bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐T‐17: A Feasibility Study for the Transit Dosimetry with a Glass Dosimeter in Brachytherapy
Authors: Moon S , Yoon M , Chung W , Chung M , Kim D
Published: July 2016

Purpose:

Confirming the dose delivered to a patient is important to make sure the treatment quality and safety of the radiotherapy. Measuring a transit dose of the patient during the radiotherapy could be an interesting way to confirm the patient dose. In this study, we evaluated the feasibility of the transit dosimetry with a glass dosimeter in brachytherapy.

Methods:

We made a phantom that inserted the glass dosimeters and placed under patient lying on a couch for cervix cancer brachytherapy. The 18 glass dosimeters were placed in the phantom arranged 6 per row. A point putting 1cm vertically from the source was prescribed as 500.00 cGy. Solid phantoms of 0, 2, 4, 6, 8, 10 cm were placed between the source and the glass dosimeter. The transit dose was measured each thickness using the glass dosimeters and compared with a treatment planning system (TPS).

Results:

When the transit dose was smaller than 10 cGy, the average of the differences between measured values and calculated values by TPS was 0.50 cGy and the standard deviation was 0.69 cGy. If the transit dose was smaller than 100 cGy, the average of the error was 1.67 ± 4.01 cGy. The error to a point near the prescription point was −14.02 cGy per 500.00 cGy of the prescription dose.

Conclusion:

The distances from the sources to skin of the patient generally are within 10 cm for cervix cancer cases in brachytherapy. The results of this preliminary study showed the probability of the glass dosimeter as the transit dosimeter in brachytherapy.
SU‐F‐T‐24: Impact of Source Position and Dose Distribution Due to Curvature of HDR Transfer Tubes
Authors: Khan A , Yue N
Published: July 2016

Purpose:

Brachytherapy is a highly targeted from of radiotherapy. While this may lead to ideal dose distributions on the treatment planning system, a small error in source location can lead to change in the dose distribution. The purpose of this study is to quantify the impact on source position error due to curvature of the transfer tubes and the impact this may have on the dose distribution.

Methods:

Since the source travels along the midline of the tube, an estimate of the positioning error for various angles of curvature was determined using geometric properties of the tube. Based on the range of values a specific shift was chosen to alter the treatment plans for a number of cervical cancer patients who had undergone HDR brachytherapy boost using tandem and ovoids. Impact of dose to target and organs at risk were determined and checked against guidelines outlined by radiation oncologist.

Results:

The estimate of the positioning error was 2mm short of the expected position (the curved tube can only cause the source to not reach as far as with a flat tube). Quantitative impact on the dose distribution is still in the process of being analyzed.

Conclusion:

The accepted positioning tolerance for the source position of a HDR brachytherapy unit is plus or minus 1mm. If there is an additional 2mm discrepancy due to tube curvature, this can result in a source being 1mm to 3mm short of the expected location. While we do always attempt to keep the tubes straight, in some cases such as with tandem and ovoids, the tandem connector does not extend as far out from the patient so the ovoid tubes always contain some degree of curvature. The dose impact of this may be significant.
SU‐F‐T‐26: A Study of the Consistency of Brachytherapy Treatments for Vaginal Cuff
Authors: Shojaei M , Pella S , Dumitru N
Published: July 2016

Purpose:

To evaluate to treatment consistency over the total number of fractions when treatment what HDR brachytherapy using the ML cylinders. At the same time the dosimetric impact on the critical organs is monitored over the total number of fractions.

Methods:

A retrospective analysis of 10 patients treated with Cylinder applicators, from 2015–2016 were considered for this study. The CT scans of these patients, taken before each treatment were separately imported in to the treatment planning system and paired with the initial CT scan after completing the contouring. Two sets of CT images were fused together with respective to the applicator, using landmark registration. The doses of each plan were imported as well and a cumulative dosimetric analysis was made for bladder, bowels, and rectum and PTV.

Results:

No contour of any of the OAR was exactly similar when CT images were fused on each other. The PTV volumes vary from fraction to fraction. There was always a difference between the doses received by the OARs between treatments. The maximum dose varied between 5% and 30% in rectum and bladder. The minimum dose varied between 5% and 8% in rectum and bladder. The average dose varied between 15% and 20% in rectum and bladder. Deviation in placement were noticed between fractions.

Conclusion:

The variation in volumes of OARs and isodoses near the OARs, indicate that the estimated doses to OARs on the planning system may not be the same dose delivered to the patient in all the fractions. There are no major differences between the prescribed dose and the delivered dose over the total number of fractions. In some cases the critical organs will benefit if the consecutive plans will made after the CT scans will be registered with the initial scan and then planned.
SU‐F‐T‐31: Shape and Isodose Distributions in Co60 HDR Brachytherapy for Different Utero‐Vaginal Time Ratios
Authors: Gonzalez‐Sprinberg G , Piriz G
Published: July 2016

Purpose:

To optimize the dose in bladder and rectum and show the different shapes of the isodose volumes in Co60‐HDR brachytherapy, considering different utero and vaginal sources dwell ratio times (TU:TV).

Methods:

Besides Ir192‐HDR, new Co60‐HDR sources are being incorporated. We considered different TU:TV times and computed the dosis in bladder, rectum and at the reference points of the Manchester system. Also, we calculated the isodose volume and shape in each case. We used a EZAG‐BEBIG Co0.A86 model with TPS HDRplus3.0.4. and LCT42‐7, LCT42‐2(R,L) applicators. A reference dose RA= 1.00 Gy was given to the A‐right point. We considered the TU:TV dwell time ratios 1:0.25, 1:0.33, 1:0.5, 1:1, 1:2, 1:3, and 1:4. Given TU:TV, the stop time at each dwell position is fixed for each applicator.

