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. 2026 Sep 28;44(3):190–200. doi: 10.3857/roj.2026.00465

Clinical utility of endorectal balloons in prostate cancer external beam radiotherapy: a systematic review and meta-analysis

You Lim Kim 1, Jeong Il Yu 2,✉, Jae Kyung Suh 1,✉
PMCID: PMC13639676  PMID: 42810974

Abstract

Purpose

This study aimed to systematically evaluate the clinical utility of endorectal balloons (ERB) for motion management and organ-at-risk sparing in prostate cancer patients receiving external beam radiotherapy (EBRT) or stereotactic body radiotherapy (SBRT).

Materials and Methods

A systematic search was conducted in Ovid MEDLINE, Embase, the Cochrane Library, and Korean databases through May 8, 2024. Primary outcomes included safety, toxicity, prostate motion, and dosimetric parameters. The risk of bias was assessed using the Risk of Bias Assessment tool for Non-randomized Studies 2.0 tools. Meta-analysis was conducted using Review Manager 5.3.

Results

Twenty-seven studies (3 prospective cohort studies, 24 retrospective studies) were included, covering 22 EBRT and 5 SBRT cohorts. Reported adverse events were mild and transient. One prospective study demonstrated a significant reduction in grade 1 late rectal toxicity (p = 0.003). ERB use significantly stabilized the prostate, reducing both intra- and interfractional motion, particularly minimizing displacements >5 mm. Meta-analysis revealed that ERB significantly lowered the mean radiation dose to the rectum (mean difference [MD], –3.40 Gy; 95% confidence interval [CI], –6.70 to –0.10) and anal wall (MD, –6.06 Gy; 95% CI, –9.78 to –2.35) in EBRT. Similarly, in SBRT, ERB was associated with reduced rectal wall dose (MD, –2.63 Gy; 95% CI, –4.49 to –0.77).

Conclusion

ERB appears to be a relatively safe and clinically useful adjunct for enhancing treatment precision in prostate cancer radiotherapy. By stabilizing prostate motion and reducing radiation exposure to the rectum and anal wall, ERB optimizes the therapeutic ratio.

Keywords: Prostate neoplasms, Endorectal balloon, Radiotherapy, Adverse effects

Introduction

Prostate cancer remains one of the most prevalent malignancies in men globally and has recently emerged as the most frequently diagnosed cancer among the male population in Korea [1,2]. External beam radiotherapy (EBRT) is a cornerstone of management for localized disease [3]. The landscape of EBRT is undergoing a major transition, however, moving away from conventional fractionation in favor of hypofractionated schedules. These approaches, including ultra-hypofractionated stereotactic body radiotherapy (SBRT), have become a preferred standard of care due to their biological advantages and the logistical benefits of abbreviated treatment courses [4,5].

Despite these technological advancements, the intrinsic mobility of the prostate remains a significant hurdle. Physiological factors, including respiratory motion, varying bladder filling, and rectal peristalsis, cause unpredictable positional displacement of the prostate during treatment [6-8]. Such motion not only risks a geographical miss of the target but also necessitates wider treatment margins, which inadvertently increase the radiation burden on adjacent organs-at-risk (OARs) [9].

To mitigate these uncertainties, various internal immobilization strategies have been developed, most notably the endorectal balloon (ERB). When inserted, the ERB serves a dual clinical purpose. It mechanically stabilizes the prostate to minimize motion and physically displaces the posterior rectal wall away from the high-dose region [10]. By creating a predictable and reproducible interface, ERB use has been associated with significant rectal sparing and improved target localization [10-12].

However, despite the widespread use of ERB, there is a lack of high-level evidence syntheses that comprehensively evaluate its impact on late toxicities, symptomatic outcomes, and precise motion metrics in the context of both conventional and SBRT regimens. Therefore, this systematic review and meta-analysis aimed to evaluate the clinical utility of the ERB, with a specific focus on its role as an internal immobilization device for optimizing treatment accuracy and minimizing OAR exposure in modern prostate cancer radiotherapy.

Materials and Methods

1. Literature search

This systematic review was conducted and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 guidelines [13]. To evaluate the clinical utility of radiotherapy using an ERB as an internal immobilization device in patients with prostate cancer, a comprehensive literature search was performed in international databases (Ovid-MEDLINE, Ovid-Embase, and the Cochrane Library) and Korean databases (KoreaMed, KMbase, and RISS) up to May 8, 2024.

