bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐519: Is Geometry Based Setup Sufficient for All of the Head and Neck Treatment Cases?: A Feasibility Study Towards the Dose Based Setup
Authors: Lee S , Chen S , Zhang B , Xu H , Prado K , D'Souza W , Yi B 
Published: July 2016

Purpose:This study compares the geometric‐based setup (GBS) which is currently used in the clinic to a novel concept of dose‐based setup (DBS) of head and neck (H&N) patients using cone beam CT (CBCT) of the day; and evaluates the clinical advantages.Methods:Ten H&N patients who underwent re‐simulation and re‐plan due to noticeable anatomic changes during the course of the treatments were retrospectively reviewed on dosimetric changes in the assumption of no plan modification was performed. RayStation planning system (RaySearch Laboratories AB, Sweden) was used to match (ROI fusion module) between prescribed isodoseline (IDL) in the CBCT imported along with ROIs from re‐planned CT and the IDL of original plan (Dose‐based setup: DBS). Then, the CBCT plan based on daily setup using the GBS (previously used for a patient) and the DBS CBCT plan recalculated in RayStation compared against the original CT‐sim plan.Results:Most of patients’ tumor coverage and OAR doses got generally worsen when the CBCT plans were compared with original CT‐sim plan with GBS. However, when DBS intervened, the OAR dose and tumor coverage was better than the GBS. For example, one of patients’ daily average doses of right parotid and oral cavity increased to 26% and 36%, respectively from the original plan to the GBS planning. However, it only increased by 13% and 24%, respectively with DBS. GTV D95 coverage also decreased by 16% with GBS, but only 2% decreased with DBS.Conclusion:DBS method is superior to GBS to prevent any abrupt dose changes to OARs as well as PTV/CTV or GTV at least for some H&N cases. Since it is not known when the DBS is beneficial to the GBS, a system which enables the on‐line DBS may be helpful for better treatment of H&N.
SU‐F‐T‐523: Radiobiological Comparison of Helical Tomotherapy and VMAT in the Treatment of Head and Neck Tumors
Authors: Woods R , Mavroidis P , Lehman‐Davis M , Kostich M , Cook T , Chera B , Das S , Lian J 
Published: July 2016

Purpose:This study aims at comparing the efficacy of Helical Tomotherapy (TOMO) and Volumetric Modulated Arc Therapy (VMAT) in producing highly conformal dose distributions in challenging head & neck cancer patients. Furthermore, to interpret the dosimetric findings into expected tissue response rates in order to estimate their clinical impact.Methods:Seven patients were studied and for each patient two treatment plans (one TOMO and one VMAT) were created. Structures used for optimization were: high risk PTV, standard risk PTV, brainstem, spinal cord, parotid gland, larynx, mandible and surrounding tissue. The prescription varied between 60 – 74.4Gy to the HR. The same dosimetric constraints were used for both pairs of plans. Additionally, the TCP and NTCP values of the different targets and organs at risk (OAR) were calculated and compared together with the P+, which is the probability of achieving tumor control without normal tissue complications.Results:The proposed plan evaluation shows that the VMAT gives better results than TOMO in terms of expected clinical outcome. Specifically, the average difference in P+ = 3.3±1.8%, TCP = 3.3±1.8%, NTCP = 0.0±0.0%. The difference observed mainly stems from the lower TCP with TOMO (average difference of 2.9% for the high risk PTV and 3.1% for the standard risk PTV). The NTCP differences between the two modalities are very small even though their average differences in BEUD can be large (e.g. −21.9 Gy in brainstem, 27.2 Gy in larynx).Conclusion:The findings of the analysis indicate that VMAT achieves better coverage to the targets with lower doses to the OARs compared to TOMO for the patients tested. However, the dosimetric differences appear to have a measurable impact only in the expected TCP rates of the targets. Radiobiological evaluation of treatment plans should provide a closer association of the delivered treatment with the clinical outcome.
SU‐F‐T‐524: Investigation of the Dosimertric Benefits of Interchangeable Source Size of a Novel Rotating Gamma System
Authors: Eldib A , Chibani O , Chen L , Li J , Price R , Ma C 
Published: July 2016

