bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐01: (In)dependence of Plan Quality On Treatment Modalities and Target‐To‐Critical Structure Geometry for Brain Tumor
Authors: Ruan D , Shao W , Low D , Kupelian P , Qi S X
Published: June 2015

Purpose:

To evaluate and test the hypothesis that plan quality may be systematically affected by treatment delivery techniques and target‐tocritical structure geometric relationship in radiotherapy for brain tumor.

Methods:

Thirty‐four consecutive brain tumor patients treated between 2011–2014 were analyzed. Among this cohort, 10 were planned with 3DCRT, 11 with RadipArc, and 13 with helical IMRT on TomoTherapy. The selected dosimetric endpoints (i.e., PTV V100, maximum brainstem/chiasm/ optic nerve doses) were considered as a vector in a highdimensional space. A Pareto analysis was performed to identify the subset of Pareto‐efficient plans.The geometric relationships, specifically the overlapping volume and centroid‐of‐mass distance between each critical structure to the PTV were extracted as potential geometric features. The classification‐tree analyses were repeated using these geometric features with and without the treatment modality as an additional categorical predictor. In both scenarios, the dominant features to prognosticate the Pareto membership were identified and the tree structures to provide optimal inference were recorded. The classification performance was further analyzed to determine the role of treatment modality in affecting plan quality.

Results:

Seven Pareto‐efficient plans were identified based on dosimetric endpoints (3 from 3DCRT, 3 from RapicArc, 1 from Tomo), which implies that the evaluated treatment modality may have a minor influence on plan quality. Classification trees with/without the treatment modality as a predictor both achieved accuracy of 88.2%: with 100% sensitivity and 87.1% specificity for the former, and 66.7% sensitivity and 96.0% specificity for the latter. The coincidence of accuracy from both analyses further indicates no‐to‐weak dependence of plan quality on treatment modality. Both analyses have identified the brainstem to PTV distance as the primary predictive feature for Pareto‐efficiency.

Conclusion:

Pareto evaluation and classification‐tree analyses have indicated that plan quality depends strongly on geometry for brain tumor, specifically PTV‐tobrain‐stem‐distance but minimally on treatment modality.
SU‐E‐T‐02: 90Y Microspheres Dosimetry Calculation with Voxel‐S‐Value Method: A Simple Use in the Clinic
Authors: Maneru F , Otal A , Gracia M , Gallardo N , Olasolo J , Fuentemilla N , Bragado L , Martin‐Albina M , Lozares S , Pellejero S , Miquelez S , Rubio A
Published: June 2015

Purpose:

To present a simple and feasible method of voxel‐S‐value (VSV) dosimetry calculation for daily clinical use in radioembolization (RE) with 90Y microspheres. Dose distributions are obtained and visualized over CT images.

Methods:

Spatial dose distributions and dose in liver and tumor are calculated for RE patients treated with Sirtex Medical miscrospheres at our center. Data obtained from the previous simulation of treatment were the basis for calculations: Tc‐99m maggregated albumin SPECT‐CT study in a gammacamera (Infinia, General Electric Healthcare.). Attenuation correction and ordered‐subsets expectation maximization (OSEM) algorithm were applied.For VSV calculations, both SPECT and CT were exported from the gammacamera workstation and registered with the radiotherapy treatment planning system (Eclipse, Varian Medical systems). Convolution of activity matrix and local dose deposition kernel (S values) was implemented with an in‐house developed software based on Python code. The kernel was downloaded from www.medphys.it. Final dose distribution was evaluated with the free software Dicompyler.

Results:

Liver mean dose is consistent with Partition method calculations (accepted as a good standard). Tumor dose has not been evaluated due to the high dependence on its contouring. Small lesion size, hot spots in health tissue and blurred limits can affect a lot the dose distribution in tumors. Extra work includes: export and import of images and other dicom files, create and calculate a dummy plan of external radiotherapy, convolution calculation and evaluation of the dose distribution with dicompyler. Total time spent is less than 2 hours.

Conclusion:

VSV calculations do not require any extra appointment or any uncomfortable process for patient. The total process is short enough to carry it out the same day of simulation and to contribute to prescription decisions prior to treatment. Three‐dimensional dose knowledge provides much more information than other methods of dose calculation usually applied in the clinic.
SU‐E‐T‐04: 3D Dose Based Patient Compensator QA Procedure for Proton Radiotherapy
Authors: Zou W , Reyhan M , Zhang M , Davis R , Jabbour S , Khan A , Yue N
Published: June 2015

Purpose:

In proton double‐scattering radiotherapy, compensators are the essential patient specific devices to contour the distal dose distribution to the tumor target. Traditional compensator QA is limited to checking the drilled surface profiles against the plan. In our work, a compensator QA process was established that assess the entire compensator including its internal structure for patient 3D dose verification.

Methods:

The fabricated patient compensators were CT scanned. Through mathematical image processing and geometric transformations, the CT images of the proton compensator were combined with the patient simulation CT images into a new series of CT images, in which the imaged compensator is placed at the planned location along the corresponding beam line. The new CT images were input into the Eclipse treatment planning system. The original plan was calculated to the combined CT image series without the plan compensator. The newly computed patient 3D dose from the combined patientcompensator images was verified against the original plan dose. Test plans include the compensators with defects intentionally created inside the fabricated compensators.

