AFI manual planning versus HyperArc auto-planning: A head-to-head comparison of SRS plan quality.

INTRODUCTION: HyperArc (HA) auto-planning offers simplicity for the end user and consistently high-quality SRS plans. The "Ask For It" (AFI) optimization strategy offers a manual planning technique that, when coupled with R50%Analytic, can be guided to deliver a plan with an intermediate dose spill "as low as reasonably achievable" and high target dose conformity. A direct comparison of SRS plan quality obtained using the manual planning AFI strategy and HA has been performed. METHODS: Using a CT data set available from the Radiosurgery Society, 54 PTVs were created and used to generate 19 individual SRS/SRT cases. Case complexity ranged from single PTV plans to multiple PTV plans with a single isocenter. PTV locations ranged from relative isolation from critical structures to lesions within 1.5 mm of the optic apparatus and abutting the brainstem. All cases were planned using both the AFI and HA optimization strategies as implemented in the Varian Medical Systems Eclipse Treatment Planning System. A range of treatment plan quality metrics were obtained including Intermediate Dose Spill (R50%), Conformity Indices CIRTOG and CIPaddick, PTV Dose Coverage (Dn%), PTV Mean Dose, and Modulation Factor. The Wilcoxon Signed Rank Sum non-parametric statistical method was utilized to compare the obtained plan quality metrics. RESULTS: Statistically significant improvements were found for the AFI strategy for metrics R50%, CIRTOG, CIPaddick, and PTV Mean Dose (p < 0.001). HA achieved superior coverage for Dn% (p = 0.018), while the Modulation Factors were not significantly different for AFI compared to HA optimization (p = 0.13). CONCLUSION: This study provides evidence that the AFI manual planning strategy can produce high-quality planning metrics similar to the HA auto-planning method.

Targeting spectroscopic accuracy for dispersion bound systems from ab initio techniques: Translational eigenstates of Ne@C70.

We investigate the endofullerene system Ne@C70 by constructing a three-dimensional Potential Energy Surface (PES) describing the translational motion of the Ne atom. This is constructed from electronic structure calculations from a plethora of methods, including MP2, SCS-MP2, SOS-MP2, RPA@PBE, and C(HF)-RPA, which were previously used for He@C60 in Panchagnula et al. [J. Chem. Phys. 160, 104303 (2024)], alongside B86bPBE-25X-XDM and B86bPBE-50X-XDM. The reduction in symmetry moving from C60 to C70 introduces a double well potential along the anisotropic direction, which forms a test of the sensitivity and effectiveness of the electronic structure methods. The nuclear Hamiltonian is diagonalized using a symmetrized double minimum basis set outlined in Panchagnula and Thom [J. Chem. Phys. 159, 164308 (2023)], with translational energies having error bars ±1 and ±2 cm-1. We find no consistency between electronic structure methods as they find a range of barrier heights and minima positions of the double well and different translational eigenspectra, which also differ from the Lennard-Jones (LJ) PES given in Mandziuk and Bacic [J. Chem. Phys. 101, 2126-2140 (1994)]. We find that generating effective LJ parameters for each electronic structure method cannot reproduce the full PES nor recreate the eigenstates, and this suggests that the LJ form of the PES, while simple, may not be best suited to describe these systems. Even though MP2 and RPA@PBE performed best for He@C60, due to the lack of concordance between all electronic structure methods, we require more experimental data in order to properly validate the choice.

Critical care nurses' experiences of communication-vulnerable patients in the intensive care unit and the influence on rendering compassionate care.

