Presented at the 51st Annual Meeting of the American Society of Radiation Oncology, Chicago, Illinois, November 1-5, 2009.
A survey of image-guided radiation therapy use in the United States†
Article first published online: 17 MAY 2010
Copyright © 2010 American Cancer Society
Volume 116, Issue 16, pages 3953–3960, 15 August 2010
How to Cite
Simpson, D. R., Lawson, J. D., Nath, S. K., Rose, B. S., Mundt, A. J. and Mell, L. K. (2010), A survey of image-guided radiation therapy use in the United States. Cancer, 116: 3953–3960. doi: 10.1002/cncr.25129
- Issue published online: 4 AUG 2010
- Article first published online: 17 MAY 2010
- Manuscript Accepted: 27 OCT 2009
- Manuscript Revised: 26 OCT 2009
- Manuscript Received: 16 SEP 2009
- image-guided radiation therapy;
- radiation oncology
Image-guided radiation therapy (IGRT) is a novel array of in-room imaging modalities that are used for tumor localization and patient setup in radiation oncology. The prevalence of IGRT use among US radiation oncologists is unknown.
A random sample of 1600 radiation oncologists was surveyed by Internet, e-mail and fax regarding the frequency of IGRT use, clinical applications, and future plans for use. The definition of IGRT included imaging technologies that are used for setup verification or tumor localization during treatment.
Of 1089 evaluable respondents, 393 responses (36.1%) were received. The proportion of radiation oncologists using IGRT was 93.5%. When the use of megavoltage (MV) portal imaging was excluded from the definition of IGRT, the proportion using IGRT was 82.3%. The majority used IGRT rarely (in <25% of their patients; 28.9%) or infrequently (in 25%-50% of their patients; 33.1%). The percentages using ultrasound, video, MV-planar, kilovoltage (kV)-planar, and volumetric technologies were 22.3%, 3.2%, 62.7%, 57.7%, and 58.8%, respectively. Among IGRT users, the most common disease sites treated were genitourinary (91.1%), head and neck (74.2%), central nervous system (71.9%), and lung (66.9%). Overall, 59.1% of IGRT users planned to increase use, and 71.4% of nonusers planned to adopt IGRT in the future.
IGRT is widely used among radiation oncologists. On the basis of prospective plans of responders, its use is expected to increase. Further research will be required to determine the safety, cost efficacy, and optimal applications of these technologies. Cancer 2010. © 2010 American Cancer Society.
Image-guided radiation therapy (IGRT) consists of an array of imaging technologies designed to improve target localization and patient setup. In recent years, new in-room technologies have provided the opportunity for unprecedented accuracy in radiation therapy (RT) delivery. The concomitant expanding use of intensity-modulated RT (IMRT)1 and hypofractionated stereotactic techniques2 has required improved accuracy, providing a strong impetus to adopt IGRT.
Numerous IGRT technologies have been applied to treat cancer over the last half century. Early technologies to improve patient setup included kilovoltage (kV)-planar, x-ray–based3 and video-based systems.4-6 Subsequently, megavoltage (MV)-planar imaging technologies were developed, notably electronic portal imaging devices (EPID).7, 8 Various types of floor-mounted9-12 or gantry-mounted13-16 kV-planar imaging technologies also have been implemented over the years. Ultrasound17-24 and EPID with implanted radio-opaque (fiducial) markers25-33 were relatively early developments to improve target localization. Recently, in-room volumetric imaging systems, such as MV computed tomography (CT)34, 35 and MV36-38 or kV16, 39-43 cone-beam computed tomography (CBCT), have been introduced, providing greater soft tissue definition and improved target localization. Collectively, these IGRT technologies provide the potential to escalate target doses while decreasing normal tissue doses, thereby improving the therapeutic ratio of RT.
Although there is considerable interest in IGRT technologies, little is known about their use in the radiation oncology community. It is unclear how many radiation oncologists currently use these technologies, which technologies are used and to what extent, and how they are being applied. To answer these questions, we conducted a nationwide survey of practicing radiation oncologists.
MATERIALS AND METHODS
We randomly selected 1600 of approximately 5000 radiation oncologists who were listed in the 2008 American Society for Radiation Oncology (ASTRO) directory. All physicians who were designated as active and allied members were included. Emeritus professors and radiation oncologists practicing outside of the United States were excluded. The survey was sent in 3 forms: as an e-mail attachment, as a link to an online survey, and by facsimile. We attempted to contact each physician using the listed e-mail address or fax number. If neither were valid, then we searched for updated contact information in the 2009 ASTRO online directory. If no information could be found or if the fax or e-mail information was invalid, then the physician was designated as uncontactable and was excluded from further analysis. Those who had retired also were excluded. Physicians who returned the survey blank were counted as nonrespondents.