Results:

The calculated 3D dose with the combined compensator and patient CT images reflects the impact of the fabricated compensator to the patient. For the test cases in which no defects were created, the dose distributions were in agreement between our method and the corresponding original plans. For the compensator with the defects, the purposely changed material and a purposely created internal defect were successfully detected while not possible with just the traditional compensator profiles detection methods.

Conclusion:

We present here a 3D dose verification process to qualify the fabricated proton double‐scattering compensator. Such compensator detection process assesses the patient 3D impact of the fabricated compensator surface profile as well as the compensator internal material and structure changes.

This research receives funding support from CURA Medical Technologies.
SU‐E‐T‐07: 4DCT Robust Optimization for Esophageal Cancer Using Intensity Modulated Proton Therapy
Authors: Liao L , Yu J , Li Y , Zhu X , Li H , Lim G , Zhang X
Published: June 2015

Purpose:

To develop a 4DCT robust optimization method to reduce the dosimetric impact from respiratory motion in intensity modulated proton therapy (IMPT) for esophageal cancer.

Methods:

Four esophageal cancer patients were selected for this study. The different phases of CT from a set of 4DCT were incorporated into the worst‐case dose distribution robust optimization algorithm. 4DCT robust treatment plans were designed and compared with the conventional non‐robust plans. Result doses were calculated on the average and maximum inhale/exhale phases of 4DCT. Dose volume histogram (DVH) band graphic and ΔD95%, ΔD98%, ΔD5%, ΔD2% of CTV between different phases were used to evaluate the robustness of the plans.

Results:

Compare to the IMPT plans optimized using conventional methods, the 4DCT robust IMPT plans can achieve the same quality in nominal cases, while yield a better robustness to breathing motion. The mean ΔD95%, ΔD98%, ΔD5% and ΔD2% of CTV are 6%, 3.2%, 0.9% and 1% for the robustly optimized plans vs. 16.2%, 11.8%, 1.6% and 3.3% from the conventional non‐robust plans.

Conclusion:

A 4DCT robust optimization method was proposed for esophageal cancer using IMPT. We demonstrate that the 4DCT robust optimization can mitigate the dose deviation caused by the diaphragm motion.
SU‐E‐T‐09: A Clinical Implementation and Optimized Dosimetry Study of Freiberg Flap Skin Surface Treatment in High Dose Rate Brachytherapy
Authors: Syh J , Syh J , Patel B , Wu H , Durci M
Published: June 2015

Purpose:

This case study was designated to confirm the optimized plan was used to treat skin surface of left leg in three stages. 1. To evaluate dose distribution and plan quality by alternating of the source loading catheters pattern in flexible Freiberg Flap skin surface (FFSS) applicator. 2. To investigate any impact on Dose Volume Histogram (DVH) of large superficial surface target volume coverage. 3. To compare the dose distribution if it was treated with electron beam.

Methods:

The Freiburg Flap is a flexible mesh style surface mold for skin radiation or intraoperative surface treatments. The Freiburg Flap consists of multiple spheres that are attached to each other, holding and guiding up to 18 treatment catheters. The Freiburg Flap also ensures a constant distance of 5mm from the treatment catheter to the surface. Three treatment trials with individual planning optimization were employed: 18 channels, 9 channels of FF and 6 MeV electron beam. The comparisons were highlighted in target coverage, dose conformity and dose sparing of surrounding tissues.

Results:

The first 18 channels brachytherapy plan was generated with 18 catheters inside the skin‐wrapped up flap (Figure 1A). A second 9 catheters plan was generated associated with the same calculation points which were assigned to match prescription for target coverage as 18 catheters plan (Figure 1B). The optimized inverse plan was employed to reduce the dose to adjacent structures such as tibia or fibula. The comparison of DVH's was depicted on Figure 2. External beam of electron RT plan was depicted in Figure 3. Overcall comparisons among these three were illustrated in

Conclusion:

The 9‐channel Freiburg flap flexible skin applicator offers a reasonably acceptable plan without compromising the coverage. Electron beam was discouraged to use to treat curved skin surface because of low target coverage and high dose in adjacent tissues.
SU‐E‐T‐11: A Cloud Based CT and LINAC QA Data Management System
Authors: Wiersma R , Grelewicz Z , Belcher A , Liu X
Published: June 2015

Purpose:

The current status quo of QA data management consists of a mixture of paper‐based forms and spreadsheets for recording the results of daily, monthly, and yearly QA tests for both CT scanners and LINACs. Unfortunately, such systems suffer from a host of problems as, (1) records can be easily lost or destroyed, (2) data is difficult to access — one must physically hunt down records, (3) poor or no means of historical data analysis, and (4) no remote monitoring of machine performance off‐site. To address these issues, a cloud based QA data management system was developed and implemented.

Methods:

A responsive tablet interface that optimizes clinic workflow with an easy‐to‐navigate interface accessible from any web browser was implemented in HTML/javascript/CSS to allow user mobility when entering QA data. Automated image QA was performed using a phantom QA kit developed in Python that is applicable to any phantom and is currently being used with the Gammex ACR, Las Vegas, Leeds, and Catphan phantoms for performing automated CT, MV, kV, and CBCT QAs, respectively. A Python based resource management system was used to distribute and manage intensive CPU tasks such as QA phantom image analysis or LaTeX‐to‐PDF QA report generation to independent process threads or different servers such that website performance is not affected.

Results:

To date the cloud QA system has performed approximately 185 QA procedures. Approximately 200 QA parameters are being actively tracked by the system on a monthly basis. Electronic access to historical QA parameter information was successful in proactively identifying a Linac CBCT scanner's performance degradation.

