bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐CAMPUS‐I‐01: Nanometric Organic Photovoltaic Thin Film X‐Ray Detectors for Clinical KVp Beams
Authors: Elshahat Bassem , Filipyev Ilya , Shrestha Suman , Hesser Jurgen , Gill Hardeep , Kumar Jayant , Karellas Andrew , Zygmanski Piotr , Sajo Erno
Published: July 2014

Purpose:

To fabricate and test nanometric organic photovoltaic (OPV) cells made of various active‐layer/electrode thicknesses and sizes; to determine the optimal material combinations and geometries suitable for dose measurements in clinical kilovoltage x‐ray beams.

Methods:

The OPV consisted of P3HT:PCBM photoactive materials sandwiched between aluminum and Indium Tin Oxide (ITO) electrodes. Direct conversion of xrays in the active layer composed of donor and acceptor semiconducting organic materials generated signal in photovoltaic mode (without external voltage bias). OPV cells were fabricated with different active layer thicknesses (150, 270, 370 nm) and electrode areas (0.4, 0.7, 0.9, 1.4, 2.6 cm2). A series of experiments were preformed in the energy range of 60–150 kVp. The net current per unit area (nA/cm2) was measured using 200 mAs time‐integrated beam current.

Results:

The net OPV current as function of beam energy (kVp) was proportional to ∼E0,4 5 when adjusted for beam output. The best combination of parameters for these cells was 270 nm active layer thicknesses for 0.7 cm2 electrode area. The measured current ranged from 0.69 to 2.43 nA/cm2 as a function of x‐ray energy between 60 and 150 kVp, corresponding to 0.09 – 0.06 nA/cm2/mGy, respectively, when adjusted for the beam output.

Conclusion:

The experiments indicate that OPV detectors possessing 270 nm active layer and 0.7 cm2 Al electrode areas have sensitivity by a factor of 2.5 greater than commercial aSi thin film PV. Because OPV can be made flexible and they do not require highvoltage bias supply, they open the possibility for using as in‐vivo detectors in radiation safety in x‐ray imaging beams.
SU‐E‐CAMPUS‐I‐02: Estimation of the Dosimetric Error Caused by the Voxelization of Hybrid Computational Phantoms Using Triangle Mesh‐Based Monte Carlo Transport
Authors: Lee C , Badal A
Published: July 2014

Purpose:

Computational voxel phantom provides realistic anatomy but the voxel structure may result in dosimetric error compared to real anatomy composed of perfect surface. We analyzed the dosimetric error caused from the voxel structure in hybrid computational phantoms by comparing the voxel‐based doses at different resolutions with triangle mesh‐based doses.

Methods:

We incorporated the existing adult male UF/NCI hybrid phantom in mesh format into a Monte Carlo transport code, penMesh that supports triangle meshes. We calculated energy deposition to selected organs of interest for parallel photon beams with three mono energies (0.1, 1, and 10 MeV) in antero‐posterior geometry. We also calculated organ energy deposition using three voxel phantoms with different voxel resolutions (1, 5, and 10 mm) using MCNPX2.7.

Results:

Comparison of organ energy deposition between the two methods showed that agreement overall improved for higher voxel resolution, but for many organs the differences were small. Difference in the energy deposition for 1 MeV, for example, decreased from 11.5% to 1.7% in muscle but only from 0.6% to 0.3% in liver as voxel resolution increased from 10 mm to 1 mm. The differences were smaller at higher energies. The number of photon histories processed per second in voxels were 6.4×104, 3.3×104, and 1.3×104, for 10, 5, and 1 mm resolutions at 10 MeV, respectively, while meshes ran at 4.0×104 histories/sec.

Conclusion:

The combination of hybrid mesh phantom and penMesh was proved to be accurate and of similar speed compared to the voxel phantom and MCNPX. The lowest voxel resolution caused a maximum dosimetric error of 12.6% at 0.1 MeV and 6.8% at 10 MeV but the error was insignificant in some organs. We will apply the tool to calculate dose to very thin layer tissues (e.g., radiosensitive layer in gastro intestines) which cannot be modeled by voxel phantoms.
SU‐E‐CAMPUS‐I‐03: Dosimetric Comparison of the Hypoxia Agent Iodoazomycin Arabinoside (IAZA) Labeled with the Radioisotopes I‐123, I‐131 and I‐124
Authors: Jans H‐S , Stypinski D , Mcquarrie S , Kumar P , Mercer J , Wiebe L , McEwan S
Published: July 2014

Purpose:

To compare the radiation dose to normal organs from the radio‐iodinated, hypoxia‐binding radiosensitizer iodoazomycin arabinoside (IAZA) for three different isotopes of iodine.

Methods:

Dosimety studies with normal volunteers had been carried out with [123I]IAZA, a drug binding selectively to hypoxic sites. Two other isotopes of iodine, 131I and 124I, offer the opportunity to use IAZA as an agent for radioisotope therapy and as an imaging tracer for Positron Emission Tomography. Radioisotope dosimetry for 131I and 124I was performed by first deriving from the [123I]IAZA studies biological uptake and excretion data. The cumulated activities for 131I or 124I where obtained by including their half‐lives when integrating the biological data and then extrapolating to infinite time points considering a) physical decay only or b) physical and biological excretion. Doses were calculated using the Medical Internal Radiation Dose (MIRD) schema (OLINDA1.1 code, Vanderbilt 2007).

