bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐725: The Analysis of Different Diagonal Profiles Used for Commissioning in Eclipse
Authors: Mabhouti H , Acar H , Kucuk N , Kucukmorkoc E , Doyuran M , Caglar M , Altinok A , Cebe M , Yilidir G , Caglar H
Published: June 2015

Purpose:

The effect of diagonal profiles measured with different types of detectors to the improvement of the quality of the algorithm configuration is analysed.

Methods:

For commissioning of Truebeam STx machine, Eclipse requires a diagonal profiles of the largest field size. The left side of the beam profile with 5cm overscan at depths of 30cm for a 40×40cm2 field at 100cm SSD was scanned. The scan was made using PTW 0.125cc semiflex ionization chamber and PTW microDiamond with 0.004mm3 sensitive volume. Two different machnines were created in Eclipse with the same beam data except for diagonal profiles. A single 6 FFF beam with zero gantry and collimator angle for 10×10cm2 field size was planned on the CT scan of RW3 solid water. The dose calculation was done with 1mm grid size using AcurosXB v13 algorithm. Dose profile measurements were made in a RW3 solid water phantom at depths of 5, 10, 15cm using EBT3 Gafchromic film extending from field edge up to 15cm. The gamma index analysis of measured and calculated dose profiles were compared.

Result:

For the plan using semiflex configured machine, the measured and the calculated dose distributions gamma analysis passing rate was 98.1% within ±2% dose difference and ±2mm distance‐to‐agreement for in field doses. However they decreases to 96.8% for out of field doses. For the plan using microDiamond configured machine had 98.9% passing rate for ±2% in field but it decreases to 97.6% for out of field doses. Although passing rates were increasing with the depth for in field doses they were decreasing with depth for out of field doses.

Conclusion:

Diagonal profiles are used for source configuration in Eclipse. Because of that it can be advisable to use fine resolution detector.
SU‐E‐T‐726: The Analysis of Different Percentage Depth Dose Curves Used for Commissioning in Eclipse
Authors: Cebe M , Acar H , Kucuk N , Kucukmorkoc E , Doyuran M , Caglar M , Altinok A , Yilidir G , Mabhouti H , Caglar H
Published: June 2015

Purpose:

Percentage Depth Doses (PDDs) used for balance fitting of the calculation model in Eclipse. The effect of PDD curves measured with two different detectors for the commissioning of Truebeam STx machine to the improvement of the quality of the algorithm configuration is analysed.

Methods:

The measurement of open field PDD for 2×2cm2 to 40×40cm2 field sizes were done with two different detector types. The scan was made using 0.125cc semiflex thimble ionization chamber (PTW TM31010) and PTW 60019 microDiamond with 0.004mm3 sensitive volume. Two different machines were created in Eclipse with the same beam data except for PDD measured with two different detector types. A single 6 FFF beam with zero gantry and collimator angles for 2×2, 3×3, 5×5cm2 field sizes were planned on the CT scan of RW3 solid water. The dose calculation was done with 1mm grid size using AcurosXB v13 algorithm using two different machine created. PDD measurements were made in a RW3 solid water phantom using EBT3 Gafchromic film extending from surface to 30cm. The gamma index analysis of measured and calculated PDD curves were compared.

Result:

For the plan made using machine configured with semiflex measured PDD curves, the measured and the calculated dose distributions for 2×2cm2 field size gamma analysis passing rate was 97.6% within 2% dose difference and 2mm distance‐to‐agreement. For the plan made using machine configured with microDiamond measured PDD curves had 98.1% passing rate for ±2% in field but the passing rates. Passing rates were increasing with the field sizes. For 5×5cm2 field size they are 98.3% and 99.1% respectively.

Conclusion:

The agrement with treatment planning system and measurement was better when fine resolution detector was used especially for small field sizes.
SU‐E‐T‐729: The Dosimetric Impact of Moving Small Size Lung Tumor Using Helical Tomotherapy
Authors: Tu P , Nien H , Lee H , Wu C , Lin C , Lin C
Published: June 2015

Purpose:

Respiration during radiotherapy irradiation causes dose delivery uncertainty to the lung tumor. This phantom study was designed to investigate the dosimetric impact of tumor motion during respiration with TomoTherapy treatment.

Methods:

Dynamic thorax phantom (CIRS. Inc, Norfolk, VA), was used to mimic small size lung tumors (1, 2, and 3cm in diameter) motion during respiration. CT images of tumors under static condition were imported into TomoTherapy Hi‐Art system. Plans were calculated with different jaw sizes for each size of tumor. Dose measurement was performed under both static and respiratory simulation produced by dynamic thorax phantom. Our respiratory simulation setting was chosen due to more compatible with clinical breathing cycle pattern including 1cm amplitude movement in SI direction, 4s breathing period and cos6 breathing pattern. Two‐dimensional dose of DQA plans were measured by EBT3 films. The point dose was measured in the center of each tumor using A1SL ion chamber.

Results:

The point dose of 1 cm motion tumor was 9% higher than plan dose, and decreased variation by increasing jaw size. The point dose of 1 cm and 2 cm motion tumors were greater than static tumors, but the results of 3 cm tumor were in contrast. Dose coverage was improved by increasing tumor size and jaw size. The width of 50% dose level of motion tumors on horizontal 2D dose profile were similar with widths of static tumor, but dose distribution shifted toward inferior direction. The widths of 60% dose level of motion tumors were smaller than widths of static tumor and difference decreased by increasing tumor and jaw size.