Background: Interventions administered to critically ill patients, including mechanical ventilation, sedation or other treatments may hinder communication between patients and nurses. These communication challenges may affect critical care nurses' ability to provide compassionate, person-centred care. Objectives: To identify nurses' experiences with patients who are communication-vulnerable in the intensive care unit and how they affect nurses' ability to offer compassionate care. Methods: This qualitative explorative descriptive study involved nurses who worked in intensive care units from four private hospitals in Gauteng, South Africa. Focus groups were conducted with 30 critical care nurses in groups of two to six participants each. Thematic analysis was used to identify themes. Results: Five main themes were identified based on nurses' reports of their experiences with critically ill patients who experience communication difficulties and their impact on rendering compassionate care. Themes were deductively identified based on the social purposes of communication categories. Participants indicated that communication-vulnerable patients influence their ability to provide compassionate care. Generally, the physical, emotional, social and communication difficulties of assisting communication-vulnerable patients caused nurses to feel frustrated and negative towards their work environment, which added to their work stress and sometimes resulted in compassion fatigue. Conclusion: The study shows that various factors could impact the nurses' ability to provide compassionate care and that they require support to provide person-centred care. These factors can include the physical environment, the patient's alertness and awareness and institutional barriers. To support nurses in providing compassionate care, communication partner training may be warranted. Contribution of the study: This study aims to increase awareness of the aspects that may contribute to compassion fatigue for nurses. By identifying these aspects greater support can be provided by facilities where nurses work.

Effects of free versus restricted arm movements on postural control in normal and modified sensory conditions in young and older adults.

The purpose of this study was to explore the effects of arm movements on postural control when standing under different sensory conditions in healthy young and older adults. Fifteen young (mean ± SD age; 21.3 ± 4.2 years) and 15 older (mean ± SD age; 73.3 ± 5.0 years) adults completed the modified Romberg test, which uses four task manipulations (i.e. eyes open and eyes closed on a firm and foam surface) to compromise the fidelity of sensory feedback mechanisms. Each participant completed the tasks under two arm movement conditions: restricted and free arm movements. Centre of pressure (COP) range and frequency were calculated to characterise postural performance and strategy, respectively. Older adults showed greater COP range with restricted compared to free arm movements during all modified sensory conditions, with these effects most prominent in the medio-lateral (ML) plane (all p < .05, Cohen's d = 0.69-1.61). Compared to the free arm movement condition, there was an increase in ML displacement and frequency when arm movements were restricted during only the most challenging (i.e. vestibular dominant) task in young adults (all p < .05, d = 0.645-0.83). Finally, main age effects for the arm restriction cost (p < .05) indicates a greater reliance on an upper body strategy in older compared to young adults, independent of sensory availability/accuracy. These findings indicate that older adults compensate for the loss of accuracy in sensory input by increasing reliance on upper body movement strategies.

Implementing a cirrhosis order set in a tertiary healthcare system: a theory-informed formative evaluation.

BACKGROUND: Standardized order sets are a means of increasing adherence to clinical practice guidelines and improving the quality of patient care. Implementation of novel quality improvement initiatives like order sets can be challenging. Before the COVID-19 pandemic, we conducted a formative evaluation to understand healthcare providers' perspectives on implementing clinical changes and the individual, collective and organizational contextual factors that might impact implementation at eight hospital sites in Alberta, Canada. METHODS: We utilized concepts from the Consolidated Framework for Implementation Research (CFIR) and Normalisation Process Theory (NPT) to understand the context, past implementation experiences, and perceptions of the cirrhosis order set. Eight focus groups were held with healthcare professionals caring for patients with cirrhosis. Data were coded deductively using relevant constructs of NPT and CFIR. A total of 54 healthcare professionals, including physicians, nurses, nurse practitioners, social workers and pharmacists and a physiotherapist, participated in the focus groups. RESULTS: Key findings revealed that participants recognized the value of the cirrhosis order set and its potential to improve the quality of care. Participants highlighted potential implementation challenges, including multiple competing quality improvement initiatives, feelings of burnout, lack of communication between healthcare provider groups, and a lack of dedicated resources to support implementation. CONCLUSIONS: Implementing a complex improvement initiative across clinician groups and acute care sites presents challenges. This work yielded insights into the significant influence of past implementation of similar interventions and highlighted the importance of communication between clinician groups and resources to support implementation. However, by using multiple theoretical lenses to illuminate what and how contextual and social processes will influence uptake, we can better anticipate challenges during the implementation process.

