bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐T‐266: Dynalogs Based Evaluation of Different Dose Rate IMRT Using DVH and Gamma Index
Authors: Ahmed S , Ahmed S , Ahmed F , Hussain A
Published: July 2016

Purpose:

This work investigates the impact of low and high dose rate on IMRT through Dynalogs by evaluating Gamma Index and Dose Volume Histogram.

Methods:

The Eclipse™ treatment planning software was used to generate plans on prostate and head and neck sites. A range of dose rates 300 MU/min and 600 MU/min were applied to each plan in order to investigate their effect on the beam ON time, efficiency and accuracy. Each plan had distinct monitor units per fraction, delivery time, mean dose rate and leaf speed. The DVH data was used in the assessment of the conformity and plan quality.The treatments were delivered on Varian™ Clinac 2100C accelerator equipped with 120 leaf millennium MLC. Dynalogs of each plan were analyzed by MATLAB™ program. Fluence measurements were performed using the Sun Nuclear™ 2D diode array and results were assessed, based on Gamma analysis of dose fluence maps, beam delivery statistics and Dynalogs data.

Results:

Minor differences found by adjusted R‐squared analysis of DVH's for all the plans with different dose rates. It has been also found that more and larger fields have greater time reduction at high dose rate and there was a sharp decrease in number of control points observed in dynalog files by switching dose rate from 300 MU/min to 600 MU/min. Gamma Analysis of all plans passes the confidence limit of ≥95% with greater number of passing points in 300 MU/min dose rate plans.

Conclusion:

The dynalog files are compatible tool for software based IMRT QA. It can work perfectly parallel to measurement based QA setup and stand‐by procedure for pre and post delivery of treatment plan.
SU‐F‐T‐304: Complex Multi‐PTV Treatment Evaluation Using a Remotely Processed 3D Gel Dosimeter
Authors: Hoisak J , Dragojevic I , Sutlief S
Published: July 2016

Purpose:

A new 3D gel dosimeter (ClearView™, Modus Medical Systems) was investigated for use as a QA tool for stereotactic radiosurgery (SRS) plans exhibiting high dose gradients and spatially separated treatment targets. The unique feature of this gel dosimeter is the remote processing service provided by Modus Medical Systems.

Methods:

The gel dosimeters were filled in either 10 cm diameter or 15 cm diameter clear plastic jars. The jars were then shipped in ice‐cooled containers to our department for irradiation. Clinical SRS plans for treatment of multiple metastases and plans with simulated concave structures were applied to a CT scan of the gel dosimeter. The gel was irradiated in treatment position using modulated arcs and then returned in the cooled container for processing. The 3D gel dose was compared to the DICOM‐RT dose from the treatment plan to assess dosimetric and geometric agreement.

Results:

There was no discernible difference between the planned and measured dose for dose gradients as high as 10%/mm, which was the highest gradient we evaluated. Geometric agreement for distant metastases separated by 6 cm was within 1.5 mm. Among three identically irradiated gels using a plan intended for nine metastases, the 3%/3mm gamma passing rate was 84.5% with a range of 14.7%, measured over the entire volume of the dosimeter. Regions of larger gamma values correlated with geometric offsets between the planned and measured data.

Conclusion:

The gel dosimeter exhibits the dosimetric and geometric characteristics necessary for 3D evaluation of treatment plan deliverability. The range of observed gamma passing rates suggests a high sensitivity to geometric registration. With proper management of geometric registration between planned and measured data, this service should enable a radiation oncology department to use 3D dosimetry in end‐to‐end testing or patient plan delivery QA without the expense of an in‐house processing system.
SU‐F‐T‐309: Radiochromic Film Calibration Rescaling for Patient‐Specific CyberKnife MLC QA
Authors: McCaw T , Jang S , Huq M
Published: July 2016

Purpose:

This work investigated the development of EBT3 film as a function of dose rate, and also the accuracy of a commercial calibrationrescaling analysis method, to determine potential application to patientspecific QA of CyberKnife MLC treatments.

Methods:

EBT3 films were exposed to 300cGy at dose rates ranging from 5–300cGy/min, and scanned repeatedly from 2–5760min after exposure using a flatbed scanner. All other films were scanned 1 and 24hr after exposure. Ten calibration films were exposed to doses between 0 and 800cGy. Four verification films were exposed to doses between 80 and 290cGy, and 0 to 30min later, reference films were exposed to 450cGy. The verification and reference films were scanned together and analyzed both with and without calibration rescaling. The dose distribution of a 36min treatment plan was measured. Immediately prior to the measurement, a reference film was exposed. Both films were scanned together and analyzed both with and without calibration rescaling.

Results:

The development of EBT3 film is linear with the logarithm of time after exposure. If the midpoint of the exposure duration is taken as time zero, then film development is independent of dose rate. The doses measured with the verification films agreed with the expected dose within 1‐ 2% with calibration rescaling for all reference films. The delay between the exposure of the reference and QA films was 24min relative to the midpoint of exposure. Analysis of the scan at 60min post‐exposure using rescaling of the calibration at 24hr had a gamma passing rate of 92% with 2%/1mm criteria, consistent with analysis of the scan at 24hr post‐exposure without calibration rescaling.

