bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐430: Feasibility Study On Using Overlap Volume Histogram to Predict the Dose Difference by Respiratory Motion
Authors: Shin D , Kang S , Kim D , Kim T , Kim K , Cho M , Suh T
Published: June 2015

Purpose:

The dose difference between three‐dimensional dose (3D dose) and 4D dose which considers motion due to respiratory can be varied according to geometrical relationship between planning target volume (PTV) and organ at risk (OAR). The purpose of the study is to investigate the dose difference between 3D and 4D dose using overlap volume histogram (OVH) which is an indicator that quantify geometrical relationship between a PTV and an OAR.

Methods:

Five liver cancer patients who previously treated stereotactic body radiotherapy (SBRT) were investigated. Four‐dimensional computed tomography (4DCT) images were acquired for all patients. ITV‐based treatment planning was performed. 3D dose was calculated on the end‐exhale phase image as a reference phase image. 4D dose accumulation was implemented from all phase images using dose warping technique used deformable image registration (DIR) algorithm (Horn and Schunck optical flow) in DIRART. In this study OVH was used to quantify geometrical relationship between a PTV and an OAR. OVH between a PTV and a selected OAR was generated for each patient case and compared for all cases. The dose difference between 3D and 4D dose for normal organ was calculated and compared for all cases according to OVH.

Results:

The 3D and 4D dose difference for OAR was analyzed using dose‐volume histogram (DVH). On the basis of a specific point which corresponds to 10% of OAR volume overlapped with expanded PTV, mean dose difference was 34.56% in minimum OVH distance case and 13.36% in maximum OVH distance case. As the OVH distance increased, mean dose difference between 4D and 3D dose was decreased.

Conclusion:

The tendency of dose difference variation was verified according to OVH. OVH is seems to be indicator that has a potential to predict the dose difference between 4D and 3D dose.

This work was supported by the Radiation Technology R&D program (No. 2013M2A2A7043498) and the Mid‐career Researcher Program (2014R1A2A1A10050270) through the National Research Foundation of Korea funded by the Ministry of Science, ICT&Future Planning.
SU‐E‐T‐433: Field‐In‐Field Irradiation for Breast Cancer with VERO‐4DRT System: A Feasibility Study
Authors: Hayashi N , Mizuno T , Takada Y , Murai T
Published: June 2015

Purpose:

The Vero‐4DRT system is a dedicated system for high precision radiation therapy. However, the field size is limited at 15 cm × 15 cm and shapes by using multi‐leaf collimator (MLC) without X‐Jaw and Y‐Jaw. Therefore VERO‐4DRT system is not available to simple wedged irradiation for breast cancer. In this study, we suppose FIF with ring and/or tilt/pan angles whole breast irradiation (FIFWBI). The purpose of this study is to verify the feasibility of FIFWBI with VERO‐4DRT system.

Methods:

As fundamental evaluation, we performed commissioning test with phantom. The absorbed dose evaluation at several reference points and dose distribution including split area were performed. We planned 10 demonstrative shapes in phantom for measuring these contents with i‐plan workstation (BrainLAB). As clinical evaluation, the dose distribution and dose indexes were evaluated with actual patient data. Five patients with breast cancer were designed FIFWBI radiotherapy plan with split fields. Then, the dose distribution and dose indexes (including Dmax, Dmin, D95, D5 and Homogeneity index) were evaluated in these plans.

Results:

As the results of fundamental evaluation, all absorbed dose errors between calculated and measured doses were within 2%. The gamma passing rates with 2 mm/3% criteria in all cases were 96±2%. As the results of clinical evaluation, the values of Dmax, D95, D50, D5, and Homogeneity Index were 41.7±0.90 Gy, 49.4±0.34 Gy, 52.26±0.24 Gy, and 1.39±0.03, respectively. For Japanese breast cancer patients, this technique was feasible. However, the large split region was happened in FIFWBI in case of patient with large breast.

Conclusion:

We evaluated the FIFWBI technique with VERO‐4DRT system. This technique is feasible for Japanese patients, but the patient with large breast should be disagreed with this technique.
SU‐E‐T‐435: Flattening Filter Free Beams for Head and Neck IMRT and VMAT Optimization
Authors: Ghahremani S , Chavez R , Li Y , Crownover R , Baacke D , Papanikolaou N , Stathakis S
Published: June 2015

Purpose:

To investigate if there is benefits of using flattening filter free (FFF) versus flattening filter (FF) beams during plan optimization for head and neck targets.

Methods:

Five head and neck cancer patients previously treated were selected for this study. Each plan was optimized for volumetric modulated arc therapy (VMAT) using 2 full arcs. Target volumes and the organs at risk (OAR) were outlined by the same physician. The prescription doses for each patient and the dose limits for each OAR were specified by the physician. For each patient four plans were created by varying the photon beam energy (6MV vs 10MV) and the use of FF or FFF. For each patient the prescription dose and OAR dose limits remained unchanged. Furthermore, the number of optimization iterations remained the same for each plan without user interference. The plans were compared using dose volume histograms, conformity and homogeneity indices.

Results:

Our results showed that the plans optimized with FF beams produced more homogeneous dose distributions in the PTV than the ones with FFF beams (0.92 vs. 0.86 and 0.92 vs.85 for 6MVFF, 6MVFFF, 10MVFF and 10MVFFF respectively). The conformity was better for FFF beams than for FF beams (1.26 vs. 1.20 and 1.27 vs. 1.21 for 6MVFF, 6MVFFF, 10MVFF and 10MVFFF respectively). The overall minimum, maximum and means doses were reduced for the FFF plans by approximately 4% to 6%. All FFF plans allowed more sparing of organs at risk by 7% to 9% on average. Only one 10MVFFF plan had a 1% higher dose than the respective 10MVFF for the spinal cord.