Purpose:Tremendous technological developments were made for conformal therapy techniques with linear accelerators, while less attention was paid to cobalt‐60 units. The aim of the current study is to explore the dosimetric benefits of a novel rotating gamma ray system enhanced with interchangeable source sizes and multi‐leaf collimator (MLC).Material and Methods:CybeRT is a novel rotating gamma ray machine with a ring gantry that ensures an iso‐center accuracy of less than 0.3 mm. The new machine has a 70cm source axial distance allowing for improved penumbra compared to conventional machines. MCBEAM was used to simulate Cobalt‐60 beams from the CybeRT head, while the MCPLAN code was used for modeling the MLC and for phantom/patient dose calculation. The CybeRT collimation will incorporate a system allowing for interchanging source sizes. In this work we have created phase space files for 1cm and 2cm source sizes. Evaluation of the system was done by comparing CybeRT beams with the 6MV beams in a water phantom and in patient geometry. Treatment plans were compared based on isodose distributions and dose volume histograms.Results:Profiles for the 1cm source were comparable to that from 6MV in the order of 6mm for 10×10 cm2 field size at the depth of maximum dose. This could ascribe to Cobalt‐60 beams producing lowerenergy secondary electrons. Although, the 2cm source have a larger penumbra however it could be still used for large targets with proportionally increased dose rate. For large lung targets, the difference between cobalt and 6MV plans is clinically insignificant. Our preliminary results showed that interchanging source sizes will allow cobalt beams for volumetric arc therapy of both small lesions and large tumors.Conclusion:The CybeRT system will be a cost effective machine capable of performing advanced radiation therapy treatments of both small tumors and large target volumes.
SU‐F‐T‐525: Monitordeep‐Inspiratory Breathhold with a Laser Sensor for Radiation Therapy of Left Breast Cancer
Authors: Tai A , Li DJ , Currey A , Li X Allen 
Published: July 2016

Purpose:Radiation therapy (RT) of left sided breast cancers with deep‐inspiratory breathhold (DIBH) can reduce the dose to heart. The purpose of this study is to develop and test a new laser‐based tool to improve ease of RT delivery using DIBH.Methods:A laser sensor together with breathing monitor device (Anzai Inc., Japan) was used to record the surface breathing motion of phantom/volunteers. The device projects a laser beam to the chestwall and the reflected light creates a focal spot on a light detecting element. The position change of the focal spot correlates with the patient's breathing motion and is measured through the change of current in the light detecting element. The signal is amplified and displayed on a computer screen, which is used to trigger radiation gating. The laser sensor can be easily mounted to the simulation/treatment couch with a fixing plate and a magnet base, and has a sensitivity range of 10 to 40 cm from the patient. The correlation of breathing signals detected by laser sensor and visionRT is also investigated.Results:It is found that the measured breathing signal from the laser sensor is stable and reproducible and has no noticeable delay. It correlates well with the VisionRT surface imaging system. The DIBH reference level does not change with movement of the couch because the laser sensor and couch move together.Conclusion:The Anzai laser sensor provides a cost‐effective way to improve beam gating with DIBH for treating left breast cancer. It can be used alone or together with VisionRT to determine the correct DIBH level during the radiation treatment of left breast cancer with DIBH.
SU‐F‐T‐527: A Novel Dynamic Multileaf Collimator Leaf‐Sequencing Algorithm in Radiation Therapy
Authors: Jing J , Lin H , Chow J 
Published: July 2016

Purpose:A novel leaf‐sequencing algorithm is developed for generating arbitrary beam intensity profiles in discrete levels using dynamic multileaf collimator (MLC). The efficiency of this dynamic MLC leaf‐sequencing method was evaluated using external beam treatment plans delivered by intensity modulated radiation therapy technique.Methods:To qualify and validate this algorithm, integral test for the beam segment of MLC generated by the CORVUS treatment planning system was performed with clinical intensity map experiments. The treatment plans were optimized and the fluence maps for all photon beams were determined. This algorithm started with the algebraic expression for the area under the beam profile. The coefficients in the expression can be transformed into the specifications for the leaf‐setting sequence. The leaf optimization procedure was then applied and analyzed for clinical relevant intensity profiles in cancer treatment.Results:The macrophysical effect of this method can be described by volumetric plan evaluation tools such as dose‐volume histograms (DVHs). The DVH results are in good agreement compared to those from the CORVUS treatment planning system.Conclusion:We developed a dynamic MLC method to examine the stability of leaf speed including effects of acceleration and deceleration of leaf motion in order to make sure the stability of leaf speed did not affect the intensity profile generated. It was found that the mechanical requirements were better satisfied using this method.The Project is sponsored by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.
SU‐F‐T‐528: Relationship Between Tumor Size and Plan Quality Using FFF and Non‐FFF Modes in Rapidarc
Authors: Chen F 
Published: July 2016

