Efficacy and safety of SBRT for spine metastases: A systematic review and meta-analysis for preparation of an ESTRO practice guideline.

BACKGROUND AND PURPOSE: Advances in characterizing cancer biology and the growing availability of novel targeted agents and immune therapeutics have significantly changed the prognosis of many patients with metastatic disease. Palliative radiotherapy needs to adapt to these developments. In this study, we summarize the available evidence for stereotactic body radiotherapy (SBRT) in the treatment of spinal metastases. MATERIALS AND METHODS: A systematic review and meta-analysis was performed using PRISMA methodology, including publications from January 2005 to September 2021, with the exception of the randomized phase III trial RTOG-0631 which was added in April 2023. Re-irradiation was excluded. For meta-analysis, a random-effects model was used to pool the data. Heterogeneity was assessed with the I2-test, assuming substantial and considerable as I2 > 50 % and I2 > 75 %, respectively. A p-value < 0.05 was considered statistically significant. RESULTS: A total of 69 studies assessing the outcomes of 7236 metastases in 5736 patients were analyzed. SBRT for spine metastases showed high efficacy, with a pooled overall pain response rate of 83 % (95 % confidence interval [CI] 68 %-94 %), pooled complete pain response of 36 % (95 % CI: 20 %-53 %), and 1-year local control rate of 94 % (95 % CI: 86 %-99 %), although with high levels of heterogeneity among studies (I2 = 93 %, I2 = 86 %, and 86 %, respectively). Furthermore, SBRT was safe, with a pooled vertebral fracture rate of 9 % (95 % CI: 4 %-16 %), pooled radiation induced myelopathy rate of 0 % (95 % CI 0-2 %), and pooled pain flare rate of 6 % (95 % CI: 3 %-17 %), although with mixed levels of heterogeneity among the studies (I2 = 92 %, I2 = 0 %, and 95 %, respectively). Only 1.7 % of vertebral fractures required surgical stabilization. CONCLUSION: Spine SBRT is characterized by a favorable efficacy and safety profile, providing durable results for pain control and disease control, which is particularly relevant for oligometastatic patients.

ESTRO clinical practice guideline: Stereotactic body radiotherapy for spine metastases.

BACKGROUND AND PURPOSE: Recent progress in diagnostics and treatment of metastatic cancer patients have improved survival substantially. These developments also affect local therapies, with treatment aims shifting from short-term palliation to long-term symptom or disease control. There is consequently a need to better define the value of stereotactic body radiotherapy (SBRT) for the treatment of spinal metastases. METHODS: This ESTRO clinical practice guideline is based on a systematic literature review conducted according to PRISMA standards, which formed the basis for answering four key questions about the indication and practice of SBRT for spine metastases. RESULTS: The analysis of the key questions based on current evidence yielded 22 recommendations and 5 statements with varying levels of endorsement, all achieving a consensus among experts of at least 75%. In the majority, the level of evidence supporting the recommendations and statements was moderate or expert opinion, only, indicating that spine SBRT is still an evolving field of clinical research. Recommendations were established concerning the selection of appropriate patients with painful spine metastases and oligometastatic disease. Recommendations about the practice of spinal SBRT covered technical planning aspects including dose and fractionation, patient positioning, immobilization and image-guided SBRT delivery. Finally, recommendations were developed regarding quality assurance protocols, including description of potential SBRT-related toxicity and risk mitigation strategies. CONCLUSIONS: This ESTRO clinical practice guideline provides evidence-based recommendations and statements regarding the selection of patients with spinal metastases for SBRT and its safe implementation and practice. Enrollment of patients into well-designed prospective clinical trials addressing clinically relevant questions is considered important.

Outcomes and toxicities in oligometastatic patients treated with stereotactic body radiotherapy for adrenal gland metastases: A multi-institutional retrospective study.