Exploring how arm movement moderates the effect of task difficulty on balance performance in young and older adults.

Emerging evidence highlights that arm movements exert a substantial and functionally relevant contribution on quiet standing balance control in young adults. Ageing is associated with "non-functional" compensatory postural control strategies (i.e., lower limb co-contraction), which in turn, may increase the reliance on an upper body strategy to control upright stance. Thus, the primary purpose of this study was to compare the effects of free versus restricted arm movements on balance performance in young and older adults, during tasks of different difficulty. Fifteen young (mean ± SD age; 21.3 ± 4.2 years) and fifteen older (mean ± SD age; 73.3 ± 5.0 years) adults performed bipedal, semi-tandem and tandem balance tasks under two arm position conditions: restricted arm movements and free arm movements. Centre of pressure (COP) amplitude and frequency were calculated as indices of postural performance and strategy, respectively. Especially in older adults, restriction of arm movement resulted in increased sway amplitude and frequency, which was primarily observed for the mediolateral direction. Further, increasing balance task difficulty raised the arm restriction cost (ARC; a new measure to quantify free vs. restricted arm movement differences in postural control) that was more prominent in older adults. These findings indicate the ARC provides a measure of reliance on the upper body for balance control and that arm movement is important for postural control in older adults, especially during tasks of greater difficulty.

Small molecule binding to surface-supported single-site transition-metal reaction centres.

Despite dominating industrial processes, heterogeneous catalysts remain challenging to characterize and control. This is largely attributable to the diversity of potentially active sites at the catalyst-reactant interface and the complex behaviour that can arise from interactions between active sites. Surface-supported, single-site molecular catalysts aim to bring together benefits of both heterogeneous and homogeneous catalysts, offering easy separability while exploiting molecular design of reactivity, though the presence of a surface is likely to influence reaction mechanisms. Here, we use metal-organic coordination to build reactive Fe-terpyridine sites on the Ag(111) surface and study their activity towards CO and C2H4 gaseous reactants using low-temperature ultrahigh-vacuum scanning tunnelling microscopy, scanning tunnelling spectroscopy, and atomic force microscopy supported by density-functional theory models. Using a site-by-site approach at low temperature to visualize the reaction pathway, we find that reactants bond to the Fe-tpy active sites via surface-bound intermediates, and investigate the role of the substrate in understanding and designing single-site catalysts on metallic supports.

A synopsis of global frontiers in fertility preservation.

Since 2007, the Oncofertility Consortium Annual Conference has brought together a diverse network of individuals from a wide range of backgrounds and professional levels to disseminate emerging basic and clinical research findings in fertility preservation. This network also developed enduring educational materials to accelerate the pace and quality of field-wide scientific communication. Between 2007 and 2019, the Oncofertility Consortium Annual Conference was held as an in-person event in Chicago, IL. The conference attracted approximately 250 attendees each year representing 20 countries around the world. In 2020, however, the COVID-19 pandemic disrupted this paradigm and precluded an in-person meeting. Nevertheless, there remained an undeniable demand for the oncofertility community to convene. To maintain the momentum of the field, the Oncofertility Consortium hosted a day-long virtual meeting on March 5, 2021, with the theme of "Oncofertility Around the Globe" to highlight the diversity of clinical care and translational research that is ongoing around the world in this discipline. This virtual meeting was hosted using the vFairs ® conference platform and allowed over 700 people to participate, many of whom were first-time conference attendees. The agenda featured concurrent sessions from presenters in six continents which provided attendees a complete overview of the field and furthered our mission to create a global community of oncofertility practice. This paper provides a synopsis of talks delivered at this event and highlights the new advances and frontiers in the fields of oncofertility and fertility preservation around the globe from clinical practice and patient-centered efforts to translational research.