Purpose:For a give PTV dose, beam‐on time is shorter in the FFF than the non‐FFF mode because of higher MU/min. Larger tumors usually require more complex intensity modulation, which might affect plan quality and total MU. We investigated the relationship between PTV size and plan quality using FFF and non‐FFF modes.Methods:Two different PTV volumes (PTV and PTV+1 cm margin) were drawn in brain, lung and liver. 3‐full to 7‐partial arc (Rapidarc) of 6 MV, 1400 MU/min were studied. Plan quality was evaluated by: (a) DVH for PTV and normal tissues, (b) total MU and beam‐on time, and (c) passing rate for IMRT plan QA.Results:For the same PTV coverage, DVH for normal tissue was the same or slightly lower in the FFF compared with non‐FFF. Total MU was 13% higher in FFF than non‐FFF in the 3‐arc, 7 Gy treatment, but the difference became smaller when arc number increased to 6–7 for 10–24 Gy. Larger PTV did not affect the difference in the total MU. FFF required a short beam‐on time and the ratio of FFF and non‐FFF was 0.34 to 0.88 for 7‐ and 3‐arc, respectively. For larger PTV, the ratio increased to 0.45–0.90. Ratio of total MU for large PTV was 3–8% lower in the non‐FFF plans. Although the small difference in MU, beam‐on time was 1.1 to‐1.6 times longer in the 3‐ and 7‐arc non‐FFF plans. Plan verification showed the similar gamma index passing rate.Conclusion:While total MU was similar with FFF and non‐FFF modes, the beam‐on time was shorter in the FFF treatment. The advantage of FFF was greater in treatments with high dose per fraction using more arc numbers. For dose less than 10 Gy, using FFF and non‐FFF modes, tumor size did not affect the relationship of total MU, beam‐on time.
SU‐F‐T‐529: Dosimetric Investigation of a Rotating Gamma Ray System for ImagedGuided Modulated Arc Radiotherapy
Authors: Ma C , Chibani O , Eldib A , Li J , Chen L 
Published: July 2016

Purpose:Because of their effectiveness and efficiency, rotational arc radiotherapy (MAT) techniques have been developed on both specialty machines such as Tomotherapy and conventional linear accelerators. This work investigates a new rotating Gamma therapy system for image guided MAT and SBRT of intra/extracranial tumors.Methods:The CyberMAT system (Cyber Medical Corp., China) consists of a ring gantry with a gamma source (effective source size 1cm and 1.7cm respectively), a 120‐leaf MLC, a kV CBCT and an EPID. The treatment couch provides 6‐degrees‐of‐freedom motion compensation and the kV CBCT system has a spatial resolution of 0.4mm for target localization. The maximum dose rate is >4.0 Gy/min and the maximum field size is 40cm × 40cm. Monte Carlo simulations were used to compute dose distributions and compare with measurements. A retrospective study of 125 previously treated SBRT patients was performed to evaluate the dosimetric characteristics of CyberMAT in comparison with existing VMAT systems.Results:Monte Carlo results confirmed the CyberMAT design parameters including output factors and 3D dose distributions. Its beam penumbra is 5mm to 10mm for field sizes 1cm to 10cm, respectively and its isocenter accuracy is <0.5mm. Compared to the 6 MV photons of Tomotherapy and conventional linacs, Cobalt beams produce lower‐energy secondary electrons that exhibit better dose properties in low‐density lung tissues. Cobalt beams are ideal for peripheral lung tumors with half‐arc arrangements to spare the opposite lung and other critical structures. Superior dose distributions have been obtained for brain, head and neck, breast, spine and lung tumors with half/full arc arrangements.Conclusion:Because of the unique dosimetric properties of Cobalt sources and its accurate stereotaxy/dose delivery CyberMAT is ideally suited for image guided MAT and SBRT. Full‐arc arrangements are superior for brain and H&N treatments while half‐arc arrangements produce best dose distributions for thoracic tumors.
SU‐F‐T‐531: Determination of Site‐Specific Dynamic‐Jaw Versus Static‐Jaw RapidArc Delivery
Authors: Tien C , Brewer M , Studenski M 
Published: July 2016

