bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐T‐06: Development of a Formalism for Practical Dose Measurements in Brachytherapy in the German Standard DIN 6803
Authors: Hensley F , Chofor N , Schoenfeld A , Harder D
Published: July 2016

Purpose:

In the steep dose gradients in the vicinity of a radiation source and due to the properties of the changing photon spectra, dose measurements in Brachytherapy usually have large uncertainties. Working group DIN 6803‐3 is presently discussing recommendations for practical brachytherapy dosimetry incorporating recent theoretical developments in the description of brachytherapy radiation fields as well as new detectors and phantom materials. The goal is to prepare methods and instruments to verify dose calculation algorithms and for clinical dose verification with reduced uncertainties.

Methods:

After analysis of the distance dependent spectral changes of the radiation field surrounding brachytherapy sources, the energy dependent response of typical brachytherapy detectors was examined with Monte Carlo simulations. A dosimetric formalism was developed allowing the correction of their energy dependence as function of source distance for a Co‐60 calibrated detector. Water equivalent phantom materials were examined with Monte Carlo calculations for their influence on brachytherapy photon spectra and for their water equivalence in terms of generating equivalent distributions of photon spectra and absorbed dose to water.

Results:

The energy dependence of a detector in the vicinity of a brachytherapy source can be described by defining an energy correction factor kQ for brachytherapy in the same manner as in existing dosimetry protocols which incorporates volume averaging and radiation field distortion by the detector. Solid phantom materials were identified which allow precise positioning of a detector together with small correctable deviations from absorbed dose to water. Recommendations for the selection of detectors and phantom materials are being developed for different measurements in brachytherapy.

Conclusion:

The introduction of kQ for brachytherapy sources may allow more systematic and comparable dose measurements. In principle, the corrections can be verified or even determined by measurement in a water phantom and comparison with dose distributions calculated using the TG43 dosimetry formalism.

Project is supported by DIN Deutsches Institut fuer Normung
SU‐F‐T‐09: In Phantom Full‐Implant Validation of Plastic Scintillation Detectors for in Vivo Dosimetry During Low Dose Rate Brachytherapy
Authors: Therriault‐Proulx F , Beaulieu L , Bruno T , Beddar S
Published: July 2016

Purpose:

To validate in a water phantom the use of plastic scintillation detectors to measure dose to the urethra and the rectal wall during a clinically realistic low dose rate (LDR) brachytherapy implant.

Methods:

A template was designed to replicate a clinically realistic LDR brachytherapy prostate implant inside a water phantom. Twenty‐two catheters were inserted, including one mimicking the urethra and another the rectal wall. The needles inserted in the remaining 20 catheters were composed of thin‐walled nylon tubes in which I‐125 radioactive seeds (Air Kerma Strengths of (0.328±0.020)U) were abutted together with plastic spacers to replicate a typical loading. A plastic scintillation detector (PSD) with a 5‐mm long × 1‐mm diameter sensitive element was first placed inside the urethra and 1‐second measurements were performed for 60s after each needle implant. Measurements were also performed at multiple positions along the urethra once all the needles were inserted. The procedure was then repeated with the PSD placed at the rectal wall.

Results:

Individual dose‐rates ranging from 0.07µGy/s to 1.5µGy/s were measured after each needle implant. The average absolute relative differences were (6.2±3.6)% and (6.9±6.5)% to the values calculated with the TG‐43 formalism, for the urethra and rectal wall respectively. These results are within expectations from the error uncertainty budget once accounting for uncertainties in seeds’ strength and positioning. Interestingly, the PSD allowed for unplanned error detection as the study was performed. Finally, the measured dose after the full implant at different positions along the mimicked organs at risk were in agreement with TG‐43 values for all of the positions tested.

