Intracranial Stereotactic Radiotherapy Research Articles

Comparison of patient setup accuracy for optical surface-guided andX-ray-guided imaging with respect to the impact on intracranial stereotactic radiotherapy.

The objective of this work is to estimate the patient positioning accuracy of asurface-guided radiation therapy (SGRT) system using an optical surface scanner compared to an X‑ray-based imaging system (IGRT) with respect to their impact on intracranial stereotactic radiotherapy (SRT) and intracranial stereotactic radiosurgery (SRS). Patient positioning data, both acquired with SGRT and IGRT systems at the same linacs, serve as abasis for determination of positioning accuracy. Atotal of 35patients with two different open face masks (578 datasets) were positioned using X‑ray stereoscopic imaging and the patient position inside the open face mask was recorded using SGRT. The measurement accuracy of the SGRT system (in a"standard" and an SRS mode with higher resolution) was evaluated using both IGRT and SGRT patient positioning datasets taking into account the measurement errors of the X‑ray system. Based on these clinically measured datasets, the positioning accuracy was estimated using Monte Carlo (MC) simulations. The relevant evaluation criterion, as standard of practice in cranial SRT, was the 95th percentile. The interfractional measurement displacement vector of the SGRT system, σSGRT, in high resolution mode was estimated at 2.5 mm (68th percentile) and 5 mm (95th percentile). If the standard resolution was used, σSGRT increased by about 20%. The standard deviation of the axis-related σSGRT of the SGRT system ranged between 1.5 and 1.8 mm interfractionally and 0.5 and 1.0 mm intrafractionally. The magnitude of σSGRT is mainly due to the principle of patient surface scanning and not due to technical limitations or vendor-specific issues in software or hardware. Based on the resulting σSGRT, MC simulations served as ameasure for the positioning accuracy for non-coplanar couch rotations. If an SGRT system is used as the only patient positioning device in non-coplanar fields, interfractional positioning errors of up to 6 mm and intrafractional errors of up to 5mm cannot be ruled out. In contrast, MC simulations resulted in apositioning error of 1.6 mm (95th percentile) using the IGRT system. The cause of positioning errors in the SGRT system is mainly achange in the facial surface relative to adefined point in the brain. In order to achieve the necessary geometric accuracy in cranial stereotactic radiotherapy, use of an X‑ray-based IGRT system, especially when treating with non-coplanar couch angles, is highly recommended.

External validation of three prognostic scores for brain metastasis velocity in patients treated with intracranial stereotactic radiotherapy

Background and introductionBrain metastasis velocity (BMV) has been proposed as a prognostic factor for overall survival (OS) in patients with brain metastases (BMs). In this study, we conducted an external validation and comparative assessment of the performance of all three BMV scores. Materials and methodsPatients treated with intracranial stereotactic radiotherapy (SRT) for BM at a single center between 2014 and 2018 were identified. Where possible, all three BMV scores were calculated. Log-rank tests and linear, logistic and Cox regression analysis were used for validation and predictor identification of OS. ResultsFor 333 of 384 brain metastasis patients, at least one BMV score could be calculated. In a sub-group of 187 patients, “classic” BMV was validated as categorical (p < 0.0001) and continuous variable (HR 1.02; 95% CI 1.02–1.03; p < 0.0001). In a sub-group of 284 patients, “initial” BMV was validated as categorical variable (high-risk vs. low-risk; p < 0.01), but not as continuous variable (HR 1.02; 95% CI 0.99–1.04; p = 0.224). “Volume-based” BMV could not be validated in a sub-group of 104 patients. On multivariable Cox regression analysis, iBMV (HR 1.85; 95% CI 1.01–3.38; p < 0.05) and cBMV (HR 2.32; 95% CI 1.15 4.68; p < 0.05) were predictors for OS for intermediate-risk patients after first SRT and first DBFs, respectively. cBMV proved to be the dominant predictor for OS for high-risk patients (HR 2.99; 95% CI 1.30–6.91; p < 0.05). ConclusionThis study externally validated cBMV and iBMV as prognostic scores for OS in patients treated with SRT for BMs whereas validation of vBMV was not achieved.