Reactive granulomatous dermatitis as a clinically relevant and unifying term: a retrospective review of clinical features, associated systemic diseases, histopathology and treatment for a series of 65 patients at Mayo Clinic.

BACKGROUND: Reactive granulomatous dermatitis (RGD) is an umbrella term used to describe interstitial granulomatous dermatitis (IGD), palisaded neutrophilic and granulomatous dermatitis (PNGD), and interstitial granulomatous drug eruption (IGDR). OBJECTIVE: The aim of this study was to describe systemic associations of RGD, explore possible associations between histopathologic findings and systemic RGD associations and determine clinical relevance of RGD subtypes. METHODS: We retrospectively studied clinical and histopathologic characteristics of patients with RGD from 1990 through 2020. RESULTS: Of 65 patients with RGD (41 women, 24 men; median age at diagnosis, 62 years), 37 had IGD, 26 had PNGD, and 2 had IGDR. Fifty patients (76.9%) had an associated systemic condition; rheumatologic conditions were identified for 34 (52.3%) patients. The associated systemic condition occurred before RGD in approximately 75% of patients. Statistical analyses did not show significant associations between specific subtypes of RGD and systemic diseases or treatment response, and specific histopathologic findings were not predictive of an associated systemic disease. CONCLUSIONS: Although most patients with RGD had an associated systemic condition, subtypes of RGD did not correlate with systemic associations, lending support to the use of the umbrella term RGD.

A measure of SRS/SRT plan quality: Quantitative limits for intermediate dose spill (R50%) in linac-based delivery.

Stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) of multiple cranial targets using a single isocenter on conventional C-arm linear accelerators are rapidly developing clinical techniques. However, no universal guidelines for acceptable intermediate dose spill limits are currently available or widely accepted. In this work, we propose an intermediate dose spill guidance range for cranial SRS/SRT delivered on C-arm linacs with MLC collimation for single PTV plans and single isocenter multiple target plans with PTV volumes in the range 0.02-57.9 cm3 . We quantify intermediate dose spill with the R50% metric (R50% = volume of 50% of prescription isodose cloud / volume of PTV) and test the proposed range using three clinical data sets, containing both 6 MV and 10 MV beams, previously published by other authors. Our proposed lower limit of R50% (LowerR50%) and upper limit of acceptable R50% (UpperR50%) bound over 90% of the clinical data used in this study, yet still provide a challenging benchmark for optimization and plan assessment of linac-based, MLC collimated SRS/SRT.

Traumatic Zone II Flexor Tendon Injury Repair Through a Traumatic Dorsal Approach.

Zone II flexor tendons present unique challenges for repair because of their complex anatomy in a confined space. The approach for zone II injuries is often dictated by preexisting traumatic skin lacerations, with a midaxial or volar approach being most common. In some injuries, this approach is not viable, and alternative approaches must be considered. A 45-year-old man presented with a traumatic crush injury that caused complete disruption of the skin, tendon, capsule, collateral ligament, and volar plate and laceration of the flexor digitorum profundus in zone II near the proximal interphalangeal joint. Given the large, near-circumferential zone of injury, we used the traumatic dorsal wound for the flexor tendon for repair. There are no reports of this approach in the literature. Postoperatively, the proximal interphalangeal joint was immobilized for 6 weeks with a K-wire. The patient was followed in the clinic and prescribed occupational therapy. At the 4-month postoperative visit, the patient had a healed incision, no signs of infection, and intact median/radial sensations. Functional testing showed a loose composite fist, improved range of motion, and 2-cm tip-to-palm deficiency of the index finger. Grip strength was 85 lb in the right hand and 60 lb in the left hand. Although patients are not always expected to regain full function, their postoperative course may be further complicated by adhesion and the need for tenolysis. Given these historical complications of tendon repair and our patient's ability to return to work with satisfactory functional outcomes, this approach may be a viable option for treating this unique injury pattern. [Orthopedics. 2022;45(4):e216-e219.].