Purpose:Dynamic‐jaw tracking maximizes the area blocked by both jaw and MLC in RapidArc. We developed a method to quantify jaw tracking.Methods:An Eclipse Scripting API (ESAPI) was used to export beam parameters for each arc's control points. The specific beam parameters extracted were: gantry angle, control point number, meterset, x‐jaw positions, y‐jaw positions, MLC bank‐number, MLC leaf‐number, and MLC leaf‐position. Each arc contained 178 control points with 120 MLC positions. MATLAB routines were written to process these parameters in order to calculate both the beam aperture (unblocked) size for each control point. An average aperture size was weighted by meterset. Jaw factor was defined as the ratio between dynamic‐jaw to static‐jaw aperture size. Jaw factor was determined for forty retrospectively replanned patients treated with static‐jaw delivery sites including lung, brain, prostate, H&N, rectum, and bladder.Results:Most patients had multiple arcs and reduced‐field boosts, resulting in 151 fields. Of these, the lowest (0.4722) and highest (0.9622) jaw factor was observed in prostate and rectal cases, respectively. The median jaw factor was 0.7917 meaning there is the potential unincreased blocking by 20%. Clinically, the dynamic‐jaw tracking represents an area surrounding the target which would receive MLC‐only leakage transmission of 1.68% versus 0.1% with jaws. Jaw‐tracking was more pronounced at areas farther from the target. In prostate patients, the rectum and bladder had 5.5% and 6.3% lower mean dose, respectively; the structures closer to the prostate such as the rectum and bladder both had 1.4% lower mean dose.Conclusion:A custom ESAPI script was coupled with a MATLAB routine in order to extract beam parameters from static‐jaw plans and their replanned dynamic‐jaw deliveries. The effects were quantified using jaw factor which is the ratio between the meterset weighted aperture size for dynamic‐jaw fields versus static‐jaw fields.
SU‐F‐T‐532: Wobble: A New Metric to Quantify Dynamic‐Jaw VMAT Delivery
Authors: Tien C , Studenski M 
Published: July 2016

Purpose:Dynamic‐jaw tracking minimizes the unblocked area to account for changes in the target's projection as a function of gantry angle. To more fully quantify the benefit of dynamic‐jaw tracking, we have introduced a “wobble” metric that accounts for both target offset and eccentricity as opposed to a jaw factor which only accounts for the increase in blocked areaMethods:The wobble is the unblocked area divided by target crosssectional area, and incorporates target offset and eccentricity. The jaw factor is simply the ratio of unblocked area with and without dynamic‐jaws. Forty patients treated to different sites were replanned with dynamic‐jaw tracking in Eclipse. The majority had multiple arcs and reduced‐field boosts resulting in 151 fields. We quantified the relationship between wobble and jaw factor.Results:The highest jaw factor measured was 0.9692, for a prostate case, and corresponded to a wobble of 0.355. The lowest jaw factor was 0.4722, for a rectal case, and corresponded to a wobble of 2.410. The median jaw factor was 0.7917. The wobble values ranged from 0.2145 to 2.575. The minimum value of wobble was found in a PTV containing prostate‐only site while the maximum value of wobble was found in a PTV containing prostate, seminal vesicle, and lymph nodes. The median wobble was 1.013. For all sites other than brain, there is approximately 20% reduction in jaw factor per 1 unit of wobble. For brain, there was 30% jaw factor reduction per unit of wobble.Conclusion:The wobble metric was introduced to fully quantify dynamic‐jaw tracking and potential dose reduction. There was good correlation observed between wobble and jaw factor. Increasing wobble indicates either large offset or more eccentricity and the potential for substantial dose reduction with dynamic tracking.
SU‐F‐T‐536: Contra‐Lateral Breast Study for Prone Versus Supine Patients
Authors: Marrero M , Joseph K , Klein E 
Published: July 2016

Purpose:There are several advantages to utilizing the prone technique for intact breast cancer patients. However, as the topography changes, accompanied by the influence of a supporting breast board and patient treatment couch, the question that arises is to whether there is a concern for contralateral breast dose for intact breast cancer patients being treated with this technique.Methods:An anthropomorphic phantom with breast mounds to duplicate intact breast cancer treatment was planned in prone and supine position. Two tangential beams were executed in the similar manner for as the radiotherapy planning system. For the prone setup, a breast dense foam board was used to support the phantom. A grid of 24 OSL nanodots was placed at 6cm, 4cm, and 2cm apart from the medial border for both prone and supine setups. The phantom was set up using megavoltage imaging and treated as per plan. Additional, a similar study was performed on a patient treated in prone position.Results:Overall, the contralateral breast dose was generally higher for prone setups at all locations especially when close to the medial border. The average mean dose was found to be 1.8%, 2.5% of the prescribed dose for supine respectively prone position. The average of the standard deviation is 1.04%, 1.38% for supine respectively prone position. As for patient treated in prone position average mean dose was found to be 1.165% of the prescribed dose and average of the standard deviation is 9.456%.Conclusion:There is minimal influence of scatter from the breast board. It appears that the volatility of the setup could lead to higher doses than expected from the planning system to the contralateral breast when the patient is in the prone position
SU‐F‐T‐547: Off‐Isocenter Winston‐Lutz Test for Stereotactic Radiosurgery/stereotactic Body Radiotherapy
Authors: Gao J , Liu X 
Published: July 2016

