biopsy of Peripheral Pulmonary Lesions.

Background:Bronchoscopic diagnosis of small peripheral lung lesions suspected of lung cancer remains a challenge. A successful endobronchial diagnosis comprises navigation, confirmation, and tissue acquisition. In all steps, 3-dimensional information is essential. Cone-beam computed tomography (CBCT) imaging can provide computed tomography information and 3-dimensional augmented fluoroscopy imaging. We assessed whether CBCT imaging can improve navigation and diagnosis of peripheral lesions by 2 clinical workflows with a cross-over design: (1) a primary CBCT and radial endobronchial ultrasound mini probe imaging–based approach and (2) a primary electromagnetic navigation (EMN) and radial endobronchial ultrasound mini probe imaging–based approach.Methods:All patients with a peripheral lung lesion biopsy indication were eligible for study inclusion and randomly assigned to study arms. Commercially available equipment was used. The main study goals were to assess CBCT-confirmed navigation success and diagnostic accuracy. Surgery or unambiguous clinical follow-up served as the gold standard.Results:Eighty-seven patients with 107 lesions were included. Lesion mean longest axis size in the CBCT arm was 16.6 mm (n=47) and 14.2 mm in the EMN arm (n=40). The primary CBCT approach and primary EMN approach had 76.3% and 52.2% navigation success, respectively. Addition of EMN to the CBCT approach increased navigation success to 89.9%. Addition of CBCT imaging to the EMN approach significantly increased navigation success to 87.5% per lesion. The overall diagnostic accuracy per patient was significantly lower than the navigation success, being 72.4%.Conclusion:CBCT imaging is a valuable addition to navigation bronchoscopy. Although overall navigation success was high, the diagnostic accuracy remains to be improved. Future research should focus on improving the tissue acquisition methodology.

Contemporary Practice Patterns for Radiotherapy of Bone Metastases: Preliminary Analysis of Prospective Data from a Statewide Consortium Focusing on Extended Fractionation

National guidelines recommend various effective dose and fractionation schemes for palliative radiotherapy (RT) of bone metastases, including noninferior outcomes with single fraction regimens. For Choosing Wisely, ASTRO advocated against use of extended fractionation schemes with greater than 10 fractions. We previously reported a retrospective assessment of heterogeneity in RT management of bone metastases. Herein, we sought to prospectively analyze current practice patterns of palliative RT in the treatment of bone metastases in diverse clinical settings. Specifically, we investigated possible predictors of extended treatment courses. Within a statewide radiation oncology quality consortium, patients were consecutively enrolled between March 2018 and February 2019 in both academic and non-academic facilities. Data on patient characteristics, provider and facility characteristics, dose and fractionation schedules, treatment planning and delivery techniques and image guidance were collected. Multivariable binary logistic regression was employed to assess use of extended fractionation (>10 fractions) RT. A total of 444 consecutive patients were enrolled by 24 treating facilities. The median case volume per center was 15 (range, 1-55), with a total of 608 plans from 411 patients available for analysis. The median number of plans per patient was 1 (range, 1-4). The most commonly employed dose and fractionation schedules were 3 Gy x 10 fractions (54%), 4 Gy x 5 fractions (14%), and 8 Gy x 1 fraction (11%). A minority of plans (5%) used extended fractionation. IMRT was utilized for 9% of plans, while cone beam CT image guidance was used in 14% of cases. A majority of plans (64%) were designed for uncomplicated osseous metastatic lesions. For uncomplicated lesions 13% of plans were prescribed 8 Gy x 1 fraction, while 5% were prescribed greater than 10 fractions. The only significant predictor of use of extended fractionation was type of treatment facility with academic centers significantly less likely to use more than 10 fractions per plan (OR=0.16, 95% CI: 0.04-0.72, p<0.02). This is our initial analysis of contemporary practice patterns of palliative RT for bone metastases using prospective data recently collected from our statewide consortium. Within a large, consecutively enrolled patient cohort, we demonstrate that palliative RT for management of bone metastases remains diverse. Resource-intensive treatments including image guidance and extended fractionation exist, with type of treatment facility significantly predicting use of extended fractionation. Taken together, these preliminary results support our ongoing collection of the prospective data needed to more clearly understand the barriers to high value RT approaches in this setting.

