Stereotactic Conformal Radiotherapy Research Articles

Stereotactic Ablative Radiotherapy for Early-Stage Glottic Larynx Carcinoma: Results From the Phase II LT-SABR Study

<h3>Purpose/Objective(s)</h3> Traditional radiotherapy for early-stage larynx cancer irradiates the whole larynx over 5.5-6 weeks. Phase I data suggest that stereotactic ablative radiotherapy (SAbR) is a viable strategy in this population to reduce the irradiated volume and compress the treatment time. This phase II study evaluated the efficacy of gLoTtic larynx SAbR (LT-SABR), utilizing a 5 or 16 fraction regimen depending on treatment volume and smoking status. <h3>Materials/Methods</h3> Eligibility required stage 0-II biopsy-proven carcinoma of the true glottic larynx, including squamous cell variants. The arytenoid cartilage could not be involved beyond the vocal process, and patients smoking more than one pack-per-day were excluded. The planning target volume (PTV) consisted of the gross tumor volume, including respiratory motion assessed on a 4D-CT, with a 3 mm AP/LR margin and 5 mm SI margin. Patients without active smoking and PTV volume < 10 cc receive 42.5 Gy in 5 fractions, two fractions per week; all other patients received 58.08 Gy in 16 daily fractions. The routine beam arrangement included 2 coplanar VMAT arcs and 2 non-coplanar arcs. Patients were treated with swallow-gating using surface imaging. The study required 25 patients to show that the local control probability is non-inferior to 75% at 2 years. <h3>Results</h3> A total of 25 patients were accrued to this study, with 21 and 4 treated with 5 and 16 factions, respectively. The stage distribution was CIS (n=1), T1a (n=16), T1b (n=5), and T2 (n=3). The median age was 72 years, with a prior smoking history in 16 and active smoking in one. Dosimetry metrics (mean values) are summarized in the Table. At a median follow-up of 21.1 months (IQR 14-31.8) in surviving patients, there have been two in-field recurrences (one in each dose cohort). One was salvaged with partial laryngectomy and the other died from local and regional disease. The cumulative risks of local failure were 4.2% and 9.3% at 1 and 2 years, respectively. There have been no acute or late grade 3+ toxicities. The baseline, 6 and 12 month total Voice Handicap Index (VHI) scores were: 53.0 (n=25), 9.8 (n=18), and 18.4 (n=15). The improvements in VHI between 6/12 months and baseline were both statistically significant (p<0.001). <h3>Conclusion</h3> Highly conformal stereotactic radiotherapy is safe and efficacious for early-stage glottic larynx cancer, with encouraging patient-reported outcomes. Additional follow-up and ultimately comparative studies are necessary to validate this paradigm.

Pyrotinib plus capecitabine for HER2-positive metastatic breast cancer patients with brain metastases (PERMEATE): A multicenter, single-arm phase II study.

