Stereotactic Body Radiosurgery Research Articles

SU-F-T-616: Comparison of Different Techniques Using RTOG0631 Guidelines in Spine SBRT

Purpose: Stereotactic body radiosurgery (SBRT) for spine metastases involves irradiation using a single high dose fraction. The purpose of this study was to investigate a Hybrid VMAT/IMRT technique which combines volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) for spine SBRT in terms of its dosimetric quality and treatment efficiency using Radiation Therapy Oncology Group (RTOG) 0631 guidelines. Methods: 7 fields IMRT, 2 full arcs VMAT and Hybrid VMAT/IMRT were created for ten previously treated patients. The Hybrid VMAT/IMRT technique consisted of 1 full VMAT arc and 5 IMRT fields. Hybrid VMAT/IMRT plans were compared with IMRT and VMAT plans in terms of the dose distribution, spinal cord sparing, homogeneity, conformity and gradient indexies, monitor unit (MU) and beam on time (BOT). RTOG 0631 recommendations were applied for treatment planning. All plans were normalized and prescribed to deliver 18.0 Gy in a single fraction to 90% of the target volume. Results: The Hybrid VMAT/IMRT technique significantly improved target dose homogeneity and conformity compared with IMRT and VMAT techniques. Providing sharp dose gradient Hybrid VMAT/IMRT plans spare the spinal cord and healthy tissue more effectively. Although, both MU and BOT slightly increased in Hybrid VMAT/IMRT plans there is no statistically meaningful difference between VMAT and Hybrid VMAT/IMRT plans. Conclusion: In IMRT, a smaller volume of healthy tissue can be irradiated in the low dose region, VMAT plans provide better target volume coverage, favorable dose gradient, conformity and better OAR sparing and also they require a much smaller number of MUs and thus a shorter treatment time than IMRT plans. Hybrid plan offers a sinergy through combination of these two techniques with slightly increased number of MU and thus more treatment time.

TU-FG-BRA-00: Optimizing the Treatment Planning Process

The radiotherapy treatment planning process has evolved over the years with innovations in treatment planning, treatment delivery and imaging systems. Treatment modality and simulation technologies are also rapidly improving and affecting the planning process. For example, Image-guided-radiation-therapy has been widely adopted for patient setup, leading to margin reduction and isocenter repositioning after simulation. Stereotactic Body radiation therapy (SBRT) and Radiosurgery (SRS) have gradually become the standard of care for many treatment sites, which demand a higher throughput for the treatment plans even if the number of treatments per day remains the same. Finally, simulation, planning and treatment are traditionally sequential events. However, with emerging adaptive radiotherapy, they are becoming more tightly intertwined, leading to iterative processes. Enhanced efficiency of planning is therefore becoming more critical and poses serious challenge to the treatment planning process; Lean Six Sigma approaches are being utilized increasingly to balance the competing needs for speed and quality. In this symposium we will discuss the treatment planning process and illustrate effective techniques for managing workflow. Topics will include: 1. Planning techniques: (a) beam placement, (b) dose optimization, (c) plan evaluation (d) export to RVS. 2. Planning workflow: (a) import images, (b) Image fusion, (c) contouring, (d) plan approval (e) plan check (f) chart check, (g) sequential and iterative process 3. Influence of upstream and downstream operations: (a) simulation, (b) immobilization, (c) motion management, (d) QA, (e) IGRT, (f) Treatment delivery, (g) SBRT/SRS (h) adaptive planning 4. Reduction of delay between planning steps with Lean systems due to (a) communication, (b) limited resource, (b) contour, (c) plan approval, (d) treatment. 5. Optimizing planning processes: (a) contour validation (b) consistent planning protocol, (c) protocol/template sharing, (d) semi-automatic plan evaluation, (e) quality checklist for error prevention, (f) iterative process, (g) balance of speed and quality Learning Objectives: 1. Gain familiarity with the workflow of modern treatment planning process. 2. Understand the scope and challenges of managing modern treatment planning processes. 3. Gain familiarity with Lean Six Sigma approaches and their implementation in the treatment planning workflow.