Varian IX accelerator kV class CBCT image ring-shaped artifact troubleshooting

The hardware and software faults in the image guidance system may cause ring-shaped artifacts, which is more commonly induced by the aging of the hardware. During troubleshooting, the first step should be checking whether there are obvious faults in the basic hardware. Subsequently, OBI background image is collected to confirm the bad point status. If the bad point is not shielded, it can be compensated by updating the image processing bad point. The invoked Pixel Correction Maps are adopted compensate for the bad point and calibrate the image. If it is still unable to repair, replacing the detection board can be considered. Cone-beam CT (CBCT) image guidance system is an important approach to verify the position orientation and positioning accuracy in modern radiotherapy, which effectively guarantees for the safety and accuracy of radiotherapy. We should fully understand its law of aging, maintain the equipment on a regular basis and verify the image quality to ensure the normal operation of the equipment. Key words: Cone-beam CT; Image artifact; Troubleshooting

Online daily assessment of dose change in head and neck radiotherapy without dose-recalculation.

BackgroundHead and neck cancers are commonly treated with radiation therapy, but due to possible volume changes, plan adaptation may be required during the course of treatment. Currently, plan adaptations consume significant clinical resources. Existing methods to evaluate the need for plan adaptation requires deformable image registration (DIR) to a new CT simulation or daily cone beam CT (CBCT) images and the recalculation of the dose distribution. In this study, we explore a tool to assist the decision for plan adaptation using a CBCT without re‐computation of dose, allowing for rapid online assessment.MethodsThis study involved 18 head and neck cancer patients treated with CBCT image guidance who had their treatment plan modified based on a new CT simulation (ReCT). Dose changes were estimated using different methods and compared to the current gold standard of using DIR between the planning CT scan (PCT) and ReCT with recomputed dose. The first and second methods used DIR between the PCT and daily CBCT with the planned dose or recalculated dose from the ReCT respectively, with the dose transferred to the CBCT using rigid registration. The necessity of plan adaptation was assessed by the change in dose to 95% of the planning target volume (D95) and mean dose to the parotids.ResultsThe treatment plans were adapted clinically for all 18 patients but only 7 actually needed an adaptation yielding 11 unnecessary adaptations. Applying a method using the daily CBCT with the planned dose distribution would have yielded only four unnecessary adaptations and no missed adaptations: a significant improvement from that done clinically.ConclusionUsing the DIR between the planning CT and daily CBCT can flag cases for plan adaptation before every fraction while not requiring a new re‐planning CT scan and dose recalculation.

OA026] Design of an optimised bow-tie filter for cone-beam CT image guidance for children

Purpose Children can receive excessive imaging dose from cone-beam CT (CBCT) during image-guided radiotherapy due to use of protocols designed for adults. Lower dose CBCT is a high priority for reducing the risk of radiation induced late effects in children. The range of imaging doses can be reduced by lowering exposure using an optimal ‘child-sized’ bow-tie filter with additional attenuation and tailored shape. We present a filter design using measurements from paediatric CBCT data and simulate its impact on image quality and registration accuracy. Methods The filter was designed to produce uniform signal across the average paediatric patient and provide additional attenuation compared to a standard (adult) bow-tie filter. To estimate the average patient thickness across the detector plane, we used the signal intensity profiles of projection images acquired from 15 paediatric patients (ages 3–17 years) with various tumour sites. The intensity values were converted to an estimate of patient thickness using the Beer-Lambert law, with all tissues approximated as water. We produced a symmetrical design accounting for attenuation through the average patient across the detector. CBCT scans including the added noise resulting from attenuation of the new filter were simulated by modifying projection images before reconstruction. Simulated scan quality was assessed visually and by testing registration accuracy, comparing the table correction to that for the original higher dose images. Results The resulting filter had a central thickness of 15.53 mm of Aluminium, corresponding to a fivefold reduction in signal compared to the use of the standard filter (approximately decreasing dose from 1.5 mGy to 0.33 mGy per scan). The thickness increased to 29.87 mm at the outer edge, following a curvature described by a polynomial function relating filter thickness to patient thickness across the detector. Simulated scans showed increased noise but clear bone/soft tissue boundaries. Registration remained accurate; most scans had table correction vector discrepancies within 1 mm (max 1.09 mm). Conclusions We have designed an optimised bow-tie filter for children. This dedicated filter design should allow considerable dose reduction to the patient, maintaining sufficient image quality and accurate registration. Observer studies on the acceptability of very low dose images in clinical practice are underway.