Conclusion:

Plastic scintillation detectors could be used as in vivo detectors for LDR brachytherapy as they would provide accurate dose information after each needle implant as well as along the organs at risk at the end of the implant.
SU‐F‐T‐10: Validation of ELP Dosimetry Using PRESAGE Dosimeter: Feasibility Test and Practical Considerations
Authors: Lambson K , Lafata K , Schaal J , Miles D , Yoon S , Liu W , Oldham M , Cai J
Published: July 2016

Purpose:

To validate the use of a PRESAGE dosimeter as a method to quantitatively measure dose distributions of injectable brachytherapy based on elastin‐like polypeptide (ELP) nanoparticles. PRESAGE is a solid, transparent polyurethane‐based dosimeter whose dose is proportional to a change in optical density, making it useful for visualizing the dose from a radionuclide‐tagged‐ELP injection.

Methods:

A PRESAGE dosimeter was designed to simulate an ELP injection. To calibrate, cuvette samples from the batch of PRESAGE were exposed to varying levels of radiation from 0–35.9Gy applied via a linear accelerator, then placed into a spectrophotometer to obtain the optical density change as a function of dose. A pre‐optical‐CT scan was acquired of the phantom to obtain a baseline tomographic optical density. A 1cc saline solution of I‐125 tagged‐ELP with and activity concentration of 1mCi/cc was injected into the phantom and left for five days. After five days, the ELP was removed and the cavity cleaned of all remaining radioactive material. Post tomographic optical images were acquired to obtain a differential optical density dataset.

Results:

Initial results after the 5‐day exposure revealed an opaque white film that resembled the volume of the ELP solution injected into the phantom. We think this is possibly due to the saline solution diffusing into the PRESAGE and causing a change in the index of refraction at this shallow depth. Therefore, initially the optical scanner yielded inconclusive results. After several more days, the saline seemed to have evaporated out of the injection site and the ELP dose distribution was visible via color change in the dosimeter.

Conclusion:

We have created the first experimental design to measure the dose distribution of I‐125‐tagged‐ELP. The PRESAGE formulation proves to be a feasible option for such measurements. Future experimental measurements need to be obtained to further characterize ELP dosimetry.
SU‐F‐T‐11: Scintillator Based Quality Assurance Device for HDR Brachytherapy
Authors: Jozsef G
Published: July 2016

Purpose:

To build a test device for HDR afterloaders capable of checking source positions, times at positions and estimate the activity of the source.

Methods:

A catheter is taped on a plastic scintillation sheet. When a source travels through the catheter, the scintillator sheet lights up around the source. The sheet is monitored with a video camera, and records the movement of the light spot. The center of the spot on each image on the video provides the source location, and the time stamps of the images can provide the dwell time the source spend in each location. Finally, the brightness of the light spot is related to the activity of the source. A code was developed for noise removal, calibrate the scale of the image to centimeters, eliminate the distortion caused by the oblique view angle, identifying the boundaries of the light spot, transforming the image into binary and detect and calculate the source motion, positions and times. The images are much less noisy if the camera is shielded. That requires that the light spot is monitored in a mirror, rather than directly. The whole assembly is covered from external light and has a size of approximately 17×35×25cm (H×L×W)

Results:

A cheap camera in BW mode proved to be sufficient with a plastic scintillator sheet. The best images were resulted by a 3mm thick sheet with ZnS:Ag surface coating. The shielding of the camera decreased the noise, but could not eliminate it. A test run even in noisy condition resulted in approximately 1 mm and 1 sec difference from the planned positions and dwell times. Activity tests are in progress.

Conclusion:

The proposed method is feasible. It might simplify the monthly QA process of HDR Brachytherapy units.
SU‐F‐T‐13: Transit Dose Comparisons for Co‐60 and Ir‐192 HDR Sources
Authors: Gimenez‐Alventosa V , Vijande J , Ballester F , Perez‐Calatayud J
Published: July 2016

Purpose:

The purpose of this study is to compare the transit dose due to the movement of high dose rate (HDR) Ir‐192 and Co‐60 sources along the transfer tube. This is performed by evaluating air‐kerma differences in the vicinity of the transfer tube when both sources are moved with the same velocity from a HDR brachytherapy afterloader into a patient.