1037 Background: HER2-positive metastatic breast cancer (BC) has a high risk of brain metastases (BM), leading to poor survival. Small molecule tyrosine kinase inhibitor (TKI) with enhanced penetrability to the blood brain barrier combined with capecitabine have demonstrated promising clinical outcomes in HER2-positive metastatic BC patients with untreated (such as lapatinib) or previously treated (such as neratinib) BM. The randomized phase III PHOEBE trial has proved better efficacy of pyrotinib, an irreversible pan-HER receptor TKI, versus lapatinib when in combination with capecitabine in HER2-positive local relapsed or metastatic BC. This study was conducted to investigate the efficacy and safety of pyrotinib plus capecitabine in HER2-positive metastatic BC patients with BM. Methods: In this multicenter phase II trial (NCT03691051), eligible patients received pyrotinib 400 mg orally once daily without breaks and capecitabine 1000 mg/m2 orally twice daily for 14 days followed by 7 days off. Treatment was continued until disease progression or intolerable toxicity. Prior HER2 TKIs were not allowed. Cohort A included patients with radiotherapy-naive BM, and cohort B included those with progressive BM after whole brain radiotherapy or stereotactic conformal radiotherapy. The primary endpoint was confirmed central nervous system (CNS) objective response rate (ORR), as assessed according to the Response Evaluation Criteria In Solid Tumors version 1.1. Results: Between January 2018 and July 2020, a total of 78 female patients were included (Table). For cohort A (n = 59), the CNS ORR was 74.6% (95%CI: 61.6%-85.0%). For cohort B (n = 19), the CNS ORR was 42.1% (95%CI: 20.3%-66.5%). By the cutoff date on 25 January 2021, the median progression-free survival was 12.1 months (95%CI: 9.0-14.7) in cohort A and 5.6 months (95%CI: 3.4-10.7) in cohort B. The most common grade ≥3 adverse events were diarrhea (23.1% [18/78]), neutrophil count decreased (12.8% [10/78]), white blood cell count decreased (12.8% [10/78]), anemia (9.0% [7/78]), hand-foot syndrome (7.7% [6/78]), hypertriglyceridemia (6.4% [5/78]), and hypokalemia (5.1% [4/78]). Conclusions: Pyrotinib plus capecitabine resulted as an effective and safe treatment for HER2-positive BC patients with radiotherapy-naive BM, but the efficacy was modest in those with radiotherapy-treated BM. Clinical trial information: NCT03691051 .[Table: see text]

A randomized trial of stereotactic versus conventional radiotherapy in young patients with low-grade brain tumors: occupational therapy-based neurocognitive data.

BackgroundRadiotherapy for brain tumors in young patients is not only associated with improved survival but also long-term neurocognitive sequelae. We aimed to compare group differences in the executive neurocognitive outcomes in young patients with low-grade brain tumors treated with stereotactic conformal radiotherapy (SCRT) and conventional RT (ConvRT) techniques.MethodsThis a phase 3 randomized trial that enrolled 200 young patients with benign brain tumors and low-grade gliomas. Patients were randomly allocated (1:1) to either SCRT or ConvRT arms and treated to a dose of 54 Gy in 30 fractions over 6 weeks. Lowenstein Occupational Therapy Cognitive Assessment battery was performed at preradiotherapy baseline, 6 months, and annually thereafter until 5 years. Executive functions measures included orientation, visual perception, spatial perception, motor praxis, visuomotor organization, thinking operations, and attention and concentration. The trajectory of these parameters was compared between the treatment arms over 5 years.ResultsTwo hundred patients were enrolled in the study (SCRT: 104 and ConvRT: 96). The median age was 13 years (interquartile range: 9–17); mean total neurocognitive scores over 5 years were significantly superior in SCRT arm as compared to ConvRT (difference in slope: 2.27, P = .024). Outcomes improved in the SCRT arm vis-à-vis ConvRT for the subdomain of visuomotor organization (difference in slope: 0.66, P < .001). Visuomotor organization scores significantly improved in majority of the substratification groups. Spatial perception improved in craniopharyngioma patients with SCRT technique as opposed to ConvRT.ConclusionsSCRT achieved superior outcomes compared to ConvRT in certain executive neurocognitive functional domains. We provide high level of evidence in favor of SCRT. Trial Registration. ClinicalTrials.gov Identifier: NCT00517959.

Long-term neurocognitive and other side effects of radiotherapy, with or without chemotherapy, for glioma.

Long-term neurocognitive and other side effects of radiotherapy, with or without chemotherapy, for glioma.

Calculation of Electron-Beam Dynamics in a C-Band Accelerator for a Radiotherapy Complex

The dynamics of the electron beam in a C-band linear accelerator, a bremsstrahlung source with a boundary energy switched between 2.5 MeV and 6 MeV, which is intended for stereotactic and three-dimensional conformal radiotherapy in static and rotational modes, was calculated.