Evaluation of Differences Between Estimated Delivered Dose and Planned Dose in Nasopharynx Patients Using Deformable Image Registration and Dose Accumulation

To investigate differences in planned dose and estimated delivered dose using deformable image registration (DIR) and dose accumulation for clinical target volumes (CTV) and organs at risk (OAR). Fifty-two nasopharynx patients treated with chemoradiotherapy [70 Gy (high-dose) and 56Gy (low-dose) in 35 fractions] from 2013 and 2015 were included. All clinical plans used 6 MV intensity modulated radiation therapy (IMRT) and daily 3D kV cone beam CT (CBCT) image guidance. Retrospective dose accumulation was performed in RayStation v4.5.2 as follows: DICOM RT data (CT image, plan, dose, and contours) were imported from the clinical planning system. Daily CBCTs were also imported and deformably registered to the planning CT. Daily delivered dose was calculated on the CBCTs and deformed back to and accumulated onto the planning CT to estimate the delivered dose. The planned and delivered doses were compared using representative dose metrics for primary CTVs and OARs including brainstem, mandible, spinal cord, and right and left parotid glands. The impact of daily set-up variation and anatomical changes on target coverage and OAR doses was evaluated by comparing planned dose vs. delivered dose. Relative differences in CTV D98 calculated as percentage of planned dose was used to assess target coverage. The mean relative difference in D98 for 70 Gy CTVs was 0.8% (median 1.1%, range -1.8 to2.6%). The mean relative difference in D98 for 56 Gy CTVs was negligible (median 0.1%, range -2.8 to2.2%). The median (range) maximum dose to 0.1 cc of the brainstem was similar between planned and delivered: 53.0 Gy (40.7-61.5 Gy) and 52.2 Gy (40.0-61.7 Gy). Although some cases exceeded the nominal tolerance dose of 54 Gy in the plan, other cases planned under this tolerance did not exceed 54 Gy in estimated delivered dose. The median maximum dose to 0.1cc of the spinal cord and mandible was 37.8 Gy and 72.0 Gy and delivered dose (range) was 38.8 Gy (30.4-45.8 Gy) and 72.2 Gy (62.9-75.4 Gy), respectively. The D50 planned median dose, delivered median dose (range) for the right and left parotid was 34.4 Gy, 39.3 Gy (23.5-72.3 Gy), and 37.3 Gy, 40.6 Gy (18.6-68.1 Gy). The median planned, delivered dose (range) for the right and left parotid mean dose was 38.4 Gy, 40.3 Gy (30.1-69.8 Gy) and 40.5 Gy, 41.7 Gy (25.3-61.9 Gy). No large differences were seen between planned and delivered OAR doses for the evaluated metrics. Outliers were identified (±2 SD from the average) for the parotids, indicating that variation can be expected for this OAR and warrants further investigation. There was minimal dosimetric change on the serial OARs; the right and left parotids received greater dose than planned. Further studies are required to investigate the impact of this dosimetric change and to identify patients who can benefit from adaptive radiotherapy.

Optimal Patient Selection for Stereotactic Body Radiation Therapy: A Practical Approach in a High-Volume Community-Based Private Setting