Results:

Increasing TU:TV systematically results in a decreasing of the dose in bladder and rectum, e.g. 9% and 27% reduction were found in 1:0.25 with respect to 1:1, while 12% and 34% increase were found in 1:4 with respect to 1:1. Also, the isodose volume parameters height (h), width (w), thickness (t) and volume (hwt) increased from the 1:0.25 case to the 1:4 value: hwt is 25% lower and 31% higher than the 1:1 reference volume in these cases. Also w decreased for higher TU:TV and may compromise the tumoral volume coverage, decreasing 17% in the 1:0.25 case compared to the 1:1 case. The shape of the isodose volume was obtained for the different TU:TV considered.

Conclusion:

We obtained the shape of isodose volumes for different TU:TV values in gynecological Co60‐HDR. We studied the dose reduction in bladder and rectum for different TU:TV ratios. The volume parameters and hwt are strongly dependent on this ratio. This information is useful for a quantitative check of the TPS and as a starting point towards optimization.
SU‐F‐T‐34: Transition Form CT‐Based to Ultrasound‐Based HDR Treatment Planning for Prostate Cancer
Authors: Veltchev I , Price R , Horwitz E , Ma C
Published: July 2016

Purpose:

We discuss our experience with the transition from CT‐based to ultrasound‐based HDR treatment planning for prostate cancer in a high‐volume clinical setting. The details of switching from one afterloader vendor to another are also discussed. The four main stages of prostate HDR planning (image acquisition, target delineation, needle reconstruction, and plan optimization) are significantly modified when ultrasound imaging is used.

Methods:

We employ a time‐efficient needle reconstruction procedure that provides the necessary level of accuracy to rival the traditional CT‐based method. A total of 80 consecutive prostate treatments are part of this comparative study: 40 CT‐based and 40 ultrasound‐based. Various dosimetric parameters are investigated as points of comparison: target DVH points (V100, V150, V200) and dose non‐homogeneity ratio (DNR). An ultrasound‐guided peripheral needle‐placement strategy with two central needles is maintained for both groups of patients. Any differences in plan quality can therefore be attributed to target delineation, accuracy of needle reconstruction, and plan optimization capabilities of the two planning systems.

Results:

Statistical analysis of the dosimetric end‐points suggests that as a result of the implementation of ultrasound planning, target delineation consistency was improved; target volumes were reduced, leading to lower normal tissue dose while consistently improving all dosimetric parameters (DNR is reduced by ∼4%) as compared to the CT‐based treatment work‐flow.

Conclusion:

The introduction of ultrasound‐based real‐time treatment planning significantly reduced the operating room time for all patients ‐ from 4 hours to 2.5 hours, allowing us to double the patient load in a single 5 hour slot. Dosimetric quality of the plans was only slightly improved after the switch to ultrasound planning. Reproducibility however, saw the greatest improvement, eliminating the needle position uncertainties associated with the addition of a CT scan.
SU‐F‐T‐42: MRI and TRUS Image Fusion as a Mode of Generating More Accurate Prostate Contours
Authors: Petronek M , Purysko A , Balik S , Ciezki J , Klein E , Wilkinson D
Published: July 2016

Purpose:

Transrectal Ultrasound (TRUS) imaging is utilized intra‐operatively for LDR permanent prostate seed implant treatment planning. Prostate contouring with TRUS can be challenging at the apex and base. This study attempts to improve accuracy of prostate contouring with MRI‐TRUS fusion to prevent over‐ or under‐estimation of the prostate volume.

Methods:

14 patients with previous MRI guided prostate biopsy and undergone an LDR permanent prostate seed implant have been selected. The prostate was contoured on the MRI images (1 mm slice thickness) by a radiologist. The prostate was also contoured on TRUS images (5 mm slice thickness) during LDR procedure by a urologist. MRI and TRUS images were rigidly fused manually and the prostate contours from MRI and TRUS were compared using Dice similarity coefficient, percentage volume difference and length, height and width differences.

Results:

The prostate volume was overestimated by 8 ± 18% (range: 34% to −25%) in TRUS images compared to MRI. The mean Dice was 0.77 ± 0.09 (range: 0.53 to 0.88). The mean difference (TRUS‐MRI) in the prostate width was 0 ± 4 mm (range: −11 to 5 mm), height was −3 ± 6 mm (range: −13 to 6 mm) and length was 6 ± 6 (range: −10 to 16 mm). Prostate was overestimated with TRUS imaging at the base for 6 cases (mean: 8 ± 4 mm and range: 5 to 14 mm), at the apex for 6 cases (mean: 11 ± 3 mm and range: 5 to 15 mm) and 1 case was underestimated at both base and apex by 4 mm.

Conclusion:

Use of intra‐operative TRUS and MRI image fusion can help to improve the accuracy of prostate contouring by accurately accounting for prostate over‐ or under‐estimations, especially at the base and apex. The mean amount of discrepancy is within a range that is significant for LDR sources.
SU‐F‐T‐46: The Effect of Inter‐Seed Attenuation and Tissue Composition in Prostate 125I Brachytherapy Dose Calculations
Authors: Tamura K , Araki F , Ohno T
Published: July 2016

Purpose:

To investigate the difference of dose distributions with/without the effect of inter‐seed attenuation and tissue compositions in prostate 125I brachytherapy dose calculations, using Monte Carlo simulations of Particle and Heavy Ion Transport code System (PHITS).

