bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐69: A Radiobiological Investigation of Dose Escalation in Lower Oesophageal Tumours with a Focus On Gastric Toxicity
Authors: Carrington R , Staffurth J , Warren S , Partridge M , Spezi E , Gwynne S , Hawkins M , Crosby T 
Published: June 2015

The incidence of lower third oesophageal tumours is increasing in most Western populations. With the role of radiotherapy dose escalation being identified as a research priority in improving outcomes, it is important to quantify the increased toxicity that this may pose to sites such as the lower oesophagus. This study therefore aims to investigate the feasibility of lower oesophageal dose escalation with a focus on stomach tissue toxicity.The original 3D‐conformal plans (50Gy3D) from 10 patients in the SCOPE1 trial were reviewed and compared to two RapidArc plans created retrospectively to represent the treatment arms of the forthcoming SCOPE2 trial: 50GyRA and 60GyRA (50Gy to PTV1 with a simultaneously integrated boost of 60Gy to PTV2). The stomach was contoured as stomach wall and dose constraints set according to QUANTEC. Normal tissue complication probability (NTCP) was estimated for the stomach wall for an endpoint of gastric bleeding. There was a mean increase of 5.93% in NTCP from 50Gy3D to 60GyRA and a mean increase of 8.15% in NTCP from the 50GyRA to 60GyRA. With NTCP modelling restricted to volumes outside PTV2, there was a mean decrease of 0.92% in NTCP from the 50Gy3D to 60GyRA, and a mean increase of 2.25% from 50GyRA to 60GyRA. There was a strong correlation between the NTCP and Stomach Wall/PTV1 overlap volume for all plans (R=0.80, 0.77 and 0.77 for 60GyRA, 50GyRA and 50Gy3D respectively). There was also a strong correlation between NTCP and the Stomach Wall/PTV2 overlap volume for 60GyRA (R= 0.82).Radiobiological modelling suggests that increasing the prescribed dose to 60Gy may be associated with a significantly increased risk of toxicity to the stomach within the boost volume. It is recommended that stomach toxicity be closely monitored prospectively when treating patients with lower oesophageal tumours in the forthcoming SCOPE 2 trial.Rhys Carrington received a PhD studentship grant from Cancer Research Wales. Grant number: 2445; Dr Warren and Dr Partridge are supported by Cancer Research UK. Grant number: C5255/A15935. Dr Hawkins is supported by MRC grant MC_PC_12001/2
SU‐E‐T‐72: A Retrospective Correlation Analysis On Dose‐Volume Control Points and Treatment Outcomes
Authors: Roy A , Refaat T , Bacchus I , Cutright D , Sathiaseelan V , Mittal B , Nohadani O 
Published: June 2015

Purpose:To quantify correlation between dose‐volume control points and treatment outcomes. Specifically, two outcomes are analyzed: occurrence of radiation induced dysphagia and target complications. The results inform the treatment planning process when competing dose‐volume criteria requires relaxations.Methods:32 patients, treated with whole‐field sequential intensity modulated radiation therapy during 2009–2010 period, are considered for this study. Acute dysphagia that is categorized into 3 grades is observed on all patients. 3 patients are observed in grade 1, 17 patients in grade 2, and 12 patients in grade 3. Ordinal logistic regression is employed to establish correlations between grades of dysphagia and dose to cervico‐thoracic esophagus. Particularly, minimum (Dmin), mean (Dmean), and maximum (Dmax) dose control points are analyzed. Additionally, target complication, which includes local‐regional recurrence and/or distant metastasis, is observed on 4 patients. Binary logistic regression is used to quantify correlation between target complication and four dose control points. Namely, ICRU recommended dose control points, D2, D50, D95, and D98 are analyzed.Results:For correlation with dysphagia, Dmin on cervico‐thoracic esophagus is statistically significant (p‐value = 0.005). Additionally, Dmean on cervico‐thoracic esophagus is also significant in association with dysphagia (p‐value = 0.012). However, no correlation was observed between Dmax and dysphagia (p‐value = 0.263). For target complications, D50 on the target is a statistically significant dose control point (p‐value = 0.032). No correlations were observed between treatment complications and D2 (p‐value = 0.866), D95 (p‐value = 0.750), and D98 (p‐value = 0.710) on the target.Conclusion:Significant correlations are observed between radiation induced dysphagia and Dmean (and Dmin) to cervico‐thoracic esophagus. Additionally, correlation between target complications and median dose to target (D50) is observed. Quantification of these correlations can inform treatment planners when any competing objectives requires relaxation of target D50 or Dmean (or Dmin) to cervico‐thoracic esophagus.
SU‐E‐T‐75: A Simple Technique for Proton Beam Range Verification
Authors: Burgdorf B , Kassaee A , Garver E 
Published: June 2015