A 10-question survey was designed to collect demographic information and address the use of IGRT technologies in patients who received RT (Fig. 1). This survey was conducted between February 1 and March 31, 2009 as part of a larger, comprehensive survey on IGRT that included the use of advanced imaging modalities to augment target delineation. The results of other aspects of the IGRT survey will be the subject of a separate report.
Survey responses were considered evaluable if the survey was at least partially completed. For the purposes of this survey, we defined IGRT as the use of any of the following imaging modalities: ultrasound, video, planar, and volumetric imaging performed in the treatment room to aid in patient setup or tumor localization. Each of the 4 categories included home-grown and multiple commercial systems (Table 1). Accompanying the survey was a cover letter outlining the goals of the project and confidential nature of the results obtained. In particular, it was stressed that the findings were to be used for academic purposes only and that company-specific data would not be disclosed or presented.
|B-mode acquisition and targeting (BAT) system|
|Planar (MV) (EPID)|
In addition to inquiring about practice type (academic vs private practice) and size of practice group, physicians were asked about the type(s) of IGRT technologies used, the year they had adopted them, the percentage of patients in their practice they currently treat with IGRT, disease sites treated, and future plans for IGRT use. Nonusers were asked whether or not they intended to adopt IGRT technologies in the future.
The survey results are presented as the percentage of evaluable responses. Differences in proportions between various groups were analyzed using chi-square and Fisher exact tests. The Holm step-down method was used to adjust the P values for multiple comparisons.44
Of 1600 randomly selected physicians, 1089 physicians (68.1%) were contactable (Fig. 2). From these, we received a total of 393 responses (36.1%). Of the 393 respondents, 7 were retired, and 1 returned the survey blank; thus, in total, 385 responses were evaluable.
Responses were received from physicians in 45 states (Table 2). One-hundred thirty-three responses were from academic physicians (34.5%), and 252 responses were from private-practice physicians (65.5%). Three respondents returned the survey with incomplete demographic information.
|Characteristic||No. of Respondents (%)|
|No. of physicians||385|
|Sex, n (%)|
|Median time in practice (range), y||16 (1-44)|
|Median no. of physicians per practice (range)||5 (1-55)|
Of 385 evaluable respondents, 360 respondents (93.5%; 95% confidence interval, 91-96%) reported having used IGRT technologies in their practices. When the use of MV portal imaging was excluded from the definition of IGRT, the proportion using IGRT was 82.3%. The majority reported using such technologies either rarely (in <25% of their patients; 8.9%) or infrequently (in 25%-50% of their patients; 33.1%). The percentages of physicians who reported using IGRT frequently (in 51%-75% of their patients) or routinely (in >75% of their patients) were 18.7% and 19.3%, respectively.
The most commonly used IGRT modalities were MV-planar (62.7%), volumetric (58.8%), and kV-planar (57.7%) imaging. The percentage of respondents using at least 1 or more of these technologies was 89.4%. Ultrasound and video technologies were used by 22.3% and 3.2% of physicians, respectively.
IGRT was applied in all disease sites, most commonly genitourinary (GU) (91.1%), head and neck (74.2%), and central nervous system (CNS) (71.9%) (Table 3). Volumetric-based technologies were the most commonly used modalities in lung (59.3%), head and neck (56.9%), gastrointestinal (56.9%), and GU (55.3%) tumors; whereas kV-planar–based technologies were the most commonly used in CNS tumors (62.6%). Ultrasound (with the exception of GU tumors) and video were the least commonly used modalities in all sites (Fig. 3).
|Disease Site||No. of Users (% of All Users)|
|Head and neck||267 (74.2)|
|Central nervous system||259 (71.9)|
A similar proportion of academic and private-practice radiation oncologists used IGRT overall (94.7% and 94.8%, respectively; P = .78). Figure 4 indicates that no difference was observed in the proportion of academic and private-practice physicians using video, ultrasound, or MV-planar modalities. However, academic physicians were more likely to use volumetric techniques (75.2% vs 50.8%; P < .001) and kV-planar techniques (72.2% vs 50%; P < .001) than private-practice physicians. In addition, academic physicians were more likely to use IGRT frequently or routinely (in >50% of their patients) compared with private-practice physicians (47.5% vs 31.8%; P < .01).