Methods:

Monte Carlo simulations have been performed using PENELOPE2014. mHDR‐v2 and Flexisource sources have been considered. Collisional kerma has been scored. The sources were simulated within a plastic catheter located in an infinite air phantom. The movement of the seed was included by displacing their positions along the connecting catheter from z=−75 cm to z=+75 cm and combining them. Backscatter from the afterloader and the patient was not considered. Since modern afterloaders like Flexitron (Elekta) or Saginova (Bebig) are able to use equally Ir‐192 and Co‐60 sources it was assumed that both sources are displaced with equal speed. Typical content activity values were provided by the manufacturer (460 GBq for Ir‐192 and 75 GBq for Co‐60).

Results:

2D distributions were obtained with type‐A uncertainties (k=2) less than 0.01%. From those, the air kerma ratio Co‐60/Ir‐192 was evaluated weighted by their corresponding activities. It was found that it varies slowly with distance (less than 10% variation) but strongly in time due to the shorter half‐life of the Ir‐192 (73.83 days). The maximum ratio is located close to the catheter with a value of 0.57 when both sources are installed by the manufacturer, while increasing up to 1.25 at the end of the recommended working life (90 days) of the Ir‐192 source.

Conclusion:

Air‐kerma ratios are almost constant (0.51–0.57) in the vicinity of the source. Nevertheless, air‐kerma ratios increase rapidly whenever the Ir‐192 is approaching the end of its life.
SU‐F‐T‐14: Dosimetric Impacts of Various Uncertainties in Cervical Cancer HDR Brachytherapy: Are Conventional Point Doses Good Surrogates for 3D Dosimetry?
Authors: Liang X , Zheng D , Zhang X , Narayanasamy G , Morrill S , Penagaricano J , Paudel N , Li Z
Published: July 2016

Purpose:

In the context of evaluating dosimetric impacts of a variety of uncertainties involved in HDR Tandem‐and‐Ovoid treatment, to study the correlations between conventional point doses and 3D volumetric doses.

Methods:

For 5 cervical cancer patients treated with HDR T&O, 150 plans were retrospectively created to study dosimetric impacts of the following uncertainties: (1) inter‐fractional applicator displacement between two treatment fractions within a single insertion by applying Fraction#1 plan to Fraction#2 CT; (2) positional dwell error simulated from −5mm to 5mm in 1mm steps; (3) simulated temporal dwell error of 0.05s, 0.1s, 0.5s, and 1s. The original plans were based on point dose prescription, from which the volume covered by the prescription dose was generated as the pseudo target volume to study the 3D target dose effect. OARs were contoured. The point and volumetric dose errors were calculated by taking the differences between original and simulated plans. The correlations between the point and volumetric dose errors were analyzed.

Results:

For the most clinically relevant positional dwell uncertainty of 1mm, temporal uncertainty of 0.05s, and inter‐fractional applicator displacement within the same insertion, the mean target D90 and V100 deviation were within 1%. Among these uncertainties, the applicator displacement showed the largest potential target coverage impact (2.6% on D90) as well as the OAR dose impact (2.5% and 3.4% on bladder D2cc and rectum D2cc). The Spearman correlation analysis shows a correlation coefficient of 0.43 with a p‐value of 0.11 between target D90 coverage and H point dose.

Conclusion:

With the most clinically relevant positional and temporal dwell uncertainties and patient interfractional applicator displacement within the same insertion, the dose error is within clinical acceptable range. The lack of correlation between H point and 3D volumetric dose errors is a motivator for the use of 3D treatment planning in cervical HDR brachytherapy.
SU‐F‐T‐15: Evaluation of 192Ir, 60Co and 169Yb Sources for High Dose Rate Prostate Brachytherapy Inverse Planning Using An Interior Point Constraint Generation Algorithm
Authors: Mok Tsze Chung E , Safigholi H , Nicolae A , Davidson M , Ravi A , Aleman D , Song W
Published: July 2016

Purpose:

The effectiveness of using a combination of three sources, 60Co, 192Ir and 169Yb, is analyzed. Different combinations are compared against a single 192Ir source on prostate cancer cases. A novel inverse planning interior point algorithm is developed in‐house to generate the treatment plans.

