Simulation-free palliative radiotherapy using diagnostic CT scans– is less more? A systematic review

Highlights

• •Diagnostic CT-based planning shortens time to treatment.
• •Dosimetric uncertainty when using a diagnostic CT is <5 % in most cases.
• •Suitable locations for SFRT include thoracic spine, lumbar spine, sacrum, pelvis.
• •Exclusion criteria include steep dose gradients and reirradiation.
• •Clinical outcome data showed low toxicity and effective symptom relief.

Abstract

Background

Cancer incidence continues to rise globally, with nearly half of patients requiring radiotherapy. Simulation-free radiotherapy (SFRT) using diagnostic CT scans instead of dedicated planning CTs is a streamlined alternative that may reduce patient visits and shorten time to treatment without impacting quality of care. This systematic review evaluates the practical aspects, dosimetric accuracy, and clinical outcomes of SFRT in palliative radiotherapy.

Methods

Following PRISMA guidelines, PubMed and Embase were searched for publications on SFRT using multiple search terms. Included studies reported clinical or logistical endpoints such as treatment timing, toxicity, dosimetric errors, and patient-reported outcomes.

Results

Eleven studies met inclusion criteria, comprising retrospective and prospective cohorts with patient numbers ranging from 10 to 1000. SFRT was associated with significantly reduced intervals from consultation to treatment start compared to conventional workflows. Dosimetric uncertainties using diagnostic CT scans were generally low, with higher variability observed in thoracic cases. Patient selection typically excluded treatments involving steep dose gradients, reirradiation, or requiring immobilization devices. Limited clinical outcome data showed favourable toxicity profiles and effective symptom relief.

Conclusions

SFRT offers a practical, efficient alternative for palliative radiotherapy, enabling faster treatment initiation and optimized resource use without compromising safety or efficacy in selected patients. The overall dosimetric accuracy appears acceptable for most cases, though caution is advised for thoracic lesions and complex treatment plans. Additional prospective studies with robust clinical endpoints are needed to further validate the role of SFRT in palliative radiotherapy.

Background

Globally, the burden of cancer has been steadily increasing, with approximately 20 million new cases reported in 2022 [1]. It is estimated that around 50 % of cancer patients will require radiotherapy during the course of their disease [2,3]. In metastatic cancer patients, this can range from locally ablative treatments like stereotactic body radiotherapy (SBRT) to palliative treatments aimed solely at symptom relief [4,5].

While advanced technologies like SBRT have demonstrated substantial benefits in numerous clinical settings [4], not every treatment requires sub-milimeter accuracy. In cases where slightly more uncertainty represents an acceptable trade-off to achieve increased efficiency, using a diagnostic computed tomography (CT) scan for treatment planning, and thus eliminating the need for a dedicated planning CT scan can yield comparable outcomes [6]. Diagnostic CT scan based planning, referred to as sim-free radiotherapy (SFRT) has been suggested as a viable option for certain patients [[6], [7], [8], [9], [10]]. SFRT may provide similar clinical results but with reduced burden from multiple hospital visits. Several studies have also suggested that SFRT significantly shortens the time to treatment start [6,9]. The estimated overall error associated with using a diagnostic CT scan for treatment planning is expected to be minimal in most cases, with a maximum of approximately 5 % for most localisations [[9], [10], [11], [12], [13]]. Clinical data thus far indicate good efficacy and no safety concerns, supporting the use of SFRT as a reasonable alternative in palliative radiotherapy [6,13]. This approach may be particularly beneficial for patients receiving palliative care, especially given the decreasing utilization of direct treatment at the machine in many centres.

To further elaborate on the data at hand, we did this systematic review to report on practical aspects, pitfalls and possible benefits of SFRT.

Methods/material

Publication search and selection

This systematic review was done using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [14]. The Population, Intervention, Control and Outcome (PICO) criteria used were the following [15,16]: Population – patients receiving palliative radiotherapy, Intervention – palliative radiotherapy using a simulation-free approach, Comparison/Control − historical controls from published studies, Outcome – logistical outcomes (e.g. time to treatment), patient reported outcomes (e.g. pain relieve).

The Pubmed and Embase databases were searched in April and May 2025 for several search queries (title/abstract): “diagnostic CT” AND “radiotherapy”, “diagnostic CT” AND “radiation therapy”, “sim-free” AND “radiotherapy”, “sim-free” AND “radiation therapy”, “simulation free” AND “radiotherapy”, “simulation free” AND “radiation therapy”, “dCT” AND “radiotherapy”, “dCT” AND “radiation therapy”.

