B Clark

Patient safety improvements in radiation treatment through 5 years of incident learning

PURPOSE To quantify the impact of a comprehensive incident learning system in terms of safety improvements. METHODS AND MATERIALS An incident learning system tailored for radiation treatment and based on published principles has been used consistently in our large academic cancer center for more than 5 years. In the adopted system, every incident, whether or not there is a resulting direct impact on a patient treatment, is recorded and investigated to determine basic causes. The scope of the program thus includes potential, or near miss, events which have no impact on patients but which provide valuable insights into program weaknesses and hence facilitate proactive measures to minimize risk. RESULTS Analysis of 2506 incident reports generated over a 5-year period demonstrate a substantial decline in actual, nonminor incidents; ie, those with a dose variation from that prescribed of greater than 5%. Only 49 incidents (1.95%) had an impact on patients. The actual incident rate at the point of treatment delivery, the most vulnerable point in our process, has also decreased. The system has provided rapid feedback to monitor several initiatives including implementation of new technology and several new treatment techniques. Using the evidence provided by these incident reports, strategies were developed by a multidisciplinary team to address system weaknesses. Interventions introduced include several human error reduction strategies including forcing functions and constraints to improve system resilience. CONCLUSIONS Our results demonstrate that effective use of an incident learning system will strongly encourage the reporting of incidents, whether or not they directly impact a patient, and serve as a proactive means of enhancing safety and quality. As a side benefit, addressing and overcoming the cultural barriers between the 3 professional groups involved in radiation treatment has resulted in an improvement in the safety culture in our center.

Direct aperture optimization for online adaptive radiation therapy.

This paper is the first investigation of using direct aperture optimization (DAO) for online adaptive radiation therapy (ART). A geometrical model representing the anatomy of a typical prostate case was created. To simulate interfractional deformations, four different anatomical deformations were created by systematically deforming the original anatomy by various amounts (0.25, 0.50, 0.75, and 1.00 cm). We describe a series of techniques where the original treatment plan was adapted in order to correct for the deterioration of dose distribution quality caused by the anatomical deformations. We found that the average time needed to adapt the original plan to arrive at a clinically acceptable plan is roughly half of the time needed for a complete plan regeneration, for all four anatomical deformations. Furthermore, through modification of the DAO algorithm the optimization search space was reduced and the plan adaptation was significantly accelerated. For the first anatomical deformation (0.25 cm), the plan adaptation was six times more efficient than the complete plan regeneration. For the 0.50 and 0.75 cm deformations, the optimization efficiency was increased by a factor of roughly 3 compared to the complete plan regeneration. However, for the anatomical deformation of 1.00 cm, the reduction of the optimization search space during plan adaptation did not result in any efficiency improvement over the original (nonmodified) plan adaptation. The anatomical deformation of 1.00 cm demonstrates the limit of this approach. We propose an innovative approach to online ART in which the plan adaptation and radiation delivery are merged together and performed concurrently-adaptive radiation delivery (ARD). A fundamental advantage of ARD is the fact that radiation delivery can start almost immediately after image acquisition and evaluation. Most of the original plan adaptation is done during the radiation delivery, so the time spent adapting the original plan does not increase the overall time the patient has to spend on the treatment couch. As a consequence, the effective time allotted for plan adaptation is drastically reduced. For the 0.25, 0.5, and 0.75 cm anatomical deformations, the treatment time was increased by only 2, 4, and 6 s, respectively, as compared to no plan adaptation. For the anatomical deformation of 1.0 cm the time increase was substantially larger. The anatomical deformation of 1.0 cm represents an extreme case, which is rarely observed for the prostate, and again demonstrates the limit of this approach. ARD shows great potential for an online adaptive method with minimal extension of treatment time.

Integration of on-line imaging, plan adaptation and radiation delivery: proof of concept using digital tomosynthesis

The main objective of this manuscript is to propose a new approach to on-line adaptive radiation therapy (ART) in which daily image acquisition, plan adaptation and radiation delivery are integrated together and performed concurrently. A method is described in which on-line ART is performed based on intra-fractional digital tomosynthesis (DTS) images. Intra-fractional DTS images were reconstructed as the gantry rotated between treatment positions. An edge detection algorithm was used to automatically segment the DTS images as the gantry arrived at each treatment position. At each treatment position, radiation was delivered based on the treatment plan re-optimized for the most recent DTS image contours. To investigate the feasibility of this method, a model representing a typical prostate, bladder and rectum was used. To simulate prostate deformations, three clinically relevant, non-rigid deformations (small, medium and large) were modeled by systematically deforming the original anatomy. Using our approach to on-line ART, the original treatment plan was successfully adapted to arrive at a clinically acceptable plan for all three non-rigid deformations. In conclusion, we have proposed a new approach to on-line ART in which plan adaptation is performed based on intra-fractional DTS images. The study findings indicate that this approach can be used to re-optimize the original treatment plan to account for non-rigid anatomical deformations. The advantages of this approach are 1) image acquisition and radiation delivery are integrated in a single gantry rotation around the patient, reducing the treatment time, and 2) intra-fractional DTS images can be used to detect and correct for patient motion prior to the delivery of each beam (intra-fractional patient motion).

