Spinal Field Research Articles

Thoracic spinal cord injury after surgical removal of a ruptured cerebellar arteriovenous malformation in a patient in the Concorde position: illustrative case.

Thoracic spinal cord injury after posterior cranial fossa surgery in younger patients is a rare complication. There have been reports of this complication in tumor and spine fields but not in vascular surgery. A 22-year-old-man experienced cerebellar arteriovenous malformation rupture, and the malformation was surgically removed with the man in the Concorde position. After surgery, the man had severe paraplegia, and a thoracic spinal cord injury was diagnosed. In younger patients, cervical hyperflexion in the Concorde position can cause thoracic spinal cord injury even in surgery for cerebrovascular disease.

646 Publication Speed Across Neurosurgical Journals: A Bibliometric Analysis

INTRODUCTION: Many factors influence an author’s choice for journal submission, including the journal impact factor and publication speed. These bibliometric data points, amongst others, have not yet been assessed in neurosurgical research. METHODS: Eight neurosurgical journals were analyzed for original articles, collected via randomized sampling per issue per year from 2016-2020. Publication speed data was gathered from published articles. Journal Impact Factors were gathered using Clarivate Journal Citation Reports. Spearman’s correlation analysis was used to analyze the findings. RESULTS: A total of 1617 original articles and systematic reviews across 8 neurosurgical journals were reviewed. The mean (standard deviation; SD, range) time from submission to print publication (SP) in neurosurgery journals is 344 (190) days, while the submission to acceptance (SA) time is 130 (104) days, acceptance to online print (AO) time is 76 (61) days, and the online publication to print publication (OP) is 137 (114) days. Most articles were from authors from the United States (n = 833; 52%), with the second and third highest contributions coming from China (n = 100; 6%) and Japan (n = 83, 5%) respectively. The top three neurosurgical topics published were spine (n = 417; 26%), vascular (n = 316; 20%) and oncology (n = 275; 17%). There were significant correlations across all determinants of publication speed and journal Impact Factors (SP: r = 0.457, SA: r = 0.204, AO: 0.481, OP: 0.317, p < 0.001). CONCLUSIONS: Neurosurgical journal publication speeds vary between journals and are significantly correlated with the journal’s impact factor. The majority of neurosurgical research in the past five years has been focused in spine, vascular, and oncology fields and has originated from the United States. The information on individual journals could serve as a guide for publishing neurosurgeons to determine the appropriate journal for submission.

Automating the treatment planning process for 3D-conformal pediatric craniospinal irradiation therapy.

Pediatric patients with medulloblastoma in low- and middle-income countries (LMICs) are most treated with 3D-conformal photon craniospinal irradiation (CSI), a time-consuming, complex treatment to plan, especially in resource-constrained settings. Therefore, we developed and tested a 3D-conformal CSI autoplanning tool for varying patient lengths. Autocontours were generated with a deep learning model trained:tested (80:20 ratio) on 143 pediatric medulloblastoma CT scans (patient ages: 2-19years, median=7years). Using the verified autocontours, the autoplanning tool generated two lateral brain fields matched to a single spine field, an extended single spine field, or two matched spine fields. Additional spine subfields were added to optimize the corresponding dose distribution. Feathering was implemented (yielding nine to 12 fields) to give a composite plan. Each planning approach was tested on six patients (ages 3-10years). A pediatric radiation oncologist assessed clinical acceptability of each autoplan. The autocontoured structures' average Dice similarity coefficient ranged from .65 to .98. The average V95 for the brain/spinal canal for single, extended, and multi-field spine configurations was 99.9%±0.06%/99.9%±0.10%, 99.9%±0.07%/99.4%±0.30%, and 99.9%±0.06%/99.4%±0.40%, respectively. The average maximum dose across all field configurations to the brainstem, eyes (L/R), lenses (L/R), and spinal cord were 23.7±0.08, 24.1±0.28, 13.3±5.27, and 25.5±0.34Gy, respectively (prescription=23.4Gy/13 fractions). Of the 18 plans tested, all were scored as clinically acceptable as-is or clinically acceptable with minor, time-efficient edits preferred or required. No plans were scored as clinically unacceptable. The autoplanning tool successfully generated pediatric CSI plans for varying patient lengths in 3.50±0.4minutes on average, indicating potential for an efficient planning aid in a resource-constrained settings.

