Intraoperative Radiotherapy Research Articles

Dosimetric characteristics of the LIAC intraoperative radiotherapy beams: Assessment of sensitivity to measurement errors at the commissioning phase

Commissioning of the LIAC intraoperative electron radiotherapy (IOERT) unit relies on the vendor's SWL-LIAC software. This software simulates the percentage depth-doses (PDDs), off-axis dose profiles and relative output factors (ROFs) for all beams based on a small set of input measurements. To date, the impact of various possible measurement errors during commissioning on LIAC dosimetric characteristics has not been studied in detail. We aimed to assess the sensitivity of the dosimetric characteristics of the ‘LIAC 12 MeV’ IOERT unit beams to various measurement errors in the commissioning phase by obtaining the magnitude of the influence of each error.The required SWL-LIAC inputs (PDDs of applicator diameters 3, 7, and 10 cm and open field) were measured with intentional applicator misalignments including 1° rotation or lateral (2 mm) or vertical (±2 mm) displacements. Also, inaccurate water surface definition for the detector was simulated by using PDDs that were shifted by ±2 mm. The errors were applied one at a time. To identify the most influential errors, the computed relative dosimetric characteristics resulting from such erroneous measurement conditions were compared to the corresponding ‘error-free’ ones. The depths of 90% and 50% doses (R90 and R50, respectively) were investigated further.All the resulting errors in R90, R50, flatness, symmetry and penumbra were within 3.9 mm, 2.8 mm, 4.3%, 4.6% and 3.5 mm, respectively. The overall averages of the absolute differences in these indices from the error-free fields were 0.8 mm, 0.8 mm, 0.6%, 0.4% and 0.5 mm, respectively. Errors in water surface definition for the detector had 4.4 to 22 times greater influence on PDDs than the other errors. The corresponding values for the profiles were 1.3–5.8 times. Among the errors in applicator alignment, PDDs and profiles were more affected by rotational and vertical ‘stand-in’ applicator misalignments, respectively. The R90 and R50 values were less affected by the errors in the small (3 and 4 cm diameter) and 45° bevelled applicators.To conclude, on average, the studied errors caused relatively small changes in beam characteristics although the maximum magnitudes of the observed errors were fairly substantial. Among the investigated errors, defining the water surface inaccurately has the largest impact on the dosimetric characteristics. Overall, sensitivity to the studied errors was found to be greatest with large-diameter flat applicators and/or lower electron energies. Although individual errors in applicator alignment have less effect on dosimetric characteristics compared to water surface error, given that these errors may occur simultaneously during dosimetry, special attention should be paid to placing the applicator correctly at the surface. Special set-up aids, such as our in-house tool for aligning applicators, are therefore indicated. The findings also further highlight the need for checking the water level periodically in long-term dosimetry procedures.

Low-Energy X-Ray Intraoperative Radiation Therapy (Lex-IORT) for Resected Brain Metastases: A Single-Institution Experience

Resection followed by local radiation therapy (RT) is the standard of care for symptomatic brain metastases. However, the optimal technique, fractionation scheme and dose are still being debated. Lately, low-energy X-ray intraoperative RT (lex-IORT) has been of increasing interest. Eighteen consecutive patients undergoing BM resection followed by immediate lex-IORT with 16-30 Gy applied to the spherical applicator were retrospectively analyzed. Demographic, RT-specific, radiographic and clinical data were reviewed to evaluate the effectiveness and safety of IORT for BM. Descriptive statistics and Kaplan-Meyer analysis were applied. The mean follow-up time was 10.8 months (range, 0-39 months). The estimated local control (LC), distant brain control (DBC) and overall survival (OS) at 12 months post IORT were 92.9% (95%-CI 79.3-100%), 71.4% (95%-CI 50.2-92.6%) and 58.0% (95%-CI 34.1-81.9%), respectively. Two patients developed radiation necrosis (11.1%) and wound infection (CTCAE grade III); both had additional adjuvant treatment after IORT. For five patients (27.8%), the time to the start or continuation of systemic treatment was ≤15 days and hence shorter than wound healing and adjuvant RT would have required. In accordance with previous series, this study demonstrates the effectiveness and safety of IORT in the management of brain metastases despite the small cohort and the retrospective characteristic of this analysis.

