Characterization and commissioning of a Leksell Gamma Knife ICON system for framed and frameless stereotactic radiosurgery.

PURPOSE: The Leksell Gamma Knife Icon unit (IU) was introduced recently as an upgrade to the Perfexion unit (PU) at our Gamma Knife practice. In the current study, we sought mainly to characterize dosimetry and targeting accuracy of the IU treatment deliveries using both invasive frame and frameless treatment workflows. METHODS: Relative output factors were measured by delivering single-shot 4, 8 and 16 mm radiation profiles in the manufacturer's acrylonitrile butadiene styrene spherical phantom in coronal and sagittal planes using EBT3 film. Resultant dosimetry was compared with the manufacturer's dose calculation and derived output factors were compared with the manufacturer's published value. Geometric consistency of stereotactic coordinates based on cone-beam computed tomography (CBCT) versus the traditional conventional CT-based method was characterized using a rigid phantom containing nine fiducial indicators over four separate trials. End-to-end (E2E) testing using EBT3 film was designed to evaluate both dosimetric and geometric accuracy for hypothetical framed and frameless workflows. RESULTS: Relative output factors as measured by the manufacturer were independently confirmed using EBT3 film measurements to within 2%. The mean 3D radial discrepancy in stereotactic space between CBCT and CT-based definition over the sampled locations in our rigid geometry phantom was demonstrated to be between 0.40 mm and 0.56 mm over the set of trials, larger than prior reported values. E2E performed in 2D demonstrates sub-mm (and typically < 0.5 mm) accuracy for framed and frameless workflows; geometric accuracy of framed treatments using CBCT-defined stereotactic coordinates was shown to be slightly improved in comparison with those defined using conventional CT. Furthermore, in phantom, frameless workflows exhibited better accuracy than framed workflows for fractionated treatments, despite large magnitudes of introduced interfraction setup error. Accuracy of dosimetric delivery was confirmed in terms of qualitative comparisons of dose profiles and in terms of 2D gamma pass rates based on 1%/1 mm criteria. CONCLUSION: The IU was commissioned for clinical use of frameless and framed treatment protocols. The present study outlines an extensive E2E methodology for confirmation of dosimetric and geometric treatment accuracy.

Technique for the administration of high-dose-rate brachytherapy to the bile duct using a nasobiliary catheter.

PURPOSE: Cholangiocarcinoma patients who are potential candidates for liver transplantation may be treated with high-dose-rate (HDR) brachytherapy using a minimally invasive nasobiliary catheter in an effort to escalate the radiotherapy dose to the tumor and maximize local control rates. This work describes the equipment, procedures, and quality assurance (QA) that enables successful administration. METHODS AND MATERIALS: This work describes the nasobiliary catheter placement, simulation, treatment planning, treatment delivery, and QA. In addition, a chart review was performed of all patients who received endoscopic retrograde cholangiopancreatography for HDR bile duct brachytherapy at our institution from 2007 to 2017. The review evaluated how many patients were treated and the number of patients who could not be treated because of anatomic and/or equipment limitations. RESULTS: From 2007 to 2017, 122 cholangiocarcinoma patients have been treated with HDR brachytherapy using a nasobiliary catheter. Three patients underwent catheter placement but did not receive brachytherapy treatment due to catheter migration between placement and treatment or because the HDR afterloader was unable to extend the source wire into the treatment site. Periodic QA is recommended for ensuring whether the HDR afterloader is capable of extending the source wire through an extensive and curved path. CONCLUSIONS: Intraluminal HDR brachytherapy with a nasobiliary catheter can be successfully administered. Procedures and QA are described for ensuring safety and overcoming technical challenges.

Patient safety is improved with an incident learning system-Clinical evidence in brachytherapy.

BACKGROUND AND PURPOSE: Health leaders have advocated for incident learning systems (ILSs) to prevent errors, but there is limited evidence demonstrating that ILSs improve cancer patient safety. Herein, we report a long-term retrospective review of ILS reports for the brachytherapy practice at a large academic institution. MATERIAL AND METHODS: Over a nine-year period, the brachytherapy practice was encouraged to report all standard operating procedure deviations, including low risk deviations. A multidisciplinary committee assigned root causes and risk scores to all incidents. Evidence based practice changes were made using ILS data, and relevant incidents were communicated to all staff in order to reduce recurrence rates. RESULTS: 5258 brachytherapy procedures were performed and 2238 incidents were reported from 2007 to 2015. A ramp-up period was observed in ILS participation between 2007 (0.12 submissions/procedures) and 2011 (1.55 submissions/procedures). Participation remained stable between 2011 and 2015, and we achieved a 60% (p<0.001) decrease in the risk of dose error or violation of radiation safety policy and a 70% (p<0.001) decrease in frequency of high composite-risk scores. Significant decreases were also observed in incidents with root causes of poor communication (60% decrease, p<0.001) and poor quality of written procedures (59% decrease, p<0.001). CONCLUSIONS: Implementation of an ILS in brachytherapy significantly reduced risk during cancer patient care. Safety improvements have been sustained over several years.