Metastatic bladder neoplasms treated with stereotactic body radiosurgery.

397 Background: Stereotactic Body Radiosurgery (SBR) as treatment for metastatic bladder cancer delivers high dose radiation precisely to the site of cancer. In our prospective data analysis, 20 sites of extravesical bladder cancer treated with SBR were analyzed. Methods: Twenty metastatic bladder neoplasms were treated in 15 patients. Sixteen were transitional cell carcinoma, 2 adenocarcinoma, 1 squamous cell carcinoma, and 1 rhabdomyosarcoma. Ages ranged from 39 to 82 years (mean 64) with 4 females and 11 males. Tumor volumes ranged from 10.2 to 563 cc (mean 129.8 cc). Patients were treated with 500-900 cGy (median 800) in 5-8 fractions (median 5) for a total dose of 3000-4500 cGy (median 4000). Cancers were radiographically evaluated with contrast CT and/or MRI studies and reviewed independently by radiologists. Disease control is defined as cessation of growth, shrinkage or disappearance of the tumor after treatment. Results: Follow-up ranged from 1 to 20 months (mean 8 months). The overall control rate was 90%. Both patients who did not respond to treatment were males with transitional cell carcinoma. By dose, volume, age, sex and prior treatment, there was no statistically significant difference in outcome among the 20 patients treated. Conclusions: SBR for metastatic bladder cancer offers a well-tolerated, non-invasive technique with a high rate of tumor control. Patients continue to be evaluated for longer follow up, possible benefits of local control and potential survival advantage. SBR remains an option for those whom standard approaches have not produced desired results or in patients seeking an alternative to surgical or chemotherapeutic treatment.

Treatment of Metastatic Melanoma Using Stereotactic Body Radiosurgery

To investigate the therapeutic effect of Stereotactic Body Radiosurgery (SBR) for the treatment of extracranial metastatic melanoma. Thirty three metastatic melanomas were treated in 19 patients. The majority were treated in the liver and lung (10 and 8 respectively). All the patients were evaluated prospectively before and after treatment. Age ranged from 41 to 81 years (mean 62) with 10 females and 9 males. Tumor volumes ranged from 2.3 to 3315 cc (mean 459.6 cc). Patients were treated with 400-800 cGy (median 600) in 3-6 fractions (median 5) for a total dose of 2000-4000 cGy (median 3000). Cancers were radiographically evaluated with contrast CT and/or MRI studies and reviewed independently by radiologists. Control of the treated cancer is defined as cessation of growth, shrinkage or disappearance of the cancer after treatment. Follow-up ranged from 1 to 57 months (mean 7.7). The overall control rate was 87.8%. Two of the 19 patients did not respond to treatment. They both had lung metastases, with one of the patients having additional liver metastases. By dose, volume, age, sex and prior treatment, there was no statistically significant difference in outcome. Melanoma metastases treated with SBR offers a generally well-tolerated, non-invasive method with a high rate of tumor control. Patients continue to be evaluated for longer follow-up, possible benefits of local control and potential survival advantage.

Quantifying isocenter measurements to establish clinically meaningful thresholds.

A dataset range of isocenter congruency verification tests have been examined from a statistical perspective for the purpose of establishing tolerance levels that are meaningful, based on the fundamental limitation of linear accelerator isocentricity and the demands of a high‐precision stereotactic radiosurgery program. Using a laser‐defined isocenter, a total of 149 individual isocenter congruency tests were examined with recorded values for ideal spatial corrections to the isocenter test tool. These spatial corrections were determined from radiation exposures recorded on an electronic portal imaging device (EPID) at various gantry, collimator, and treatment couch combinations. The limitations of establishing an ideal isocenter were quantified from each variable which contributed to uncertainty in isocenter definition. Individual contributors to uncertainty, specifically, daily positioning setup errors, gantry sag, multileaf collimator (MLC) offset, and couch walkout, were isolated from isocenter congruency measurements to determine a clinically meaningful isocenter measurement. Variations in positioning of the test tool constituted, on average, 0.38 mm magnitude of correction. Gantry sag and MLC offset contributed 0.4 and 0.16 mm, respectively. Couch walkout had an average degrading effect to isocenter of 0.72 mm. Considering the magnitude of uncertainty contributed by each uncertainty variable and the nature of their combination, an appropriate schedule action and immediate action level were determined for use in analyzing daily isocenter congruency test results in a stereotactic radiosurgery (SRS) program. The recommendations of this study for this linear accelerator include a schedule action level of 1.25 mm and an immediate action level of 1.50 mm, requiring prompt correction response from clinical medical physicists before SRS or stereotactic body radiosurgery (SBRT) is administered. These absolute values were derived from considering relative data from a specific linear accelerator and, therefore, represent a means by which a numerical quantity can be used as a test threshold with relative specificity to a particular linear accelerator.PACS number: 87.53Ly, 29.20.Ej, 87.56.Fc