Results:

Compared to 123I, organ doses were elevated on average by a factor 6 and 9 for 131I and 124I, respectively, if both physical decay and biological excretion were modeled. If only physical decay is considered, doses increase by a factor 18 (131I) and 19 (124I). Highest organ doses were observed in intestinal walls, urinary bladder and thyroid. Effective doses increased by a factor 11 and 14 for 131I and 124I, respectively, if biological and physical decay are present. Purely physical decay yields a 23‐fold increase over 123I for both, 131I and 124I.

Conclusion:

Owing to the significant dose increase, caused by their longer half life and the approximately 10 times larger electronic dose deposited in tissue per nuclear decay, normal tissue doses of IAZA labeled with 131I and 124I need to be carefully considered when designing imaging and therapy protocols for clinical trials. Effective blocking of iodine uptake in the thyroid is essential. Alberta Innovates – Health Solutions (AIHS) and Canadian Institutes of Health Research (CIHR)
SU‐E‐CAMPUS‐I‐04: Automatic Skin‐Dose Mapping for An Angiographic System with a Region‐Of‐Interest, High‐Resolution Detector
Authors: Vijayan S , Rana V , Setlur Nagesh S , Ionita C , Rudin S , Bednarek D
Published: July 2014

Purpose:

Our real‐time skin dose tracking system (DTS) has been upgraded to monitor dose for the micro‐angiographic fluoroscope (MAF), a high‐resolution, small field‐of‐view x‐ray detector.

Methods:

The MAF has been mounted on a changer on a clinical C‐Arm gantry so it can be used interchangeably with the standard flat‐panel detector (FPD) during neuro‐interventional procedures when high resolution is needed in a region‐of‐interest. To monitor patient skin dose when using the MAF, our DTS has been modified to automatically account for the change in scatter for the very small MAF FOV and to provide separated dose distributions for each detector. The DTS is able to provide a color‐coded mapping of the cumulative skin dose on a 3D graphic model of the patient. To determine the correct entrance skin exposure to be applied by the DTS, a correction factor was determined by measuring the exposure at the entrance surface of a skull phantom with an ionization chamber as a function of entrance beam size for various beam filters and kVps. Entrance exposure measurements included primary radiation, patient backscatter and table forward scatter. To allow separation of the dose from each detector, a parameter log is kept that allows a replay of the procedure exposure events and recalculation of the dose components. The graphic display can then be constructed showing the dose distribution from the MAF and FPD separately or together.

Results:

The DTS is able to provide separate displays of dose for the MAF and FPD with field‐size specific scatter corrections. These measured corrections change from about 49% down to 10% when changing from the FPD to the MAF.

Conclusion:

The upgraded DTS allows identification of the patient skin dose delivered when using each detector in order to achieve improved dose management as well as to facilitate peak skin‐dose reduction through dose spreading.

Research supported in part by Toshiba Medical Systems Corporation and NIH Grants R43FD0158401, R44FD0158402 and R01EB002873
SU‐E‐CAMPUS‐I‐05: Internal Dosimetric Calculations for Several Imaging Radiopharmaceuticals in Preclinical Studies and Quantitative Assessment of the Mouse Size Impact On Them. Realistic Monte Carlo Simulations Based On the 4D‐MOBY Model
Authors: Kostou T , Papadimitroulas P , Loudos G , Kagadis GC
Published: July 2014

Purpose:

Commonly used radiopharmaceuticals were tested to define the most important dosimetric factors in preclinical studies. Dosimetric calculations were applied in two different whole‐body mouse models, with varying organ size, so as to determine their impact on absorbed doses and S‐values. Organ mass influence was evaluated with computational models and Monte Carlo(MC) simulations.

Methods:

MC simulations were executed on GATE to determine dose distribution in the 4D digital MOBY mouse phantom. Two mouse models, 28 and 34 g respectively, were constructed based on realistic preclinical exams to calculate the absorbed doses and S‐values of five commonly used radionuclides in SPECT/PET studies (18F, 68Ga, 177Lu, 111In and 99mTc).Radionuclide biodistributions were obtained from literature. Realistic statistics (uncertainty lower than 4.5%) were acquired using the standard physical model in Geant4. Comparisons of the dosimetric calculations on the two different phantoms for each radiopharmaceutical are presented.

Results:

Dose per organ in mGy was calculated for all radiopharmaceuticals. The two models introduced a difference of 0.69% in their brain masses, while the largest differences were observed in the marrow 18.98% and in the thyroid 18.65% masses.Furthermore, S‐values of the most important target‐organs were calculated for each isotope. Source‐organ was selected to be the whole mouse body.Differences on the S‐factors were observed in the 6.0–30.0% range. Tables with all the calculations as reference dosimetric data were developed.

Conclusion:

Accurate dose per organ and the most appropriate S‐values are derived for specific preclinical studies. The impact of the mouse model size is rather high (up to 30% for a 17.65% difference in the total mass), and thus accurate definition of the organ mass is a crucial parameter for self‐absorbed S values calculation.Our goal is to extent the study for accurate estimations in small animal imaging, whereas it is known that there is a large variety in the anatomy of the organs.
SU‐E‐CAMPUS‐I‐06: Y90 PET/CT for the Instantaneous Determination of Both Target and Non‐Target Absorbed Doses Following Hepatic Radioembolization
Authors: Pasciak A , Kao J
Published: July 2014

Purpose

The process of converting Yttrium‐90 (Y90) PET/CT images into 3D absorbed dose maps will be explained. The simple methods presented will allow the medical physicst to analyze Y90 PET images following radioembolization and determine the absorbed dose to tumor, normal liver parenchyma and other areas of interest, without application of Monte‐Carlo radiation transport or dose‐point‐kernel (DPK) convolution.