Purpose:To develop a measurement‐based technique to verify the range of proton beams for quality assurance (QA).Methods:We developed a simple technique to verify the proton beam range with in‐house fabricated devices. Two separate devices were fabricated; a clear acrylic rectangular cuboid and a solid polyvinyl chloride (PVC) step wedge. For efficiency in our clinic, we used the rectangular cuboid for double scattering (DS) beams and the step wedge for pencil beam scanning (PBS) beams. These devices were added to our QA phantom to measure dose points along the distal fall‐off region (between 80% and 20%) in addition to dose at mid‐SOBP (spread out Bragg peak) using a two‐dimensional parallel plate chamber array (MatriXX™, IBA Dosimetry, Schwarzenbruck, Germany). This method relies on the fact that the slope of the distal fall‐off is linear and does not vary with small changes in energy. Using a multi‐layer ionization chamber (Zebra™, IBA Dosimetry), percent depth dose (PDD) curves were measured for our standard daily QA beams. The range (energy) for each beam was then varied (i.e. ±2mm and ±5mm) and additional PDD curves were measured. The distal fall‐off of all PDD curves was fit to a linear equation. The distal fall‐off measured dose for a particular beam was used in our linear equation to determine the beam range.Results:The linear fit of the fall‐off region for the PDD curves, when varying the range by a few millimeters for a specific QA beam, yielded identical slopes. The calculated range based on measured point dose(s) in the fall‐off region using the slope resulted in agreement of ±1mm of the expected beam range.Conclusion:We developed a simple technique for accurately verifying the beam range for proton therapy QA programs.
SU‐E‐T‐76: A Software System to Monitor VMAT Plan Complexity in a Large Radiotherapy Centre
Authors: Arumugam S , Xing A , Vial P , Thwaites D , Holloway L 
Published: June 2015

Purpose:To develop a system that analyses and reports the complexity of Volumetric Modulated Arc Therapy (VMAT) plans to aid in the decision making for streamlining patient specific dosimetric quality assurance (QA) tests.Methods:A software system, Delcheck, was developed in‐house to calculate VMAT plan and delivery complexity using the treatment delivery file. Delcheck has the functionality to calculate multiple plan complexity metrics including the Li‐Xing Modulation Index (LI‐MI), multiplicative combination of Leaf Travel and Modulation Complexity Score (LTMCSv), Monitor Units per prescribed dose (MU/D) and the delivery complexity index (MIt) that incorporates the modulation of dose rate, leaf speed and gantry speed. Delcheck includes database functionality to store and compare plan metrics for a specified treatment site. The overall plan and delivery complexity is assessed based on the 95% conformance limit of the complexity metrics as Similar, More or Less complex. The functionality of the software was tested using 42 prostate conventional, 10 prostate SBRT and 15 prostate bed VMAT plans generated for an Elekta linear accelerator.Results:The mean(σ) of LI‐MI for conventional, SBRT and prostate bed plans were 1690(486), 3215.4(1294) and 3258(982) respectively. The LTMCSv of the studied categories were 0.334(0.05), 0.325(0.07) and 0.3112(0.09). The MU/D of the studied categories were 2.4(0.4), 2.7(0.7) and 2.5(0.5). The MIt of the studied categories were 21.6(3.4), 18.2(3.0) and 35.9(6.6). The values of the complexity metrics show that LI‐MI appeared to resolve the plan complexity better than LTMCSv and MU/D. The MIt value increased as the delivery complexity increased.Conclusion:The developed software was shown to be working as expected. In studied treatment categories Prostate bed plans are more complex in both plan and delivery and SBRT is more complex in plan and less complex in delivery as demonstrated by LI‐MI and MIt.This project was funded through a Cancer Council NSW Project Grant (RG14‐11)
SU‐E‐T‐78: A Study of Dose Falloff Gradient in RapidArc Planning of Lung SBRT
Authors: Desai D , Srinivasan S , Elasmar H , Johnson E 
Published: June 2015