Evaluation of efficacy and safety of robotic stereotactic body radiosurgery and hypofractionated stereotactic radiotherapy for vertebral metastases.

Aim of the studyThe purpose of this study was to evaluate the efficacy and safety of applying CyberKnife (CK) radiosurgery in patients with spinal metastases.Material and methodsTwenty-eight patients with vertebral metastases treated using the CK system were included in the study. Eleven patients suffered from pain, and in 1 case neurological symptoms were observed. The remaining patients were free from clinical symptoms of metastatic disease. The doses applied ranged between 8 and 40 Gy delivered in 4 fractions of 8–15 Gy.ResultsIn the first follow-up evaluation (mean 4.5 months after the treatment), pain was stable in 5 of 8 evaluable cases and in 3 regression occurred. The last follow-up examination (mean 11 months after stereotactic radiosurgery) revealed stable ailments in 3 of 6 evaluable cases, improvement in 3 and new complaints in another 4 patients. In 17 patients imaging studies were conducted after a mean time of 11 months after CK treatment. Stabilization was confirmed in 11, regression in 4 and progression in 2 cases. Median overall survival was 20.6 months. Median progression-free survival was 12.6 months. No side effects attributable to the treatment were observed, but during follow-up transient or permanent deterioration in neurological status as a consequence of disease progression was diagnosed in 4 patients. Delivery time of a single fraction ranged between 0.5 and 1.5 hours.ConclusionsRobotic stereotactic radiosurgery as part of multimodality therapy for metastatic spinal tumours is safe and effective. Because of long irradiation times, this kind of treatment is not suitable for patients in poor general condition.

Stereotactic Ablative Body Radiosurgery (SABR) in Early-Stage Lung Cancer: Can Results of Advanced Cancer Care in an Innovative De-Centralized Cancer Institute Replicate Favorable Clinical Trial Results?

Stereotactic Ablative Body Radiosurgery (SABR) in Early-Stage Lung Cancer: Can Results of Advanced Cancer Care in an Innovative De-Centralized Cancer Institute Replicate Favorable Clinical Trial Results?

Treatment of Adrenal Metastases Using Hypofractionated Stereotactic Body Radiosurgery

Hypofractionated Stereotactic Body Radiosurgery (HFSR) is a non-invasive focused beam technique that delivers high dose radiation to extracranial cancers. The use of HFSR was evaluated for the treatment of adrenal metastases.

Volumetric intensity modulated arc therapy for stereotactic body radiosurgery in oligometastatic breast and gynecological cancers: feasibility and clinical results.