Anniversary Paper: The role of medical physicists in developing stereotactic radiosurgery

This article is a tribute to the pioneering medical physicists over the last 50years who have participated in the research, development, and commercialization of stereotactic radiosurgery (SRS) and stereotactic radiotherapy utilizing a wide range of technology. The authors have described the evolution of SRS through the eyes of physicists from its beginnings with the Gamma Knife™ in 1951 to proton and charged particle therapy; modification of commercial linacs to accommodate high precision SRS setups; the multitude of accessories that have enabled fine tuning patients for relocalization, immobilization, and repositioning with submillimeter accuracy; and finally the emerging technology of SBRT. A major theme of the article is the expanding role of the medical physicist from that of advisor to the neurosurgeon to the current role as a primary driver of new technology that has already led to an adaptation of cranial SRS to other sites in the body, including, spine, liver, and lung. SRS continues to be at the forefront of the impetus to provide technological precision for radiation therapy and has demonstrated a host of downstream benefits in improving delivery strategies for conventional therapy as well. While this is not intended to be a comprehensive history, and the authors could not delineate every contribution by all of those working in the pursuit of SRS development, including physicians, engineers, radiobiologists, and the rest of the therapy and dosimetry staff in this important and dynamic radiation therapy modality, it is clear that physicists have had a substantial role in the development of SRS and theyincreasingly play a leading role in furthering SRS technology.

Medical physics staffing for radiation oncology: a decade of experience in Ontario, Canada

The January 2010 articles in The New York Times generated intense focus on patient safety in radiation treatment, with physics staffing identified frequently as a critical factor for consistent quality assurance. The purpose of this work is to review our experience with medical physics staffing, and to propose a transparent and flexible staffing algorithm for general use. Guided by documented times required per routine procedure, we have developed a robust algorithm to estimate physics staffing needs according to center‐specific workload for medical physicists and associated support staff, in a manner we believe is adaptable to an evolving radiotherapy practice. We calculate requirements for each staffing type based on caseload, equipment inventory, quality assurance, educational programs, and administration. Average per‐case staffing ratios were also determined for larger‐scale human resource planning and used to model staffing needs for Ontario, Canada over the next 10 years. The workload specific algorithm was tested through a survey of Canadian cancer centers. For center‐specific human resource planning, we propose a grid of coefficients addressing specific workload factors for each staff group. For larger scale forecasting of human resource requirements, values of 260, 700, 300, 600, 1200, and 2000 treated cases per full‐time equivalent (FTE) were determined for medical physicists, physics assistants, dosimetrists, electronics technologists, mechanical technologists, and information technology specialists, respectively. PACS numbers: 87.55.N‐, 87.55.Qr

The role of medical physicists in developing stereotactic radiosurgery

This article is a tribute to the pioneering medical physicists over the last 50years who have participated in the research, development, and commercialization of stereotactic radiosurgery (SRS) and stereotactic radiotherapy utilizing a wide range of technology. The authors have described the evolution of SRS through the eyes of physicists from its beginnings with the Gamma Knife™ in 1951 to proton and charged particle therapy; modification of commercial linacs to accommodate high precision SRS setups; the multitude of accessories that have enabled fine tuning patients for relocalization, immobilization, and repositioning with submillimeter accuracy; and finally the emerging technology of SBRT. A major theme of the article is the expanding role of the medical physicist from that of advisor to the neurosurgeon to the current role as a primary driver of new technology that has already led to an adaptation of cranial SRS to other sites in the body, including, spine, liver, and lung. SRS continues to be at the forefront of the impetus to provide technological precision for radiation therapy and has demonstrated a host of downstream benefits in improving delivery strategies for conventional therapy as well. While this is not intended to be a comprehensive history, and the authors could not delineate every contribution by all of those working in the pursuit of SRS development, including physicians, engineers, radiobiologists, and the rest of the therapy and dosimetry staff in this important and dynamic radiation therapy modality, it is clear that physicists have had a substantial role in the development of SRS and theyincreasingly play a leading role in furthering SRS technology.