Purpose:Rapid dose falloff beyond PTV is an important criterion for normal tissue sparing in SBRT. RTOG protocols use D2cm and R50% for plan quality evaluation. This study is aimed at analyzing the dose falloff gradient beyond the PTV extending into normal tissue structures and to ascertain the impact of PTV geometry and location on the dose falloff gradient in RapidArc planning of lung SBRTMethods:In this retrospective study, we analyzed 39 clinical RapidArc lung SBRT treatment plans that met RTOG‐0915 criteria. Planning was done on Eclipse 8.9 for delivery on either Novalis NTx or TrueBeam STx equipped with HD MLCs. PTV volumes ranged between 5.3 and 113 cc (2.2 to 6 cm sphere equivalent diameter respectively) and their geographic locations were distributed in both lungs. 6X, 6X‐FFF, 10X, and 10X‐FFF energies were used for planning. All of these SBRT plans were planned using either 2 or 3 full or hemi arcs, with moderate couch kicks. Dose falloff gradients were obtained by generating 7 concentric 5 mm rings beyond PTV surface. Mean dose in each ring is used to evaluate percentage dose falloff gradient as a function of distance from the PTV surface.Results:The mean percentage dose falloff beyond PTV surface in all plans followed an exponential decay and the data was modeled with double exponential decay fit. Photon energy selection in the plan had a minimal impact on the mean percentage dose fall off beyond PTV surface.Conclusion:Dose falloff beyond PTV surface as a function of distance can be ascertained by the use of the double exponential decay fit coefficients in RapidArc planning of lung SBRT. This will help also in plan quality evaluation in addition to D2cm and R50% defined by RTOG.
SU‐E‐T‐86: A Systematic Method for GammaKnife SRS Fetal Dose Estimation
Authors: Geneser S , Paulsson A , Sneed P , Braunstein S , Ma L 
Published: June 2015

Purpose:Estimating fetal dose is critical to the decision‐making process when radiation treatment is indicated during pregnancy. Fetal doses less than 5cGy confer no measurable non‐cancer developmental risks but can produce a threefold increase in developing childhood cancer. In this study, we estimate fetal dose for a patient receiving Gamma Knife stereotactic radiosurgery (GKSRS) treatment and develop a method to estimate dose directly from plan details.Methods:A patient underwent GKSRS on a Perfexion unit for eight brain metastases (two infratentorial and one brainstem). Dose measurements were performed using a CC13, head phantom, and solid water. Superficial doses to the thyroid, sternum, and pelvis were measured using MOSFETs during treatment. Because the fetal dose was too low to accurately measure, we obtained measurements proximally to the isocenter, fitted to an exponential function, and extrapolated dose to the fundus of the uterus, uterine midpoint, and pubic synthesis for both the preliminary and delivered plans.Results:The R‐squared fit for the delivered doses was 0.995. The estimated fetal doses for the 72 minute preliminary and 138 minute delivered plans range from 0.0014 to 0.028cGy and 0.07 to 0.38cGy, respectively. MOSFET readings during treatment were just above background for the thyroid and negligible for all inferior positions. The method for estimating fetal dose from plan shot information was within 0.2cGy of the measured values at 14cm cranial to the fetal location.Conclusion:Estimated fetal doses for both the preliminary and delivered plan were well below the 5cGy recommended limit. Due to Pefexion shielding, internal dose is primarily governed by attenuation and drops off exponentially. This is the first work that reports fetal dose for a GK Perfexion unit. Although multiple lesions were treated and the duration of treatment was long, the estimated fetal dose remained very low.
SU‐E‐T‐89: Accuracy of Absolute Three‐Dimensional Dose Distribution Measurement Using the Delta4
Authors: Uehara R , Tachibana H , Ohyoshi H , Matsumoto S , Baba H , Tanaka F , Ariji T 
Published: June 2015