In the present study, the preliminary results of the first stereotactic body radiosurgery (SRS) experience with volumetric intensity modulated arc therapy (VMAT) in oligometastatic breast and recurrent gynecological tumors (OBRGT) are reported in terms of feasibility, toxicity and efficacy. Patients were treated in a head-first supine treatment position on a customized body frame immobilization shell. SRS-VMAT treatment plans were optimized using the ERGO++ treatment planning system. Response assessment was performed 8-12 weeks after treatment by morphologic imaging modalities, or if feasible, also by functional imaging. Thirty-six lesions in 24consecutive patients (median age, 63years; range, 40-81) were treated: 13.9% had primary or metastatic lung lesions, 30.5% had liver metastases, 36.1% had bone lesions, 16.7% had lymph node metastases and 2.8% had a primary vulvar melanoma. The median dose was 18Gy (BED2Gy, α/β: 10=50.4Gy), the minimal dose was 12Gy (BED2Gy, α/β: 10=26.4Gy) and the maximal dose was 28Gy (BED2Gy, α/β: 10=106.4Gy). Seven patients (29.2%) experienced acute toxicity, which however was grade2 in only 1case. Moreover, only 3patients (12.5%) developed late toxicity of which only 1 was grade2. Objective response rate was 77.7% including 16lesions achieving complete response (44.4%) and 12lesions achieving partial response (33.3%). The median duration of follow-up was 15.5months (range, 6-50). Recurrence/progression within the SRS-VMAT treated field was observed in 6patients (total lesions=7) with a 2-year inside SRS-VMAT field disease control expressed on a per lesion basis of 69%. Recurrence/progression of disease outside the SRS-VMAT field was documented in 15patients; the 2-year outside SRS-VMAT field metastasis‑free survival, expressed on a per patient basis, was 35%. Death due to disease was documented in 6patients and the 2-year overall survival was 58%. Although the maximum tolerated dose was not reached, SRS-VMAT resulted in positive early clinical results in terms of tumor response, local control rate and toxicity.

Evaluation of the use of average intensity projection for the localisation of mobile lung tumours treated using stereotactic ablative body radiosurgery (SABR)

Evaluation of the use of average intensity projection for the localisation of mobile lung tumours treated using stereotactic ablative body radiosurgery (SABR)

Can an alternative backround-corrected [18F] fluorodeoxyglucose (FDG) standard uptake value (SUV) be used for monitoring tumor local control following lung cancer stereotactic body radiosurgery?

Purpose: Although [ 18 F] FDG-positron emission tomography (PET) provides vital information in diagnosing lung malignancies, the inherent uncertainties of standard uptake value (SUV) compromises its confidence. People have attempted to reduce this uncertainty by comparing the normal tissues, such as liver and spleen. However, those common reference structures may be inappropriate in some cases when pathological conditions exist. Hence, using alternative reference structures becomes valuable in such practice. The purpose of this study is to explore an alternative reference-correction method to reduce the inherent variation of SUV in the tumor or irradiated region. Methods : 106 analyzable FDG-PET scans from 49 cases who received lung SBRT for non-small cell lung cancer were retrospectively analyzed. The follow-up time ranges from 14.5 weeks to 113.2 weeks. The maximal SUV (SUVmax) was measured within the lung lesion or its corresponding region in post-SBRT. SUVmax was then corrected (or divided) by a reference SUV, or the mean SUV of the adjacent aorta, and results in the new SUVcmax. Results: SUVcmax of the positive group are significant higher than that of locally controlled cases (5.82 ± 3.10 vs. 1.45 ± 0.55, p = 0.026), while inconsequential differences were identified between the groups (p = 0.086). Respectively 85.2% and 96.3% of locally controlled cases post SBRT showed decreased values in the latter PET using SUVmax and SUVcmax. PET taken 24 weeks or sooner post-SBRT yielded higher uncertainties. Conclusion : Comparing with the conventional SUVmax, the alternative regional background-corrected SUV indicator, SUVcmax of PTV suggests a stronger correlation between low (<2.5 - 3.0) values and the local tumor control post lung SBRT for NSCLC. However, FDG-PET images taken earlier than 24 weeks post-SBRT presents larger variations in SUV of the irradiated region due to underlying radiation induced inflammatory changes, and is not recommended for assessing local tumor control after lung SBRT. ..................................................... Cite this article as: Shang CY, Kasper ME, Kathriarachchi V, Benda RK, Kleinman JH, Cole J, Williams TR. Can an alternative backround-corrected [18F] fluorodeoxyglucose (FDG) standard uptake value (SUV) be used for monitoring tumor local control following lung cancer stereotactic body radiosurgery? Int J Cancer Ther Oncol 2014; 2 (4):020317. DOI : 10.14319/ijcto.0203.17