The main search terms included “prostate cancer,” “endorectal balloon,” and “radiotherapy.” The search strategy incorporated Medical Subject Headings, Boolean operators, and truncation (Supplementary Table S1). The study design was restricted to comparative studies, and publications were limited to those written in English or Korean.

2. Study selection

Studies were selected according to predefined population, intervention, comparison, and outcome criteria. The population included patients with prostate cancer receiving radiotherapy. The intervention was radiotherapy with an ERB, compared with radiotherapy without ERB. Outcomes included safety (adverse events) and effectiveness outcomes, including toxicity, prostate motion, and radiation dose to organs at risk. Comparative studies reporting relevant clinical, motion-related, or dosimetric outcomes were included.

The study selection process was conducted in two stages: title and abstract screening, followed by full-text review. Two reviewers (JKS and YLK) independently screened the studies, and disagreements were resolved through consensus.

Non-human studies, non-original articles (e.g., reviews, editorials, comments, letters, and conference abstracts), studies without an appropriate comparator, studies lacking relevant outcome data, and duplicate or overlapping publications were excluded. Only studies published in English or Korean were considered.

3. Data extraction, outcome measures, and risk of bias assessment

Data extraction was performed independently by two reviewers using a standardized form, with any discrepancies resolved through consensus. Extracted information encompassed general study characteristics, safety profiles (procedure-related adverse events), and clinical/dosimetric effectiveness.

The primary endpoint of this study was radiation exposure to OARs, specifically assessed through dosimetric parameters (absolute dose in Gy) and irradiated volume of the rectum and anal wall. Secondary endpoints for clinical utility included rectal and genitourinary toxicities as well as prostate motion stability (both intra- and interfractional). All outcomes were stratified by radiotherapy technique (EBRT or SBRT) to account for differences in treatment delivery.

Methodological quality was evaluated using the Risk of Bias Assessment for Non-randomized Studies (RoBANS) version 2.0 (Health Insurance Review and Assessment Service, Wonju, Korea) for all included studies. This multi-dimensional assessment ensured a rigorous synthesis of both clinical and technical outcomes.

4. Statistical analysis

Quantitative meta-analysis was performed using Review Manager (RevMan) version 5.3 (The Cochrane Collaboration, Copenhagen, Denmark) when data were amenable to pooling. Otherwise, a qualitative synthesis was conducted. The primary effect estimate was the mean difference (MD). For studies reporting outcomes as median and interquartile range, the values were converted to mean and standard deviation using the quantile estimation method proposed by Luo et al. [14] to enable inclusion in the meta-analysis.

Statistical heterogeneity was assessed using the I² statistic. An I² value ≥50% was considered to indicate substantial heterogeneity, in which case a random-effects model was applied. Statistical significance was determined at a two-sided p < 0.05. This study was conducted in accordance with standard methodological approaches for systematic reviews [15].

5. Quality of evidence assessment

The importance of outcomes was evaluated using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. Safety outcomes (procedure-related complications or adverse events) were classified as “important but not critical,” whereas effectiveness outcomes (rectal and genitourinary toxicity, prostate motion, and radiation dose to normal tissues) were classified as “critical.”

Results

1. Literature search and selection process

A total of 1,021 studies were identified through the database search. After removing duplicate records, title and abstract screening were performed. Subsequently, a full-text review was conducted, and 27 studies were included in the final analysis (Fig. 1).

Fig. 1.

Fig. 1.

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Flow diagram of study selection.

2. Clinical and technical profiles of the included studies

A total of 27 studies evaluating ERB in patients with prostate cancer were included (447 participants in the intervention group and 614 in the control group).

In terms of study design, the included studies consisted of three prospective cohort studies and 24 retrospective comparative studies. Among the 27 included studies, 18 compared ERB and non-ERB conditions within the same patients. Regarding radiotherapy techniques, 22 studies used EBRT, while five studies used SBRT. Most studies were conducted in patients with localized prostate cancer (Table 1) [16-42]. Notably, most dosimetric assessments were based on comparisons of computed tomography simulation images within the same patient rather than evaluations of actual treatment delivery during the radiotherapy course.

Table 1.