Conclusion:

A fully comprehensive cloud based QA data management system was successfully implemented for the first time. Potential machine performance issues were proactively identified that would have been otherwise missed by a paper or spreadsheet based QA system.
SU‐E‐T‐12: A Comparative Dosimetric Study of Pre and Post Prostate Iodine‐125 Permanent Seed Implants
Authors: Liu X , Rahimian J , Goy B , Cosmatos H , Qian Y
Published: June 2015

Purpose:

Post‐implant dosimetry has become the gold standard for prostate implant evaluation. The goal of this research is to compare the dosimetry between pre‐plan and post‐plan in permanent prostate seed implant brachytherapy.

Methods:

A retrospective study of 91 patients treated with Iodine‐125 prostate seed implant between year 2012∼2014 were performed. All plans were created using a VariSeed 8.0 planning system. Pre‐plan ultrasound images were acquired using 0.5 cm slice thickness. Post‐plan CT images acquired about 1–4 weeks after implant, fused with the preplan ultrasound images. The prostate and urethra contours were generated using the fusion of ultrasound and CT images. Iodine‐125 seed source activities varied between 0.382 to 0.414 mCi per seed. The loading patterns varied slightly between patients depending on the prostate size. Statistical analysis of pre and post plans for prostate and urethra volumes, V100%, V150% and D90, and urethra D10 were performed and reported.

Results:

The pre and post implant average prostate size was 36.90cc vs. 38.58cc; V100% was 98.33% vs. 96.89%; V150% was 47.09% vs. 56.95%; D90 was 116.35Gy vs. 116.12Gy, urethra volume was 1.72cc vs. 1.85cc, urethra D10% was 122.0% vs. 135.35%, respectively. There was no statistically significant difference between the pre and post‐plan values for D90(p‐value=0.43). However, there are significant differences between other parameters most likely due to post surgical edema; prostate size (p‐value= 0.00015); V100% (p‐value=3.7803E‐07); V150% (p‐value=1.49E‐09); urethra volume (p‐value= 2.77E‐06); Urethra D10 (p‐value=7.37E‐11).

Conclusion:

The post‐plan dosimetry using CT image set showed similar D90 dose coverage to the pre‐plan using the ultrasound image dataset. The study showed that our prostate seed implants have consistently delivered adequate therapeutic dose to the prostate while sparing urethra. Future studies to correlate dose versus biochemical response using patients’ PSA values as well as patients’ survival are warranted.
SU‐E‐T‐14: A Comparative Study Between Forward and Inverse Planning in Gamma Knife Radiosurgery for Acoustic Neuroma Tumours
Authors: Gopishankar N , Agarwal Priyanka , Bisht Raj Kishor , Kale S S , Rath G K , Chander S , Sharma B S
Published: June 2015

Purpose:

To evaluate forward and inverse planning methods for acoustic neuroma cases treated in Gamma Knife Perfexion.

Methods:

Five patients with acoustic neuroma tumour abutting brainstem were planned twice in LGP TPS (Version 10.1) using TMR10 algorithm. First plan was entirely based on forward planning (FP) in which each shot was chosen manually. Second plan was generated using inverse planning (IP) for which planning parameters like coverage, selectivity, gradient index (GI) and beam‐on time threshold were set. Number of shots in IP was automatically selected by objective function using iterative process. In both planning methods MRI MPRAGE sequence images were used for tumour localization and planning. A planning dose of 12Gy at 50% isodose level was chosen. Results and Discussion: Number of shots used in FP was greater than IP and beam‐on time in FP was in average 1.4 times more than IP. One advantage of FP was that the brainstem volume subjected to 6Gy dose (25% isodose) was less in FP than IP. Our results showed use of more number of shots as in FP results in GI less than or equal to 2.55 which is close to its lower limit. Dose homogeneity index (DHI) analysis of FP and IP showed average values of 0.59 and 0.67 respectively. General trend in GK for planning in acoustic neuroma cases is to use small collimator shots to avoid dose to adjacent critical structures. More number of shots and prolonged treatment time causes inconvenience to the patients. Similarly overuse of automatic shot shaping as in IP results in increased scatter dose. A compromise is required in shot selection for these cases.

Conclusion:

IP method could be used in acoustic neuroma cases to decrease treatment time provided the source sector openings near brainstem are shielded or adjusted appropriately to reduce brainstem dose.
SU‐E‐T‐15: A Comparison of COMS and EP917 Eye Plaque Applicators Using Different Radionuclides
Authors: Aryal P , Molloy JA , Rivard MJ
Published: June 2015

Purpose:

To investigate the effect of plaque design and radionuclides on eye plaque dosimetry.

Methods:

The Monte Carlo N‐particle Code version 6 (MCNP6) was used for radiation transport simulations. The 14 mm and 16 mm diameter COMS plaques and the model EP917 plaque were simulated using brachytherapy seeds containing I‐125, Pd‐103, and Cs‐131 radionuclides. The origin was placed at the scleral inner surface. The central axis (CAX) doses of both COMS plaques at −1 mm, 0 mm, 1 mm, 2 mm, 5 mm, 10 mm, 15 mm, 20 mm, and 22.6 mm were compared to the model EP917 plaque. Dose volume histograms (DVHs) were also created for both COMS plaques for the tumor and outer sclera then compared to results for the model EP917 plaque.