Conclusion:

Using calibration rescaling, measured doses were accurate within 1–2% 60min after exposure. If the midpoint of exposure is taken as time zero, then calibration rescaling can be applied to patient‐specific QA for CyberKnife MLC treatments.
SU‐F‐T‐310: Does a Head‐Mounted Ionization Chamber Detect IMRT Errors?
Authors: Wegener S , Herzog B , Sauer O
Published: July 2016

Purpose:

The conventional plan verification strategy is delivering a plan to a QA‐phantom before the first treatment. Monitoring each fraction of the patient treatment in real‐time would improve patient safety. We evaluated how well a new detector, the IQM (iRT Systems, Germany), is capable of detecting errors we induced into IMRT plans of three different treatment regions. Results were compared to an established phantom.

Methods:

Clinical plans of a brain, prostate and head‐and‐neck patient were modified in the Pinnacle planning system, such that they resulted in either several percent lower prescribed doses to the target volume or several percent higher doses to relevant organs at risk. Unaltered plans were measured on three days, modified plans once, each with the IQM at an Elekta Synergy with an Agility MLC. All plans were also measured with the ArcCHECK with the cavity plug and a PTW semiflex 31010 ionization chamber inserted. Measurements were evaluated with SNC patient software.

Results:

Repeated IQM measurements of the original plans were reproducible, such that a 1% deviation from the mean as warning and 3% as action level as suggested by the manufacturer seemed reasonable. The IQM detected most of the simulated errors including wrong energy, a faulty leaf, wrong trial exported and a 2 mm shift of one leaf bank. Detection limits were reached for two plans ‐ a 2 mm field position error and a leaf bank offset combined with an MU change. ArcCHECK evaluation according to our current standards also left undetected errors. Ionization chamber evaluation alone would leave most errors undetected.

Conclusion:

The IQM detected most errors and performed as well as currently established phantoms with the advantage that it can be used throughout the whole treatment. Drawback is that it does not indicate the source of the error.
SU‐F‐T‐314: Estimation of Dose Distributions with Different Types of Breast Implants in Various Radiation Treatment Techniques for Breast Cancer
Authors: Lee M , Jung J , Lee S , Kim S , Cho Y , Lee I , Suh T
Published: July 2016

Purpose:

This study investigates the effects of different kinds and designs of commercialized breast implants on the dose distributions in breast cancer radiotherapy under a variety of conditions.

Methods:

The dose for the clinical conventional tangential irradiation, Intensity Modulated Radiation Therapy (IMRT), volumetric modulated arc therapy (VMAT) breast plans was measured using radiochromic films and stimulated luminescence dosimeter (OSLD). The radiochromic film was used as an integrating dosimeter, while the OSLDs were used for real‐time dosimetry to isolate the contribution of dose from individual segment. The films were placed at various slices in the Rando phantom and between the body and breast surface OSLDs were used to measure skin dose at 18 positions spaced on the two (right/left) breast. The implant breast was placed on the left side and the phantom breast was remained on the right side. Each treatment technique was performed on different size of the breasts and different shape of the breast implant. The PTV dose was prescribed 50.4 Gy and V47.88≥95%.

Results:

In different shapes of the breast implant, because of the shadow formed extensive around the breast implant, dose variation was relatively higher that of prescribed dose. As the PTV was delineated on the whole breast, maximum 5% dose error and average 3% difference was observed averagely. VMAT techniques largely decrease the contiguous hot spot in the skin by an average of 25% compared with IMRT. The both IMRT and VMAT techniques resulted in lower doses to normal critical structures than tangential plans for nearly all dose analyzation.

Conclusion:

Compared to the other technique, IMRT reduced radiation dose exposure to normal tissues and maintained reasonable target homogeneity and for the same target coverage, VMAT can reduce the skin dose in all the regions of the body.
SU‐F‐T‐316: A Model to Deal with Dosimetric and Delivery Uncertainties in Radiotherapy Treatment Planning
Authors: Haering P , Lang C , Splinter M
Published: July 2016

Purpose

The conventional way of dealing with uncertainties resulting from dose calculation or beam delivery in IMRT, is to do verification measurements for the plan in question. Here we present an alternative based on recommendations given in the AAPM 142 report and treatment specific parameters that model the uncertainties for the plan delivery.

Methods

Basis of the model is the assignment of uncertainty parameters to all segment fields or control point sequences of a plan. The given field shape is analyzed for complexity, dose rate, number of MU, field size related output as well as factors for in/out field position and penumbra regions. Together with depth related uncertainties, a 3D matrix is generated by a projection algorithm. Patient anatomy is included as uncertainty CT data set as well. Therefore, object density is classified in 4 categories close to water, lung, bone and gradient regions with additional uncertainties. The result is then exported as a DICOM dose file by the software tool (written in IDL, Exelis), having the given resolution and target point.

Results

Uncertainty matrixes for several patient cases have been calculated and compared side by side in the planning system. The result is not quite always intuitive but it clearly indicates high and low uncertainties related to OARs and target volumes as well as to measured gamma distributions.ConclusionThe imported uncertainty datasets may help the treatment planner to understand the complexity of the treatment plan. He then might decide to change the plan to produce a more suited uncertainty distribution, e.g. by changing the beam angles the high uncertainty spots can be influenced or try to use another treatment setup, resulting in a plan with lower uncertainties. A next step could be to include such a model into the optimization algorithm to add a new dose uncertainty constraint.
SU‐F‐T‐319: The Impact of Radiation Beam Obliquity and Air Gap Thickness On Optically Stimulated Luminescent in Vivo Dosimetry for Radiation Therapy
Authors: Riegel A , Sea P , Klein E
Published: July 2016

Purpose:

Optically‐stimulated luminescent dosimeters (OSLDs) are increasingly utilized for in vivo dosimetry of complex radiation delivery techniques. Measured doses, however, underestimate planned doses for plans that utilize thermoplastic mask immobilization. The purpose of this work was to quantify the effect of beam obliquity and air gap span between the mask and backscatter material, on measured‐to‐planned OSLD dose agreement.