Methods:

The dose distributions in 125I prostate brachytherapy were calculated using PHITS for non‐simultaneous and simultaneous alignments of STM1251 sources in water or prostate phantom for six patients. The PHITS input file was created from DICOM‐RT file which includes source coordinates and structures for clinical target volume (CTV) and organs at risk (OARs) of urethra and rectum, using in‐house Matlab software. Photon and electron cutoff energies were set to 1 keV and 100 MeV, respectively. The dose distributions were calculated with the kerma approximation and the voxel size of 1 × 1 × 1 mm3. The number of incident photon was set to be the statistical uncertainty (1σ) of less than 1%. The effect of inter‐seed attenuation and prostate tissue compositions was evaluated from dose volume histograms (DVHs) for each structure, by comparing to results of the AAPM TG‐43 dose calculation (without the effect of inter‐seed attenuation and prostate tissue compositions).

Results:

The dose reduction due to the inter‐seed attenuation by source capsules was approximately 2% for CTV and OARs compared to those of TG‐43. In additions, by considering prostate tissue composition, the D90 and V100 of CTV reduced by 6% and 1%, respectively.

Conclusion:

It needs to consider the dose reduction due to the inter‐seed attenuation and tissue composition in prostate 125I brachytherapy dose calculations.
SU‐F‐T‐50: Evaluation of Monte Carlo Simulations Performance for Pediatric Brachytherapy Dosimetry
Authors: Chatzipapas C , Papadimitroulas P , Loudos G , Papanikolaou N , Kagadis G
Published: July 2016

Purpose:

Pediatric tumors are generally treated with multi‐modal procedures. Brachytherapy can be used with pediatric tumors, especially given that in this patient population low toxicity on normal tissues is critical as is the suppression of the probability for late malignancies. Our goal is to validate the GATE toolkit on realistic brachytherapy applications, and evaluate brachytherapy plans on pediatrics for accurate dosimetry on sensitive and critical organs of interest.

Methods:

The GATE Monte Carlo (MC) toolkit was used. Two High Dose Rate (HDR) 192Ir brachytherapy sources were simulated (Nucletron mHDR‐v1 and Varian VS2000), and fully validated using the AAPM and ESTRO protocols. A realistic brachytherapy plan was also simulated using the XCAT anthropomorphic computational model .The simulated data were compared to the clinical dose points. Finally, a 14 years old girl with vaginal rhabdomyosarcoma was modelled based on clinical procedures for the calculation of the absorbed dose per organ.

Results:

The MC simulations resulted in accurate dosimetry in terms of dose rate constant (Λ), radial dose gL(r) and anisotropy function F(r,θ) for both sources.The simulations were executed using ∼1010 number of primaries resulting in statistical uncertainties lower than 2%.The differences between the theoretical values and the simulated ones ranged from 0.01% up to 3.3%, with the largest discrepancy (6%) being observed in the dose rate constant calculation.The simulated DVH using an adult female XCAT model was also compared to a clinical one resulting in differences smaller than 5%. Finally, a realistic pediatric brachytherapy simulation was performed to evaluate the absorbed dose per organ and to calculate DVH with respect to heterogeneities of the human anatomy.

Conclusion:

GATE is a reliable tool for brachytherapy simulations both for source modeling and for dosimetry in anthropomorphic voxelized models. Our project aims to evaluate a variety of pediatric brachytherapy schemes using a population of pediatric phantoms for several pathological cases.

This study is part of a project that has received funding from the European Union Horizon2020 research and innovation programme under the MarieSklodowska‐Curiegrantagreement.No691203.The results published in this study reflect only the authors view and the Research Executive Agency (REA) and the European Commission is not responsible for any use that may be madeof the information it contains.
SU‐F‐T‐52: Study of Energy Dependent Effect of Dosimetry Systems Used in Therapeutic Soft X‐Ray Energy Range
Authors: Souri S , Qian X , Gill G , Jamshidi A , Cao Y , Chen Y
Published: July 2016

Purpose:

To investigate energy dependent effects of different dosimetry systems which can be used as in vivo dosimetry monitoring for intraoperative radiotherapy in therapeutic soft x‐ray energy range.

Methods:

Three dosimetry systems were evaluated in therapeutic soft x‐ray energy range: optically stimulated luminescent dosimeter (OSLD) nanoDots, radiochromic EBT2 and EBT3 films. The x‐ray photons were produced by a Zeiss Intrabeam 50 kV x‐ray radiotherapy system. Solid water and bolus slabs with different thicknesses were used in the process of irradiation. An aluminum filter set was used to measure HVLs of X‐rays. Calibration curves were made at different depth of boluses.

Results:

Half Value Layers at depths of 0, 3, 10, and 20 mm of solid water were measured to represent the energy change versus depth, yielding 0.306, 0.482, 0.865 and 0.901 respectively and indicating nearly unchanged HVL beyond 1 cm depth. The responses of each system at different depths were normalized to the response at 2 cm depth. In film dosimetry, the response is calculated as optical density (OD). The results show that there is nearly the same energy dependence for EBT2 and EBT3. At a HVL of 0.482 mm Al, the relative responses of nanoDots and EBT3 are 0.85 ± 0.04 and 0.89 ± 0.03 compared to those at 0.901 mm Al HVL, respectively, indicating no obvious difference between those two systems within the measurement uncertainty.

