Summary

METHODS
A total of 34 questions were asked by an online survey through Google Forms (SurveyMonkey) in October 2021. This nationwide survey focused on the demographic information of participants, SRT application techniques, treatment planning, and the utilization of SRT in clinical practice.

RESULTS
The survey was completed by a total of 106 respondents. A predominant number of participants belonged to the 40-50 age group, with <10 years of experience. Linear accelerators (92%) were the most common devices used for SRT, followed by CyberKnife (27%), Gamma Knife (5%), and Magnetic resonance imaging-Linac (3%). Combined kilovolt/megavolt portal imaging with cone-beam computed tomography (CBCT) was the most commonly used imaging verification method (58%). Treatments typically began within 2-7 days (76%) after simulation. The number of patients treated with SRT/SBRT over the past year varied in a wide range, with a median of 50 (range: 0-1000) patients. SRT/SBRT was applied in many cancer types including mostly brain (98%), lung (89%), bone (89%), adrenal (64%), liver (47%), prostate (42%), head and neck (41%), pancreas (35%), and other tumors (3%).

CONCLUSION
SRT/SBRT applications in our country vary in terms of number, experience, and treated tumor groups. These results are crucial for understanding the current status of SRT, treatment indications, challenges, and diversity in application approaches in our country.

Introduction

The introduction of stereotactic radiosurgery (SRS) for the treatment of arteriovenous malformations was undertaken by Leksell in 1951.[3] Initially developed for intracranial tumors, SRT utilized the Gamma Knife, but nowadays, most centers employ conventional linear accelerators (Linacs) for intracranial SRT. Since 1995, SBRT has been employed to treat small primary or metastatic tumors outside the brain, predominantly in the lungs and liver.[4,5]

Modern Linacs integrate advanced 2-D and 3-D imaging technologies, providing superior image quality for precise daily patient set-up using bony structures, fiducials, or the target itself.[6] Kilovoltage X-ray capabilities enhance soft-tissue contrast, while cone-beam computed tomography (CBCT) reconstruction offers high-resolution imaging for direct target alignment. These advancements, combined with software-assisted registration and error calculation, have made imageguided radiotherapy (IGRT) the standard, reducing uncertainties related to target movement and improving treatment accuracy.[7] To address the challenge of target motion during radiotherapy (RT) in the thorax and upper abdomen, a 4-D CT scan with simultaneous respiratory registration is often used for treatment planning.[8,9] Other techniques, such as active breathing or applying pressure on the upper abdominal wall, have been effective in minimizing respiratory motion, reducing internal target movement by up to 50%. Ongoing developments involve tracking the target using continuous modulation of the multi-leaf collimator in conjunction with real-time imaging during treatment delivery. Currently, the CyberKnife, a robotic armmounted linear accelerator that synchronizes with respiration, is the sole commercially available beamtracking RT system.[4,10-12]

Due to the considerable variation observed in SRT utilization among the radiation oncology community concerning the devices, application methods, motion management, and clinical use in daily practice, related to experience and other factors, we aimed to present a comprehensive survey encompassing a detailed analysis of the workflow, technological aspects, indications, and limitations of SRT/SBRT among participants from various regions across Türkiye. To the best of our knowledge, this is the first survey assessing the use of SRT/SBRT among Turkish radiation oncologists, although nationwide surveys of SBRT have been recently conducted in a few other countries.[13-21]

Methods

The distribution of the survey among TSRO members was carried out through email notifications, and a link, also through WhatsApp, accompanied by a request to complete it within the subsequent 2 weeks. Respondents were assured that the survey would take maximum 5 min to complete. Before initiating the data collection process, the study obtained ethical approval from the Ankara University Scientific Research Ethics Board.

The initial segment of the survey was dedicated to gathering demographic information and work-related data from participating physicians. This included details such as age, type of hospital they practiced, and their respective professional titles. Hospital categories were classified into university hospitals, state training and research hospitals, public/city hospitals, and private hospitals. Regarding professional designations, they were divided into professor, associate professor, radiation oncology specialist, and radiation oncology resident.

In the second section of the survey, seven questions were presented to explore general clinical information. These questions covered topics such as the educational background before starting SRT practice, multidisciplinary assessment practices, the type of device, clinical protocols, and communication with other centers, SRT experience in years, and the regularity of reports on SRT treatment results.

The third section of the survey comprised 15 questions concerning simulation techniques, simulation tools, imaging fusion, treatment planning, treatment verification methods, and tumor tracking systems, real-time imaging, 6D coach, and surface-guided RT.

Finally, the fourth part of the questionnaire consisted of five questions related to the clinical application of SRT. This section aimed to gather information on the number of patients treated with SRT in the previous year, SRT indication rates, the cancer types, and the reasons of unable to perform SRT.

The collected data were analyzed in the online platform and also imported into the SPSS 23.0 package program to obtain further descriptive analysis. Because respondents could choose more than one answer for certain questions, the overall percentage for selected questions did not reach or sometimes exceeded 100%.