A Retrospective Review of Re-irradiating Patients' Recurrent High-grade Gliomas

AimsAfter radical treatment, most high-grade gliomas (HGG) recur locally. Upon recurrence, no standard treatment exists. Options include re-resection, salvage systemic therapy and re-irradiation. This retrospective study evaluated patients who underwent re-irradiation for recurrent HGGs and assessed prognostic factors and their influence on management. Materials and methodsEighty-two patients who underwent re-irradiation for HGG from 2009 to 2014 were retrospectively identified. Re-irradiation consisted of either standard three-dimensional conformal, intensity-modulated radiotherapy or highly conformal stereotactic radiotherapy using mostly volumetric modulated arc therapy. Patient survival from re-irradiation was the primary end point. Survival was estimated via the Kaplan–Meier method with differences assessed using the Log-rank test; hazard ratios were estimated using Cox regression analysis. ResultsThe median overall survival from re-irradiation was 9.5 months. Re-irradiation, to a median dose of 35 Gy in 10 fractions, was well tolerated: 4% developed grade 3 toxicity, no patients experienced grade ≥4 or radionecrosis. In the multivariate analysis, factors significantly associated with increased survival included: longer duration from initial radiotherapy, better performance status at re-irradiation of 0–1 versus ≥2, unifocal versus multifocal recurrence and higher total re-irradiation dose (≥35 Gy versus <35 Gy). Re-resection, salvage systemic therapy and age were unrelated to survival. ConclusionPatients with recurrent HGG tolerated re-irradiation well with minimal toxicity. Those patients in good prognostic groups, including good performance status can achieve durable control, suggesting managing patients with regular magnetic resonance imaging surveillance post-radical treatment, identifying early radiological progression and instituting salvage therapy when performance status is best.

A feasibility study of independent verification of dose calculation for Vero4DRT using a Clarkson-based algorithm

Dose verification for a gimbal-mounted image-guided radiotherapy system, Vero4DRT (Mitsubishi Heavy Industries Ltd., Tokyo, Japan) is usually carried out by pretreatment measurement. Independent verification calculations using Monte Carlo methods for Vero4DRT have been published. As the Clarkson method is faster and easier to use than measurement and Monte Carlo methods, we evaluated the accuracy of an independent calculation verification program and its feasibility as a secondary check for Vero4DRT. Computed tomography (CT)-based dose calculation was performed using a modified Clarkson-based algorithm. In this study, 120 patients' treatment plans were collected in our institute. The treatments were performed using conventional irradiation for lung and prostate, 3-dimensional (3D) conformal stereotactic body radiotherapy (SBRT) for the lung, and intensity-modulated radiation therapy (IMRT) for the prostate. Differences between the treatment planning system (TPS) and the Clarkson-based independent dose verification software were computed, and confidence limits (CLs, mean ± 2 standard deviation %) for Vero4DRT were compared with the CLs for the C-arms linear accelerators in the previous study. The results of the CLs, the conventional irradiation, SBRT, and IMRT showed 2.2 ± 3.5% (CL of the C-arms linear accelerators: 2.4 ± 5.3%), 1.1 ± 1.7% (−0.3 ± 2.0%), 4.8 ± 3.7% (5.4 ± 5.3%), and −0.5 ± 2.5% (−0.1 ± 3.6%) differences, respectively. The dose disagreement between the TPS and CT-based independent dose verification software was less than the 5% action level of American Association of Physicists in Medicine (AAPM) Task Group 114 (TG114). The CLs for the gimbal-mounted Vero4DRT were similar to the deviations for C-arms linear accelerators.