Bevacizumab reduces peritumoral brain edema in lung cancer brain metastases after radiotherapy.

The aim of this study was to investigate the efficacy of bevacizumab (Bev) in reducing peritumoral brain edema (PTBE) after stereotactic radiotherapy (SRT) for lung cancer brain metastases. A retrospective analysis was conducted on 44 patients with lung cancer brain metastases (70 lesions) who were admitted to our oncology and Gamma Knife center from January 2020 to May 2022. All patients received intracranial SRT and had PTBE. Based on treatment with Bev, patients were categorized as SRT + Bev and SRT groups. Follow-up head magnetic resonance imaging was performed to calculate PTBE and tumor volume changes. The edema index (EI) was used to assess the severity of PTBE. Additionally, the extent of tumor reduction and intracranial progression-free survival (PFS) were compared between the two groups. The SRT + Bev group showed a statistically significant difference in EI values before and after radiotherapy (p = 0.0115), with lower values observed after treatment, but there was no difference in the SRT group (p = 0.4008). There was a difference in the distribution of EI grades in the SRT + Bev group (p = 0.0186), with an increased proportion of patients at grades 1-2 after radiotherapy, while there was no difference in the SRT group (p > 0.9999). Both groups demonstrated a significant reduction in tumor volume after radiotherapy (p < 0.05), but there was no difference in tumor volume changes between the two groups (p = 0.4089). There was no difference in intracranial PFS between the two groups (p = 0.1541). Bevacizumab significantly reduces the severity of PTBE after radiotherapy for lung cancer. However, its impact on tumor volume reduction and intracranial PFS does not reach statistical significance.

Single-Fraction vs. Fractionated Radiosurgery and the Development of Post-Treatment Hemorrhage for Intact Melanoma Brain Metastases

<h3>Purpose/Objective(s)</h3> To assess whether intracranial stereotactic radiotherapy fractionation is associated with increased risk of post-treatment lesional hemorrhage in patients with intact melanoma brain metastases (MBM). <h3>Materials/Methods</h3> A single institution retrospective review was performed of patients with previously unresected MBM treated with robotic SRS/fSRT between 2013 to 2021. The presence of lesional hemorrhage was determined by multi-disciplinary neuroradiology review of magnetic resonance imaging (MRI). Dosimetric variables were reported as biologically effective doses using an estimated α/β ratio of 2.5 (BED_2.5) for melanoma to permit comparison across varying fractionation schedules. The effect of fractionation and additional prognostic factors on the rate of post-treatment development of hemorrhage was statistically analyzed using logistic regression with random effects to account for interactions between lesions of the same patient. A Cox model was used for local control (LC) with a frailty term to account for dependence between lesions. <h3>Results</h3> The cohort included 48 patients with 226 intact MBM treated with SRS/fSRT. Evidence of hemorrhage prior to treatment was demonstrated in 69 of 226 metastases (30.5%). For lesions without signs of prior hemorrhage, 65 of 157 (41.4%) demonstrated evidence of hemorrhage after radiosurgical treatment. 63 of 133 lesions (47.4%) receiving single-fraction SRS demonstrated evidence of post-treatment hemorrhage versus 2 of 24 lesions (8.3%) treated with fSRT (<i>p=0.01</i>). Treatment factors including lesion size, prescription isodose line, as well as receipt of corticosteroids, targeted, or immune therapy were not predictive of hemorrhage occurrence. A larger maximum BED_2.5 was observed in lesions developing hemorrhage compared to no hemorrhage (mean 238.3 Gy vs. 211.4 Gy; <i>p=0.022</i>). LC at twelve-months was 65.7% (95% CI 37.2-87.3%) and 77.5% (95% CI 58.5-91.2%) for lesions demonstrating pre-treatment and post-treatment hemorrhage, respectively, with no local failure events observed in non-hemorrhagic lesions (<i>p=<0.001</i>). <h3>Conclusion</h3> Intact MBM without prior evidence of hemorrhage receiving single-fraction SRS were associated with an increased incidence of post-treatment hemorrhage when compared to those treated with fractionated stereotactic radiotherapy. The presence of lesion hemorrhage, either pre- or post-treatment, was associated with inferior local control. Post-treatment hemorrhage was correlated with a larger maximum BED_2.5. Further investigations of the clinical impact of lesional hemorrhage, factors influencing lesion control, as well as optimal dose and fractionation schedules for treatment of MBM in the era of immunotherapy are warranted.