Methods:

A previously‐used thermoplastic mask was cut, reheated, and flattened to form a 33 by 9 cm2 stage approximately 2 mm thick. Two OSLDs were placed on the stage on 5 cm of solid water, covered with 50 by 50 by 5 mm3 square of bolus, and scanned in the CT simulator. Plans were created with 10 by 10 cm2 open fields using 4, 6, 10, and 15 MV photon beams at 0°, 45°, and 90° incidence. The isocenter was placed between the OSLDs at 5 mm depth. Dose was calculated and averaged for two OSLDs. Artificial air gaps of 3, 5, 10, and 20 mm were introduced in the plan and dose was recalculated for each energy/angle/gap combination. The experimental setup was replicated on a linear accelerator and air gaps were introduced by “bridging” the thermoplastic stage across solid water plastic of varying thickness. Fields were delivered as planned. OSLDs were read 12–15 hours after irradiation.

Results:

Measured‐toplanned percent differences were constant with increasing gap thickness for 0° and 45° beam angles. At 90° and 0 cm gap, planned dose underestimated measured dose by 10–23% for all energies. This discrepancy decreased linearly to 0% with a 20 mm gap. OSLD signal did not decrease more than 6% for any gap span and energy.

Conclusion:

With the exception of parallel beam incidence, beam obliquity and air gap thickness did not have a substantial effect on measured‐to‐planned dose agreement.
SU‐F‐T‐388: Comparison of Biophysical Indices in Hippocampal‐Avoidance Whole Brain VMAT and IMRT Radiation Therapy Treatment Plans
Authors: Kendall E , Ahmad S , Algan O , Higby C , Hossain S
Published: July 2016

Purpose:

To compare biophysical indices of Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Radiation Therapy (IMRT) treatment plans for whole brain radiation therapy following the NRG‐CC001 protocol.

Methods:

In this retrospective study, a total of fifteen patients were planned with Varian Eclipse Treatment Planning System using VMAT (RapidArc) and IMRT techniques. The planning target volume (PTV) was defined as the whole brain volume excluding a uniform three‐dimensional 5mm expansion of the hippocampus volume. Prescribed doses in all plans were 30 Gy delivered over 10 fractions normalized to a minimum of 95% of the target volume receiving 100% of the prescribed dose. The NRG Oncology protocol guidelines were followed for contouring and dose‐volume constraints. A single radiation oncologist evaluated all treatment plans. Calculations of statistical significance were performed using Student's paired t‐test.

Results:

All VMAT and IMRT plans met the NRG‐CC001 protocol dose‐volume criteria. The average equivalent uniform dose (EUD) for the PTV for VMAT vs. IMRT was respectively (19.05±0.33 Gy vs. 19.38±0.47 Gy) for α/β of 2 Gy and (19.47±0.30 Gy vs. 19.84±0.42 Gy) for α/β of 10 Gy. For the PTV, the average mean and maximum doses were 2% and 5% lower in VMAT plans than in IMRT plans, respectively. The average EUD and the normal tissue complication probability (NTCP) for the hippocampus in VMAT vs. IMRT plans were (15.28±1.35 Gy vs. 15.65±0.99 Gy, p=0.18) and (0.305±0.012 Gy vs. 0.308±0.008 Gy, p=0.192), respectively. The average EUD and NTCP for the optic chiasm were both 2% higher in VMAT than in IMRT plans.

Conclusion:

Though statistically insignificant, VMAT plans indicate a lower hippocampus EUD than IMRT plans. Also, a small variation in NTCP was found between plans.
SU‐F‐T‐390: Dosimetric Impact of Leaf Interdigitation in Prostate Cancer Dynamic IMRT Treatment Planning
Authors: Duan J
Published: July 2016

Purpose:

The aim of this work is to study the dosimetric impact of leaf interdigitation in prostate cancer dynamic IMRT treatment planning.

Methods:

Fifteen previously treated prostate cancer patients were replanned for dynamic IMRT (dMLC) with and without leaf interdigitation using Monaco 3.3 TPS on the Elekta Synergy linear accelerator. The prescription dose of PTV was 70Gy/35 fractions. Various dosimetric variables, such as PTV coverage, OAR sparing, delivery efficiency and optimization time, were evaluated for each plan.

Results:

Interdigitation did not improve the coverage, HI and CI for PTV. Regarding OARs, sparing was equivalent with and without interdigitation. Interdigitation shown an increase in MUs and segments. It was worth noting that leaf interdigitation saved the optimization time.