Methods:

Thirteen prostate cancer patients are separated into two groups: Group A includes eight patients with the prostate as target volume, while group B consists of four patients with a boost nodule inside the prostate that is assigned 150% of the prescription dose. The mean target volume is 35.7±9.3cc and 30.6±8.5cc for groups A and B, respectively. All patients are treated with each source individually, then with paired sources, and finally with all three sources. To compare the results, boost volume V150 and D90, urethra Dmax and D10, and rectum Dmax and V80 are evaluated. For fair comparison, all plans are normalized to a uniform V100=100.

Results:

Overall, double‐ and triple‐source plans were better than single‐source plans. The triple‐source plans resulted in an average decrease of 21.7% and 1.5% in urethra Dmax and D10, respectively, and 8.0% and 0.8% in rectum Dmax and V80, respectively, for group A. For group B, boost volume V150 and D90 increased by 4.7% and 3.0%, respectively, while keeping similar dose delivered to the urethra and rectum. 60Co and 192Ir produced better plans than their counterparts in the double‐source category, whereas 60Co produced more favorable results than the remaining individual sources.

Conclusion:

This study demonstrates the potential advantage of using a combination of two or three sources, reflected in dose reduction to organs‐at‐risk and more conformal dose to the target. three sources, reflected in dose reduction to organs‐at‐risk and more conformal dose to the target. Our results show that 60Co, 192Ir and 169Yb produce the best plans when used simultaneously and can thus be an alternative to 192Ir‐only in high‐dose‐rate prostate brachytherapy.
SU‐F‐T‐16: Experimental Determination of Ionization Chamber Correction Factors for In‐Phantom Measurements of Reference Air Kerma Rate and Absorbed Water Dose Rate of Brachytherapy 192Ir Source
Authors: Chan M , Lee V , Wong M , Leung R , Law G , Lee K , Cheung S , Tung S
Published: July 2016

Purpose:

Following the method of in‐phantom measurements of reference air kerma rate (Ka) at 100cm and absorbed water dose rate (Dw1) at 1cm of high‐dose‐rate 192Ir brachytherapy source using 60Co absorbed‐dose‐to‐water calibrated (ND,w,60Co) ionization chamber (IC), we experimentally determined the in‐phantom correction factors (kglob) of the PTW30013 (PTW, Freiburg, Germany) IC by comparing the Monte Carlo (MC)‐calculated kglob of the other PTW30016 IC.

Methods:

The Dw1 formalism of in‐phantom measurement is: M*ND,w,60Co*(kglob)Dw1, where M is the collected charges, and (kglob)Dw1 the in‐phantom Dw1 correction factor. Similarly, Ka is determined by M*ND,w,60Co*(kglob)ka, where (kglob)ka the in‐phantom Ka correction factor. Two thimble ICs PTW30013 and another PTW30016 having a ND,w,60Co from the German primary standard laboratory (PTB) were simultaneously exposed to the microselectron 192Ir v2 source at 8cm in a PMMA phantom. A reference well chamber (PTW33004) with a PTB transfer Ka calibration Nka was used for comparing the in‐phantom measurements to derive the experimental (kglob)ka factors. We determined the experimental (kglob)Dw1 of the PTW30013 by comparing the PTW30016 measurements with MC‐calculated (kglob)Dw1.

Results:

Ka results of the PTW30016 based on ND,w,60Co and MC‐calculated (kglob)ka differ from the well chamber results based on Nka by 1.6% and from the manufacturer by 1.0%. Experimental (kglob)ka factors for the PTW30016 and two other PTW30013 are 0.00683, 0.00681 and 0.00679, and vary <0.5% with 1mm source positioning uncertainty. Experimental (kglob)Dw1 of the PTW30013 ICs are 75.3 and 75.6, and differ by 1.6% from the conversion by dose rate constant from the AAPM report 229.