Characteristics of included studies

No. Study Country Study design Patient population Radiotherapy technique Dose (Gy) Fractions (fx) No. of ERBs No. of no-ERBs
1 van Lin et al. (2007) [16] Netherlands Prospective study Localized prostate cancer EBRTb) 67.5 30 24 24
2 Streller et al. (2017) [17] Switzerland Prospective cohorta) Prostate cancer EBRTc) NR 33 10 10
3 Wang et al. (2012) [18] USA Retrospective study Prostate cancer EBRTc) 79.2 44 30 29
4 van Lin et al. (2005) [19] Netherlands Prospective cohort Localized prostate cancer EBRTb) 63–67.5 28–30 22 30
5 Gundog et al. (2020) [20] Türkiye Retrospective study Prostate cancer SBRT 36.25 5 15 17
6 Jaccard et al. (2019) [21] Switzerland Retrospective studya) Localized prostate cancer SBRT 36.25 5 12 12
7 Dubouloz et al. (2018) [22] Switzerland Retrospective studya) Prostate cancer SBRT 36.25 5 10 10
8 Wortel et al. (2017) [23] Netherlands Retrospective study Intermediate-risk prostate cancer EBRTc) 64.6–78 19–39 85 242
9 Xiang et al. (2017) [24] USA Retrospective study Prostate cancer SBRT 36.25 5 10 10
10 Wong et al. (2016) [25] USA Retrospective studya) Prostate cancer SBRT 36.25 5 11 11
11 de Leon et al. (2015) [26] Australia Retrospective studya) Post-prostatectomy EBRTc) 70 35 7 7
12 Jameson et al. (2013) [27] Australia Retrospective study Post-prostatectomy EBRTc) 64.4–70 35 10 10
13 Smeenk et al. (2012) [28] Netherlands Retrospective study Localized prostate cancer EBRTc) 80 40 15 15
14 Hung et al. (2011) [29] USA Retrospective study Prostate cancer EBRTc) 75.6 42 14 15
15 Smeenk et al. (2011) [30] Netherlands Retrospective studya) Prostate cancer EBRTc) 70 35 20 20
16 Takayama et al. (2011) [31] Japan Retrospective studya) Localized prostate cancer EBRTb)c) 70 35 7 7
17 Vargas et al. (2010) [32] USA Retrospective studya) Prostate cancer EBRTc) NR NR 7 7
18 Smeenk et al. (2009) [33] Netherlands Retrospective studya) Localized prostate cancer EBRTb)c) 78 39 24 24
19 Cho et al. (2009) [34] Korea Retrospective studya) Prostate cancer EBRTb)c) 50.4–75.6 28 10 10
20 Elsayed et al. (2007) [35] Germany Retrospective studya) Localized prostate cancer EBRTb) 59.4 33 12 12
21 Hille et al. (2005) [36] Germany Retrospective studya) Localized prostate cancer EBRTb) 72 NR 14 14
22 van Lin et al. (2005) [37] Netherlands Retrospective studya) Localized prostate cancer EBRTb)c) 78 39 20 20
23 Lee et al. (2005) [39] Korea Retrospective studya) Localized prostate cancer EBRTc) 50 NR 5 5
24 Sanghani et al. (2004) [40] USA Retrospective studya) Localized prostate cancer EBRTb) 75.6 40 28 28
25 Patel et al. (2003) [38] USA Retrospective studya) Localized prostate cancer EBRTb)c) 76 38 5 5
26 Wachter et al. (2002) [41] Austria Retrospective studya) Localized prostate cancer EBRTb) 66 NR 10 10
27 D’Amico et al. (2001) [42] USA Retrospective studya) Prostate cancer EBRTb) 75.6 NR 10 10
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fx, fractions; ERB, endorectal balloon; No-ERB, endorectal balloon not applied; EBRT, external beam radiotherapy; NR, not reported; SBRT, stereotactic body radiotherapy.

a)

Within-patient comparative study comparing ERB and non-ERB conditions in the same patients.

b)

Three-dimensional conformal radiation therapy.

c)

Intensity modulated radiation therapy.

3. Methodological quality and risk of bias assessment

All 27 included studies were assessed using the RoBANS version 2.0 to ensure methodological consistency. The overall risk of bias was low across most domains; however, some studies showed a high or unclear risk of bias in the participant selection domain (Supplementary Fig. S1).