Methods

Absorbed dose can be computed from Y90 PET/CT images based on the premise that radioembolization is a permanent implant with a constant relative activity distribution after infusion. Many Y90 PET/CT publications have used DPK convolution to obtain 3D absorbed dose maps. However, this method requires specialized software limiting clinical utility. The Local Deposition method, an alternative to DPK convolution, can be used to obtain absorbed dose and requires no additional computer processing. Pixel values from regions of interest drawn on Y90 PET/CT images can be converted to absorbed dose (Gy) by multiplication with a scalar constant.

Results

There is evidence that suggests the Local Deposition method may actually be more accurate than DPK convolution and it has been successfully used in a recent Y90 PET/CT publication. We have analytically compared dose‐volume‐histograms (DVH) for phantom hot‐spheres to determine the difference between the DPK and Local Deposition methods, as a function of PET scanner point‐spread‐function for Y90. We have found that for PET/CT systems with a FWHM greater than 3.0 mm when imaging Y90, the Local Deposition Method provides a more accurate representation of DVH, regardless of target size than DPK convolution.

Conclusion

Using the Local Deposition Method, post‐radioembolization Y90 PET/CT images can be transformed into 3D absorbed dose maps of the liver. An interventional radiologist or a Medical Physicist can perform this transformation in a clinical setting, allowing for rapid prediction of treatment efficacy by comparison to published tumoricidal thresholds.
SU‐E‐CAMPUS‐J‐01: TG142 Complied Comprehensive Commissioning and Quality Assurance Procedure for Respiratory Gating
Authors: Woods K , Rong Y , Weldon M , Gupta N
Published: July 2014

Purpose:

To develop and establish a comprehensive gating commissioning and quality assurance procedure in compliance with TG142.

Methods:

Quality assurance tests on three Varian LINACs included beam output and energy constancy, calibration of surrogate, as well as phase and amplitude gating temporal accuracy. A diode array (MapCHECK 2) and film (Gafchromic EBT2) were used to measure the temporal accuracy of phase and amplitude gating windows. A motion simulation device (MotionSim) was used to simulate respiratory motion for both detectors. An end‐to‐end test was also performed on all three machines. The overall accuracy and uncertainty was analyzed and compared.

Results:

The end‐to‐end test using an anthropomorphic lung phantom (CIRS) results in an OSL dose difference reading within 5% (within measurement uncertainty) for both phase and amplitude gated treatment. Film results showed < 1% agreement between profiles for gated delivery and predicted dose. The diode array demonstrated an 80% passing rate for gamma criteria of 2%/0.2 mm, which results in a 111 msec temporal accuracy. However, the diode array is limited by its spatial resolution of measurements, due to its 7.07 mm diode spacing. Film provided higher measuring resolution, thus demonstrated a temporal accuracy of <100 msec.

Conclusion:

Results showed consistent respiratory gating stability and accuracy. MapCHECK 2 may not be sufficient for the temporal accuracy test in the respiratory gating treatment in order to meet the corresponding tolerance in TG142. One would need to decrease respiratory motion speed from the surrogate or tighten the gating window in order to be within tolerance of 100 msec temporal accuracy per TG‐142. The end‐to‐end test offers insight to the overall accuracy and uncertainties with a gated protocol. Compared to static delivery, respiratory motion increases the overall uncertainty of treatment delivery from 3% to 5% dose difference.
SU‐E‐CAMPUS‐J‐02: Implementation of Routine Clinical Daily Dose Evaluation for Patient Specific Quality Control
Authors: Brock K , Lee C , Lockhart C , Balter J , Ten Haken R , Eisbruch A
Published: July 2014

Purpose:

The use of deformable registration and dose assessment in prospective clinical trials and routine patient quality control has been limited, largely due to lack of integration of the tools into standard clinical practice and decision support tools. A clinical workflow has been developed and implemented in a standard planning system using in room image.

Methods:

A patient‐specific quality control procedure has been initiated to ensure safe and accurate treatment delivery and develop decision making guidelines for future adaptation scenarios. Deformable registration, contour propagation, and dose calculation was performed in a clinical system (Varian, Eclipse v11). Twenty head and neck patients diagnosed with base of tongue cancer and treated with volumetric modulated arc therapy (VMAT) following daily kV‐CBCT were evaluated. The planning CT was deformed to the daily CBCT to propagate the planning contours. Daily dose was calculated on the CBCT using a density calibration table and evaluated using the mapped contours. Deviations in the normal tissues were evaluated including the mean dose to the superior constrictors, left and right parotid glands (LPG, RPG), and left and right submandibular glands (LSG, RSG). The CTV D95 was also evaluated.

Results:

Deformable registration and contour propagation was qualitatively evaluated and deemed acceptable for each fraction. The average (SD) daily fluctuation (planned‐daily) in mean dose to the superior constrictor, LPG, RPG, LSG, and RSG was −3.0(6.0), 1.4(8.8), −1.1(10.7), 1.0(5.4), −2.0(8.5) cGy, respectively. The average (SD) daily fluctuation in D95 for the CTV was 3.7(3.8) cGy.