Systematic review of intraoperative radiation therapy for head and neck cancer.

Multidisciplinary treatments with surgery, radiation therapy, and chemotherapy are the cornerstones in the management of locally advanced head and neck malignancies. In most cases, radiation is delivered via external beam radiation therapy (EBRT). Intraoperative radiation therapy (IORT), on the other hand, is the delivery of precise doses of radiation to selected target volumes within the exposed surgical field while at the operating room. Most studies on its use on head and neck cancers are limited to single-institutional retrospective case series. We performed a systematic review to consolidate the existing literature on IORT for head and neck malignancies. Fifty-two studies representing a mixed population of 2,389 patients were included in this review. IORT via electrons (intraoperative electron radiation therapy), brachytherapy (intraoperative high dose-rate brachytherapy) or photons was administered in numerous settings, but most commonly as part of a reirradiation regimen following salvage surgery for recurrent tumours. Often, additional EBRT was also planned postoperatively. This review illustrates that IORT is a promising treatment modality in head and neck cancer. Multiple single-institutional studies spanning several decades have demonstrated benefit in terms of local control with reasonable toxicity. However, randomised trials comparing it with current standards of care are still needed.

Comparison of commercially available detectors used for the dosimetry of the High Energy Electron Beams.

In modern radiotherapy, electron beams are used less and less often. However, there are still techniques where this type of particles is irreplaceable, like intraoperative radiotherapy (IORT) or total skin electron irradiation (TSEI). Due to low range of electrons penetrating the medium, dosimetric measurements and beam characteristics are challenging. One of the most important steps during this process is to select the right detector in order to collect reliable data. The purpose of this work was to perform beam characteristics using six commercially available detectors: Semiflex 3D (Type 31021), Advanced Markus (Type 34045), Markus (Type 23343), Roos (Type 34001), microDiamond (Type 60019), Diode E (Type 60017). Collected data shows various parameters describing electron beams, depending on the used detector. Obtained results showed that the most useful detector for beam characteristics is microDiamond Type 60019. Thanks to the very small effective volume, microDiamond showed a superior spatial resolution, which is especially handful during the measurements of dose profiles, allowing estimating beam parameters very precisely.

Canadian Spine Society

# Abstract 57. Radiographic reporting in adolescent idiopathic scoliosis: Is there a discrepancy comparing radiologists’ reports and surgeons’ assessments? {#article-title-2} Cobb angle measurement is the standard method for quantification of scoliosis in adolescent idiopathic scoliosis (AIS),

Dosimetric characterization of a mobile accelerator dedicated for intraoperative radiation therapy: Monte Carlo simulations and experimental validation

PurposeThis Technical Note validates previously published data about the dosimetry of the electron beams produced by a mobile accelerator dedicated for intraoperative radiation therapy (IORT). The evaluation of the directional response of a PTW microDiamond detector is presented together with a detailed analysis of the output factors (OFs) for bevelled applicators. MethodsThe OFs of the 6, 8, 10 and 12 MeV electron beams produced by a light intraoperative accelerator (LIAC, SIT, Italy) were measured in a commercial water phantom using the microDiamond. A set of flat and bevelled applicators with sizes ranging from 4 to 10 cm was characterized. For bevelled applicators, a correction for the angular dependence of the microDiamond was calculated using a home-made spherical phantom. Correction factors were obtained through measurements performed rotating the accelerator treatment head at 0°, 15°, 30° and 45°. ResultsFor flat applicators, the average deviation between measured and simulated OFs was (−1.1 ± 0.7)%. The microDiamond showed a higher angular dependence for the 6 MeV beam (∼8% for angles up to 45°, range 92 % ÷ 100 %), while the variations for 8, 10 and 12 MeV beams were ∼ 4 % (range 97 % ÷ 101 %). Correcting for this dependence, the average deviation of the OFs for bevelled applicators was (-0.9 ± 1.6)%. ConclusionsThe presented results were in very good agreement with those reported in literature. Very similar deviations were found between flat and bevelled applicators confirming the suitability of our method to determine the angular dependence correction factors of the microDiamond detector.