Conclusion:

The 1.7% difference between MC and experimental (kglob)ka for the PTW30016 IC is within the PTB 2.5% expanded uncertainty in Ka calibration standard. Using a single IC with ND,w,60Co to calibrate the brachytherapy source and dose output in external radiotherapy is feasible. MC validation of the PTW30013(kglob)Dw1 is warranted.
SU‐F‐T‐18: The Importance of Immobilization Devices in Brachytherapy Treatments of Vaginal Cuff
Authors: Shojaei M , Dumitru N , Pella S
Published: July 2016

Purpose:

High dose rate brachytherapy is a highly localized radiation therapy that has a very high dose gradient. Thus one of the most important parts of the treatment is the immobilization. The smallest movement of the patient or applicator can result in dose variation to the surrounding tissues as well as to the tumor to be treated. We will revise the ML Cylinder treatments and their localization challenges.

Methods:

A retrospective study of 25 patients with 5 treatments each looking into the applicator's placement in regard to the organs at risk. Motion possibilities for each applicator intra and inter fractionation with their dosimetric implications were covered and measured in regard with their dose variance. The localization immobilization devices used were assessed for the capability to prevent motion before and during the treatment delivery.

Results:

We focused on the 100% isodose on central axis and a 15 degree displacement due to possible rotation analyzing the dose variations to the bladder and rectum walls. The average dose variation for bladder was 15% of the accepted tolerance, with a minimum variance of 11.1% and a maximum one of 23.14% on the central axis. For the off axis measurements we found an average variation of 16.84% of the accepted tolerance, with a minimum variance of 11.47% and a maximum one of 27.69%. For the rectum we focused on the rectum wall closest to the 120% isodose line. The average dose variation was 19.4%, minimum 11.3% and a maximum of 34.02% from the accepted tolerance values

Conclusion:

Improved immobilization devices are recommended. For inter‐fractionation, localization devices are recommended in place with consistent planning in regards with the initial fraction. Many of the present immobilization devices produced for external radiotherapy can be used to improve the localization of HDR applicators during transportation of the patient and during treatment
SU‐F‐T‐20: Novel Catheter Lumen Recognition Algorithm for Rapid Digitization
Authors: Dise J , McDonald D , Ashenafi M , Peng J , Mart C , Koch N , Vanek K
Published: July 2016

Purpose:

Manual catheter recognition remains a time‐consuming aspect of high‐dose‐rate brachytherapy (HDR) treatment planning. In this work, a novel catheter lumen recognition algorithm was created for accurate and rapid digitization.

Methods:

MatLab v8.5 was used to create the catheter recognition algorithm. Initially, the algorithm searches the patient CT dataset using an intensity based k‐means filter designed to locate catheters. Once the catheters have been located, seed points are manually selected to initialize digitization of each catheter. From each seed point, the algorithm searches locally in order to automatically digitize the remaining catheter. This digitization is accomplished by finding pixels with similar image curvature and divergence parameters compared to the seed pixel. Newly digitized pixels are treated as new seed positions, and hessian image analysis is used to direct the algorithm toward neighboring catheter pixels, and to make the algorithm insensitive to adjacent catheters that are unresolvable on CT, air pockets, and high Z artifacts. The algorithm was tested using 11 HDR treatment plans, including the Syed template, tandem and ovoid applicator, and multi‐catheter lung brachytherapy. Digitization error was calculated by comparing manually determined catheter positions to those determined by the algorithm.

Results:

he digitization error was 0.23 mm ± 0.14 mm axially and 0.62 mm ± 0.13 mm longitudinally at the tip. The time of digitization, following initial seed placement was less than 1 second per catheter. The maximum total time required to digitize all tested applicators was 4 minutes (Syed template with 15 needles).

Conclusion:

This algorithm successfully digitizes HDR catheters for a variety of applicators with or without CT markers. The minimal axial error demonstrates the accuracy of the algorithm, and its insensitivity to image artifacts and challenging catheter positioning. Future work to automatically place initial seed positions would improve the algorithm speed.
SU‐F‐T‐21: A Novel Beam‐Light View, Collimating Applicator for HDR Ocular Conjunctiva Brachytherapy‐Treatments
Authors: Koren S , Kindler J , Tafo A Guemnie , Cohen G , Reich E
Published: July 2016

Purpose:

We propose the use of a HDR X‐ray source collimator to apply a conformal, relatively small, radiation suitable for a single fraction with short delivery time. In addition, this technique can be applied using a radioactive source.