4. Safety of ERB application

Safety of ERB use in patients with prostate cancer undergoing radiotherapy was assessed based on procedure-related rectal discomfort and adverse events associated with the device application. Safety outcomes were documented in six studies [19,26,30,34,38,40].

Among the included studies, three studies reported discontinuation of ERB use in 7.1% of patients (3/42), primarily due to pre-existing conditions such as hemorrhoids. Four studies reported cases requiring supportive management, including prescription of local anesthetics or oral analgesics, or temporary interruption of treatment associated with ERB application. In addition, two studies reported transient local anorectal irritation or increased rectal pressure in 91.3% of patients (42/46).

5. Dosimetric and volumetric outcomes for OARs

In studies using EBRT, the use of ERB in EBRT resulted in significant sparing of the lower gastrointestinal OARs. Pooled analysis demonstrated a significant reduction in the mean dose to the rectum (MD, –3.40 Gy; 95% confidence interval [CI], –6.70 to –0.10; p = 0.04) and the anal wall (MD, –6.06 Gy; 95% CI, –9.78 to –2.35; p = 0.001). Volumetrically, ERB significantly decreased the irradiated volume of the anal wall (MD, –5.24%; p = 0.03). While the pooled analysis for rectal and rectal wall volumes did not reach statistical significance, individual studies highlighted benefits in high-dose regions; for instance, the volume of the posterior rectal wall receiving 60% or more of the dose was significantly reduced (28% vs. 40%, p = 0.006). Bladder dose and volume remained comparable between the two groups (Figs. 2A, 3A).

Fig. 2.

Fig. 2.

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Forest plots of radiation dose to normal tissues (Gy) comparing radiotherapy with versus without an endorectal balloon (ERB). Using an inverse-variance random-effects model, the pooled analysis demonstrates that ERB use significantly reduces mean radiation doses to the rectum and anal wall in external beam radiotherapy (EBRT) (A), as well as to the rectum and rectal wall in stereotactic body radiotherapy (SBRT) (B). Data points plotted to the left of the solid vertical line signify a statistically significant dosimetric sparing effect favoring the ERB cohort [20,22-24,28,30,33-35,37]. CI, confidence interval; SD, standard deviation.

Fig. 3.

Fig. 3.

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Forest plots of irradiated volume to normal tissues (%) comparing radiotherapy with versus without an endorectal balloon (ERB). Synthesized via a random-effects model, the pooled estimates show a significant reduction in the irradiated volume of the anal wall during external beam radiotherapy (EBRT) (A), whereas volumetric outcomes for other organs-at-risk in both EBRT and stereotactic body radiotherapy (SBRT) (B) settings exhibit high heterogeneity without reaching statistical significance. Displacement to the left of the central vertical line denotes a volumetric benefit favoring the use of an ERB [17,18,21,22,24,30,31,33,34,36,40]. CI, confidence interval; SD, standard deviation.

In studies using SBRT, ERB provided robust protection of the rectal interface. Meta-analysis showed a significant decrease in both the rectal wall dose (MD, –2.63 Gy; 95% CI, –4.49 to –0.77; p = 0.006) and the overall rectal dose (MD, –5.27 Gy; 95% CI, –9.56 to –0.97; p = 0.02). Beyond the rectum, ERB contributed to the sparing of other critical structures: significant dose reductions were observed for the pudendal artery (mean, 10.5 Gy vs. 12.8 Gy; p = 0.023) and the penile bulb (mean, 3.7 Gy vs. 6.5 Gy; p < 0.01). However, volumetric outcomes for the rectum and bladder in SBRT were inconsistent across studies and exhibited high heterogeneity, necessitating cautious interpretation (Figs. 2B, 3B).

6. Rectal and genitourinary toxicity

Rectal and genitourinary toxicity outcomes were reported in only two studies (one prospective and one retrospective study) [16,23].

For rectal toxicity, one prospective study reported that late rectal toxicity (13–30 months) of grade ≥2 did not occur in the intervention group, whereas two cases (8.3%) occurred in the control group. Among these, one patient experienced grade 2 rectal toxicity and required two sessions of laser coagulation, while the other developed grade 3 rectal toxicity with rectal bleeding, requiring two blood transfusions and five sessions of laser coagulation.

