bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐54: A New Method for Optimizing Radiation Isocenter for Linac‐Based SRS
Authors: Hancock S , Hyer D , Nixon E
Published: June 2015

Purpose:

To develop a new method to minimize deviation of linac x‐ray beams from the centroid of the volumetric radiation isocenter for all combinations of gantry and table angle.

Methods:

A set of ball‐bearing (Winston‐Lutz) images was used to determine the gantry radiation isocenter as the midrange of deviation values. Deviations in the cross‐plane direction were minimized by calibration of MLC leaf position offset, and by adjusting beam position steering for each energy. Special attention was also paid to matching the absolute position of isocenter across all energies by adjusting position steering in the gun‐target axis. Displacement of table axis from the gantry isocenter, and recommended table axis adjustment for contemporary Elekta linacs, was also determined. Eight images were used to characterize the volumetric isocenter for the full range of gantry and table rotations available. Tabulation of deviation for each beam was used to test compliance with isocenter tolerance.

Results:

Four contemporary Elekta linacs were evaluated and the radius in the gun‐target axis of the radiation isocenter was 0.5 to 0.7 mm. After beam steering adjustment, the radius in the cross‐plane direction was typically 0.2 to 0.4 mm. Position matching between energies can be reduced to 0.28 mm. Maximum total deviation was 0.68 to 1.07 mm, depending primarily on the effect of systematic table axis wobble with rotation.

Conclusion:

This new method effectively facilitates minimization of deviation between beam center and target position. The test, which requires a few minutes to perform, can be easily incorporated into a routine machine QA program. A tighter radiation isocenter for contemporary Elekta linacs would require reducing the effect of gantry arm flex and/or table axis wobble that are the two main components of deviation from the designated isocenter point.
SU‐E‐T‐57: A Novel Method to Improve Dose Heterogeneity of Target and Organs at Risk Sparing in the Intensity‐Modulated Radiotherapy for Stage III Lung Cancer
Authors: Huang B‐T , Lu J‐Y
Published: June 2015

Purpose:

Intensity‐modulated radiotherapy (IMRT) treatment for lung cancer is difficult due to the heterogeneous dose distribution and excessive dose to the organs at risk (OARs). We introduce a simple method based on the base dose function (BDF) in Eclipse treatment planning system to overcome the difficulties.

Methods:

Thirteen patients suffered from stage III non‐small cell lung cancer (NSCLC) were enrolled in the study. Three kinds of approaches were applied to obtain clinically acceptable treatment plans: 1) conventionally optimizing method with hot and cold spots re‐optimization (CO); 2) target‐divided optimizing method (TDO) in which the optimization objective in the lung density of planning target volume (PTV) was set to 2 to 4 Gy higher than in the soft tissue density; 3) base dose function (BDF) in which the treatment plan was produced based on the original plan for re‐optimization. CO, TDO and BDF methods were then compared in terms of conformity index (CI), homogeneity index (HI), OARs sparing and monitor units (MUs). Additionally, delta4, portal dosimetry and IMSure were used to measure the dose delivering accuracy.

Results:

The BDF technique provided more superior CI and HI than the other two methods. Moreover, the new method also reduced the lung, esophagus, heart and spinal cord dose. However, the BDF plans needed extra 15% and 10% MUs than the CO and TDO methods. Dose verification results demonstrated good and comparable γ pass rates among the three methods.

Conclusion:

The proposed BDF method greatly improves the dose homogeneity and OARs sparing in the IMRT treatment for lung cancer.
SU‐E‐T‐63: A Preliminary Study of Gold Nanoparticles Enhanced Cone Beam Computed Tomography
Authors: Chen K , Sha H , Yang Y
Published: June 2015

Purpose:

Gold nanoparticles (GNPs) have potential of being used as a new‐generation contrast agent to enhance CT imaging of cancer. This feasibility study is to determine the GNP concentration required to provide sufficient image contrast in small animal cone beam CT (CBCT) imaging.