Conclusion:

Daily dose assessment is feasible in a clinically available system. Data to guide adaptive decision making guidelines have been suggested, but require evaluation on additional patients for validity, which is ongoing. Dose accumulation, which is necessary for optimizing adaptive replanning, is needed within the clinical system to fully take advantage of this data.
SU‐E‐CAMPUS‐J‐03: Commissioning of the On‐Board Cone‐Beam CT System Equipped On the Rotating Gantry of a Proton Therapy System
Authors: Takao S , Shimizu S , Miyamoto N , Matsuura T , Toramatsu C , Nihongi H , Yamada T , Matsuda K , Sasaki T , Nagamine Y , Baba R , Umekawa T , Umegaki K , Shirato H
Published: July 2014

Purpose:

Proton therapy requires highly‐precise image guidance in patient setup to ensure accurate dose delivery. Cone‐beam CT (CBCT) is expected to play an important role to reduce uncertainties in patient setup. Hokkaido University has developed a new proton therapy system dedicated to spot‐scanning under a collaborative work with Hitachi Ltd. In our system, an orthogonal X‐ray imaging system is mounted on a full‐rotating gantry. On‐board CBCT imaging is therefore available. We have conducted commissioning of the CBCT system for clinical use in proton therapy.

Methods:

The orthogonal X‐ray imaging system, which consists of two sets of X‐ray tubes and flat panel detectors (FPDs), are equipped on the rotating gantry. The FPDs are mounted on the proton beam nozzle and can be retracted when not in use. The distance between the X‐ray source and the FPD is about 2.1 m. The maximum rotation speed of the gantry is 1 rpm, so CBCT images can be acquired in approximately 1 minute. The maximum reconstruction volume is nearly 40 cm in diameter and 20 cm in axial length. For commissioning of the CBCT system, mechanical accuracy of the rotating gantry first was evaluated. Imaging performance was examined via quantitative evaluation of image quality.

Results:

Through the mechanical test, the isocentricity of the gantry was confirmed to be less than 1 mm. Moreover, it was improved to 0.5 mm with an appropriate correction. The accurate rotation of the gantry contributes to the CBCT image quality. In the image quality test, objects with 7 line‐pairs per cm, which corresponds to a line spacing of 0.071 cm, could be discerned. Spatial linearity and uniformity were also sufficient.

Conclusion:

Clinical commissioning of the on‐board CBCT system for proton therapy was conducted, and CBCT images with sufficient quality were successfully obtained.

This research was supported by the Cabinet Office, Government of Japan and the Japan Society for the Promotion of Science (JSPS) through the Funding Program for World‐Leading Innovative R&D on Science and Technology (FIRST Program), initiated by the Council for Science and Technology Policy (CSTP).
SU‐E‐CAMPUS‐J‐04: Image Guided Radiation Therapy (IGRT): Review of Technical Standards and Credentialing in Radiotherapy Clinical Trials
Authors: Giaddui T , Cui Y , Chen W , Yu J , Gong Y , Craig T , Dawson L , Al‐Hallaq H , Chmura S , Yin F , Galvin J , Xiao Y
Published: July 2014

Purpose:

To review IGRT credentialing experience and unexpected technical issues encountered in connection with advanced radiotherapy technologies as implemented in RTOG clinical trials. To update IGRT credentialing procedures with the aim of improving the quality of the process, and to increase the proportion of IGRT credentialing compliance. To develop a living disease site‐specific IGRT encyclopedia.

Methods:

Numerous technical issues were encountered during the IGRT credentialing process. The criteria used for credentialing review were based on: image quality; anatomy included in fused data sets and shift results. Credentialing requirements have been updated according to the AAPM task group reports for IGRT to ensure that all required technical items are included in the quality review process. Implementation instructions have been updated and expanded for recent protocols.

Results:

Technical issues observed during the credentialing review process include, but are not limited to: poor quality images; inadequate image acquisition region; poor data quality; shifts larger than acceptable; no soft tissue surrogate. The updated IGRT credentialing process will address these issues and will also include the technical items required from AAPM: TG 104; TG 142 and TG 179 reports. An instruction manual has been developed describing a remote credentialing method for reviewers. Submission requirements are updated, including images/documents as well as facility questionnaire. The review report now includes summary of the review process and the parameters that reviewers check. We have reached consensus on the minimum IGRT technical requirement for a number of disease sites. RTOG 1311(NRG‐BR002A Phase 1 Study of Stereotactic Body Radiotherapy (SBRT) for the Treatment of Multiple Metastases) is an example, here; the protocol specified the minimum requirement for each anatomical sites (with/without fiducials).

Conclusion:

Technical issues are identified and reported. IGRT guidelines are updated, with the corresponding credentialing requirements. An IGRT encyclopedia describing site‐specific implementation issues is currently in development.
SU‐E‐CAMPUS‐J‐05: Quantitative Investigation of Random and Systematic Uncertainties From Hardware and Software Components in the Frameless 6DBrainLAB ExacTrac System
Authors: Keeling V , Jin H , Hossain S , Ahmad S , Ali I
Published: July 2014

Purpose:

To evaluate setup accuracy and quantify individual systematic and random errors for the various hardware and software components of the frameless 6D‐BrainLAB ExacTrac system.

Methods:

35 patients with cranial lesions, some with multiple isocenters (50 total lesions treated in 1, 3, 5 fractions), were investigated. All patients were simulated with a rigid head‐and‐neck mask and the BrainLAB localizer. CT images were transferred to the IPLAN treatment planning system where optimized plans were generated using stereotactic reference frame based on the localizer. The patients were setup initially with infrared (IR) positioning ExacTrac system. Stereoscopic X‐ray images (XC: X‐ray Correction) were registered to their corresponding digitally‐reconstructed‐radiographs, based on bony anatomy matching, to calculate 6D‐translational and rotational (Lateral, Longitudinal, Vertical, Pitch, Roll, Yaw) shifts. XC combines systematic errors of the mask, localizer, image registration, frame, and IR. If shifts were below tolerance (0.7 mm translational and 1 degree rotational), treatment was initiated; otherwise corrections were applied and additional X‐rays were acquired to verify patient position (XV: X‐ray Verification). Statistical analysis was used to extract systematic and random errors of the different components of the 6D‐ExacTrac system and evaluate the cumulative setup accuracy.