Conclusion:

This study shows that leaf interdigitation does not improve plan quality when performing dMLC treatment plan for prostate cancer. However, it influences delivery efficiency and optimization time. Interdigitation may gain efficiency for dosimetrist when designing the prostate cancer dMLC plans.
SU‐F‐T‐391: Comparative Study of Treatment Planning Between IMRT and IMAT for Malignant Pleural Mesothelioma
Authors: Duan J
Published: July 2016

Purpose:

The purpose of this study was to compare the dosimetric differences between intensitymodulated radiation therapy (IMRT) and intensity modulated arc therapy (IMAT) for malignant pleural mesothelioma (MPM) patients with regard to the sparing effect on organs at risk (OARs), plan quality, and delivery efficiency.

Methods:

Ten MPM patients were recruited in this study. To avoid the inter‐operator variability, IMRT and IMAT plans for each patient were performed by one experienced dosimetrist. The treatment planning optimization process was carried out using the Eclipse 13.0 software. For a fair comparison, the planning target volume (PTV) coverage of the two plans was normalized to the same level. The treatment plans were evaluated on the following dosimetric variables: conformity index (CI) and homogeneity index (HI) for PTV, OARs dose, and the delivery efficiency for each plan.

Results:

All plans satisfied clinical requirements. The IMAT plans gained better CI and HI. The IMRT plans performed better sparing for heart and lung. Less MUs and control points were found in the IMAT plans. IMAT shortened delivery time compared with IMRT.

Conclusion:

For MPM, IMAT gains better conformity and homogeneity for PTV with IMRT, but increases the irradiation dose for OARs. IMAT shows an advantage in delivery efficiency.
SU‐F‐T‐392: Superior Brainstem and Cochlea Sparing with VMAT for Glioblastoma Multiforme
Authors: Briere TM , McAleer MF , Levy LB , Yang JN , Anderson MD
Published: July 2016

Purpose:

Volumetric arc therapy (VMAT) can provide similar target coverage and normal tissue sparing as IMRT but with shorter treatment times. At our institution VMAT was adopted for the treatment glioblastoma multiforme (GBM) after a small number of test plans demonstrated its non‐inferiority. In this study, we compare actual clinical treatment plans for a larger cohort of patients treated with either VMAT or IMRT.

Methods:

90 GBM patients were included in this study, 45 treated with IMRT and 45 with VMAT. All planning target volumes (PTVs) were prescribed a dose of 50 Gy, with a simultaneous integrated boost to 60 Gy. Most IMRT plans used 5 non‐coplanar beams, while most VMAT plans used 2 coplanar beams. Statistical analysis was performed using Fisher's exact test or the Wilcoxon‐Mann‐Whitney rank sum test. Included in the analysis were patient and treatment characteristics as well as the doses to the target volumes and organs at risk.

Results:

Treatment times for the VMAT plans were reduced by 5 minutes compared with IMRT. The PTV coverage was similar, with at least 95% covered for all plans, while the median boost PTV dose differed by 0.1 Gy between the IMRT and VMAT cohorts. The doses to the brain, optic chiasm, optic nerves and eyes were not significantly different. The mean dose to the brainstem, however, was 9.4 Gy less with VMAT (p<0.001). The dose to the ipsilateral and contralateral cochleae were respectively 19.7 and 9.5 Gy less (p<0.001).

Conclusion:

Comparison of clinical treatment plans for separate IMRT and VMAT cohorts demonstrates that VMAT can save substantial treatment time while providing similar target coverage and superior sparing of the brainstem and cochleae. To our knowledge this is the first study to demonstrate this benefit of VMAT in the management of GBM.
SU‐F‐T‐405: Development of a Rapid Cardiac Contouring Tool Using Landmark‐Driven Modeling
Authors: Pelletier C , Mosher E , Lee C , Lee C , Jung J
Published: July 2016

Purpose:

This study aims to develop a tool to rapidly delineate cardiac substructures for use in dosimetry for large‐scale clinical trial or epidemiological investigations. The goal is to produce a system that can semi‐automatically delineate nine cardiac structures to a reasonable accuracy within a couple of minutes.

Methods:

The cardiac contouring tool employs a Most Similar Atlas method, where a selection criterion is used to pre‐select the most similar model to the patient from a library of pre‐defined atlases. Sixty contrast‐enhanced cardiac computed tomography angiography (CTA) scans (30 male and 30 female) were manually contoured to serve as the atlas library. For each CTA 12 structures were delineated. Kabsch algorithm was used to compute the optimum rotation and translation matrices between the patient and atlas. Minimum root mean squared distance between the patient and atlas after transformation was used to select the most‐similar atlas. An initial study using 10 CTA sets was performed to assess system feasibility. Leave‐one patient out method was performed, and fit criteria were calculated to evaluate the fit accuracy compared to manual contours.

Results:

For the pilot study, mean dice indices of .895 were achieved for the whole heart, .867 for the ventricles, and .802 for the atria. In addition, mean distance was measured via the chord length distribution (CLD) between ground truth and the atlas structures for the four coronary arteries. The mean CLD for all coronary arteries was below 14mm, with the left circumflex artery showing the best agreement (7.08mm).

Conclusion:

The cardiac contouring tool is able to delineate cardiac structures with reasonable accuracy in less than 90 seconds. Pilot data indicates that the system is able to delineate the whole heart and ventricles within a reasonable accuracy using even a limited library. We are extending the atlas sets to 60 adult males and females in total.
SU‐F‐T‐410: Investigation of Treatment Planning Accuracy with the Presence of Magnetic Injection Port (breast Tissue Expander)
Authors: Cai W , Wagar M , Lyatskaya Y , Czerminska M
Published: July 2016

Purpose:

Mastectomy patients with breast reconstruction usually have a magnetic injection port inside the breast during radiation treatments. The magnet has a very high CT number and produces severe streaking artifact across the entire breast in CT images. Our routine strategy is to replace the artifact volumes with uniform water, and it is necessary to validate that the planned dose, with such an artifact correction, is sufficiently accurate.

