Implementation and operation of incident learning across a newly-created health system

PURPOSE

The purpose of this work is to describe our experience launching an expanded incident learning system for patient safety and quality that takes into account aspects beyond therapeutic dose delivery, specifically imaging/simulation incidents, medical care incidents, and operational issues.

METHODS

Our ILS was designed for a newly created health system comprised of a midsized academic hospital and two smaller community hospitals. The main design goal was to create a highly sensitive system to capture as much information throughout the department as possible. Reports were classified according to incidents and near misses involving therapeutic radiation, imaging/simulation, and patient care (not involving radiation), unsafe conditions, operational issues, and accolades/suggestions. Reports were analyzed according to impact on various steps in the process of care. Actions made in response to reports were assessed and characterized by intervention reliability.

RESULTS

A total of 1125 reports were submitted in the first 23 months. For all three departments, therapeutic radiation incidents and near misses consisted of less than one-third of all reports submitted. For the midsized academic department, operational issues and unsafe conditions comprised the largest percentage of reports (70%). Although the majority of reports impacted steps related to the technical aspects of treatment (simulation, planning, and treatment delivery), 20% impacted other steps such as scheduling or clinic visits. More than 160 actions were performed in response to reports. Of these actions, 63 were quality improvement interventions to improve practices, while 97 were learning actions for raising awareness.

CONCLUSIONS

We have developed an ILS that identifies issues related to the entire process of care delivery in radiation oncology, as evidenced by frequent and varied reported events. By identifying a broad spectrum of issues in a department, opportunities for improvement can be identified.

Calculating tumor trajectory and dose-of-the-day using cone-beam CT projections

PURPOSE

Cone-beam CT (CBCT) projection images provide anatomical data in real-time over several respiratory cycles, forming a comprehensive picture of tumor movement. The authors developed and validated a method which uses these projections to determine the trajectory of and dose to highly mobile tumors during each fraction of treatment.

METHODS

CBCT images of a respiration phantom were acquired, the trajectory of which mimicked a lung tumor with high amplitude (up to 2.5 cm) and hysteresis. A template-matching algorithm was used to identify the location of a steel BB in each CBCT projection, and a Gaussian probability density function for the absolute BB position was calculated which best fit the observed trajectory of the BB in the imager geometry. Two modifications of the trajectory reconstruction were investigated: first, using respiratory phase information to refine the trajectory estimation (Phase), and second, using the Monte Carlo (MC) method to sample the estimated Gaussian tumor position distribution. The accuracies of the proposed methods were evaluated by comparing the known and calculated BB trajectories in phantom-simulated clinical scenarios using abdominal tumor volumes.

RESULTS

With all methods, the mean position of the BB was determined with accuracy better than 0.1 mm, and root-mean-square trajectory errors averaged 3.8% ± 1.1% of the marker amplitude. Dosimetric calculations using Phase methods were more accurate, with mean absolute error less than 0.5%, and with error less than 1% in the highest-noise trajectory. MC-based trajectories prevent the overestimation of dose, but when viewed in an absolute sense, add a small amount of dosimetric error (<0.1%).

CONCLUSIONS

Marker trajectory and target dose-of-the-day were accurately calculated using CBCT projections. This technique provides a method to evaluate highly mobile tumors using ordinary CBCT data, and could facilitate better strategies to mitigate or compensate for motion during stereotactic body radiotherapy.

Safety of contralateral submandibular gland sparing in locally advanced oropharyngeal cancers: A multicenter review

BACKGROUND

Previous groups have shown contralateral submandibular gland sparing to improve xerostomia with safe outcomes, but primarily in early-stage disease. In this study, we present a large cohort of patients with locally advanced head and neck cancer that underwent contralateral submandibular gland-sparing radiotherapy, to demonstrate feasibility and safety specifically in patients with locally advanced disease.

METHODS

We retrospectively analyzed patients who were treated prospectively with contralateral submandibular gland sparing. Only patients who underwent bilateral neck radiotherapy with contralateral submandibular gland doses <39 Gy were included.

RESULTS

We identified 71 patients. Approximately 80% of patients had ≥N2b disease. The contralateral submandibular gland mean dose was 33 Gy and, at a median follow-up of 27.3 months, no patients experienced treatment failure in the contralateral level IB lymph nodes.

CONCLUSION

Xerostomia remains a significant morbidity despite parotid sparing and can be minimized further by contralateral submandibular gland sparing. These data provide important preliminary evidence that contralateral submandibular gland sparing is feasible and may be safe even in locally advanced cancers.