Efficacy of Stereotactic Conformal Radiotherapy vs Conventional Radiotherapy on Benign and Low-Grade Brain Tumors

ImportanceEvidence for application of stereotactic and other conformal radiotherapy techniques in treating brain tumors is largely based on data derived from dosimetric, retrospective, or small prospective studies. Therefore, we conducted a randomized clinical trial of stereotactic conformal radiotherapy (SCRT) compared with conventional radiotherapy (ConvRT) evaluating clinically meaningful end points.ObjectiveTo compare neurocognitive and endocrine functional outcomes and survival at 5 years in young patients with residual and/or progressive benign or low-grade brain tumors treated with SCRT and ConvRT techniques.Design, Setting, and ParticipantsThis phase 3 randomized clinical trial enrolled 200 young patients (ages 3-25 years) with residual or progressive benign or low-grade brain tumors at a single center between April 2001 to March 2012. Patients were randomly allocated (1:1) to either SCRT (n = 104) or ConvRT (n = 96) arms.InterventionsPatients were randomly assigned to either high-precision SCRT or ConvRT to a dose of 54 Gy in 30 fractions over 6 weeks.Main Outcomes and MeasuresDetailed neuropsychological and neuroendocrine assessments were performed at preradiotherapy baseline, at 6 months, and annually thereafter until 5 years on longitudinal follow-up. Change in these functional parameters was compared between the 2 arms as the primary end point and overall survival (OS) as the secondary end point.ResultsIn total, 200 young patients (median [interquartile range] age, 13 [9-17] years; 133 males and 67 females) were enrolled. Mean full-scale or global intelligence quotient (IQ) and performance IQ scores over a period of 5 years were significantly superior in patients treated with SCRT compared with those treated with ConvRT (difference in slope = 1.48; P = .04 vs difference in slope = 1.64; P = .046, respectively). Cumulative incidence of developing new neuroendocrine dysfunction at 5 years was significantly lower in patients treated with SCRT compared with ConvRT (31% vs 51%; P = .01) while developing a new neuroendocrine axis dysfunction in patients with preexisting dysfunction in at least 1 axis at baseline was also significantly lower in the SCRT arm compared with the ConvRT arm (29% vs 52%; P = .02). Five-year OS in SCRT and ConvRT arms was 86% and 91%, respectively (P = .54).Conclusions and RelevanceIn young patients with residual and/or progressive benign or low-grade brain tumors requiring radiotherapy for long-term tumor control, SCRT compared with ConvRT achieves superior neurocognitive and neuroendocrine functional outcomes over 5 years without compromising survival.Trial Registrationclinicaltrials.gov Identifier: NCT00517959

OS02.7 Dose constraint model to predict neuroendocrine dysfunction in young patients with brain tumours- Data from a prospective study of stereotactic conformal radiotherapy

OS02.7 Dose constraint model to predict neuroendocrine dysfunction in young patients with brain tumours- Data from a prospective study of stereotactic conformal radiotherapy

TU‐H‐CAMPUS‐TeP1‐01: Variable‐Beam Fractionation for SAbR

Purpose:In current conventionally‐fractionated as well as hypofractionated 3D conformal radiotherapy (CRT), the same beam arrangement is employed from fraction to fraction. We challenge this notion and postulate that by varying the beam arrangement between fractions we can achieve greater sparing of organs at risk (OARs) while maintaining PTV coverage. We use an inverse planning strategy using a swarm intelligence‐based global optimization algorithm to exploit the additional degree of freedom represented by inter‐fractional variation in beam angles.Methods:To evaluate our variable‐beam fractionation (VBF) method, a 10‐beam ITV‐based conformal stereotactic ablative radiotherapy (CRT‐SAbR) plan was optimized. In the clinical plan, 54 Gy was delivered to a 41cc lung tumor over 3 fractions. In VBF, each original clinically‐assigned beam was multiplied to a bundle of n α‐degree‐spaced beams, n being number of fractions. Selection of α was a compromise between retaining similar tumor irradiation and separating inline OAR sub‐regions. We optimized the beam fluence weights setting an upper limit for beam delivery duration (and implicitly, monitor units) along with clinical organ‐based dose‐volume constraints. Zero weights were allowed so that the optimization algorithm could remove unnecessary beams. All fractions in final plan had to deliver identical monitor units (MU) while satisfying a soft constraint on having no more than one beam from every n‐beam bundle in each fraction. α was 10 degrees and the dose rate was 600 MU/min.Results:The VBF plan achieved significantly superior OAR sparing compared to the clinical internal target volume (ITV)‐based plan. Setting maximum beam delivery duration to 13 seconds (well within breath‐hold range), Esophagus Dmax, Heart Dmax, Spinal cord Dmax and Lung V13 were improved by 25%, 81%, 0% and 27%, respectively.Conclusion:We investigated a simple approach to inter‐fractional VBF planning and demonstrated its potential in reducing dose to OARs.This work was partially supported through research funding from National Institutes of Health (R01CA169102) and Varian Medical Systems, Palo Alto, CA, USA.

