Public interest in stereotactic body radiation therapy (SBRT) and stereotactic radiosurgery (SRS) in the United States

Abstract

Stereotactic body radiation therapy (SBRT) and stereotactic radiosurgery have become widely used in both palliative and curative treatments for variety of primary and secondary malignancies. Although the indications and use of stereotactic techniques have increased substantially in the past decades, there been no studies to date analyzing public interest in these techniques. Using Google Trends (Google LLC, Mountain View, CA), four search terms (“SBRT,” “stereotactic radiosurgery,” “Gamma Knife” and “Cyberknife”) were analyzed in the U.S. from January 2004 to June 2019. Each term was assigned a relative interest score based on frequency of searches. “SBRT” is becoming an increasingly popular search term, reaching peak interest in October 2018. Conversely, “stereotactic radiosurgery” and “Gamma Knife” radiosurgery initially had high interest, before declining over the past decade. “Cyberknife” was most popular in the mid-2000s but decreased steadily since that time. These trends were subsequently compared against PubMed publication data over the same time.

Introduction

Although stereotactic radiation was initially introduced as a means of intracranial radiosurgery, it has emerged as a standard form of treatment for many extracranial malignancies as well (1, 2). The advantage of stereotactic radiation therapy lies primarily in its ability to accurately deliver an ablative radiation dose to the proposed target while largely sparing normal tissues (2). Today, stereotactic body radiation therapy (SBRT) is regularly employed in the treatment of various primary and metastatic tumors, such as early stage lung cancer, primary and metastatic liver lesions, osseous metastases, and prostate cancer. Given that a multitude of studies have shown that SBRT improves patient outcomes, particularly in those patients who have limited treatment options due to medical inoperability or close proximity to critical organs, it has been widely accepted by the general radiation oncology community as a viable treatment option (1, 3-6). Various methods of stereotactic radiation including Gamma Knife (Elekta AB, Stockholm, Sweden) and Cyberknife (Accuray, Inc., Sunnyvale, CA) continue to be heavily utilized in the treatment of intracranial lesions (1).

Along with the growth of stereotactic radiation in clinical use, there has been an increase in direct-to-consumer advertising and aggressive marketing of stereotactic technologies from manufacturers (7). A study by Narang et al. showed that 76% of cancer treatment centers had brand-specific SBRT marketing material on their websites (7). Whether the continued growth of SBRT and aggressive marketing regarding its benefits has impacted public knowledge and perception of this technology is yet to be fully determined.

A 2019 survey revealed that 59% of American adults obtain health information via online sources (8), with Google searches (Google LLC, Mountain View, CA) being one of the most common ways of obtaining information online. Google Trends has previously been utilized as a surrogate means to examine the public interest in novel radiation oncology techniques and practice guidelines (9). We aim to objectively assess public interest in stereotactic techniques by utilizing Google Trends as a surrogate for public interest from 2004 to 2019.

Methods and Materials

Google Trends, a freely available service through Google (available at https://trends.google.com/trends/?geo=US), allows users to analyze the popularity of common search terms using the Google search engine. An “interest score”, ranging from 100 (peak activity) to 0 (not enough data), is assigned to each term monthly since January 2004 and is normalized for the term. The absolute number of individual searches was not reported; however, geographic data is reported, with a relative score (RS) given to the states that search the term most frequently (i.e. a score of 100 in the state with the most searches). This study was considered exempt by our institutional IRB.

The search engine was quarried for four of the most common stereotactic techniques, including “SBRT,” “Stereotactic radiosurgery,” “Gamma Knife,” and “Cyberknife.” Terms were chosen in part based on the availability of data, and based on their exclusivity of the topic of interest. For example, terms such as “stereotactic body radiation therapy” yielded few results and “SRS” carried numerous medical and nonmedical uses. Only search results from the U.S. were included to avoid bias regarding availability of the techniques in other countries. Results ranged from January 2004, which was the first recorded data available in Google Trends, to June 2019. The four terms were then searched in PubMed (http://pubmed.gov) to provide comparison over the same time period.