Conclusion:

Small size motion tumor has greater dose difference than bigger tumors. Large jaw size leads to more penumbra but provides better dose coverage. Larger margin was suggested at the longitudinal superior direction to compensate the dose distribution deviation during respiration.
SU‐E‐T‐731: The Effect of Thermoplatic Mask to the Surface Dose in Sterotactic Brain Treatments with Flattening Filter Free Beams with EBT3 Gafchromic Film and OSL Dosimeter
Authors: Yilidir G , Acar H , Kucuk N , Kucukmorkoc E , Doyuran M , Caglar M , Altinok A , Cebe M , Mabhouti H , Caglar H
Published: June 2015

Purpose:

The surface dose of flattening filter free beams is higher than conventional flattening filter beams. In this study, The effect of thermoplatic mask to the surface dose in sterotactic brain treatments was compared using EBT3 Gafchromic film and OSL dosimeter.

Methods:

Treatment planning were done using 2 full arc VMAT technique with 6 FFF beam on the CT scan of Randophantom simulating the treatment of sterotactic treatments for one brain metastasis.1×1 cm2 Gafchromic EBT 3 film pieces were placed under the thermoplastic mask on the lens of the phantom. Then OSL dosimeter was also placed at the same way in the same place. Then phantom was irradiated without mask with film and OSL again. The surface doses with or without mask was compared for film and OSL dosimeter seperately.

Results:

The calibration of film and OSL dosimetry were done at first. Surface dosemeasurements made using the EBT3 film showed good agreement with results of the OSL dosimetry for standard fields of FFF beams within the measurement uncertainty of 3.1%. The surface dose determined using EBT3 film was found to change from 57 % to 93 % to with the mask. The surface dose determined using OSL dosimeter was found to change from 56 % to 93 % to with the mask. This study also demonstrates the suitability of Gafchromic EBT3 film and OSL dosimeter for surface dose measurements in FFF beams.

Conclusion:

The skin sparing effect FFF beams are lower than conventional beams. Significant bolus effect on skin dose in the presence of thermoplastic mask was seen. The skin reactions resulting from thermoplastic masks should be monitored especially for FFF beams and corrective measures should be taken during treatment to avoid skin toxicity.
SU‐E‐T‐732: The Effects of Calcification Modeling for Monte Carlo Dose Calculations of Low Dose Rate Prostate Brachytherapy
Authors: Sutherland J , Miksys N , Soubiran P , Cygler J , Thomson R
Published: June 2015

Purpose:

Retrospective Monte Carlo calculations recently revealed that tissue calcifications cause significant dose perturbations in low dose rate prostate brachytherapy patients. This work investigates dose differences due to calcification modeling schemes of varying complexity for MC dose calculations.

Methods:

A prostate cancer patient with a large prostatic calcification (∼2.3 cm3) treated with 125I seeds was studied. MC calculations were performed using the EGSnrc user‐code BrachyDose with dose scored to medium in medium. Computational phantoms were generated from CT images acquired one month post‐implant. Tissues were assigned to voxels within structure contours based on CT number: prostate and calcification within the target, air and muscle within the rectum, urinary bladder within the bladder, and ICRU 46 soft tissue and bone in remaining voxels. Target models included: water only (TG‐43), prostate tissue with CT‐derived mass densities except for higher calcification densities over¬ridden with prostate nominal density, only prostate with unmodified CT‐derived densities, prostate and 100% calcification with CT‐derived densities (PC), and prostate and incremental mixtures of prostate and calcification with CT‐derived densities (PCmix).

Results:

Local dose differences of up to a factor of 3 or more were found between the various models including significant dose differences between PC and PCmix inside and adjacent to the calcification. Dose metrics differ between the models with the minimum dose that 90% of the target received (D90) differing by 4% between PC and PCmix. Adjacent to calcification, doses for calcification models were approximately 50% less than those calculated by TG‐43. D90 for calcification models was approximately 80–90% the value of that calculated by TG‐43.

Conclusions:

Considerable dose differences were found between calculations using various calcification modeling schemes for a low dose rate prostate brachytherapy patient with prostatic calcifications, highlighting the importance of detailed and accurate calcification modeling for MC dose calculations of these treatments.
SU‐E‐T‐737: The Impact of the Size of Custom Lead Shields On the Dosimetry of Electron Beam Therapy
Authors: Georgiev G , Jacobs K , Zuro D , Kim Y
Published: June 2015

Purpose:

Often the management of deeply penetrated skin cancer (>1cm) involves a standard open election field that is blocked with lead shields at patient's surface to shield adjacent organs at risk. This may Result in change of the known dose distribution inherent to the respective standard electron cone size. The purpose of this study is to investigate the impact of such shield on the depth dose and profile and to provide more accurate dose distribution.

Methods:

Gafchromic EBT2 film was used to measure the doses and dose profiles in solid water for 6 MeV and 9 MeV electron beams. The film was calibrated up to 300 cGy. Each film was scanned 24 hours after irradiation. The doses at central axes were measure at 3 different depths (dmax, 90% and 80% isodose lines (IDL)) for two standard circular sizes (5 cm and 8 cm diameters). Each field was either open or partially blocked at the surface of the solid water by 1, 2 and/or 3 cm wide and 5mm thick lead strips from two opposite edges of the light field.

Results:

For the majority of the cases the dose to the central axes decreases with increase of the blocked area of the field. This difference is more pronounced for smaller field size and higher energy. Compared to the depth of 80% and 90% IDL, the dose at d max is less influenced by increasing of the blocked area.