Methods:

The GNPs used are nanorods with 10nm diameter and 44nm length. A 50µl GNP colloid with an original GNP concentration of 3.6mg/ml was diluted to five different concentrations at 2.4, 2.1, 2.0, 1.9 and 1.8mg/ml, respectively. The GNP colloid was enclosed in a 150µl vial, and the GNP colloid vial was submerged in a water bottle for CBCT. CBCTs were acquired with x‐ray energy of 65kVp and tube current of 1.5mA. In addition, to evaluate the optimal x‐ray energy for GNP detection in CBCT, the GNP colloid of 1.8mg/ml was also imaged at x‐ray energy of 45kVp and 85kVp. Regions of interest were placed in axial CBCT slices contouring the GNP colloid volume and a same volume in the surrounding water to calculate the signal and contrast.

Results:

For the GNP colloid at concentrations of 3.6, 2.4, 2.1, 2.0, 1.9 and 1.8mg/ml, the image contrasts between GNP colloid and water were 68±4, 33±4, 23±3, 20±3, 13±4, and 10±3 HU, respectively. At 1.8mg/ml concentration level, the image contrasts were 16±3 and 7±4 HU, respectively, when the x‐ray energy was set at 45kVp and 85kVp.

Conclusion:

The minimal GNP concentration required on our small animal CBCT was estimated to be around 1.8mg/ml due to the fact that the minimum image contrast for adequate differentiation in CT is about 8 HU. CBCT at lower x‐ray energy, i.e. 45kVp, can provide better image contrast than at higher energies, i.e., 65kVp and 85kVp. A study of GNP enhanced CBCT for in vivo small animal imaging is ongoing efforts in our group.
SU‐E‐T‐65: A Prospective Trial of Open Face Masks for Head and Neck Radiotherapy
Authors: Wiant D , Squire S , Maurer J , Liu H , Hayes L , Sintay B
Published: June 2015

Purpose:

Open face head and neck masks allow for active patient monitoring during treatment and may reduced claustrophobia and anxiety compared to closed masks. The ability of open masks to limit intrafraction motion and to preserve the patient shape/position from simulation over protracted treatments should be considered.

Methods:

Thirty‐two head and neck patients were prospectively randomized to treatment in a closed mask or a novel open face mask. All patients received daily volumetric imaging. The daily images were automatically rigidly registered to the planning CT's offline using a commercial image processing tool. The shifts needed to optimize the registration, the mutual information coefficient (MI), and the Pearson correlation (PC) coefficients were recorded to evaluate shape preservation. The open group was set‐up and monitored with surface imaging at treatment. The real time surface imaging information was recorded to evaluate intrafraction motion.

Results:

Sixteen patients were included in each group. Evaluations were made over a total of 984 fractions. The mean MI and PC showed significantly higher shape preservation for the open group than for the closed group (p = 0). The mean rotations for the open group were smaller or < 0.15° larger versus the closed group. The mean intrafraction motion for the open group was 0.93 +/−0.99 mm (2 SD). The maximum single fraction displacement was 3.2 mm. Fourteen of 16 patients showed no significant correlation of motion with fraction number (p > 0.05).

Conclusion:

The open masks preserved shape as well as the closed masks, and they limited motion to < 2 mm for 95% of the treated fractions. These results are consistent over treatment courses of up to 35 fractions. The open mask is suitable for treatment with or without active monitoring.

This work was partially supported by Qfix.
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 SBRT

Methods:

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 film

Methods:

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 21EX

Conclusion:

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.
SU‐E‐T‐108: An Investigation of Cerenkov Light Production in the Exradin W1 Scintillator Under Various Measurement Conditions
Authors: Simiele E , Culberson W
Published: June 2015

Purpose:

To investigate the effects of depth, fiber‐optic cable bends, and incident radiation angle on Cerenkov production in the Standard Imaging Exradin W1.