A Bibliometric Analysis of the Field of Computer-Assisted Orthopedic Surgery during 2002-2021.

This study aimed to investigate the characteristics of research articles and research trends in computer-assisted orthopedic surgery (CAOS) by conducting bibliometric analyses. CAOS-related research articles published in international journals from 2002 to 2021 were collected using the PubMed database and analyzed using the bibliometric method. Their publication year, journal name, corresponding author's country name, and the number of citations of all collected articles were noted. Contents of the articles were analyzed to evaluate the time point and anatomical site at which the digital technique was applied. Further, the 20-year period was divided into two halves of 10 years each to analyze the research trends. A total of 639 CAOS-related articles were identified. An average of 32.0 CAOS-related articles were published annually, with an average of 20.6 and 43.3 published in the first half and second half, respectively. Of all articles, 47.6% were published in the top 10 journals, and 81.2% were written in the top 10 countries. The total numbers of citations were 11.7 and 6.3 in the first and second halves, respectively, but the average annual number of citations was higher in the second half than in the first one. Articles on application of digital techniques during surgery were 62.3% and those on pre-surgery application were 36.9%. Further, articles in the knee (39.0%), spine (28.5%), and hip and pelvis (21.5%) fields accounted for 89.0% of the total publications. But the increase in publications in the said period was highest in the fields of the hand and wrist (+1,300.0%), ankle (+466.7%), and shoulder (+366.7%). Over the last 20 years, the publication of CAOS-related research articles in international journals has grown steadily. Although the knee, spine, hip, and pelvis fields account for most CAOS-related research, research in new fields is also increasing. This study analyzed the types of articles and trends in CAOS-related research and provided useful information for future research in the field of CAOS.

Dosimetric comparison of short and full arc in spinal PTV in volumetric-modulated arc therapy-based craniospinal irradiation

Since 2011 when it was first described, the volumetric-modulated arc therapy (VMAT) technique for craniospinal irradiation (CSI) has always seen the use of large arc lengths for the spine fields ranging from 200° to 360°. This study was aimed to do a dosimetric comparison between the large and shorter spinal arc for CSI. For a cohort of 10 patients, 2 VMAT CSI plans were created for each patient, one using the conventional full 360° arc (VMAT_FA) for the spine and the other using 100° posterior arc (VMAT_PA) for 23.4 Gy and 35 Gy prescriptions. In both the plans, 360° arc fields were employed for treating cranial volume. Spillage dose (DBody-PTV) to Body-PTV (DBody-PTV: dose to body excluding planning target volume) was compared with VMAT_FA and VMAT_PA plans. In addition to these VMAT plans, a 3-dimensional conformal radiotherapy plan was also created for all these patients to compare the DBody-PTV and target volume related dose constraints. Mean D95% difference between the two VMAT plans did not exceed 1.3% for cranial and spinal targets for both prescription levels. The conformity index (CI) was averaged over both prescription doses. Average CI shows a similar value for VMAT_FA (0.84 ± 0.04) and VMAT_PA (0.82 ± 0.05) plans. D95%, V110% and CI did not exhibit a statistically significant difference between partial and full-arc VMAT plans. However, the VMAT_PA plan exhibited a lower DBody-PTV compared to VMAT_FA plans (0.007 ≤ p < 0.05) in the 1 to 5 Gy range. Nevertheless, partial arc plans could not offer a statistically significant dose reduction for delineated organs compared to full arc plans, except for bilateral kidneys.