Results

Fig. 1. Demographic characteristics of participants; (a) age, (b) institution, (c) academic affiliation, (d) training completion duration.

Table 1 Clinical-technical information about SRT/SBRT

Table 2 Details in SBRT simulation, planning, and treatment

Table 2 Cont.

The majority of participants were in the 40-50 age group and 84% of them had already completed their training. Most of the respondents (64.2%) had more than 5 years of experience. In majority (76.4%) of the respondents, a multidisciplinary council decision was required for SRT. Moreover, 74.5% of respondents followed their written protocols, and 59.4% collaborated with other experienced centers.

Linear accelerators (92.4%) were the most commonly used devices for SRT, followed by CyberKnife (27.4%), Gamma Knife (4.7%), and Magnetic resonance imaging -Linac (2.8%). Various immobilization methods were employed, including head frames and thermoplastic masks (88.7%), vacuum bags (77.4%), T board (48.1%), and abdominal compression body frame (34%). Respiratory motion management was provided by mostly four-dimensional computed tomography (4DCT) with respiratory gating (71.7%), followed by breath-hold techniques (58.5%), abdominal compression (28.3%), and fiducial tracking (25.5%), respectively. Surface tracking was used in only 20.8% of cases.

Regarding image fusion during treatment planning, 79.2% of participants utilized deformable registration, with 97.2% reassessing the quality of fusion. Concerning treatment, 67.9% of them had systems to integrate old and new plans for second fractionation. Treatments typically commenced within 2-7 days (75.5%) after simulation. Combined kilovolt/megavolt (kV/mV) portal imaging with CBCT was the most commonly used imaging method (57.6%), primarily performed before each fraction (73.6%). Six-dimensional table correction was used in 57.5% of cases, while real-time imaging was not widely implemented (70%). The real- time imaging modalities varied among respondents depending on their therapy device.

The number of patients treated with SRT/SBRT over the past year was reported as a median of 50 (range: 0-1000) among 103 of 106 respondents (97.1%). Among these respondents, the distribution of treated patients over the past year was as follows: 0-49 patients by 51 individuals (49.5%), 50-199 patients by 41 individuals (39.8%), 200-499 patients by 7 individuals (6.8%), and 500-1000 patients by 4 individuals (3.9%). Only one person indicated that no SRT/SBRT patient had been treated yet. The proportion of patients who received SRT/SBRT constituted a median 12% (1-80%) of all patients they treated that year according to 103 of 106 respondents. Among these respondents, 4 (3.7%) of them stated that treatment with SRT accounted for more than 50%, 40 (37.4%) of them between 20% and 50%, and 59 (55.1%) of them <20% of the whole group, respectively.

SRT was applied to various tumor groups, including brain (98.1%), lung (88.7%), bone (88.7%), adrenal (64.2%), liver (47.2%), prostate (41.5%), head and neck (40.6%), pancreas (34.9%), and other tumors (2.7%). In cranial tumors, SRT was most applicable to metastatic lesions (99.1%) after malign tumors (74.5%) following benign (56.6%) tumors. In lung SBRT cases, SBRT was mostly applied to peripheral tumors (98%), followed by central (72.4%), and ultracentral tumors (27.6%). The reasons for not treating certain tumor groups were issued by respondents as mostly the absence of fiducial tracking systems (55.6%) or lack of suitable devices and ancillary equipment (48.1%). For lung (63.2%), brain (60.4%), adrenal (31.1%), prostate (27.4%), liver (22.6%), bone (22.6%), head and neck (20.8%), and pancreas (16%) tumors, as well as re-irradiation cases (3.2%), alternateday SRT was the preferred treatment approach.

Discussion

The survey primarily drew participation from radiation oncologists, predominantly affiliated with university hospitals and training and research institutions equipped for SRT/SBRT implementation. A considerable proportion of respondents, nearly half, reported possessing a 5 year or longer experience in SRT/SBRT practice. While this level of experience surpasses that reported in other national surveys conducted in countries such as India [21] and Korea,[19] it does indicate relatively less experience compared to counterparts in the United States [14] and numerous European countries.[20]

In terms of training, the survey revealed variability in the education received by respondents before engaging in SRT applications. A similar observation was made in a European survey conducted across selected countries, including England, Netherlands, Belgium, Denmark, Germany, and Austria.[20] Participants in both Türkiye and Europe acknowledged the absence of standardized training protocols and the lack of participation in specific educational programs. A noteworthy parallel between Türkiye and European countries is the tendency for more than half of the respondents to collaborate with more experienced clinics. In daily practice, our survey respondents predominantly adhere to their clinical protocols or relevant guidelines.[20] This practice closely aligns with the approach reported in other contexts.