A body image and a quality of life after stereotactic hypofractionated radiotherapy (HRT) and standard three-dimensional conformal radiotherapy (3DCRT) of prostate cancer patients.

e16624Background: Prostate cancer is the second most common solid tumor in men worldwide. There are over 1 million new prostate cases each year in the world. Several patients are diagnosed at an ea...

NCO-05LONG TERM FUNCTIONAL AND CLINICAL OUTCOME IN CHILDREN WITH CRANIOPHARYNGIOMA TREATED WITH HIGH PRECISION STEREOTACTIC CONFORMAL RADIOTHERAPY (SCRT): DATA FROM A PROSPECTIVE TRIAL

BACKGROUND: To report prospective detailed outcome data in young patients with residual/recurrent craniopharyngioma treated with Stereotactic Conformal focal radiotherapy (SCRT). METHODS: 39 patients (27 males, 12 females; median age-11 years) underwent prospective detailed serial longitudinal evaluation of neuropsychological/ neurocognitive, and neuroendocrine function at baseline and follow-up after RT. RESULTS: Near total excision as the commonest surgery (82%). Mild/moderate hydrocephalus was observed in 85% and severe in 15%. Impaired vision was observed in 2 patients (5.2%). At a median follow-up of 49.5months (IQ range 12-67 months). 37 patients were controlled at last follow-up with a 10-yr OS of 92% and 10-yr PFS of 84%. Pre-RT mean VQ/MQ, performance IQ (PQ) and FSIQ were 84.95, 80.5 and 77.1 respectively and improved to 96.9,104 and 91 respectively at 5 years follow-up following RT. Pre RT endocrine deficit in 1 or 2 axes was seen in 50% of patients. Involvement of additional axes was seen in 21% patients. LOTCA scores showed improvement with time in attention concentration domain following SCRT. Mean trait-anxiety scores both in children and adolescents was poor at baseline which improved at 5-years follow-up following SCRT. CONCLUSION: The clinical outcome of craniopharyngioma patients had borderline to below average IQ and poor endocrinal function even before starting RT. We observed an improvement in IQ status 5 years post SCRT.