Intracranial stereotactic radiotherapy in off-isocenter target with SyncTraX FX4

PurposeWe investigated the localization accuracy of the off-isocenter targets using SyncTraX FX4, a new image registration device. MethodsIn a phantom study, we used a MultiMet-WL Cube with metal targets at different distances from the isocenter. Image registrations were performed with SyncTraX and cone-beam computed tomography (CBCT). Nineteen fields with different gantry, collimator, and couch angles were delivered to each target. Localization errors of the off-isocenter targets were then evaluated. In a clinical study, localization accuracy was evaluated for 32 patients. First, image registration was performed using SyncTraX, and the accuracy of patient positioning was evaluated using CBCT. Next, positioning corrections were performed for intracranial setup errors exceeding the threshold (0.5 mm/0.5°) in each field. Finally, total setup uncertainty was evaluated using CBCT. Differences in dosimetric errors from planned doses between no patient positioning corrections during treatment and positioning corrections with SyncTraX were also evaluated. ResultsIn the phantom study, the positioning accuracy on targets up to 7 cm from the isocenter was within 1 mm. In the clinical practice, the localization accuracies of SyncTraX were 0.35 ± 0.39 mm, 0.30 ± 0.24 mm, and 0.03 ± 0.27 mm in the lateral, vertical, and longitudinal directions, respectively. Post-treatment setup errors were reduced by correcting intrafractional setup errors with SyncTraX during treatment. Positioning corrections with SyncTraX reduced the maximum dosimetric error from 1.6% to 1.0%. ConclusionsSyncTraX provides satisfactory localization accuracy for the off-isocenter targets within 7 cm. SyncTraX reduce dosimetric errors caused by intrafractional setup errors during treatment.

Current status of intra-cranial stereotactic radiotherapy and stereotactic radiosurgery in Australia and New Zealand: key considerations from a workshop and surveys

Recently, there has been increased interest worldwide in the use of conventional linear accelerator (linac)-based systems for delivery of stereotactic radiosurgery/radiotherapy (SRS/SRT) contrasting with historical delivery in specialised clinics with dedicated equipment. In order to gain an understanding and define the current status of SRS/SRT delivery in Australia and New Zealand (ANZ) we conducted surveys and provided a single-day workshop. Prior to the workshop ANZ medical physicists were invited to complete two surveys: a departmental survey regarding SRS/SRT practises and equipment; and an individual survey regarding opinions on current and future SRS/SRT practices. At the workshop conclusion, attendees completed a second opinion-based survey. Workshop discussion and survey data were utilised to identify areas of consensus, and areas where a community consensus was unclear. The workshop was held on the 8th Sept 2020 virtually due to pandemic-related travel restrictions and was attended by 238 radiation oncology medical physicists from 39 departments. The departmental survey received 32 responses; a further 89 and 142 responses were received to the pre-workshop and post-workshop surveys respectively. Workshop discussion indicated a consensus that for a department to offer an SRS/SRT service, a minimum case load should be considered depending on availability of training, peer-review, resources and equipment. It was suggested this service may be limited to brain metastases only, with less common indications reserved for departments with comprehensive SRS/SRT programs. Whilst most centres showed consensus with treatment delivery techniques and image guidance, opinions varied on the minimum target diameter and treatment margin that should be applied.

CBCT Verification of SRT for Patients With Brain Metastases.