Feasibility and full-course dosimetry of an intraoperatively placed multichannel brachytherapy catheter for accelerated partial breast irradiation.

PURPOSE: Determine feasibility and resultant dosimetry of an intraoperatively placed multichannel intracavitary brachytherapy catheter for accelerated partial breast irradiation (APBI). METHODS: Patients with breast cancer underwent intraoperative brachytherapy catheter placement based on frozen section analysis with immediate postoperative APBI. The planning target volume evaluation (PTVEval) and organs at risk were contoured on daily pretreatment CT scans for each patient, and the original treatment plan was applied to assess full-course dosimetry. RESULTS: Of the first 21 patients consented for intraoperative catheter placement, 20 (95%) were able to proceed with treatment as planned. The mean volume of PTVEval receiving 90% of prescription dose (V90%) and mean percentage of prescription dose to 90% of the PTVEval (D90%) on initial planning were 96.7 (±1.1%) and 100.2 (±2.1%), respectively. Full-course dose coverage remained excellent with a mean PTVEval V90% and D90% of 95.0 (±4.4%) and 100.2 (±9.6%), respectively. Mean full-course maximum dose constraints for chest wall and skin were met by 70% and 95% of patients, respectively. Air accumulation >1 cc during treatment increased the risk of a daily fraction with PTVEval coverage below goal (odds ratio, 9.8; p = 0.05), whereas those with applicators <0.5 cm from the chest wall at planning were at risk of exceeding that organ's maximum dose constraint on a daily fraction (odds ratio, 45; p = 0.02). CONCLUSIONS: Intraoperative catheter placement and early initiation of APBI based on frozen section pathology is feasible, yields acceptable dosimetry, and is an option for completing breast conserving therapy in less than 10 days.

Experimental and theoretical dosimetry of the RIC-100 phosphorus-32 brachytherapy source for implant geometries encountered in the intraoperative setting.

PURPOSE: Experimental and theoretical dosimetry of the RIC-100 phosphorus-32 brachytherapy source is presented for implant geometries that may occur in an intraoperative setting during treatment of localized spinal tumors with temporary superficial radiation. Dose variation, due to source shape and size, is evaluated, and nonideal implant conditions are simulated. METHODS AND MATERIALS: Calibration, depth dose, and dose profiles were evaluated for several implant geometries and source sizes. Experimental measurements were performed using EBT3 gafchromic film. Theoretical calculations were performed using dose point kernel (DPK) formalism, which simulates isotropic, monoenergetic point sources distributed uniformly throughout the source and emitting electrons radially outward. RESULTS: Calibration and depth dose for RIC-100 are independent of source size for diameters >1 cm. Sources should be ordered with physical dimensions ∼0.2 cm larger than the target size, in all dimensions, to deliver >90% prescription dose to target edges. Relative dose profile shape is approximately constant as a function of target depth. Air gaps between the source and target cause narrower dose profile widths and shallower depth dose in the therapeutic range. DPK for RIC-100 agrees with published P-32 kernels, and DPK calculations agree with measurement (within 5%) for many depths and geometries. CONCLUSIONS: Intraoperative placement and measurement dosimetry of RIC-100 require careful setup due to steep dose gradients. Physical source dimensions should be chosen carefully based on treatment site dimensions, and air gaps between source and target should be minimized, to prevent underdosing the target in the lateral extent. Radiological scaling should be used to calculate expected dose when nonwater materials are used in experimental measurements, such as calibration or depth dose.

Report on use of a methodology for commissioning and quality assurance of a VMAT system.

INTRODUCTION: Results of use of methodology for VMAT commissioning and quality assurance, utilizing both control point tests and dosimetric measurements are presented. METHODS AND MATERIALS: A generalizable, phantom measurement approach is used to characterize the accuracy of the measurement system. Correction for angular response of the measurement system and inclusion of couch structures are used to characterize the full range gantry angles desirable for clinical plans. A dose based daily QA measurement approach is defined. RESULTS: Agreement in the static vs. VMAT picket fence control point test was better than 0.5 mm. Control point tests varying gantry rotation speed, leaf speed and dose rate, demonstrated agreement with predicted values better than 1%. Angular dependence of the MatriXX array, varied over a range of 0.94-1.06, with respect to the calibration condition. Phantom measurements demonstrated central axis dose accuracy for un-modulated four field box plans was ≥2.5% vs. 1% with and without angular correction respectively with better results for VMAT (0.4%) vs. IMRT (1.6%) plans. Daily QA results demonstrated average agreement all three chambers within 0.4% over 9 month period with no false positives at a 3% threshold. DISCUSSION: The methodology described is simple in design and characterizes both the inherit limitations of the measurement system as well at the dose based measurements that may be directly related to patient plan QA.