Results:

For all radionuclides, the EP917 plaque delivered higher dose (max 343%) compared to the COMS plaques, except for the 14 mm COMS plaque with Cs‐131 at 1 mm and 2 mm depths from outer sclera surface. This could be due to source design. For all radionuclides, the 14 mm COMS plaque delivered higher doses compared to the 16 mm COMS plaque for the depths up to 5 mm. Dose differences were not significant beyond depths of 10 mm due to ocular lateral scatter for the different plaque designs. Tumor DVHs for the 16 mm COMS plaque with Cs‐131 provided better dose homogeneity and conformity compared to other COMS plaques with I‐125 and Pd‐103. Using Pd‐103, DVHs for the 16 mm COMS plaque delivered less dose to outer sclera compared to other plaques.

Conclusion:

This study identified improved tumor homogeneity upon considering radionuclides and plaque designs, and found that scleral dose with the model EP917 plaque was higher than for the 16 mm COMS plaque for all the radionuclides studied.
SU‐E‐T‐16: A Comparison of Expected Dwell Times and Dose Variations for NAMD Patients Treated with An Episcleral Brachytherapy Device
Authors: Hamilton R , Patel P , Balaggan K , Restori M , Ilginis T , Drew M , McGovern M , Vitali J , Marsteller L
Published: June 2015

Purpose:

To evaluate the variations in dwell times and doses expected when using an episcleral brachytherapy device for treatment of neovascular agerelated macular degeneration (n‐AMD) based on accurate imaging modalities

Methods:

Data from 40 eyes from 40 subjects with known n‐ AMD acquired through the Distance of Choroid Study (DOCS) conducted at Moorfields Eye Hospital was used to determine the target depth; the distance from the outer scleral surface of the eye, through the choroid, to the apex of the choroidal neovascularization (CNV). Each subject underwent, in triplicate, enhanced‐depth Spectral Domain Optical Coherence Tomography (SD‐OCT), Swept Source Optical Coherence Tomography, (SS‐OCT) and Ocular Ultrasound (O‐US). These data are the most comprehensive and accurate measurements of the dimensions of the CNV and adjacent layers of the eye for this cohort of patients. During treatment of n‐AMD, patients receive a dose of 24Gy to the apex at the target depth. Using the percentage depth dose for a Sr‐90 episcleral brachytherapy device, dwell times and doses to the apex were computed to determine the expected variations.

Results:

The mean target depth and the 95% confidence interval (CI) determined by combining O‐US with SD‐OCT were 1326 (956,1696)µm and with SS‐OCT were 1332 (970,1693)µm. The calculated corresponding mean dwell times and 95% (CI) were 334 (223,445)s and 335 (226,445)s for SD‐OCT and SS‐OCT determined depths, respectively. The corresponding mean apex dose and 95% (CI) were 24 (35.9,18.0)Gy (SD‐OCT) and 24 (35.6,18.1)Gy (SS‐OCT).

Conclusion:

For episcleral brachytherapy treatment of n‐AMD, using a patient population average target depth for treatment planning is inadequate, resulting in dose variations of a factor of approximately two over the 95% CI and larger variations for a nontrivial segment of the population. Each patient should have individualized imaging studies to determine the target depth for use in the dwell time calculation.

Study was sponsored by Salutaris Medical Devices, Ltd., a subsidiary of Salutaris Medical Devices, Inc. Hamilton and Marsteller are founders of Salutaris Medical Devices, Inc. Drew, McGovern and Vitali are minor equity holders in Salutaris Medical Devices, Inc.
SU‐E‐T‐18: A Comparison of Planning Techniques for Bilateral Reconstructed Chest Wall Patients Undergoing Whole Breast Irradiation
Authors: Volpe T , Margiasso R , Saleh Z , Kuo L , Hong L , Ballangrud A , Gelblum D , Zinovoy M , Deasy J , Tang X
Published: June 2015

Purpose:

As we continuously see more bilateral reconstructed chest wall cases, new challenges are being presented to deliver left‐sided breast irradiation. We herein compare three Deep Inspiration Breath Hold (DIBH) planning techniques (tangents, VMAT, and IMRT) and two free breathing techniques (VMAT and IMRT).

Methods:

Three left‐sided chest wall patients with bilateral implants were studied. Tangents, VMAT, and IMRT plans were created for DIBH scans. VMAT and IMRT plans were created for free breathing scans. All plans were normalized so that 95% of the prescription dose was delivered to 95% of the planning target volume (PTV). The maximum point dose was constrained to less than 120% of the prescription dose. Since the success of DIBH delivery largely depends on patient's ability to perform consistent breath hold during beam on time, smaller number of Monitor Units (MU) is in general desired. For each patient, the following information was collected to compare the planning techniques: heart mean dose, left and right lung V20 Gy, contra‐lateral (right) breast mean dose, cord max dose, and MU.

Results:

The average heart mean dose over all patients are 1561, 692, 985, 1245, and 1121 cGy, for DIBH tangents, VMAT, IMRT, free breathing VMAT and IMRT, respectively. For left lung V20 are 60%, 28%, 26%, 30%, and 29%. For contra‐lateral breast mean dose are 244, 687, 616, 783, 438 cGy. MU are 253, 853, 2048, 1035, and 1874 MUs.