Conclusion:

The 6MVFFF and 10MVFFF beams illustrated the improvement of normal tissue sparing while achieving similar target dose distribution compared to 6MVFF and 10MVFF beams. Further investigation is required to determine the magnitude of improvement. case specific, fluence‐based optimization improved both PTV and OAR dosimetry in 80% of cases.
SU‐E‐T‐437: Four‐Dimensional Treatment Planning for Lung VMAT‐SBRT
Authors: Hashimoto M , Oohira S , Ueda Y , Miyazaki M , Isono M , Masaoka A , Takashina M , Koizumi M , Teshima T
Published: June 2015

Purpose:

To assess optimal treatment planning approach of Volumetric Modulated Arc Therapy for lung Stereotactic Body Radiation Therapy (VMAT‐SBRT).

Methods:

Subjects were 10 patients with lung cancer who had undergone 4DCT. The internal target volume (ITV) volume ranged from 2.6 to 16.5cm3 and the tumor motion ranged from 0 to 2cm. From 4DCT, which was binned into 10 respiratory phases, 4 image data sets were created; maximum intensity projection (MIP), average intensity projection (AIP), AIP with the ITV replaced by 0HU (RITV‐AIP) and RITV‐AIP with the planning target volume (PTV) minus the internal target volume was set to −200 HU (HR‐AIP). VMAT‐SBRT plans were generated on each image set for a patient. 48Gy was prescribed to 95% of PTV. The plans were recalculated on all phase images of 4DCT and the dose distributions were accumulated using a deformable image registration software MIM Maestro™ as the 4D calculated dose to the gross tumor volume (GTV). The planned dose to the ITV and 4D calculated dose to the GTV were compared.

Results:

In AIP plan, 10 patients average of all dose parameters (D1%, D_mean, and D99%) discrepancy were 1Gy or smaller. MIP and RITV‐AIP plans resulted in having common tendency and larger discrepancy than AIP plan. The 4D dose was lower than the planned dose, and 10 patients average of all dose parameters discrepancy were in range 1.3 to 2.6Gy. HR‐AIP plan had the largest discrepancy in our trials. 4D calculated D1%, D_mean, and D99% were resulted in 3.0, 4.1, and 6.1Gy lower than the expected in plan, respectively.

Conclusion:

For all patients, the dose parameters expected in AIP plan approximated to 4D calculated. Using AIP image set seems optimal treatment planning approach of VMAT‐SBRT for a mobile tumor.

Funding Support: This work was supported by the Japan Society for the Promotion of Science Core‐to‐Core program (No. 23003).
SU‐E‐T‐439: Fundamental Verification of Respiratory‐Gated Spot Scanning Proton Beam Therapy
Authors: Hamano H , Hayashi N , Yamakawa T , Yasui K , Kato H
Published: June 2015

Purpose:

The spot‐scanning proton beam irradiation with respiratory gating technique provides quite well dose distribution and requires both dosimetric and geometric verification prior to clinical implementation. The purpose of this study is to evaluate the impact of gating irradiation as a fundamental verification.

Methods:

We evaluated field width, flatness, symmetry, and penumbra in the gated and non‐gated proton beams. The respiration motion was distinguished into 3 patterns: 10, 20, and 30 mm. We compared these contents between the gated and non‐gated beams. A 200 MeV proton beam from PROBEAT‐III unit (Hitachi Co.Ltd) was used in this study. Respiratory gating irradiation was performed by Quasar phantom (MODUS medical devices) with a combination of dedicated respiratory gating system (ANZAI Medical Corporation). For radiochromic film dosimetry, the calibration curve was created with Gafchromic EBT3 film (Ashland) on FilmQA Pro 2014 (Ashland) as film analysis software.

Results:

The film was calibrated at the middle of spread out Bragg peak in passive proton beam. The field width, flatness and penumbra in non‐gated proton irradiation with respiratory motion were larger than those of reference beam without respiratory motion: the maximum errors of the field width, flatness and penumbra in respiratory motion of 30 mm were 1.75% and 40.3% and 39.7%, respectively. The errors of flatness and penumbra in gating beam (motion: 30 mm, gating rate: 25%) were 0.0% and 2.91%, respectively. The results of symmetry in all proton beams with gating technique were within 0.6%.

Conclusion:

The field width, flatness, symmetry and penumbra were improved with the gating technique in proton beam. The spot scanning proton beam with gating technique is feasible for the motioned target.
SU‐E‐T‐440: Gain Calibration Stability Study of a MV Flat‐Panel‐Detector (FPD) On Siemens ARTISTE Linac
Authors: Lei Y , Zheng D , Wang S , Zhu X , Zhang Q , Li S , Driewer J , Zhou S
Published: June 2015

Purpose:

To study gain calibration variation over time for an MV flat‐panel‐detector (FPD).

Methods:

Gain calibration images (1024×1024 pixels) of a FPD (PerkinElmer AN‐9 on a Siemens ARTISTE) acquired in 40 consecutive months were studied. Using Python programming language, the images were processed to analyze the central 900×900 pixels with a threshold applied to exclude dead pixels. Month1 was set as the base image, then the difference images between it and the following months were calculated. The pixel intensity mean and standard deviation of the difference images were used to study the gain variation over time. Two other months’ images were also randomly selected as the base image and the above analyses were repeated. Finally, to investigate the equivalence of monthly calibration and quarterly calibration, the results from comparing neighboring months’ images, such as (month2‐month1), (month3 ‐month2) et al, were compared with those from comparing images taken in 3‐month intervals, such as (month4‐month1), (month7‐month4) et al, using Welch's t‐test.