Stereotactic radiotherapy for spinal meningiomas and neurinomas

Over the past decades, stereotactic conformal radiotherapy of intracranial meningiomas and schwannomas has been recognized as an effective and safe procedure. Due to the wide use of the CyberKnife system and the procedure of extracranial stereotactic radiotherapy and radiosurgery, the positive experience can be used to treat spinal tumors. This study assessed the effectiveness of stereotactic radiaotherapy of spinal meningiomas and neurinomas using the CyberKnife system. 46 patients (34 females and 12 males) received treatment between November 2009 and December 2013 (65 tumor nodules). The median age of patients receiving radiotherapy was 49 years (range: 20 to 82 years). Twenty neoplasms were subjected to surgical treatment. In 11 patients, formation of the recurrent tumor foci following treatment was observed along with the systemic disease, neurofibromatosis. Six patients had multiple meningiomas. The median total dose of radiation therapy of neurinomas was 13.6 Gy (12.1-14.1 Gy) per fraction; up to 18.2 Gy (16.0-21.1 Gy) per three fractions; and up to 25.6 Gy (24.8-27.6 Gy) per five fractions. Higher doses were used for meningiomas: 15.9 Gy (14.1-16.2 Gy) per fraction; 20.9 Gy (19.5-21.1 Gy) per three fractions; and 27.5 Gy (25.0-29.9 Gy) per five fractions. The load to 0.15 cm3 of the spinal cord was no higher than the maximum permissible load of 12 Gy per fraction. The mean catamnestic follow-up was 18.1 (4-52) months: 21,1 (4-52) months for neurinomas and 18 (4-31) months for meningiomas. We have not observed complete tumor elimination (i.e., complete response to radiation therapy) in our series. Partial response was observed in 9 (13.8%) cases; stabilization was achieved in 54 (83.1%) cases; and tumor continued to grow in 2 (3.1%) cases. The patients' status was evaluated using the Frankel, the Karnofsky, and the VAS scales. Our findings clearly demonstrate the short-term benefits of using CyberKnife radiotherapy for benign spinal cord tumors. The catamnestic follow-up needs to be extended to elaborate recommendations for radiation. The progress in this therapy type will considerably improve the quality of medical care provided to this cohort of patients.

PT-06 * RANDOMIZED TRIAL OF HIGH-PRECISION CONFORMAL RADIATION THERAPY COMPARED TO CONVENTIONAL RADIOTHERAPY IN PRESERVATION OF LONG-TERM NEURO-COGNITIVE OUTCOMES IN YOUNG PATIENTS WITH PROGRESSIVE OR RESIDUAL BENIGN/LOW-GRADE BRAIN TUMORS

BACKGROUND: To report neuro-psychological outcomes in young patients with progressive benign and low-grade brain tumors treated with high-precision stereotactic conformal radiotherapy (SCRT) versus conventional radiotherapy (Conv RT) ({type:clinical-trial,attrs:{text:NCT00517959,term_id:NCT00517959}}NCT00517959). METHODS: Between 2001-10, 200 patients (median age 13 years, commonest histology craniopraryngioma) were randomized to SCRT (n = 105; 6MV, non-coplanar fields using micromultileaf collimators) or Conv RT (n = 95; 6MV, 2-4 open fields) to 54 Gy/30 fractions. Neuropsychological battery included full-scale IQ (FSIQ), verbal quotient (VQ), performance quotient (PQ), memory quotient (MQ in patients > 16 years) by Wechsler scores, LOTCA battery and state-trait Anxiety Inventory and Hamilton Anxiety-Depression Scales. Serial evaluations were performed at baseline (pre-RT), 6-months and 2, 3, 4, and 5-years post-RT and analyzed using generalized linear-mixed model (GLMM). RESULTS: Pre- RT baseline revealed considerable proportion of patients with low intelligence in both arms indicating effects of tumor and prior treatments. GLMM for repeated measures demonstrated significantly better preservation of FSIQ over time in SCRT versus Conv RT arm at 3 years (p = 0.0003) and 5 years (p = 0.012). There was significantly better preservation of VQ (age 16 years) (p = 0.049) in SCRT than Conv RT arm. Anxiety scores between two arms was not significant at 5 years but mean depression scores at 5 years in age group <16 years was found significantly higher in Conv RT arm (p = 0.01). Patients in Conv RT also had significantly more neurocognitive decline in LOTCA battery at 5 years (p = 0.019), particularly in visuomotor organization and attention-concentration domains. CONCLUSIONS: We demonstrate high-precision conformal radiotherapy superior to conventional radiotherapy in preservation of neuropsychological functions in young patients with benign/low grade brain tumors. This is among few trials generating evidence for use of modern conformal RT from an appropriately-powered trial with clinically relevant endpoints and act as suitable benchmark for testing newer RT- technologies.