Histopathological Evaluation of Orthopedic Medical Devices: The State-of-the-art in Animal Models, Imaging, and Histomorphometry Techniques

Orthopedic medical devices are continuously evolving for the latest clinical indications in craniomaxillofacial, spine, trauma, joint arthroplasty, sports medicine, and soft tissue regeneration fields, with a variety of materials from new metallic alloys and ceramics to composite polymers, bioresorbables, or surface-treated implants. There is great need for qualified medical device pathologists to evaluate these next generation biomaterials, with improved biocompatibility and bioactivity for orthopedic applications, and a broad range of knowledge is required to stay abreast of this ever-changing field. Orthopedic implants require specialized imaging and processing techniques to fully evaluate the bone-implant interface, and the pathologist plays an important role in determining the proper combination of histologic processing and staining for quality slide production based on research and development trials and validation. Additionally, histomorphometry is an essential part of the analysis to quantify tissue integration and residual biomaterials. In this article, an overview of orthopedic implants and animal models, as well as pertinent insights for tissue collection, imaging, processing, and slide generation will be provided with a special focus on histopathology and histomorphometry evaluation.

OA238] Verification of field junctions in craniospinal proton radiotherapy

Introduction Craniospinal irradiation (CSI) is a very important element in treating of medulloblastoma. Two laterally opposed cranial fields and several posterior spine fields are usually used for Proton Radiotherapy (PT) in medulloblastoma. In the case a potential dose inhomogeneity at the field junctions can appear. We propose the method of field junction verification based on ionization chambers array measurements and γ -index analysis. Materials and Methods For field junction investigation, clinical plans for two anthropomorphic phantoms have been prepared. There were two opposed lateral brain fields and 2 posterior spine fields in the plan of 5-year-old child phantom. A plan for 10-year-old child phantom consisted of two opposed lateral brain fields and three posterior spine fields. Therefore we investigated two field junctions for 5-year-old child phantom and three field junctions for 10-year-old child phantom. We have chosen the same depth of isocenter for all fields. Dose distribution at the junctions were verified with ionization chambers array mounted in dedicated water phantom and centered in the overlap regions. Measured dose distributions were compared with planes exported from treatment planning system (TPS) by calculating γ -index: 3%/3 mm and 2%/2 mm. Each field junction was investigated at 5 different depths. Results For 5-year-old child phantom we obtained better than 96% of measured points with γ -index ≤ 1 3%/3 mm criteria for all junctions. For 10-year-old child phantom we reached 99% for the same criterion. For both phantoms standard γ -index acceptance criteria of 2%/2 mm were above 87% for all junctions. Conclusions The main benefit of PT of medulloblastoma is sparing of intermediate-to-low-dose to healthy tissues. This feature could translate into clinical reduction of side effects, including a lower risk for secondary cancers. However the crucial condition for a successful treatment is a careful and accurate field junction. We have proved that an ionization chamber array can be successfully used for field junction verification. The γ -index analysis of investigated junction areas shows that PT is a clinically acceptable method for medulloblastoma. The method we have developed can be widely used in proton therapy centers.

P206] Gafchromic and alanine detectors for verification of field junctions in craniospinal proton irradiation

Purpose Radiotherapy is one of essential methods of treatment for medulloblastoma – a primitive neuroectodermal tumor growing in cerebellum. Proton craniospinal irradiations are recommended because of sparing of intermediate-to-low-dose to healthy tissues and reduction of side effects, including secondary cancers. Two laterally opposed cranial fields and several posterior spine fields are usually used for irradiation in medulloblastoma as well in conventional radiotherapy as in proton one. In this field configuration a potential dose inhomogeneity at the field junctions can appear. We have investigated the dose homogeneity in the junction areas using Gafchromic films and alanine detectors. Methods A clinical plan for an anthropomorphic phantom of a 5-year-old child have been prepared. There were two opposed lateral brain fields and 2 posterior spine fields. Therefore two field junctions were investigated. Then the phantom was equipped with alanine detectors and Gafchromic films at chosen positions mainly in junction areas and irradiated. Alanine doses were assessed using proton beam calibration (5–20 Gy). The calibration curve was designed upon developed protocol based on ISO/WD 15566.1 document. Alanine doses were then compared with doses in the treatment plan. Gafchromic films were analyzed using in-house developed AnalyseGafchromic software allowing to calculate dose based on triple channel calibration and apply corrections on scanner spatial inhomogeneity and scan-to-scan instability. Finally, the measured 2D dose distributions were compared with dose planes exported from TPS (Treatment Planning System) using gamma index analysis. Results The compatibility of alanine doses and TPS doses was at the level of 1%. For all the dose planes measured with Gafchromic passing rates of gamma index test (3%/3 mm) was higher than 95%. Conclusions Patients with medulloblastoma may benefit greatly from proton radiotherapy, however the main condition for a successful treatment is a careful and accurate field junctions, where all the uncertainties of beam model in TPS, CT calibration curve and Patient Positioning may affect the dose delivered to the patient. We have proved that Gafchromic films and alanine detectors can be successfully used for complex system check for ability to irradiate the target with sufficient accuracy.