Conclusion:

It was observed that the studied dosimeter response increases about 13% from the x‐ray energy of 0.48 mm Al to 0.90 mm Al. Therefore, caution should be exercised in using an appropriate calibration curve, and x‐ray beam hardening effect has to be taken into account.
SU‐F‐T‐72: Experimental Determination of the Positionuncertainties for ROOS Ionization Chambers in Clinical Electron Beams
Authors: von Voigts‐Rhetz P , Pretzsch T , Czarnecki D , Vorwerk H , Zink K
Published: July 2016

Purpose:

National and international dosimetry protocols assume a position accuracy for ionization chambers of less than 0.2mm. To follow this precept the manufacturer PTW‐Freiburg introduced a positioning assistance system (TRUFIX) for their particular ion chambers. Aim of this study is an experimental investigation of the positioning uncertainties for ROOS‐type ionization chambers.

Methods:

For all measurements a linear accelerator Elekta Synergie was used. The experiments were performed in a water‐phantom. To collimate the electron beam a 10×10cm2 applicator was installed. All measured depth dose curves were normalized to their maximum. In all cases the TRUFIX system was applied for chamber positioning. For the first measurement series, to determine the positioning reproducibility of a ROOS chamber, one person placed the chamber three times in a 6 MeV electron beam. The mean value of this three measurements was the reference for further six random persons who repeated this procedure. The results were compared for different depths (R50, zref and Rp). To investigate the impact of different individual chambers of the same type 10 different ROOS chambers were placed by the same person in a 6, 12 and 18MeV electron beam and the measured reference depths zref were compared.

Results:

The absolute positioning reproducibility is less than 0.1mm for the same person. The positioning uncertainties are increasing up to +/−0.3mm if different persons perform the chamber's positioning within the water phantom. The comparison of the 10 different ROOS chambers resulted in reference depths zref with deviations in the range of +/−0.45mm for all energies.

Conclusion:

The position accuracy of 0.2mm can be fulfilled with the TRUFIX system. The comparison of the 10 different ROOS ionization chambers showed noticeable deviations in the determined reference depth. The impact of a positioning uncertainty of about 0.3–0.4mm on the total perturbation correction will be considered.
SU‐F‐T‐79: Monte Carlo Investigation of Optimizing Parameters for Modulated Electron Arc Therapy
Authors: Al Ashkar E , Eldib A , Eraba K , Imam M , Ma C
Published: July 2016

Purpose:

Electron arc therapy provides excellent dose distributions for treating superficial tumors along curved surfaces. However this modality has not received widespread application due to the lack of needed advancement in electron beam delivery, accurate electron dose calculation and treatment plan optimization. The aim of the current work is to investigate possible parameters that can be optimized for electron arc (eARC) therapy.

Methods:

The MCBEAM code was used to generate phase space files for 6 and 12MeV electron beam energies from a Varian trilogy machine. An Electron Multi‐leaf collimator eMLC of 2cm thickness positioned at 82 cm source collimated distance was used in the study. Dose distributions for electron arcs were calculated inside a cylindrical phantom using the MCSIM code. The Cylindrical phantom was constructed with 0.2cm voxels and a 15cm diameter. Electron arcs were delivered with two different approaches. The first approach was to deliver the arc as segments of very small field widths. In this approach we also tested the impact of the segment size and the arc increment angle. The second approach is to deliver the arc as a sum of large fields each covering the whole target as seen from the beam eye view.

Results:

In considering 90 % as the prescription isodose line, the first approach showed a region of buildup proceeding before the prescription zone. This build up is minimizing with the second approach neglecting need for bolus. The second approach also showed less x‐ray contamination. In both approaches the variation of the segment size changed the size and location of the prescription isodose line. The optimization process for eARC could involve interplay between small and large segments to achieve desired coverage.

Conclusion:

An advanced modulation of eARCs will allow for tailored dose distribution for superficial curved target as with challenging scalp cases
SU‐F‐T‐82: Dosimetric Evaluation of a Shield Used for Hemi‐Body Skin Electron Irradiation
Authors: Rivers C , AlDahlawi I , Wang I , Singh A , Podgorsak M
Published: July 2016

Purpose:

We had several mycosis fungoides patients with a limited disease to about half of the skin surface. A custom‐made plywood shield was used to protect the non‐targeted skin region with our total skin electron irradiation (TSEI) technique. We report a dosimetric evaluation for our “hemi‐body” skin electron irradiation technique.

Methods:

The technique is similar to our clinical total skin electron irradiation (TSEI), performed with a six‐pair dual field (Stanford technique) at an extended source‐to‐skin distance (SSD) of 377 cm, with the addition of a plywood shield placed 50 cm from the patient. The shield is made of three layers of standard 5/8″ thick plywood (total thickness of 4.75 cm) that are clamped securely on an adjustable‐height stand. Gafchromic EBT3 films were used in assessing the shield's transmission factor and the extend of the dose penumbra region. To verify the dose delivered for hemi‐body skin radiation in a real patient treatment, in‐vivo dosimetry using Gafchromic EBT3 films were performed. Film pieces were taped on the patient skin to measure the dose received during the first two fractions, placed on the forehead and upper body (shielded region); and also at the level of pelvic area, left thigh, and left ankle.

Results:

The shield transmission factor was found to be 10%, and the width of the penumbra (80‐to‐20% dose fall‐off) was about 12 cm. In‐vivo dosimetry of a real case confirmed the expected shielded area dose.

Conclusion:

Hemi‐Body skin electron irradiation at an extended SSD is feasible with the addition of a plywood shield at a distance from patient skin. The penumbra dose region and the shield's transmission factor should be evaluated prior to clinical use. We have treated several hemi‐body skin patients with our custom‐made plywood shield, the current patient measurements are representative of these for other patients as well.
SU‐F‐T‐91: Development of Real Time Abdominal Compression Force (ACF) Monitoring System
Authors: Kim T , Kim S , Kim D , Kang S , Cho M , Kim K , Shin D , Noh Y , Suh T
Published: July 2016

Purpose:

Hard‐plate based abdominal compression is known to be effective, but no explicit method exists to quantify abdominal compression force (ACF) and maintain the proper ACF through the whole procedure. In addition, even with compression, it is necessary to do 4D CT to manage residual motion but, 4D CT is often not possible due to reduced surrogating sensitivity. In this study, we developed and evaluated a system that both monitors ACF in real time and provides surrogating signal even under compression. The system can also provide visual‐biofeedback.