Fan-beam intensity modulated proton therapy

PURPOSE

This paper presents a concept for a proton therapy system capable of delivering intensity modulated proton therapy using a fan beam of protons. This system would allow present and future gantry-based facilities to deliver state-of-the-art proton therapy with the greater normal tissue sparing made possible by intensity modulation techniques.

METHODS

A method for producing a divergent fan beam of protons using a pair of electromagnetic quadrupoles is described and particle transport through the quadrupole doublet is simulated using a commercially available software package. To manipulate the fan beam of protons, a modulation device is developed. This modulator inserts or retracts acrylic leaves of varying thickness from subsections of the fan beam. Each subsection, or beam channel, creates what effectively becomes a beam spot within the fan area. Each channel is able to provide 0-255 mm of range shift for its associated beam spot, or stop the beam and act as an intensity modulator. Results of particle transport simulations through the quadrupole system are incorporated into the MCNPX Monte Carlo transport code along with a model of the range and intensity modulation device. Several design parameters were investigated and optimized, culminating in the ability to create topotherapy treatment plans using distal-edge tracking on both phantom and patient datasets.

RESULTS

Beam transport calculations show that a pair of electromagnetic quadrupoles can be used to create a divergent fan beam of 200 MeV protons over a distance of 2.1 m. The quadrupole lengths were 30 and 48 cm, respectively, with transverse field gradients less than 20 T/m, which is within the range of water-cooled magnets for the quadrupole radii used. MCNPX simulations of topotherapy treatment plans suggest that, when using the distal edge tracking delivery method, many delivery angles are more important than insisting on narrow beam channel widths in order to obtain conformal target coverage. Overall, the sharp distal falloff of a proton depth-dose distribution was found to provide sufficient control over the dose distribution to meet objectives, even with coarse lateral resolution and channel widths as large as 2 cm. Treatment plans on both phantom and patient data show that dose conformity suffers when treatments are delivered from less than approximately ten angles. Treatment time for a sample prostate delivery is estimated to be on the order of 10 min, and neutron production is estimated to be comparable to that found for existing collimated systems.

CONCLUSIONS

Fan beam proton therapy is a method of delivering intensity modulated proton therapy which may be employed as an alternative to magnetic scanning systems. A fan beam of protons can be created by a set of quadrupole magnets and modified by a dual-purpose range and intensity modulator. This can be used to deliver inversely planned treatments, with spot intensities optimized to meet user defined dose objectives. Additionally, the ability of a fan beam delivery system to effectively treat multiple beam spots simultaneously may provide advantages as compared to spot scanning deliveries.

MRI patterns of T1 enhancing radiation necrosis versus tumour recurrence in high-grade gliomas

INTRODUCTION

Despite the emergence of new imaging technologies, the differentiation of treatment-related changes from recurrent tumour in patients with high-grade gliomas remains a difficult challenge. We evaluated whether specific MRI (magnetic resonance imaging) T1 post-contrast enhancement patterns can help to distinguish between radiation necrosis and tumour recurrence.

METHODS

This study was approved by local institutional review board. Fifty-one patients with World Health Organization grade III-IV glioma underwent reoperation after prior chemoradiation. The percentage of radiation necrosis versus recurrent tumour in reoperation specimens was estimated by an experienced neuropathologist. Enhancement patterns on T1 post-contrast sequences from the MRIs obtained prior to reoperation were evaluated according to pathology.

RESULTS

T1 contrast enhancement patterns correlating with recurrent tumour included focal solid nodules and solid uniform enhancement with distinct margins. Eighty-five per cent (17/20) of patients with ≥70% recurrent tumour at reoperation demonstrated one of these patterns on preoperative MRI. Enhancement patterns correlating with radiation necrosis included a hazy mesh-like diffuse enhancement and rim enhancement with feathery indistinct margins. Ninety-four per cent (17/18) of patients with ≥70% radiation necrosis demonstrated one of these two patterns. Thirteen cases had more mixed pathology (>30% of tumour/necrosis) and demonstrated patterns associated with recurrence and/or necrosis. Compared to MR spectroscopy performed in 10 patients, enhancement patterns on MRI were just as accurate in predicting pathologic diagnosis.

CONCLUSION

Identifying distinct patterns of contrast enhancement on MRI may help to differentiate between radiation necrosis and tumour recurrence in high-grade gliomas.