Establishment of an objective and documentable selection process of patients for free-breathing stereotactic body radiation therapy (SBRT) in a high-volume community-based private setting. A vendor-based respiratory gating system and wide-bore multi-slice CT simulation acquire 4-dimensional image data sets throughout full respiratory cycles. SBRT is delivered on modern linear accelerators including SBRT-dedicated systems, with respiratory gating control and multiple volumetric modulated arc therapy (VMAT) techniques. Flattening Filter Free (FFF) mode of RT delivery is available as needed. Use of cone-beam CT image guidance and 6 degrees of freedom patient repositioning are also available to optimize target alignment. Patients were observed closely at time of CT simulation to select those with optimal and stable respiratory patterns with or without the need for supplemental oxygen. Selection of appropriate patients for SBRT is needed to assure optimal CT simulation image capture, prediction for subsequent treatment deliverability, and reproducibility of high dose SBRT. Typical SBRT is up to 10 Gy per fraction for 5 fractions. Through real-time evaluation of respiratory patterns, appropriate patients can be selected for SBRT. Compliance rate of selected patients during simulation and subsequent SBRT is 100% without significant interruption during SBRT delivery. Use of respiratory gating control effectively prevents out-of-range SBRT delivery during fits of coughing and dyspnea. Use of FFF mode and VMAT via multiple arcs significantly reduces SBRT delivery time and optimizes normal tissue protection. The selection ”process“ is also recorded via screen capture of the respiratory cycles with a corresponding graphical representation of steady breathing patterns. These graphics can then be inserted into the CT simulation documentation as part of the permanent electronic health record. Appropriate selection of patients for SBRT via objective analysis and recorded respiratory patterns ensures optimal conditions for clinical setup, tumor targeting, and reproducible delivery of SBRT. This process is also recorded in the electronic health records of each patient for permanent documentation, future reference, and chart review.

The use of a Colapinto TIPS Needle under cone-beam computed tomography guidance for true lumen re-entry in subintimal recanalization of chronic iliac artery occlusion

BackgroundTo report the technique and clinical outcome of subintimal re-entry in chronic iliac artery occlusion by using a Colapinto transjugular intrahepatic portosystemic shunt (TIPS) needle under rotational angiography (cone-beam computed tomography; CT) imaging guidance. MethodsPatients with chronic iliac artery occlusion with earlier failed attempts at conventional percutaneous recanalization during the past 5 years were enrolled in our study. In these patients, an ipsilateral femoral access route was routinely utilized in a retrograde fashion. A Colapinto TIPS Needle was used to aid the true lumen re-entry after failed conventional intraluminal or subintimal guidewire and catheter-based techniques. The puncture was directed under rotational angiography cone-beam CT guidance to re-enter the abdominal aorta. Bare metallic stents 8–10 mm in diameter were deployed in the common iliac artery, and followed by balloon dilation. ResultsTen patients (9 male; median age, 75 years) were included in our investigation. The average occlusion length was 10.2 cm (range, 4–15 cm). According to the Trans-Atlantic Inter-Society Consensus (TASC) II classification, there were five patients each with Class B and D lesions. Successful re-entry was achieved in all patients without procedure-related complications. The ankle–brachial index (ABI) values increased from 0.38–0.79 to 0.75–1.28 after the procedure. Imaging follow-up (> 6 months) was available in six patients with patency of all stented iliac artery. Thereafter, no complaints of recurrent clinical symptoms occurred during the follow-up period. ConclusionThe use of Colapinto TIPS needle, especially under cone-beam CT image guidance, appears to be safe and effective to re-enter the true lumen in a subintimal angioplasty for a difficult chronic total iliac occlusion.

Image-guided intrathecal baclofen pump catheter implantation: a technical note and case series.