Purpose:In this study, we investigated the accuracy of the absolute dose distribution measurement using the Delta4 phantom compared to the measurements using a ionization chamber and EDR2 filmMethods:Several conventional and intensity‐modulated radiation therapy plans were used to compare the dose distribution measured using the Delta4 phantom to the absolute point dose using the chamber and the relative two‐dimensional dose distribution using the EDR2 film. For the absolute dose distribution evaluation, the measurements using the Delta4, the chamber and the film were performed in similar measurement geometry. For point dose measurement using the chamber, an acrylic slab phantom with the PTW Semiflex chamber was inserted into the Delta4 phantom, alternative to the Delta4 main unit. Similarly, for dose distribution measurement using the film, the EDR2 film sandwiched with two acrylic slab phantoms were inserted to the phantom. Dose difference and gamma analysis were done for point dose and relative dose distribution comparisons, respectively.Results:The point dose measurements show slight negative systematic dose difference of −0.5 ± 0.1% and −1.0 ± 0.4% in the conventional and the IMRT plans, respectively. The additional measurement for direction dependency for Delta4 shows similar negative systematic dose difference even the phantom analysis software consider the directional dependency. The pass rate of the gamma evaluation was 77.7 ± 5.8% and 88.8±3.3% in the conventional and the IMRT plans, respectively.Conclusions:The Delta4 phantom shows a 1%‐systematic dose difference derived from directional dependency and lower resolution compared to the film. Thus it is necessary to comprehensively evaluate the phantom to verify the IMRT/VMAT plans. Especially, the dosimetry tool is needed to have high resolution and high measurement accuracy in IMRT/VMAT‐SBRT plan with small fields using intensity modulation in which the analysis area is limited and the higher correspondence between calculation and measurement is needed.
SU‐E‐T‐92: Achieving Desirable Lung Doses in Total Body Irradiation Based On in Vivo Dosimetry and Custom Tissue Compensation
Authors: Cui G , Shiu A , Zhou S , Cui J , Ballas L 
Published: June 2015

Purpose:To achieve desirable lung doses in total body irradiation (TBI) based on in vivo dosimetry and custom tissue compensation.Methods:The 15 MV photon beam of a Varian TrueBeam STx linac was used for TBI. Patients were positioned in the lateral decubitus position for AP/PA treatment delivery. Dose was calculated using the midpoint of the separation distance across the patient's umbilicus. Patients received 200 cGy twice daily for 3 days. The dose rate at the patient's midplane was approximately 10 cGy/min. Cerrobend blocks with a 5‐HVL thickness were used for the primary lung shielding. A custom styrofoam holder for rice‐flour filled bags was created based on the lung block cutouts. This was used to provide further lung shielding based on in vivo dose measurements. Lucite plates and rice‐flour bags were placed in the head, neck, chest, and lower extremity regions during the treatment to compensate for the beam off‐axis output variations. Two patients were included in the study. Patients 1 and 2 received a craniospinal treatment (1080 cGy) and a mediastinum treatment (2520 cGy), respectively, before the TBI. During the TBI nanoDot dosimeters were placed on the patient skin in the forehead, neck, umbilicus, and lung regions for dose monitoring. The doses were readout immediately after the treatment. Based on the readings, fine tuning of the thickness of the rice‐flour filled bags was exploited to achieve the desirable lung doses.Results:For both patients the mean lung doses, which took into consideration all treatments, were controlled within 900 +/−10% cGy, as desired. Doses to the forehead, neck, and umbilicus were achieved within +/−10% of the prescribed dose (1200 cGy).Conclusion:A reliable and robust method was developed to achieve desirable lung doses and uniform body dose in TBI based on in vivo dosimetry and custom tissue compensator.
SU‐E‐T‐93: Activation of Psoralen at Depth Using Kilovoltage X‐Rays: Physics Considerations in Implementing a New Teletherapy Paradigm
Authors: Adamson J , Nolan M , Gieger T , Walder H , Yoon P , Fathi Z , Beyer W , Liu L , Alcorta D , Spector N , Oldham M 
Published: June 2015

Purpose:Psoralen is a UV‐light activated anti‐cancer biotherapeutic used for treating skin lesions (PUVA) and advanced cutaneous T‐cell lymphoma (ECP). To date psoralen has not been used to treat deep seated tumors due to difficulty in generating UV‐light at depth. We recently demonstrated psoralen activation at depth by introducing energy converting particles that absorb kV x‐ray radiation and re‐emit UV‐light. Our in‐vitro work found that 0.2–1Gy using 40–100kVp x‐rays combined with psoralen and particles can induce a substantial apoptotic response beyond that expected from the sum of individual components. In preparation for a phase I clinical trial of canine companion animals, we address the physics and dosimetry considerations for applying this new teletherapy paradigm to an in‐vivo setting.Methods:The kV on‐board imaging (OBI) system mounted on a medical linear accelerator (Varian) was commissioned to deliver the prescribed dose (0.6Gy) using 80 and 100kVp. Dosimetric measurements included kVp, HVL, depth dose, backscatter factors, collimator and phantom scatter factors, field size factors, and blade leakage. Absolute dosimetry was performed following AAPM TG61 recommendations and verified with an independent kV dose meter. We also investigated collimated rotational delivery to minimize skin dose using simple dose calculations on homogeneous cylindrical phantoms.Results:Single beam delivery is feasible for shallow targets (<5cm) without exceeding skin tolerance, while a rotational delivery may be utilized for deeper targets; skin dose is ∼75% of target dose for 80kVp collimated rotational delivery to a 3cm target within a 20cm phantom. Heat loading was tolerable; 0.6Gy to 5cm can be delivered before the anode reaches 75% capacity.Conclusion:KV teletherapy for Psoralen activation in deep seated tissue was successfully commissioned for a Varian OBI machine for use in a phase I clinical trial in canines. Future work will use Monte Carlo dosimetry to investigate dose in presence of bone.Research funded by Immunolight LLC. H. Walder, Z. Fathi, & W. Beyer are employees of Immunolight LLC which holds a patent on the technology. Drs. Adamson and Oldham are consultants to Immunolight LLC.
SU‐E‐T‐99: An Analysis of the Accuracy of TPS Extrapolation of Commissioning Data
Authors: Alkhatib H , Oves S , Gebreamlak W , Mihailidis D 
Published: June 2015