Results were also compared based on geography, years of experience, size of practice, and specialization. The percentages of radiation oncologists using IGRT in the East, South, Midwest, and West were 92.6%, 93.1%, 94.4%, and 97.4%, respectively (P = .56). No differences were observed in IGRT use according to the number of years in practice: The percentages of users with 1 to 10 years, 11 to 20 years, and >20 years in practice were 96.1%, 93.9%, and 96.5%, respectively (P = .38). However, a difference in the type of IGRT used was observed among physicians with ≤10 years in practice, who were less likely to use MV-planar–based technologies than physicians with >10 years in practice (50% vs 65%; P = .02). The percentages of respondents in practices that included 1 physician, 2 to 10 physicians, and >10 physicians who reported using IGRT were similar (90.7%, 94.8%, and 97.2%, respectively; P = .31). Overall, IGRT use was similar for specialists and nonspecialists. However, specialists were more likely to use IGRT frequently or routinely (in >50% of their patients) compared with nonspecialists (47.1% vs 19.1%; P < .001).
Figure 5 illustrates the cumulative adoption of each IGRT modality based on reported years of adoption and cessation. Ultrasound and MV-planar–based systems were adopted earliest. The majority of respondents who were using ultrasound (54.5%) reported having adopted it by 2001. However, the percentage of respondents adopting ultrasound peaked in 2006, then declined. The majority of respondents who were using MV-planar technologies (53.4%) reported having implemented them by 2004. The adoption of kV-planar–based modalities followed, and the majority of users (54.3%) had adopted them by 2006. Volumetric-based imaging modalities were implemented more recently, and the majority of users (67.1%) had adopted them by 2007. Of the responders who were using IGRT, 40.6% planned to maintain their current level of use, and 59.1% planned to increase use. Among rare or infrequent users (in ≤50% of their patients), 65.8% planned to increase their use, and 47% of frequent or routine users (in >50% of their patients) planned to increase use. One current user planned to decrease use. Among nonusers, 71.4% planned to adopt IGRT technologies in the future.
The objective of this study was to assess the use of IGRT technologies among radiation oncologists in the United States. We observed that the great majority of practicing radiation oncology physicians currently use IGRT, and >90% of respondents are using at least 1 form of IGRT in their practice. However, the majority of users implemented IGRT in <50% of their patients.
Although no overall difference in IGRT use was observed between academic and private-practice physicians, academic physicians tended to use IGRT in a larger proportion of their patients. Moreover, we observed that certain modalities (notably, kV-planar and volumetric imaging) were used more commonly among academic physicians. The reasons underlying such differences are uncertain but may include different levels of access to these technologies, greater use by specialists, or use of volumetric-based imaging for research trials at academic centers.
We noted that, among the various IGRT modalities, MV-planar and ultrasound modalities were adopted earliest, followed later by kV-planar and volumetric modalities. The use of ultrasound appears to be decreasing, probably in favor of alternative technologies. This may be caused in part by studies that compared ultrasound with other technologies and reported that planar imaging with implanted seeds and volumetric modalities provided superior accuracy in terms of setup and tumor localization.45-47 We also observed that physicians who had fewer years in practice tended to use MV-planar modalities less commonly, possibly signifying a decline in their use in the future. Overall, however, based on future plans of both users and nonusers, IGRT use is expected to increase. Notably, even physicians who reported using IGRT in the majority of patients planned to increase its use within their practices.
To our knowledge, this is the first study to assess the overall use of in-room IGRT in the radiation oncology community. We randomly sampled a large cohort of radiation oncologists representative of physicians with a wide range of characteristics. However, despite diligent attempts to collect responses from the sample, nonresponse and recall bias are potential limitations of this study. It is possible that IGRT nonusers or users of specific technologies were less likely to respond, which would lead to biased estimates of the true prevalence of IGRT use. The survey also was brief and could not address questions concerning reasons for IGRT adoption. To address some of these limitations, we intend to conduct a follow-up survey in 2011.
Our current findings indicate a need for further research to assess the efficacy and safety of IGRT use.48 IGRT technologies come with added cost, time, and, in the case of some imaging modalities, dose delivered to patients during treatment.49-51 Most of the literature published on these technologies has reported on dosimetric consequences and setup accuracy, but there are limited data regarding clinical outcomes, such as disease recurrence and treatment toxicity. Given the widespread and apparently increasing use of IGRT, prospective studies on clinical outcomes are needed to assess its clinical impact, safety, and cost efficacy.
CONFLICT OF INTEREST DISCLOSURES
Supported by National Institutes of Health T32 grant RR023254.
- 15Image-guided radiation therapy (IGRT) in gastrointestinal tumors [serial online]. JOP. 2006; 7: 372-381., , , , , .
- 44A simple sequentially rejective multiple test procedure. Scand J Stat. 1979; 6: 65-70..