Methods:

We have built a stainless steel 1.5 mm thick applicator, to accommodate the needle applicator of the Intra‐Beam X‐ray source. Additional cavity is created in the applicator to allow the hosting/nesting/positioning of a LED diode. This LED is allowing a pre‐irradiation beam marking on the tissue. The visible light emitted from the opening of the collimated applicator will delineate/verify the aperture of the kV beam to be applied, as well as serve as distance indicator and will assist in the determination of dose to be delivered. For the evaluation of the collimated spatial dose distribution we have performed water tank measurements using (IBA Dosimetry) with a 0.4 cc ion chamber (IBA Dosimetry). We have scanned a two dimensional array with 1mm pitch in depth and 0.3 mm step size laterally. Additional verifications were conducted using Gaf‐Chromic film for PDD measurements and Optical Stimulated Luminescence Dosimetry (OSLD, Landauer inc.) for absolute dosimetry.

Results:

The collimated applicator enables a conformal irradiated cross‐section of about 3 mm square at the applicator surface was used in this study. A 180 seconds of 50 kVp delivery yielded 29 Gy, 20.6 Gy and 14.5 Gy at 5, 10 and 15 mm depths respectively. These results are in good agreement with the needle applicator depth dose curve published data.

Conclusion:

We have demonstrated the feasibility of focal HDR brachytherapy for conjunctival and ocular tumors, using the Intra‐Beam needle applicator with in‐house developed collimator. The delivery time was found to be several minutes‐ suitable for an intra‐operative procedure and will allow dose fractionation deliveries.
SU‐F‐T‐23: Correspondence Factor Correction Coefficient for Commissioning of Leipzig and Valencia Applicators with the Standard Imaging IVB 1000
Authors: Donaghue J , Gajdos S
Published: July 2016

Purpose:

To determine the correction factor of the correspondence factor for the Standard Imaging IVB 1000 well chamber for commissioning of Elekta's Leipzig and Valencia skin applicators.

Methods:

The Leipzig and Valencia applicators are designed to treat small skin lesions by collimating irradiation to the treatment area. Published output factors are used to calculate dose rates for clinical treatments. To validate onsite applicators, a correspondence factor (CFrev) is measured and compared to published values. The published CFrev is based on well chamber model SI HDR 1000 Plus. The CFrev is determined by correlating raw values of the source calibration setup (Rcal,raw) and values taken when each applicator is mounted on the same well chamber with an adapter (Rapp,raw). The CFrev is calculated by using the equation CFrev =Rapp,raw/Rcal,raw. The CFrev was measured for each applicator in both the SI HDR 1000 Plus and the SI IVB 1000. A correction factor, CFIVB for the SI IVB 1000 was determined by finding the ratio of CFrev (SI IVB 1000) and CFrev (SI HDR 1000 Plus).

Results:

The average correction factors at dwell position 1121 were found to be 1.073, 1.039, 1.209, 1.091, and 1.058 for the Valencia V2, Valencia V3, Leipzig H1, Leipzig H2, and Leipzig H3 respectively. There were no significant variations in the correction factor for dwell positions 1119 through 1121.

Conclusion:

By using the appropriate correction factor, the correspondence factors for the Leipzig and Valencia surface applicators can be validated with the Standard Imaging IVB 1000. This allows users to correlate their measurements with the Standard Imaging IVB 1000 to the published data. The correction factor is included in the equation for the CFrev as follows: CFrev= Rapp,raw/(CFIVB*Rcal,raw). Each individual applicator has its own correction factor, so care must be taken that the appropriate factor is used.
SU‐F‐T‐25: Design and Implementation of a Multi‐Purpose Applicator for Pelvic Brachytherapy Applications
Authors: Bogue J , Parsai E
Published: July 2016

Purpose:

The current generation of inflatable multichannel brachytherapy applicators, such as the Varian Capri, have limited implementation to only vaginal and rectal cancers. While there are similar designs utilizing rigid, non‐inflatable applicators, these alternatives could cause increased dose to surrounding tissue due to air gaps. Modification of the Capri could allow for easier treatment planning by reducing the number of channels and increased versatility by modifying the applicator to include an attachable single tandem for cervical or multiple tandems for endometrial applications.