Methods:

Measurements were completed using a Varian Clinac 21EX linear accelerator with an Exradin W1 scintillator as well as a cable‐only scintillator (no scintillation material) to isolate the Cerenkov signal. The effects of cable bend radius and location were investigated by bending the fiber‐optic cable into a circle with radii ranging from 1.0 to 10.8 cm and positioning the center of the coil at distances ranging from 10.0 to 175.0 cm from the photodiode. The effects of depth and incident radiation angle were investigated by performing measurements in water at depths ranging from 1.0 cm to 25.0 cm and angles ranging from 0° to 80°. Eclipse treatment‐planning software was utilized to ensure a consistent dose was delivered to the W1 regardless of depth or angle.

Results:

Measured signal in both channels of the cable‐only scintillator decreased as the bend radius decreased and as the distance between the bend and photodiode increased. A fiber bend of 1.0 cm radius produced a 17.1% decrease in the green channel response in the cable‐only scintillator. The effect of depth was less severe; a maximum increase of 6.6% in the green channel response was observed at a depth of 25.0 cm in the W1. In the angular dependence investigation, the signal in both channels of the W1 peaked at an angle of 40°; which is in agreement with the nominal Cerenkov emission angle of 45°.

Conclusion:

The green channel response in the W1 (mainly Cerenkov signal) varied with depth, fiber‐optic cable bends, and incident radiation angle. Fully characterizing Cerenkov production is essential to ensure it is properly accounted for in scintillator measurements.

Research funding and materials received by Standard Imaging, Inc. (Middleton WI)
SU‐E‐T‐132: Assess the Shielding of Secondary Neutrons From Patient Collimator in Proton Therapy Considering Secondary Photons Generated in the Shielding Process with Monte Carlo Simulation
Authors: Yamanaka M , Takashina M , Kurosu K , Moskvin V , Das I , Koizumi M
Published: June 2015

Purpose:

In this study we present Monte Carlo based evaluation of the shielding effect for secondary neutrons from patient collimator, and secondary photons emitted in the process of neutron shielding by combination of moderator and boron‐10 placed around patient collimator.

Methods:

The PHITS Monte Carlo Simulation radiation transport code was used to simulate the proton beam (Ep = 64 to 93 MeV) from a proton therapy facility. In this study, moderators (water, polyethylene and paraffin) and boron (pure 1⁰B) were placed around patient collimator in this order. The rate of moderator and boron thicknesses was changed fixing the total thickness at 3cm. The secondary neutron and photons doses were evaluated as the ambient dose equivalent per absorbed dose [H*(10)/D].

Results:

The secondary neutrons are shielded more effectively by combination moderators and boron. The most effective combination of shielding neutrons is the polyethylene of 2.4 cm thick and the boron of 0.6 cm thick and the maximum reduction rate is 47.3 %. The H*(10)/D of secondary photons in the control case is less than that of neutrons by two orders of magnitude and the maximum increase of secondary photons is 1.0 µSv/Gy with the polyethylene of 2.8 cm thick and the boron of 0.2 cm thick.

Conclusion:

The combination of moderators and boron is beneficial for shielding secondary neutrons. Both the secondary photons of control and those emitted in the shielding neutrons are very lower than the secondary neutrons and photon has low RBE in comparison with neutron. Therefore the secondary photons can be ignored in the shielding neutrons.This work was supported by JSPS Core‐to‐Core Program (No.23003).

This work was supported by JSPS Core‐to‐Core Program (No.23003).
SU‐E‐T‐195: Commissioning the Neutron Production of a Varian TrueBeam Linac
Authors: Irazola L , Brualla L , Rosello J , Terron JA , Sanchez‐Nieto B , Bedogni R , Sanchez‐Doblado F
Published: June 2015

Purpose:

The purpose of this work is the characterization of a new Varian TrueBeam™ facility in terms of neutron production, in order to estimate neutron equivalent dose in organs during radiotherapy treatments.