BACKGROUND: Studies reporting SBRT outcomes in oligometastatic patients with adrenal gland metastases (AGM) are limited. Herein, we present a multi-institutional analysis of oligometastatic patients treated with SBRT for AGM. MATERIAL/METHODS: The Consortium for Oligometastases Research (CORE) is among the largest retrospective series of patients with oligometastases. Among CORE patients, those treated with SBRT for AGM were included. Clinical and dosimetric data were collected. Adrenal metastatic burden (AMB) was defined as the sum of all adrenal GTV if more than one oligometastases is present.Competing risk analysis was used to estimate actuarial cumulative local recurrence (LR) and widespread progression (WP). Kaplan-Meier method was used to report overall survival (OS), local recurrence-free survival (LRFS), and progression-free survival (PFS). Treatment related toxicities were also reported. RESULTS: The analysis included 47 patients with 57 adrenal lesions. Median follow-up was 18.2 months. Median LRFS, PFS, and OS were 15.3, 5.3, and 19.1 months, respectively. A minimum PTV dose BED10 > 46 Gy was associated with an improved OS and LRFS. A prescribed BED10 > 70 Gy was an independent predictor of a lower LR probability. AMB>10 cc was an independent predictor of a lower risk for WP. Only one patient developed an acute Grade 3 toxicity consisting of abdominal pain. CONCLUSION: SBRT to AGM achieved a satisfactory local control and OS in oligometastatic patients. High minimum PTV dose and BED10 prescription doses were predictive of improved LR and OS, respectively. Prospective studies are needed to determine comprehensive criteria for patients SBRT eligibility and dosimetric planning.

The Changing Landscape for the Treatment of Painful Spinal Metastases: is Stereotactic Body Radiation Therapy the New Standard of Care?

Due to advancements in systemic targeted and immunotherapies resulting in improved disease control and overall survival, and the increasing use of computed tomography and spine magnetic resonance imaging surveillance, the number of patients presenting with both asymptomatic and symptomatic spinal metastases is increasing. The need for versatile tumour ablative local management strategies, beyond the limits afforded by conventional palliative external beam radiation therapy (cEBRT), is increasingly more important. Stereotactic body radiation therapy (SBRT) was developed to meet such a need. This highly conformal technique allows the delivery of high biologically effective doses of radiation to the vertebral target, while controlling the differential dose exposure to the adjacent critical neural tissue. Identifying patients with painful spine metastases who would gain the most benefit from this important therapeutic option can be challenging. Here we summarise the randomised evidence specific to spine SBRT, comparing cEBRT with SBRT for pain control in patients with spine metastases in the palliative setting to better understand the role of spine SBRT in modern oncological spinal care.

Stereotactic Radiosurgery and Stereotactic Body Radiotherapy in the Management of Oligometastatic Disease.

Stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT) represent non-invasive, efficacious and safe radiation treatments for the ablation of intracranial and extracranial metastases. Although the use of SRS has been established by level 1 evidence for patients presenting with up to three or four brain metastases for at least a decade, the paradigm of ablating a limited number of extracranial metastases (typically up to five, known as oligometastatic disease) has yet to be proven beyond the few reported but highly encouraging phase II randomised trials. In this overview, we summarise the phase III randomised controlled trials evaluating SRS for intact brain metastases and postoperative surgical cavities and introduce the limited literature and future concepts for treating patients with more than five intracranial metastases. Next, we summarise the published phase II randomised controlled trials specific to SBRT and oligometastatic disease, while briefly describing and contrasting the technical principles and biological mechanisms of SBRT versus conventional radiation. Phase III evidence for SBRT is needed, and we summarise ongoing trials in this overview. Ultimately, SRS and SBRT have become cornerstone therapeutic options for patients with oligometastatic disease and the future is bright for these patients, considering that not so long ago they were considered incurable and relegated to palliation alone.

Knowledge-based isocenter selection in radiosurgery planning.

PURPOSE: We present a new method for knowledge-based isocenter selection for treatment planning in radiosurgery. Our objective is to develop a prediction model that can learn from past manually designed treatment plans. We leverage recent advances in deep learning to predict isocenter locations in treatment plans in order to provide a decision support tool. METHODS: The proposed method adapts a geometric approach using orthogonal moment expansions as a feature vector for describing the shape of the tumor. Our approach accounts primarily for tumor shape and OAR proximity, the two factors that are known to greatly affect the isocenter placement. We solve the prediction problem by training a residual neural network with skip connections on the formed shape descriptors. Our network was trained on 533 patient cases and was validated on a set of out-of-sample cases. RESULTS: Our method generates heatmap predictions for isocenter locations that are in most cases comparable to the experienced human planners, which shows that the method can be used in treatment planning to guide the users for determining the isocenters. CONCLUSIONS: Our numerical experiments indicate a positive predictive value on an independent validation set when compared against a test dataset that was not seen by the model during training.