Conclusion:

This work accentuates on the important aspect of the use of custom shields in clinical electron radiation therapy. Particularly when smaller field sizes are used, the dose difference at the prescription depth could be as high as 60%.
SU‐E‐T‐741: The Resources and Cost to Operate An Intraoperative Radiation Therapy Program for Accelerated Partial Breast Irradiation Using a Low‐Energy X‐Ray Source
Authors: Morales‐Paliza M , Ding G
Published: June 2015

Purpose:

To report our experience regarding resource requirements and cost to operate an intraoperative‐radiation therapy (IORT) since 2011, for accelerated‐partial‐breast irradiation (APBI) using the Axxent controller (Xoft Inc.).

Methods:

To start an IORT program for APBI utilizing the Axxent controller with 50‐keV x‐ray source, the required resources include acquisition of the Axxent controller and a set of quality assurance (QA) tools, the training of involved professionals‐surgeons, oncologists, nurses, and physicists‐to use and operate the system, state license, storage room for the equipment, full‐time availability of the operating personnel on the procedure day, a survey meter, an ultrasound unit, sparing for x‐ray source (at least, two) and cooling‐tubing system, shielding equipment, etc. In each treatment day, QA procedures are required to test the controller performance before patient irradiation in the operation room (OR).

Results:

During 40 months, 76 procedures were performed. Six surgeons, two oncologists, three nurses and three physicists were trained for the procedure. Irradiation times ranged 7.4–28.6 (mean=11.7) minutes. Eight different x‐ray sources were utilized with usage times ranging 33.4–166.8 (mean=108.7) minutes. Sixteen different combinations of spherical‐balloon applicators and volumes were employed, with 40‐cc (22%) and 30‐cc (20%) volumes of the 3–4‐cm applicator being the most used. Replacement of the x‐ray sources due to arcing during patient irradiation and leak of the cooling‐water system in the OR occurred twice and once, respectively. A defective brand‐new x‐ray source (arcing) happened once.

Conclusion:

To start and maintain a successful IORT program, for APBI using a low‐energy x‐ray source, institutional commitment‐in addition to the resource requirements that are specific to the program‐is necessary. Based on our over‐3‐year experience, the cost of the x‐ray sources and equipment services along with vendor contract averaged US$1,000–2,000 per treatment, without considering manpower and any other resource expenses.
SU‐E‐T‐742: The Risk of Secondary Malignancies as An Evaluation Factor in the Comparison of Prostate Cancer Intensity Modulated Radiotherapy (IMRT) and Conformal Radiotherapy (CRT) Treatment Plans
Authors: Komisopoulos G , Buckey C , Stathakis S , Sakellaropoulos G , Kardamakis D , Nikoforidis G , Papanikolaou N , Mavroidis P
Published: June 2015

Purpose:

To examine the clinical efficacy of both MLC‐based IMRT, and 3D‐Conformal Radiation Therapy modalities (CRT) to treat prostate cancer using radiobiological measures. Furthermore, to investigate the risk for developing secondary malignancies in bladder and rectum due to radiotherapy from the corresponding modalities.

Methods:

Treatment plans for prostate cancer were developed using IMRT and CRT for ten patients. For the IMRT plans, two different treatment protocols were used (RTOG and FCCC). For the evaluation of these plans, the complication‐free tumor control probability, the total probability of injury, the total probability of control/benefit, and the biologically effective uniform dose were employed. Furthermore, based on the dosimetric data of IMRT and CRT, the risk for secondary malignancies was calculated for bladder and rectum.

Results:

The average risk for secondary malignancy was lower for the bladder (0.37%) compared to the rectum (0.81%) based on all the treatment plans of the ten prostate cancer patients. The highest average risk for secondary malignancy for bladder and rectum was for the 6X 3D modality (0.46% and 1.12%, respectively) and the lowest was for the 18X IMRT RTOG modality (0.33% and 0.56%, respectively). The response probability was lower for the bladder than for the rectum in all the plans. For the bladder the highest value was for the 18X IMRT FCCC (0.03%) and the lowest was for the 18X 3D modality (0.0%). For the rectum, the highest value was for the 6X IMRT RTOG (3.52%) and the lowest was for the 18X IMRT FCCC modality (0.41%).

Conclusion:

By using radiobiological measures it is shown that the IMRT FCCC plans had the lowest risks for normal tissue complications, whereas the IMRT RTOG had the highest. Regarding the risk for secondary malignancies, the CRT plans showed the highest values both in bladder and rectum.
SU‐E‐T‐743: The Simple Monitor Unit Calculation for Irregular Field in Passive Proton Beam
Authors: Yamakawa T , Hayashi N , Hamano H , Yasui K , Kato H
Published: June 2015

Purpose:

We try to apply the monitor unit (MU) calculation procedure for passively proton beam therapy. For estimation of field size factor (FSF) in the process, we used root A method for conversion from irregular field to equivalent field so far. In this time, we changed the conversion from root A method to Clarkson method. The purpose of this study is to ensure the calculation accuracy by comparative evaluation between root A and Clarkson methods.

Methods:

As fundamental study, we measured absolute dose with several circular field. Then we performed experimental fitting of conversion curve. With this method, the conversion from the equivalent circular field to equivalent square field is available by the assumed equation. As clinical study, we compared the measured MU with the calculated MU (root A and Clarkson method) in 28 prostate patients (76 fields) for the purpose of evaluating the feasibility of our procedure. To simplify the comparison of the calculation procedure, we built the dedicated MU calculation software.

Results:

As the Result of fundamental study, the assumed equation for conversion from circular field to square field was estimated. As the Result of clinical study, the differences between the measured MU and the calculated MU were within 2% in all cases. All calculated MU were calculated by our software. The differences of MU calculation between measurement MU and calculation MU (root A and Clarkson) were less than 2% for all cases. The average difference and standard deviation of MU calculation between the root A and Clarkson was 0.05±0.05%. However, the calculation accuracy of Clarkson method should be verified in the complicated cases.

Conclusion:

The MU calculation by use of Clarkson method was supposed and verified in this study. For prostate cases, the Clarkson method is feasible for MU calculation procedure.
SU‐E‐T‐756: Tissue Inhomogeneity Corrections in Intra‐Operative Radiotherapy
Authors: Sethi A , Chinsky B , Gros S , Diak A , Roeske J , Emami B , Small W
Published: June 2015

Purpose:

Investigate the impact of tissue inhomogeneities on dose distributions produced by low‐energy X‐rays in intra‐operative radiotherapy (IORT).

Methods:

A 50‐kV INTRABEAM X‐ray device with superficial (Flat and Surface) applicators was commissioned at our institution. For each applicator, percent depth‐dose (PDD), dose‐profiles (DP) and output factors (OF) were obtained. Calibrated GaFchromic (EBT3) films were used to measure dose distributions in solid water phantom at various depths (2, 5, 10, and 15 mm). All recommended precautions for film‐handling, film‐exposure and scanning were observed. The effects of tissue inhomogeneities on dose distributions were examined by placing air‐cavities and bone and tissue equivalent materials of different density (ρ), atomic number (Z), and thickness (t = 0–4mm) between applicator and film detector. All inhomogeneities were modeled as a cylindrical cavity (diameter 25 mm). Treatment times were calculated to deliver 1Gy dose at 5mm depth. Film results were verified by repeat measurements with a thin‐window parallel plate ion‐chamber (PTW 34013A) in a water tank.

Results:

For a Flat‐4cm applicator, the measured dose rate at 5mm depth in solid water was 0.35 Gy/min. Introduction of a cylindrical air‐cavity resulted in an increased dose past the inhomogeneity. Compared to tissue equivalent medium, dose enhancement due to 1mm, 2mm, 3mm and 4mm air cavities was 10%, 16%, 24%, and 35% respectively. X‐ray attenuation by 2mm thick cortical bone resulted in a significantly large (58%) dose decrease.

Conclusion:

IORT dose calculations assume homogeneous tissue equivalent medium. However, soft X‐rays are easily affected by non‐tissue equivalent materials. The results of this study may be used to estimate and correct IORT dose delivered in the presence of tissue inhomogeneities.
SU‐E‐T‐757: TMRs Calculated From PDDs Versus the Direct Measurements for Small Field SRS Cones
Authors: Li H , Zhong H , Song K , Qin Y , Snyder K , Gordon J , Chetty I , Wen N
Published: June 2015

Purpose:

To investigate the variation of TMR for SRS cones obtained by TMR scanning, calculation from PDDs, and point measurements. The obtained TMRs were also compared to the representative data from the vendor.

Methods:

TMRs for conical cones of 4, 5, 7.5, 10, 12.5, 15, and 17.5 mm diameter (jaws set to 5×5 cm) were obtained for 6X FFF and 10X FFF energies on a Varian Edge linac. TMR scanning was performed with a Sun Nuclear 3D scanner and Edge detector at 100 cm SDD. TMR point measurements were measured with a Wellhofer tank and Edge detector, at multiple depths from 0.5 to 20 cm and 100 cm SDD. PDDs for converting to TMR were scanned with a Wellhofer system and SFD detector. The formalism of converting PDD to TMR, given in Khan's book (4th Edition, p.161) was applied. Sp values at dmax were obtained by measuring Scp and Sc of the cones (jaws set to 5×5 cm) using the Edge detector, and normalized to the 10×10 cm field.

Results:

Along the central axis beyond dmax, the RMS and maximum percent difference of TMRs obtained with different methods were as follows: (a) 1.3% (max=3.5%) for the calculated TMRs from PDDs versus direct scanning; (b) 1.2% (max=3.3%) for direct scanning versus point measurement; (c) 1.8% (max=5.1%) for the calculated versus point measurements; (d) 1.0% (max=3.6%) for direct scanning versus vendor data; (e) 1.6% (max=7.2%) for the calculated versus vendor data.

Conclusion:

The overall accuracy of TMRs calculated from PDDs was comparable with that of direct scanning. However, the uncertainty at depths greater than 20 cm, increased up to 5% when compared to point measurements. This issue must be considered when developing a beam model for small field SRS planning using cones.
SU‐E‐T‐758: To Determine the Source Dwell Positions of HDR Brachytherapy Using 2D 729 Ion Chamber Array
Authors: Kumar Syam , Sitha
Published: June 2015

Purpose:

Determination of source dwell positions of HDR brachytherapy using 2D 729 ion chamber array

Methods:

Nucletron microselectron HDR and PTW 2D array were used for the study. Different dwell positions were assigned in the HDR machine. Rigid interstitial needles and vaginal applicator were positioned on the 2D array. The 2D array was exposed for this programmed dwell positions. The positional accuracy of the source was analyzed after the irradiation of the 2D array. This was repeated for different dwell positions. Different test plans were transferred from the Oncentra planning system and irradiated with the same applicator position on the 2D array. The results were analyzed using the in house developed excel program.

Results:

Assigned dwell positions versus corresponding detector response were analyzed. The results show very good agreement with the film measurements. No significant variation found between the planned and measured dwell positions. Average dose response with 2D array between the planned and nearby dwell positions was found to be 0.0804 Gy for vaginal cylinder applicator and 0.1234 Gy for interstitial rigid needles. Standard deviation between the doses for all the measured dwell positions for interstitial rigid needle for 1 cm spaced positions were found to be 0.33 and 0.37 for 2cm spaced dwell positions. For intracavitory vaginal applicator this was found to be 0.21 for 1 cm spaced dwell positions and 0.06 for 2cm spaced dwell positions. Intracavitory test plans reproduced on the 2D array with the same applicator positions shows the ideal dose distribution with the TPS planned.

Conclusion:

2D array is a good tool for determining the dwell position of HDR brachytherapy. With the in‐house developed program in excel it is easy and accurate. The traditional way with film analysis can be replaced by this method, as the films will be more costly.
SU‐E‐T‐759: To Replan Or Not To Replan for Each Fraction Using Inverse Optimization for Multichannel Vaginal Cylinder
Authors: Balik M , Rybak M , Andrews M , Strongosky M , Blair H , Obi B , Vermont C
Published: June 2015

Purpose:

This study investigates whether replanning each fraction for vaginal cuff HDR therapy using a multichannel cylinder (MC) and brachytherapy inverse optimization (BIO) provides dosimetric benefits to organs‐at‐risk (OAR). The goal was to appropriately cover the target and limit dose to OAR, as well as evaluate dosimetric changes for each fraction, while doing this in a timely and cost effective manner.

Methods:

From an initial selection of 57 patients that were treated with 3 fractions using a MC and BIO, a subset of n=12 patients was selected based on the criterion that one plan was used for all 3 fractions. A simulation CT was acquired prior to each fraction. CT scans for fractions 2 and 3 were fused to the initial CT. Contours for the bladder and rectum were manually drawn on CTs for all 3 fractions, and the clinical treatment volume (PTVeval) was defined. Cylinders were reconstructed using applicator modeling library, influencing time and cost effectiveness. Planning objectives were at least 95% prescription dose to 95% (D95%) of target volume and limiting high dose to OAR. Dose to 2 cm3 (D2cc) for each OAR was analyzed using a t‐test.

Results:

This study concentrated on comparing 2cm3 of highest dose to OAR (D2cc), for each fraction for the plans that were used to treat all 3 fraction. Based on statistical analysis, using the initial plan for fractions 2 and 3 resulted in approximately 6% change to the highest D2cc of the bladder (p=0.03).

Conclusion:

Performing CT fusion and contours of each OAR on each fraction allows objective plan evaluation and supports decision making on the necessity of replanning based on improved dose sparing for OAR. Future studies will investigate the effects of replanning on maximum dose (D0.1cc) using the same physician‐drawn OAR contours to avoid subjectivity.
SU‐E‐T‐761: TOMOMC, A Monte Carlo‐Based Planning VerificationTool for Helical Tomotherapy
Authors: Chibani O , Ma C
Published: June 2015

Purpose:

Present a new Monte Carlo code (TOMOMC) to calculate 3D dose distributions for patients undergoing helical tomotherapy treatments. TOMOMC performs CT‐based dose calculations using the actual dynamic variables of the machine (couch motion, gantry rotation, and MLC sequences).

Methods:

TOMOMC is based on the GEPTS (Gama Electron and Positron Transport System) general‐purpose Monte Carlo system (Chibani and Li, Med. Phys. 29, 2002, 835). First, beam models for the Hi‐Art Tomotherpy machine were developed for the different beam widths (1, 2.5 and 5 cm). The beam model accounts for the exact geometry and composition of the different components of the linac head (target, primary collimator, jaws and MLCs). The beams models were benchmarked by comparing calculated Pdds and lateral/transversal dose profiles with ionization chamber measurements in water. See figures 1–3. The MLC model was tuned in such a way that tongue and groove effect, inter‐leaf and intra‐leaf transmission are modeled correctly. See figure 4.

Results:

By simulating the exact patient anatomy and the actual treatment delivery conditions (couch motion, gantry rotation and MLC sinogram), TOMOMC is able to calculate the 3D patient dose distribution which is in principal more accurate than the one from the treatment planning system (TPS) since it relies on the Monte Carlo method (gold standard). Dose volume parameters based on the Monte Carlo dose distribution can also be compared to those produced by the TPS. Attached figures show isodose lines for a H&N patient calculated by TOMOMC (transverse and sagittal views). Analysis of differences between TOMOMC and TPS is an ongoing work for different anatomic sites.

Conclusion:

A new Monte Carlo code (TOMOMC) was developed for Tomotherapy patient‐specific QA. The next step in this project is implementing GPU computing to speed up Monte Carlo simulation and make Monte Carlo‐based treatment verification a practical solution.
SU‐E‐T‐762: Toward Volume‐Based Independent Dose Verification as Secondary Check
Authors: Tachibana H , Tachibana R
Published: June 2015

Purpose:

Lung SBRT plan has been shifted to volume prescription technique. However, point dose agreement is still verified using independent dose verification at the secondary check. The volume dose verification is more affected by inhomogeneous correction rather than point dose verification currently used as the check. A feasibility study for volume dose verification was conducted in lung SBRT plan.

Methods:

Six SBRT plans were collected in our institute. Two dose distributions with / without inhomogeneous correction were generated using Adaptive Convolve (AC) in Pinnacle3. Simple MU Analysis (SMU, Triangle Product, Ishikawa, JP) was used as the independent dose verification software program, in which a modified Clarkson‐based algorithm was implemented and radiological path length was computed using CT images independently to the treatment planning system. The agreement in point dose and mean dose between the AC with / without the correction and the SMU were assessed.

Results:

In the point dose evaluation for the center of the GTV, the difference shows the systematic shift (4.5% ± 1.9 %) in comparison of the AC with the inhomogeneous correction, on the other hands, there was good agreement of 0.2 ± 0.9% between the SMU and the AC without the correction. In the volume evaluation, there were significant differences in mean dose for not only PTV (14.2 ± 5.1 %) but also GTV (8.0 ± 5.1 %) compared to the AC with the correction. Without the correction, the SMU showed good agreement for GTV (1.5 ± 0.9%) as well as PTV (0.9% ± 1.0%).

Conclusion:

The volume evaluation for secondary check may be possible in homogenous region. However, the volume including the inhomogeneous media would make larger discrepancy. Dose calculation algorithm for independent verification needs to be modified to take into account the inhomogeneous correction.
SU‐E‐T‐763: Towards the Mechanical Doping of Plastic Scintillators
Authors: Nusrat H , Pang G , Au P , Sarfehnia A
Published: June 2015

Purpose:

The doping of plastic scintillators with high‐Z elements changes the radiation interaction cross section of the medium and therefore changes the intrinsic response of the detector. The selection of doped plastic scintillators available commercially is limited. This research aims to develop a novel methodology for the mechanical doping of plastic scintillating materials. The ultimate goal of this project is to use doped scintillators of varying intrinsic behavior to unfold the LET (energy) spectrum of any radiation beam.

Methods:

Commercially available BC408 plastic scintillator was obtained and crushed into uniform powder (using ball mill). Two separate materials were tested for light output signal: uncrushed scintillator and scintillating powder bound by glue. Commercially available U301 UV‐hardening glue was used. Scintillation response was measured by creating a thin housing of black acrylic that allowed light from each scintillator to be guided to an optical fiber via a taper. The optical fiber was connected to a PMT; signal was measured using an electrometer. Tests were conducted to determine if crushing+bonding distorted linearity and energy dependence of detector response. Linearity was tested for by irradiating (uncrushed and crushed+glued) for varying durations ensuring signal scaled accordingly; this was done using 300kV x‐rays and 6MeV electrons. The effect on energy dependence was examined by obtaining a signal ratio (100kV vs. 300kV; 6MeV vs. 18MeV) for both uncrushed and crushed+glued scintillating material.

Results:

Crushing and binding with U301 glue did not have an effect on linearity. Energy dependence was changed by 20.3%; crushing+bonding decreased the sensitivity at low energy radiation.

Conclusion:

This work indicates that crushing and binding of plastic scintillating material does not change the linearity of its response to radiation but does have an effect on the energy dependence. Future work involves addition of high‐Z dopants (W, Mo, Pb) and characterization of the detector response.
SU‐E‐T‐767: Treatment Planning Study of Prostate Cancer by CyberKnife with Respect to the Urethral Dose
Authors: Mizuno H , Mizuno H , Sumida I , Otani Y , Yagi M , Takashina M , Suzuki O , Yoshioka Y , Koizumi M , Ogawa K
Published: June 2015

Purpose:

Hypo‐fractionated stereotactic body radiation therapy (SBRT) with intensity modulated radiation therapy (IMRT) is nowadays one of the treatment strategies for prostate cancer. There are few reports on planning study of prostate cancer by CyberKnife with respect to the urethral dose because of the invisibility in CT. We have investigated a planning method using fixed collimators with considering dose homogeneity, conformity and urethral dose.

Methods:

Radiotherapy treatment planning of prostate cancer were under a clinical trial approved by the institutional review board. The prescription dose of 35 Gy were delivered to the PTV in five fractions with the urethral catheter. Urethra position was identified by pretreatment CT and catheter, which was inserted before treatment planning CT and released after the treatment. All plans agreed to the criteria as shown in table 1, and the following constraints were recommended as well: the prescribed iso‐dose line should be from 70% to 90%; the total MU should be below 50,000 MU; the minimum MU per beam should be larger than 15 MU; the estimated delivery time (excluding patient setup time) by Multiplan with image time interval of 60 s should be less than 35 min. Collimator size and position were decided as shown in figure 1. Fixed collimator of 15 mm was positioned around urethra and PTV for avoiding high dose of urethra and achieving conformity, and fixed collimator of 30 or 40 were positioned around PTV for achieving dose homogeneity.

Results:

With this method, all constraints were achieved. (Table 1, Figure 2) Max dose of urethra was ranging from 103.9% to 114.2%, because urethra position was identified by pretreatment CT and urethral catheter.

Conclusion:

Hypo‐fractionated SBRT with IMRT utilizing urethral catheter could be a promising new treatment option for prostate cancer.

This work was supported by JSPS Core‐to‐Core program Number 23003.
SU‐E‐T‐772: Uncertainties in Treatment Planning for IROC‐Houston Proton Phantom QA Program Due to Variable CT Technique and Proton Energy
Authors: McInnis M , Taylor P , Poenisch F , Court L , Guindani M , Followill D
Published: June 2015

Purpose:

To understand the uncertainties in proton therapy treatment planning for the IROC‐ Houston proton phantom QA program due to variations in CT technique and proton energy.

Methods:

A CT phantom used by IROC‐H during therapy site visits was scanned using three CT techniques (80, 120, 140kV) with a CT scanner used for proton therapy simulations and irradiated with a passively scattered beam at three energies (140, 200, 250 MeV) to measure, respectively, HU and Relative Linear Stopping Power (RLSP) in order to create HU to RLSP calibration curves for comparison with reference curves used by current proton treatment planning systems. The phantom has proton equivalent materials with a wide variety of HU and RLSPs to allow for the creation of a calibration curve for common tissue equivalent materials. Treatment plans were created for a lung phantom using the various CT technique/ beam energy calibration curves to determine the differences in the dose distributions by performing a gamma analysis.

Results:

Comparison of the calibration curves created using the phantom materials showed a maximum difference of 12% for a given material between the custom curve and the reference curve currently used by the treatment planning system. The highest differences were a Result of using an 80 kV CT technique and a 250 MeV high proton energy. A comparison of the completed treatment plans will be presented.