EVALUATION OF TARGETING ERRORS IN ULTRASOUND-ASSISTED RADIOTHERAPY

A method for validating the start-to-end accuracy of a 3-D ultrasound (US)-based patient positioning system for radiotherapy is described. A radiosensitive polymer gel is used to record the actual dose delivered to a rigid phantom after being positioned using 3-D US guidance. Comparison of the delivered dose with the treatment plan allows accuracy of the entire radiotherapy treatment process, from simulation to 3-D US guidance, and finally delivery of radiation, to be evaluated. The 3-D US patient positioning system has a number of features for achieving high accuracy and reducing operator dependence. These include using tracked 3-D US scans of the target anatomy acquired using a dedicated 3-D ultrasound probe during both the simulation and treatment sessions, automatic 3-D US-to-US registration and use of infrared LED (IRED) markers of the optical position-sensing system for registering simulation computed tomography to US data. The mean target localization accuracy of this system was 2.5 mm for four target locations inside the phantom, compared with 1.6 mm obtained using the conventional patient positioning method of laser alignment. Because the phantom is rigid, this represents the best possible set-up accuracy of the system. Thus, these results suggest that 3-D US-based target localization is practically feasible and potentially capable of increasing the accuracy of patient positioning for radiotherapy in sites where day-to-day organ shifts are greater than 1 mm in magnitude.

3D ultrasound-based patient positioning for radiotherapy

A new 3D ultrasound-based patient positioning system for target localisation during radiotherapy is described. Our system incorporates the use of tracked 3D ultrasound scans of the target anatomy acquired using a dedicated 3D ultrasound probe during both the simulation and treatment sessions, fully automatic 3D ultrasound-toultrasound registration, and OPTOTRAK IRLEDs for registering simulation CT to ultrasound data. The accuracy of the entire radiotherapy treatment process resulting from the use of our system, from simulation to the delivery of radiation, has been validated on a phantom. The overall positioning error is less than 5mm, which includes errors from estimation of the irradiated region location in the phantom.

SU‐GG‐T‐267: Evaluation of the Accuracy of TomoTherapy Dose Calculations for Shallow‐Depth PTVs

Purpose: To investigate the accuracy of TomoTherapy dose calculations for shallow‐depth PTVs, and to examine the sensitivity of the resulting plans to positional variations. Method and Materials: TomoTherapy treatment plans were created and delivered for a cylindrical phantom with surface‐to‐PTV margins of 0 to 10 mm in 2 mm increments. Dose in the coronal plane was measured using EDR2 film and compared to the dose predicted by the TomoTherapy software. Treatment was also delivered with the phantom intentionally misaligned to investigate the sensitivity of each plan to imperfect patient alignment. Results: A margin of 0mm resulted in an excess dose on the order 15% to the region just below the surface of the phantom. This was consistent with the dose predicted by the planning software. Using a PTV to skin margin of 2mm or more resulted in only a negligible overdose to the phantom. With a margin of 0mm, the dose delivered was very sensitive to misalignment of the phantom. Moving the phantom by 4mm in one direction resulted in a peak dose slightly higher than predicted; moving it 4mm in the other direction substantially reduced the peak dose, nearly eliminating the overdosing altogether. With a margin of 4mm, misalignment had only negligible impact on the maximum dose. Conclusion: The results suggest that when treating breast cancer using tomotherapy, the PTV should be kept at least 2mm back from the surface of the skin to avoid severe dose dumping just below the skin and a maximum dose that changes significantly with only small misalignment of the patient.

Sci‐Fri PM: Planning‐05: Saving trees and improving workflow

Patient treatment preparation is a multi-step process requiring inputs from a range of disciplines and technologies. Our centre generates just over 4500 treatment plans annually and operates from two main campuses. A large, split program presents unique challenges during treatment preparation and has provided the impetus for a completely electronic treatment process. Throughout 2006 and 2007, we migrated our external beam treatment planning to the Computerized Medical Systems (CMS) product line. Utilizing a thin-client architecture, CMS supports distributed (multi-site) planning. Coincident with the treatment planning upgrade, IMPAC Multi-Access was configured to provide a paperless and filmless treatment record and electronic patient workflow. Standardized treatment objectives were also implemented in the form of site-group approved care plans. Details of the pretreatment process and the CMS / IMPAC implementation will be presented as well as a workflow time analysis. To date, treatment preparation times have been reduced by 25% (2.5 days) as a result of workflow improvements, representing a clear benefit to both staff and patients.