Results:

Mask systematic errors (translational; rotational) were the largest and varied from one patient to another in the range (−15 to 4mm; −2.5 to 2.5degree) obtained from mean of XC for each patient. Setup uncertainty in IR positioning (0.97,2.47,1.62mm;0.65,0.84,0.96degree) was extracted from standard‐deviation of XC. Combined systematic errors of the frame and localizer (0.32,−0.42,−1.21mm; −0.27,0.34,0.26degree) was extracted from mean of means of XC distributions. Final patient setup uncertainty was obtained from the standard deviations of XV (0.57,0.77,0.67mm,0.39,0.35,0.30degree).

Conclusion:

Statistical analysis was used to calculate cumulative and individual systematic errors from the different hardware and software components of the 6D‐ExacTrac‐system. Patients were treated with cumulative errors (<1mm,<1degree) with XV image guidance.
SU‐E‐CAMPUS‐J‐06: The Impact of CT‐Scan Energy On Range Uncertainty in Proton Therapy Planning
Authors: Grantham K , Li H , Zhao T , Klein E
Published: July 2014

Purpose:

To investigate the impact of tube potential (kVp) on the CTnumber (HU) to proton stopping power ratio (PSPR) conversion table; the range uncertainty and the dosimetric change introduced by a mismatch in kVp between the CT and the HU to PSPR table used to calculate dose are analyzed.

Methods:

A CIRS CT‐ED phantom was scanned with a Philips Brilliance 64‐slice scanner under 90kVp and 120kVp tube potentials. Two HU to PSPR curves were then created. Using Eclipse (Varian) a treatment plan was created for a single beam in a water phantom (HU=0) passing through a wedge‐shaped heterogeneity (HU=1488). The dose was recalculated by changing only the HU to PSPR table used in the dose calculation. The change in range (the distal 90% isodose line) relative to a distal structure was recorded as a function of heterogeneity thickness in the beam. To show the dosimetric impact of a mismatch in kVp between the CT and the HU to PSPR table, we repeated this procedure using a clinical plan comparing DVH data.

Results:

The HU to PSPR tables diverge for low‐density bone and higher density structures. In the phantom plan, the divergence of the tables results in a change in range of ~1mm per cm of bone in the beam path for the HU used. For the clinical plan, a mismatch in kVp showed a 28% increase in mean dose to the brainstem along with a 10% increase in maximum dose to the brainstem center.

Conclusion:

A mismatch in kVp between the CT and the HU to PSPR table can introduce significant uncertainty in the proton beam range. For dense bone, the measured range uncertainty is about 1mm per cm of bone in the beam. CT‐scan energy verification should be employed, particularly when high‐density media is in the proton beam path.
SU‐F‐19A‐01: APBI Brachytherapy Treatment Planning: The Impact of Heterogeneous Dose Calculations
Authors: Loupot S , Han T , Salehpour M , Gifford K
Published: July 2014

Purpose:

To quantify the difference in dose to PTV_EVAL and OARs (skin and rib) as calculated by (TG43) and heterogeneous calculations (CCC).

Methods:

25 patient plans (5 Contura and 20 SAVI) were selected for analysis. Clinical dose distributions were computed with a commercially available treatment planning algorithm (TG43‐D_(w,w)) and then recomputed with a pre‐clinical collapsed cone convolution algorithm (CCCD_(m,m)). PTV_EVAL coverage (V90%, V95%), and rib and skin maximum dose were compared via percent difference. Differences in dose to normal tissue (V150cc, V200cc of PTV_EVAL) were also compared. Changes in coverage and maximum dose to organs at risk are reported in percent change, (100*(TG43 − CCC) / TG43)), and changes in maximum dose to normal tissue are absolute change in cc (TG43 − CCC).

Results:

Mean differences in V90, V95, V150, and V200 for the SAVI cases were −0.2%, −0.4%, −0.03cc, and −0.14cc, respectively, with maximum differences of −0.78%, −1.7%, 1.28cc, and 1.01cc, respectively. Mean differences in the 0.1cc dose to the rib and skin were −1.4% and −0.22%, respectively, with maximum differences of −4.5% and 16%, respectively. Mean differences in V90, V95, V150, and V200 for the Contura cases were −1.2%, −2.1%, −1.8cc, and −0.59cc, respectively, with maximum differences of −2.0%, −3.16%, −2.9cc, and −0.76cc, respectively. Mean differences in the 0.1cc dose to the rib and skin were −2.6% and −3.9%, respectively, with maximum differences of −3.2% and −5.7%, respectively.

Conclusion:

The effects of translating clinical knowledge based on D_(w,w) to plans reported in D_(m,m) are minimal (2% or less) on average, but vary based on the type and placement of the device, source, and heterogeneity information.
SU‐F‐19A‐02: Comparison of Absorbed Dose to Water Standards for HDR Ir‐192 Brachytherapy Between the LCR, Brazil and NRC, Canada
Authors: Salata C , David M , de Almeida C , El Gamal I , Cojocaru C , Mainegra‐Hing E , McEwen M
Published: July 2014

Purpose:

To compare absorbed dose to water standards for HDR brachytherapy dosimetry developed by the Radiological Science Laboratory of Rio de Janeiro State University (LCR) and the National Research Council, Canada (NRC).