Methods:

The system developed consists of a compression plate, an ACF monitoring unit and a visual‐biofeedback device. The ACF monitoring unit contains a thin air balloon in the size of compression plate and a gas pressure sensor. The unit is attached to the bottom of the plate thus, placed between the plate and the patient when compression is applied, and detects compression pressure. For reliability test, 3 volunteers were directed to take several different breathing patterns and the ACF variation was compared with the respiratory flow and external respiratory signal to assure that the system provides corresponding behavior. In addition, guiding waveform were generated based on free breathing, and then applied for evaluating the effectiveness of visual‐biofeedback.

Results:

We could monitor ACF variation in real time and confirmed that the data was correlated with both respiratory flow data and external respiratory signal. Even under abdominal compression, in addition, it was possible to make the subjects successfully follow the guide patterns using the visual biofeedback system.

Conclusion:

The developed real time ACF monitoring system was found to be functional as intended and consistent. With the capability of both providing real time surrogating signal under compression and enabling visual‐biofeedback, it is considered that the system would improve the quality of respiratory motion management in radiation therapy.

This research was supported by the Mid‐career Researcher Program through NRF funded by the Ministry of Science, ICT & Future Planning of Korea (NRF‐2014R1A2A1A10050270) and by the Radiation Technology R&D program through the National Research Foundation of Korea funded by the Ministry of Science, ICT & Future Planning (No. 2013M2A2A7038291)
SU‐F‐T‐101: Insight into Dosimetry Workload and Planning Timelines: A 6 Year Review at One Institution
Authors: Cardan R , Popple R , Smith H , Fiveash J
Published: July 2016

Purpose:

To elucidate realistic clinical treatment planning workload and timelines to improve understanding for patients, payers, and other institutions involved in radiotherapy processes.

Methods:

A web based tool was developed using Oracle Express (Oracle Corp, Redwood City, CA) which allowed communication between the physicians and staff about the current state of the patient plan. For 6 years, all patient courses were logged and time‐stamped in 22 discreet steps which detailed start and stop times for simulation, contouring, and treatment planning tasks. This data was combined with the treatment planning database (TPDB) using the Eclipse Scripting API (Varian Medical Systems, Palo Alto, CA) to cross‐identify plans between the two systems. This time data was analyzed across our dosimetry staff and treatment modality.

Results:

In 6 years, 110,477 patient statuses were time‐logged for 9683 courses of treatment using our internal software. The courses contained 8305 unique patients who were binned into one of 11 diagnosis site categories. 8253 courses could be reconciled against the TPDB using timestamp data from patient statuses. The average planning volume per dosimetrist was 375.8 ± 142.4 plans per year with the average number of planning revisions per dosimetrist of 71.0 ± 27.1 plans per year. The median treatment planning times by modality ranged from to 48.3 hours for IMRT plans 5 fields or less to 119.6 hours for IMRT with 8 or more fields. Two arc VMAT, three arc VMAT, and 3D plans median times were 89.1 hours, 113.8 hours, and 50.9 hours respectively.

Conclusion:

Using our web based tool, we have demonstrated the ability to quantify treatment planning timelines and workloads which could help in setting appropriate expectations for patients, payers, and hospital administration.

COI: Author received monies from Varian Medical Systems for research and teaching honorarium.
SU‐F‐T‐104: Determining the NTCP Parameters of Pharyngeal Constrictors and Proximal Esophagus for Radiation Induced Swallowing Problems Recorded Six Months After Radiation Therapy for Head and Neck Tumors
Authors: Mavroidis P , Price A , Kostich M , Amdur R , Mendenhall W , Sheets N , Green R , Das S , Marks L , Chera B
Published: July 2016

Purpose:

To estimate the radiobiological parameters of four NTCP models that describe the dose‐response relations of pharyngeal constrictors and proximal esophagus regarding the severity of patient reported swallowing problems 6 months post chemo‐radiotherapy. To identify the section/structure that best correlates with the manifestation of the clinical endpoints. Finally, to compare the goodness‐of‐fit of those models.

Methods:

Forty‐three patients were treated on a prospective multi‐institutional phase II study for oropharyngeal squamous cell carcinoma. All the patients received 60 Gy IMRT and they reported symptoms using the novel patient reported outcome version of the CTCAE. We derived the individual patient dosimetric data of superior, medium and inferior sections of pharyngeal constrictors (SPC, MPC and IPC), superior and inferior sections of esophagus (SES and IES) as separate structures as well as combinations. The Lyman‐Kutcher‐Burman (LKB), Relative Seriality (RS), Logit and Relative Logit (RL) NTCP models were used to fit the patient data. The fitting of the different models was assessed through the area under the receiver operating characteristic curve (AUC) and the Odds Ratio methods.

Results:

The AUC values were highest for the SPC for Grade ≥ 2 (0.719 for the RS and RL models, and 0.716 for LKB and Logit). For Grade ≥ 1, the respective values were 0.699 for RS, LKB and Logit and 0.676 for RL. For MPC the AUC values varied between 0.463–0.477, for IPC between 0.396–0.458, for SES between 0.556–0.613 and for IES between 0.410–0.519. The Odds Ratio for the SPC was 15.6 (1.7–146.4) for RS, LKB and Logit for NTCP of 55%.