In addition, the incidence of grade 1 late rectal toxicity was significantly lower in the intervention group than in the control group (p = 0.003). For early rectal toxicity (≤12 months), no statistically significant difference was observed between the two groups.

In the retrospective study, mucus loss and rectal discomfort occurred less frequently in the intervention group than in the control group at 6 weeks and 48 months (p < 0.01). Bowel frequency was also lower in the intervention group at 48 months, whereas no difference in rectal bleeding was observed between the two groups at the same time point.

For genitourinary toxicity, while one prospective study showed no significant difference in chronic adverse events, data from the retrospective study revealed a clear benefit. The incidence of urinary incontinence at 48 months was significantly lower in the ERB group compared to the control group (11.1% vs. 20.7%, p < 0.001).

7. Target immobilization and motion management

Prostate motion was reported in eight studies using EBRT, and the outcomes were evaluated according to intrafraction and interfraction motion. In addition, directional prostate motion was reported in four studies.

Intrafraction prostate motion was reported in three studies [28,32,42]. In some studies, the number of patients with prostate motion ≥5 mm was lower in the intervention group than in the control group. In addition, the mean three-dimensional prostate motion was smaller in the intervention group than in the control group (1.0 mm vs. 1.3 mm, p = 0.03). However, some studies reported no significant differences between the two groups.

Interfraction prostate motion was also reported in three studies [25,31,41]. In one study, the number of patients with prostate motion ≥5 mm was significantly lower in the intervention group (p = 0.008). Another study reported that the mean three-dimensional prostate motion was significantly smaller in the intervention group (p = 0.014). In contrast, some studies reported no significant differences between the two groups. Detailed study-level data are provided in Supplementary Table S2. In a separate analysis, prostate displacement was evaluated by direction in four studies. Intrafraction directional displacement was reported in one study [28], whereas interfraction directional displacement was reported in four studies [28,29,31,37].

Four studies evaluated direction-specific prostate motion [28,29,31,37]. Among these, one study assessed intrafraction prostate motion in the anterior–posterior, left–right, and superior–inferior directions [28]. In the anterior–posterior direction, the proportion of motion exceeding 1 mm within 10 minutes was significantly lower in the intervention group (3.8%) than in the control group (9.4%) (p < 0.05).

Four studies reporting interfraction prostate motion evaluated displacement in five directions (anterior–posterior, left–right, superior–inferior, cranio–caudal, and lateral) [28,29,31,37]. However, these studies reported no significant differences between the two groups or did not report the statistical significance of between-group differences.

8. Quality of evidence

According to the GRADE approach, the overall quality of evidence was rated as low to very low. In the one prospective study, risk of bias due to unclear judgments in several domains was identified, and the sample size was limited. In non-randomized studies, imprecision was identified because the sample sizes did not meet the optimal information size or the CIs included the null value, contributing to the overall low certainty of the evidence.

Discussion and Conclusion

This systematic review and meta-analysis comprehensively evaluated the clinical utility of ERB in prostate cancer patients treated with EBRT, including SBRT. Our findings demonstrate that ERB not only significantly reduces late rectal toxicity and patient-reported symptoms but also minimizes both interfractional and intrafractional prostate motion. These results suggest that in the current era of high-precision radiotherapy, the ERB should be recognized as a critical stabilizing component rather than a simple rectal displacement tool.

The paradigm of prostate cancer management in terms of EBRT has shifted toward hypofractionated regimens [43]. Both moderate hypofractionation (>2.5 to 4 Gy/fraction) and ultra-hypofractionation (SBRT, >6 Gy/fraction) have become standard-of-care, offering noninferior oncologic outcomes with enhanced patient convenience [44]. This transition is fundamentally driven by the unique radiobiological profile of prostate cancer unlike most other malignancies, its α/β ratio is notably lower than that of the surrounding late-responding normal tissues [45]. While this characteristic provides a clear biological rationale for delivering higher doses per fraction to enhance the therapeutic ratio, it simultaneously amplifies the clinical concerns regarding treatment uncertainties [46]. Specifically, the delivery of high-dose fractions increases the system's vulnerability to both interfractional setup errors and, more critically, intrafractional organ motion [47]. In this high-dose gradient environment, even minor displacements can lead to a geographical miss of the target or unintended high-dose exposure to adjacent organs at risk, such as the rectum. Consequently, the imperative for robust anatomical stabilization and precise motion management has never been more paramount.