Posterolateral Floating Technique for the Thoracic Ossification of the Posterior Longitudinal Ligament with Navigation: A Technical Note.

We describe a floating technique via a posterolateral approach with intraoperative O-arm navigation to facilitate decompression of the spinal cord in thoracic myelopathy due to severe ossification of the posterior longitudinal ligament (OPLL). A 62-year-old man with myelopathy due to thoracic OPLL had left-leg muscle weakness, urinary disturbance, and spastic gait. Bilateral leg pain and gait disturbance had persisted for 2 years. He was successfully treated by the posterolateral OPLL floating procedure and posterior pedicle fixation under O-arm navigation. At a 2-year follow-up, manual muscle testing results and sensory function of the left leg had recovered fully. His cervical Japanese Orthopedic Association score had improved from 5/12 to 11/12. The novel intraoperative O-arm navigation-guided posterolateral floating procedure for thoracic OPLL is effective for achieving precise decompression and strong fixation with a posterior approach only and can provide an excellent result for severe thoracic OPLL without the risk of adverse events from intraoperative radiation.

Which Is Better in Clinical and Radiological Outcomes for Lumbar Degenerative Disease of Two Segments: MIS-TLIF or OPEN-TLIF?

To compare the clinical and radiological outcomes of minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) and traditional open transforaminal lumbar interbody fusion (OPEN-TLIF) in the treatment of two-level lumbar degenerative diseases. The clinical data of 112 patients were retrospectively analyzed, and were divided into an MIS-TLIF group and OPEN-TLIF group. The operative time, intraoperative fluoroscopy, blood loss, postoperative drainage volume, bed rest time, the content of creatine kinase(CK) and complications, were recorded. VAS score and ODI index were used to evaluate clinical efficacy. Bridwell grading was used to evaluate postoperative interbody fusion. Screw position was evaluated by Rao grading. Compared with the OPEN-TLIF group, the MIS-TLIF group had longer operation times, more intraoperative fluoroscopy times, but shorter postoperative bed times (p < 0.05). There were no significant differences in blood loss, postoperative drainage and postoperative CK content between the two groups (p > 0.05). There was no difference in VAS score and ODI index during the follow-up (p > 0.05). There was no significant difference in the interbody fusion rate between the two groups (p > 0.05). There was no significant difference in the distribution of type A screws, but the type B screw in the MIS-TLIF group was higher (p < 0.05). There was no difference in the incidence of complications between the two groups (p > 0.05). The postoperative quality of life score and radiological outcomes of the two types of surgery in two-level lumbar degenerative diseases was similar, and there was no significant difference in muscle injury and complications, but the operation time and intraoperative radiation exposurewere higher than in the OPEN-TLIF group, and the pedicle screws were more likely to deviate laterally out of the vertebral body. Therefore, OPEN-TLIF is recommended for patients with lumbar degenerative diseases of two segments.