Conclusion:

In the setting of bilateral chest wall reconstruction, opposed tangent beams cannot consistently achieve desired heart and left lung sparing. DIBH consistently achieves better healthy tissue sparing. VMAT appears to be preferential to IMRT for planning and delivering radiation to patients with bilaterally reconstructed chest walls being treated with DIBH.
SU‐E‐T‐19: A Comparison of the Dosimetric Effects of Brass Mesh and Superflab Boluses
Authors: Irwin JS , Gong J , Pavord D
Published: June 2015

Purpose:

We compared the dosimetric effects of brass mesh (Whiting and Davis, Attleboro Falls, MA) and Superflab (CNMC, Nashville, TN) boluses to verify equivalence between the two. Brass mesh bolus may be a convenient alternative to traditional bolus as it better conforms to the skin surface.

Methods:

Measurements were taken using a 6MV 10×10cm field produced by an Infinity linear accelerator (Elekta, Stockholm, Sweden) in a solid water phantom using a parallel plate ion chamber (Model 96035, Keithley Instruments, Cleveland, OH). Measurements compared 0.5cm and 1cm of Superflab to one to six layers of brass bolus mesh. Measurements were performed at depths from 0cm (‘skin’) to 10cm. Oblique beams were not studied.

Results:

Four layers of brass mesh were equivalent to 0.5cm Superflab within 5% at all depths. Six layers of brass compares most favorably with 0.5cm Superflab, with doses at all depths within 3%. Six layers of brass were not fully equivalent to 1cm Superflab, although the agreement was within 5% for depths greater than 3mm. Surface dose was 12% lower than 1cm Superflab. Surface dose can be up to 34% different between Superflab and brass mesh, but is less than 5% different with 4–6 layers of brass when compared to 0.5cm Superflab. To achieve surface dose agreement better than 5% compared to 1cm Superflab, more than 6 layers would be needed. The attenuation at depth was a maximum of 0.17cm per layer.

Conclusion:

Between four and six layers of brass mesh can be equivalent to 0.5cm Superflab, depending on the level of agreement desired. Equivalence within 5% at all depths to 1cm Superflab was not achieved even with six layers. This data agrees with measurements taken by Utsunomiya et al. (2010). More point measurements at shallower depths should be taken prior to clinical implementation of brass bolus mesh.
SU‐E‐T‐26: A Dosimetric Comparison of Two Treatment Setups for Lung Stereotactic Body Radiation Therapy (SBRT) Patients
Authors: Lewis D , Wang X , Gao S , Nitsch P , Pollard J , Sadagopan R , Balter P
Published: June 2015

Purpose:

To assess the feasibility of treating lung SBRT patients with the ipsilateral arm adducted beside the body instead of elevated above the head.

Methods:

Patients receiving lung SBRT at our institution are typically treated with both arms raised above their head. However, several patients had difficulty maintaining their arms in an elevated position. In this study, lung SBRT patients who underwent PET‐CT imaging with an adducted ipsilateral arm were selected to investigate the dosimetric effects of this treatment setup. PET‐CT datasets were fused with treatment planning CT images to simulate the adducted arm position. One VMAT treatment plan was created per patient using the Pinnacle treatment planning system. Plans were optimized to achieve minimal dose to the ipsilateral arm while keeping the target coverage and critical structure doses within clinical limits. The target dose coverage, conformity index (CI) for the target, and DVHs of critical structures for the adducted arm plan were calculated. These parameters were compared with the clinical plan and reported along with the mean and maximum doses of the ipsilateral arm.

Results:

The target coverage, CI and DVHs for the adducted arm plans of two patients (one with peripheral lesion and one with central lesion) were comparable with the clinical plans. Dose constraints for the chest wall limited further reduction of ipsilateral arm doses for the peripheral lesion plan. The mean ipsilateral arm doses for the central and peripheral lesions were 0.33 Gy and 2.4 Gy, respectively. The maximum ipsilateral arm doses for the central and peripheral lesions were 1.0 Gy and 6.2 Gy, respectively.

Conclusion:

The results suggested patients with central lung SBRT tumors were more suitable for treatment with the adducted arm position. More patients with various lung tumor locations will be studied to find optimal tumor locations for treatment with this arm position.
SU‐E‐T‐27: A Dosimetric Evaluation of Boney Anatomy Versus Fiducial Marker Alignment for the Treatment of Prostate Cancer Using Scanned Beam Proton Therapy
Authors: Freund D , Ding X , Zhang J , Rosen L , Wu H
Published: June 2015

Purpose:

In prostate proton radiotherapy, three fiducial markers are used for patient daily alignment. However fiducial alignment can change beamline heterogeneity in proton therapy. The purpose of this study is to determine the difference in fiducial and boney anatomy alignment for patient treatment.

Methods and materials:

Prostate cancer patients who received proton treatment were included in this study. 3 fiducial markers were implanted before the initial CT. All the patients were re‐CT'd every 2 weeks to check the fiducial marker position reproducibility as well as dosimetric consistence of target coverage. In geometry study, re‐CT were fused to the initial CT base on the boney anatomy and the average fiducial marker displacement was measured the centers of the fiducials. Dosimetrically, the initial plan was recalculated directly to re‐CT image set based on the boney alignment and fiducial alignment to determine the difference from daily treatment. Prostate coverage and hotspots were evaluated using the dose to 98% of the CTV (D98) and dose to 2% (D2), respectively.

Results:

The shift from the initial 6 patient CT image sets resulted in an average change in the fiducial location of 5.70 +/− 3 mm. Dosimetric comparison from a single patient revealed that differences from the planned dose resulted from both boney and fiducial alignment. Planned clinical treatment volume coverage resulted in a D98 of 70.44Gy and D2 of 70.84Gy compared to a D98 of 70.13Gy and D2 70.94Gy for boney alignment and a D98 of 70.08Gy and D2 71.18Gy for fiducial alignment respectively.