Methods:

A phantom was made with a gelatine‐filled container sitting on a Matrixx detector, and the magnetic port was inserted into gelatine with specific depths and orientations. The phantom was scanned on a CT simulator and imported into Eclipse for treatment planning. The dose distribution at the Matrixx detector plane was calculated for raw CT images and artifact‐corrected images. The treatment beams were then delivered to the phantom and the dose distributions were acquired by the Matrixx detector. Gamma index was calculated to compare the planned dose and the measurement.

Results:

Three field sizes (10×10, 15×15 and 20×20) and two depths (50mm and 20mm) were investigated. With the 2%/2mm or 3%/3mm criteria, several points (6–10) failed in the plan for raw CT images, and the number of failure was reduced close to zero for the corrected CT images. An assignment of 10,000 HU to the magnet further reduced the dose error directly under the magnet.

Conclusion:

It is validated that our routine strategy of artifact correction can effectively reduce the number of failures in the detector plane. It is also recommended to set the magnet with a CT number of 10,000HU, which could potentially improve the dose calculation at the points right behind the magnet.
SU‐F‐T‐426: Measurement of Dose Enhancement Due to Backscatter From Modern Dental Materials
Authors: Hurwitz M , Tso T , Lee S , Rosen E , Margalit D , Williams C
Published: July 2016

Purpose:

High‐density materials used in dental restoration can cause significant localized dose enhancement due to electron backscatter in head‐and‐neck radiotherapy, increasing the risk of mucositis. The materials used in prosthetic dentistry have evolved in the last decades from metal alloys to ceramics. We aim to determine the dose enhancement caused by backscatter from currently‐used dental materials.

Methods:

Measurements were performed for three different dental materials: lithium disilicate (Li2Si2O5), zirconium dioxide (ZrO2), and gold alloy. Small thin squares (2×2×0.15 cm3) of the material were fabricated, and placed into a phantom composed of tissue‐equivalent material. The phantom was irradiated with a single 6 MV photon field. A thin‐window parallel‐plate ion chamber was used to measure the dose at varying distances from the proximal interface between the material and the plastic.

Results:

The dose enhancement at the interface between the high‐density and tissue‐equivalent materials, relative to a homogeneous phantom, was 54% for the gold alloy, 31% for ZrO2, and 9% for Li2Si2O5. This enhancement decreased rapidly with distance from the interface, falling to 11%, 5%, and 0.5%, respectively, 2 mm from the interface. Comparisons with the modeling of this effect in treatment planning systems are performed.

Conclusion:

While dose enhancement due to dental restoration is smaller with ceramic materials than with metal alloys, it can still be significant. A spacer of about 2–3 mm would be effective in reducing this enhancement, even for metal alloys.
SU‐F‐T‐427: Utilization and Evaluation of Diagnostic CT Imaging with MAR Technique for Radiation Therapy Treatment Planning
Authors: Xu M , Foster R , Parks H , Pankuch M
Published: July 2016

Purpose:

The objective was to utilize and evaluate diagnostic CT‐MAR technique for radiation therapy treatment planning.

Methods:

A Toshiba‐diagnostic‐CT acquisition with SEMAR(Single‐energy‐MAR)‐algorism was performed to make the metal‐artifact‐reduction (MAR) for patient treatment planning. CT‐imaging datasets with and without SEMAR were taken on a Catphan‐phantom. Two sets of CT‐numbers were calibrated with the relative electron densities (RED). A tissue characterization phantom with Gammex various simulating material rods was used to establish the relationship between known REDs and corresponding CT‐numbers. A GE‐CT‐sim acquisition was taken on the Catphan for comparison. A patient with bilateral hip arthroplasty was scanned in the radiotherapy CT‐sim and the diagnostic SEMAR‐CT on a flat panel. The derived SEMAR images were used as a primary CT dataset to create contours for the target, critical‐structures, and for planning. A deformable registration was performed with VelocityAI to track voxel changes between SEMAR and CT‐sim images. The SEMAR‐CT images with minimal artifacts and high quality of geometrical and spatial integrity were employed for a treatment plan. Treatment‐plans were evaluated based on deformable registration of SEMAR‐CT and CT‐sim dataset with assigned CT‐numbers in the metal artifact regions in Eclipse v11 TPS.

Results:

The RED and CT‐number relationships were consistent for the datasets in CT‐sim and CT's with and without SEMAR. SEMAR datasets with high image quality were used for PTV and organ delineation in the treatment planning process. For dose distribution to the PTV through the DVH analysis, the plan using CT‐sim with the assigned CT‐number showed a good agreement to those on deformable CT‐SEMAR.