A prospective analysis of hypofractionated stereotactic body radiosurgery for the treatment of adrenal metastases.

e15619 Background: Hypofractionated Stereotactic Body Radiosurgery (HFSR) is a non-invasive focused beam technique delivering high dose radiation to extracranial cancers. We analyzed the use of HFSR as a treatment for adrenal metastases. Methods: 49 adrenal metastases were treated in 45 patients during a 74 month period. 61% of metastases were from a lung cancer origin. All the patients were evaluated prospectively before and after treatment. Age ranged from 42 to 78 years (mean 60.6) with 19 females and 26 males. 75% of patients had prior chemotherapy. Tumor volumes ranged from 2.3 to 892 cc (mean 116.35 cc). Patients were treated with 500-900 cGy (median 800) in 5-8 fractions (median 5) for a total dose of 2500-4500 cGy (median 4000). Cancers were radiographically evaluated with contrast CT and/or MRI studies and reviewed independently by radiologists. Control of the treated cancer is defined as cessation of growth, shrinkage or disappearance of the cancer after treatment. Results: Follow up ranged from 1 to 54 months (mean 10.4). Overall control rate was 88%. For tumors < 116.35cc there was an 87% control rate, and a 91% control rate for tumors ≥ 116.35cc. For tumors receiving < 4000 cGy there was an 80% control rate compared to 93% for adrenal metastases that received ≥ 4000 cGy. Of the tumors treated with ≥ 4000 cGy, the control rate for those < 116.35cc was 91%, and 100% for metastases ≥ 116.35. Adrenal metastases from lung cancer had an 83% control rate, while those from non-lung primaries had a 95% control rate. Conclusions: HFSR for adrenal metastases offers a generally well-tolerated, non-invasive method with a high rate of tumor control. A larger patient group may show a dose-response relationship, as is suggested in this study. Patients will continue to be evaluated to provide longer follow up, possible benefits of local control and potential survival advantage. HFSR for adrenal metastases remains an option for those whom standard approaches have not produced desired results or in patients seeking a non-surgical, non-chemotherapeutic treatment.

Stereotactic body radiosurgery versus intensity modulated radiotherapy for prostate cancer: Comparison of toxicity.

89 Background: Stereotactic body radiosurgery (SBRT) is a recent innovation in the treatment of prostate cancer that has begun to disseminate into national practice. Comparative studies have yet to be performed and little is known about the cost to Medicare or difference in toxicity between SBRT and intensity modulated radiation therapy (IMRT). Methods: We performed a retrospective study using a national sample of all Medicare beneficiaries age 66 or older who received SBRT or IMRT as primary treatment for prostate cancer during 2008 through 2011. Each SBRT patient was matched to two IMRT patients with similar follow-up (6, 12, or 24 months) and clinical and demographic characteristics. Cost of treatment was calculated for matched patients with six months of follow-up. We assessed toxicity by searching Medicare claims for procedure or diagnosis codes indicative of treatment related toxicity. We used a random effects model to compare the likelihood of genitourinary (GU), gastrointestinal (GI), and other toxicity from 0 to 6, 0 to 12, and 0 to 24 months after the initiation of SBRT or IMRT treatment. Results: The study sample consisted of 1,335 SBRT patients matched to 2,670 IMRT patients. The mean cost of SBRT was $11,668 compared to $15,838 for IMRT. At all follow-up points, SBRT patients were significantly more likely to experience GU toxicity. In the first six months after treatment initiation, 15.6% of SBRT versus 12.6% of IMRT patients had claim indicative of a GU complication (p=.009). In the first 12 months, 27.1% of SBRT versus 23.2% of IMRT had a GU complication (p=.014). Finally, from 0-24 months, 43.9% of SBRT versus 36.3% of IMRT had a GU complication (p=.001). The higher rate of GU toxicity after SBRT was largely due to an increase in urethral strictures and bladder outlet obstructions and urinary incontinence or obstruction. Conclusions: In this retrospective observational study, while SBRT was associated with lower costs, there was a greater rate of urinary obstructive toxicity for patients undergoing SBRT compared to IMRT at all time points studied. Whether this increased rate of complication is offset by a higher cure rate or lower cost should be the subject of further study.