BackgroundThe aim of our work is to demonstrate the role of image guidance and volumetric imaging in stereotactic radiotherapy (SRT) of brain metastases.MethodsBetween 2018 and 2020, 106 patients underwent intracranial stereotactic radiotherapy. 10 patients with metastatic brain tumors treated with SRT were randomly selected and included in our study model. Patients were scanned pre- and post-treatment with cone beam CT. Total of 100 verifications of 50 stereotaxic treatments were performed and analyzed.ResultsPopulation mean X, Y, Z values were -0.13 cm, -0.04 cm, -0.03 cm, respectively, rotation values 0.81°, 0.51°, 0.46°, respectively. Systematic error components for translational displacements pre corrections were as follows: 0.14 cm for X, 0.13 cm for Y and 0.1 cm for Z. Systematic error components of the post-treatment HR 3D CBCTs were as follows: 0.01 cm for X, 0.06 cm for Y and 0.04 cm for Z.ConclusionsPopulation mean values close to 0 confirmed that there is no systematic variation in our system and the accuracy of our equipment and tools is reliable. HR 3D CBCT scans performed pre SRTs further refine patient and target volume setting, support medical decision making and eliminate the possibility of gross error.

Cost Comparison From a Patient Perspective for Intracranial Stereotactic Radiation Therapy

PurposeHistorically, opaque health care pricing in the US has prevented patients from identifying opportunities to lower costs. Attempting to promote price transparency, the US government recently mandated that hospitals publish prices for all services in a document called a chargemaster. Patients often travel to tertiary centers for intracranial stereotactic radiation therapy (SRT), but cost comparison is complicated by multiple delivery systems and fractionation schemes. We hypothesized that prices published in chargemasters vary widely between SRT techniques and institutions. Methods and MaterialsWe obtained chargemasters published online by National Cancer Institute–designated clinical centers. Technical charges for Gamma Knife single-fraction stereotactic radiosurgery (GK), single-fraction linear-accelerator stereotactic radiation surgery (SRS), and 3-fraction fractionated stereotactic radiation therapy (FSRT) were obtained from chargemasters by billing code and keyword searches. Prices were adjusted by the Medicare geographic cost price index (GPCI). Pairwise comparisons were conducted to compare prices between modalities and geographic regions. Relationships with cost index were examined using Spearman correlations, as was the price interrelationship between modalities across institutions. ResultsOf 62 chargemasters obtained, 58 listed SRT prices. Median prices were $49,529 for GK, $31,834 for FSRT, and $22,915 for SRS. Prices varied widely, with large ranges corresponding to 2 to 9 times the magnitude of median prices (GK, $111,298; FSRT, $312,480; and SRS, $104,396). Adjusting for GPCI, GK (P = .0003) and FSRT (P = .001) were more expensive than SRS, and no difference in price was noted between regions. The FSRT price was positively correlated with GPCI (P = .033), but prices for the other techniques were not. Modality prices were all positively correlated (all P < .001), meaning that institutions with prices greater than the median price for SRS were similarly expensive for GK and FSRT. ConclusionsPublished prices for SRT vary by delivery system, fractionation, and institution without a clear explanation. Obtaining personalized price estimates may offer cost savings for patients. Policy changes encouraging reliable access to insurer-negotiated cost estimates for SRT are needed.

Cost Comparison From a Patient Perspective for Gamma Knife and Linear Accelerator-Based Intracranial Stereotactic Radiation Therapy