Methods:

The two institutions have separately developed absorbed dose standards based on the Fricke dosimetry system. There are important differences between the two standards, including: preparation and read‐out of the Fricke solution, irradiation geometry of the Fricke holder in relation to the Ir‐192 source, and determination of the G‐value to be used at Ir‐192 energies. All measurements for both standards were made directly at the NRC laboratory (i.e., no transfer instrument was used) using a single Ir‐192 source (microSelectron v2). In addition, the NRC group has established a self‐consistent method to determine the G‐value for Ir‐192, based on an interpolation between G‐values obtained at Co‐60 and 250kVp X‐rays, and this measurement was repeated using the LCR Fricke solution to investigate possible systematic uncertainties.

Results:

G‐values for Co‐60 and 250 kVp x‐rays, obtained using the LCR Fricke system, agreed with the NRC values within 0.5 % and 1 % respectively, indicating that the general assumption of universal G‐values is appropriate in this case. The standard uncertainty in the determination of G for Ir‐192 is estimated to be 0.6 %. For the comparison of absorbed dose measurements at the reference point for Ir‐192 (1 cm depth in water, perpendicular to the seed long‐axis), the ratio Dw(NRC)/Dw(LCR) was found to be 1.011 with a combined standard uncertainty of 1.7 %, k=1.

Conclusion:

The agreement in the absorbed dose to water values for the LCR and NRC systems is very encouraging. Combined with the lower uncertainty in this approach compared to the present air‐kerma approach, these results reaffirm the use of Fricke solution as a potential primary standard for HDR Ir‐192 brachytherapy.
SU‐F‐19A‐03: Dosimetric Advantages in Critical Structure Dose Sparing by Using a Multichannel Cylinder in High Dose Rate Brachytherapy to Treat Vaginal Cuff Cancer
Authors: Syh J , Syh J , Patel B , Zhang J , Wu H , Rosen L
Published: July 2014

Purpose:

The multichannel cylindrical vaginal applicator is a variation of traditional single channel cylindrical vaginal applicator. The multichannel applicator has additional peripheral channels that provide more flexibility in the planning process. The dosimetric advantage is to reduce dose to adjacent organ at risk (OAR) such as bladder and rectum while maintaining target coverage with the dose optimization from additional channels.

Methods:

Vaginal HDR brachytherapy plans are all CT based. CT images were acquired in 2 mm thickness to keep integrity of cylinder contouring. The CTV of 5mm Rind with prescribed treatment length was reconstructed from 5mm expansion of inserted cylinder. The goal was 95% of CTV covered by 95% of prescribed dose in both single channel planning (SCP)and multichannel planning (MCP) before proceeding any further optimization for dose reduction to critical structures with emphasis on D2cc and V2Gy .

Results:

This study demonstrated noticeable dose reduction to OAR was apparent in multichannel plans. The D2cc of the rectum and bladder were showing the reduced dose for multichannel versus single channel. The V2Gy of the rectum was 93.72% and 83.79% (p=0.007) for single channel and multichannel respectively (Figure 1 and Table 1). To assure adequate coverage to target while reducing the dose to the OAR without any compromise is the main goal in using multichannel vaginal applicator in HDR brachytherapy.

Conclusion:

Multichannel plans were optimized using anatomical based inverse optimization algorithm of inverse planning simulation annealing. The optimization solution of the algorithm was to improve the clinical target volume dose coverage while reducing the dose to critical organs such as bladder, rectum and bowels. The comparison between SCP and MCP demonstrated MCP is superior to SCP where the dwell positions were based on geometric array only. It concluded that MCP is preferable and is able to provide certain features superior to SCP.
SU‐F‐19A‐04: Dosimetric Evaluation of a Novel CT/MR Compatible Fletcher Applicator for Intracavitary Brachytherapy of the Cervix Uteri
Authors: Gifford K , Han T , Mourtada F , Eifel P
Published: July 2014

Purpose:

To validate a Monte Carlo model and evaluate the dosimetric capabilities of a novel commercial CT/MR compatible Fletcher applicator for cervical cancer brachytherapy.

Methods:

MCNPX 2.7.0 was used to model the Fletcher CT/MR shielded applicator (FA) and 192Ir HDR source. Energy deposition was calculated with a track length estimator modified by an energy‐dependent heating function. A high density polystyrene phantom was constructed with three film pockets for validation of the MCNPX model. Three planes of data were calculated with the MCNPX model corresponding to the three film planes in phantom. The planes were located 1 cm from the most anterior, posterior, and medial extents of the FA right ovoid. Unshielded distributions were calculated by modeling the shielded cells as air instead of the tungsten alloy. A third order polynomial fit to the OD to dose curve was used to convert OD of the three film planes to dose. Each film and MCNPX plane dose distribution was normalized to a point 2 cm from the center of the film plane and in a region of low dose gradient. MCNPX and film were overlaid and compared with a distance‐to‐agreement criterion of (±2%/±2mm). Shielded and unshielded distributions were overlaid and a percent shielded plot was created.

Results:

85.2%, 97.1%, and 96.6% of the MCNPX points passed the (±2%/±2mm) criterion respectively for the anterior, lateral, and posterior film comparison planes. A majority of the points in the anterior plane that exceeded the DTA criterion were either along edges of where the film was cut or near the terminal edges of the film. The percent shielded matrices indicated that the maximum % shielding was 50%.