Conclusion:

A diagnostic‐CT with MAR‐algorithm can be utilized for radiotherapy treatment planning with CT‐number calibrated to the RED. Treatment planning comparison and DVH shows a good agreement in the PTV and critical organs between the plans on CT‐sim with assigned CT‐number and the deformable SEMAR CT datasets.
SU‐F‐T‐430: Validation of IBEAM Evo Couch Top for Different Relative Electron Density (RED) Combination During Photon Beam Dose Calculation in Monaco− Treatment Planning System
Authors: Manigandan D , Kumar M , Mohandas P , Puri A , Bhalla N
Published: July 2016

Purpose:

Validation of iBEAM™ evo couch‐top for different relative electron density (RED) combination during photon beam dose calculation in Monaco− TPS.

Methods:

The iBEAM™ evo couch‐top has two layers:outer carbon fiber (CF) and inner foam core (FC). To study the beam intensity attenuation of couch‐top, measured doses were compared with doses calculated for different REDs. Measurements were performed in solid water phantom with PTW‐0.125cc ion‐chamber positioned at center of the phantom with 5.3cm thickness slabs placed above and below the chamber. Similarly, in TPS, iBEAM™ evo couch‐top was simulated and doses were calculated for different RED combinations (0.2CF‐0.2FC, 0.4CF‐0.2FC, 0.6CF‐0.2FC, 0.8CF‐0.2FC, and 1.0CF‐0.2FC) by using Monte Carlo dose calculation algorithm in Monaco TPS (V5.1). Doses were measured for every 10 degree gantry angle separation, 10×10cm2 field size and 6MV photons. Then, attenuation is defined as the ratio of output at posterior gantry angle to output of its opposed anterior gantry angle (e.g.225°/45°). output fluctuation with different gantry angle was within ±0.21%. To confirm above results, dose‐planes were measured for five pelvic VMAT plans (360°arc) in PTW two‐dimensional array and compared with different calculated dose‐planes of above‐mentioned couch REDs. Gamma pass rates<1.00) were analyzed for 3%/2mm criteria.

Results:

Measured and calculated attenuation was in good agreement for the RED combination of 0.2CF‐0.2FC and difference was within ±0.515%. However, other density combination showed difference of ±0.9841%, ±1.667%, ±2.9241% and ±2.8832% for 0.4CF‐0.2FC, 0.6CF‐0.2FC, 0.8CF‐0.2FC, and 1.0CF‐0.2FC, respectively. Maximum couch‐top attenuation was observed at 110°–120° and 240°–250° and decreases linearly as the gantry angle approaches 180°. Moreover, gamma pass rate confirmed the above results and showed maximum pass rate of 96.23% for 0.2CF‐0.2FC, whereas others were 95.72%, 95.12%, 94.31% and 93.24%.

Conclusion:

RED value of 0.2CF‐0.2FC was found to be suitable for accurate couch‐top modeling for 6MV photon beam Monte Carlo calculations in Monaco TPS.
SU‐F‐T‐435: Helical Tomotherapy for Craniospinal Irradiation: What We Have Learned from a Multi‐Institutional Study
Authors: Du D , Han C , Chen J , Perez‐Andujar A , Lee B , Kaprealian T , Low D , Qi X
Published: July 2016

Purpose:

To report cranio‐spinal irradiation (CSI) planning experience, compare dosimetric quality and delivery efficiency with Tomotherapy from different institutions, and to investigate effect of planning parameters on plan quality and treatment time.

Methods:

Clinical helical tomotherapy IMRT plans for thirty‐nine CSI cases from three academic institutions were retrospectively evaluated. The planning parameters: field width (FW), pitch, modulation factor (MF), and achieved dosimetric endpoints were cross‐compared. A fraction‐dose‐delivery‐timing index (FDTI), defined as treatment time per fraction dose per PTV length, was utilized to evaluate plan delivery efficiency. A lower FDTI indicates higher delivery efficiency. We studied the correlation between planning quality, treatment time and planning parameters by grouping the plans under specific planning parameters. Additionally, we created new plans using 5cm jaw for a subset of plans that used 2.5cm jaw to exam if treatment efficiency can be improved without sacrificing plan quality.

Results:

There were significant dosimetric differences for organ at risks (OARs) among different institutions (A,B,C). Using the lowest average MF (1.9±0.4) and 5cm field width, C had the highest lung, heart, kidney, liver mean doses and maximum doses for lens. Using the same field width of 5cm, but higher MF (2.6±0.6), B had lower doses to the OARs in the thorax and abdomen area. Most of A's plans were planned with 2.5cm jaw, the plans yielded better PTV coverage, higher OAR doses and slightly shorter FDTI compared to institution B. The replanned 5cm jaw plans achieved comparable PTV coverage and OARs sparing, while saving up to 44.7% treatment time.

Conclusion:

Plan quality and delivery efficiency could vary significantly in CSI planning on Tomotheapy due to choice of different planning parameters. CSI plans using a 5cm jaw, with proper selection of pitch and MF, can achieve comparable/ better plan quality with shorter delivery time compared to 2.5cm jaw plans.
SU‐F‐T‐436: A Method to Evaluate Dosimetric Properties of SFGRT in Eclipse TPS
Authors: Xu M , Wei J , Tobias R , Dick J , Crawford S , Swanson J , Pankuch M
Published: July 2016

Purpose:

The objective was to develop a method for dose distribution calculation of spatially‐fractionated‐GRID‐radiotherapy (SFGRT) in Eclipse treatment‐planning‐system (TPS).