Financial toxicity is a highly prevalent and damaging consequence of oncologic therapy that is partially driven by inability to make copayments. The US Centers for Medicare and Medicaid Services recently mandated that all hospitals publish a "shoppable" list of negotiated prices for ≥ 300 common services as well as a "chargemaster" documenting non-negotiated list charges for every provided service. Patients often travel to tertiary centers for intracranial stereotactic radiotherapy (SRT), but cost comparison is complicated by multiple delivery systems and fractionation schemes. SRT is not included in shoppable price listing, and it is unknown whether list prices have utility in this complex setting. We hypothesized that list prices for intracranial SRT vary by delivery system and fractionation schemes and by institution.In August 2020, we obtained online available chargemasters for the 63 US clinical National Cancer Institute (NCI)-designated centers. Listed technical charges for Gamma Knife (GK), single fraction linear-accelerator stereotactic radiosurgery (SRS), and 3-fraction fractionated stereotactic radiation therapy (FSRT) were obtained by searching for Current Procedural Terminology (CPT) billing codes first and then keywords. Institutional cost data was adjusted by the Medicare geographic cost price index (GPCI) to control for cost-of-living associated reimbursement differences. Pairwise comparisons were conducted to compare prices across modalities and geographic regions. Price association between modalities and relationships with cost index were examined using Spearman correlations.62 chargemasters were obtainable, and 58 listed intracranial SRT prices. For each modality, prices varied widely, and after adjusting for GPCI, GK (P = 0.0003) and FSRT (P = 0.001) were more expensive than SRS (Table 1). No adjusted difference in price was noted between regions. FSRT price was positively correlated with GPCI (P = 0.033) but other modalities were not. All modality prices were positively correlated (all P < 0.001).Despite overlapping indications, GK and FSRT list prices outpace SRS. Overall, institutional prices varied significantly, but differences in cost of living do not explain variability. A high institutional price for one modality corresponded to higher prices for the others. Although list prices are ill suited for absolute price estimates, motivated patients may use chargemasters to attempt relative cost comparisons. However, the impact of ancillary fees and negotiations by insurers on relative price differences is difficult to assess. Thus, policy changes promoting improved patient access to streamlined cost data are necessary to address therapy-related economic distress in this population.

Efficacy and Safety of a Second Course of Stereotactic Radiation Therapy for Locally Recurrent Brain Metastases: A Systematic Review.

Simple SummaryApproximately 30% of patients diagnosed with cancer will ultimately develop brain metastases. Many improvements have been made in systemic and local cancer treatments, which have increased overall survival but also, as a consequence, the number of patients who present with local recurrence following intracranial stereotactic radiotherapy. The management of these recurrences remains controversial. The aim of our review is to evaluate the efficacy and tolerance of a second course of stereotactic radiotherapy. Recent advances in cancer treatments have increased overall survival and consequently, local failures (LFs) after stereotactic radiotherapy/radiosurgery (SRS/SRT) have become more frequent. LF following SRS or SRT may be treated with a second course of SRS (SRS2) or SRT (SRT2). However, there is no consensus on whenever to consider reirradiation. A literature search was conducted according to PRISMA guidelines. Analysis included 13 studies: 329 patients (388 metastases) with a SRS2 and 135 patients (161 metastases) with a SRT2. The 1-year local control rate ranged from 46.5% to 88.3%. Factors leading to poorer LC were histology (melanoma) and lack of prior whole-brain radiation therapy, large tumor size and lower dose at SRS2/SRT2, poorer response at first SRS/SRT, poorer performance status, and no controlled extracranial disease. The rate of radionecrosis (RN) ranged from 2% to 36%. Patients who had a large tumor volume, higher dose and higher value of prescription isodose line at SRS2/SRT2, and large overlap between brain volume irradiated at SRS1/SRT1 and SRS2/SRT2 at doses of 18 and 12 Gy had a higher risk of developing RN. Prospective studies involving a larger number of patients are still needed to determine the best management of patients with local recurrence of brain metastases

PO-1842: Set-up accuracy of BrainLab immobilization mask for intracranial stereotactic radiotherapy

PO-1842: Set-up accuracy of BrainLab immobilization mask for intracranial stereotactic radiotherapy

Surface guided imaging during stereotactic radiosurgery with automated delivery.