Conclusion:

These results indicate the possibility of differences in proton HU to RLSP calibration curves caused by varying CT technique and proton energy that could manifest as differences in planned and delivered dose distributions, particularly at high proton energies and low kV CT techniques. These differences could Result in discrepancies not accounted for by IROC‐Houston and could possibly affect proton institutions’ pass rate when irradiating the proton phantoms.
SU‐E‐T‐778: Use of the 2D MatriXX Detector for Measuring Scanned Ion Beam Parameters
Authors: Anvar M Varasteh , Giordanengo S , Donetti M , Marchetto F , Ciocca M , Panizza D , Monaco V , Sacchi R , Vignati A , Guarachi L Fanola , Cirio R
Published: June 2015

Purpose:

The quality assurance (QA) procedure has to check the most relevant beam parameters to ensure the delivery of the correct dose to patients. Film dosimetry, which is commonly used for scanned ion beam QA, does not provide immediate results. The purpose of this work is to answer whether, for scanned ion beam therapy, film dosimetry can be replaced with the 2D MatriXX detector as a real‐time tool.

Methods:

MatriXX, equipped with 32×32 parallel plate ion‐chambers, is a commercial device intended for pre‐treatment verification of conventional radiation therapy.The MatriXX, placed at the isocenter, and GAFCHROMIC films, positioned on the MatriXX entrance, were exposed to 131.44 MeV proton and 221.45 MeV/u Carbon‐ion beams.The OmniPro‐I'mRT software, applied for the data taking of MatriXX, gives the possibility of acquiring consecutive snapshots. Using the NI LabVIEW, the data from snapshots were logged as text files for further analysis. Radiochromic films were scanned with EPSON scanner and analyzed using software programs developed in‐house for comparative purposes.

Results:

The field dose uniformity, flatness, beam position and beam width were investigated. The field flatness for the region covering 6×6 cm2 square field was found to be better than 2%. The relative standard deviations, expected to be constant over 2×2, 4×4 and 6×6 pixels from MatriXX measurement gives a uniformity of 1.5% in good agreement with the film results.The beam center position is determined with a resolution better than 200 µm for Carbon and less than 100 µm for proton beam.The FWHM determination for a beam wider than 10 mm is satisfactory, whilst for smaller beams the determination is uncertain.

Conclusion:

Precise beam position and fast 2D dose distribution can be determined in real‐time using MatriXX detector. The results show that MatriXX is quick and accurate enough to be used in charged‐particle therapy QA.
SU‐E‐T‐781: Using An Electronic Portal Imaging Device (EPID) for Correlating Linac Photon Beam Energies
Authors: Yaddanapudi S , Cai B , Sun B , Noel C , Goddu S , Mutic S
Published: June 2015

Purpose:

Electronic portal imaging devices (EPIDs) have proven to be useful for measuring several parameters of interest in linear accelerator (linac) quality assurance (QA). The purpose of this project was to evaluate the feasibility of using EPIDs for determining linac photon beam energies.

Methods:

Two non‐clinical Varian TrueBeam linacs (Varian Medical Systems, Palo Alto, CA) with 6MV and 10MV photon beams were used to perform the measurements. The linacs were equipped with an amorphous silicon based EPIDs (aSi1000) that were used for the measurements. We compared the use of flatness versus percent depth dose (PDD) for predicting changes in linac photon beam energy. PDD was measured in 1D water tank (Sun Nuclear Corporation, Melbourne FL) and the profiles were measured using 2D ion‐chamber array (IC‐Profiler, Sun Nuclear) and the EPID. Energy changes were accomplished by varying the bending magnet current (BMC). The evaluated energies conformed with the AAPM TG142 tolerance of ±1% change in PDD.

Results:

BMC changes correlating with a ±1% change in PDD corresponded with a change in flatness of ∼1% to 2% from baseline values on the EPID. IC Profiler flatness values had the same correlation. We observed a similar trend for the 10MV beam energy changes. Our measurements indicated a strong correlation between changes in linac photon beam energy and changes in flatness. For all machines and energies, beam energy changes produced change in the uniformity (AAPM TG‐142), varying from ∼1% to 2.5%.

Conclusions:

EPID image analysis of beam profiles can be used to determine linac photon beam energy changes. Flatness‐based metrics or uniformity as defined by AAPM TG‐142 were found to be more sensitive to linac photon beam energy changes than PDD.

Research funding provided by Varian Medical Systems. Dr. Sasa Mutic receives compensation for providing patient safety training services from Varian Medical Systems, the sponsor of this study.
SU‐E‐T‐783: Using Matrixx to Determine Transit Dose Contribution Over Clinically Useful Limits of HDR Source Activity
Authors: Bhagwat M , O'Farrell D , Wagar M , Buzurovic I , Friesen S , Damato A , Devlin P , Cormack R
Published: June 2015

Purpose:

Most HDR brachytherapy treatment planning systems (TPS) use TG‐43 formalism to calculate dose without including transit dose corrections. Historically, measurement of this contribution has required sophisticated apparatus unavailable in most hospitals. We use Matrixx to investigate several scenarios where transit dose contribution may effect a clinical treatment.