Conclusion:

These data confirm the validity of the FA Monte Carlo model. The FA ovoid can shield up to 50% of the dose in the anteroposterior direction.
SU‐F‐19A‐05: Experimental and Monte Carlo Characterization of the 1 Cm CivaString 103Pd Brachytherapy Source
Authors: Reed J , Rivard M , Micka J , Culberson W , DeWerd L
Published: July 2014

Purpose:

To determine the in‐air azimuthal anisotropy and in‐water dose distribution for the 1 cm length of the CivaString 103Pd brachytherapy source through measurements and Monte Carlo (MC) simulations. American Association of Physicists in Medicine Task Group No. 43 (TG‐43) dosimetry parameters were also determined for this source.

Methods:

The in‐air azimuthal anisotropy of the source was measured with a NaI scintillation detector and simulated with the MCNP5 radiation transport code. Measured and simulated results were normalized to their respective mean values and compared. The TG‐43 dose‐rate constant, line‐source radial dose function, and 2D anisotropy function for this source were determined from LiF:Mg,Ti thermoluminescent dosimeter (TLD) measurements and MC simulations. The impact of 103Pd well‐loading variability on the in‐water dose distribution was investigated using MC simulations by comparing the dose distribution for a source model with four wells of equal strength to that for a source model with strengths increased by 1% for two of the four wells.

Results:

NaI scintillation detector measurements and MC simulations of the in‐air azimuthal anisotropy showed that ≥95% of the normalized data were within 1.2% of the mean value. TLD measurements and MC simulations of the TG‐43 dose‐rate constant, line‐source radial dose function, and 2D anisotropy function agreed to within the experimental TLD uncertainties (k=2). MC simulations showed that a 1% variability in 103Pd well‐loading resulted in changes of <0.1%, <0.1%, and <0.3% in the TG‐43 dose‐rate constant, radial dose distribution, and polar dose distribution, respectively.

Conclusion:

The CivaString source has a high degree of azimuthal symmetry as indicated by the NaI scintillation detector measurements and MC simulations of the in‐air azimuthal anisotropy. TG‐43 dosimetry parameters for this source were determined from TLD measurements and MC simulations. 103Pd well‐loading variability results in minimal variations in the in‐water dose distribution according to MC simulations.

This work was partially supported by CivaTech Oncology, Inc. through an educational grant for Joshua Reed, John Micka, Wesley Culberson, and Larry DeWerd and through research support for Mark Rivard.
SU‐F‐19A‐06: Experimental Investigation of the Energy Dependence of TLD Sensitivity in Low‐Energy Photon Beams
Authors: Chen Z , Nath R
Published: July 2014

Purpose:

To measure the energy dependence of TLD sensitivity in lowenergy photon beams with equivalent mono‐energetic energy matching those of 103Pd, 125I and 131Cs brachytherapy sources.

Methods:

A Pantek DXT 300 x‐ray unit (Precision X‐ray, Branford, CT), with stable digital voltage control down to 20 kV, was used to establish three lowenergy photon beams with narrow energy spread and equivalent monoenergetic energies matching those of 103Pd, 125I and 131Cs brachytherapy sources. The low‐energy x‐ray beams and a reference 6 MV photon beam were calibrated according to the AAPM TG‐61 and TG‐51 protocols, respectively, using a parallel‐plate low‐energy chamber and a Farmer cylindrical chamber with NIST traceable calibration factors. The dose response of model TLD‐100 micro‐cubes (1×1×1 mm3) in each beam was measured for five different batches of TLDs (each contained approximately 100 TLDs) that have different histories of irradiation and usage. Relative absorbed dose sensitivity was determined as the quotient of the slope of dose response for a beam‐of‐interest to that of the reference beam.

Results:

Equivalent mono‐energetic photon energies of the low‐energy beams established for 103Pd, 125I and 131Cs sources were 20.5, 27.5, and 30.1 keV, respectively. Each beam exhibited narrow spectral spread with energyhomogeneity index close to 90%. The relative absorbed‐dose sensitivity was found to vary between different batches of TLD with maximum differences of up to 8%. The mean and standard deviation determined from the five TLD batches was 1.453 ± 0.026, 1.541 ± 0.035 and 1.529 ± 0.051 for the simulated 103P, 125I and 131Cs beams, respectively.

Conclusion:

Our measured relative absorbed‐dose sensitivities are greater than the historically measured value of 1.41. We find that the relative absorbed‐dose sensitivity of TLD in the 103P beam is approximately 5% lower than that of 125I and 131Cs beams. Comparison of our results with other studies will be presented.
SU‐F‐19A‐07: Is a Day30 Scan Necessary to Evaluate Activity‐Based Regulatory Compliance in Permanent Interstitial Brachytherapy for Prostate Cancer?
Authors: Kapur P , Ford J , Moghanaki D , Datsang R , Chang M , Hagan M , Palta J , Rosu M
Published: July 2014

Purpose:

To evaluate the Medical Event (ME) criteria for I‐125 prostate implants based on the assessment of post implant dosimetry on “Day0”/“Day30” imaging. The new ME criteria do not mandate a timeframe for this assessment. The compliance criteria are: more than 80% of the activity from the written directive for treatment site (TS) must be implanted inside TS, and doses to 1cc of either uninvolved rectum (D1_UR) or uninvolved bladder (D1_UB), or 2cc of other non‐specified tissue (D2_UT) must be less than 150% of the planned dose.

Methods:

“Day0”/“Day30” post‐implant analyses for 25 patients were evaluated. Treatment plans had a peripheral loading pattern with 2 core needles placed at least 10 mm away from urethra, with several seeds planned outside of the prostate for adequate target coverage. TS were a uniform 5 mm expansion of the prostate, except posteriorly (no expansion).