PurposeTo report on the use of surface guided imaging during frameless intracranial stereotactic radiotherapy with automated delivery via HyperArcTM (Varian Medical Systems, Palo Alto, CA).MethodsAll patients received intracranial radiotherapy with HyperArcTM and were monitored for intrafraction motion by the AlignRT® (VisionRT, London, UK) surface imaging (SI) system. Immobilization was with the EncompassTM (Qfix, Avondale, PA) aquaplast mask device. AlignRT® log files were correlated with trajectory log files to correlate treatment parameters with SI reported offsets. SI reported offsets were correlated with gantry angle and analyzed for performance issues at non‐zero couch angles and during camera‐pod blockage during gantry motion. Demographics in the treatment management system were used to identify race and determine if differences in SI reported offsets are due to skin tone settings.ResultsA total of 981 fractions were monitored over 14 months and 819 were analyzed. The median AlignRT® reported motion from beginning to the end of treatment was 0.24 mm. The median offset before beam on at non‐zero couch angles was 0.55 mm. During gantry motion when camera pods are blocked, the median magnitude was below 1 mm. Median magnitude of offsets at non‐zero couch angles was not found to be significantly different for patients stratified by race.ConclusionsSurface image guidance is a viable alternative to scheduled mid‐treatment imaging for monitoring intrafraction motion during stereotactic radiosurgery with automated delivery.

Intracranial Stereotactic Radiation Therapy With a Jawless Ring Gantry Linear Accelerator Equipped With New Dual Layer Multileaf Collimator

PurposeTo test the feasibility of a simplified, robust, workflow for intracranial stereotactic radiation therapy (SRT) using a ring gantry linear accelerator (RGLA) equipped with a dual-layer stacked, staggered, and interdigitating multileaf collimator. Materials and MethodsTwenty recent clinical SRT cases treated using a radiosurgery c-arm linear accelerator were anonymized. From these data sets, a new planning workflow was developed and used to replan these cases, which then were compared to their clinical counterparts. Population-based dose-volume histograms were analyzed for target coverage and sparing of healthy brain. All plans underwent plan review and quality assurance and were delivered on an end-to-end verification phantom using image guidance to simulate treatment. ResultsThe RGLA plans were able to meet departmental standards for target coverage and organ-at-risk sparing and showed plan quality similar to the clinical plans. RGLA plans showed increases in the 50% isodose in the axial plane but decreases in the sagittal and coronal planes. There were no statistically significant differences in the homogeneity index or number of monitor units between the 2 systems. There were statistically significant increases in conformity and gradient indices, with median values of 1.09 versus 1.11 and 2.82 versus 3.13, respectively, for the c-arm versus RGLA plans. These differences were not believed to be clinically significant because they met clinical goals. The population-based dose-volume histograms showed target coverage and organ-at-risk sparing similar to that of the clinical plans. All plans were able to meet the departmental quality assurance requirements and were delivered under image guidance on an end-to-end phantom with measurements agreeing within 3% of the expected value. RGLA plans showed a median reduction in delivery time of ≈50%. ConclusionsThis work describes a simplified and efficient workflow that could reduce treatment times and expand access to SRT to centers using an RGLA.

Gestion du projet de mise en place de la radiothérapie stéréotaxique intracrânienne au Centre finistérien de radiothérapie et d’oncologie

The Centre Finistérien de radiothérapie et d’oncologie, based in Brest (France), wanted to expand its activity by offering intracranial stereotactic radiation therapy to improve patient care. The desire of the Centre was to invest in this innovative and efficient technique and thus modernize its technical platform and its offer of care. The introduction of intracranial stereotactic radiation therapy requires vigilance for the technical and human organization. Therefore, the Centre prepared the implementation of this technique upstream by a structured and timed preliminary project management.

Long-Term Follow-up of Patients Treated at a Single Institution Using a Passively Scattered Proton Beam; Observations Around the Occurrence of Second Malignancies

To investigate the occurrence of second malignancies resulting from the secondary radiation from a passively scattered proton beam. A cohort of patients with long-term follow-up was defined. All were treated at the same institution with the same proton delivery system, consisting of a 200MeV fixed, horizontal, passively scattered beam combined with a robotic chair. This setup allows for stereotactic positioning and permits fractionated treatments. The majority of patients underwent cranial or intracranial stereotactic radiation therapy. Patients with previous photon therapy or a follow-up of 24months or less were excluded. For out-of-field secondary malignancies (SMs), the observed incidence in the study population was compared to the risk of developing a malignancy in the general population, taking patient sex into account. From September 1993 to May 2016, a total of 524 patients received proton beam therapy, and 322 patients could be evaluated for this study (164 female and 158 male). Age ranged from 2 to 85years, with a median of 40years. Follow-up ranged from 25 to 276months, with a median of 150months (12.5years). During the study observation period, 7 patients had out-of-field new malignant disease. Three female patients developed a malignancy, compared with an expected incidence of 4.09 (standardized incidence ratio, 0.73 [95% confidence interval, 0.24-2.27]); 4 male patients developed a malignancy, versus an expected incidence of 3.99 (standardized incidence ratio, 1.00 [95% confidence interval, 0.38-2.67]). New intracranial disease developed in 9 patients: 8 meningiomas and 1 carcinoma. For out-of-field SMs, no increased risk of developing a variety of malignancies was observed. For in-field SMs, only 1 malignant histology was noted 15years after the original proton therapy. No SM was observed in children and young adults.