The queries were filtered for the years 2005–2025. There was no language limitation at this stage. Later, publications in languages other than English, French or German were excluded.

All records that were identified using the above-mentioned methodology were copied in an Excel Sheet (Microsoft Cooperation, Redmond, WA, USA). Any duplicates were automatically identified and removed with further manual removal where necessary. Only full-text articles were further processed. The references of review articles etc. were checked to identify any further records which had not been identified, yet.

As the next step, only full-text articles reporting primary data were considered. Afterwards, all studies not reporting data for SFRT or without any clinical endpoints (including stakeholder endpoints) or clear dosimetric endpoints were removed. In a last step, data on magnetic resonance imaging (MRI)-or cone beam CT (CBCT) based workflows were excluded to report on diagnostic CT-based workflows only. However, a short overview of trials with similar patients and fractionations was included in the Supplement (see Table S1) [[17], [18], [19], [20], [21]].

This process was done twice by two different people (RF and CS) with a third person serving as a judge if necessary (PW). Quality assessment of the included publications was done using a modified Delphi tool for case-series studies [22,23]. The results are shown in Table S2 in the Supplement.

Data extraction

The following parameters were extracted from every included publication: title, author, publication year, number of patients, number of treatment sites, years treated, type of study (retrospective/prospective), interval planning CT to treatment, inclusion/exclusion criteria, max. interval from dCT, fractionation, type of treatment planning (3D-CRT, IMRT, etc.), type of matching at the machine, time intervals (e.g. treatment time, time to treatment), expected dosimetric errors, toxicity, overall survival and patient reported outcome.

The data extraction process was done twice by two different people (RF and CS) with a third person serving as a judge if necessary (PW).

Results

Selected publications

Using the process described above, 782 publications were initially identified of which a total of 11 publications were included in this systematic review [[6], [7], [8], [9], [10], [11], [12], [13],[24], [25], [26]]. Several papers on adaptive workflows, either MR- or CT based were also identified. However, they were not included into this systematic review as they were out of the direct scope of this review which was to report on palliative RT using diagnostic CT scans.

Fig. 1 shows the data selection process.

Fig. 1.

Publication selection process.

All of the 11 included publication were published in the last five years. The number of included patients ranged from 10 to 1000. The only trial to randomize patients was the DART trial by O'Neil et al. [8]. Further information is shown in Table 1.

Table 1.

Overview of included trials.

Author	Year published	Months/Years treated	Patients (n)	Treatment sites (n)
O'Neil et al. [8]	2024	06/22–04/23	33	42
Schuler et al. [7]	2020	05/18–11/19	160	190
Schuler et al. [6]	2024	04/2018–02/2024	788	1000
Bush et al. [9]	2023	05/21–10/22	45	52
Schiff et al. [26]	2022	01/20–11/20	30	37
Glober et al. [12]	2020	not specified	planning study 25, treatment 10	planning study 25, treatment 10
Larjavaara et al. [11]	2023	from 03/2020	43	60
Strengell et al. [25]	2024	from 01/2020	38	38
Nierer et al. [24]	2020	01/16–08/19	18	18
Wong et al. [10]	2021	04/18–09/18	retrospective 150, prospective 30	36P
Ho et al. [13]	2021	05/2019–08/2019	10	10

Patient and treatment related endpoints

Eligible patients

The inclusion criteria for SFRT often were defined as anatomical areas and/or clinical scenarios (e.g. emergency treatment, critically ill patients). Reirradiation, steep gradients and a near definite treatment doses are among the exclusion criteria. Table 2 shows a summary of the inclusion and exclusion criteria.

Table 2.

Summary of inclusion and exclusion criteria.