Conclusion:

All the examined NTCP models could fit the clinical data with similar accuracy. The SPC appear to correlate best with the clinical endpoints of swallowing problems. A prospective study could establish the use of NTCP values of SPC as a constraint in treatment planning.
SU‐F‐T‐108: Texture Analysis for Toxicity Prediction From Dose Surface Maps
Authors: Witztum A , Warren S , Partridge M , Hawkins M
Published: July 2016

Purpose:

To find spatial features that best predict acute duodenal related toxicity grade ≥ 3 from 2D dose surface maps in pancreatic chemoradiotherapy.

Methods:

Nineteen patients from the ARCII trial (EudraCT 2008‐006302‐42) treating locally‐advanced pancreatic cancer (LAPC) with chemoradiotherapy were analysed. Previous work considering traditional dose‐volume and dose‐surface metrics as predictors had little power. We investigate the use of texture analysis to improve predictive capabilities. 2D duodenal dose surface maps (DSMs) were converted to 4, 8, and 16 gray (dose) levels. A gray‐level co‐occurrence matrix (GLCM) was produced and statistics (contrast, correlation, energy and homogeneity) were extracted. ROC curves were produced for each statistic for three different gray level maps (4, 8, and 16). The area under curve (AUC) was recorded and used to find the best predictor for acute duodenal related toxicity grade ≥ 3.

Results:

For all GLCM statistics there were only small differences in AUC between 4, 8 and 16 gray levels. Homogeneity had an AUC of 0.87, 0.88 and 0.85 for 4, 8 and 16 gray levels respectively. Using cut point analysis on homogeneity using 8 gray levels it was found that a value of 0.945 correctly predicted toxicity for 17/19 patients (4/6 patients with, 13/13 patients without toxicity). The two incorrectly predicted patients had a mean dose of 59 Gy and 28 Gy. The AUC for traditional dose‐volume (V45 = 0.57, V50 = 0.60, V55 = 0.47) and dose‐surface metrics (S45 (surface area receiving at least 45 Gy) = 0.50, S50 = 0.57, S55 = 0.49) were much lower.

Conclusion:

Use of texture analysis improves our ability to predict grade ≥ 3 GI toxicity in pancreatic chemoradiotherapy. The additional spatial information may give better predictors than traditional dose‐volume and dose‐surface metrics. The mechanism behind this predicted toxicity will be studied on a larger patient set.

Alon Witztum is supported by an MRC/Gray Institute DPhil Studentship. Sam Warren and Mike Partridge are supported by CRUK grant C5255/A15935. Maria Hawkins received an MRC Fellowship MC_PC_12001/2.
SU‐F‐T‐111: Investigation of the Attila Deterministic Solver as a Supplement to Monte Carlo for Calculating Out‐Of‐Field Radiotherapy Dose
Authors: Mille M , Lee C , Failla G
Published: July 2016

Purpose:

To use the Attila deterministic solver as a supplement to Monte Carlo for calculating out‐of‐field organ dose in support of epidemiological studies looking at the risks of second cancers. Supplemental dosimetry tools are needed to speed up dose calculations for studies involving large‐scale patient cohorts.

Methods:

Attila is a multi‐group discrete ordinates code which can solve the 3D photon‐electron coupled linear Boltzmann radiation transport equation on a finite‐element mesh. Dose is computed by multiplying the calculated particle flux in each mesh element by a medium‐specific energy deposition cross‐section. The out‐of‐field dosimetry capability of Attila is investigated by comparing average organ dose to that which is calculated by Monte Carlo simulation. The test scenario consists of a 6 MV external beam treatment of a female patient with a tumor in the left breast. The patient is simulated by a whole‐body adult reference female computational phantom. Monte Carlo simulations were performed using MCNP6 and XVMC. Attila can export a tetrahedral mesh for MCNP6, allowing for a direct comparison between the two codes. The Attila and Monte Carlo methods were also compared in terms of calculation speed and complexity of simulation setup. A key perquisite for this work was the modeling of a Varian Clinac 2100 linear accelerator.

Results:

The solid mesh of the torso part of the adult female phantom for the Attila calculation was prepared using the CAD software SpaceClaim. Preliminary calculations suggest that Attila is a user‐friendly software which shows great promise for our intended application. Computational performance is related to the number of tetrahedral elements included in the Attila calculation.

Conclusion:

Attila is being explored as a supplement to the conventional Monte Carlo radiation transport approach for performing retrospective patient dosimetry. The goal is for the dosimetry to be sufficiently accurate for use in retrospective epidemiological investigations.
SU‐F‐T‐113: Inherent Functional Dependence of Spinal Cord Doses of Variable Irradiated Volumes in Spine SBRT
Authors: Ma L , Braunstein S , Chiu J , Sahgal A
Published: July 2016

Purpose:

Spinal cord tolerance for SBRT has been recommended for the maximum point dose level or at irradiated volumes such as 0.35 mL or 10% of contoured volumes. In this study, we investigated an inherent functional relationship that associates these dose surrogates for irradiated spinal cord volumes of up to 3.0 mL.

Methods:

A hidden variable termed as Effective Dose Radius (EDR) was formulated based on a dose fall‐off model to correlate dose at irradiated spinal cord volumes ranging from 0 mL (point maximum) to 3.0 mL. A cohort of 15 spine SBRT cases was randomly selected to derive an EDR‐parameterized formula. The mean prescription dose for the studied cases was 21.0±8.0 Gy (range, 10–40Gy) delivered in 3±1 fractions with target volumes of 39.1 ± 70.6 mL. Linear regression and variance analysis were performed for the fitting parameters of variable EDR values.