Clinical commissioning of a new patient positioning system, SyncTraX FX4, for intracranial stereotactic radiotherapy.

Background & AimsA new real‐time tracking radiotherapy (RTRT) system, the SyncTraX FX4 (Shimadzu, Kyoto, Japan), consisting of four X‐ray tubes and four ceiling‐mounted flat panel detectors (FPDs) combined with a linear accelerator, was installed at Uonuma Kikan Hospital (Niigata, Japan) for the first time worldwide. In addition to RTRT, the SyncTraX FX4 system enables bony structure‐based patient verification. Here we provide the first report of this system's clinical commissioning for intracranial stereotactic radiotherapy (SRT).Materials & MethodsA total of five tests were performed for the commissioning: evaluations of (1) the system's image quality; (2) the imaging and treatment coordinate coincidence; and (3) the localization accuracy of cone‐beam computed tomography (CBCT) and SyncTraX FX4; (4) the measurement of air kerma; (5) an end‐to‐end test.Results & DiscussionThe tests revealed the following. (1) All image quality evaluation items satisfied each acceptable criterion in all FPDs. (2) The maximum offsets among the centers were ≤0.40 mm in all combinations of the FPD and X‐ray tubes (preset). (3) The isocenter localization discrepancies between CBCT and preset #3 in the SyncTraX FX4 system were 0.29 ± 0.084 mm for anterior‐posterior, −0.19 ± 0.13 mm for superior‐inferior, 0.076 ± 0.11 mm for left‐right, −0.11 ± 0.066° for rotation, −0.14 ± 0.064° for pitch, and 0.072±0.058° for roll direction. the Pearson's product‐moment correlation coefficient between the two systems was >0.98 in all directions. (4) The mean air kerma value for preset #3 was 0.11 ± 0.0002 mGy in predefined settings (80 kV, 200 mA, 50 msec). (5) For 16 combinations of gantry and couch angles, median offset value in all presets was 0.31 mm (range 0.14–0.57 mm).ConclusionOur results demonstrate a competent performance of the SyncTraX FX4 system in terms of the localization accuracy for intracranial SRT.

298P - Outcomes of intracranial stereotactic radiotherapy (SRT) in metastatic breast cancer (BC)

298P - Outcomes of intracranial stereotactic radiotherapy (SRT) in metastatic breast cancer (BC)

Clinical Positioning Accuracy for Multisession Stereotactic Radiotherapy With the Gamma Knife Perfexion.

Multisession stereotactic radiation therapy is increasingly being seen as a preferred option for intracranial diseases in close proximity to critical structures and for larger target volumes. The objective of this study is to investigate the reproducibility of the Extend system from Elekta. A retrospective review was conducted for all patients treated with multisession Gamma Knife between July 2010 and June 2015, including both malignant and benign lesions. Eighty-four patients were treated in this 5-year span. The average residual daily setup uncertainty was 0.48 (0.19) mm. We compare measurements of setup uncertainty from the Extend system to measurements performed with a linac-based approach previously used in our center. The Extend system has significantly reduced setup uncertainty for fractionated intracranial treatments at our institution. Positive results were observed in a small population of edentulous patients. The Extend system compares favorably with other approaches to delivering intracranial stereotactic radiotherapy and is a robust, simple-to-use, and precise method for treating multisession intracranial lesions.