Author	Inclusion	Exclusion
O'Neil et al. [8]	simple palliative radiation therapy for thoracic, abdominal, pelvic or proximal limb target, maximum three sites per patient
Schuler et al. [7]	palliative cases with lesion(s) of chest, abdomen, lumbar and thoracic spine, pelvis, or sacrum	lung, cervical spine, head and neck, extremity regions, SBRT
Schuler et al. [6]	same as reference (7)	masks for immobilization, SBRT, high dose with near definite doses, lung
Bush et al. [9]	palliative-intent treatment to bone metastases of the thorax, abdomen, pelvis or proximal extremity	dCT position not reproducible, previous overlapping irradiated area or a nearby implanted device
Schiff et al. [26]	at RO discretion, minimum requirements − recent diagnostic imaging of the intended target site that fully visualized the tissue from beam entry to beam exit at the axial slices of the target	major anatomic changes since the date of the diagnostic imaging
Glober et al. [12]	critically ill patients (on the ICU), oncologic indications or ossification prophylaxis
Larjavaara et al. [11]	bone metastases located in cervical, thoracic, lumbar, sacral vertebrae, iliac bone, acetabulum, costa, and long bones
Strengell et al. [25]	soft tumour metastases adhering to thoracic cage, pelvic bones, subcutaneous metastases and lymph node metastases (inguinal, clavicular fossa), soft tissue mediastinal masses related to superior vena cava syndrome and urinary bladder	tumours in the central nervous system
Nierer et al. [24]	emergency treatments
Wong et al. [10]	metastases in the chest, abdomen, lumbar and thoracic spine, pelvis, and sacrum	lung, customized immobilization (masks etc), insufficient field of view
Ho et al. [13]	in-patients, CT simulation and first fraction during hospitalization, dCT no older than 14 days, dCT was compatible with planning software

Treatment planning and application

Some publications defined minimum requirements for the diagnostic CT scan used for SFRT planning. This usually includes a maximum time interval since dCT acquisition (e.g. max. 1 months) but also factors like a sufficient field of view or reproducible positioning. Certain planning CT parameters already included in the inclusion/exclusion part. Usually dCT within the last months, reproducible and sufficient field of view (FOV).

The treatment planning and delivery techniques used range from simple opposing fields to modulated techniques like VMAT. Steep gradients as used in SBRT were not used for SFRT planning. Additionally, no specific immobilization e.g. masks was done. Matching at the treatment machine was usually done using CBCT, although simpler approaches include clinical positioning. A summary of treatment planning and application parameters is specified in Table 3.

Table 3.

Treatment Planning and application parameters.

Author	Max. interval from dCT (days)	Fractionation	Planning	Matching at the treatment machine
O'Neil et al. [8]	28	several (max. 30 Gy/10Fx)	Max. 2 fields, multileaf only, no IMRT	CBCT and surface scanning
Schuler et al. [7]	28 (4 weeks)	several, most 8 Gy/1Fx	3D-CRT and IMRT	CBCT at first fraction, then kV/kV if no concerns
Schuler et al. [6]	28 (4 weeks)	several, most 8 Gy/1Fx	3D-CRT and IMRT	CBCT at first fraction, then kV/kV if no concerns
Bush et al. [9]	30	8 Gy/1Fx or 20 Gy/5Fx	simple, ap/pa and/or lateral fields	CBCT, MV
Schiff et al. [26]	not specified	several, most 8 Gy/1Fx	not specified	CBCT
Glober et al. [12]	not specified	not specified	simple (ap/pa fields)	kV, clinical landmarks
Larjavaara et al. [11]	30	several (max. 30 Gy/10Fx)	IMRT/VMAT	CBCT
Strengell et al. [25]	30	several (max. 30 Gy/10Fx, most 20 Gy/5Fx)	VMAT	CBCT
Nierer et al. [24]	not specified	several (max. 36 Gy/12Fx)	3D-CRT und IMRT	CBCT
Wong et al. [10]	28 (4 weeks)	several (most single fraction)	3D-CRT	not specified
Ho et al. [13]	14	several, most 8 Gy/1Fx	3D-CRT	not specified

* Fx – fractions, 3D-CRT – 3D conformal radiotherapy, IMRT – intensity modulated radiotherapy, VMAT – volumetric modulated arc therapy, CBCT – cone beam CT, ap – anterior-posterior, pa – posterior-anterior, kV/kV – kilovolt imaging, MV – megavolt imaging.

Time to treatment

A total of five studies reported on multiple timing related outcomes [6,8,9,12,26]. These range from the actual time on the treatment couch to the time in the department, and to further aspects like time from first consultation to treatment. For most of the reported data, a comparison between SFRT and a workflow including a planning CT were done. A significantly longer time for the actual treatment was reported in 2 trials with an increased time on the treatment couch of 2.7 min and 13 min for SFRT patients, respectively [6,26]. A third did not show a statistically significant difference [9]. For time intervals related to the start of treatment, 3 publications showed a significant shorter interval for SFRT patients [6,9,26]. Schuler et al. for example showed a significantly reduced time from consultation to the start of RT in SFRT patients with 5.1 days as opposed to 7.0 days [6]. Table 4 shows the details.