Survey of current practices from an international task force for gynecological stereotactic ablative radiotherapy.

BACKGROUND: Stereotactic Ablative Radiotherapy (SABR) is an effective treatment that improves local control for many tumours. However, the role of SABR in gynecological cancers (GYN) has not been well-established. We hypothesize that there exists considerable variation in GYN-SABR practice and technique. The goal of this study is to describe clinical and technical factors in utilization of GYN-SABR among 11 experienced radiation oncologists. MATERIALS AND METHODS: A 63 question survey on GYN-SABR was sent to 11 radiation oncologists (5 countries) who have published original research, conducted trials or have an established program at their institutions. Responses were combined and analyzed at a central institution. RESULTS: Most respondents indicated that salvage therapy (non-irradiated or re-irradiated field) for nodal (81%) and primary recurrent disease (91%) could be considered standard options for SABR in the setting of inability to administer brachytherapy. All other indications should be considered on clinical trials. Most would not offer SABR as a boost in primary treatment off-trial without absolute contraindications to brachytherapy. Multi-modality imaging is often (91%) used for planning including PET, CT contrast and MRI. There is a wide variation for OAR tolerances however small bowel is considered the dose-limiting structure for most experts (91%). Fractionation schedules range from 3 to 6 fractions for nodal/primary definitive and boost SABR. CONCLUSIONS: Although SABR has become increasingly standard in other oncology disease sites, there remains a wide variation in both clinical and technical factors when treating GYN cancers. Nodal and recurrent disease is considered a potential indication for SABR whereas other indications should be offered on clinical trials. This study summarizes SABR practices among GYN radiation oncologists while further studies are needed to establish consensus guidelines for GYN-SABR treatment.

Simultaneous optimization of isocenter locations and sector duration in radiosurgery.

Stereotactic radiosurgery is an effective technique to treat brain tumors for which several inverse planning methods may be appropriate. We propose an integer programming model to simultaneous sector duration and isocenter optimization (SDIO) problem for Leksell Gamma Knife® IconTM (Elekta, Stockholm, Sweden) to tractably incorporate treatment time. We devise a Benders decomposition scheme to solve the SDIO problem to optimality. The performances of our approaches are assessed using anonymized data from eight previously treated cases, and obtained treatment plans are compared against each other and against the clinical plans. The plans generated by our SDIO model all meet or exceed clinical guidelines while demonstrating high conformity.

Modeling and comparison of alternative approaches for sector duration optimization in a dedicated radiosurgery system.

Stereotactic radiosurgery (SRS) is an effective technique to treat brain metastasis for which several inverse planning methods may be appropriate. We compare three different optimization models for segment duration optimization in SRS using Leksell Gamma Knife® IconTM (Elekta, Stockholm, Sweden). We investigate (1) a linear programming approach, (2) a piecewise quadratic penalty approach, and (3) an unconstrained convex moment-based penalty approach. We examine the performances of these approaches using anonymized data from 14 previously treated cases. In addition, we investigate the important modeling question of selecting weights for the objective functions where we use a simulated annealing algorithm to determine these weights for each model. The inverse plans obtained via optimization models are compared against each other and against the clinical plans. The three inverse planning models can all yield optimal treatment plans in a reasonable amount of time and the treatment plans obtained by these models meet or exceed clinical guidelines while displaying high conformity.

Re-irradiation of Vertebral Body Metastases: Treatment in the Radiosurgery Era.

Vertebral bodies remain one of the most common sites of metastases. In cases where surgical intervention is not indicated or appropriate, conventional external radiation therapy (cEBRT) has been the standard treatment modality. Unfortunately, cEBRT is typically limited, with low complete response and poor local control rates. Disappointing results with re-irradiation using cEBRT highlight the need for innovative salvage therapeutic strategies, such as stereotactic body radiotherapy. A detailed description of this complex treatment strategy is outlined, as is a systematic review of current literature. Although data are limited to single institution series, re-irradiation has consistently been found to be effective with respect to local control (1 year rates range from 66 to 90%) and pain response. Importantly, the treatment is shown to be safe, with the crude rate of radiation myelopathy <1% and a rate of vertebral compression fracture of 12%. As further research and technologic advances continue to refine therapy, stereotactic body radiotherapy is now a recommended option for the treatment of previously irradiated vertebral body metastases.