Purpose:To perform a quantitative study to verify that the mechanical field center coincides with the radiation field center when both are off from the isocenter during the single‐isocenter technique in linear accelerator‐based SRS/SBRT procedure to treat multiple lesions.Methods:We developed an innovative method to measure this accuracy, called the off‐isocenter Winston‐Lutz test, and here we provide a practical clinical guideline to implement this technique. We used ImagePro V.6 to analyze images of a Winston‐Lutz phantom obtained using a Varian 21EX linear accelerator with an electronic portal imaging device, set up as for single‐isocenter SRS/SBRT for multiple lesions. We investigated asymmetry field centers that were 3 cm and 5 cm away from the isocenter, as well as performing the standard Winston‐Lutz test. We used a special beam configuration to acquire images while avoiding collision, and we investigated both jaw and multileaf collimation.Results:For the jaw collimator setting, at 3 cm off‐isocenter, the mechanical field deviated from the radiation field by about 2.5 mm; at 5 cm, the deviation was above 3 mm, up to 4.27 mm. For the multileaf collimator setting, at 3 cm off‐isocenter, the deviation was below 1 mm; at 5 cm, the deviation was above 1 mm, up to 1.72 mm, which is 72% higher than the tolerance threshold.Conclusion:These results indicated that the further the asymmetry field center is from the machine isocenter, the larger the deviation of the mechanical field from the radiation field, and the distance between the center of the asymmetry field and the isocenter should not exceed 3 cm in of our clinic. We recommend that every clinic that uses linear accelerator, multileaf collimator‐based SRS/SBRT perform the off‐isocenter Winston‐Lutz test in addition to the standard Winston‐Lutz test and use their own deviation data to design the treatment plan.
SU‐F‐T‐549: Validation of a Method for in Vivo 3D Dose Reconstruction for SBRT Using a New Transmission Detector
Authors: Nakaguchi Y , Shimohigashi Y , Onizuka R , Ohno T 
Published: July 2016

Purpose:Recently, there has been increased clinical use of stereotactic body radiation therapy (SBRT). SBRT treatments will strongly benefit from in vivo patient dose verification, as any errors in delivery can be more detrimental to the radiobiology of the patient as compared to conventional therapy. In vivo dose measurements, a commercially available quality assurance platform which is able to correlate the delivered dose to the patient's anatomy and take into account tissue inhomogeneity, is the COMPASS system (IBA Dosimetry, Germany) using a new transmission detector (Dolphin, IBA Dosimetry). In this work, we evaluate a method for in vivo 3D dose reconstruction for SBRT using a new transmission detector, which was developed for in vivo dose verification for intensity‐modulated radiation therapy (IMRT).Methods:We evaluated the accuracy of measurement for SBRT using simple small fields (2×2−10×10 cm2), a multileaf collimator (MLC) test pattern, and clinical cases. The dose distributions from the COMPASS were compared with those of EDR2 films (Kodak, USA) and the Monte Carlo simulations (MC). For clinical cases, we compared MC using dose‐volume‐histograms (DVHs) and dose profiles.Results:The dose profiles from the COMPASS for small fields and the complicated MLC test pattern agreed with those of EDR2 films, and MC within 3%. This showed the COMPASS with Dolphin system showed good spatial resolution and can measure small fields which are required for SBRT. Those results also suggest that COMPASS with Dolphin is able to detect MLC leaf position errors for SBRT. In clinical cases, the COMPASS with Dolphin agreed well with MC. The Dolphin detector, which consists of ionization chambers, provided stable measurement.Conclusion:COMPASS with Dolphin detector showed a useful in vivo 3D dose reconstruction for SBRT. The accuracy of the results indicates that this approach is suitable for clinical implementation.