Table 4.

Summary time to treatment and treatment time.

	Parameter	SFRT	CT planned (if applicable)
O‘Neil et al. [8]	Time in centrea	0.41 h	4.7 h (p < 0.001)
Schiff et al. [26]	Time order approved to first treatment	3.6 d	4.2 d (p = 0.26)
	Time order approved to plan generation	0.88 d	1.9 d (p = 0.02)
	Time on couch	25 min	12 min (p = 0.01)
Schuler et al. [6]	Time on couch2	20.5 min	17.8 min (p < 0.001)
	Time consultation to RT3	5.1 d	7.0 d (p < 0.001)
Bush et al. [9]	Time consultation to RT	3.7 d	7.5 d (p < 0.001)
	Time initiation of treatment planning to start RT	4.3 d	7.4 d (p < 0.001)
	Treatment duration	11.3 min	10.3 min (p = 0.27)
Glober et al. [12]	Time check in department to completion of RT	28 min

^aDefined as total time at the cancer centre from the scheduled CT simulation (Arm 1) or treatment delivery (Arm 2) appointment until beam delivery completion; ²On-couch treatment time based on treatment plan-ning system records; ³Defined as time of booking form submission to fraction 1.

Dosimetric endpoints

Seven studies reported dosimetric data [[9], [10], [11], [12], [13],25,26]. The most common method to analyse this was to do comparative planning on the dCT and a planning CT if both were acquired. In most studies, the expected dosimetric uncertainty when using SFRT was reported to be below 5 % [[9], [10], [11],13,26]. In selected cases however, differences from up to 15.5 % have been reported [13,25]. This refers patients being treated for tumours of the chest wall, thoracic cage or intrathoracic. Table S3 shows a summary of the reported dosimetric data available for targets and organs at risk (OAR).

Clinical endpoints

Two studies reported clinical outcome data after SFRT. Ho et al. reported on 10 in-patients treated with SFRT [13]. They found no >G2 acute toxicity and a median survival 66.5 days (range, 3–374 days).

Schuler et al. patient included outcome data of 1000 patients that were treated with SFRT. Data on pain response at 4 weeks was available for 358 patients showing an overall and complete pain response of 71 % and 20 % in patients with moderate or severe baseline pain. Patient-reported acute toxicity at 2 weeks of 130 patients showed grade 3 and 2 toxicities of 9 % and 10 %, respectively [6].

Summary of suitability for SFRT

Taking the existing data into account we created a summary of anatomical sites and scenarios for which there is sufficient data showing good reproducibility and low overall error rates. Fig. 2 shows the summary.

Fig. 2.

Summary of suitably anatomical sites and scenarios for SFRT.

Discussion

Given that up to 50 % of patients treated at a radiation oncology department are treated in a palliative intent with often very limited life expectancy [27,28], SFRT is a reasonably alternative to shorten time to treatment and to optimize resource utilization without reducing the quality of care.

Although this concept is certainly not new, most studies identified in this systematic review were published within the last years and include patients that were treated no longer than 10 years ago. We hypothesize that this may correlate with a reduction of the utilization of clinical setup at the machine in many centres, especially in Europe and North America.

There has been a parallel increase in the utilization of adaptive direct-to treatment approaches, e.g. using an MR-Linac or CBCT based system for adaptive radiotherapy [17,21,29,30]. There have been numerous studies on this as well with excellent results for specialised techniques like SBRT. However, the question arises whether such a specialised approach is clinically necessary for all patients treated with a direct-to-unit approach.

For palliative patients treated for symptom reduction, SFRT seems to be a simple and feasible approach to streamline treatment. The time to treatment was significantly reduced in several publications, thereby enabling a faster treatment, resulting in a faster symptom relief [6,9,26]. Although time to treatment was significantly shorter in several studies, the actual treatment time was slightly but significantly longer in 2 publications. Schuler et al. reported a longer median crude time on the treatment couch of 2.7 min while Schiff et al. reported a difference of 13 min [6,26]. This likely depends on the individual treatment setup (positioning aids, clinical landmarks vs. CBCT, acceptable shifts) as well as on how regularly SFRT is utilized. Schuler et al. for example reported on a very dedicated program with many patients being treated with SFRT [6].