Methods:

The existing methodology [1] was used with the reference SRAMnd detector, calibrated in terms of thermal neutron fluence at the reference field operated by PTB (Physikalisch‐Technische‐Bundesanstalt) at the GeNF (Geesthacht‐Neutron‐Facility) with the GKSS reactor FRG‐1 [2]. Thermal neutron fluence for the 5 available possibilities was evaluated: 15 MV and 10&6 MV with and without Flattening Filter (FF and FFF, respectively). Irradiation conditions are as described in [3]. In addition, three different collimator‐MLC configurations were studied for 15 MV: (a) collimator of 10×10 cm2 and MLC fully retracted (reference), (b) field sizes of 20×20 cm2 and 10×10 cm2 for collimator and MLC respectively, and (c) collimator and MLC aperture of 10×10 cm2.

Results:

Thermal fluence rate at the “reference point” [3], as a consequence of the neutron production, obtained for (a) conformation in 15 MV is (1.45±0.11) x10⁴ n•cm2/MU. Configurations (b) and (c) gave fluences of 96.6% and 97.8% of the reference (a). Neutron production decreases up to 8.6% and 5.7% for the 10 MV FF and FFF beams, respectively. Finally, it decreases up to 2.8% and 0.1% for the 6 MV FF and FFF modes, respectively.

Conclusion:

This work evaluates thermal neutron production of Varian TrueBeam™ system for organ equivalent dose estimation. The small difference in collimator‐MLC configuration shows the universality of the methodology [3]. A decrease in this production is shown when decreasing energy from 15 to 10 MV and an almost negligible production was found for 6 MV. Moreover, a lower neutron contribution is observed for the FFF modes.[1]Phys Med Biol,2012;57:6167–6191.[2]Radiat Meas,2010;45:1513–1517.[3]Med Phys,2015;42:276–281.
SU‐E‐T‐205: Comparison of Dose‐Volume and Dose‐Mass 4D Inverse Optimization in NSCLC
Authors: Mihaylov I , Moros E
Published: June 2015

Purpose:

To compare dose‐volume (Dvh) and dose‐mass (Dmh) inverse treatment planning results, performed on time‐resolved (4D) CT scans for non‐small cell lung cancers (NSCLC), thereby accounting for the temporal variation in lung volume and mass.

Methods:

Ten NSCLC cases were retrospectively studied. The estimated range of tumor motion was in excess of 0.5 cm (0.7 cm to 1.8 cm) in at least one principal direction. For each case five phases, uniformly distributed over the breathing cycle, were chosen for planning. For each of the phases two IMRT plans, with Dvh and with Dmh quadratic objective cost function applied only for the organs at risk (OARs), were generated. Pure dose objective functions were used for the targets. The final dose in each case for each optimization scheme was achieved through a deformable dose accumulation over the five breathing phases. Plan quality of Dvh and Dmh optimization was evaluated by several dose indices (DIs), represented by the dose to certain volume of an OAR. Tallied DIs were cord1%, heart33%, lungs20%, lungs30%, and esophagus50%, as well as lung volumes encompassed by 20 Gy and 30 Gy isodose lines. Statistical significance in the differences among those indices was quantified with two‐tailed paired t‐tests with a significance level of 5%.

Results:

On average Dmh optimized plans outperformed the 4D Dvh optimized plans. The statistically significant dose reduction in cord DI1, heart DI33, esophagus DI50, lung DI20 and DI30 were 27.5%, 9.9%, 21.3%, 5.6%, and 14.7% respectively. Isovolumes of 20 Gy and 30 Gy differed by 9.6% and 6.7% respectively.

Conclusions:

The presented findings suggest that on average 4D Dmh optimized plans Result in better OAR sparing than 4D Dvh optimized plans. This is true for the majority of the tallied dosimetric endpoints, indicating that the potential sparing and its magnitude are patient specific.