Purpose:To investigate discrepancies between measured percent depth dose curves of a linear accelerator at depths beyond the commissioning data and those generated by the treatment planning system (TPS) via extrapolation.Methods:Relative depth doses were measured on an Elekta Synergy™ linac for photon beams of 6 ‐MV and 10‐MV. SSDs for all curves were 100‐cm and field sizes ranged from 4×4 to 35×35‐cm2. As most scanning tanks cannot provide depths greater than about 30‐cm, percent depth dose measurements, extending 45‐cm depths, were performed in Solid Water™ using a 0.125‐cc ionization chamber (PTW model TN31012). The buildup regions of the curves were acquired with a parallel plate chamber (PTW model TN34001). Extrapolated curves were generated by the TPS (Phillips Pinnacle3 v. 9.6) by applying beams to CT images of 50‐cm of Solid Water™ with density override set to 1.0‐g/cc.Results:Percent difference between the two sets of curves (measured and TPS) was investigated. There is significant discrepancy in the buildup region to a depth of 7‐mm. Beyond this depth, the two sets show good agreement. When analyzing the tail end of the curves, we saw percent difference of between 1.2% and 3.2%. The highest disagreement for the 6‐MV curves was 10×10‐cm2 (3%) and for the 10‐MV curves it was the 35×35‐cm2 (3.2%).Conclusion:A qualitative analysis of the measured data versus PDD curves generated by the TPS shows generally good agreement beyond 1‐cm. However, a measurable percent difference was observed when comparing curves at depths beyond that provided by the commissioning data and at depths in the buildup region. Possible explanations for this include inaccuracies in modeling of the Solid Water™ or drift in beam energy since commissioning. Additionally, closer attention must be paid for measurements in the buildup region.
SU‐E‐T‐100: An Approach to Improving the Dynamic Delivery Accuracy for Breast IMRT
Authors: Grigorov G , Darko J , Kitor M , Redekop R , Osei E 
Published: June 2015

Purpose:A method is established to improve the accuracy of the IMRT dose delivery for the treatment of breast and chest wall tumors when the higher dose gradient is delivered at the end of the leaf sequence.Methods:Dynamic MLC deliveries on Varian Linacs are achieved through the motion of the leaves from X1 to X2 direction. If the higher dose gradient is at the end of the leaf motion sequence, this can Result in an increased error in the overall dose delivery. Such errors have been observed in Lateral beams for Left‐sided and Medial beams for Right‐sided treatments. To evaluate and resolve this issue we adopted an approach where the fluence for such beams was geometrically flipped (mirrored) to treat the higher end of the dose gradient first.Results:Using this method, it was possible to deliver the optimized dose map to the area of interest still using only the X1–X2 direction of the leaf motion. The accuracy of this method was tested on different beam as part of our pre‐treatment QA program on both Varian delivery systems. With this approach we found that there was significant improvement in delivery accuracy on both 21EX and TrueBeam systems. Beams of initial Gamma index (3% and 3mm) 89–93% were increased to 98–99%. We also observed superior delivery accuracy with TB compared to the 21EXConclusion:This work demonstrate the need for a delivery sequence option from X2–X1 in situations where the MLC sequence indicates higher dose gradient component is being delivered at the end of the sequence. Results from this work can be considered in the IMRT beam optimization in the treatment planning systems. Further work will be required to establish the application of this approach in clinical setting.