OBJECTIVE Medically refractory spasticity and dystonia are often alleviated with intrathecal baclofen (ITB) administration through an indwelling catheter inserted in the lumbar spine. In patients with cerebral palsy, however, there is a high incidence of concomitant neuromuscular scoliosis. ITB placement may be technically challenging in those who have severe spinal deformity or who have undergone prior instrumented thoracolumbar fusion. Although prior reports have described drilling through the lumbar fusion mass with a high-speed bur, as well as IT catheter implantation at the foramen magnum or cervical spine, these approaches have notable limitations. To the authors' knowledge, this is the first report of ITB placement using cone beam CT (CBCT) image guidance to facilitate percutaneous IT catheterization. METHODS Data were prospectively collected on patients treated between November 2012 and June 2014. In the interventional radiology suite, general anesthesia was induced and the patient was positioned prone. Imaging was performed to identify the optimal trajectory. Percutaneous puncture was performed at an entry site with image-guided placement of a sheathed needle. CBCT provided real-time 2D projections and 3D reconstructions for detailed volumetric imaging. A biopsy drill was passed through the sheath, and subsequently a Tuohy needle was advanced intrathecally. The catheter was threaded cephalad under fluoroscopic visualization. After tip localization and CSF flow were confirmed, the stylet was replaced, the external catheter tubing was wrapped sterilely in a dressing, and the patient was transported to the operating room. After lateral decubitus positioning of the patient, the IT catheter was exposed and connected to the distal abdominal tubing with typical pump placement. RESULTS Of 15 patients with Gross Motor Function Classification System Levels IV and V cerebral palsy and instrumented thoracolumbar fusion, 8 had predominantly spasticity, and 7 had mixed spasticity and dystonia. The mean age of patients was 20.1 years (range 13-27 years). Nine patients underwent initial catheter and pump placement, and 6 underwent catheter replacement. The procedure was technically successful, with accurate spinal catheter placement in all patients. The median hospital stay was 4 days (IQR 3-5 days). One patient had an early postoperative urinary tract infection. With a mean follow-up of 25.8 months (median 26, range 18-38 months), no CSF leakage or catheter failure occurred. One late infection due to Pseudomonas aeruginosa (requiring pump explantation) occurred at 4 months, probably secondary to recurrent urinary tract infections. CONCLUSIONS Image-guided CBCT navigation resulted in accurate percutaneous placement of the IT catheter for ITB pumps in patients with prior instrumented thoracolumbar fusion. The multimodality approach is an alternate technique that may be used for IT catheter insertion in patients with complex lumbar spine anatomy, extending the potential to provide safe, durable ITB therapy in this population.

Deep inspiration breath-hold radiotherapy for lung cancer: impact on image quality and registration uncertainty in cone beam CT image guidance

We investigated the impact of deep inspiration breath-hold (DIBH) and tumour baseline shifts on image quality and registration uncertainty in image-guided DIBH radiotherapy (RT) for locally advanced lung cancer. Patients treated with daily cone beam CT (CBCT)-guided free-breathing (FB) RT had an additional CBCT in DIBH at three fractions. These CBCT scans were offline rigidly registered (on tumour) to FB and DIBH CT scans acquired at planning. All registrations were repeated to evaluate the intraobserver uncertainty. CBCT scans were scored on degree of streak artefacts and visualization of tumour and anatomical structures. We examined the impact of tumour baseline shift between consecutive DIBHs on CBCT image quality. CBCT scans from 15 patients were analysed. Intraobserver image registration uncertainty was approximately 2 mm in both FB and DIBH, except for the craniocaudal direction in FB, where it was >3 mm. On the 31st fraction, the intraobserver uncertainty increased compared with the second fraction. This increase was more pronounced in FB. Image quality scores improved in DIBH compared with FB for all parameters in all patients. Simulated tumour baseline shifts ≤2 mm did not affect the CBCT image quality considerably. DIBH CBCT improved image quality and reduced registration uncertainty in the craniocaudal direction in image-guided RT of locally advanced lung cancer. Baseline shifts ≤2 mm in DIBH during CBCT acquisition did not affect image quality. Advances in knowledge: DIBH RT has dosimetric advantages over FB; this work demonstrates an additional benefit of DIBH in terms of registration accuracy because of improved image quality.

SU‐F‐T‐40: Can CBCT Images Be Used for Volume Studies of Prostate Seed Implants for Boost Treatment?

Purpose:In our clinic, the planning CT is used for definitive and boost low‐dose‐rate (LDR) brachytherapy treatments to determine the ultrasound volume in the operating room (OR) at the time of the implant. While the CT overestimation of OR volume is known, a larger estimation discrepancy has been observed for boost treatments. A possible reason is the prostate size reduction during EBRT for boost patients. Since cone‐beam CT (CBCT) is often used as routine imaging guidance of EBRT, this prostate volume change may be captured. This study investigates if CBCT taken during EBRT includes the volume change information and therefore beats CT in estimating the prostate OR volumes.Methods:9 prostate patients treated with EBRT (45Gy in 1.8Gy per fractions to the whole pelvis) and I‐125 seed implants (108Gy) were involved in this study. During EBRT, CBCT image guidance was performed on a weekly basis. For each patient, the prostate volumes on the first and the last available CBCT images were manually contoured by a physician. These volumes were then compared to each other and with the contoured volumes from the planning CT and from the ultrasound images in the OR.Results:The first and the last CBCT images did not show significant prostate volume change. Their average +/− standard deviation of prostate volumes were 24.4cc+/−14.6cc and 29.9cc+/−16.1cc, respectively (T‐test p=0.68). The ratio of the OR volume to the last CBCT (0.71+/−0.21) was not significantly different from the ratio of OR volumes to the planning CT (0.61+/−0.13) (p=0.25).Conclusion:In this study, CBCT does not show significant prostate volume changes during EBRT. CBCT and CT volumes are quite consistent and no improvement of volume estimation using CBCT is observed. The advantage of CBCT as a replacement of CT for volume study of boost LDR brachytherapy is limited.