Representation of Racial and Ethnic Minority Populations in Dementia Prevention Trials: A Systematic Review.

Despite older racial and ethnic minorities (REMs) being more likely to develop dementia they are underrepresented in clinical trials focused on neurological disorders. Inclusion of REMs in dementia prevention studies is vital to reducing the impact of disparities in dementia risk. We conducted a systematic review to characterize the number of REM enrolled in brain health and prevention randomized controlled trials (RCTs). RTCs published from January 1, 2004 to April 21, 2020 were included. Participants were normal cognitive adults aged 45 years and older who participated in a Phase II or Phase III U.S. based preventative trial. Analyses were performed to examine differences in trial characteristics between RCTs that did and those that did not report race/ethnicity and to calculate the pooled proportion of each racial/ethnic group in randomized brain healthy prevention trials. A total of 42 studies consisting of 100,748 participants were included in the final analyses. A total of 26 (62%) reported some racial/ethnic identity data. The pooled proportion of REM participants was 0.256 (95% CI, 0.191, 0.326). There is a lack of racial/ethnic reporting of participants and REMs remain underrepresented in brain health prevention RCTs.

Analysis of R50% location dependence on LINAC-based VMAT cranial stereotactic treatments.

Stereotactic radiosurgery (SRS) and stereotactic radiation therapy (SRT) techniques are used to deliver high doses per fraction to various types of intra-cranial targets. LINAC-based solutions are growing in prevalence due to recent advances in technologies such as high-definition multi-leaf collimators and volumetric arc therapy radiation delivery. A wide variety of clinical pathologies including intracranial metastases, meningioma, glioblastoma, arteriovenous malformation, acoustic neuroma, and trigeminal neuralgia have been successfully treated using SRS/SRT techniques. These lesions can be in virtually at any location within the cranium. Several publications have shown a wide dispersion of intermediate dose conformality (intermediate dose spill) indices such as the Paddick Gradient Index or R50% for lesions of a specific volume. A complete explanation of this dispersion is lacking but location has been suggested as a contributing factor. While prior studies of PTV location in SRS/SRT are retrospective in nature, we have conducted a prospective study to ascertain the potential effects of location within the cranium on plan intermediate dose conformality as measured by R50% while controlling for lesion volume, lesion shape, prescription (Rx) dose, and Rx isodose surface. Lesion volumes utilized in this study are consistent with metastatic disease presentation. Results indicate only a weak relationship between intermediate dose conformality as measured by R50% and the lesion location when considering nine different, strategically placed lesions. Close proximity to critical structures can reduce the degree of conformality, but the effect appears to be minimal. Single isocenter multiple target cases were studied in addition to single target plans. All critical structure doses observed in this study were found to be within the recommendations of AAPM Task Group report 101. Lesion location does not appear to be a significant contributing factor to the observed variation of dose conformality seen in several SRS/SRT publications.

Introducing BITTSy: The Behavioral Infant & Toddler Testing System.

This manuscript introduces BITTSy, the Behavioral Infant & Toddler Testing System. This software system is capable of running the headturn preference procedure, preferential looking, conditioned headturn, and visual fixation/habituation procedures. It uses only commercial-off-theshelf (COTS) hardware to implement the procedures in an affordable and space-efficient setup. The software package, example protocols and data sets, and manual are freely available and downloadable from go.umd.edu/BITTSy, making this entire set of procedures available to resource-limited labs. Researchers can easily use BITTSy at multiple sites in a uniform manner, resulting in a standardized, powerful research tool that can enhance cross-site research collaborations.

Efficient optimization of R50% when planning multiple cranial metastases simultaneously in single isocenter SRS/SRT.