Methods:

A Varian Capri applicator was simulated in water to replicate a patient. Multiple plans were optimized to deliver a prescribed dose of 100 cGy at 5mm away from the exterior of the applicator using six to thirteen existing channels. The current model was expanded upon to include a detachable tandem or multiple tandoms to increase its functionality to both cervical and endometrial cancers. Models were constructed in both threedimensional rendering software and Monte Carlo to allow prototyping and simulations.

Results:

Treatment plans utilizing six to thirteen channels produced limited dosimetric differences between channel arrangements, with a seven channel plan very closely approximating the thirteen channels. It was concluded that only seven channels would be necessary in future simulations to give an accurate representation of the applicator. Tandem attachments were prototyped for the applicator to demonstrate the ease of which they could be included. Future simulation in treatment planning software and Monte Carlo results will be presented to further define the ideal applicator geometry

Conclusion:

The current Capri applicator design could be easily modified to increase applicability to include cervical and endometrial treatments in addition to vaginal and rectal cancers. This new design helps in a more versatile single use applicator that can easily be inserted and to further reduce dose to critical structures during brachytherapy treatments.
SU‐F‐T‐27: A Comparative Case Study Among Four Modalities for the Superficial Treatment of Squamous Cell Carcinoma
Authors: Ashenafi M , Koch N , Peng J , Terwillinger L , Wilder J , McDonald D , Mart C , Jenrette J , Vanek K
Published: July 2016

Purpose:

We performed a comparative planning study among High Dose Rate (HDR) brachytherapy, superficial electrons, Volume Modulated Arc Therapy (VMAT), and Helical IMRT (Tomotherapy) for squamous cell carcinoma of the abdominal wall with consideration for the underlining bowel.

Methods:

A 69‐year old female presented with squamous cell carcinoma protruding 8mm beyond the anterior skin surface of the midabdomen was considered for treatment. The patient had a ventral hernia which resulted in the reduction of the abdominal wall thickness and the adjacent small bowel being the dose limiting structure. Four plans were generated using different treatment modalities: a) an enface electron field (eMC, Eclipse v. 11), b) Tomotherapy (HI‐Art II v.5.0.5), c) VMAT (Acuros, Eclipse v. 11), and d) HDR using a Freiburg applicator (Oncentra v. 4.3). The following plan objectives were used for all four plans: for the CTV target, V90% ≥90% (61.8Gy2/2).For the small bowel, D0.1cc < 56.2 Gy2/2 was a hard constraint and expressed as a percentage of the prescription for comparison to demonstrate the dose fall‐off achieved among the modalities.For HDR, V200% <0.1cc was an additional constraint. Multiple dosimetric parameters, including those listed above, were compared among the four modalities.

Results:

The HDR plan showed comparable target coverage compared to the Tomotherapy plan and better coverage compared to the electron plan. Small bowel doses (D0.1cc) were lower in HDR plan compared to Tomotherapy, electron, & VMAT plans (88.8%, 89.6%, 90.9%, & 96.6%). Integral dose to the whole body (V5%) was much higher for HDR, VMAT, and Tomotherapy when compared to electron plan by factors of seven, eight, and ten, respectively. After reviewing all treatment modalities, the physician selected HDR owing to better control of the small bowel dose while maintaining adequate target coverage.