TH‐CD‐207A‐10: Using the Gamma Index to Flag Changes in Anatomy During Radiation Therapy of Head and Neck Cancer

Purpose:This article presents a fast algorithm for comparing 3‐D anatomy from Cone‐Beam CT (CBCT) imaging using the gamma comparison index and to demonstrate how this can be used to flag patients for possible re‐planning of treatment.Methods:CBCT scans acquired on a Varian linear accelerator during treatment were used as input to the gamma comparator using thresholds of 5 mm distance to agreement and 30 Hounsfield Unit CT number difference. The fraction 1 CBCT study was initially used as the reference. Should there be a re‐plan during treatment, the reference resets to the CBCT study acquired on the day 1 of the re‐plan. Histograms of failing pixels (γ &gt; 1) were generated from each 3‐D gamma map. An indicator of anatomy congruence, the match quality parameter (MQP), was derived from failed pixel histograms using the 90th percentile gamma value. The MQP was plotted versus fraction number and related to actual repeat computed tomography (re‐CT) order dates as decided by a radiation oncologist. From this, decision criteria were derived for the algorithm to “trigger” re‐CT consideration and predictive power was scored using receiver‐operator characteristic (ROC) analysis.Results:The MQP plot generally showed that the on‐line match from CBCT image guidance deteriorated as the treatment progressed due to weight loss and tumor regression. The optimized MQP criteria for triggering re‐CT consideration demonstrated high sensitivity and specificity, consistent with actual re‐CT order dates within ± 3 fractions. Out of 20 patients that were actually re‐planned, the algorithm failed to trigger a re‐CT recommendation only twice and this was caused by CBCT ring artifacts.Conclusion:We have demonstrated that gamma comparisons can be used to evaluate CBCT‐acquired anatomy pairs and, from this, an algorithm can be “trained” to flag patients for possible re‐planning in a manner consistent with local radiation oncology practice.

Ultratight Margin (2-3 mm) Intensity Modulated Radiation Therapy With Daily Cone Beam CT Image Guidance Yields Excellent Locoregional Control in Head and Neck Cancer

Ultratight Margin (2-3 mm) Intensity Modulated Radiation Therapy With Daily Cone Beam CT Image Guidance Yields Excellent Locoregional Control in Head and Neck Cancer

SU‐E‐T‐708: Spatial Accuracy of Small‐Target SRS Using Conebeam CT Guidance and Static Arcs with MLC‐Defined Fields

Purpose:To measure the spatial accuracy of dose delivery under conebeam CT guidance to small targets using static arcs with MLC‐defined fields.Methods:A plastic (PMMA) phantom simulating a small brain lesion was constructed. The lesion was a cylindrical air cavity having 3 mm length and 3.175 mm diameter. Gafchromic EBT 2 film passing through the cavity was pin pricked at the exact geometric cavity center. Following CT simulation treatment plans involving static arcs with MLC‐defined fields were designed, similar to radiotherapy with circular tertiary cones. 5×2 mm fields were generated by opening two centrally located leaf pairs of a high‐definition MLC to 2.0 mm. The target was irradiated with 6 MV photons on a STx linac under conebeam CT image guidance to 600 cGy at isocenter. Films from coronal and sagittal planes were scanned and evaluated using the ImageJ software. The distance between the centroid of the 50% isodose line and the center of the pin prick was the measure of geographic accuracy.Results:Single arcs resulted in ellipsoidal 50% isodose surfaces having diameters of 5.0 mm along the gantry axis and 7.7 mm in the cross‐sectional directions. 4‐arc delivery at couch angles of 0, 45, 90 and 315 degrees produced 50% isodose surfaces having diameters of 5.6, 5.7 and 7.5 mm diameters along the lateral, longitudinal and anterior‐posterior directions, respectively. In any of the experiments, the largest distance by which the centroid of the 50% isodose line missed the center of the target was 0.36 mm or less.Conclusion:MLC‐defined static arcs delivered under conebeam CT guidance provide precise irradiation of small targets. The method is very efficient since no special attachments or modifications of the accelerator are required. Since MLC leaves are stationary throughout the treatment, patient‐specific QA involving phantoms should not be required.