Spinal navigation with preoperative computed tomography

Safe placement of posterior cervical-sacral pedicle screws, S2-Ala-iliac screws, iliac screws, transarticular screws C1/2, translaminar screws C2 or cervical lateral mass screws under the guidance of spinal navigation. All posterior spinal instrumentations with screws: instabilities and deformities of rheumatic, traumatic, neoplastic, infectious, iatrogenic or congenital origin; multilevel cervical spinal stenosis with degenerative instability or kyphosis of the affected spinal segment. There are no absolute contraindications for spinal navigation. Cervical spine: Prone position on agel mattress, rigid head fixation, e.g., with Mayfield tongs; if appropriate, closed reduction under lateral image intensification; thoracic + lumbar spine: prone position on acushioned frame; midline posterior surgical approach at the level of the segments to be instrumented; if necessary, open reduction; insertion of the cervical/upper thoracic screws under the guidance of spinal navigation; if necessary, posterior decompression; instrumentation longitudinal rods; if fusion is to be obtained, decortication of the posterior bone elements with ahigh-speed burr and onlay of cancellous bone or bone substitutes. In stable instrumentations, no postoperative immobilization with orthosis is necessary, removal of drains (if used) 2-3days postoperatively (postop), removal of the sutures 14days postop, clinical and x‑ray controls 3and 12months postop or in case of clinical or neurological deterioration. Numerous studies showed that the use of spinal navigation significantly reduces implant malplacement rates, complications, and revision surgery. Furthermore, intraoperative radiation exposure to the operation team can be reduced by up to 90%.

Trend of gastric cancer incidence and death rate in adolescents and young adults: A retrospective cohort study based on the Surveillance, Epidemiology, and End Results (SEER) database.

Less attentions are paid into the adolescents and young adults (AYAs) diagnosed with gastric cancer (GC). Our study aims to explore incidence rate trend, death rate trend, and prognostic factors for overall survival (OS) and cancer-specific survival (CSS) in AYAs with GC. A retrospective cohort study based on the Surveillance, Epidemiology, and End Results (SEER) database was performed. Joinpoint regression analysis was used to calculate average annual percent change (AAPC) with 95% confidence interval (CI) for incidence and death rate trends. Prognostic factors for OS and CSS were investigated using Cox proportional hazard model and gray test, respectively, with results shown as hazard ratio (HR) with 95% CI. Although no statistical significance, incidence rate trend showed a tendency to an increase in AYAs (AAPC=0.2, 95% CI: -0.2-0.6). All-cause death rate trends were declined both in AYAs and middle-aged and elderly people (MAEP), with AAPC value of -0.6 (95% CI: -0.8 to -0.5) and -0.5 (95% CI: -0.6 to -0.4), respectively. AYAs had a lower risk of all-cause death (HR: 0.87, 95% CI: 0.84-0.90) but a higher risk of GC-specific death (HR: 1.11, 95% CI: 1.07-1.15) than MAEP. Chemotherapy (HR: 1.27, 95% CI: 1.16-1.40) and intraoperative radiation (HR: 2.89, 95% CI: 1.13-7.37) were, respectively, identified as risk factors for worse OS and CSS in AYAs. AYAs had a higher risk of GC-specific death, indicating more attention should be paid into AYAs with GC.

Factors Associated With Cosmetic Outcomes After Treatment With a Novel Form of Breast Intraoperative Radiation Therapy

IntroductionPrecision breast intraoperative radiation therapy (PB-IORT) incorporates computed tomography–guided treatment planning and high dose rate brachytherapy to deliver a single dose of highly conformal radiational therapy. The purpose of this study is to determine factors associated with poor cosmetic outcomes after treatment with PB-IORT. MethodsThe study included all consecutive participants enrolled in an ongoing phase II clinical trial that had completed a minimum of 12 mo of follow-up. A poor cosmetic outcome was defined as scoring “fair” or “poor” on the Harvard Cosmesis evaluation, or “some” or “very much” on any of the three general cosmesis categories. Statistical analysis was performed utilizing R. ResultsThe final cohort included 201 participants, of which 181 (90%) had an overall good/excellent cosmetic outcome. Group 1 consisted of 162 (81%) participants who reported only excellent/good cosmetic outcomes. Group 2 consisted of 39 (19%) participants who reported some aspect of a poor cosmetic outcome. On multivariable analysis, participants with ductal carcinoma in situ were significantly more likely to experience a poor cosmetic outcome (odds ratio 2.45, 95% confidence interval 1.03-5.82, P = 0.04), and those who received subsequent whole breast irradiation were also more likely to have a poor cosmetic outcome (odds ratio 10.20, 95% confidence interval CI 1.04-99.95, P = 0.04). ConclusionsPatients with need for further radiation after PB-IORT are at increased risk for a poor cosmetic outcome. Larger balloon volume and distance between the skin do not have deleterious effects on cosmetic outcomes.