Results:

For most months’ gain calibration images, the differences (mean and standard deviation) from base images were constant. In three months, the differences were relatively larger compared to other months but seemed instantaneous without any worsening trend. In those 3 months no clinical portal image quality degradation was observed. The difference between monthly and quarterly calibration tested by Welch's t‐test were insignificant for both means (p=0.9) and standard deviations (p=0.8).

Conclusion:

Long term stability of the FPD gain calibration images was observed. Therefore, the vendor‐recommended calibration frequency of 2–4 weeks is unnecessary. Less frequent, such as quarterly, calibration is sufficient.
SU‐E‐T‐447: Growth of Metal Whiskers Under External Beam Irradiation: Experimental Evidence and Implications in Medical Electronic Devices for Radiation Therapy Treatments
Authors: Shvydka D , Warrell G , Parsai E , Karpov V , Vasko A
Published: June 2015

Purpose:

Thin metallic protrusions, termed “whiskers,” have been identified as a cause of failure in devices ranging from satellites to pacemakers. For decades, lead was used in tin‐based soldering alloys to suppress whisker formation. With the adoption of the Restriction of Hazardous Substances act and the expiration of its exemption on medical devices, including implanted medical devices (IMDs), electronic circuits are required to be lead‐free as of July 2014. The effect of radiation on such soldering components remains unknown.

Methods:

We have irradiated a thin (150 nm) tin metal layer, deposited on a 3 mm thick glass substrate, with a 6 MeV medical linac (Varian TrueBeam) electron beam in five 2‐hour long sessions. After receiving ∼10 kGy, whisker growth on the sample was assessed with scanning electron microscopy and compared to a reference sample not exposed to radiation.

Results:

After 10 hours of irradiation, the sample was found to develop intense whisker infestation, while the reference sample remained in its pristine as‐deposited condition. Repeating the same irradiation schedule generated more and longer whiskers. The observed phenomenon can be explained through charge accumulation in the glass substrate, generating an electric field that promotes whisker growth. The observed substrate glass darkening under irradiation points towards development of color centers related to charge trapping. Experiments on the same type of samples with direct application of the external field in a capacitor‐like setting also resulted in intense whisker growth.

Conclusion:

Extreme care should be taken in dealing with all electronic devices, especially IMDs, produced with lead‐free solder and components, subject to radiation exposure. While in our experiments strong electric fields were intentionally generated to accelerate whisker growth over hours, in everyday use the circuit soldering may cause problems in a matter of days or months. Designated reliability testing under radiation must be conducted.

This work is partially supported by NRC grant No. NRC‐HQ‐12‐G‐38‐0042
SU‐E‐T‐454: Impact of Air Gap On PDDs of 6 MV Photon Beam for Various Field Sizes in Inhomogeneous Phantoms
Authors: Oyewale S , Pokharel  , Singh H , Islam M , Rana S
Published: June 2015

Purpose:

To investigate how the shape of air gap and its size will impact the percent depth doses (PDDs) of a 6MV photon beam for various field sizes.

Methods:

Two in‐house phantoms were manufactured containing rectangular (phantom A) and circular (phantom B) air gaps. Both phantoms A and B were composed of same top layer (solid‐water; 30×30cm2,5cm thickness) and bottom layer (solid‐water; 30×30cm 2,8cm thickness), but middle layer was varied to observe air gap effects and scatter contribution to the measurement point. In phantom A, a rectangular shaped air gap (30×30cm2,7cm thickness) was created by placing Styrofoam blocks between top and bottom layers of the phantom. In phantom B, middle layer was replaced by “inhomogenous block”, composed of acrylic plate (30×30cm2, 4cm thickness) followed by PVC(30×30cm2,3cm thickness). Additionally, circular air gap was created by drilling a hole (diameter=2.8cm, length=7cm) at the center of “inhomogenous block”. In both phantoms, measurement readings were obtained at 13cm depth (i.e., 1cm after air gap) and depth of maximum dose(6MV energy; 100 MUs; field sizes ranged from 3×3cm2 to 10×10cm2). The PDDs at 13cm depth were compared in both phantoms.

Results:

The measurements in both phantoms A and B showed an almost linear increase in PDDs with increasing field size, especially for smaller field sizes (from 3×3 to 7×7cm2). For each field size, the PDD in phantom A was smaller compared to the one in phantom B. The difference in PDDs between two phantoms decreased with an increase in field size as the PDD difference decreased from 9.0% to 6.4%.

Conclusion:

The shape and size of air gap affect the PDD measurements in secondary build‐up region as 6 MV primary beam traverses through the center of air gap. The scatter contribution due to increase in field size was more noticeable for field sizes ≤7×7cm2.
SU‐E‐T‐455: Impact of Different Independent Dose Verification Software Programs for Secondary Check
Authors: Itano M , Yamazaki T , Yamashita M , Ishibashi S , Higuchi Y , Kosaka M , Kobayashi N , Tachibana H
Published: June 2015

Purpose:

There have been many reports for different dose calculation algorithms for treatment planning system (TPS). Independent dose verification program (IndpPro) is essential to verify clinical plans from the TPS. However, the accuracy of different independent dose verification programs was not evident. We conducted a multi‐institutional study to reveal the impact of different IndpPros using different TPSs.

Methods:

Three institutes participated in this study. They used two different IndpPros (RADCALC and Simple MU Analysis (SMU), which implemented the Clarkson algorithm. RADCALC needed the input of radiological path length (RPL) computed by the TPSs (Eclipse or Pinnacle3). SMU used CT images to compute the RPL independently from TPS). An ion‐chamber measurement in water‐equivalent phantom was performed to evaluate the accuracy of two IndpPros and the TPS in each institute. Next, the accuracy of dose calculation using the two IndpPros compared to TPS was assessed in clinical plan.

Results:

The accuracy of IndpPros and the TPSs in the homogenous phantom was +/−1% variation to the measurement. 1543 treatment fields were collected from the patients treated in the institutes. The RADCALC showed better accuracy (0.9 ± 2.2 %) than the SMU (1.7 ± 2.1 %). However, the accuracy was dependent on the TPS (Eclipse: 0.5%, Pinnacle3: 1.0%). The accuracy of RADCALC with Eclipse was similar to that of SMU in one of the institute.

Conclusion:

Depending on independent dose verification program, the accuracy shows systematic dose accuracy variation even though the measurement comparison showed a similar variation. The variation was affected by radiological path length calculation. IndpPro with Pinnacle3 has different variation because Pinnacle3 computed the RPL using physical density. Eclipse and SMU uses electron density, though.
SU‐E‐T‐458: Impact of Parameters for Volumetric Modulated Arc Therapy (VMAT) for Rectal Cancer
Authors: Runxiao L , Yankun C , Rong Q , Yuzhi S , Kai S , Mingchang M
Published: June 2015

Purpose:

Different parameters Result in different plans. As the developing of volumetric modulated arc therapy for rectal cancer, the purpose of this study was to work out appropriate parameters for the optimization of rectal cancer.

Methods:

For ten cases which were optimized using Oncentra4.3 version, varying systematically the number of arcs, collimator angle and the delivery time to create different plans. Homogeneity in planning target volume, median dose in the organs at risk and number of monitor units were evaluated for statistical analysis. Measurements were performed with Delt4, taking the delivery time, and compared to the calculation by the gamma method.

Results:

Plans with collimator 45° were little superior to plans with collimator 0°. Single arc achieved lower homogeneous indices in the planning target volume compared with dual arc, but also requiring less monitor units per fraction dose than dual arc. Single arc needs less monitor units for the treatment; the measured delivery time was reduced from 4 min of dual arc to 2.5 min of single arc. All the plans could achieve good pass rate with gamma method.

Conclusion:

Some of the parameters have been found as the appropriate sets which can be used as standard for volumetric modulated arc therapy of rectal cancer.
SU‐E‐T‐462: Impact of the Radiochromic Film Energy Response On Dose Measurements of Low Energy Electronic Brachytherapy Sources
Authors: Liang L , Bekerat H , Tomic N , DeBlois F , Devic S , Morcos M , Popovic M , Watson P , Seuntjens J
Published: June 2015

Purpose:

We investigated the effect of the EBT3 GafChromicTM film model absorbed dose energy response when used for percent depth dose (PDD) measurements in low‐energy photon beams.

Methods:

We measured PDDs in water from a Xoft 50 kVp source using EBT3 film, and compared them to PDD measurements acquired with a PTW‐TN34013 parallel‐plate ionization chamber. For the x‐ray source, we simulated spectra using the EGSnrc (BEAMnrc) Monte Carlo code, and calculated Half Value Layer (HVL) at different distances from the source in water. Pieces of EBT3 film were irradiated in air and calibration curves were created in terms of air‐kerma in air ((Kair)air) for different beam qualities. Pieces of EBT3 film were positioned at distances of 2–6 cm from the Xoft source in a water phantom using a custom‐made holder, and irradiated at the same time. As scatter is incorporated in the measured film signal in water, measured (Kair)wat was subsequently converted into absorbed dose to water by the ratio of mass energy absorption coefficients following the AAPM TG‐61 dosimetry protocol.

Results:

Our results show that film calibration curves obtained at beam qualities near the effective energy of the Xoft 50 kVp source in water lead to variation in absorbed dose energy dependence of the response of around 3%. However, if the calibration curve was established at MV beam quality, the error in absorbed dose could be as large as 15%. We observed agreement within 1% between PDD measurements using EBT3 film model (using a calibration curve obtained at 80 kVp, HVL=2.18 mm Al, Eeff=29.5 keV) and the parallel‐plate ionization chamber.

Conclusion:

Accurate dose measurements using radiochromic films at low photon energies require that the radiochromic film dosimetry system be calibrated at corresponding low energies, as large absorbed dose errors are expected for calibrations performed at MV beam qualities.
SU‐E‐T‐463: Impact to Total Scatter Factors On the Calculated Dose Distribution in Radiosurgery
Authors: Garcia O , Larraga‐Gutierrez J
Published: June 2015

Purpose:

To assess the impact of relative measurements: off axis ratios (OAR), tissue phantom ratios (TPR) and especially total scatter factor (TSF) on the calculated dose distribution in stereotactic radiosurgery with circular cones.

Methods:

Six detectors were employed to characterize circular collimated photon beams of 6 MV: three diodes (SFD, E, SRS), one ionization chamber (CC01) and two radiochromic films (EBT, EBT2). The relative measurements were incorporated in the treatment planning system (TPS) in order to compare and analyze the calculated dose distributions (DD). Each dose distribution was re‐scaled by the TSF to observe its effect in the final dose distribution. The comparison was performed by using the gamma index. A Monte Carlo generated dosimetry was used as reference.

Results:

The results showed that in terms of relative dosimetry all the detectors have a good agreement within 2%, with the exception of the CC01 and EBT2 film. However, the analysis performed with the dose distributions re‐scaled relative to the TSF for each detector showed that the impact it was not only to the isocenter dose. The dose to the PTV and normal tissue showed differences up to 13% depending of the dosimeter used for TSF measurements.

Conclusion:

With the exception of the CC01 ionization chamber and EBT2 radiochromic film, all the studied dosimeters were adequate for the measurement of OAR and TPR. However, attention must be put in the measurement of TSF. The use of the wrong detector does not only affect the isocenter dose, it may have an impact in the PTV and normal tissue dose.
SU‐E‐T‐464: Implementation and Validation of 4D Acuros XB Dose Calculations
Authors: Thomas S , Huang V , Milette M , Yuen C , Teke T
Published: June 2015

Purpose:

In this abstract we implement and validate a 4D VMAT Acuros XB dose calculation using Gafchromic film. Special attention is paid to the physical material assignment in the CT dataset and to reported dose to water and dose to medium.

Methods:

A QUASAR phantom with a 3 cm sinusoidal tumor motion and 5 second period was scanned using 4D computed tomography. A CT was also obtained of the static QUASAR phantom with the tumor at the central position. A VMAT plan was created on the average CT dataset and was delivered on a Varian TrueBeam linear accelerator. The trajectory log file from this treatment was acquired and used to create 10 VMAT subplans (one for each portion of the breathing cycle). Motion for each subplan was simulated by moving the beam isocentre in the superior/inferior direction in the Treatment Planning System on the static CT scan. The 10 plans were calculated (both dose to medium and dose to water) and summed for 1) the original HU values from the static CT scan and 2) the correct physical material assignment in the CT dataset. To acquire a breathing phase synchronized film measurements the trajectory log was used to create a VMAT delivery plan which includes dynamic couch motion using the Developer Mode. Three different treatment start phases were investigated (mid inhalation, full inhalation and full exhalation).

Results:

For each scenario the coronal dose distributions were measured using Gafchromic film and compared to the corresponding calculation with Film QA Pro Software using a Gamma test with a 3%/3mm distance to agreement criteria. Good agreement was found between calculation and measurement. No statistically significant difference in agreement was found between calculations to original HU values vs calculations to over‐written (material‐assigned) HU values.

Conclusion:

The investigated 4D dose calculation method agrees well with measurement.
SU‐E‐T‐465: Implementation of An Automated Collision Detection Program Using Open Source Software for the Pinnacle Treatment Planning System
Authors: Tanny S , Bogue J , Parsai E , Sperling N
Published: June 2015

Purpose:

Potential collisions between the gantry head and the patient or table assembly are difficult to detect in most treatment planning systems. We have developed and implemented a novel software package for the representation of potential gantry collisions with the couch assembly at the time of treatment planning.

Methods:

Physical dimensions of the Varian Edge linear accelerator treatment head were measured and reproduced using the Visual Python display package. A script was developed for the Pinnacle treatment planning system to generate a file with the relevant couch, gantry, and isocenter positions for each beam in a planning trial. A python program was developed to parse the information from the TPS and produce a representative model of the couch/gantry system. Using the model and the Visual Python libraries, a rendering window is generated for each beam that allows the planner to evaluate the possibility of a collision.

Results:

Comparison against heuristic methods and direct verification on the machine validated the collision model generated by the software. Encounters of <1 cm between the gantry treatment head and table were visualized as collisions in our virtual model. Visual windows were created depicting the angle of collision for each beam, including the anticipated table coordinates. Visual rendering of a 6 arc trial with multiple couch positions was completed in under 1 minute, with network bandwidth being the primary bottleneck.

Conclusion:

The developed software allows for quick examination of possible collisions during the treatment planning process and helps to prevent major collisions prior to plan approval. The software can easily be implemented on future planning systems due to the versatility and platform independence of the Python programming language. Further integration of the software with the treatment planning system will allow the possibility of patient‐gantry collision detection for a range of treatment machines.
SU‐E‐T‐473: Improvements of GPU Based Calculations Over CPU Based Calculations and the Effects of Variable Computer Hardware
Authors: Donaghue J , Gajdos S
Published: June 2015

Purpose:

To compare the calculation times in Raystation treatment planning system (TPS) for different graphical processor units (GPU). Also, to determine the amount of time saved by using a GPU based calculation.

Methods:

Four different hardware configurations were utilized. (DC1) – Intel Xeon E5‐2650 dual CPU with 64 GB RAM and nVidia Quadro K4000 GPU. (DC1 Titan Black) – Same configuration as (DC1) but with nVidia Titan Black GPU. (RVW1) – Intel Xeon E5‐2650 CPU with 32 GB RAM and nVidia Quadro K4000 GPU. (RVW2) – Intel Xeon E5‐2650 CPU with 16 GB of RAM and Quadro K2000 GPU. Dose calculation was also performed without the GPU on DC1 and RVW2. Seven clinically delivered treatment plans were elected. The plans were picked with varying IMRT complexities. Each plan was calculated consecutively eleven times, and each plan had a uniform dose grid voxel size of 2 mm3.

Results:

When compared to non‐GPU calculation, the average time on DC1 with GPU improved by 21.8% (range: 9.4%–38.9%). Similarly, the average time on RVW2 with GPU improved by 42.3% (range: 35.3%–50.5%). Also, the DC1 Titan Black average calculation time was 48.6% faster (range: 13.1%–73.4%) than the nVidia Quadro GPU models. Overall, the DC1 Titan Black calculation times outperformed DC1 non‐GPU by an average of 58.3% (range: 32.9%–77.5%) For the prostate and nodes study, the DC1 Titan Black reduced times from 724±2.5 seconds 205±1.0 seconds.

Conclusion:

Dose calculation time is reduced with the addition of a GPU. Also, the nVidia Titan Black GPU provided better time savings than the nVidia Quadro GPU models. Available RAM also plays a role in calculation time due to system lag when the memory reaches capacity. The clinical user must determine the best hardware specifications for his or her institution based on speed but also on monetary cost.
SU‐E‐T‐477: IMPT Vs. VMAT: A Treatment Planning Study for High‐Risk Prostate Cancer
Authors: Rana S , Zheng Y , Cheng C
Published: June 2015

Purpose:

The purpose of this study was to compare the dosimetric results between intensity modulated proton therapy (IMPT) and volumetric modulated arc therapy (VMAT) plans for a high‐risk prostate cancer.

Methods:

Six high‐risk prostate cancer cases were included in this retrospective study. For each case, IMPT plans were generated using multiple field optimization (MFO) technique (2 fields) with XiO treatment planning system (TPS), whereas VMAT plans were generated using RapidArc technique (2 full arcs) with Eclipse TPS. IMPT and VMAT plans were optimized for a total prescription dose of 79.2 Gy[RBE] and 79.2 Gy, respectively. IMPT and VMAT plans were compared using physical dose‐volume parameters. The absolute differences in a dosimetric parameter between IMPT and VMAT plans were calculated. The results were averaged over six cases.

Results:

For the planning target volume (PTV), the mean dose was comparable between IMPT (80.65 Gy[RBE]) and VMAT (80.33 Gy) plans, whereas the PTV coverage was slightly better in IMPT (97.41%) than in VMAT (95.00%) plans. The mean dose to the rectum and bladder were lower in IMPT (17.68 Gy[RBE] and 15.70 Gy[RBE], respectively) when compared to VMAT (42.17 Gy and 30.29 Gy, respectively) plans. The rectal V₇₀, V5₀, and V₃₀ were lower in IMPT plans than in VMAT plans by 4.91%, 28.34%, and 46.74%, respectively. For bladder, V₇₀ was comparable (8.92 Gy(RBE) vs. 9.03 Gy), whereas V5₀ and V₃₀ were lower in IMPT plans by 6.25% and 25.92%, respectively, when compared to VMAT plans. The mean doses to the left and right femoral heads were lower in VMAT plans (18.08 Gy and 21.91 Gy, respectively) than in VMAT plans (31.35 Gy[RBE] and 29.52 Gy[RBE], respectively)

Conclusion:

Both IMPT and VMAT plans provided excellent target coverage and acceptable femoral head dose. IMPT provided better tissue sparing for the rectum and bladder compared to VMAT.
SU‐E‐T‐478: IMRT Delivery Parameter Dependence of Dose‐Mass Optimization
Authors: Couto M , Mihaylov I
Published: June 2015

Purpose:

To compare DMH and DVH optimization sensitivity to changes in IMRT delivery parameters.

Methods:

Two lung and two head and neck (HN) cases were retrospectively optimized using DVH and DMH optimization. For both optimization approaches, changes to two parameters were studied: number of IMRT segments (5 and 10 per beam) and the minimum segment area (2 and 6 cm2). The number of beams, beam angles, and minimum MUs per segment were the same for both optimizations approaches for each patient. During optimization, doses to the organs at risk (OARs) were iteratively lowered until the standard deviation across the PTV was above ∼3.0%. For each patient DVH and DMH plans were normalized such that 95% of the PTV received the same dose. Plan quality was evaluated by dose indices (DIs), which represent the dose delivered to a certain anatomical structure volume. For the lung cases, DIs assessed included: 1% cord, 33% heart, both lungs 20% and 30%, and 50% esophagus. In the HN cases: 1% cord, 1% brainstem, left/right parotids 50%, 50% larynx, and 50% esophagus.

Results:

When increasing the number of segments, while keeping a small segment area (2cm2), the average percent change of all DIs for DVH/DMH optimizations for each patient were: −4.66/4.71, 3.21/3.46, −9.62/21.69 and −3.28/−7.62. For a large segment area (6cm2): −0.26/−1.46, −5.04/−1.92, −5.23/−2.19 and 4.12/19.63. Results from increasing segment area while keeping a small number of segments (5segments/beam) were: 1.41/7.90, 8.17/11.66, 0.09/33.58 and −4.83/−11.60 for each case. For large number of segments (10 segments/beam): 8.35/1.30, −0.91/5.77, 6.29/7.08 and 2.62/5.16.

Conclusion:

This preliminary study showed case dependent results. Changes in IMRT parameters did not show consistent DI changes for either optimization approach. A larger population of patients is warranted for such comparison.
SU‐E‐T‐488: Incorporating In‐House Treatment Planning Software Into Clinical Auto‐Planning Workflow
Authors: Lu W , Chen M , Tan J , Jiang S
Published: June 2015

Purpose:

To report the process of incorporating in‐house software tools into clinical workflow of auto‐planning with the objectives of achieving efficiency and quality plans.With multi‐year research and development, we built in‐house software suites of various GPU‐based components of a treatment planning system (TPS), which includes DICOM import/export, various deformable image registration (DIR) and contour generation algorithms, multiple dose calculators and optimizers, and plan generation with or without reference guidance. However, to meet clinical quality, we need to further test the robustness of the tools, streamline the processes, including the front and back end processes.

Methods:

We build an in‐house patient database management system and collect patient data of various delivery modalities, such as IMRT, VMAT, etc., and of various disease sites, such as head and neck, breast, lung, prostate, etc., to be used as repository for part of simulating the clinical workflow and subsequent testing.A unit‐testing tool was developed that any input parameter can be loaded from a configuration file for batch processing. Modular inputs and outputs were part of the design, and button clicking and human interaction can be bypassed.

Results:

The database with various delivery modalities and various disease sites allows the auto‐planning tools to test on variety of cases. The unit‐testing tools allow mass data processing and analysis. As testing showed, the whole auto‐planning process can be done in a couple of minutes without any human interaction.

Conclusion:

A database and unit‐testing tools are essential in incorporating the in‐house software into the clinical auto‐planning workflow and greatly facilitate the implementation by allowing component testing and mass data processing and analysis. Thus, desired functional behavior may be ensured, the impact of any code modification can be more easily identified, and any unintended alteration can be avoided.
SU‐E‐T‐489: Incorporating Skin Flash Into VMAT WBI: Impacts On Surface Dosimetry
Authors: Buele A Bejarano , Tanny S , Warrell G , Parsai E
Published: June 2015

Purpose:

Increased use of inverse planning limits the amount of skin flash in whole breast irradiation (WBI). Strategies to incorporate flash into inverse‐planned treatments involve overriding air to the density of water or tissue. This introduces uncertainties to the superficial dose distribution, potentially degrading the coverage at the skin‐bolus interface. We investigate the accuracy of various commonly used bolus materials to incorporate flash in VMAT WBI plans while minimizing the perturbation near the skin.

Methods:

We obtained a CT‐simulation of an anthropomorphic phantom with a breast attachment. Three VMAT plans were created with different boluses: 1 cm of 1 g/cm3 bolus (Superflab), 1 cm of 0.65 g/cm3 bolus (wet towels), and 1 cm of g/cm3 bolus with 2 dose levels accounting for the difference between bolus and tissue density. The PTV was extended into the bolus, outside the patient body contour to incorporate flash. OSLDs were used to obtain surface doses at the medial, lateral and tip sites of the breast. Each plan was irradiated four times using CBCT for positioning and dosimeter localization.

Results:

The average thickness of the wet‐towel bolus on delivery was 8 mm with a CBCT‐measured density of 0.6 g/cm3. OSLD measurements demonstrated good agreement with predicted doses from Pinnacle. Average deviations were −5.7%, −2.5%, and −2.6% for plans 1, 2, and 3, respectively. OSLDs placed at the medial and lateral portions of the breast showed the largest average deviations. The maximum recorded deviation from planned values was −8.6%. The largest dose fluctuations occurred near areas where the bolus failed to properly conform to the breast contour.

Conclusion:

Use of wet‐towel bolus improved dose delivery accuracy compared to standard Superflab bolus. Areas of poor bolus conformity adversely affected dose delivery. We recommend the use of wet‐towel bolus over Superflab bolus for VMAT WBI.
SU‐E‐T‐494: Influence of Proton Track‐Cell Nucleus Incidence Angle On Relative Biological Effectiveness
Authors: Pater P , Backstrom G , Enger S , Villegas F , Ahnesjo A , Seuntjens J , El Naqa I
Published: June 2015

Purpose:

To explain a Monte Carlo (MC) simulation artifact whereby differences in relative biological effectiveness (RBE) in the induction of initial double strand breaks are observed as a function of the proton track incidence angles in a geometric cell nucleus model. Secondly, to offer an alternative isotropic irradiation procedure to mitigate this effect.

Methods:

MC tracks of 1 MeV protons were generated in an event‐by‐event mode. They were overlaid on a cylindrical model of a cell nucleus containing 6×109 nucleotide base pairs. The tracks incidence angle θ with respect to the cell nucleus's axis was varied in 10 degrees intervals, each time generating one hundred fractions of ∼2 Gy. Strand breaks were scored in the modeled DNA sugar‐phosphate groups and further sub‐classified into single or double strand breaks (ssbs or dsbs). For each angle, an RBE for the induction of initial dsbs with reference to Co‐60 was calculated.

Results:

Our results show significant angular dependencies of RBE, with maximum values for incidence angles parallel to the nucleus central axis. Further examination shows that the higher cross‐sections for the creation of dsbs is due to the preferential alignment of tracks with geometrical sub‐parts of the cell nucleus model, especially the nucleosomes containing the sugar‐phosphate groups. To alleviate the impact of this simulation artifact, an average RBE was calculated with a procedure based on a weighted sampling of the angular data.

Conclusion:

This work demonstrates a possible numerical artifact in estimated RBE if the influence of the particle incidence angle is not correctly taken into account. A correction procedure is presented to better conform the simulations to real‐life experimental conditions.

We would like to acknowledge support from the Fonds de recherche du Quebec Sante (FRQS), from the CREATE Medical Physics Research Training Network grant (number 432290) of NSERC, support from NSERC under grants RGPIN 397711‐11 and RGPIN‐2014‐06475 and support from the CIHR under grants MOP‐114910, MOP‐136774 and MOP‐102550.
SU‐E‐T‐504: Intensity‐Modulated Radiosurgery Treatments Derived by Optimizing Delivery of Sphere Packing Treatment Plans
Authors: Hermansen M , John T St. , Velasco B , Bova F
Published: June 2015

Purpose

To minimize the number of monitor units required to deliver a sphere packing stereotactic radiosurgery (SRS) plan by eliminating overlaps of individual beam projections.

Methods

An algorithm was written in C++ to calculate SRS treatment doses using sphere packing. Three fixed beams were used to approximate each arc in a typical SRS treatment plan. For cases involving multiple isocenters, at each gantry and table angle position beams directed to individual spheres overlap to produce regions of high dose, resulting in intensity modulated beams. These high dose regions were dampened by post‐processing of the combined beam profile. The post‐process dampening involves removing the excess overlapping fluence from all but the highest contributing beam. The dampened beam profiles at each table and gantry angle position were then summed to produce the new total dose distribution.

Results

Delivery times for even the most complex multiple sphere plans can be reduced to consistent times of about 20 to 30 minutes. The total MUs required to deliver the plan can also be reduced by as much as 85% of the original plan's MUs.

Conclusion

Regions of high dose are removed. Dampening overlapping radiation fluence can produce the new beam profiles that have more uniform dose distributions using less MUs. This results in a treatment that requires significantly fewer intensity values than traditional IMRT or VAMT planning.
SU‐E‐T‐507: Internal Dosimetry in Nuclear Medicine Using GATE and XCAT Phantom: A Simulation Study
Authors: Fallahpoor M , Abbasi M , Sen A , Parach A , Kalantari F
Published: June 2015

Purpose

Monte Carlo simulations are routinely used for internal dosimetry studies. These studies are conducted with humanoid phantoms such as the XCAT phantom. In this abstract we present the absorbed doses for various pairs of source and target organs using three common radiotracers in nuclear medicine.

Methods

The GATE software package is used for the Monte Carlo simulations. A typical female XCAT phantom is used as the input. Three radiotracers 153Sm, 131I and 99mTc are studied. The Specific Absorbed Fraction (SAF) for gamma rays (99mTc, 153Sm and 131I) and Specific Fraction (SF) for beta particles (153Sm and 131I) are calculated for all 100 pairs of source target organs including brain, liver, lung, pancreas, kidney, adrenal, spleen, rib bone, bladder and ovaries.

Results

The source organs themselves gain the highest absorbed dose as compared to other organs. The dose is found to be inversely proportional to distance from the source organ. In SAF results of 153Sm, when the source organ is lung, the rib bone, gain 0.0730 (Kg‐1) that is more than lung itself.

Conclusion

The absorbed dose for various organs was studied in terms of SAF and SF. Such studies hold importance for future therapeutic procedures and optimization of induced radiotracer.
SU‐E‐T‐510: Interplay Between Spots Sizes, Spot / Line Spacing and Motion in Spot Scanning Proton Therapy
Authors: Lee TK
Published: June 2015

Purpose

In proton beam configuration for spot scanning proton therapy (SSPT), one can define the spacing between spots and lines of scanning as a ratio of given spot size. If the spacing increases, the number of spots decreases which can potentially decrease scan time, and so can whole treatment time, and vice versa. However, if the spacing is too large, the uniformity of scanned field decreases. Also, the field uniformity can be affected by motion during SSPT beam delivery. In the present study, the interplay between spot/ line spacing and motion is investigated.

Methods

We used four Gaussian‐shape spot sizes with 0.5cm, 1.0cm, 1.5cm, and 2.0cm FWHM, three spot/line spacing that creates uniform field profile which are 1/3*FWHM, σ/3*FWHM and 2/3*FWHM, and three random motion amplitudes within, +/−0.3mm, +/−0.5mm, and +/−1.0mm. We planned with 2Gy uniform single layer of 10×10cm2 and 20×20cm2 fields. Then, mean dose within 80% area of given field size, contrubuting MU per each spot assuming 1cGy/MU calibration for all spot sizes, number of spots and uniformity were calculated.

Results

The plans with spot/line spacing equal to or smaller than 2/3*FWHM without motion create ∼100% uniformity. However, it was found that the uniformity decreases with increased spacing, and it is more pronounced with smaller spot sizes, but is not affected by scanned field sizes.

Conclusion

It was found that the motion during proton beam delivery can alter the dose uniformity and the amount of alteration changes with spot size which changes with energy and spot/line spacing. Currently, robust evaluation in TPS (e.g. Eclipse system) performs range uncertainty evaluation using isocenter shift and CT calibration error. Based on presented study, it is recommended to add interplay effect evaluation to robust evaluation process. For future study, the additional interplay between the energy layers and motion is expected to present volumetric effect.
SU‐E‐T‐516: Investigation of a Novel Radiochromic Radiation Reporting System Utilizing the Reduction of Ferric Ion
Authors: Lee H , Alqathami M , Wang J , Blencowe A , Ibbott G
Published: June 2015

Purpose

To introduce and characterize a new “reverse‐Fricke” radiation reporting system utilizing the reduction of ferric ions (Fe3+) to ferrous ions (Fe2+).

Methods

Two formulations of the radiochromic reporting system, referred to as A and B, were prepared for investigation. Formulation‐A consisted of 14 mM 1,10‐phenanthroline, 42 mM ethanol, and 57 mM ammonium ferric oxalate in water. Formulation‐B consisted of 27 mM 1,10‐phenanthroline, 42 mM ethanol, and 28 mM ammonium ferric oxalate in water. Solutions were prepared immediately prior to irradiation with a Cobalt‐60 unit with radiation doses of 0, 1, 5, 10, 15, 20, and 25 Gy. The change in optical density over the visible range of 450–650 nm was measured using a spectrophotometer immediately after irradiation. The effective atomic numbers of the formulations were calculated using Mayneord's formula.

Results

Ionizing radiation energy absorbed in the solutions causes the reduction of ferric ions (Fe3+) into ferrous ions (Fe2+), which then forms a 1:3 red colored complex with 1,10‐phenanthroline ([(C1 2H8N2)3Fe]2+) that can be measured spectrophotometrically. The absorbance spectra of the resulting complex displayed a peak maximum at 512 nm with a greater change in absorbance for Formulation‐B after receiving comparable radiation doses. The change in absorbance relative to dose exhibited a linear response up to 25 Gy for both Formulation‐A (R2 = 0.98) and Formulation‐B (R2 = 0.97). The novel formulations were also nearly water equivalent (Zeff = 7.42) with effective atomic numbers of 7.65 and 7.52 and mass densities within 0.2% of water.

Conclusion

Both formulations displayed visible Fe2+ complex formation with 1,10‐phenanthroline after irradiation using a Cobalt‐60 source. The higher sensitivity measured for Formulation‐B is attributed to the increase in 1,10‐phenanthroline concentration and the increase in the 1,10‐phenanthroline to ammonium ferric oxalate ratio. Further investigation of this radiation reporting system in a 3D matrix material is encouraged.

NSF GRFP Grant Award #LH‐102SPS