Concurrent irradiation with the anti-programmed cell death ligand-1 immune checkpoint blocker durvalumab: Single centre subset analysis from a phase 1/2 trial

PurposeTo assess preliminary safety and efficacy results of the anti-programmed cell death ligand-1 (anti-PD-L1) durvalumab in combination with radiotherapy (RT) in an expansion cohort of patients included in a phase 1/2 trial at our institution. Patients and methodsData from patients who received concurrent palliative RT with durvalumab (10 mg/kg every 2 weeks via intravenous infusion) were analysed in terms of safety (CTCAE v4.0) and efficacy (RECIST v1.1 and tumour growth rate [TGR]). ResultsBetween 02/2014 and 04/2016, 10 patients received palliative local irradiation of 15 isolated lesions. Most patients (90%) had received one or more prior lines of systemic therapy for advanced disease. The median duration of exposure to durvalumab was 5.2 months with a median delivery of 11 cycles (range, 4–38 cycles). RT (conformal 3D RT, 79% and intracranial stereotactic RT, 21%) was delivered at a median biologically-effective dose of 28 Gy (range, 6–92), in a median number of five fractions (range, 1–10) and over a median duration of 6 d (range, 1–14). Five patients (50%) reported an irradiation-related adverse event (AE) grade (G) 1 or 2 and one patient had two G2 AEs. The most frequently reported AE (3/6) was G2 mucositis. There was no G3 or more RT-related AEs. All AEs were transient, lasted less than one week, and were manageable by standard guidelines. There was no unexpected AE. On 10/15 in-field (IF) evaluable lesions, the objective response (OR) rate was 60% (complete response, 2/10 and partial response, 4/10) and 4/10 stable disease (SD). All evaluated IF lesions had a TGR decrease resulting in a significant decrease in the TGR between the two periods (before versus after RT; p < 0.01). Outfields disease evaluation retrieved 10/14 SD and 4/14 progressive disease (PD). There was no out-field OR, no abscopal effect and no out-field difference between the two periods according to TGR (p = 0.09). ConclusionIn this small data set of patients, concurrent palliative RT with the anti-PD-L1 durvalumab was well tolerated.ClinicalTrials.gov number: NCT01693562; EudraCT number: 2012-002206-52.

Treatment accuracy without rotational setup corrections in intracranial SRT.

The aim of this study was to evaluate the impact of actual rotational setup errors on dose distributions in intracranial stereotactic radiotherapy (SRT) with different alternatives for treatment position selection. A total of 38 SRT fractions from 18 patients were retrospectively evaluated with rotational setup errors obtained from actual treatments. The planning computed tomography (CT) images were rotated according to online cone‐beam CT (CBCT) images and the dose distribution was recalculated to the rotated CT images using three different patient positionings derived from: 1) an automatic 6D match neglecting rotation correction (Auto6D); 2) an automatic 3D match (Auto3D); and 3) a manual 3D match from actual treatment (Treat3D). The mean conformity index (CI) was 0.92 for the original plans and 0.91 for the Auto6D plans. The mean CI decreased significantly (p<0.01) to 0.78 and 0.80 for the Auto3D and the Treat3D plans, respectively. The mean minimum dose of the planning target volume (PTVmin) was 91.9% of the prescribed dose for the original plans and 92.1% for the Auto6D plans, while for the Auto3D and the Treat3D plans PTVmin decreased significantly (p<0.01) to 78.9% and 80.2%, respectively. No significant differences were seen between the Auto6D and the original treatment plans in terms of the dose parameters. However, the Auto3D and the Treat3D plans were statistically significantly inferior (p<0.01) to the Auto6D and the original plans. In addition, a significant negative correlation (p<0.01,|r|>0.38) was found in the Auto3D and the Treat3D cases between the rotation error and CI, PTVmin or minimum dose of gross tumour volume. In SRT, a treatment plan of comparable quality to 6D rotation correction can be achieved by using 6D registration without a rotational correction in the selection of patient positioning. This was demonstrated for typical rotation errors seen in clinical practice.PACS number(s): 87.55, 87.57