Conclusion:

This study demonstrates that with boney anatomy alignment there is little change to CTV coverage and only slightly worse CTV coverage and hotspot production with fiducial alignment. An increase patient cohort and further investigation is necessary to determine the whether boney alignment can help better control dose heterogeneity.
SU‐E‐T‐28: A Dosimetric Evaluation of IMRT Versus 4 Arc VMAT in the Treatment of Bilateral Head and Neck Cancer Using Concavity Ratio Defined PTVs
Authors: Ulizio V , Pearson D
Published: June 2015

Purpose:

VMAT has been shown to produce dosimetrically equivalent or superior plans than step and shoot IMRT for many different common cancer types. Bilateral H&N treatment plans are particularly challenging due to the concave shape of the target volume. We aim to compare the two techniques for various levels of concavity and we quantify the concavity of the target, and thus the difficulty of the plan, with a simple but novel ratio.

Methods:

20 bilateral H&N patients were chosen for this study, all with different concavity ratios (CR). The original treatments were generated using 9‐field 6 MV IMRT. The plans were then converted to 4 arc VMAT and planned using the same constraints. A ratio was created to quantify the concave shape of each PTV. The patients were then initially split into two categories; CR >2 and CR<2. Each plan was evaluated for two conformity indices, as well as OAR doses.

Results:

Initial results show better IMRT conformity indexes, averaged over all patients. The spinal cord maximum dose was lower for VMAT but the mandible mean dose was higher. The parotid mean dose was lower in VMAT plans that had CR<2, but higher with CR>2. This was also the case for the oral cavity mean dose and the mandible maximum dose.

Conclusion:

In the preliminary results, VMAT plans with CR< 2 spare OARs better. The conformity indices in these plans are worse but are insignificant. The RTOG conformity index as well as OAR sparing, excluding the spinal cord, is significantly worse when CR>2. Thus, when a patient is targeted, the CR should be calculated and if the ratio is below two then it should be planned with VMAT, but if the ratio is above two then the traditional IMRT planning should be used.
SU‐E‐T‐35: A General Fill Factor Definition Serving to Characterise the MLC Misalignment Detection Capabilities of Two‐Dimensional Detector Arrays
Authors: Stelljes T.S. , Looe H.K. , Harder D. , Poppe B.
Published: June 2015

Purpose:

To present a general definition of the fill factor realistically characterizing the “field coverage”, i.e. the MLC misalignment detection capabilities of a detector array.

Methods:

According to Gago‐Arias et al.1 the fill factor of a 2D array is defined as the ratio of the area enclosed by the FWHM of the fluence response function KM(x) of a single detector and its cell area defined by the detector spacing. More generally ‐ accounting also for the possible overlap between FWHM's of neighboured detectors ‐ the fill factor is here defined as that fraction of the sum of the detector cell areas in which a defined MLC misalignment is detectable when the induced percentage signal changes exceed a detection threshold d. Ideally the generalized fill factor may reach 100 %. With user code EGS_chamber and a 2 MeV photon slit beam 0.25 mm wide, both types of the fill factor were calculated for an array with total cell area 100 cm2 for chamber widths 1–9 mm, using =1mm, d=5%.

Results:

For single chamber width 5 mm, fill factors were 0.49 (FWHM) and 0.61 (generalized). For chamber width 2 mm the FWHM fill factor was 0.13 whereas the generalized fill factor was 0.32. For chamber widths above 7 mm, the FWHM fill factor exceeds unity, and the general fill factor is exactly 1.00.

Conclusions:

An updated fill factor definition is introduced which, as a generalization of the FWHM‐based definition, more closely estimates the performance of small array chambers and gives a realistic value in the case of overlapping sensitive areas of neighboured chambers. References:1A. Gago‐Arias, L. Brualla‐Gonzalez, D.M. Gonzalez‐Castano, F. Gomez, M.S. Garcia, V.L. Vega, J.M. Sueiro, J. Pardo‐Montero, “Evaluation of chamber response function influence on IMRT verification using 2D commercial detector arrays,” Phys. Med. Biol. 57, 2005–2020 (2012).
SU‐E‐T‐40: A Method for Improving Dose Gradient for Robotic Radiosurgery
Authors: Li T , Burton S , Flickinger J , Heron D E , Huq M Saiful
Published: June 2015

Purpose:

For targets with substantial volume, collimators of relatively large sizes are usually selected to minimize the treatment time in robotic radiosurgery. Their large penumbrae may adversely affect the dose gradient around the target. In this study, we implement and evaluate an inner‐shell planning method to increase the dose gradient.

Methods:

Ten patients previously treated with CyberKnife M6 system were randomly selected with the only criteria that PTV be larger than 2cm3. A new plan was generated for each patient, in which the PTV was split into two regions: an inner shell and a core, where the core was created by shrinking the PTV by 5mm using 3D erosion, and the shell was obtained by subtracting the core from the PTV; then a 7.5mm Iris collimator was exclusively applied to the shell, with other appropriate collimators applied to the core depending on its size. The optimization objective functions and constraints were kept the same as the corresponding clinical plans. The results were analyzed for V12Gy, V9Gy, V5Gy, and gradient index (GI).