Prostate motion, driven by bladder filling and rectal peristalsis, remains a primary challenge in achieving this precision. Our analysis confirms that ERB significantly reduces prostate displacement across all dimensions (Supplementary Table S2). While interfractional motion can often be mitigated by daily image guidance [48], intrafractional motion occurring during the actual beam-on time is far more difficult to manage. ERB provides a unique mechanical "fixation" that dampens the influence of rectal gas and peristalsis. By stabilizing the prostate-rectum interface, ERB ensures that the delivered dose distribution remains faithful to the optimized treatment plan, which is particularly vital for SBRT, where steep dose gradients and tight margins leave little room for error.

Recently, absorbable hydrogel spacers have gained popularity for rectal sparing by physically increasing the distance between the prostate and the anterior rectal wall [49]. However, spacers involve an invasive procedure, carry risks of infection or misplaced injection, and are associated with higher costs. Furthermore, ERB offers unique advantages in specific clinical scenarios where spacers may be less effective or inapplicable, including cases with extraprostatic extension, neurovascular invasion, or local recurrence after prostatectomy [50].

Against this clinical backdrop, the present meta-analysis confirms that ERB significantly mitigates rectal and genitourinary toxicities, specifically reducing the incidence of late rectal toxicity and alleviating patient-reported symptoms such as mucus loss, rectal discomfort, and bowel frequency. This clinical benefit is fundamentally driven by the mechanical displacement of the rectal wall posteriorly, increasing the distance from the high-dose region, consistent with previous systematic reviews that highlight the role of ERB in rectal sparing [10,51]. Beyond dose reduction, our results demonstrate that ERB use leads to superior stabilization of the prostate, reducing both intrafractional and interfractional motion. The significant reduction in cases where prostate motion exceeded 5 mm underscores the contribution of ERB in enhancing overall treatment accuracy and positional stability.

From a dosimetric perspective, the pooled analysis revealed that the ERB group received significantly lower radiation doses to the rectum and anal wall compared to the control group. Although some inconsistencies were observed in bladder and rectal wall doses, likely due to variations in radiotherapy techniques, fractionation schemes, and balloon inflation volumes, the overall trend confirms a clear dosimetric advantage for critical organ sparing. These findings align with current international standards, including the National Comprehensive Cancer Network guidelines and European Society for Radiotherapy and Oncology–Advisory Committee on Radiation Oncology Practice guidelines, which endorse ERB as an effective tool for stabilizing rectal anatomy and improving target localization [44,52]. However, noting the cautious guidance regarding routine use in the post-prostatectomy prostate bed, our study suggests that while ERB is a highly effective adjunctive technique, its application should be selectively and strategically integrated based on the specific clinical context and the individual patient’s anatomical requirements to maximize the therapeutic ratio.

Several limitations warrant consideration. First, the majority of included studies were non-randomized, which may introduce selection bias. Second, only English- and Korean-language publications were included, which may have introduced language bias and resulted in the omission of relevant studies published in other languages. Third, the considerable statistical heterogeneity observed in this study (I2 values up to 96%) likely stems from the clinical diversity of the included studies, such as variations in ERB inflation volumes (40–100 mL) and filling materials (air vs. water), alongside heterogeneous EBRT techniques and fractionation schedules. Consequently, the pooled dosimetric estimates should be interpreted as indicative of clinical trends rather than absolute definitive values, highlighting the need for caution when generalizing these results. Fourth, while we observed a reduction in grade 1 late toxicity, the impact on grade 2 or higher toxicities was less pronounced, likely due to the low absolute event rates across studies. Additionally, since clinical evidence for late rectal toxicity reduction relies primarily on a prospective study using three-dimensional conformal radiotherapy and conventional fractionation, its direct extrapolation to modern EBRT techniques, which offer superior dose conformality, presents clear limitations. Fifth, while the literature search was current as of May 2024, potential publication bias could not be formally assessed using funnel plots or Egger’s test due to the limited number of studies available for each specific outcome, and the possibility of missing very recent publications remains a limitation. Lastly, many included studies were dosimetric planning comparisons based on static computed tomographic simulation images, which may not fully reflect the actual delivered dose considering the dynamic uncertainties of real-world radiotherapy. Furthermore, differences in radiotherapy techniques across the literature may limit the generalizability of these dosimetric benefits, particularly as the evidence for SBRT remains relatively limited by smaller sample sizes and paired comparative designs compared to conventional EBRT. Despite these limitations, this study provides a comprehensive synthesis of clinical outcomes associated with ERB use in the radiotherapy management of prostate cancer. However, further prospective trials are essential to validate the clinical benefits of ERBs under contemporary high-precision techniques and hypofractionated schedules, ensuring their optimal application in modern clinical practice.