Delivery of intensity-modulated electron therapy by mechanical scanning: An algorithm study.

In principle, intensity-modulated electron therapy (IMET) can be delivered through mechanical scanning, with a robotic arm mounting a linac. Here is a scanning algorithm to identify the back-and-forth, top-to-bottom (zigzag) pattern scan sequence. The algorithm includes generating beam positions with a uniform resolution according to the applicator size; adopting discrete energies to achieve the depth of 90% dose by compositing energies; selecting energy by locating the target's distal edge; and employing the energy-by-energy scan strategy for step-and-shoot discrete scanning. After a zigzag scan sequence is obtained, the delivery order of the scan spots is optimized by fast simulated annealing (FSA) to minimize the path length. For algorithm evaluation, scan sequences were generated using the computed tomography data of 10 patients with pancreatic cancer undergoing intraoperative radiotherapy, and the results were compared between the zigzag path and an optimized path. A simple calculation of the treatment delivery time, which comprises the irradiation time, the total robotic arm moving time, the time for energy switch, and the time to stop and restart the beam, was also made. In these clinical cases, FSA optimization shortened the path lengths by 12%-43%. Assuming the prescribed dose was 15 Gy, machine dose rate was 15 Gy/s, energy switch time was 2 s, stop and restart beam time was 20 ms, and robotic arm move speed was 50 mm/s, the average delivery time was 124±38 s. The largest reduction in path length yielded an approximately 10% reduction in the delivery time, which can be further reduced by increasing the machine dose rate and the robotic arm speed, decreasing the time for energy switch, and/or developing more efficient algorithms. Mechanically scanning IMET is potentially feasible and worthy of further exploration.

Intraoperative electron radiotherapy in early invasive ductal breast cancer: 6-year median follow-up results of a prospective monocentric registry

BackgroundIntraoperative electron radiotherapy (IOERT) can be used to treat early breast cancer during the conservative surgery thus enabling shorter overall treatment times and reduced irradiation of organs at risk. We report on our first 996 patients enrolled prospectively in a registry trial.MethodsAt Jules Bordet Institute, from February 2010 onwards, patients underwent partial IOERT of the breast. Women with unifocal invasive ductal carcinoma, aged 40 years or older, with a clinical tumour size ≤ 20 mm and tumour-free sentinel lymph node (on frozen section and immunohistochemical analysis). A 21 Gy dose was prescribed on the 90% isodose line in the tumour bed with the energy of 6 to 12 MeV (Mobetron®-IntraOp Medical).ResultsThirty-seven ipsilateral tumour relapses occurred. Sixteen of those were in the same breast quadrant. Sixty patients died, and among those, 12 deaths were due to breast cancer. With 71.9 months of median follow-up, the 5-year Kaplan–Meier estimate of local recurrence was 2.7%.ConclusionsThe rate of breast cancer local recurrence after IOERT is low and comparable to published results for IORT and APBI. IOERT is highly operator-dependent, and appropriate applicator sizing according to tumour size is critical. When used in a selected patient population, IOERT achieves a good balance between tumour control and late radiotherapy-mediated toxicity morbidity and mortality thanks to insignificant irradiation of organs at risk.

Biological and clinical review of IORT-induced wound fluid in breast cancer patients.

