[en] Purpose/Objective: LINAC based non-coplanar arc stereotactic radiotherapy is being used to boost malignant brain tumors. This approach can be done in one or multiple treatment sessions and is optimal for small, spherically shaped targets. Conformal treatment planning using 3D fixed non-coplanar beams or beam modulation should increase the ability to treat irregularly shaped and/or large tumors, especially when combined with stereotactic immobilization. We compare the dose conformity and homogeneity of three stereotactic techniques for various non-spherical targets including an ellipsoid, a hemisphere and an irregularly shaped patient tumor. Methods: Three intracranial targets were constructed using a 3D treatment planning system after a patient underwent CT simulation in a stereotactic frame. The three targets include an ellipsoid with x, y, z dimensions of 3.0, 2.0 and 2.0 cm, a hemisphere with a diameter of 4.0 cm, and an irregularly shaped patient tumor with a maximum diameter of 5.3 cm. The following three stereotactic techniques were compared; a) 5 non-coplanar arcs (ARC) as used in traditional LINAC based radiosurgery, b) intensity beam modulation using linear optimization of 5 coplanar beams (MOD), and c) 6 non-coplanar custom blocked fields (3D). The prescription isodose line was chosen as the percent of maximum dose that encompassed at least 95% of the tumor volume. For the 3D and MOD plans blocking was made 4-5 mm from the tumor edge. The following parameters were calculated for each technique/target combination: max dose/prescription dose (MDPD), vol. prescription isodose/vol. target (PITV), percent vol. nontarget brain encompassed in the 30, 50 and 80% (% brain 30, 50, 80) of prescription isodose. For the MOD plans, volume estimates were obtained from two dimensional isodose distributions. Results: Dose inhomogeneity as measured by MDPD is greatest for the ARCS plan for all three targets. Dose conformity is optimal with the MOD and 3D plans for all three targets. The perecnt of brain in the high dose (80%) isodose volume is least for the 3D and MOD plan for the patient tumor and least for the ARC plan of the hemisphere and ellipsoid. Conclusion: For the targets described above, fixed field techniques (3D and MOD) result in improved dose conformity and homogeneity as compared to the standard non-coplanar arc technique, especially for the irregularly shaped patient tumor. Depending on the shape and size of the target, the potential advantage of fixed custom shaped fields may result in a larger amount of normal brain to be included in the lower isodose volumes. Fixed field stereotactic radiotherapy with multiple non-coplanar beams or beam modulation results in favorable dose distributions for non-spherical targets as compared to non-coplanar arcs

[en] Increased use of SBRT and hypo fractionation in radiation oncology practice has posted a number of challenges to medical physicist, ranging from planning, image-guided patient setup and on-treatment monitoring, to quality assurance (QA) and dose delivery. This symposium is designed to provide updated knowledge necessary for the safe and efficient implementation of SBRT in various linac platforms, including the emerging digital linacs equipped with high dose rate FFF beams. Issues related to 4D CT, PET and MRI simulations, 3D/4D CBCT guided patient setup, real-time image guidance during SBRT dose delivery using gated/un-gated VMAT or IMRT, and technical advancements in QA of SBRT (in particular, strategies dealing with high dose rate FFF beams) will be addressed. The symposium will help the attendees to gain a comprehensive understanding of the SBRT workflow and facilitate their clinical implementation of the state-of-art imaging and planning techniques. Learning Objectives: Present background knowledge of SBRT, describe essential requirements for safe implementation of SBRT, and discuss issues specific to SBRT treatment planning and QA. Update on the use of multi-dimensional (3D and 4D) and multi-modality (CT, beam-level X-ray imaging, pre- and on-treatment 3D/4D MRI, PET, robotic ultrasound, etc.) for reliable guidance of SBRT. Provide a comprehensive overview of emerging digital linacs and summarize the key geometric and dosimetric features of the new generation of linacs for substantially improved SBRT. Discuss treatment planning and quality assurance issues specific to SBRT. Research grant from Varian Medical Systems