Methods:

Patient treatment‐plans with SFGRT for bulky tumors were generated in Varian Eclipse version11. A virtual structure based on the GRID pattern was created and registered to a patient CT image dataset. The virtual GRID structure was positioned on the iso‐center level together with matching beam geometries to simulate a commercially available GRID block made of brass. This method overcame the difficulty in treatment‐planning and dose‐calculation due to the lack o‐the option to insert a GRID block add‐on in Eclipse TPS. The patient treatment‐planning displayed GRID effects on the target, critical structures, and dose distribution. The dose calculations were compared to the measurement results in phantom.

Results:

The GRID block structure was created to follow the beam divergence to the patient CT images. The inserted virtual GRID block made it possible to calculate the dose distributions and profiles at various depths in Eclipse. The virtual GRID block was added as an option to TPS. The 3D representation of the isodose distribution of the spatially‐fractionated beam was generated in axial, coronal, and sagittal planes. Physics of GRID can be different from that for fields shaped by regular blocks because the charge‐particle‐equilibrium cannot be guaranteed for small field openings. Output factor (OF) measurement was required to calculate the MU to deliver the prescribed dose. The calculated OF based on the virtual GRID agreed well with the measured OF in phantom.

Conclusion:

The method to create the virtual GRID block has been proposed for the first time in Eclipse TPS. The dosedistributions, in‐plane and cross‐plane profiles in PTV can be displayed in 3D‐space. The calculated OF's based on the virtual GRID model compare well to the measured OF's for SFGRT clinical use.
SU‐F‐T‐444: Quality Improvement Review of Radiation Therapy Treatment Planning in the Presence of Dental Implants
Authors: Parenica H , Ford J , Mavroidis P , Li Y , Papanikolaou N , Stathakis S
Published: July 2016

Purpose:

To quantify and compare the effect of metallic dental implants (MDI) on dose distributions calculated using Collapsed Cone Convolution Superposition (CCCS) algorithm or a Monte Carlo algorithm (with and without correcting for the density of the MDI).

Methods:

Seven previously treated patients to the head and neck region were included in this study. The MDI and the streaking artifacts on the CT images were carefully contoured. For each patient a plan was optimized and calculated using the Pinnacle3 treatment planning system (TPS). For each patient two dose calculations were performed, a) with the densities of the MDI and CT artifacts overridden (12 g/cc and 1 g/cc respectively) and b) without density overrides. The plans were then exported to the Monaco TPS and recalculated using Monte Carlo dose calculation algorithm. The changes in dose to PTVs and surrounding Regions of Interest (ROIs) were examined between all plans.

Results:

The Monte Carlo dose calculation indicated that PTVs received 6% lower dose than the CCCS algorithm predicted. In some cases, the Monte Carlo algorithm indicated that surrounding ROIs received higher dose (up to a factor of 2).

Conclusion:

Not properly accounting for dental implants can impact both the high dose regions (PTV) and the low dose regions (OAR). This study implies that if MDI and the artifacts are not appropriately contoured and given the correct density, there is potential significant impact on PTV coverage and OAR maximum doses.
SU‐F‐T‐506: Development and Commissioning of the Effective and Efficient Grid Therapy Using High Dose Rate Flattening Filter Free Beam and Multileaf Collimator
Authors: Liu M , Wen N , Beyer C , Siddiqui F , Chetty I , Zhao B
Published: July 2016

Purpose:

Treating bulky tumors with grid therapy (GT) has demonstrated high response rates. Long delivery time (∼15min), with consequent increased risk of intrafraction motion, is a major disadvantage of conventional MLC‐based GT (MLC‐GT). The goal of this study was to develop and commission a MLC‐GT technique with similar dosimetric characteristics, but more efficient delivery.

Methods:

Grid plan was designed with 10X‐FFF (2400MU/min) beam and MLC in a commercial treatment planning system (TPS). Grid size was 1cm by 1cm and grid‐to‐grid distance was 2cm. Field‐in‐field technique was used to flatten the dose profile at depth of 10cm. Prescription was 15Gy at 1.5cm depth. Doses were verified at depths of 1.5cm, 5cm and 10cm. Point dose was measured with a plastic scintillator detector (PSD) while the planar dose was measured with calibrated Gafchromic EBT3 films in a 20cm think, 30cmx30cm solid water phantom. The measured doses were compared to the doses calculated in the treatment planning system. Percent depth dose (PDD) within the grid was also measured using EBT3 film. Five clinical cases were planned to compare beam‐on time.

Results:

The valley‐to‐peak dose ratio at the 3 depths was approximately 10–15%, which is very similar to published result. The average point dose difference between the PSD measurements and TPS calculation is 2.1±0.6%. Film dosimetry revealed good agreement between the delivered and calculated dose. The average gamma passing rates at the 3 depths were 95% (3%, 1mm). The average percent difference between the measured PDD and calculated PDD was 2.1% within the depth of 20cm. The phantom plan delivery time was 3.6 min. Average beam‐on time was reduced by 66.1±5.6% for the 5 clinical cases.

Conclusion:

An effective and efficient GT technique was developed and commissioned for the treatment of bulky tumors using FFF beam combined with MLC and automation.