Intraoperative radiotherapy (IORT) has become a growing therapy for early-stage breast cancer (BC). Some studies claim that wound fluid (seroma), a common consequence of surgical excision in the tumor cavity, can reflect the effects of IORT on cancer inhibition. However, further research by our team and other researchers, such as analysis of seroma composition, affected cell lines, and primary tissues in two-dimensional (2D) and three-dimensional (3D) culture systems, clarified that seroma could not address the questions about IORT effectiveness in the surgical site. In this review, we mention the factors involved in tumor recurrence, direct or indirect effects of IORT on BC, and all the studies associated with BC seroma to attain more information about the impact of IORT-induced seroma to make a better decision to remove or remain after surgery and IORT. Finally, we suggest that seroma studies cannot decipher the mechanisms underlying the effectiveness of IORT in BC patients. The question of whether IORT-seroma has a beneficial effect can only be answered in a trial with a clinical endpoint, which is not even ongoing.

Assessment of out-of-field radiation doses for high dose per pulse intraoperative electron beam radiotherapy using TLD-100

PurposeThis research aims to assess the out-of-field surface doses for different combinations of electron energy, applicator size, and distance from the applicator wall of high dose-per-pulse IntraOperative electron Radiation Therapy (IOeRT) using thermoluminescent dosimeters (TLDs). Materials and methodsThe out-of-field doses for various combinations of IOeRT electron beam energy/applicator size were measured using ionometric dosimetry. The calibrated LiF:Mg,Ti dosimeters (TLD-100) were used to make the measurements. TLD results were benchmarked using an Advanced Markus chamber and a polymethyl methacrylate slab phantom. TLDs were read out using a HARSHAW (type 4000) manual TLD reader. ResultsThe TLDs received out-of-field absorbed doses ranging from 0.033 to 0.545 mGy/MU depending on the applicator size, electron energy, and distance from the applicator's outer wall. The mean discrepancies between TLDs and Advanced Markus ion chamber measured data were about 1.82% in the PMMA slab phantom at a depth of maximum dose for each electron energy. ConclusionThe skin surface dose can be significant during IOeRT. The maximum out-of-field doses have occurred at high electron beam energy and closer distances around the applicator wall. TLD can measure the skin's dose level according to its good agreement with the reference Advanced Markus dosimeter. The TLD-100 can be used as a reliable dosimeter for intraoperative radiation dosimetry.

A case report on a novel use of intraoperative Intrabeam™ radiation therapy for a recurrent malignant peripheral nerve sheath tumor with sciatic nerve involvement

BackgroundMalignant peripheral nerve sheath tumors (MPNST) are sarcomas that arise from peripheral nerves. They generally have a poor prognosis which is exacerbated by high local recurrence rates. This case report discusses the treatment of a patient with a MPNST with local recurrence. This case report is novel due to the use of intraoperative Intrabeam™ (Zeiss, Dublin, CA) radiation therapy use in the protection of neurovascular structures such as the sciatic nerve.Case presentation:The patient was a 65-year-old male who noticed a right posterior thigh mass slowly increasing in size over two months. A planned positive margin wide-resection excision was performed due to sciatic nerve abutment. The mass was determined to be a MPNST via postoperative pathology with positive margins along the sciatic nerve. The patient began adjuvant radiation therapy to the upper and lower thigh fields over a period of three months. Thirty-two months later, the patient was found to have a hypermetabolic mass with venous congestion and hyperemia at the prior surgical site which was confirmed by core needle biopsy to be local recurrence of the MPNST. Re-excision of the tumor was planned and performed followed by intraoperative Intrabeam™ radiation therapy. At two years of follow-up, the patient was doing well with minimal pain in his right buttock region with no new or recurrent neurological deficits. Radiologic imaging was negative for local recurrence of the MPNST.ConclusionWe believe this case report demonstrates a novel treatment strategy for sarcoma management. The unique use of intraoperative Intrabeam™ radiation therapy, which had not previously been used for this indication, may be efficacious in cases involving neurovascular structures. In this case, focal radiation from the intraoperative Intrabeam™ radiation device was used in a way to affect the recurrent tumor yet protect the sciatic nerve.