[en] Big Data in Radiation Oncology: (1) Overview of the NIH 2015 Big Data Workshop, (2) Where do we stand in the applications of big data in radiation oncology?, and (3) Learning Health Systems for Radiation Oncology: Needs and Challenges for Future Success The overriding goal of this trio panel of presentations is to improve awareness of the wide ranging opportunities for big data impact on patient quality care and enhancing potential for research and collaboration opportunities with NIH and a host of new big data initiatives. This presentation will also summarize the Big Data workshop that was held at the NIH Campus on August 13–14, 2015 and sponsored by AAPM, ASTRO, and NIH. The workshop included discussion of current Big Data cancer registry initiatives, safety and incident reporting systems, and other strategies that will have the greatest impact on radiation oncology research, quality assurance, safety, and outcomes analysis. Learning Objectives: To discuss current and future sources of big data for use in radiation oncology research To optimize our current data collection by adopting new strategies from outside radiation oncology To determine what new knowledge big data can provide for clinical decision support for personalized medicine L. Xing, NIH/NCI Google Inc.

[en] In this interactive session, lung SBRT patient cases will be presented to highlight real-world considerations for ensuring safe and accurate treatment delivery. An expert panel of speakers will discuss challenges specific to lung SBRT including patient selection, patient immobilization techniques, 4D CT simulation and respiratory motion management, target delineation for treatment planning, online treatment alignment, and established prescription regimens and OAR dose limits. Practical examples of cases, including the patient flow thought the clinical process are presented and audience participation will be encouraged. This panel session is designed to provide case demonstration and review for lung SBRT in terms of (1) clinical appropriateness in patient selection, (2) strategies for simulation, including 4D and respiratory motion management, and (3) applying multi imaging modality (4D CT imaging, MRI, PET) for tumor volume delineation and motion extent, and (4) image guidance in treatment delivery. Learning Objectives: Understand the established requirements for patient selection in lung SBRT Become familiar with the various immobilization strategies for lung SBRT, including technology for respiratory motion management Understand the benefits and pitfalls of applying multi imaging modality (4D CT imaging, MRI, PET) for tumor volume delineation and motion extent determination for lung SBRT Understand established prescription regimes and OAR dose limits

[en] Purpose: Continuous monitoring of the SBRT lung patient motion during delivery is critical for ensuring adequate target volume margins in stereotactic body radiotherapy (SBRT). This work assesses the deviation of the patient surface motion using a real-time surface tracking system throughout treatment delivery. Methods: Our SBRT protocol employs abdominal compression to reduce the diaphragm movement to within 1 cm, and this is confirmed daily with fluoroscopy. Most patients are prescribed 3–5 fractions, and on treatment day a repeat motion analysis with fluoroscopy is performed, followed by a kV CBCT is aligned with the original planning CT image for 3D setup confirmation. During this entire process a patient surface data restricted to whole chest or the sternum at the middle of the breathing cycle was captured using AlignRT optical surface tracking system and defined as a reference surface. For 10 patients, the deviation of the patient position from the reference surface was recorded during the SBRT delivery in the anterior-posterior (AP) direction at 3–6 measurements per second. Results: On average, the patient position deviated from the reference surface more than 4 mm, 3 mm and 2 mm in the AP direction for 0.95%, 3.7% and 11.1% of the total treatment time, respectively. Only one of the 10 patients showed that the maximum deviation of the patient surface during the SBRT delivery was greater than 1 cm. The average deviation of the patient surface from the reference surface during the SBRT delivery was not greater than 1.6 mm for any patient. Conclusion: This investigation indicates that AP motion can be significant even though the frequency is low. Continuous monitoring during SBRT has demonstrated value in monitoring patient motion ensuring that margins selected for SBRT are appropriate, and the use of non-ionizing and high-frequency imaging can provide useful indicators of motion during treatment