Clinical efficacy and safety of a highly conformal, supine, hybrid forward and inverse planned intensity modulated radiation therapy technique for craniospinal irradiation

Purpose: To demonstrate the clinical efficacy and safety of a highly conformal, supine, hybrid forward and inverse planned intensity modulated radiation therapy (IMRT) technique for photon craniospinal irradiation (CSI).Methods: Patients who received supine, hybrid IMRT CSI from 2009 to 2014 were included in this retrospective review. Clinical target volume (CTV) was defined as intracranial contents and thecal sac, including nerve roots. Dose was prescribed such that >99% of CTV received >99% of prescription and >95% of the planning target volume received >95% of prescription, with no attempt to include vertebral bodies. Lateral fields were utilized at the cranium and upper cervical spine. Spine fields were either single posterior or 2–3 obliques. Plans were generated with a hybrid of forward and inverse planned IMRT. Inferior borders of the cranium fields and superior border of the lower spine field were designed with 6–15 cm long, gradual dose gradients by sequential closing of multileaf collimator leaves using forward planned multiple static segment IMRT delivery. The sliding window upper spine IMRT field was created by the inverse planning system to match gradients of the brain and lower spine fields. The lower spine field gradient was similarly completed.Results: The cohort consisted of 34 patients. Median CSI dose was 36 Gy (range: 18–39.6 Gy). With a median follow up of 59.4 months, there were no isolated recurrences or spinal myelopathies at CTV margins or field gradients. Eleven patients had recurrence, all of which were intracranial.Conclusions: Our hybrid forward and inverse planned IMRT supine CSI technique did not result in any isolated recurrences or myelopathies at CTV margins or field gradients. This suggests our target volumes and blended gradients are appropriate for highly conformal three-dimensional planning.

Chest CT findings among adult survivors of childhood and young adult cancer with a history of chest radiation.

103 Background: While survivors of childhood and young adult cancer with a history of radiation therapy (RT) to the chest are known to be at increased risk for lung cancer, whether a CT-based lung cancer screening program is appropriate for this population is unknown. We sought to describe CT findings in a clinic-based population of childhood and young adult cancer survivors. Methods: We performed a detailed review of all diagnostic chest CT scans performed among patients seen in the Adult Long-Term Follow-Up Program at Memorial Sloan Kettering between August 2005 and May 2016. Included survivors were at least 5 years from diagnosis and had a history of RT to the mediastinum, mantle, axilla, lung, thoracic spine, or total body irradiation fields. Results were reviewed by at least two authors (ET, DB, or AK) and discrepancies were resolved by consultation with a pulmonologist (RK). Results: We identified 620 survivors with a history of chest field RT who were at least 5 years from diagnosis. The population was 48% male, with a median age at diagnosis of 17.2 years. Approximately half were survivors of Hodgkin Lymphoma (N=306; 49.5%) and almost one-third had undergone hematopoietic cell transplant (N=188; 31%); other diagnoses included non-Hodgkin Lymphoma and sarcoma. The most frequently cited RT field was mantle (N=219; 36%), followed by total body irradiation (N=142; 24%) and whole lung (N=110;18%). Among 351 survivors with at least one chest CT, 206 (59%) had at least one pulmonary nodule, 174 (50%) had fibrosis, and 132 (38%) had a ground glass opacity. Among those with a pulmonary nodule, the large majority (91% of those with a nodule) were followed expectantly or underwent repeat imaging; these patients were spared biopsy or resection. Among 18 patients who underwent biopsy, wedge resection, fine needle aspiration, or bronchoscopy, 4 were diagnosed with lung adenocarcinoma, 3 with metastatic sarcoma, and one with marginal zone lymphoma (MALT). Conclusions: Benign pulmonary nodules among adults with a history of RT for childhood or young adult cancer are common. Any strategy for lung cancer screening in this population will need to account for a high likelihood of benign findings on chest CT.