Methods:

Treatment plans were generated using Oncentra Brachy TPS (Version 4.3.0.410, Nucletron ) on a CT scan of a 24‐catheter Freiburg applicator (Nucletron ) laid flat on the MatriXX (IBA) detector. This detector is an array of 1020 parallel plate ion chambers. All 24 catheters were digitized and dwells within a central square region of 5×5cm of the applicator were activated. Each of the active catheters had 6 dwells in increments of 1.0cm. The plans were normalized to 10mm. This places the 100% isodose line at the correct effective point of measurement, which lies half‐way between the parallel plates of the ion chambers. It is also within the clinically relevant treatment depth for superficial applications. A total of 6 plans were delivered for 3 prescription doses, 1Gy, 2Gy and 4Gy using source activities of 2.9Ci and 11.2Ci. The MatriXX array was operated to capture dosimetric snaps every 500ms and yielded an integral dose at the end of treatment.

Results:

A comparison of integral dose from 2 different source activities shows that the transit dose contribution is larger when the source activity is higher. It is also observed that the relative transit dose contribution decreases as prescription dose increases. This is quantified by the Gamma analysis.

Conclusion:

We have demonstrated that the Matrixx detector can be used to evaluate the contribution for a HDR source during transit from the HDR afterloader to a dwell location, and between adjacent dwell locations.
SU‐E‐T‐787: Utility of the Two Candidate 192‐Ir and 169‐Yb HDR Sources for Use with a Novel Direction Modulated Brachytherapy Tandem Applicator for Cervical Cancer Treatment
Authors: Safigholi H , Han D , Soliman A , Meigooni A Soleimani , Song W
Published: June 2015

Purpose:

A novel tungsten alloy shielded, MRI‐compatible, direction modulated brachytherapy (DMBT) concept tandem applicator, which enables unprecedented intensity modulation, was used to evaluate treatment plan quality improvement over a conventional tandem. The utility of the 192‐Ir and 169‐Yb HDR sources, for use with the DMBT applicator, was evaluated.

Methods:

The total diameter of the DMBT tandem applicator is 6.0 mm, which consists of 5.4‐mm diameter tungsten alloy and 0.3 mm thick plastic sheath. The tandem has 6 symmetric peripheral 1.3‐mm diameter grooves for the source to travel. MCNPX v.2.6 was used to simulate the 192‐Ir and 169‐Yb sources inside the DMBT applicator. First, TG‐43 source parameters were evaluated. Second, 3D dose matrix with 1 mm3 resolution were imported into an in‐house‐coded inverse optimization treatment planning program to obtain optimal plans for 19 clinical cases. All plans were compared with the standard tandem and ring plans. Prescription dose was 15.0 Gy. All plans were normalized to receive the same HRCTV D90.

Results:

Generally, the DMBT tandem (and ring) plans were better than the conventional tandem and ring plans for 192‐Ir and 169‐Yb HDR sources. The mean data of D2cc for bladder, rectum, and sigmoid were 11.65±2.30 Gy, 7.47±3.05 Gy, and 9.84±2.48 Gy for Ir‐192 DMBT tandem, respectively. These data for Yb‐169 were 11.67±2.26 Gy, 7.44±3.02 Gy, and 9.83±2.38 Gy, respectively. The HR‐CTV D98 and V100 were 16.37±1.86 Gy and 97.37 ± 1.92 Gy for Ir‐192 DMBT, respectively. The corresponding values for Yb‐169 were 16.43±1.86 Gy, and 97.51 ± 1.91 Gy. Plans with the 169‐Yb source generally produced more favorable results where V100 increased by 13.65% while D2cc across all OARs reduced by 0.54% compared with the 192‐Ir plans.

Conclusion:

For the DMBT tandem applicator, 169‐Yb source seems to produce more directional beams resulting in increased intensity modulation capacity, thus resulting in more conformal plans
SU‐E‐T‐790: Validation of 4D Measurement‐Guided Dose Reconstruction (MGDR) with OCTAVIUS 4D System
Authors: Lee V , Blanck O , Leung R , Wong M , Law G , Lee K , Tung S , Chan M
Published: June 2015

Purpose:

To validate the MGDR of OCTAVIUS 4D system (PTW, Freiburg, Germany) for quality assurance (QA) of volumetric‐modulated arc radiotherapy (VMAT).

Methods:

4D‐MGDR measurements were divided into two parts: 1) square fields from 2×2 to 25×25 cm2 at 0°, 10° and 45° gantry, and 2) 8 VMAT plans (5 nasopharyngeal and 3 prostate) collapsed to gantry 40° in QA mode in Monaco v5.0 (Elekta, CMS, Maryland Heights, MO) were delivered on the OCTAVIUS 4D phantom with the OCTAVIUS 1500 detector plane perpendicular to either the incident beam to obtain the reconstructed dose (OCTA4D) or the 0° gantry axis to obtain the raw doses (OCTA3D) in Verisoft 6.1 (PTW, Freiburg, Germany). Raw measurements of OCTA3D were limited to < 45° gantry to avoid >0.5% variation of detector angular response with respect to 0° gantry as determined previously. Reconstructed OCTA4D and raw OCTA3D doses for all plans were compared at the same detector plane using γ criteria of 2% (local dose)/2mm and 3%/3mm criteria.

Results:

At gantry 0° and 10°, the γ results for all OCTA4D on detector plane coinciding with OCTA3D were over 90% at 2%/2mm except for the largest field (25×25 cm2 ) showing >88%. For square field at 45° gantry, γ passing rate is > 90% for fields smaller than 15x 15cm2 but < 80% for field size of 20 x20 cm2 upward. For VMAT, γ results showed 94% and 99% passing rate at 2%/2mm and 3%/3mm, respectively.

Conclusion:

OCTAVIUS 4D system has compromised accuracy in reconstructing dose away from the central beam axis, possibly due to the off‐axis softening correction and errors of the percent depth dose data necessary as input for MGDR. Good results in

VMAT delivery suggested that the system is relatively reliable for VMAT with small segments.