In conclusion, ERB use in prostate cancer radiotherapy appears to be relatively safe without major complications and is associated with reduced prostate motion and decreased radiation exposure to the rectum. Further research is needed to better evaluate the clinical effectiveness of ERB use in the context of advancing radiotherapy techniques. In particular, prospective randomized comparative studies with standardized designs and adequate sample sizes are required.

Footnotes

Statement of Ethics

Institutional Review Board (IRB) approval was not required for this study as it is a systematic review and meta-analysis based on previously published literature and does not involve direct interaction with human participants or the collection of identifiable private information.

Conflict of Interest

No potential conflict of interest relevant to this article was reported.

Acknowledgments

This study was derived from a report published by the National Evidence-based Healthcare Collaborating Agency (NECA). The authors would like to acknowledge Drs. Woo Chul Kim (Inha University Hospital), Jong Kil Nam (Pusan National University, School of Medicine, Pusan National University Yangsan Hospital), Hakmin Lee (Seoul National University Bundang Hospital), and Young Geon Ji (CHA University) for their expert advisory contributions to the Medical Technology Reassessment Subcommittee.

During the preparation of this work, the authors used Gemini 3.1 Pro in order to translate the manuscript into English, refine expressions, improve phrasing, and verify grammatical accuracy. After using this tool, the authors reviewed and edited the content as needed and take full responsibility for the content of the published article.

Funding

This study was based on a health technology reassessment report published by the National Evidence-based Healthcare Collaborating Agency (NECA) (Project No. NECA-R-24-001-21).

Author Contributions

Conceptualization, YLK, JIY, JKS; Literature search, YLK, JKS; Data collection, YLK, JKS; Figures, YLK; Data analysis, YLK, JKS; Data access and verification, YLK, JIY, JKS; Data interpretation, YLK, JIY, JKS; Obtained funding, JKS; Writing of the original draft, YLK, JKS; Writing of the review and editing, YLK, JIY, JKS.

Data Availability Statement

The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.

Supplementary Materials

Supplementary materials can be found via https://doi.org/10.3857/roj.2026.00465.

Supplementary Table S1.

Search strategies for electronic databases

Supplementary Table S2.

Prostate motion

Supplementary Fig. S1.

Risk of bias assessment for nonrandomized studies using the Risk of Bias Assessment for Non-randomized Studies (RoBANS) version 2.0. The assessment includes 27 nonrandomized comparative studies across eight domains: comparability of groups, selection of participants, confounding variables, measurement of exposure, blinding of outcome assessment, outcome assessment, incomplete outcome data, and selective outcome reporting. The overall risk of bias was low across most domains. However, high or unclear risks were identified in the "selection of participants" domain for a subset of studies. Green, yellow, and red circles indicate low, unclear, and high risk of bias, respectively.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplementary Table S1.

Search strategies for electronic databases

roj-2026-00465-Supplementary-Table-S1.pdf (435KB, pdf)
Supplementary Table S2.

Prostate motion

roj-2026-00465-Supplementary-Table-S2.pdf (421.8KB, pdf)
Supplementary Fig. S1.

Risk of bias assessment for nonrandomized studies using the Risk of Bias Assessment for Non-randomized Studies (RoBANS) version 2.0. The assessment includes 27 nonrandomized comparative studies across eight domains: comparability of groups, selection of participants, confounding variables, measurement of exposure, blinding of outcome assessment, outcome assessment, incomplete outcome data, and selective outcome reporting. The overall risk of bias was low across most domains. However, high or unclear risks were identified in the "selection of participants" domain for a subset of studies. Green, yellow, and red circles indicate low, unclear, and high risk of bias, respectively.

roj-2026-00465-Supplementary-Fig-S1.pdf (642KB, pdf)

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