Highly Conformal Hybrid Forward and Inverse Planned Intensity Modulated Radiation Therapy for Supine Craniospinal Irradiation (CSI): Long-term Results and Implications for Pencil Beam Proton Planning

Proton pencil beam scanning allows for highly conformal radiation therapy making target volume definition and treatment localization increasingly important. Since 2009 we have utilized a highly conformal, supine, hybrid forward and inverse IMRT technique for photon craniospinal irradiation (CSI). We report clinical outcomes utilizing our CSI technique and implications for pencil beam proton planning. Charts of 35 patients who received supine, hybrid IMRT CSI from 2009-2014 were retrospectively reviewed. Craniospinal CTV was defined as intracranial contents on bone windows with special attention to cribriform plate, without intentional inclusion of optic nerves or globes; and thecal sac defined as spinal canal including nerve roots terminating at the lateral border of the vertebral body. PTV was expanded 2 mm at cribriform plate/orbit, 5 mm for remaining intracranial CTV, 3-5 mm ant/post, and 5-8 mm right/left/inferior for thecal sac depending on age and size of patient. Dose was prescribed such that >95% of PTV received > 95% of prescription dose and >99% of CTV received >99% of prescription with no attempt to include vertebral bodies. Lateral fields were utilized at the cranium and upper cervical spine; inferior spine fields were either single posterior, 2-3 obliques, or VMAT depending on patient age and depth to CTV. Plans were generated with a hybrid of forward and inverse planned IMRT. Inferior borders of the brain fields and the superior border of the lower spine field were designed with 6-10 cm long, gradual dose gradients by sequential closing of MLC leaves using forward planned multiple static segment IMRT delivery. The sliding window upper spine IMRT field was created by the inverse planning system to match gradients of the brain and lower spine fields. Onboard kV imaging of cranial fields and a single posterior spine image confirmed daily patient position. Subsequent shifts were calculated based on couch coordinates and planned isocenter shifts. Histologies included 19 medulloblastomas, 9 primitive neuroectodermal tumors, 4 germ cell tumors, 1 pineoblastoma, 1 anaplastic ganglioglioma, and 1 atypical teratoid/rhabdoid tumor. Median CSI dose was 36 Gy (range: 18-39.6 Gy) and median boost dose was 55.8 Gy (range: 30.6-60 Gy). At a median follow up of 51 months (range: 3.2-89.2 months), there were no isolated recurrences or spinal myelopathies at field gradients or CTV margins. Fourteen patients had recurrence, all of which were intracranial. Our hybrid forward and inverse planned IMRT supine CSI technique did not result in any isolated recurrences or myelopathies at field gradients. Furthermore, the safety and efficacy of this highly conformal technique suggests our target volumes and blended gradients are appropriate for incorporation into spot scanning proton therapy plans.