Results

The initial interest score for “SBRT” was 36 in January 2004 and remained relatively stable until 2009 (Figure 1A and Figure 2). Interest scores began to increase significantly in 2009, and continued to gain interest through October 2018, with a peak score of 100. “SBRT” still remains heavily searched, with a score of 79 noted for June 2019. “SBRT” was most searched in Minnesota (Figure 4A, RS=100), followed by Pennsylvania (RS=95), Massachusetts (RS=92), Kentucky (RS=90) and Ohio (RS=84). A total of 26 states were reported and had interest scores above 45. The same trends are seen in the medical literature, with two articles published on PubMed in 2004. There were a peak of 515 articles published in 2018, and currently 313 are published as of July 2019 (Figure 3).

Figure 1.

Search popularity from January 2004 to June 2019 for (A) “SBRT”, (B) “Stereotactic radiosurgery”, (C) “Gamma Knife”, and (D) “Cyberknife”. Values range from 100 (peak interest) to 0 (not enough data). The annotation “Note” signifies dates of improvement in the search software.

Figure 2.

Combined figure showing relative search popularity from January 2004 to June 2019.

Figure 4.

States with high frequency of search terms for (A) “SBRT”, (B) “Stereotactic radiosurgery”, (C) “Gamma Knife”, and (D) “Cyberknife”. Dark blue signifies a high interest score.

Figure 3.

Combined figure showing number of articles published in PubMed from 2004 to 2019.

Interest in “stereotactic radiosurgery” has remained relatively consistent since 2004, with an initial interest score of 22 in January 2004 and the most recent score of 18 in June 2019 (Figure 1B). Interest was highest in the mid-2000s, with a peak score of 100 in June 2004 and an average score of 50 from 2004-2007. “Stereotactic radiosurgery” was a common search term in only 5 states, with the most populous states of New York having the highest score (RS=100; Figure 4B), followed by Pennsylvania (RS=84), Florida (RS=77), California (RS=68), and Texas (RS=55). There were 133 articles on PubMed published in 2004, with a steady increase to a maximum of 554 in 2018 (Figure 3).

Public interest in “Gamma Knife” has declined from the peak incidence in January 2004 (100) to June 2019 (RS=29; Figure 1C), with the most rapid decline from May 2005 (RS=80) to April 2012 (RS=29). “Gamma Knife” is most commonly searched in Montana (RS=100; Figure 4C), followed by Ohio (RS=89), Pennsylvania (RS=85), Washington (RS=83), and South Carolina (RS=73). In 2004, 154 articles were published on PubMed. The number of articles remained relatively stable over the next decade, reaching a maximum of 337 in 2018(Figure 3).

Interest in “Cyberknife” was 32 in January 2004, and rapidly increased to its peak incidence in September 2007 (RS=100; Figure 1D). Interest remained high through January 2009 (RS=85), and slowly declined through December 2013 (RS=35) before remaining stable through June 2019 (RS=32). “Cyberknife” was searched most commonly in New Jersey (RS=100; Figure 4D), Colorado (RS=94), Oklahoma (RS=90), Nevada (RS=82) and Connecticut (RS=82). Similar trends were identified on PubMed. There were 16 articles published in 2004, with a rapid increase to 140 in 2012. The number of articles published has remained stable since that time (157 in 2018; Figure 3).

Discussion

Our data suggest that public interest in stereotactic radiation therapy techniques remains high, specifically in states with large populations. In particular, SBRT interest has increased substantially in the past decade, a trend that is persistent across the majority of states and likely reflects the increasing use of the technique. Additionally, the indications for SBRT are rapidly expanding, which is reflected in the increasing use nationally (1, 3, 10). McClelland et al. reported a significant increase in utilization for spinal SBRT since the early 2000s, closely paralleling the trends noted in our data (10). Use of SBRT, and public awareness of the technique, is expected to continue to grow, especially with recent interest in expanding the use of SBRT to prostate cancer, breast cancer, and in oligometastatic disease. The SABR-COMET trial recently randomized patients with oligometastatic disease to ablative radiation/SBRT compared to palliative radiation alone, and found improved overall survival with patients receiving ablative radiation (4). This is seen when analyzing PubMed trends, as there has been a significant increase in the number of published articles in the past decade. As more trials investigate SBRT in the oligometastatic setting, indications and public excitement surrounding the technique are also expected to increase.