Investigating the accuracy of microstereotactic-body-radiotherapy utilizing anatomically accurate 3D printed rodent-morphic dosimeters.

Sophisticated small animal irradiators, incorporating cone-beam-CT image-guidance, have recently been developed which enable exploration of the efficacy of advanced radiation treatments in the preclinical setting. Microstereotactic-body-radiation-therapy (microSBRT) is one technique of interest, utilizing field sizes in the range of 1-15 mm. Verification of the accuracy of microSBRT treatment delivery is challenging due to the lack of available methods to comprehensively measure dose distributions in representative phantoms with sufficiently high spatial resolution and in 3 dimensions (3D). This work introduces a potential solution in the form of anatomically accurate rodent-morphic 3D dosimeters compatible with ultrahigh resolution (0.3 mm(3)) optical computed tomography (optical-CT) dose read-out. Rodent-morphic dosimeters were produced by 3D-printing molds of rodent anatomy directly from contours defined on x-ray CT data sets of rats and mice, and using these molds to create tissue-equivalent radiochromic 3D dosimeters from Presage. Anatomically accurate spines were incorporated into some dosimeters, by first 3D printing the spine mold, then forming a high-Z bone equivalent spine insert. This spine insert was then set inside the tissue equivalent body mold. The high-Z spinal insert enabled representative cone-beam CT IGRT targeting. On irradiation, a linear radiochromic change in optical-density occurs in the dosimeter, which is proportional to absorbed dose, and was read out using optical-CT in high-resolution (0.5 mm isotropic voxels). Optical-CT data were converted to absolute dose in two ways: (i) using a calibration curve derived from other Presage dosimeters from the same batch, and (ii) by independent measurement of calibrated dose at a point using a novel detector comprised of a yttrium oxide based nanocrystalline scintillator, with a submillimeter active length. A microSBRT spinal treatment was delivered consisting of a 180° continuous arc at 225 kVp with a 20 × 10 mm field size. Dose response was evaluated using both the Presage/optical-CT 3D dosimetry system described above, and independent verification in select planes using EBT2 radiochromic film placed inside rodent-morphic dosimeters that had been sectioned in half. Rodent-morphic 3D dosimeters were successfully produced from Presage radiochromic material by utilizing 3D printed molds of rat CT contours. The dosimeters were found to be compatible with optical-CT dose readout in high-resolution 3D (0.5 mm isotropic voxels) with minimal artifacts or noise. Cone-beam CT image guidance was possible with these dosimeters due to sufficient contrast between high-Z spinal inserts and tissue equivalent Presage material (CNR ∼10 on CBCT images). Dose at isocenter measured with optical-CT was found to agree with nanoscintillator measurement to within 2.8%. Maximum dose in line profiles taken through Presage and film dose slices agreed within 3%, with FWHM measurements through each profile found to agree within 2%. This work demonstrates the feasibility of using 3D printing technology to make anatomically accurate Presage rodent-morphic dosimeters incorporating spinal-mimicking inserts. High quality optical-CT 3D dosimetry is feasible on these dosimeters, despite the irregular surfaces and implanted inserts. The ability to measure dose distributions in anatomically accurate phantoms represents a powerful useful additional verification tool for preclinical microSBRT.

Evaluation of targeting accuracy during a frameless stereotactic lung treatment using respiration correlated cone-beam CT image guidance

Evaluation of targeting accuracy during a frameless stereotactic lung treatment using respiration correlated cone-beam CT image guidance