SU‐F‐T‐424: Mitigation of Increased Surface Dose When Treating Through A Carbon Fiber Couch Top

Purpose:To study the effect of the Varian carbon fiber couch top on surface dose for patients being treated using single PA beams in the supine position and to identify simple methods for surface dose reduction.Methods:Measurements of surface dose were obtained in Solid Water phantoms using both a parallel plate ionization chamber (PTW Advanced Markus) and EBT2 Radiochromic films for both 6 and 10MV photons. All measurements were referenced to a depth considered a typical for PA Spine fields. Techniques used to reduce the surface dose included introducing an air standoff using Styrofoam sheets to suspend the phantom surface above the couch top and by adding a thin high Z scattering foil on the table surface. Surface doses were evaluated for typical field sizes, standoff heights, and various scattering materials. Comparisons were made to the surface dose obtainable when treating through a Varian Mylar covered tennis racket style couch top.Results:Dependence on typical spine field sizes was relatively minor. Dependence on air gap was much more significant. Surface doses decreased exponentially with increases in air standoff distance. Surface doses were reduced by approximately 50% for an air gap of 10cm and 40% for a 15cm air gap. Surface doses were reduced by an additional 15% by the addition of a 1mm Tin scattering foil.Conclusion:Using simple techniques, it is possible to reduce the surface dose when treating single PA fields through the Varian carbon fiber couch top. Surface doses can be reduced to levels observed when treating though transparent Mylar tops by adding about 15 cm of air gap. Further reductions are possible by adding thin scattering foils, such as Tin or Lead, on the couch surface. This is a low cost approach to reduce surface dose when using the Varian carbon fiber couch top.

FINE MAGNETIC STRUCTURE AND ORIGIN OF COUNTER-STREAMING MASS FLOWS IN A QUIESCENT SOLAR PROMINENCE

We present high-resolution observations of a quiescent solar prominence which was consisted of a vertical and a horizontal foot encircled by an overlying spine, and counter-streaming mass flows were ubiquitous in the prominence. While the horizontal foot and the spine were connecting to the solar surface, the vertical foot was suspended above the solar surface and supported by a semicircular bubble structure. The bubble first collapsed and then reformed at a similar height, finally, it started to oscillate for a long time. We find that the collapsing and oscillation of the bubble boundary were tightly associated with a flare-like feature located at the bottom of the bubble. Based on the observational results, we propose that the prominence should be composed of an overlying horizontal spine encircling a low-lying horizontal and a vertical foot, in which the horizontal foot was consisted of shorter field lines running partially along the spine and with the both ends connecting to the solar surface, while the vertical foot was consisted of piling-up dips due to the sagging of the spine fields and supported by a bipolar magnetic system formed by parasitic polarities (i.e., the bubble). The upflows in the vertical foot were possibly caused by the magnetic reconnection at the separator between the bubble and the overlying dips, which intruded into the persistent downflow field and formed the picture of counter-streaming mass flows. In addition, the counter-streaming flows in the horizontal foot were possibly caused by the imbalanced pressure at the both ends.

SU‐E‐T‐417: Experimental Verification of Robustness Optimized Intensity Modulated Proton Therapy Plans for Craniospinal Irradiation

Purpose:The robustness‐optimized intensity modulated proton therapy (RO‐IMPT) plans takes into account the setup errors to eliminate the hot/cold spots caused by setup errors at the junction for craniospinal (CSI) irradiation fields. The RO‐IMPT requires a large area for the junction of two fields. This work is to verify the treatment planning system calculated dose with introduction of setup errors by two‐dimensional (2D) dose measurement. Two fields of total lengths of 45 cm with junctions of 21 cm were measured.Methods:2D dose distributions in the coronal plane were measured by a commercial 2D ion‐chamber‐array detector in a cubic solid water phantom. A total spine field consisting of an upper and a lower spine field was measured at the depths of 5.4 and 6.9 cm. The active area for the measurement was 24×24 cm22. The junction and the area outside the junction of the spine fields were measured separately to complete the verification for the total field. Six different amounts of set‐up errors along the superior‐inferior direction up to 1.4 cm were intentionally applied. The measured dose with and without set‐up errors were compared with the calculated dose with and without set‐up errors using Gamma‐index analysis. 3%/3mm and 2%/2mm dose/distance agreement criteria were used. The point dose at the center of the junction was also compared.Results:For all fields with various introduced setup errors, 100 % of pixels passed the 3%/3mm criteria and on average 96% of pixels passed 2%/2mm criteria. Differences in the measured and calculated doses were within 1.1%.Conclusion:The efficacy of the robustness for the CSI RO‐IMPT plans were verified by measurement. The measurement method can be used for patient treatment field specific QA for CSI RO‐IMPT plans in our institution in the near future.