Simultaneous optimization of multiple Planning Target Volumes (PTVs) of varying size and location in the cranium is a non-trivial task. The rate of dose falloff around PTV structures is variable and depends on PTV characteristics such as the volume. The metric R50% is one parameter that can be used to quantify dose falloff achieved in a given treatment plan. An important treatment planning question is how to construct optimization conditions that result in the efficient production of acceptable plan outcomes considering metrics such as R50%. Guidance provided in literature suggests generating multiple shell control structures around each PTV. The constraints applied to these shells can vary significantly depending on PTV volume. Additionally, there is no clear guidance on how to prospectively determine objective constraints for the optimization shells to achieve a specified goal of R50%. Based on physical principles and empirical evidence, we provide clear quantitative guidance on how to translate the desired R50% outcome into appropriately sized optimization structures around PTVs via an equation that depends on a desired goal for R50% and the volume of PTV. Optimization schema are also provided that allow the goal R50% to be approached or achieved for all PTVs individually. We demonstrate the application of the methodology using commercially available treatment planning software and radiotherapy treatment equipment.

Association of oral contraceptives and tubal ligation with risk of early natural menopause.

STUDY QUESTION: What is the association of oral contraceptives (OCs) and tubal ligation (TL) with early natural menopause? SUMMARY ANSWER: We did not observe an association of OC use with risk of early natural menopause; however, TL was associated with a modestly higher risk. WHAT IS KNOWN ALREADY: OCs manipulate hormone levels, prevent ovulation, and may modify the rate of follicular atresia, while TL may disrupt the blood supply to the ovaries. These mechanisms may be associated with risk of early menopause, a condition associated with increased risk of cardiovascular disease and other adverse health outcomes. STUDY DESIGN, SIZE, DURATION: We examined the association of OC use and TL with natural menopause before the age of 45 years in a population-based study within the prospective Nurses' Health Study II (NHSII) cohort. Participants were followed from 1989 to 2017 and response rates were 85-90% for each cycle. PARTICIPANTS/MATERIALS, SETTING, METHODS: Participants included 106 633 NHSII members who were premenopausal and aged 25-42 years at baseline. Use, duration and type of OC, and TL were measured at baseline and every 2 years. Menopause status and age were assessed every 2 years. Follow-up continued until early menopause, age 45 years, hysterectomy, oophorectomy, death, cancer diagnosis, or loss to follow-up. We used Cox proportional hazards models to estimate hazard ratios (HRs) and 95% CIs adjusted for lifestyle, dietary, and reproductive factors. MAIN RESULTS AND THE ROLE OF CHANCE: Over 1.6 million person-years, 2579 members of the analytic cohort experienced early natural menopause. In multivariable models, the duration, timing, and type of OC use were not associated with risk of early menopause. For example, compared with women who never used OCs, those reporting 120+ months of OC use had an HR for early menopause of 1.01 (95% CI, 0.87-1.17; P for trend=0.71). TL was associated with increased risk of early menopause (HR = 1.17, 95% CI, 1.06-1.28). LIMITATIONS, REASONS FOR CAUTION: Our study population is homogenous with respect to race and ethnicity. Additional evaluation of these relations in more diverse populations is important. WIDER IMPLICATIONS OF THE FINDINGS: To our knowledge, this is the largest study examining the association of OC use and TL with early natural menopause to date. While TL was associated with a modest higher risk of early menopause, our findings do not support any material hazard or benefit for the use of OCs. STUDY FUNDING/COMPETING INTEREST(S): The study was sponsored by UO1CA176726 and R01HD078517 from the National Institutes of Health and Department of Health and Human Services. The work was supported by the Intramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development. The authors have no competing interests to report. TRIAL REGISTRATION NUMBER: N/A.

Stemless Total Shoulder Arthroplasty for a 4-Part Proximal Humerus Malunion and Post-traumatic Arthritis: A Case Report.