Detection of Volume-Changing Metastatic Brain Tumors on Longitudinal MRI Using a Semiautomated Algorithm Based on the Jacobian Operator Field.

BACKGROUND AND PURPOSE: Accurate follow-up of metastatic brain tumors has important implications for patient prognosis and management. The aim of this study was to develop and evaluate the accuracy of a semiautomated algorithm in detecting growing or shrinking metastatic brain tumors on longitudinal brain MRIs. MATERIALS AND METHODS: We used 50 pairs of successive MR imaging datasets, 30 on 1.5T and 20 on 3T, containing contrast-enhanced 3D T1-weighted sequences. These yielded 150 growing or shrinking metastatic brain tumors. To detect them, we completed 2 major steps: 1) spatial normalization and calculation of the Jacobian operator field to quantify changes between scans, and 2) metastatic brain tumor candidate segmentation and detection of volume-changing metastatic brain tumors with the Jacobian operator field. Receiver operating characteristic analysis was used to assess the detection accuracy of the algorithm, and it was verified with jackknife resampling. The reference standard was based on detections by a neuroradiologist. RESULTS: The areas under the receiver operating characteristic curves were 0.925 for 1.5T and 0.965 for 3T. Furthermore, at its optimal performance, the algorithm achieved a sensitivity of 85.1% and 92.1% and specificity of 86.7% and 91.3% for 1.5T and 3T, respectively. Vessels were responsible for most false-positives. Newly developed or resolved metastatic brain tumors were a major source of false-negatives. CONCLUSIONS: The proposed algorithm could detect volume-changing metastatic brain tumors on longitudinal brain MRIs with statistically high accuracy, demonstrating its potential as a computer-aided change-detection tool for complementing the performance of radiologists, decreasing inter- and intraobserver variability, and improving efficacy.

Constrained Source Space MR Spectroscopy: Multiple Voxels, No Gradient Readout.

BACKGROUND AND PURPOSE: Our goal was to develop a novel technique for measuring a small number of localized spectra simultaneously and in a time-efficient manner. MATERIALS AND METHODS: Using appropriate radiofrequency pulses, the magnetization from multiple voxels is excited simultaneously and then separated (reconstructed) by using the individual coil-sensitivity profiles from a multichannel receiver coil. Because no gradients are used for k-space encoding, constrained source space MR spectroscopy provides a time advantage over conventional spectroscopic imaging and an improved signal-to-noise ratio per square root of unit time over single-voxel spectroscopy applied at each successive location. In the present work, we considered prototype application of constrained source space MR spectroscopy for 2 voxels. RESULTS: Experimental data from healthy volunteers and simulation results showed that constrained source space MR spectroscopy is effective at extracting 2 independent spectra even in the challenging scenario of the voxels being closely spaced. Also, from 6 patients with various types of brain cancer we obtained 2-voxel constrained source space MR spectroscopy data, which showed spectra of clinical quality in half the time required to perform successive single-voxel MR spectroscopy. CONCLUSIONS: Constrained source space MR spectroscopy provides clinical quality spectra and could be used to probe multiple voxels simultaneously in combination with Hadamard encoding for further scan-time reductions.

Pathobiology of radiation myelopathy and strategies to mitigate injury.

STUDY DESIGN: This is a narrative review of the literature. OBJECTIVES: The objectives of this study were to review the current concepts underlying the pathobiology of radiation-induced spinal cord injury; to discuss potential biologic strategies to mitigate spinal cord injury following radiation; and to provide an update on the clinical guidelines to prevent injury in the era of image-guided stereotactic body radiotherapy (SBRT). SETTING: This study was conducted in Toronto, Canada. METHODS: A MEDLINE search was performed using the following terms: radiation injury; radiation myelopathy; CNS radiation injury; brain necrosis, radiation; demyelination, radiation; blood-brain barrier, radiation; white matter necrosis; and SBRT. RESULTS AND CONCLUSION: The biologic response of the spinal cord after radiation is a continuously evolving process. Death of vascular endothelial cells and disruption of the blood-spinal cord barrier leads to a complex injury response, resulting in demyelination and tissue necrosis. At present, there is no evidence that the pathobiology of cord injury after SBRT is different from that after standard fractionation. Although permanent myelopathy has become a rare complication following conventional fractionated radiation treatment, cases of radiation myelopathy have re-emerged with the increasing role of spine stereotactic body radiation therapy and reirradiation. Experimental biologic strategies targeting the injury response pathways hold promise in mitigating this dreaded late effect of radiation treatment.