Results:

Volume reduction is found for the inner‐shell method at all studied dose levels as compared to the clinical plans. The absolute dose volume reduction ranged from 0.05cm3 to 18.5cm3 with a mean of 5.6cm3 for 12Gy, from 0.2cm3 to 38.1cm3 with a mean of 9.8cm3 for 9Gy, and from 1.5cm3 to 115.7cm3 with a mean of 24.8cm3 for 5Gy, respectively. The relative GI reduction ranged from 3.2% to 23.6%, with a mean of 12.6%. Paired t‐test for GI has a p‐value of 0.0014. The range for treatment time increase is from −3 min to 20 min, with a mean of 7.0 min.

Conclusion:

The inner‐shell planning method can significantly increase the dose gradient outside the PTV, while maintaining good coverage, conformity, and reasonable treatment time.
SU‐E‐T‐41: A Method for Performing An In‐House Batch Assay of I‐125 Seeds Used for Prostate Implants
Authors: Muryn J , Wilkinson D
Published: June 2015

Purpose:

The purpose of this work is to evaluate a method for confirming source strength of I‐125 seeds in a bulk assay while maintaining sterility and time efficiency.

Methods:

The I‐125 seeds used in this study (STM 1251, Bard Brachytherapy, Inc.) were available as loose seeds or linked in 3, 4, or 5 seed configurations. A third party 10% assay (NIST traceable) is provided. Source strengths ranging from 0.395 to 0.504 U were available for this study. A stand was built out of aluminum to hold an exposure meter (Inovision (Fluke) 451P) at 25 cm above the I‐125 sources to measure the exposure rate. Three different seed configurations were measured: loose, linked, and loaded needles (Bard FastFil Seed Implant Needle). The measurements were made in an operating room, and a sterile sheet was used under the non‐sterile aluminum stand. Seeds and needles were placed in a sterile tray.

Results:

One hundred forty‐two loose seeds in 5 batches (0.395, 0.395, 0.409, 0.444, 0.444 U/seed) and 902 seeds in 7 batches containing various strands (0.444, 0.444,.0444, 0.466, 0.466, 0.504, 0.504 U/seed) were measured. The average exposure rate per unit activity was measured to be 0.593 mR per hr per U with a standard deviation of 0.016. The Result for loaded needles was 0.261 mR per hr per U with a standard deviation of 0.014. Once the apparatus is set up, measurements of 180 linked sources as supplied in the Bard package requires only a few minutes.

Conclusion:

The proposed method can confirm the activity of a batch of loose or stranded I‐125 seeds within a range of 5%.
SU‐E‐T‐42: A Method to Determine the Optimal Proton Scanned Beam Angle to Ensure Robust Treatment Planning
Authors: Kiely J Blanco , White B , Both S
Published: June 2015

Purpose:

The ability of pencil beam scanning (PBS) to deliver highly conformal dose distributions may be affected by patient‐ and physics‐related uncertainties. In clinical practice, selection of proton beam angles is determined qualitatively. This study investigates whether an optimal proton PBS beam angle could be quantitatively determined to ensure robust planning for pelvic targets.

Methods:

PBS beam angles were optimized based on two independent criteria; shortest and most homogeneous path from the patient surface to the distal edge of the target. The beam angle optimization criteria for gantry angles between 90°‐270° were quantified in 10° increments for each ray, calculated as the straight line distance from the surface of the skin to the CTV's distal edge. The goal was to minimize the path length of a proton PBS beam from the patient surface to the distal edge of the CTV, relative to the entry point, while minimizing HU inhomogeneity along the ray. HU homogeneity (i.e. HU variation) was quantitatively defined as the standard deviation of the average intra‐ray HU intensity distribution of the rays comprising a single beam. This method was validated relative to inter‐fraction changes on ten consecutive, locally advanced, rectal cancer patients, who underwent an average 4 verification CTs. The displacement of the 95–98% isodose lines was determined from forward calculated dose distributions on verification CTs.

Results:

The posterior beam (180°) had the average shortest path length, 132.7±17.2mm, and the most homogenous path, 31.9±4.3HU. The 95–98% isodose lines from all plans verified our path length to within 2.3±1.2% and HU homogeneity to within 1.2±0.5%.

Conclusion:

The proposed optimization algorithm determined the posterior beam dose distribution as the most robust relative to inter‐fraction variation for large pelvic targets treated with PBS and was validated via verification CT for our patient cohort. Future work will focus on further algorithm development.
SU‐E‐T‐53: A New Method for Characterizing the Stability of the Treatment Couch Isocentre
Authors: Gete E , Wilson B , Lee R
Published: June 2015

Purpose:

In this work we propose a new method for characterizing the accuracy of a linear accelerator treatment couch's isocentre. This is accomplished by a direct determination of the coordinates of the center of rotation as a function of rotation angle.

Methods:

A phantom consisting of five metallic BBs arranged in a plane was constructed. The phantom was positioned on the treatment couch such that the plane of the BBs was horizontal, while the central BB was aligned with the linac isocentre. With the gantry in the vertical position, the couch was rotated through its full range of rotation while EPID images were acquired every 10 degrees. For each rotation angle, the coordinates of the rotation center were calculated from the displacement of each of the four off‐center BBs identified on a pair of EPID images taken between successive rotations. The accuracy of the couch isocentre was evaluated from the distribution of the rotation center coordinates. Our results were compared with film based star‐shot measurements of the couch isocentre.

Results:

The measured couch center of rotation consisted of a cloud of points clustered around the linac isocentre within < 0.7 mm distance. The deviations of these points from the linac isocentre were in the range of 0.01 to 0.20 mm in the cross‐plane direction, and 0.10 to 0.61 mm in the in‐plane direction, with mean values of 0.09 mm and 0.32 mm. These results were consistent with the results obtained from the star‐shot method.