Radiotherapy of lung metastasis

Lung metastasis is one of the most common metastases.Metastasectomy is only indicated for selected patients,and most patients are unsuited to surgery.The main treatment is systemic chemotherapy,however,the long-term survival is limited.With the development of precision radiotherapies such as threedimensional conformal radiation therapy (3D-CRT) and stereotactic body radiotherapy (SBRT),it is proved that radiotherapy is favorable for the patients with lung metastasis,especially for limited lung metastasis.SBRT can be obtained better survival,but still need large prospective studies. Key words: Lung neoplasms; Radiotherapy; Neoplasm metastasis; Lung metastasis

中医药调节免疫微环境延缓肝癌复发转移

肝癌是临床上最常见的恶性肿瘤之一，手术、介入治疗及近年开展的立体定向适形放射治疗等均有良好的近期疗效，但都不能解决肝癌的复发和转移问题。中医药已经成为肿瘤辅助治疗的主要手段，有效地改善了肿瘤患者的症状、延长生存期、提高生活质量、延缓复发和转移。本文在简述肝癌的复发转移与机体免疫功能的关系基础上，总结近五年中医药调节免疫微环境延缓肝癌复发转移的研究现状。 Hepatocellular carcinoma is one of the most common malignant tumor in clinical. Surgery, interventional therapy and stereotactic conformal radiotherapy in recent years all have good short-term curative effects, but cannot solve the problem of recurrence and metastasis of hepatocellular carcinoma. Traditional Chinese medicine has become the principal means of adjuvant treatment of cancer, which effectively improves the symptoms of cancer patients, pro- longs the survival time, improves the life quality and delays the recurrence and metastasis. In this article, on the basis of outlining the relationship between the recurrence and metastasis of hepatocellular carcinoma and the immunological function, we summarize the current situation of traditional Chinese medicine regulating immune microenvironment and delaying the recurrence and metastasis of hepatocellular carcinoma in recent five years.

Stereotactic Conformal Radiotherapy in Non-small Cell Lung Cancer — An Overview

Stereotactic conformal radiotherapy is an established technique in treating cranial lesions and has made significant inroads in the treatment of extracranial sites as well. Early stage non-small cell lung cancer is one such site. This overview assesses the results that have been achieved with stereotactic conformal radiotherapy in non-small cell lung cancer so far and compares its efficacy with surgical and other non-surgical modalities.

Fractionated Stereotactic Conformal Radiotherapy for Optic Nerve Sheath Meningiomas

AimsTo assess visual outcome, tumour control and treatment-related morbidity in patients with optic nerve sheath meningiomas (ONSMs) treated with fractionated stereotactic radiotherapy (FSRT). Patients and methodsA retrospective analysis of 45 patients (13 men and 32 women, median age 46 years) with ONSMs (51 optic nerves involved) treated in a single institution between 1997 and 2010 was carried out. FSRT was delivered to a dose of 50 Gy in 30 or 33 fractions as primary treatment in 39 patients and after surgery in six patients. ResultsAt a median follow-up of 30 months (range 1–13 years), the tumour control in 41 evaluable patients (four were lost to follow-up) was 100% at 5 years with no subsequent local or distant recurrence. Of the 46 evaluable optic nerves treated, 41 had residual vision (38 with impaired vision) before radiotherapy and five were blind in one eye. There was no recovery of vision in any of the blind eyes. Of 41 optic nerves with residual vision, 13 had improvement, 24 remained stable and four deteriorated; two patients (4%) developed radiation retinopathy. One patient developed a central retinal artery occlusion in the untreated eye 10 years after treatment. ConclusionFSRT is highly effective at controlling the growth of ONSMs with improvement or stabilisation of visual deficit in 89% of the optic nerves retaining some vision, albeit with a small risk of radiation-induced retinopathy. The results support the use of FSRT as an effective approach in the management of ONSM. The lack of functional benefit in patients with severe visual impairment would argue for earlier institution of treatment before complete visual loss is established.