A prospective study of vertebroplasty with reverse designed unilateral targeted puncture for osteoporotic thoracolumbar compression fractures

To explore the feasibility and effectiveness of vertebroplasty with reverse designed unilateral targeted puncture in treatment of osteoporotic vertebral compression fracture (OVCF) by comparing with curved unilateral puncture. A total of 52 patients with OVCF met selection criteria and were admitted between January 2019 and June 2021 were selected as the research objects. According to the random number table method, they were divided into two groups ( n=26). In trial group, the reverse designed unilateral targeted puncture was used in the percutaneous vertebroplasty (PVP); while the control group used the curved unilateral puncture. There was no significant difference in gender, age, bone mineral density (T value), cause of injury, time from injury to operation, the level of responsible vertebral body, pedicle diameter of the planned puncture vertebral body, and preoperative visual analogue scale (VAS) score, anterior vertebral height, and Cobb angle between the two groups ( P>0.05). The operation time, bone cement injection volume and leakage, intraoperative radiation exposure times, and hospitalization costs in the two groups were recorded. VAS score was used to evaluate the relief degree of low back pain after operation. X-ray film was used to review the diffusion degree of bone cement in the responsible vertebral body, and Cobb angle and anterior vertebral height were measured. The operation was successfully completed in the two groups. Patients in the two groups were followed up 12-18 months, with an average of 13.6 months. The operation time, volume of injected bone cement, intraoperative radiation exposure times, and hospitalization costs in the trial group were significantly lower than those in the control group ( P<0.05). With the prolongation of time, the low back pain of the two groups gradually relieved, and the VAS score significantly decreased ( P<0.05). And there was no significant difference in VAS score between the two groups at each time point ( P>0.05). There were 2 cases (7.6%) of bone cement leakage in the trial group and 3 cases (11.5%) in the control group, and no significant difference was found in the incidence of bone cement leakage and the diffusion degree of bone cement between the two groups ( P>0.05). Imaging examination showed that compared with pre-operation, the anterior vertebral height of the two groups significantly increased and Cobb angle significantly decreased at 2 days and 1 year after operation ( P<0.05); while compared with 2 days before operation, the anterior vertebral height of the two groups significantly decreased and Cobb angle significantly increased at 1 year after operation ( P<0.05). There was no significant difference in the above indexes between the two groups at different time points after operation ( P>0.05). Compared with curved unilateral puncture, the use of reverse designed unilateral targeted puncture during PVP in the treatment of OVCF can not only achieve similar effectiveness, but also has the advantages of less radiation exposure, shorter operation time, and less hospitalization costs.

Practice-oriented solutions integrating intraoperative electron irradiation and personalized proton therapy for recurrent or unresectable cancers: Proof of concept and potential for dual FLASH effect.

Oligo-recurrent disease has a consolidated evidence of long-term surviving patients due to the use of intense local cancer therapy. The latter combines real-time surgical exploration/resection with high-energy electron beam single dose of irradiation. This results in a very precise radiation dose deposit, which is an essential element of contemporary multidisciplinary individualized oncology. Patient candidates to proton therapy were evaluated in Multidisciplinary Tumor Board to consider improved treatment options based on the institutional resources and expertise. Proton therapy was delivered by a synchrotron-based pencil beam scanning technology with energy levels from 70.2 to 228.7 MeV, whereas intraoperative electrons were generated in a miniaturized linear accelerator with dose rates ranging from 22 to 36 Gy/min (at Dmax) and energies from 6 to 12 MeV. In a period of 24 months, 327 patients were treated with proton therapy: 218 were adults, 97 had recurrent cancer, and 54 required re-irradiation. The specific radiation modalities selected in five cases included an integral strategy to optimize the local disease management by the combination of surgery, intraoperative electron boost, and external pencil beam proton therapy as components of the radiotherapy management. Recurrent cancer was present in four cases (cervix, sarcoma, melanoma, and rectum), and one patient had a primary unresectable locally advanced pancreatic adenocarcinoma. In re-irradiated patients (cervix and rectum), a tentative radical total dose was achieved by integrating beams of electrons (ranging from 10- to 20-Gy single dose) and protons (30 to 54-Gy Relative Biological Effectiveness (RBE), in 10-25 fractions). Individual case solution strategies combining intraoperative electron radiation therapy and proton therapy for patients with oligo-recurrent or unresectable localized cancer are feasible. The potential of this combination can be clinically explored with electron and proton FLASH beams.