Patient selection is an important factor. Although all patients within the included publications were either palliative oncologic patients or otherwise critically ill, the individual inclusion and exclusion criteria differed. While Glober el al. for example only included critically ill patients and or Ho et al. only included inpatients, others took a broader approach [12,13]. In the dedicated program described by Schuler et al. and Wong et al. a wide range of patients with an indication for palliative radiotherapy are being treated with SFRT [6,7,10]. A lot of studies did not limit SFRT to patients receiving single fraction treatment like 8 Gy/1 fraction but included fractionations up to 30 Gy/10 fractions. This strengthens the fact that SFRT is not only suitable for critically ill patients but can also be safely and effectively done in a broader population of palliative patients, although some limitation apply. These limitations or exclusion criteria are usually near definitive treatment doses, steep gradients (SBRT), the need for fixation using masks, and reirradiation. In these situations a more accurate positioning and dose calculation is preferred. A publication by Roderick et al. which was published after the search dates, offers similar recommendations as summarized in Fig. 2 [31].

The main concern is the overall dosimetric uncertainty when treating a patient using a dCT. This includes the quality of the dCT, positioning and the dose calculation itself. However, the evidence included in this systematic review suggests that this error is well within what would be considered clinically acceptable in these patients. Usually, the error induced by using the dCT is expected to be up to 5 % [[9], [10], [11], [12],26], although some exceptions apply [13,25]. For certain situations, errors of up to 16 % have been reported for organs at risk and the target volumes [13,25]. This referred to treatments in and around the thorax and may be the result of factors like rapid growth and positioning difficulties. The Australian program [6,7,10] also excluded intrathoracic lesions due to the concern that diagnostic CTs may have been done in breath hold techniques without this being clearly described. In this case there are concerns about geographical misses. Robust planning may be able to mitigate some of the concerns, although intensity modulated techniques have been used in many of the included studies. In the large SFRT-1000 cohort for example, 67 % of patients were treated with intensity modulated technologies.

Even in case of a larger expected dosimetric uncertainty of 10–15 %, SFRT may still be a variable option for certain patients after careful consideration. For many palliative treatment indications, various different fractionation schemes are being used with a wide range of biological radiation dose. Although fractionations like 8 Gy/1 fraction, 20 Gy/5 fractions and 30 Gy/10 fractions are considered standard fractionations and widely used in palliative RT, many other possible fractionations have been reported with similar clinical results [28,[32], [33], [34], [35], [36]]. Thereby, the clinical relevance of these uncertainties may be in fact low.

Unfortunately clinical outcome data, especially patient-reported outcome is rare in these cohorts with often limited life expectancy. In this systematic review, clinical outcome data was only available in 2 publications. Ho et al. reported no > G2 toxicity and Schuler et al. stated patient-reported toxicity and pain response showing good results [6,13]. More outcome data would be beneficial, especially when SFRT is considered for a broader range of patients.

To summarize, SFRT offers the possibility to deliver palliative treatment in a streamlined approach and thereby reducing the time to treatment as well as optimizing resource management. The overall error in dose application seems below 5 % for most cases which is unlikely to bear any clinical significance in these cohorts. There are scenarios where certain limitations may apply (see table 5). In these cases, a careful consideration should be done but SFRT may still be a reasonable option. The clinical data available to date have shown a high satisfaction and good clinical outcomes. A well-defined workflow and careful patient selection seems to be key for successfully implementing SFRT to a broader palliative cohort. More clinical outcome data would be beneficial to further elaborate on safety and efficacy of SFRT.

CRediT authorship contribution statement

Daniel R. Zwahlen: Methodology, Data curation, Writing – original draft, Writing – review & editing. Stefan Brodmann: Conceptualization, Writing – review & editing. Robert Förster: Conceptualization, Methodology, Data curation, Formal analysis, Writing – review & editing. Paul Windisch: Data curation, Methodology, Writing – review & editing. Elena Hofmann: Conceptualization, Writing – review & editing. André Buchali: Writing – review & editing. Christina Schröder: Conceptualization, Methodology, Data curation, Visualization, Supervision, Writing – original draft, Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Appendix A. Supplementary data

The following are the Supplementary data to this article: