Stereotactic Body Radiation Therapy Program Research Articles

Sharing Mono-Institutional Experience of Treating Pancreatic Cancer with Stereotactic Body Radiation Therapy (SBRT).

Stereotactic body radiotherapy (SBRT) is an evolving treatment for the local management of pancreatic cancer (PC). The main purpose of this study is to report our initial experience in terms of local control (LC) and toxicity for PC patients treated with SBRT. We conducted a retrospective review of patients treated with SBRT using abdominal compression (AC) or an end-expiratory breath-holding (EEBH) technique. The median prescribed dose was 35 Gy, delivered in five fractions. Toxicities were recorded using Common Terminology Criteria for Adverse Events (CTCAE) v5.0, and survival was estimated using the Kaplan-Meier method. From 2017 to 2023, 17 PC patients were offered SBRT. Their median age was 69 years. The median follow-up from the date of diagnosis was 22.37 months. The overall survival (OS) was 94% at 1 year and 60.9% at 2 years. The progression-free survival (PFS) was 63.1% at 6 months and 56.1% at 9 months. The median OS was 26.3 months, and the median PFS was 20.6 months. The 6-month and 1-year LC rates were 71% and 50.8%, respectively. We are successful in implementing the SBRT program at our centre. SBRT appears to be a promising treatment option for achieving LC with limited acute toxicities.

A Cancer Care Ontario Consensus-Based Organizational Guideline for the Planning and Delivery of Spine Stereotactic Body Radiation Therapy Treatment in Ontario

The proposed recommendations are primarily based on the consensus opinion and in-field experience of the Ontario Health/Cancer Care Ontario stereotactic body radiation therapy (SBRT) for Spine Metastasis Guideline Development Group and published literature when available. Primary consideration was given to the perceived benefits for patients and the small likelihood of harm arising from recommendation implementation. Apart from the magnetic resonance imaging (MRI) follow-up strategy, all evidence was considered indirect and was provided by the working group in conjunction with their collective expertise in the field of SBRT.The application of an SBRT program requires a multidisciplinary team consisting of a radiation oncologist, spine surgeon, neuroradiologist, medical physicist, medical dosimetrist, and radiation therapist. In Canada, linear accelerators are the most used treatment delivery units and should follow technology-specific quality assurance procedures. Immobilization technique is location dependant. Treatment planning MRI sequences should be acquired no more than 14 days from the date of treatment. In the case of epidural disease, simulation MRI should be completed no more than 7 days from the date of treatment. After treatment, patients should be followed with routine clinical visits every 3 months for the first year, every 3 to 6 months during years 2 and 3, and every 4 to 6 months thereafter.The recommendations enclosed provide a framework for the minimum requirements for a cancer center in Ontario, Canada to offer SBRT for spine metastases.

Surgical Outcomes for Early-Stage Non-Small Cell Lung Cancer at Facilities With Stereotactic Body Radiation Therapy Programs

<h3>Purpose/Objective(s)</h3> Patients undergoing surgery for early-stage non-small cell lung cancer (NSCLC) may be at high-risk for post-operative mortality. Access to stereotactic body radiation therapy (SBRT), a less invasive alternative, may facilitate more appropriate patient selection for surgery. <h3>Materials/Methods</h3> An analysis of all patients with early-stage NSCLC reported to the National Cancer Database between 2004-2015 was performed. Post-operative mortality rates were derived using vital status data. Utilization of SBRT was defined by each facility's SBRT Experience in years and SBRT-to-Surgery Volume Ratios, defined by quartiles. Multivariable logistic regression with backward elimination was used to test for the associations between facility-level SBRT utilization and post-operative mortality. Interaction testing of independent covariates was performed to assess the effect of SBRT utilization across subgroups. <h3>Results</h3> The study cohort consisted of 202,542 patients who underwent surgical resection of clinical stage T1-T2 N0 M0 NSCLC between 2004-2015. The 90-day post-operative mortality rate declined significantly during the study period from 4.6% to 2.6% (p < 0.001). During this period, the proportion of facilities that utilized SBRT increased from 4.6% to 77.5% (p < 0.001) and the proportion of patients treated with SBRT increased significantly from 0.7% to 15.4% (p < 0.001). On multivariable analysis, lower 90-day post-operative mortality rates were observed among patients who underwent resection at facilities with greater than six years of SBRT Experience (OR 0.84, CI 0.76-0.94, p = 0.003) and SBRT-to-Surgery Volume Ratios above 17% (OR 0.85, CI 0.79-0.92, p < 0.001). Additional covariates associated with 90-day mortality included higher surgical volume, geographic region, year of diagnosis, age, sex, race, insurance status, facility type, Charlson-Deyo score, clinical T stage, histology, anatomic location, surgery type, and prior malignancy. Interaction testing between these covariates was negative, demonstrating that findings were consistent across subgroups. <h3>Conclusion</h3> Patients who underwent surgical resection for early-stage NSCLC at facilities with higher SBRT Experience and SBRT-to-Surgery Volume Ratios had lower rates of post-operative mortality. These findings suggest that the availability of SBRT may improve allocation of patients to surgery or SBRT, particularly for higher-risk patients. The observation of higher post-operative mortality rates at facilities without an SBRT program merits further investigation.

Surgical outcomes for early-stage non-small cell lung cancer at facilities with stereotactic body radiation therapy programs.

8538 Background: Patients undergoing surgery for early-stage non-small cell lung cancer (NSCLC) may be at high-risk for post-operative mortality. Access to stereotactic body radiation therapy (SBRT) offers a less invasive alternative for this population that may facilitate more appropriate patient selection for surgery. Methods: An analysis of all patients with early-stage NSCLC reported to the National Cancer Database between 2004-2015 was performed. Post-operative mortality rates were derived using vital status data. Utilization of SBRT was defined by each facility’s SBRT Experience in years and SBRT-to-Surgery volume ratios, defined by quartiles. Multivariable logistic regression with backward elimination was used to test for independence of associations between exposures of interest and post-operative mortality. Interaction testing was performed to assess the statistical relationship of covariates found to have independent associations. Results: The study cohort consisted of 202,542 patients who underwent surgical resection of clinical stage T1-T2 NSCLC (AJCC 7th edition). The 90-day post-operative mortality rate declined significantly during the study period from 4.6% to 2.6% (p &lt; 0.001). During this period, the proportion of facilities that utilized SBRT increased from 3.3% to 77.5% (p &lt; 0.001) and the proportion of patients treated with SBRT increased significantly from 0.7% to 15.4% (p &lt; 0.001). Lower 90-day post-operative mortality rates were observed at facilities with greater than six years of SBRT experience (OR 0.84, CI 0.76-0.94, p = 0.003) and SBRT-to-Surgery volume ratios above 17% (OR 0.85, CI 0.79-0.92, p &lt; 0.001). Additional covariates associated with 90-day mortality included higher surgical volume, geographic region, year of diagnosis, age, sex, race, insurance status, facility type, Charlson-Deyo score, clinical T stage, histology, anatomic location, surgery type, and prior malignancy. Interaction testing between these covariates was negative, demonstrating that higher SBRT Experience and SBRT-to-Surgery volume ratios were independently associated with lower 90-day surgical mortality. Conclusions: Patients who underwent surgery for early-stage NSCLC at facilities with higher SBRT Experience and SBRT-to-Surgery volume ratios had lower rates of post-operative mortality. These findings suggest that the availability of SBRT may be a surrogate for a more comprehensive and safer approach to matching patients to surgery or SBRT. The observation of higher post-operative mortality rates at facilities without an SBRT program deserves further study.

Practical Considerations for the Implementation of a Stereotactic Body Radiation Therapy Program for Oligo-Metastases

PurposeWith multiple phase 2 trials supporting the use of stereotactic body radiation therapy (SBRT) in oligo-metastatic disease, we evaluated practices that could inform effective implementation of an oligo-metastasis SBRT program. Methods and MaterialsUsing a context-focused realist methodology, an advisory committee of interprofessional clinicians met over a series of semistructured teleconference meetings to identify challenges in implementing an oligo-metastasis SBRT program. Consideration was given to 2 models of care: a subspecialist anatomic expertise model versus a single-practitioner “quarterback” model. ResultsThe advisory committee structured recommendations within a context-mechanism-outcome framework. In summary, the committee recommends that during patient workup, a single practitioner arranges the minimum number of necessary tests, with case presentation at an appropriate multidisciplinary tumor board, including careful review of all previous treatments, and enrollment on clinical trials when possible. At simulation, common patient positions and immobilization on a single simulation scan for multiple sites is recommended. During radiation planning, dose-fractionation regimens should safely facilitate cumulative dose calculations, a single isocenter should be considered for multiple close targets to reduce treatment time, and adherence to strict quality assurance protocols is strongly recommended. Treatment duration should be minimized by treating multiple sites on the same day or choosing shorter dose fractionations. Team communication, thorough documentation, and standardized nomenclature can reduce system errors. Follow-up should aim to minimize redundant clinical appointments and imaging scans. Expert radiology review may be required to interpret post-SBRT imaging. ConclusionsThese guidelines inform best clinical practices for implementing an oligo-metastasis SBRT program. Iterations using a realist approach may further expand on local contexts.

Failure mode and effects analysis of linac-based liver stereotactic body radiotherapy.

Although stereotactic body radiation therapy (SBRT) is an attractive noninvasive approach for liver irradiation, it presents specific challenges associated with respiration-induced liver motion, daily tumor localization due to liver deformation, and poor visualization of target with respect to adjacent normal liver in computed tomography (CT). We aim to identify potential hazards and develop a set of mitigation strategies to improve the safety of our liver SBRT program, using failure mode and effect analysis (FMEA). A multidisciplinary group consisting of two physicians, three physicists, two dosimetrists, and two therapists was formed. A process map covering ten major stages of the liver SBRT program from the initial diagnosis to posttreatment follow-up was generated. A total of 102 failure modes (FM), together with their causes and effects, were identified. The occurrence (O), severity (S), and lack of detectability (D) were independently scored using a scale from 1 (lowest risk) to 10 (largest risk). The ranking was done using the risk probability number (RPN) defined as the product of average O, S, and D numbers for each mode. Two fault tree analyses were performed. The failure modes with the highest RPN values as well as highest severity score were considered for investigation and a set of mitigation strategies was developed to address these. The median RPN (RPNmed ) values for all modes ranged from of 9 to 105 and the highest median S score (Smed ) was 8. Fourteen FMs were identified to be significant by both RPNmed and Smed (top ten RPNmed ranked and highest Smed FMs) and 12 of them were considered for risk mitigation efforts. The remaining two were omitted due to either sufficient checks already in place, or lack of practical mitigation strategies. Implemented measures consisted of five physics tasks, two physician tasks, and three workflow changes. The application of FMEA to our liver SBRT program led to the identification of potential FMs and allowed improvement measures to enhance the safety of our clinical practice.

Single community-based institutional series of stereotactic body radiation therapy (SBRT) for treatment of liver metastases.

Stereotactic body radiation therapy (SBRT) is a safe and effective option for treatment of liver metastases. However, existing data are mostly reported by high-volume centers. There have been reports that advanced radiotherapy techniques performed at low-volume centers result in inferior outcomes. Our goal was to assess the implementation of SBRT for the treatment of liver metastases at a low-volume center by studying the efficacy and toxicity of this technology through retrospective database review at a single, community-based institution. We performed an IRB approved patient registry study. Patients had a median age of 65, KPS of at least 70 (median 90) and primary tumor controlled. All patients underwent fiducial marker placement under CT-guidance 1-2 weeks prior to planning scans. Gross tumor volume (GTV) was delineated using contrast enhanced CT scans, as well as fusion with PET and/or MRI scans. GTV was expanded by 5 mm to create the planning target volume (PTV). Treatment was delivered by image guided stereotactic robotic radiosurgery with respiratory motion tracking. Lesions were treated with 3 fractions to a median total dose of 54 Gy. Overall survival, progression-free survival (PFS) and local failure-free survival were estimated using the Kaplan-Meier method. Log-rank statistic was used to compare local control based on GTV volume. Between 2006 and 2016, 42 consecutively treated patients with 81 metastatic liver lesions were treated with SBRT. Median follow-up was 25 months. Major primary tumor sites were colon (n=18) and lung (n=7). Synchronous extrahepatic disease was present in 15% of the treated lesions and 46% had prior local treatment of liver metastases. The number of lesions treated concurrently ranged from 1 to 4. Lesions had a median maximum diameter of 2.5 cm (range, 0.5-9.5 cm), and a mean volume of 53 cc (range, 0.5-363.0 cc). Kaplan-Meier estimated 1- and 2-year overall survival was 72% and 62%. Estimated 1- and 2-year progression free survival was 32% and 23%. Estimated 1- and 2-year local control was 86% and 80%. Two-year local control was worse for lesions >50 cc compared to lesions ≤50 cc (62% vs. 84%, P=0.04). Toxicity occurred in 26% of treatment courses and included grade 1 (n=12) and grade 2 toxicity (n=3). These results are comparable to available published data regarding the safety and efficacy of liver metastasis SBRT on trial at high volume institutions. Our findings, therefore, demonstrate the successful implementation of a liver metastasis SBRT program in the low-volume, community-hospital setting. These findings suggest that low-volume and high-volume centers are both options for liver metastasis SBRT.

Keeping a Finger on the Pulse: The Potential of a Programmatic Advanced Practice Role

Stereotactic Body Radiation Therapy (SBRT) is a treatment technique that makes possible the delivery of highly focused high dose radiation in a single or few fractions. The SBRT program at our institution has grown rapidly in both anatomic sites and patient numbers since 2008; treating over 900 patients last year to sites including lung, liver, spine, prostate, kidney, pancreas, head and neck and miscellaneous oligometastases. Due to the rapid expansion and the highly technical nature of the program, a clinical specialist radiation therapy (CSRT) role was introduced in 2012 to ensure the highest quality patient care and efficient use of resources. In this role, the CSRT liaises with all disciplines within the radiation oncology program (radiation oncologists, medical physicists, radiation therapists and nurses) and across nearly all primary disease site groups. The responsibilities of the role include direct patient care through new patient, on treatment and follow up visits as well as programmatic leadership via the oversight of protocol standardization, development of new techniques and departmental education. A wide breadth of knowledge is required in this role and participation in patient care across all anatomic sites offers a unique and comprehensive perspective. A key responsibility of the CSRT is to manage and participate in peer review of all SBRT cases. The majority of peer review for SBRT cases is conducted via multi-disciplinary rounds led by the CSRT, who maintains detailed records of identified issues and recommendations. In additional to ensuring the highest quality of care for the patients, the data acquired from SBRT peer review has led to SBRT protocol standardization, process improvements and technique efficiencies. In 2017, 723 SBRT cases were peer reviewed in the multi-disciplinary setting led by the CSRT and 22 of these cases required follow up based on issues identified after peer review. Thirty-one out of 723 cases were completed outside of scheduled rounds at review initiated by the CSRT to ensure completion before more than half of the treatment was delivered. Inappropriate or missing contours was a common theme in cases requiring follow up and this lead to the standardization of chest wall, renal cortex and renal hilum contours across all sites. A trend in dose reduction in liver SBRT was observed and subsequently, a breath-hold technique was implemented in an attempt to reduce treatment volumes and facilitate the delivery of higher doses. Inconsistent dose constraints for abdominal organs were also identified and a task force to harmonize these across anatomical sites was initiated. With involvement in all anatomic sites, a programmatic advanced practice role in SBRT offers a unique perspective that ensures continuity and consistency across all anatomic sites. Continuous evaluation of treatment protocols and outcomes is imperative for the identification of opportunities for improvement across all sites.

Towards Liver SBRT – A clinical experience

Historically external beam radiation therapy has not been used to treat metastatic liver and hepatocellular carcinoma (HCC), due to the increased risk of radiation induced liver disease (RILD). Remarkable advances in imaging and delivery technology can now be harnessed to enhance target localisation and local control for patients suffering with HCC and oligometastatic liver disease. Image-Guided Radiation Therapy (IGRT) and Stereotactic Body Radiation Therapy (SBRT) are rapidly revolutionising the planning and delivery of radiation therapy in the treatment of cancer. Being able to see and track the changes that take place over a radical course of radiation therapy present numerous exciting opportunities. The treatment of liver carcinoma with radiotherapy is a highly complex non-invasive treatment option that can deliver significant benefits to non-operable patients when administered successfully. Safe administration of the world’s most advanced radiotherapy treatment techniques such as 4D-IGRT or end expiration breath-hold (EEBH), flattening filter free (FFF), SBRT volumetric arc therapy (VMAT) is a highly challenging commitment and endeavour to undertake, especially so for the clinical physicist. This presentation will highlight some of the main challenges encountered when developing and implementing a liver SBRT program across a multi-disciplinary team, which includes education and training, patient selection, physics QA and establishing process-specific documentation.

WE‐H‐BRC‐02: Failure Mode and Effect Analysis of Liver Stereotactic Body Radiotherapy

Purpose:To identify areas of improvement in our liver stereotactic body radiation therapy (SBRT) program, using failure mode and effect analysis (FMEA).Methods:A multidisciplinary group consisting of one physician, three physicists, one dosimetrist and two therapists was formed. A process map covering 10 major stages of the liver SBRT program from the initial diagnosis to post treatment follow‐up was generated. A total of 102 failure modes, together with their causes and effects, were identified. The occurrence (O), severity (S) and lack of detectability (D) were independently scored. The ranking was done using the risk probability number (RPN) defined as the product of average O, S and D numbers for each mode. The scores were normalized to remove inter‐observer variability, while preserving individual ranking order. Further, a correlation analysis on the overall agreement on rank order of all failure modes resulted in positive values for successive pairs of evaluators. The failure modes with the highest RPN value were considered for further investigation.Results:The average normalized RPN values for all modes were 39 with a range of 9 to 103. The FMEA analysis resulted in the identification of the top 10 critical failures modes as: Incorrect CT‐MR registration, MR scan not performed in treatment position, patient movement between CBCT acquisition and treatment, daily IGRT QA not verified, incorrect or incomplete ITV delineation, OAR contours not verified, inaccurate normal liver effective dose (Veff) calculation, failure of bolus tracking for 4D CT scan, setup instructions not followed for treatment and plan evaluation metrics missed.Conclusion:The application of FMEA to our liver SBRT program led to the identification and possible improvement of areas affecting patient safety.

MO‐B‐201‐00: Motion Management in Current Stereotactic Body Radiation Therapy (SBRT) Practice

The motion management in stereotactic body radiation therapy (SBRT) is a key to success for a SBRT program, and still an on‐going challenging task. A major factor is that moving structures behave differently than standing structures when examined by imaging modalities, and thus require special considerations and employments. Understanding the motion effects to these different imaging processes is a prerequisite for a decent motion management program. The commonly used motion control techniques to physically restrict tumor motion, if adopted correctly, effectively increase the conformity and accuracy of hypofractionated treatment. The effective application of such requires one to understand the mechanics of the application and the related physiology especially related to respiration. The image‐guided radiation beam control, or tumor tracking, further realized the endeavor for precision‐targeting. During tumor tracking, the respiratory motion is often constantly monitored by non‐ionizing beam sources using the body surface as its surrogate. This then has to synchronize with the actual internal tumor motion. The latter is often accomplished by stereo X‐ray imaging or similar techniques. With these advanced technologies, one may drastically reduce the treated volume and increase the clinicians’ confidence for a high fractional ablative radiation dose. However, the challenges in implementing the motion management may not be trivial and is dependent on each clinic case. This session of presentations is intended to provide an overview of the current techniques used in managing the tumor motion in SBRT, specifically for routine lung SBRT, proton based treatments, and newly‐developed MR guided RT.Learning Objectives:Through this presentation, the audience will understand basic roles of commonly used imaging modalities for lung cancer studies; familiarize the major advantages and limitations of each discussed motion control methods; familiarize the major advantages and limitations of each discussed radiation beam control methodology and tumor tacking method; understand the key points in motion management for a high quality SBRT program.

MO‐B‐201‐01: Overcoming the Challenges of Motion Management in Current Lung SBRT Practice

The motion management in stereotactic body radiation therapy (SBRT) is a key to success for a SBRT program, and still an on‐going challenging task. A major factor is that moving structures behave differently than standing structures when examined by imaging modalities, and thus require special considerations and employments. Understanding the motion effects to these different imaging processes is a prerequisite for a decent motion management program. The commonly used motion control techniques to physically restrict tumor motion, if adopted correctly, effectively increase the conformity and accuracy of hypofractionated treatment. The effective application of such requires one to understand the mechanics of the application and the related physiology especially related to respiration. The image‐guided radiation beam control, or tumor tracking, further realized the endeavor for precision‐targeting. During tumor tracking, the respiratory motion is often constantly monitored by non‐ionizing beam sources using the body surface as its surrogate. This then has to synchronize with the actual internal tumor motion. The latter is often accomplished by stereo X‐ray imaging or similar techniques. With these advanced technologies, one may drastically reduce the treated volume and increase the clinicians’ confidence for a high fractional ablative radiation dose. However, the challenges in implementing the motion management may not be trivial and is dependent on each clinic case. This session of presentations is intended to provide an overview of the current techniques used in managing the tumor motion in SBRT, specifically for routine lung SBRT, proton based treatments, and newly‐developed MR guided RT.Learning Objectives:Through this presentation, the audience will understand basic roles of commonly used imaging modalities for lung cancer studies; familiarize the major advantages and limitations of each discussed motion control methods; familiarize the major advantages and limitations of each discussed radiation beam control methodology and tumor tacking method; understand the key points in motion management for a high quality SBRT program.

MO‐B‐201‐03: MRI‐Guided Tracking and Gating

The motion management in stereotactic body radiation therapy (SBRT) is a key to success for a SBRT program, and still an on‐going challenging task. A major factor is that moving structures behave differently than standing structures when examined by imaging modalities, and thus require special considerations and employments. Understanding the motion effects to these different imaging processes is a prerequisite for a decent motion management program. The commonly used motion control techniques to physically restrict tumor motion, if adopted correctly, effectively increase the conformity and accuracy of hypofractionated treatment. The effective application of such requires one to understand the mechanics of the application and the related physiology especially related to respiration. The image‐guided radiation beam control, or tumor tracking, further realized the endeavor for precision‐targeting. During tumor tracking, the respiratory motion is often constantly monitored by non‐ionizing beam sources using the body surface as its surrogate. This then has to synchronize with the actual internal tumor motion. The latter is often accomplished by stereo X‐ray imaging or similar techniques. With these advanced technologies, one may drastically reduce the treated volume and increase the clinicians’ confidence for a high fractional ablative radiation dose. However, the challenges in implementing the motion management may not be trivial and is dependent on each clinic case. This session of presentations is intended to provide an overview of the current techniques used in managing the tumor motion in SBRT, specifically for routine lung SBRT, proton based treatments, and newly‐developed MR guided RT.Learning Objectives:Through this presentation, the audience will understand basic roles of commonly used imaging modalities for lung cancer studies; familiarize the major advantages and limitations of each discussed motion control methods; familiarize the major advantages and limitations of each discussed radiation beam control methodology and tumor tacking method; understand the key points in motion management for a high quality SBRT program.

MO‐B‐201‐02: Motion Management for Proton Lung SBR

The motion management in stereotactic body radiation therapy (SBRT) is a key to success for a SBRT program, and still an on‐going challenging task. A major factor is that moving structures behave differently than standing structures when examined by imaging modalities, and thus require special considerations and employments. Understanding the motion effects to these different imaging processes is a prerequisite for a decent motion management program. The commonly used motion control techniques to physically restrict tumor motion, if adopted correctly, effectively increase the conformity and accuracy of hypofractionated treatment. The effective application of such requires one to understand the mechanics of the application and the related physiology especially related to respiration. The image‐guided radiation beam control, or tumor tracking, further realized the endeavor for precision‐targeting. During tumor tracking, the respiratory motion is often constantly monitored by non‐ionizing beam sources using the body surface as its surrogate. This then has to synchronize with the actual internal tumor motion. The latter is often accomplished by stereo X‐ray imaging or similar techniques. With these advanced technologies, one may drastically reduce the treated volume and increase the clinicians’ confidence for a high fractional ablative radiation dose. However, the challenges in implementing the motion management may not be trivial and is dependent on each clinic case. This session of presentations is intended to provide an overview of the current techniques used in managing the tumor motion in SBRT, specifically for routine lung SBRT, proton based treatments, and newly‐developed MR guided RT.Learning Objectives:Through this presentation, the audience will understand basic roles of commonly used imaging modalities for lung cancer studies; familiarize the major advantages and limitations of each discussed motion control methods; familiarize the major advantages and limitations of each discussed radiation beam control methodology and tumor tacking method; understand the key points in motion management for a high quality SBRT program.

Practice Building: Achieving Growth Through Computed Tomographic Myelography–Based Stereotactic Body Radiation Therapy for Spinal Metastases

Stereotactic body radiation therapy (SBRT) is as an effective method to treat spinal metastases. Imaging is a critical component in the workup of patients who undergo stereotactic radiation treatment. Computed tomographic myelography may be more accurate than magnetic resonance imaging in the delineation of neural elements during SBRT. The task we faced was to offer a standardized method to rapidly and safely obtain high-quality computed tomographic myelography as part of a robust spine SBRT program. In detailing our experience, we support the greater, active participation of radiologists in the multidisciplinary care of patients with spinal metastases, while encouraging other radiologists to foster similar collaborations at their own institutions.

SU‐E‐T‐338: Dosimetric Study of Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Radiation Therapy (IMRT) for Stereotactic Body Radiation Therapy (SBRT) in Early Stage Lung Cancer

Purpose:This study evaluates the dosimetric differences using volumetric modulated arc therapy (VMAT) in patients previously treated with intensity modulated radiation therapy IMRT for stereotactic body radiotherapy (SBRT) in early stage lung cancer.Methods:We evaluated 9 consecutive medically inoperable lung cancer patients at the start of the SBRT program who were treated with IMRT from November 2010 to October 2011. These patients were treated using 6 MV energy. The 9 cases were then re‐planned with VMAT performed with arc therapy using 6 MV flattening filter free (FFF) energy with the same organs at risk (OARS) constraints. Data collected for the treatment plans included target coverage, beam on time, dose to OARS and gamma pass rate.Results:Five patients were T1N0 and four patients were T2N0 with all tumors less than 5 cm. The average GTV was 13.02 cm3 (0.83–40.87) and average PTV was 44.65 cm3 (14.06–118.08). The IMRT plans had a mean of 7.2 angles (6–9) and 5.4 minutes (3.6–11.1) per plan. The VMAT plans had a mean of 2.8 arcs (2–3) and 4.0 minutes (2.2–6.0) per plan. VMAT had slightly more target coverage than IMRT with average increase in D95 of 2.68% (1.24–5.73) and D99 of 3.65% (0.88–8.77). VMAT produced lower doses to all OARs. The largest reductions were in maximum doses to the spinal cord with an average reduction of 24.1%, esophagus with an average reduction of 22.1%, and lung with an average reduction in the V20 of 16.3% The mean gamma pass rate was 99.8% (99.2–100) at 3 mm and 3% for VMAT with comparable values for IMRT.Conclusion:These findings suggest that using VMAT for SBRT in early stage lung cancer is superior to IMRT in terms of dose coverage, OAR dose and a lower treatment delivery time with a similar gamma pass rate.

Poster — Thur Eve — 32: Stereotactic Body Radiation Therapy for Peripheral Lung Lesion: Treatment Planning and Quality Assurance

Stereotactic body radiation therapy (SBRT), due to its high precision for target localizing, has become widely used to treat tumours at various locations, including the lungs.Lung SBRT program was started at our institution a year ago. Eighteen patients with peripheral lesions up to 3 cm diameter have been treated with 48 Gy in 4 fractions.Based on four‐dimensional computed tomography (4DCT) simulation, internal target volume (ITV) was delineated to encompass the respiratory motion of the lesion. A margin of 5 mm was then added to create the planning target volume (PTV) for setup uncertainties. There was no expansion from gross tumour volume (GTV) to clinical target volume (CTV). Pinnacle 9.6 was used as the primary treatment planning system. Volumetric modulated arc therapy (VMAT) technique, with one or two coplanar arcs, generally worked well. For quality assurance (QA), each plan was exported to Eclipse 10 and dose calculation was repeated. Dose volume histograms (DVHs) of the targets and organs at risk (OARs) were then compared between the two treatment planning systems.Winston‐Lutz tests were carried out as routine machine QA. Patient‐specific QA included ArcCheck measurement with an insert, where an ionization chamber was placed at the centre to measure dose at the isocenter. For the first several patients, and subsequently for the plans with extremely strong modulation, Gafchromic film dosimetry was also employed.For each patient, a mock setup was scheduled prior to treatments. Daily pre‐ and post‐CBCT were acquired for setup and assessment of intra‐fractional motion, respectively.

Implementation and evaluation of modified dynamic conformal arc (MDCA) technique for lung SBRT patients following RTOG protocols

To implement modified dynamic conformal arc (MDCA) technique and Radiation Therapy Oncology Group (RTOG) protocols in our clinic for stereotactic body radiation therapy (SBRT) treatment of patients with Stage I/II non–small cell lung cancer. Five patients with non–small cell lung cancer have been treated with SBRT. All the patients were immobilized using CIVCO Body Pro-Lok system and scanned using GE 4-slice computed tomography. The MDCA technique that was previously published was adopted as our planning technique, and RTOG protocols for the lung SBRT were followed. The patients were treated on Novalis Tx system with cone-beam computed tomography imaging guidance. All the patient plans passed the RTOG criteria. The conformal index ranges from 0.99 to 1.12 for the planning target volume, and the biological equivalent dose for the planning target volume is overall 100Gy. Critical structures (lung, spinal cord, brachial plexus, skin, and chest wall) also meet RTOG protocols or published data. A 6-month follow-up of one of the patients shows good local disease control. We have successfully implemented the MDCA technique into our clinic for the lung SBRT program. It shows that the MDCA is useful and efficient for the lung SBRT planning, with the plan quality meeting the RTOG protocols.

Long-term Follow-up and Patterns of Failure for Patients With Medically Inoperable Stage I Non-small Cell Lung Cancer (NSCLC) Treated With Stereotactic Body Radiation Therapy (SBRT)

SBRT program at this institution began in 2002. We reviewed all patients with medically inoperable Stage I NSCLC treated with SBRT prior to 2009 as these patients would have potential minimum 3 years of follow-up.

Helical Tomotherapy-Based STAT Stereotactic Body Radiation Therapy: Dosimetric Evaluation for a Real-Time SBRT Treatment Planning and Delivery Program

Stereotactic body radiation therapy (SBRT) treatments have high-dose gradients and even slight patient misalignment from the simulation to treatment could lead to target underdosing or organ at risk (OAR) overdosing. Daily real-time SBRT treatment planning could minimize the risk of geographic miss. As an initial step toward determining the clinical feasibility of developing real-time SBRT treatment planning, we determined the calculation time of helical TomoTherapy–based STAT radiation therapy (RT) treatment plans for simple liver, lung, and spine SBRT treatments to assess whether the planning process was fast enough for practical clinical implementation. Representative SBRT planning target volumes for hypothetical liver, peripheral lung, and thoracic spine lesions and adjacent OARs were contoured onto a planning computed tomography scan (CT) of an anthropomorphic phantom. Treatment plans were generated using both STAT RT “full scatter” and conventional helical TomoTherapy “beamlet” algorithms. Optimized plans were compared with respect to conformality index (CI), heterogeneity index (HI), and maximum dose to regional OARs to determine clinical equivalence and the number of required STAT RT optimization iterations and calculation times were determined. The liver and lung dosimetry for the STAT RT and standard planning algorithms were clinically and statistically equivalent. For the liver lesions, “full scatter” and “beamlet” algorithms showed a CI of 1.04 and 1.04 and HI of 1.03 and 1.03, respectively. For the lung lesions, “full scatter” and “beamlet” algorithms showed a CI of 1.05 and 1.03 and HI of 1.05and 1.05, respectively. For spine lesions, “full scatter” and “beamlet” algorithms showed a CI of 1.15 and 1.14 and HI of 1.22 and 1.14, respectively. There was no difference between treatment algorithms with respect to maximum doses to the OARs. The STAT RT iteration time with current treatment planning systems is 45 sec, and the treatment planning required 3 iterations or 135 sec for STAT RT liver and lung SBRT plans and 7 iterations or 315 sec for STAT RT spine SBRT plans. Helical TomoTherapy–based STAT RT treatment planning with the “full scatter” algorithm provides levels of dosimetric conformality, heterogeneity, and OAR avoidance for SBRT treatments that are clinically equivalent to those generated with the Helical TomoTherapy “beamlet” algorithm. STAT RT calculation times for simple SBRT treatments are fast enough to warrant further investigation into their potential incorporation into an SBRT program with daily real-time planning. Development of methods for accurate target and OAR determination on megavoltage computed tomography scans incorporating high-resolution diagnostic image co-registration software and CT detector–based exit dose measurement for quality assurance are necessary to build a real-time SBRT planning and delivery program.