NIH
SU‐E‐T‐213: Comparison of Treatment Efficiency of Gamma Knife SRS Plans for Brain Metastases with Different Planning Methods
Authors: Feng Y , Huang Z , Lo S , Mayr N , Yuh W
Published: June 2015

Purpose:

To improve Gamma Knife SRS treatment efficiency for brain metastases and compare the differences of treatment time and radiobiological effects between two different planning methods of automatic filling and manual placement of shots with inverse planning.

Methods:

T1‐weighted MRI images with gadolinium contrast from five patients with a single brain metastatic‐lesion were used in this retrospective study. Among them, two were from primary breast cancer, two from primary melanoma cancer and one from primary prostate cancer. For each patient, two plans were generated in Leksell GammaPlan10.1.1 for radiosurgical treatment with a Leksell GammaKnife Perfexion machine: one with automatic filling, automatic sector configuration and inverse optimization (Method1); and the other with manual placement of shots, manual setup of collimator sizes, manual setup of sector blocking and inverse optimization (Method2). Dosimetric quality of the plans was evaluated with parameters of Coverage, Selectivity, Gradient‐Index and DVH. Beam‐on Time, Number‐of‐Shots and Tumor Control Probability(TCP) were compared for the two plans while keeping their dosimetric quality very similar. Relative reduction of Beam‐on Time and Number‐of‐Shots were calculated as the ratios among the two plans and used for quantitative analysis.

Results:

With very similar dosimetric and radiobiological plan quality, plans created with Method 2 had significantly reduced treatment time. Relative reduction of Beam‐on Time ranged from 20% to 51 % (median:29%,p=0.001), and reduction of Number‐of‐Shots ranged from 5% to 67% (median:40%,p=0.0002), respectively. Time of plan creation for Method1 and Method2 was similar, approximately 20 minutes, excluding the time for tumor delineation. TCP calculated for the tumors from differential DVHs did not show significant difference between the two plans (p=0.35).

Conclusion:

The method of manual setup combined with inverse optimization in LGP for treatment of brain metastatic lesions with the Perfexion can achieve significantly higher time efficiency without degrading treatment quality.
SU‐E‐T‐216: Comparison of Volumetrically Modulated Arc Therapy Treatment Using Flattening Filter Free Beams Vs. Flattened Beams for Partial Brain Irradiation
Authors: Yu S , Roa D , Hanna N , Sehgal V , Farol H , Kuo J , Daroui P , Ramsinghani N , Al‐Ghazi M
Published: June 2015

Purpose:

Flattening Filter Free (FFF) beams offer the potential for higher dose rates, short treatment time, and lower out of field dose. Therefore, the aim of this study was to investigate the dosimetric effects and out of field dose of Volumetric Modulated Arc Therapy (VMAT) plans using FFF vs Flattening Filtering (FF) beams for partial brain irradiation.

Methods:

Ten brain patients treated with a 6FF beam from a Truebeam STX were analyzed retrospectively for this study. These plans (46Gy at 2 Gy per fraction) were re‐optimized for 6FFF beams using the same dose constraints as the original plans. PTV coverage, PTV Dmax, total MUs, and mean dose to organs‐at‐risk (OAR) were evaluated. In addition, the out‐of‐field dose for 6FF and 6FFF plans for one patient was measured on an anthropomorphic phantom. TLDs were placed inside (central axis) and outside (surface) the phantom at distances ranging from 0.5 cm to 17 cm from the field edge. Paired T‐test was used for statistical analysis.

Results:

PTV coverage and PTV Dmax were comparable for the FF and FFF plans with 95.9% versus 95.6% and 111.2% versus 111.9%, respectively. Mean dose to the OARs were 3.7% less for FFF than FF plans (p<0.0001). Total MUs were, on average, 12.5% greater for FFF than FF plans with 481±55 MU (FFF) versus 429±50 MU (FF), p=0.0003. On average, the measured out of field dose was 24% less for FFF compared to FF, p<0.0001. A similar beam‐on time was observed for the FFF and FF treatment.