[en] Purpose: Approximately 30% of human glial tumors exhibit mutant forms of p53 and 80% express abnormal levels of p53 protein as seen using immunohistochemical techniques. Therefore a majority of glioblastomas may suffer a functional loss of p53 activity either by a mutant p53 gene or by a functional neutralization of normal p53 activities. The p53 gene product plays an important role in mediating radiation induced G1-S cell cycle arrest and apoptosis in normal cells. We attempt to determine if rat glioblastoma tumors exhibit increased radiosensitivity when transfected with wild type p53 and treated with high dose, single fraction irradiation. Materials and Methods: Cultures of RT2 glioblastoma cells were infected with nonreplicative adenoviral vectors containing either the wild-type p53 gene (AdVp53) or the LacZ gene (AdVLacZ). Tumors were grown intracranially in Fisher female rats. Treatment groups included; a) AdVp53, b) AdVlacZ, c) non-tranfected tumor cells. Half of each group received precision 6MV linac delivered irradiation using an adapted 13mm extended collimator and specialized immobilization. The tumors were treated to a dose of 15 Gy given in a single fraction (dose rate = 2.4 Gy/minute). Some animals in each assigned treatment group were sacrificed 24 and 48 hours after irradiation and tumors were sampled and subjected to the TUNEL assay to determine the extent of apoptosis. The remaining animals were observed until death. Results: Cultures infected with AdVp53 effectively expressed increased amounts of wild-type p53 protein as determined by western blot analysis. Median rat survival times were 12 days in control animals receiving no radiation, 14 days in control rats given irradiation and 18 days in AdVp53 transfected animals treated with irradiation. Increased apoptosis was demonstrated at 24 and 48 hours in AdVp53 rats as compared to controls receiving radiation only (50% vs. 15%). Conclusion: We have demonstrated in vivo radiosensitization/increased apoptosis of rat glioblastoma(AdVp53) tumors treated with large fraction irradiation. A comparison to other radiation modifiers (tirapazamine, RSR-13, IUDR) in this tumor system will also be discussed

[en] Purpose: The Integral Quality Monitor (IQM), developed by iRT Systems GmbH (Koblenz, Germany) is a large-area, linac-mounted ion chamber used to monitor photon fluence during patient treatment. Our previous work evaluated the change of the ion chamber’s response to deviations from static 1×1 cm2 and 10×10 cm2 photon beams and other characteristics integral to use in external beam detection. The aim of this work is to simulate two external beam radiation delivery errors, quantify the detection of simulated errors and evaluate the reduction in patient harm resulting from detection. Methods: Two well documented radiation oncology delivery errors were selected for simulation. The first error was recreated by modifying a wedged whole breast treatment, removing the physical wedge and calculating the planned dose with Pinnacle TPS (Philips Radiation Oncology Systems, Fitchburg, WI). The second error was recreated by modifying a static-gantry IMRT pharyngeal tonsil plan to be delivered in 3 unmodulated fractions. A radiation oncologist evaluated the dose for simulated errors and predicted morbidity and mortality commiserate with the original reported toxicity, indicating that reported errors were approximately simulated. The ion chamber signal of unmodified treatments was compared to the simulated error signal and evaluated in Pinnacle TPS again with radiation oncologist prediction of simulated patient harm. Results: Previous work established that transmission detector system measurements are stable within 0.5% standard deviation (SD). Errors causing signal change greater than 20 SD (10%) were considered detected. The whole breast and pharyngeal tonsil IMRT simulated error increased signal by 215% and 969%, respectively, indicating error detection after the first fraction and IMRT segment, respectively. Conclusion: The transmission detector system demonstrated utility in detecting clinically significant errors and reducing patient toxicity/harm in simulated external beam delivery. Future work will evaluate detection of other smaller magnitude delivery errors.