Türkiye possesses a broad perspective regarding its treatment device portfolio. According to the 2019 report, Türkiye housed 9 Gamma Knife units, 11 CyberKnife systems, and 2 Novalis platforms dedicated exclusively to SRS/SRT treatments.[22] However, contemporary trends, similar to findings observed in surveys conducted in other nations, indicate that SRT is now predominantly administered through Linac-based devices.[21] Our survey reveals that initial applications in the form of SRS/SRT have bestowed considerable experience, particularly in treating intracranial tumors, over an extended period. With regard to SBRT, our findings align with surveys carried out in Japan, the United States, Korea, and European countries.[13,14,19,20] Lung tumors emerge as the most frequent targets for SBRT, as documented in these surveys; however, in contrast to the majority of other countries, liver tumors are superseded by bone and adrenal tumors in Türkiye.

In the context of immobilization techniques during planning CT, our survey highlights the prevalent utilization of head frames and thermoplastic masks (88.7%), vacuum bags (77.4%), T boards (wingboards) (48.1%), and abdominal compression body frames (34%). On the contrary, in Korea, the prevailing immobilization techniques primarily consisted of alpha cradle/vacuum-lock methods (16 institutions, 42%), followed by the utilization of stereotactic body frames (10 institutions, 26%) and wingboards (10 institutions, 26%).[19] It is worth noting that surveys conducted in the United States and Europe did not incorporate this particular immobilization data.[14,20]

4DCT emerged as the prevailing method for SBRT planning, consistent with analogous national surveys conducted in the United States, Korea, and European countries.[14,16,17,19,20] Regarding motion control strategies, respiratory gating with 4DCT and active breath-hold techniques were predominantly favored in Türkiye, while abdominal compression and tumor tracking systems were employed to a lesser extent. In Korea, similar to our observations, respiratory gating with 4DCT constituted the primary approach, with abdominal compression as the subsequent choice. Conversely, in Europe, abdominal compression held precedence following respiratory gating. In the United States, addressing respiratory-induced motion in lung and liver tumor patients primarily involved respiratory gating[23,24] and abdominal compression.[9,25] Techniques such as breath-hold[26] and real-time tracking[27,28] were less commonly employed, which mirrored the Japanese lung SBRT survey highlighting the prevalence of abdominal compression.[13,14]

While SRT historically relied on external coordinates for guidance, contemporary practices predominantly emphasize IGRT for enhanced geometric precision, expedited delivery, and resource optimization.[7] For target localization, the predominant verification method in Türkiye involved a combination of kV/mV portal imaging and CBCT, typically performed before each treatment fraction. Fiducials, used sparingly in Türkiye as well as in Korea and Europe, are infrequently employed as auxiliary localization tools.[19,20] In Korea, cone-beam CT emerged as the chief verification method before each treatment, supplemented by orthogonal kilovoltage radiography, orthogonal megavoltage localization imaging, and fluoroscopy.[19] These outcomes paralleled findings in European surveys.[20] Notably, the nascent verification approach of surface-guided RT remains underutilized in numerous countries, including Türkiye.

In our survey, liver and prostate tumors emerged as the predominant types of cancer for which many centers could not administer SBRT. The primary reasons cited by non-SBRT users were predominantly attributed to the absence of suitable devices and ancillary equipment, mirroring findings documented in other national surveys.[20] Pertaining to the annual caseload, we observed a wide range of patient numbers treated per year across centers in our survey, likely influenced by factors such as clinical experience, equipment availability, patient demographics, and socio-economic status.

An inherent limitation of this study pertains to our inability to analyze participating centers in terms of regional disparities, which could have shed light on variations in patient volume and diagnoses on a center-specific basis. In addition, not every center was represented by a singular respondent due to the option for multiple participants from each center to contribute to the survey. Furthermore, this survey lacked comprehensive information on dose and prescription specifics with respect to different cancer types, as well as insights into treatment outcomes and the cost associated with SRT/SBRT. Despite governmental health insurance approval for reimbursement in numerous centers, excluding private hospitals, our survey lacked detailed data in this regard.

Conclusion

Acknowledgements: We extend our heartfelt gratitude to our colleagues in each of the participating centers for generously contributing their time and invaluable information that has been incorporated into this report.

Peer-review: Externally peer-reviewed.

Conflict of Interest: All authors declared no conflict of interest.

Ethics Committee Approval: The study was approved by the Ankara University Human Research Ethics Committee (no: İ06-415-23, date: 11/07/2023).

Financial Support: None declared.

Authorship contributions: Concept - S.D.B., E.Ö., H.B.Ç.; Design - M.T., S.D.B.; Supervision - S.Y.S., H.B.Ç., B.A.Y.; Funding - M.T., B.A.Y.; Materials - S.A., S.Y.S.; Data collection and/or processing - S.D.B., H.B.Ç., S.A.; Data analysis and/or interpretation - S.D.B., E.Ö.; Literature search - B.A.Y., M.T., S.Y.S.; Writing - S.D.B., E.Ö.; Critical review - S.A., E.Ö.

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