Survival outcomes in elderly patients with glioblastoma.

AIMS: Many elderly glioblastoma patients are excluded from randomised trials due to age, comorbidity or poor functional status. The purpose of this study was to describe the survival outcomes in all elderly patients with glioblastoma managed at a tertiary cancer centre. MATERIALS AND METHODS: A retrospective chart review identified 235 elderly patients (age 65 years or over) with a histological diagnosis of glioblastoma between 1 December 2006 and 31 December 2013. The primary outcome of this study was overall survival by treatment type. Univariate and multivariate Cox proportional hazard models were used to explore significant prognostic variables associated with overall survival. RESULTS: The median survival for all patients was 6.5 months (95% confidence interval 5.3-7.7), with 1 year overall survival of 23.7% (95% confidence interval 18.8-30.0). The median survival for patients treated with radiation and chemotherapy was 11.1 months (95% confidence interval 8.1-13.7). Patients treated with radiation alone had a median survival of 6.8 months (95% confidence interval 5.6-7.9). For patients managed with comfort measures only, the median survival was 1.9 months (95% confidence interval 1.6-2.6). Univariate analysis revealed age, performance status, surgery type (biopsy, subtotal resection, gross total resection) and type of treatment received (comfort measures only, radiotherapy alone, radiotherapy and chemotherapy) to be statistically associated with overall survival. In the multivariate analysis, only two predictive factors (treatment received and surgery type) were significant. CONCLUSIONS: Elderly patients with glioblastoma selected for treatment (surgery followed by radiation alone or radiation and chemotherapy) survive longer than patients managed with comfort measures. Prospective randomised trials will help guide management for patients eligible for therapy. Elderly patients with glioblastoma who are deemed not eligible for active therapy have very short survival.

Aprepitant and granisetron for the prophylaxis of radiotherapy-induced nausea and vomiting after moderately emetogenic radiotherapy for bone metastases: a prospective pilot study.

PURPOSE: We evaluated the novel combination of aprepitant and granisetron for the prophylaxis of radiotherapy-induced nausea and vomiting (rinv) among patients receiving moderately-emetogenic radiotherapy for thoracolumbar bone metastases. METHODS: In this single-centre two-arm nonrandomized prospective pilot study, patients undergoing single-fraction radiotherapy (8 Gy) received aprepitant 125 mg and granisetron 2 mg on the day of radiotherapy and aprepitant 80 mg on each of the first 2 days after the day of radiotherapy. Patients undergoing multiple-fraction radiotherapy (20 Gy in 5 fractions) received aprepitant 125 mg on day 1 of radiotherapy, aprepitant 80 mg on days 3 and 5 of radiotherapy, and granisetron 2 mg on every day of radiotherapy. Symptoms and total medication intake were recorded daily during the acute phase (day 1 of radiotherapy until the first day after the last day of radiotherapy), and the delayed phase (days 2-10 after the last day of radiotherapy). Control of vomiting, retching, and nausea was defined as no symptoms and no use of rescue medication. RESULTS: Control rates for single-fraction patients (n = 13) were 100% for acute nausea, 62% for delayed nausea, 100% for acute vomiting and retching, and 85% for delayed vomiting and retching. Control rates for multiple-fraction patients (n = 6) were 67% for acute nausea, 83% for delayed nausea, 67% for acute vomiting and retching, and 83% for delayed vomiting and retching. No grade 3 or 4 toxicities attributable to the study intervention were observed. CONCLUSIONS: The combination of aprepitant and granisetron was safe and efficacious for the prophylaxis of rinv after both single- and multiple-fraction moderately emetogenic radiotherapy for thoracolumbar bone metastases. Our results require confirmation in a larger population.

Magnetic resonance imaging-based tumour perfusion parameters are biomarkers predicting response after radiation to brain metastases.