Interest in “stereotactic radiosurgery” has declined in recent years, despite having high interest scores in the early 2000s. This is a surprising finding, as the indications for SRS have increased in recent year and encompass a variety of both malignant and benign conditions (11). Furthermore, the use of SRS has effectively replaced whole-brain radiation therapy as the standard of care for limited intracranial disease (12). Similarly, Gamma Knife radiosurgery, the most popular SRS technology, has also experienced a similar decrease in interest over the past decade. While SBRT has grown with a multitude of novel indications and exciting studies, Gamma Knife radiosurgery is limited to intracranial disease, and therefore does not enjoy the same public awareness and media presence that often accompanies high profile data. This trend is also seen with PubMed data, where the number of articles published discussing Gamma Knife has remained stable, compared to rapid increase of SBRT and SRS. Additionally, Gamma Knife requires technical expertise and is generally more expensive than other forms of SRS, reflected in the fact that only 5.3% of malignant tumors in North America eligible to receive Gamma Knife are treated with Gamma Knife (13). Regardless, with the introduction of new systemic therapies leading to longer overall survival, interest and use of Gamma Knife will likely increase in the next decade as intracranial failures are expected to become more common.

Cyberknife is an image-guided robotic radiosurgery tool that was first FDA approved in 2001, with a variety of clinical uses (14). The initial excitement surrounding Cyberknife is reflected in our study, which found an increase in interest in the early 2000s following FDA approval. Despite this, interest in Cyberknife declined in the mid-2000s, likely reflecting the long treatment times and limited treatment positions that restrict its widespread use. This is also seen in the medical literature, where the number of newly-published articles has remained stable since the mid-2000s.

Interestingly, there was discordance with the Google Trends results and PubMed papers for all search terms except “SBRT.” This is not surprising, as many studies discussing SBRT in a variety of new indications have been published in the past decade, generating excitement for both physicians and the public. The discordance seen with the increase in number of studies published for the other search terms may be due to more retrospective studies being performed, contributing to the medical literature but not to public excitement about the techniques. In addition, the other techniques, such as Gamma Knife and Cyberknife, may already be established in the public eye as standards of care. Further studies should be performed looking at the factors contributing to this trend. There are some limitations with our study. First, our study was limited by the search terms available for use. Certain terms, such as “GammaKnife” or “Stereotactic body radiation therapy,” yielded few results. Although these terms more accurately define the techniques than the ones used in the study, they were unable to be analyzed due to low yield. Additionally, the acronym “SRS” was unable to investigated due to its use for multiple medical and nonmedical expressions. Second, our study was limited in the data available for interpretation. Only monthly normalized scores and geographic data were available, not absolute number of searches. As the interest scores are relative only to each search term, analyzing the magnitude of searches is not possible. For instance, no conclusions can be drawn comparing the absolute number of searches for “stereotactic radiosurgery” compared to “SBRT.”

Third, Google searches are not a perfect surrogate for public interest, and there have been no studies analyzing how accurate Google search trends represent actual public interest. The study also excluded the use of other popular search engines, therefore possibly introducing bias into the results. Furthermore, other metrics for public interest, such as book sales regarding a topic, were not analyzed. Despite these limitations, our study provides insight into public interest into these specialized radiotherapy techniques.

Conclusions

Public interest in stereotactic regimens has continued to increase over the past decade. Specifically, the interest in SBRT has substantially increased over the past decade and is represented across the U.S., likely reflecting the broadening indications for SBRT. Although stereotactic radiosurgery and Gamma Knife interest has decreased in recent years, they remain heavily searched online.