SU-E-T-610: Investigation on Four-Dimensional Computed Tomography Imaging for Stereotactic Body Radiotherapy: The Patient and Programmable Respiratory Motion Phantom Study

Purpose: To compare and evaluate volumatric and dosimetric accuracy of 4DCT for stereotactic body radiotherapy between free breathing and maximum-intensity projection (MIP) imaging. Methods: Three lung cancer patients who had undergone the treatment of stereotactic body radiotherapy and QUASAR respiratory motion phantom were used in this study. The Philips 85cm Big-bore brilliance 16-slice CT scanner with bellow-belt system was used to generate the 4DCT data sets. The planning CT was done in free breathing (FB) conditions for treatment verification purpose. The patient 4DCT was obtained and its amplitude of motion parameters was used to acquire 4DCT data of moving phantom. Each patient had 13 different 4DCT sets. All these images were imported into the 3D-RTP system. Treatment planning was made using ADAC Pinnacle 8.0 system for Synergy-S linear accelerator for both phantom and patients for conformal stereotactic body radiotherapy. The treatment planning was made such as 0%-plan, 10%-plan, 20%-plan 30%-plan 40%-plan 50%-plan 60%-plan 70%-plan 80%-plan, and 90%-plan, AvgiP-plan, MIP-plan and FB-plan for both phantom and patients for comparison. Results: In the phantom study, the percent of volume differences were found to be 55%, 35%, 74% between FB vs MIP for GTV, OAR-1 and OAR-2 respectively. In the patient study, the percent of volume differences were found to be 38% for GTV and 74%, for the spinal cord between FB vs MIP, respectively. All dosimetric variations between FB vs Avg-iP CT based plans were found to be 10– 19.2% for target and OAR for both phantom and patients studies. Conclusions: The volumetric and dosimetric variations between free- breathing and MIP images for both phantom and patient targets and organs- at-risk were significant. The free-breathing CT was underestimated the volumes compared to MIP images. The effect of motion becomes important for accurate dose planning in stereotactic body radiotherapy.

SU-E-T-555: Small Field Dosimetry of the Flattening Filter Free (FFF) X-Ray Photons

Purpose: The dosimetry of small field is critical in high‐resolution photonradiation therapy, such as the highly conformal stereotactic radiosurgery(SRS) and stereotactic body radiotherapy(SBRT). The flattening filter free (FFF) linac as an emerging technique can offer highly efficient photon use and enhanced dose rate, which benefits SRS and SBRT. This study investigates the small field photondosimetry of the FFF X‐rays using diode detectors and compares results to the conventional flattened X‐ rays. Methods: A Varian's TrueBeam (TB) linac with 6X‐FFF and 6X‐flat X‐rays and a Novalis TX (NTX) linac with 6X‐flat X‐rays have been fully commissioned. Output factors (6X‐flat and 6X‐FFF of TB and 6 X‐flat NTX) were measured by a diode detector (Edge detector, Sun Nuclear) and solid water phantom with different field sizes (FS) created in Eclipse Treatment Planning System. Different FS were formed by MLC patterns rather than jaws (FS=5, 10, 20, 30, 40, 60, 100mm by MLC and the corresponding jaw size=7, 12, 22, 32, 42, 60, 100mm). A regular SSD=100cm and extended SSD=210cm with dmax=1.5cm buildup were setup for the small field dosimetry measurement and all these relative dosimetry was normalized to FS=10cm.Results: Good repeatability of the measurement was demonstrated. The regular and extended SSD results were comparable, which showed the OF of 6X‐flat was smaller than the OF of 6X‐FFFfor FS=1–10cm, likely due to the absence of flattening filter. Moreover, the OF of TB's 6X‐flat was generally lower than the OF of NTX's 6X‐flat. One possible cause is that leaf thickness of NTX is thinner than TB. Conclusions: The 6X‐FFF photons have higher output than the 6X‐ flat in the TrueBeam linac, maybe due to the removal of flattening filter. The TB's 6X‐flat photons have lower output than NTX's 6X‐flat X‐ray photons probably because NTX has thinner leaves.