Results:

No direct correlation was found between the dose at maximum point and doses at variable spinal cord volumes. For example, Pearson R2 = 0.643 and R2= 0.491 were obtained when correlating the point maximum dose with the spinal cord dose at 1 mL and 3 mL, respectively. However, near perfect correlation (R2 ≥0.99) was obtained when corresponding parameterized EDRs. Specifically, Pearson R2= 0.996 and R2 = 0.990 were obtained when correlating EDR (maximum point dose) with EDR (dose at 1 mL) and EDR(dose at 3 mL), respectively. As a result, high confidence level look‐up tables were established to correlate spinal cord doses at the maximum point to any finite irradiated volumes.

Conclusion:

An inherent functional relationship was demonstrated for spine SBRT. Such a relationship unifies dose surrogates at variable cord volumes and proves that a single dose surrogate (e.g. point maximum dose) is mathematically sufficient in constraining the overall spinal cord dose tolerance for SBRT.
SU‐F‐T‐114: A Novel Anatomically Predictive Extension Model of Computational Human Phantoms for Dose Reconstruction in Retrospective Epidemiological Studies of Second Cancer Risks in Radiotherapy Patients
Authors: Kuzmin G , Lee C , Lee C , Pelletier C , Jung J
Published: July 2016

Purpose:

Recent advances in cancer treatments have greatly increased the likelihood of post‐treatment patient survival. Secondary malignancies, however, have become a growing concern. Epidemiological studies determining secondary effects in radiotherapy patients require assessment of organ‐specific dose both inside and outside the treatment field. An essential input for Monte Carlo modeling of particle transport is radiological images showing full patient anatomy. However, in retrospective studies it is typical to only have partial anatomy from CT scans used during treatment planning. In this study, we developed a multi‐step method to extend such limited patient anatomy to full body anatomy for estimating dose to normal tissues located outside the CT scan coverage.

Methods:

The first step identified a phantom from a library of body size‐dependent computational human phantoms by matching the height and weight of patients. Second, a Python algorithm matched the patient CT coverage location in relation to the whole body phantom. Third, an algorithm cut the whole body phantom and scaled them to match the size of the patient. Then, merged the two anatomies into one whole body. We entitled this new approach, Anatomically Predictive Extension (APE).

Results:

The APE method was examined by comparing the original chest‐abdomen‐pelvis CT images of the five patients with the APE phantoms developed from only the chest part of the CAP images and whole body phantoms. We achieved average percent differences of tissue volumes of 25.7%, 34.2%, 16.5%, 26.8%, and 31.6% with an average of 27% across all patients.

Conclusion:

Our APE method extends the limited CT patient anatomy to whole body anatomy by using image processing and computational human phantoms. Our ongoing work includes evaluating the accuracy of these APE phantoms by comparing normal tissue doses in the APE phantoms and doses calculated for the original full CAP images under generic radiotherapy simulations.

This research was supported by the NIH Intramural Research Program.
SU‐F‐T‐124: Radiation Biological Equivalent Presentations OfLEM‐1 and MKM Approaches in the Carbon‐Ion Radiotherapy
Authors: Hsi W , Jiang G , Sheng Y
Published: July 2016

Purpose:

To study the correlations of the radiation biological equivalent doses (BED) along depth and lateral distance between LEM‐1 and MKM approaches.

Methods:

In NIRS‐MKM (Microdosimetric Kinetic Model) approach, the prescribed BED, referred as C‐Eq, doses aims to present the relative biological effectiveness (RBE) for different energies of carbon‐ions on a fixed 10% survival value of HCG cell with respect to convention X‐ray. Instead of a fixed 10% survival, the BED doses of LEM‐1 (Local Effect Model) approach, referred as X‐Eq, aims to present the RBE over the whole survival curve of chordoma‐like cell with alpha/beta ratio of 2.0. The relationship of physical doses as a function of C‐Eq and X‐Eq doses were investigated along depth and lateral distance for various sizes of cubic targets in water irradiated by carbon‐ions.

Results:

At the center of each cubic target, the trends between physical and C‐Eq or X‐Eq doses can be described by a linear and 2nd order polynomial functions, respectively. Using fit functions can then calculate a scaling factor between C‐Eq and X‐Eq doses to have similar physical doses. With equalized C‐Eq and X‐Eq doses at the depth of target center, over‐ and under‐estimated X‐Eq to C‐Eq are seen for depths before and after the target center, respectively. Near the distal edge along depth, sharp rising of RBE value is observed for X‐Eq, but sharp dropping of RBE value is observed for C‐Eq. For lateral locations near and just outside 50% dose level, sharp raising of RBE value is also seen for X‐Eq, while only minor increasing with fast dropping for C‐Eq.

Conclusion:

An analytical function to model the differences between the CEq and X‐Eq doses along depth and lateral distance need to further investigated to explain varied clinic outcome of specific cancers using two different approaches to calculated BED doses.
SU‐F‐T‐128: Dose‐Volume Constraints for Particle Therapy Treatment Planning
Authors: Stewart R , Smith W , Hendrickson K , Meyer J , Cao N , Lee E , Gopan O , Sandison G , Parvathaneni U , Laramore G
Published: July 2016

Purpose:

Determine equivalent Organ at Risk (OAR) tolerance dose (TD) constraints for MV x‐rays and particle therapy.