Conclusion:

It is beneficial to use 6FFF beams for regular fractionated brain VMAT treatments. VMAT treatment plans using FFF beams can achieve comparable PTV coverage but with more OAR sparing. The out of field dose is significant less with mean reduction of 24%.
SU‐E‐T‐218: Comprehensive Plan Integrity and Quality Check by Accessing Eclipse Planning Data Remotely Via a Novel Eclipse‐API Client‐Server Interface
Authors: Yang D , Wu Y , He G , Chang X , Olsen L , Mutic S
Published: June 2015

Purpose:

It is desirable to seamlessly and remotely access treatment plan data in Eclipse in order to allow sequential treatment planning and quality assurance automation, e.g. automatic plan quality check and comprehensive plan integrity check. The manual DICOM export function and the native Eclipse SQL interface cannot fully support the needs. Therefore we have developed a procedure and computer programs to enable access of Eclipse planning data remotely, and directly from Eclipse server, via Eclipse API, so to support such clinical software applications requiring advanced mathematics and extensive computation.

Methods:

A novel client‐server interface was developed to allow external software programs to remotely and seamlessly access the Eclipse planning data using Eclipse‐API from outside the Eclipse workstations. Remote (client) programs send requests as network socket messages to the server program running on an Eclipse workstation, and the server program uses Eclipse‐API functions to access planning data, and sends data back to the client programs.

Results:

The Eclipse‐API client‐server interface were implemented and successfully tested in clinical settings. Comprehensive plan integrity and quality check programs, which were previously supporting Pinnacle TPS only, have been extended to support Eclipse and are executable on any network computer in the department independent of Eclipse installation. Advanced plan check features, e.g. IMRT optimization structure overlapping check, on‐the‐fly derivation of new structures in planning quality check, that were previously not possible in C# programs via Eclipse‐API, have now been implemented, allowed by the inclusion of advanced mathematics packages e.g. MATLAB in the external programs.

Conclusion:

The new Eclipse‐API client‐server interface has enabled Eclipse data to be accessed remotely and seamlessly. It has the potential to significantly improve the comprehensiveness of third party software programs based on Eclipse‐API for both clinical and research purposes, and would be useful to extend the Eclipse / ARIA ecosystem.

This work was partially funded by Varian Medical System
SU‐E‐T‐228: Coupling Database Search with Atlas‐Based Segmentation: Application to Esophageal Delineation
Authors: Schreibmann E , Elder E
Published: June 2015

Purpose:

Atlas segmentation is a popular method of warping a pre‐segmented template to a new patient anatomy, however for anatomy in the thorax and abdomen large inter‐patient variations exists, and a single template does not provide the required clinical accuracy. With the proposed method the CT dataset to be segmented is matched to a similar case in a database of pre‐segmented templates.

Method:

The key aspect of the approach is to search in a database of images and associated segmentations for a case with similar anatomy. A set of 29 previous cases have been pre‐registered to a common reference and cropped to the esophageal region to construct a compact representation of the database through quantification with a principal component analysis algorithm that is designed to find similar cases by direct comparison of the eigenvectors for ranking database cases according to the similarity with the query case. Once a similar case at image level is identified in the database, an affine registration is performed to transfer the pre‐segmentations from the database to the images to be segmented.

Results:

The algorithm was applied for segmenting the esophageal region on 12 test cases and the conformity between the atlas and manual segmentations were measured using the Dice coefficient and the Euclidian distance. Dice coefficients ranged between (0.60, 0.87) with mean of 0.78 and standard deviation of 0.09. Mean distance ranged between (0.18,1.66) mm mean of 0.82 mm, SD of 0.51. Once registered to the database, searching in the database takes seconds as it does not compare the images directly but just the components of the PCA vectors, adding little overhead to the overall delineation algorithm.

Conclusions:

Selection of a similar atlas from a database can be achieved with little computational overhead by using a PCA‐based similarity metric as demonstrated for esophageal segmentation.