When is re-irradiation in head and neck squamous cell carcinoma not indicated?

At least as reflected by the literature, the popularity of reirradiation (rRT) for head and neck squamous cell carcinoma (HNSCC) has increased greatly in the last few years [1]. Guidelines are emerging [2, 3]. There are four reasons, two of them ‘‘old’’ and two of them influenced by recent events. First, despite continuous refinement of treatment strategies, HNSCC remains a locoregional disease with a failure rate above the clavicles in the range of 50 % [4]. Second, even in the human papillomavirus (HPV) era, these patients are subject to an increased risk of second HNSCC [5]. The third reason is that with better imaging, we can detect more local and regional recurrences when they are smaller and more amenable to either surgery or radiotherapy (RT). Finally, intensity modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT), stereotactic body radiosurgery (SBRS), tomotherapy, improved brachytherapy and protons technology allow us to deliver rRT with increased precision and hence, better patient tolerability [6, 7]. Decisions about therapy for recurrence are best undertaken in a multidisciplinary setting. At this moment, surgical salvage still remains the gold standard of care for these patients. The literature of rRT is unclear because it is dominated by low-level evidence from many retrospective studies with prospective data being sparse [3]. To ensure a maximum benefit from rRT, it is valuable to look at the problem of rRT from the opposite perspective. If we agree on ‘‘when is rRT not indicated?’’, it would lend clarity to discussions at tumor boards. There are several principles that should be respected when considering rRT. First, a curative resection should be the first consideration. Although not confirmed in a prospective and randomized fashion, one may infer that complete removal of macroscopic and microscopic tumor would optimize the chance for local control. This assumption is supported by a negative correlation between the tumor bulk left behind after salvage surgery and the survival outcome found in some studies [8]. Another argument could be raised in terms The paper was written by members of the International Head and Neck Scientific Group (http://www.IHNSG.com).

A technique using 99mTc-mebrofenin SPECT for radiotherapy treatment planning for liver cancers or metastases

Radiotherapy or stereotactic body radiosurgery (SBRT) requires a sufficient functional liver volume to tolerate the treatment. The current study extended the work of de Graaf et al. (2010) [3] on the use of 99mTc-mebrofenin imaging for presurgery planning to radiotherapy planning for liver cancer or metastases. Patient was immobilized and imaged in an identical position on a single-photon emission computed tomography/computed tomography (SPECT-CT) system and a radiotherapy simulation CT system. 99mTc-mebrofenin SPECT was registered to the planning CT through image registration of noncontrast CT from SPECT-CT system to the radiotherapy planning CT. The voxels with higher uptake of 99mTc-mebrofenin were transferred to the planning CT as an avoidance structure in optimizing a 2-arc RapidArc plan for SBRT delivery. Excellent dose coverage to the target and sparing of the healthy remnant liver volume was achieved. This report illustrated a procedure for the use of 99mTc-mebrofenin SPECT for optimizing radiotherapy for liver cancers and metastases.

Dose escalation with stereotactic body radiation therapy boost for locally advanced non small cell lung cancer

IntroductionLow survival outcomes have been reported for the treatment of locally advanced non small cell lung cancer (LA-NSCLC) with the standard of care treatment of concurrent chemoradiation (cCRT). We present our experience of dose escalation using stereotactic body radiosurgery (SBRT) following conventional cCRT for patients with LA-NSCLC.MethodsSixteen patients with a median age of 67.5 treated with fractionated SBRT from 2010 to 2012 were retrospectively analyzed. Nine (56%) of the patients had stage IIIB, 6 (38%) has stage IIIA, and 1 (6%) had recurrent disease. Majority of the patients (63%) presented with N2 disease. All patients had a PET CT for treatment planning. Patients received conventional cCRT to a median dose of 50.40 Gy (range 45–60) followed by an SBRT boost with an average dose of 25 Gy (range 20–30) given over 5 fractions.ResultsWith a median follow-up of 14 months (range, 1–14 months), 1-year overall survival (OS), progression free survival (PFS), local control (LC), regional control (RC), and distant control (DC) rates were, 78%, 42%, 76%, 79%, and 71%, respectively. Median times to disease progression and regional failure were 10 months and 18 months, respectively. On univariate analysis, advanced age and nodal status were worse prognostic factors of PFS (p < 0.05). Four patients developed radiation pneumonitis and one developed hemoptysis. Treatment was interrupted in one patient who required hospitalization due to arrhythmias and pneumonia.ConclusionRisk adaptive dose escalation with SBRT following external beam radiotherapy is possible and generally tolerated treatment option for patients with LA-NSCLC.