Methods:

Equivalent TD estimates for MV x‐rays are determined from an isoeffect, regression‐analysis of published and in‐house constraints for various fractionation schedules (n fractions). The analysis yields an estimate of (α/β) for an OAR. To determine equivalent particle therapy constraints, the MV x‐ray TD(n) values are divided by the RBE for DSB induction (RBEDSB) or cell survival (RBES). Estimates of (RBEDSB) are computed using the Monte Carlo Damage Simulation, and estimates of RBES are computed using the Repair‐Misrepair‐Fixation (RMF) model. A research build of the RayStation™ treatment planning system implementing the above model is used to estimate (RBEDSB) for OARs of interest in 16 proton therapy patient plans (head and neck, thorax, prostate and brain).

Results:

The analysis gives an (α/β) estimate of about 20 Gy for the trachea and heart and 2–4 Gy for the esophagus, spine, and brachial plexus. Extrapolation of MV x‐ray constraints (n = 1) to fast neutrons using RBEDSB = 2.7 are in excellent agreement with clinical experience (n = 10 to 20). When conventional (n > 30) x‐ray treatments are used as the reference radiation, fast neutron RBE increased to a maximum of 6. For comparison to a constant RBE of 1.1, the RayStation™ analysis gave estimates of proton RBEDSB from 1.03 to 1.33 for OARs of interest.

Conclusion:

The presented system of models is a convenient formalism to synthesize from multiple sources of information a set of self‐consistent plan constraints for MV x‐ray and hadron therapy treatments. Estimates of RBEDSB from the RayStation™ analysis differ substantially from 1.1 and vary among patients and treatment sites. A treatment planning system that incorporates patient and anatomy‐specific corrections in proton RBE would create opportunities to increase the therapeutic ratio.

The research build of the RayStation used in the study was made available to the University of Washington free of charge. RaySearch Laboratories did not provide any monetary support for the reported studies.
SU‐F‐T‐133: Uniform Scanning Proton Therapy for Lung Cancer: Toxicity and Its Correlation with Dosimetry
Authors: Zheng Y , Rana S , Larson G
Published: July 2016

Purpose:

To analyze the toxicity of uniform scanning proton therapy for lung cancer patients and its correlation with dose distribution.

Methods:

In this study, we analyzed the toxicity of 128 lung cancer patients, including 18 small cell lung cancer and 110 non small cell lung cancer patients. Each patient was treated with uniform scanning proton beams at our center using typically 2–4 fields. The prescription was typically 74 Cobalt gray equivalent (CGE) at 2 CGE per fraction. 4D Computerized Tomography (CT) scans were used to evaluate the target motion and contour the internal target volume, and repeated 3 times during the course of treatment to evaluate the need for plan adaptation. Toxicity data for these patients were obtained from the proton collaborative group (PCG) database. For cases of grade 3 toxicities or toxicities of interest such as esophagitis and radiation dermatitis, dose distributions were reviewed and analyzed in attempt to correlate the toxicity with radiation dose.

Results:

At a median follow up time of about 21 months, none of the patients had experienced Grade 4 or 5 toxicity. The most common adverse effect was dermatitis (81%: 52%‐Grade 1, 28%‐Grade 2, and 1% Grade 3), followed by fatigue (48%), Cough (46%), and Esophagitis (45%), as shown in Figure 1. Severe toxicities, such as Grade 3 dermatitis or pain of skin, had a clear correlation with high radiation dose.

Conclusion:

Uniform scanning proton therapy is well tolerated by lung cancer patients. Preliminary analysis indicates there is correlation between severe toxicity and high radiation dose. Understanding of radiation resulted toxicities and careful choice of beam arrangement are critical in minimizing toxicity of skin and other organs.
SU‐F‐T‐137: Out‐Of‐Beam Dose for a Compact Double‐Scattering Proton Beam Therapy System
Authors: Islam M , Ahmad S , Jin H
Published: July 2016

Purpose:

The out‐of‐beam dose is important for understanding the peripheral dose in radiation therapy. In proton radiotherapy, the study of out‐of‐beam dose is scarce and the treatment planning system (TPS) based on pencil beam algorithm cannot accurately predict the out‐of‐beam dose. This study investigates the out‐of‐beam dose for the single‐room Mevion S250 double scattering proton therapy system using experimentally measured and treatment planning software generated data. The results are compared with those reported for conventional photon beam therapy. However, this study does not incorporate the neutron contribution in the scattered dose.

Methods:

A total of seven proton treatment plans were generated using Varian Eclipse TPS for three different sites (brain, lung, and pelvis) in an anthropomorphic phantom. Three field sizes of 5×5, 10×10, and 20×20 cm2 (lung only) with typical clinical range (13.3–22.8 g/cm2) and modulation widths (5.3–14.0 g/cm2) were used. A single beam was employed in each treatment plan to deliver a dose of 181.8 cGy (200.0 cGy (RBE)) to the selected target. The out‐of‐beam dose was measured at 2.0, 5.0, 10.0, and 15.0 cm from the beam edge in the phantom using a thimble chamber (PTW TN31010).

Results:

The out‐of‐beam dose generally increased with field size, range, and volume irradiated. For all the plans, the scattered dose sharply fell off with distance. At 2.0 cm, the out‐of‐beam dose ranged from 0.35% to 2.16% of the delivered dose; however, the dose was clinically negligible (<0.3%) at a distance of 5.0 cm and greater. In photon therapy, the slightly greater out‐of‐beam dose was reported (TG36; 4%, 2%, and 1% for 2.0, 5.0, and 10.0 cm, respectively, using 6 MV beam).

Conclusion:

The measured out‐of‐beam dose in proton therapy excluding neutron contribution was observed higher than the TPS calculated dose and comparable to that of photon beam therapy.