The Department of Radiation Oncology at Henry Ford Health System receives research support from Varian Medical Systems and Philips Health Care
SU‐F‐T‐507: Modeling Cerenkov Emissions From Medical Linear Accelerators: A Monte Carlo Study
Authors: Shrock Z , Oldham M , Adamson J
Published: July 2016

Purpose:

Cerenkov emissions are a natural byproduct of MV radiotherapy but are typically ignored as inconsequential. However, Cerenkov photons may be useful for activation of drugs such as psoralen. Here, we investigate Cerenkov radiation from common radiotherapy beams using Monte Carlo simulations.

Methods:

GAMOS, a GEANT4‐based framework for Monte Carlo simulations, was used to model 6 and 18MV photon beams from a Varian medical linac. Simulations were run to track Cerenkov production from these beams when irradiating a 50cm radius sphere of water. Electron contamination was neglected. 2 million primary photon histories were run for each energy, and values scored included integral dose and total track length of Cerenkov photons between 100 and 400 nm wavelength. By lowering process energy thresholds, simulations included low energy Bremsstrahlung photons to ensure comprehensive evaluation of UV production in the medium.

Results:

For the same number of primary photons, UV Cerenkov production for 18MV was greater than 6MV by a factor of 3.72 as determined by total track length. The total integral dose was a factor of 2.31 greater for the 18MV beam. Bremsstrahlung photons were a negligibly small component of photons in the wavelength range of interest, comprising 0.02% of such photons.

Conclusion:

Cerenkov emissions in water are 1.6x greater for 18MV than 6MV for the same integral dose. Future work will expand the analysis to include optical properties of tissues, and to investigate strategies to maximize Cerenkov emission per unit dose for MV radiotherapy.
SU‐F‐T‐515: Increased Skin Dose in Supine Craniospinal Irradiation Due to Carbon Fiber Couch and Vacuum Bag Immobilization Device
Authors: Robertson D , Zhao Z , Wang X , Yang J
Published: July 2016

Purpose:

To measure the surface dose for supine craniospinal irradiation employing posterior beams, treating through an imaging couch and BlueBag immobilization device.

Methods:

The percentage depth dose (PDD) in the buildup region of a clinical 6 MV photon beam was measured using an Advanced Markus parallel plate ionization chamber in a solid water phantom. The PDD from a 10×10 cm2 anterior beam was measured at 100 cm SSD, simulating a traditional prone craniospinal technique. The measurements were compared to commissioning and treatment planning system data. The PDD was also measured in a posterior setup with the phantom surface laying directly on the Brainlab carbon fiber imaging couch, with the phantom surface 100 cm from the source, simulating a supine craniospinal setup. The posterior measurements were repeated with a BlueBag vacuum immobilization device between the couch and phantom, with thicknesses of 1.7 cm and 5 cm. The PDD from a 10×10 cm2 field and a typical 6×30 cm2 craniospinal field were also compared. The PDDs were normalized at 5 cm to reflect typical craniospinal prescription dose normalization.

Results:

The measured PDD curve from the anterior setup agreed well with commissioning and treatment planning data, with surface doses of 19.9%, 28.8% and 27.7%, respectively. The surface doses of the 10×10 cm2 and 6×30 cm2 fields delivered through the imaging couch were both 122.4%. The supine setup yielded surface doses of 122.4%, 121.6%, and 119.6% for the couch only, 1.7 cm bag, and 5 cm bag setups, respectively.

Conclusion:

Delivering craniospinal irradiation through a carbon fiber couch removes the majority of skin sparing. The addition of a vacuum bag immobilization device restores some skin sparing, but the magnitude of this effect is negligible.
SU‐F‐T‐518: Development and Characterization of a Gated Treatment System Implemented with An In‐House Optical Tracking System and the Elekta Response Interface
Authors: Barraclough B , Park J , Li F , Lu B , Li J , Liu C , Yan G
Published: July 2016

Purpose:

To report the development and characterization of the first in‐house gating system implemented with an optical tracking system (OTS) and the Elekta Response™ interface.

Methods:

The Response™ connects a patient tracking system with a linac, enabling the tracking system to control radiation delivery. The developed system uses an in‐house OTS to monitor patient breathing. The OTS consists of two infrared‐based cameras, tracking markers affixed on patient. It achieves gated or breath‐held (BH) treatment by calling beam ON/OFF functions in the Response™ dynamic‐link library (DLL). A 4D motion phantom was used to evaluate its dosimetric and time delay characteristics. Two FF‐ and two FFF‐IMRT beams were delivered in non‐gated, BH and gated mode. The sinusoidal gating signal had a 6 sec period and 15 mm amplitude. The duty cycle included 10%, 20%, 30% and 50%. The BH signal was adapted from the sinusoidal wave by inserting 15 sec BHs. Each delivery was measured with a 2D diode array (MapCHECK™) and compared with the non‐gated delivery using gamma analysis (3%). The beam ON/OFF time was captured using the service graphing utility of the linac.

Results:

The gated treatments were successfully delivered except the 10% duty cycle. The BH delivery had perfect agreement (100%) with non‐gated delivery; the agreement of gated delivery decreased from 99% to 88% as duty cycle reduced from 50% to 20%. The beam on/off delay was on average 0.25/0.06 sec. The delivery time for the 50%, 30% and 20% duty cycle increased by 29%, 71% and 139%, respectively. No dosimetric or time delay difference was noticed between FF‐ and FFF‐IMRT beams.

Conclusion:

The in‐house gating system was successfully developed with dosimetric and time delay characteristics in line with published results for commercial systems. It will be an important platform for further research and clinical development of gated treatment.
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.