CASE: We present a 62-year-old left-hand-dominant woman with history of renal failure, osteoporosis, and 4-part proximal humerus fracture malunion with subsequent post-traumatic arthritis of the left glenohumeral joint. After conservative treatments failed to relieve her symptoms, the patient underwent stemless total shoulder arthroplasty (TSA) because of concerns that her proximal humerus could not accommodate a stemmed implant. At 2 and a half-years postoperative, the patient demonstrated significant improvement of symptoms without signs of radiographic loosening. CONCLUSION: In the setting of proximal humerus malunion with post-traumatic arthritis, clinical improvement without implant loosening can be achieved with stemless TSA, even in the setting of compromised bone quality.

Investigating the population structure and genetic diversity of Arabian horses in Oman using SNP markers.

Arabian horses were selected for metabolic efficiency, beauty, efficiency and endurance. Therefore, Bedouins have for centuries traced their prized horses' ancestries. With the establishment of the World Arabian Horse Organization (WAHO), registration of Arabian horses became centralized and countries worldwide registered them in its database. Most existing Arabian horses in Oman today were imported after the 1970s and are predominantly flat-racing Arabians. This work aimed at revealing the genetic background and diversity of Omani Arabian horses by comparing them with Arabian horses from a diverse genetic background. To that end, we genotyped 63 randomly sampled Arabian horses from Oman using the Illumina Equine SNP70. For comparison, SNP genotypes of 12 Saudi Arabian horses, 27 French, 77 Egyptian, 11 Polish and 36 US Arabians were included in the study. We additionally included 17 Thoroughbred horses and 21 horses representing large and small breeds as an outgroup. Our MDS analysis and phylogenetic analysis showed that the Arabian horses in Oman cluster primarily with French Arabian horses, with a few horses clustering within the Polish/US Arabians. The French Arabian horse cluster was the closest to the Thoroughbred horses. Amongst the Arabian horses, plink average genomic inbreeding levels were highest in the Egyptian Arabian (0.169) followed by the Saudi Arabian horses (0.137) and lowest in the Omani and French Arabian horses, -0.041 and -0.079 respectively. To our knowledge, this is the first report on the genetic background and diversity of Arabian horses in Oman. Our results demonstrated a definite subpopulation structure among Arabian horses and this information should advise future decision-making on Arabian horse breeding.

The surface area effect: How the intermediate dose spill depends on the PTV surface area in SRS.

PURPOSE: Stereotactic radiosurgery (SRS) is rapidly becoming the standard of care for many intracranial targets. The characteristics of the planning target volume (PTV) can affect the intermediate dose spill and thus normal brain volume dose which is correlated with brain toxicity. R50% (volume receiving 50% of prescription dose divided by PTV volume) is a useful metric to quantify the intermediate dose spill. We propose a novel understanding of how the PTV surface area (SAPTV ) affects the intermediate dose spill of SRS treatments. METHODS: Using a phantom model provided by a computed tomography (CT) of the IROC Head Phantom® and Eclipse® Treatment Planning System, we investigate the relationship of R50% and SAPTV in single-target SRS treatments. The planning studies are conducted for SRS treatments on a Varian TrueBeam® linear accelerator with high-definition MLC and a 6 MVFFF beam mode. These data are analyzed to ascertain trends in R50% related to SAPTV . Since SAPTV is not available as a structure property in the Eclipse RTPS, we introduce an Eclipse script to extract PTV surface area of arbitrary-shaped PTVs. We compare a physically reasonable theoretical prediction of R50%, R50%Analytic , to the R50% achieved in treatment planning studies. RESULTS: The SRS phantom study indicates good correlation between the plan R50% and SAPTV . A near-linear relationship of plan R50% vs SAPTV is observed as predicted by the R50%Analytic model. Agreement between plan R50% values and R50%Analytic predictions is good for all but the very smallest PTV volumes. CONCLUSIONS: We demonstrate dependence of the intermediate dose spill measured by R50% on the SAPTV . We call that dependence the surface area effect. This dependence is explicit in the R50%Analytic prediction model. The predicted value of R50%Analytic for a given PTV could be used for guidance during SRS treatment plan optimization, and plan evaluation for that PTV.