PURPOSE: To investigate whether early relative cerebral blood volume (rCBV), relative cerebral blood flow (rCBF) and permeability (Ktrans(2)) measurements may serve as magnetic resonance imaging (MRI) biomarkers of radiation response or progression for brain metastases. MATERIALS AND METHODS: Seventy brain metastases in 44 patients treated with either stereotactic radiosurgery or whole brain radiotherapy were imaged with dynamic susceptibility and dynamic contrast enhancement MRI at baseline, 1 week and 1 month after treatment. The final response status was determined according to volume criteria derived from a 1 year post-treatment MRI or last available follow-up MRI. Tumours were characterised as responders, non-responders, progressors and non-progressors and compared for Ktrans(2), rCBF and rCBV differences. Uni- and multivariate analysis evaluated factors associated with tumour response and progression at 1 week and 1 month. A generalised estimating equations (GEE) model accounted for multiple tumours per subject. Receiver operator characteristic (ROC) analysis identified optimal cut-off values, sensitivity and specificity for response or progression. RESULTS: Tumour responders showed lower Ktrans(2) and reduced rCBF at 1 week (P < 0.05 each). Progressive disease showed lower rCBF and reduced rCBV at 1 month (P < 0.05 each). GEE and multivariate analysis revealed lower Ktrans(2) at 1 week, an absence of prior radiation predicted response. At 1 month only lower rCBV predicted progressive disease on GEE and multivariate analysis. Optimal cut-off points for Ktrans(2) and rCBV were 1.37 and 2.03 with sensitivity and specificity of 61.5 and 81.1% and 73.9 and 81.8%, respectively. CONCLUSION: Lower Ktrans(2) at 1 week and rCBV at 1 month discriminated responders and progressive disease, respectively.

Non Tumor Perfusion Changes Following Stereotactic Radiosurgery to Brain Metastases.

Purpose: To evaluate early perfusion changes in normal tissue following stereotactic radiosurgery (SRS). Methods: Nineteen patients harboring twenty-two brain metastases treated with SRS were imaged with dynamic susceptibility magnetic resonance imaging (DSC MRI) at baseline, 1 week and 1 month post SRS. Relative cerebral blood volume and flow (rCBV and rCBF) ratios were evaluated outside of tumor within a combined region of interest (ROI) and separately within gray matter (GM) and white matter (WM) ROIs. Three-dimensional dose distribution from each SRS plan was divided into six regions: (1) <2 Gy; (2) 2-5 Gy; (3) 5-10 Gy; (4) 10-12 Gy; (5) 12-16 Gy; and (6) >16 Gy. rCBV and rCBF ratio differences between baseline, 1 week and 1 month were compared. Best linear fit plots quantified normal tissue dose-dependency. Results: Significant rCBV ratio increases were present between baseline and 1 month for all ROIs and dose ranges except for WM ROI receiving <2 Gy. rCBV ratio for all ROIs was maximally increased from baseline to 1 month with the greatest changes occurring within the 5-10 Gy dose range (53.1%). rCBF ratio was maximally increased from baseline to 1 month for all ROIs within the 5-10 Gy dose range (33.9-45.0%). Both rCBV and rCBF ratios were most elevated within GM ROIs. A weak, positive but not significant association between dose, rCBV and rCBF ratio was demonstrated. Progressive rCBV and rCBF ratio increased with dose up to 10 Gy at 1 month. Conclusion: Normal tissue response following SRS can be characterized by dose, tissue, and time specific increases in rCBV and rCBF ratio.

Patterns of practice in the prescription of palliative radiotherapy for the treatment of bone metastases at the Rapid Response Radiotherapy Program between 2005 and 2012.

OBJECTIVE: We examined whether patterns of practice in the prescription of palliative radiation therapy for bone metastases had changed over time in the Rapid Response Radiotherapy Program (rrrp). METHODS: After reviewing data from August 1, 2005, to April 30, 2012, we analyzed patient demographics, diseases, organizational factors, and possible reasons for the prescription of various radiotherapy fractionation schedules. The chi-square test was used to detect differences in proportions between unordered categorical variables. Univariate logistic regression analysis and the simple Fisher exact test were also used to determine the factors most significant to choice of dose-fractionation schedule. RESULTS: During the study period, 2549 courses of radiation therapy were prescribed. In 65% of cases, a single fraction of radiation therapy was prescribed, and in 35% of cases, multiple fractions were prescribed. A single fraction of radiation therapy was more frequently prescribed when patients were older, had a prior history of radiation, or had a prostate primary, and when the radiation oncologist had qualified before 1990. CONCLUSIONS: For patients with bone metastasis, a single fraction of radiation therapy was prescribed with significantly greater frequency.