Results:

“Day0”/“Day30”analyses found no MEs. The relative changes for D1_UR, D1_UB, and D2_UT were (ranges): [−37.0, 38.2]%, [−96.5, 74.7]%, and [−41.2, 37.7]%. Furthermore, changes did not correlate with prostate volume changes of −18.7% [σ:16.0%, range:−60.5%, +6.4%]. These unfavorable changes did not lead to ME at “Day30” because these values were generally well below 150% at “Day0”. However, D2_UT dose values exceeded those for D1_UR and D1_UB at both “Day0”/“Day30”.

Conclusion:

The total activity was relatively insensitive to changes in target volume from “Day0” to ”Day30”. The dose metrics of interest, albeit susceptible to large, often unfavorable changes, remained less than the 150% threshold. Data from this study suggest that “Day0” can be used for the regulatory compliance evaluation. However, further evaluation at “Day30” is advisable if D2_UT is 110% or above (based on the largest D2_UT increase of 37.7% observed in this patient population). Future rigorous statistical analysis of a larger cohort will afford a refinement of this recommendation.
SU‐F‐19A‐08: Optimal Time Release Schedule of In‐Situ Drug Release During Permanent Prostate Brachytherapy
Authors: Cormack R , Ngwa W , Tangutoori S , Rajiv K , Sridhar S , Makrigiorgos G
Published: July 2014

Purpose:

Permanent prostate brachytherapy spacers can be used to deliver sustained doses of radiosentitizing drug directly to the target, in order to enhance the radiation effect. Implantable nanoplatforms for chemo‐radiation therapy (INCeRTs) have a maximum drug capacity and can be engineered to control the drug release schedule. The optimal schedule for sensitization during continuous low dose rate irradiation is unknown. This work studies the optimal release schedule of drug for both traditional sensitizers, and those that work by suppressing DNA repair processes.

Methods:

Six brachytherapy treatment plans were used to model the anatomy, implant geometry and calculate the spatial distribution of radiation dose and drug concentrations for a range of drug diffusion parameters. Three state partial differential equations (cells healthy, damaged or dead) modeled the effect of continuous radiation (radiosensitivities α,β) and cellular repair (time tr) on a cell population. Radiosensitization was modeled as concentration dependent change in α,β or tr which with variable duration under the constraint of fixed total drug release. Average cell kill was used to measure effectiveness. Sensitization by means of both enhanced damage and reduced repair were studied.

Results:

Optimal release duration is dependent on the concentration of radiosensitizer compared to the saturation concentration (csat) above which additional sensitization does not occur. Long duration drug release when enhancing α or β maximizes cell death when drug concentrations are generally over csat. Short term release is optimal for concentrations below saturation. Sensitization by suppressing repair has a similar though less distinct trend that is more affected by the radiation dose distribution.

Conclusion:

Models of sustained local radiosensitization show potential to increase the effectiveness of radiation in permanent prostate brachytherapy. INCeRTs with high drug capacity produce the greatest benefit with drug release over weeks. If in‐vivo drug concentrations are not able to approach saturation concentration, durations of days is optimal.

DOD 1R21CA16977501; A. David Mazzone Awards Program 2012PD164
SU‐F‐19A‐09: Propagation of Organ at Risk Contours for High Dose Rate Brachytherapy Planning for Cervical Cancer: A Deformable Image Registration Comparison
Authors: Bellon M , Kumarasiri A , Kim J , Shah M , Elshaikh M , Chetty I
Published: July 2014

Purpose:

To compare the performance of two deformable image registration (DIR) algorithms for contour propagation and to evaluate the accuracy of DIR for use with high dose rate (HDR) brachytherapy planning for cervical cancer.

Methods:

Five patients undergoing HDR ring and tandem brachytherapy were included in this retrospective study. All patients underwent CT simulation and replanning prior to each fraction (3–5 fractions total). CT‐to‐CT DIR was performed using two commercially available software platforms: SmartAdapt, Varian Medical Systems (Demons) and Velocity AI, Velocity Medical Solutions (B‐spline). Fraction 1 contours were deformed and propagated to each subsequent image set and compared to contours manually drawn by an expert clinician. Dice similarity coefficients (DSC), defined as, DSC(A,B)=2(AandB)/(A+B) were calculated to quantify spatial overlap between manual (A) and deformed (B) contours. Additionally, clinician‐assigned visual scores were used to describe and compare the performance of each DIR method and ultimately evaluate which was more clinically acceptable. Scoring was based on a 1–5 scale—with 1 meaning, “clinically acceptable with no contour changes” and 5 meaning, “clinically unacceptable”.

Results:

Statistically significant differences were not observed between the two DIR algorithms. The average DSC for the bladder, rectum and rectosigmoid were 0.82±0.08, 0.67±0.13 and 0.48±0.18, respectively. The poorest contour agreement was observed for the rectosigmoid due to limited soft tissue contrast and drastic anatomical changes, i.e., organ shape/filling. Two clinicians gave nearly equivalent average scores of 2.75±0.91 for SmartAdapt and 2.75±0.94 for Velocity AI—indicating that for a majority of the cases, more than one of the three contours evaluated required major modifications.

Conclusion:

Limitations of both DIR algorithms resulted in inaccuracies in contour propagation in the pelvic region, thus hampering the clinical utility of this technology. Further work is required to optimize these algorithms and take advantage of the potential of DIR for HDR brachytherapy planning.