Conclusion:

A new method for determining the location and accuracy of the couch center of rotation has been successfully implemented. This method gives explicit values of the location and the stability of the couch isocentre, and it can be extended to gantry and collimator rotations.
SU‐E‐T‐55: A Novel Applicator for High Dose Rate Brachytherapy Treatments of Ocular Conjunctiva
Authors: Koren S , Bragilovski D , Tafo A Guemnie , Cohen G
Published: June 2015

Purpose:

To evaluate the clinical feasibility of IntraBeam intra operative kV irradiation beam device for ocular conjunctiva treatments. The Intra‐Beam system offers a 4.4 mm diameter needle applicator, that is not suitable for treatment of a large surface with limits access. We propose an adaptor that will answer to this clinical need and provide initial dosimetry.

Methods:

The dose distribution of the needle applicator is non uniform and hence not suitable for treatment of relatively large surfaces. We designed an adapter to the needle applicator that will filter the X‐rays and produce a conformal dose distribution over the treatment area while shielding surfaces to be spared. Dose distributions were simulated using FLUKA is a fully integrated particle physics Monte Carlo simulation package.

Results:

We designed a wedge applicator made of Polythermide window and stainless steel for collimating. We compare the dose distribution to that of the known needle and surface applicators.

Conclusion:

Initial dosimetry shows feasibility of this approach. While further refinements to the design may be warranted, the results support construction of a prototype and confirmation of the Monte Carlo dosimetry with measured data.
SU‐E‐T‐56: A Novel Approach to Computing Expected Value and Variance of Point Dose From Non‐Gated Radiotherapy Delivery
Authors: Zhou S , Zhu X , Zhang M , Zheng D , Zhang Q , Lei Y , Li S , Driewer J , Wang S , Enke C
Published: June 2015

Purpose:

Randomness in patient internal organ motion phase at the beginning of non‐gated radiotherapy delivery may introduce uncertainty to dose received by the patient. Concerns of this dose deviation from the planned one has motivated many researchers to study this phenomenon although unified theoretical framework for computing it is still missing. This study was conducted to develop such framework for analyzing the effect.

Methods:

Two reasonable assumptions were made: a) patient internal organ motion is stationary and periodic; b) no special arrangement is made to start a non ‐gated radiotherapy delivery at any specific phase of patient internal organ motion. A statistical ensemble was formed consisting of patient's non‐gated radiotherapy deliveries at all equally possible initial organ motion phases. To characterize the patient received dose, statistical ensemble average method is employed to derive formulae for two variables: expected value and variance of dose received by a patient internal point from a non‐gated radiotherapy delivery. Fourier Series was utilized to facilitate our analysis.

Results:

According to our formulae, the two variables can be computed from non‐gated radiotherapy generated dose rate time sequences at the point's corresponding locations on fixed phase 3D CT images sampled evenly in time over one patient internal organ motion period. The expected value of point dose is simply the average of the doses to the point's corresponding locations on the fixed phase CT images. The variance can be determined by time integration in terms of Fourier Series coefficients of the dose rate time sequences on the same fixed phase 3D CT images.

Conclusion:

Given a non‐gated radiotherapy delivery plan and patient's 4D CT study, our novel approach can predict the expected value and variance of patient radiation dose. We expect it to play a significant role in determining both quality and robustness of patient non‐gated radiotherapy plan.
SU‐E‐T‐58: A Novel Monte Carlo Photon Transport Simulation Scheme and Its Application in Cone Beam CT Projection Simulation
Authors: Xu Y , Tian Z , Zhou L , Jiang S , Jia X
Published: June 2015

Purpose:

Monte Carlo (MC) simulation is an important tool to solve radiotherapy and medical imaging problems. Low computational efficiency hinders its wide applications. Conventionally, MC is performed in a particle‐by ‐particle fashion. The lack of control on particle trajectory is a main cause of low efficiency in some applications. Take cone beam CT (CBCT) projection simulation as an example, significant amount of computations were wasted on transporting photons that do not reach the detector. To solve this problem, we propose an innovative MC simulation scheme with a path‐by‐path sampling method.

Methods:

Consider a photon path starting at the x‐ray source. After going through a set of interactions, it ends at the detector. In the proposed scheme, we sampled an entire photon path each time. Metropolis‐Hasting algorithm was employed to accept/reject a sampled path based on a calculated acceptance probability, in order to maintain correct relative probabilities among different paths, which are governed by photon transport physics. We developed a package gMMC on GPU with this new scheme implemented. The performance of gMMC was tested in a sample problem of CBCT projection simulation for a homogeneous object. The results were compared to those obtained using gMCDRR, a GPU‐based MC tool with the conventional particle‐by‐particle simulation scheme.

Results:

Calculated scattered photon signals in gMMC agreed with those from gMCDRR with a relative difference of 3%. It took 3.1 hr. for gMCDRR to simulate 7.8e11 photons and 246.5 sec for gMMC to simulate 1.4e10 paths. Under this setting, both results attained the same ∼2% statistical uncertainty. Hence, a speed‐up factor of ∼45.3 was achieved by this new path‐by‐path simulation scheme, where all the computations were spent on those photons contributing to the detector signal.

Conclusion:

We innovatively proposed a novel path‐by‐path simulation scheme that enabled a significant efficiency enhancement for MC particle transport simulations.