SU-E-T-226: Junction Free Craniospinal Irradiation in Linear Accelerator Using Volumetric Modulated Arc Therapy : A Novel Technique Using Dose Tapering

Purpose: Spatially separated fields are required for craniospinal irradiation due to field size limitation in linear accelerator. Field junction shits are conventionally done to avoid hot or cold spots. Our study was aimed to demonstrate the feasibility of junction free irradiation plan of craniospinal irradiation (CSI) for Meduloblastoma cases treated in linear accelerator using Volumetric modulated arc therapy (VMAT) technique. Methods: VMAT was planned using multiple isocenters in Monaco V 3.3.0 and delivered in Elekta Synergy linear accelerator. A full arc brain and 40° posterior arc spine fields were planned using two isocentre for short ( 10 cm) at the conventional field junction. Results: In this primary study five patients were planned and three patients were delivered using this novel technique. As the dose contribution from the adjacent beams were varied (gradient) to create a complete dose distribution, therefore there is no specific junction exists in the plan. The junction were extended from 10–14 cm dependingmore » on treatment plan. Dose gradient were 9.6±2.3% per cm for brain and 7.9±1.7 % per cm for spine field respectively. Dose delivery error due to positional inaccuracy was calculated for brain and spine field for ±1mm, ±2mm, ±3mm and ±5 mm were 1%–0.8%, 2%–1.6%, 2.8%–2.4% and 4.3%–4% respectively. Conclusion: Dose tapering in junction free CSI do not require a junction shift. Therefore daily imaging for all the field is also not essential. Due to inverse planning dose to organ at risk like thyroid kidney, heart and testis can be reduced significantly. VMAT gives a quicker delivery than Step and shoot or dynamic IMRT.« less

SU‐E‐T‐522: A Multi‐Isocenter VMAT Technique for Cranio‐Spinal Irradiation

Purpose:Develop a matching VMAT field technique and investigate planning feasibility for treating the entire central nervous system (CNS) using Cranio‐Spinal Irradiation (CSI) .Methods:Two patients diagnosed with acute myeloid leukemia (AML) presented with CNS involvement, received CSI, and were included in this study. The patients were treated with the traditional CSI technique: prone position, opposing lateral brain fields, two posterior fields (upper and lower spine), and 5mm junction shifts to improve dose uniformity. The patients were retrospectively re‐planned using volumetric arc therapy (VMAT). The spine and brain were contoured to create the clinical target volume (CTV) as well as normal tissues including kidneys, lung and heart for optimization. Three isocenters were used for planning: brain, upper and lower spine. The beams were allowed to overlap by approximately 10cm. Entire 360 degree rotations were used for the brain fields and posterior 120 degree arcs were used for the spine fields. The dosimetric coverage of the target between the VMAT and traditional plans was compared, as well as the dose to normal tissues.Results:Both VMAT plans achieved improved dose uniformity in the CTV (standard deviation &lt; 2%), and reduced hot spots (&lt;110%). Dose to the heart was reduced, with the V10 being 12.7% and 28.2%, compared to 44.6% and 50.2%, respectively, for the traditional plan. Dose to the total lung V5 increased for the VMAT plans for both patients (21.6% and 27.8% compared to 12% and 13% respectively). The results for the kidneys were mixed with the mean dose increasing for one patient and decreasing for the other .Conclusion:The efficacy of planning CSI treatments using a matching VMAT technique was demonstrated. The developed technique has the potential to improve dose uniformity to the target while at the same time reduce the risk of under or over dosing the spine.

A simple planning technique of craniospinal irradiation in the eclipse treatment planning system.