SU-E-CAMPUS-J-04: Evaluating Radiation-Induced Changes with Diffusion Weighted MRI and Dynamic Contrast Enhanced MRI in Patients with Early Stage Breast Cancer Treated with Stereotactic Body Radiotherapy: Initial Results

Purpose: Pre‐operative stereotactic body radiosurgery (SBRT) was delivered in a single fraction to treat patients with early stage breast cancer; however, few data are available regarding radiation‐induced changes by SBRT. In this work, diffusion weighted imaging (DWI) and dynamic contrast enhanced (DCE) MRI were used to assess the radiation‐induced changes following SBRT. Methods: In this study, 24 patients with early stage breast cancer were enrolled. A prescription dose of 15, 18 or 21Gy was delivered in a single fraction using intensity‐modulated radiotherapy. Patients were to be scanned with MRI about 1‐week before and 1‐week after SBRT. Among the patients, 13 patients have both pre‐and post‐MRI scans, and are analyzed in the work. The 13 patients include 6 patients receivng 15Gy, 3 patients receiving 18 Gy and 4 patients receiving 21 Gy. DWI and DCE‐MRI scans were acquired on a 1.5T GE clinical scanner using a standard 4‐channel breast coil. Apprant diffusion coefficient (ADC) and initial area under the concentration‐time curve for 5‐min after injection (iAUC5min) was used to assess radiation‐induced changes. Descriptive statistics of regional ADC (rADC) and regional iAUC5min was obtained for Gross Tumor Volume (GTV). Wilcoxon signed‐rank test was used to assess the changes, with statistical significance considered at p < 0.05. Results: After delivery of SBRT, the mean rADC increased from the baseline value by about 17% (p=0.030). Similarly, the mean iAUC5min increased from 1.93+/−0.20 mM‐min to 2.31+/−0.16 mM‐min, about 16% (p= 0.012) after treatment. Conclusion: In this study, MRI data revealed significant increases in rADC and iAUC of GTV after SBRT. The radiation‐induced changes after SBRT might imply microscopic water diffusion and microvascular change with an ablative radiotherapy dose. Further work is required to investigate the dose related changes and to determine whether the differences in baseline and individual treatment‐related changes have prognostic value.

SU‐E‐J‐214: Assessment of Rotational Lung Tumor Motion and Its Influence On Treatment Margins for Stereotactic Body Radiosurgery (SBRT)

Purpose: To quantify rotational motion of lung tumors under radiotherapy based on fiducial imaging. Tumor rotational motion in lung has not been well understood due to difficulties of imaging and target delineation. In this study the rotational motion of fiducial clusters were measured for assessing the treatment margins necessary for adequate dose coverage to CTV. Methods: 25 patients who underwent CyberKnife based SBRT were recruited. Three to five fiducials were implanted in or near the tumor. The reference fiducial locations were determined using a breath‐hold CT. Orthogonal X‐ray image pairs were acquired for modeling and tumor tracking during treatment. These images were used to reconstruct the fiducial locations in 3D. A rigid‐body registration was derived between the measured and reference fiducial locations. The mean distance between the corresponding fiducial pairs was used to evaluate the registration. 2796 pairs of images in 106 fractions of treatment were analyzed. The rotational motion of fiducial clusters was used to simulate the tumor rotational motion for assessing the adequacy of the PTV margins. A margin of 3mm was used to expand the upper lobe (UL) target and 5 mm for lower lobe (LL) target. Additional tracking errors were included in the analysis for tumor coverage under alignment of the rotated CTV with the PTV. Results: The tumor rotational angles in LL and UL were 0.25°±5.7° vs 0.40°±2.1° in roll, — 0.21°±7.3° vs 0.05°±1.8° in pitch, and 0.23°±5.3° vs. 0.1°±2.1° in yaw, respectively. In 94.4% (LL) and 97.1% (UL) of the total imaged tumor locations, the CTV was 100% covered by the corresponding PTV. The mean missing coverage of the CTV for the rest locations were of 4.4% and 1%, respectively. Conclusion: The reported angles were highly correlated to the distance to the diaphragm. Appropriate margins need to be applied for different lobes to ensure CTV coverage.