[en] The major feature that separates stereotactic radiation therapy (cranial SRT) and stereotactic body radiation therapy (SBRT) from conventional radiation treatment is the delivery of large doses in a few fractions which results in a high biological effective dose (BED). In order to minimize the normal tissue toxicity, quality assurance of the conformation of high doses to the target and rapid fall off doses away from the target is critical. The practice of SRT and SBRT therefore requires a high-level of confidence in the accuracy of the entire treatment delivery process. In SRT and SBRT confidence in this accuracy is accomplished by the integration of modern imaging, simulation, treatment planning and delivery technologies into all phases of the treatment process; from treatment simulation and planning and continuing throughout beam delivery. In this report some of the findings of Task group 101 of the AAPM will be presented which outlines the best-practice guidelines for SBRT. The task group report includes a review of the literature to identify reported clinical findings and expected outcomes for this treatment modality. Information in this task group is provided for establishing an SBRT program, including protocols, equipment, resources, and QA procedures.

[en] Purpose: Two newly emerging transmission detectors positioned upstream from the patient have been evaluated for online quality assurance of external beam radiotherapy. The prototype for the Integral Quality Monitor (IQM), developed by iRT Systems GmbH (Koblenz, Germany) is a large-area ion chamber mounted on the linac accessory tray to monitor photon fluence, energy, beam shape, and gantry position during treatment. The ion chamber utilizes a thickness gradient which records variable response dependent on beam position. The prototype of Delta4 Discover™, developed by ScandiDos (Uppsala, Sweden) is a linac accessory tray mounted 4040 diode array that measures photon fluence during patient treatment. Both systems are employable for patient specific QA prior to treatment delivery. Methods: Our institution evaluated the reproducibility of measurements using various beam types, including VMAT treatment plans with both the IQM ion chamber and the Delta4 Discover diode array. Additionally, the IQM’s effect on photon fluence, dose response, simulated beam error detection, and the accuracy of the integrated barometer, thermometer, and inclinometer were characterized. The evaluated photon beam errors are based on the annual tolerances specified in AAPM TG-142. Results: Repeated VMAT treatments were measured with 0.16% reproducibility by the IQM and 0.55% reproducibility by the Delta4 Discover. The IQM attenuated 6, 10, and 15 MV photon beams by 5.43±0.02%, 4.60±0.02%, and 4.21±0.03% respectively. Photon beam profiles were affected <1.5% in the non-penumbra regions. The IQM’s ion chamber’s dose response was linear and the thermometer, barometer, and inclinometer agreed with other calibrated devices. The device detected variations in monitor units delivered (1%), field position (3mm), single MLC leaf positions (13mm), and photon energy. Conclusion: We have characterized two new transmissions detector systems designed to provide in-vivo like measurements upstream from the patient. Both systems demonstrate substantial utility for online treatment verification and QA of photon external beam radiotherapy

[en] Purpose: To document the support of radiobiological small animal research by a modern radiation oncology facility. This study confirms that a standard, human use linear accelerator can cover the range of experiments called for by researchers performing animal irradiation. A number of representative, anthropomorphic murine phantoms were made. The phantoms confirmed the small field photon and electron beams dosimetry validated the use of the linear accelerator for rodents. Methods: Laser scanning a model, CAD design and 3D printing produced the phantoms. The phantoms were weighed and CT scanned to judge their compatibility to real animals. Phantoms were produced to specifically mimic lung, gut, brain, and othotopic lesion irradiations. Each phantom was irradiated with the same protocol as prescribed to the live animals. Delivered dose was measured with small field ion chambers, MOS/FETs or TLDs. Results: The density of the phantom material compared to density range across the real mice showed that the printed material would yield sufficiently accurate measurements when irradiated. The whole body, lung and gut irradiations were measured within 2% of prescribed doses with A1SL ion chamber. MOSFET measurements of electron irradiations for the orthotopic lesions allowed refinement of the measured small field output factor to better than 2% and validated the immunology experiment of irradiating one lesion and sparing another. Conclusion: Linacs are still useful tools in small animal bio-radiation research. This work demonstrated a strong role for the clinical accelerator in small animal research, facilitating standard whole body dosing as well as conformal treatments down to 1cm field. The accuracy of measured dose, was always within 5%. The electron irradiations of the phantom brain and flank tumors needed adjustment; the anthropomorphic phantoms allowed refinement of the initial output factor measurements for these fields which were made in a large block of solid water