A new planning method for Craniospinal Irradiation by Eclipse treatment planning system using Field alignment, Field-in-Field technique was developed. Advantage of this planning method was also studied retrospectively for previously treated five patients of medulloblastoma with variable spine length. Plan consists of half beam blocked parallel opposed cranium, and a single posterior cervicospine field was created by sharing the same isocenter, which obviates divergence matching. Further, a single symmetrical field was created to treat remaining Lumbosacral spine. Matching between a inferior diverging edge of cervicospine field and superior diverging edge of a Lumbosacral field was done using the field alignment option. ′Field alignment′ is specific option in the Eclipse Treatment Planning System, which automatically matches the field edge divergence as per field alignment rule. Multiple segments were applied in both the spine field to manage with hot and cold spots created by varying depth of spinal cord. Plan becomes fully computerized using this field alignment option and multiple segments. Plan evaluation and calculated mean modified Homogeneity Index (1.04 and 0.1) ensured that dose to target volume is homogeneous and critical organ doses were within tolerance. Dose variation at the spinal field junction was verified using ionization chamber array (I′MatriXX) for matched, overlapped and gap junction spine fields; the delivered dose distribution confirmed the ideal clinical match, over exposure and under exposure at the junction, respectively. This method is simple to plan, executable in Record and Verify mode and can be adopted for various length of spinal cord with only two isocenter in shorter treatment time.

An overview of craniospinal axis fields and field matching

Many methods are implemented for craniospinal axis (CSA) radiation treatment (RT). This paper’s goal is to define correctly matched CSA RT fields. Overlap or a space between matched RT fields can create variances of dose and the possibility of negative side effects or disease recurrence, respectively. An accurate CSA RT match procedure is created with localization markers, immobilization devices, equations, feathered matches, safety gap, and portal imaging. A CS match angle is predetermined to optimize patient position before immobilization device fabrication. Various central axis (CA) placements within the brain and spine fields that effect gantry, table, and collimator rotation are described. An overview of the methods used to create CSA RT fields and matches is presented for optimal CSA RT implementation. In addition, to the author’s knowledge, this is the first time that a prone CSA RT with anesthesia has been described.

Intensity-modulated radiation therapy and volumetric-modulated arc therapy for adult craniospinal irradiation—A comparison with traditional techniques

Craniospinal irradiation (CSI) poses a challenging planning process because of the complex target volume. Traditional 3D conformal CSI does not spare any critical organs, resulting in toxicity in patients. Here the dosimetric advantages of intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) are compared with classic conformal planning in adults for both cranial and spine fields to develop a clinically feasible technique that is both effective and efficient. Ten adult patients treated with CSI were retrospectively identified. For the cranial fields, 5-field IMRT and dual 356° VMAT arcs were compared with opposed lateral 3D conformal radiotherapy (3D-CRT) fields. For the spine fields, traditional posterior-anterior (PA) PA fields were compared with isocentric 5-field IMRT plans and single 200° VMAT arcs. Two adult patients have been treated using this IMRT technique to date and extensive quality assurance, especially for the junction regions, was performed. For the cranial fields, the IMRT technique had the highest planned target volume (PTV) maximum and was the least efficient, whereas the VMAT technique provided the greatest parotid sparing with better efficiency. 3D-CRT provided the most efficient delivery but with the highest parotid dose. For the spine fields, VMAT provided the best PTV coverage but had the highest mean dose to all organs at risk (OAR). 3D-CRT had the highest PTV and OAR maximum doses but was the most efficient. IMRT provides the greatest OAR sparing but the longest delivery time. For those patients with unresectable disease that can benefit from a higher, definitive dose, 3D-CRT–opposed laterals are the most clinically feasible technique for cranial fields and for spine fields. Although inefficient, the IMRT technique is the most clinically feasible because of the increased mean OAR dose with the VMAT technique. Quality assurance of the beams, especially the junction regions, is essential.

IMRT and VMAT for Craniospinal Irradiation: A Comparison with Traditional Techniques

Craniospinal irradiation (CSI) poses a challenging planning process due to the complex target volume. This study analyzes dosimetric advantages of IMRT and volumetric modulated arc therapy (VMAT) to classic conformal (3D-CRT) planning in adults. Previous studies focused only on IMRT for spine fields but here both the cranial and the spine fields are investigated. The use of VMAT is also included.