Extracranial radiosurgery with volumetric modulated arc therapy: Feasibility evaluation of a phase I trial.

The aim of this study was to report early clinical experience in stereotactic body radiosurgery (SBRS) delivered using volumetric intensity modulated arc therapy (VMAT) in patients with primary or metastatic tumors in various extra-cranial body sites. Each enrolled subject was included in a different phase I study arm, depending on the tumor site and the disease stage (lung, liver, bone, metastatic), and sequentially assigned to a particular dose level. Technical feasibility and dosimetric results were investigated. The acute toxicity, tumor response and early local control were also studied. In total, 25 lesions in 20 consecutive patients (male/female, 11/9; median age, 67 years; age range, 47–86 years) were treated. Of these 25 lesions, 4 were primary or metastatic lung tumors, 6 were liver metastases, 8 were bone metastases and 7 were nodal metastases. The dose-volume constraints for organs at risk (OARs) were observed in 19 patients using a single-arc technique. Only in one patient were two arcs required. The treatment was performed without interruption or any other technical issues. The prescribed dose ranged from 12–26 Gy to the planning target volume (PTV). Delivery time ranged from 4 min to 9 min and 13 sec (median, 6 min and 6 sec). No incidence of grade 2–4 acute toxicity was recorded. The overall response rate was 48% (95% confidence interval (CI), 24.2–70.2) based on computed tomography (CT)/magnetic resonance imaging (MRI) and 89% (95% CI, 58.6–98.7) based on the positron emission tomography (PET) scan. SBRS delivered by means of VMAT allowed the required target coverage to be achieved while remaining within the normal tissue dose-volume constraints in the 20 consecutive patients. VMAT-SBRS resulted in adequate technical feasibility; the maximum tolerable dose has not yet been reached in any study arm.

Salvage Stereotactic Body Radiosurgery in the Management of Recurrent Gynecological Cancer

Local tumor persistence in the pelvis is the major cause of death in patients with recurrent gynecological cancer. Pelvic exenterati- on has been the only treatment option providing a chance for cure in selected patients. The aim of this study is to analyze the effi- cacy of stereotactic body radiosurgery (SBRS) in patients with recurrent gynecological cancer. Sixteen patients treated with SBRS were analyzed retrospectively. The majority of the patients had cervical cancer. Eleven patients had a history of prior radiotherapy either as postoperative adjuvant external beam radiotherapy (EBRT) with a median dose of 50.4 Gy (range 45-60 Gy) or definitive chemoradiotherapy as EBRT and high dose rate brachytherapy with a dose of 85-90 Gy low dose rate equivalent to point A. The prescribed dose of SBRS was 15-40 Gy (mean 26.6 Gy) in 3-5 fractions. Five patients with no prior radiotherapy received additional EBRT before SBRS. The median follow-up in all patients is 12 months (range 3-36 months). Six patients (37.5%) showed complete radiological and functional response to salvage SBRS. Six patients (37.5%) showed partial response and 2 (12.5%) showed stable disease. One and 2 year overall survival rates are 60.3% and 40.2% respectively. Progression free survival is 59%. All patients with complete response after SBRS are alive with no evidence of disease with a median follow up time of 20 months. SBRS is a promi- sing treatment modality with high local control and reasonable complication rates in selected patients with recurrent gynecological