SURG-02. INTRAOPERATIVE RADIOTHERAPY FOR BRAIN METASTASES: EVALUATION OF ELECTROCORTICOGRAPHY AND PERI-OPERATIVE SEIZURE RISK

Abstract BACKGROUND Intraoperative radiotherapy (IORT) has emerged as a viable tool for consolidation of surgery and radiation for brain metastases into a single episode of care, but its relative novelty compared to SRS or fractionated radiotherapy warrants evaluation of its safety. While post-operative seizure risk is typically minimal with the use of anti-epileptic drugs during the peri-operative phase, the risk of intra-operative epileptiform discharge remains unknown. METHODS Five consecutive cases of surgically resected brain metastases treated with IORT underwent electrocorticography via direct cortical electrode recordings adjacent to the resection cavity with paddle electrodes used for mapping of phase reversal. Continuous recordings were made before, during, and after radiation delivery and analyzed for evidence of radiation-associated changes. RESULTS No evidence of significant electrophysiological change was noted in any of the cases, nor was there any clinical evidence of seizure in the immediate peri-operative period. These data represent the first direct cortical recordings in human subjects during the delivery of radiation. CONCLUSIONS In this small cohort of IORT treated resected brain metastases, the delivery of intra-operative radiation does not appear to impact cortical activity or precipitate post-operative seizures. Further studies are needed to determine the long-term incidence of treatment associated changes if they exist.

CTNI-51. FEASIBILITY AND SAFETY OF NEUROSURGICAL RESECTION AND INTRA-OPERATIVE RADIATION THERAPY USING THE XOFT AXXENT ELECTRONIC BRACHYTHERAPY SYSTEM AND BEVACIZUMAB IN RECURRENT GLIOBLASTOMA

Abstract Glioblastoma (GBM) is the most common and aggressive primary brain tumor. External beam radiation therapy (EBRT) is widely recognized as an effective treatment for primary GBM. EBRT applied after GBM resection is associated with an increase in overall survival. Beyond upfront therapy with radiation and temozolomide chemotherapy, there is no standard therapy that has been proven effective. Re-irradiation with ERBT is minimally effective and with significant comorbidities. Our study uses IORT at the time of re-resection in patients who have recurrent, operable GBM after failure of who received primary EBRT and temozolamide in their first course of treatment. IORT allows the delivery of a large effective radiation dose applied directly to the tumor bed at the time of resection. This affords direct radiation to be delivered to the micro- and macroscopic tumor remnants in the vicinity of the resection cavity immediately following gross resection. In contrast, the more distant, surrounding brain tissue does not receive high radiation exposure. This Phase II study continues to accrue subjects with the primary endpoint of overall survival and several secondary endpoints that includes progression free survival, quality of life, and adverse events/safety. To date, five patients have been treated on this protocol. The technical feasibility and safety of administering intraoperative radiation with the Xoft System has been established in this cohort. Preliminary GLIOX Trial findings demonstrate the safety and feasibility of using the Xoft Axxent® Electronic Brachytherapy System to administer intracranial radiation during resection of recurrent glioblastomas. We will report new and expansive study results to include these early findings.