Conclusion:

This case study demonstrated HDR can successfully treat superficial lesions with superior sparing of underlying structures.
SU‐F‐T‐28: Evaluation of BEBIG HDR Co‐60 After‐Loading System for Skin Cancer Treatment Using Conical Surface Applicator
Authors: Safigholi H , Meigooni A S , Han D , Soliman A , Song W Y
Published: July 2016

Purpose:

To evaluate the possibility of utilizing the BEBIG HDR 60Co remote after‐loading system for malignant skin surface treatment using Monte Carlo (MC) simulation technique.

Methods:

First TG‐43 parameters of BEBIG‐Co‐60 and Nucletron Ir‐192‐mHDR‐V2 brachytherapy sources were simulated using MCNP6 code to benchmark the sources against the literature. Second a conical tungsten‐alloy with 3‐cm diameter of Planning‐Target‐Volume (PTV) at surface for use with a single stepping HDR source is designed. The HDR source is modeled parallel to treatment plane at the center of the conical applicator with a source surface distance (SSD) of 1.5‐cm and a removable plastic end‐cap with a 1‐mm thickness. Third, MC calculated dose distributions from HDR Co‐60 for conical surface applicator were compared with the simulated data using HDR Ir‐192 source. The initial calculations were made with the same conical surface applicator (standard‐applicator) dimensions as the ones used with the Ir‐192 system. Fourth, the applicator wall‐thickness for the Co‐60 system was increased (doubled) to diminish leakage dose to levels received when using the Ir‐192 system. With this geometry, percentage depth dose (PDD), and relative 2D‐dose profiles in transverse/coronal planes were normalized at 3‐mm prescription‐depth evaluated along the central axis.

Results:

PDD for Ir‐192 and Co‐60 were similar with standard and thick‐walled applicator. 2D‐relative dose distribution of Co‐60, inside the standard‐conical‐applicator, generated higher penumbra (7.6%). For thick‐walled applicator, it created smaller penumbra (<4%) compared to Ir‐192 source in the standard‐conicalapplicator. Dose leakage outside of thick‐walled applicator with Co‐60 source was approximately equal (≤3%) with standard applicator using Ir‐192 source.

Conclusion:

Skin cancer treatment with equal quality can be performed with Co‐60 source and thick‐walled conical applicators instead of Ir‐192 with standard applicators. These conical surface applicator must be used with a protective plastic end‐cap to eliminate electron contamination and over‐dosage of the skin.
SU‐F‐T‐30: Comprehensive Dosimetric Characterization of the Novel Direction Modulation Brachytherapy (DMBT) Tandem Applicator Using Monte Carlo Simulations
Authors: Safigholi H , Han D , Mashouf S , Soliman Abraam , Owrangi A , Song W Y
Published: July 2016

Purpose:

To characterize the dosimetric properties/distributions of the novel proposed direction modulated brachytherapy (DMBT) tandem applicator in combination with 192Ir HDR source, and compare against conventional tandem design, using Monte Carlo simulations.

Methods:

The proposed DMBT tandem applicator is designed for image‐guided adaptive brachytherapy, especially MRI, of cervical cancer. It has 6 peripheral holes of 1.3‐mm width, grooved along a 5.4‐mm diameter nonmagnetic tungsten alloy rod of density 18.0 g/cc, capable of generating directional dose profiles – leading to enhanced dose sculpting capacity through inverse planning. In‐water dosimetric parameters for the DMBT and conventional tandems have been calculated for various radial distances away and around the tandems. For the DMBT tandem, the cumulative dose from the 192Ir source occupying 1) one and 2) all six holes in equal dwell times was calculated and normalized to match the dose rate of the open source (in conventional tandem) at 1 cm from the center. This is done to compare and contrast the characteristic dose distributions to that of the isotropic TG43‐based 192Ir source.

Results:

All dose rates were normalized at 1‐cm radius from the center of the applicators, containing source(s). The normalized dose rates at 0.5, 3.0, and 5.0‐cm radiuses were then 388, 11.3, and 4.1% for conventional tandem, 657, 8.1, and 2.7% for DMBT tandem with the source in one hole at front entrance, and 436, 10.9, and 3.8% for DMBT tandem with the source in all six holes. For the DMBT tandem case with the source in one hole, the backside transmissions were 47, 2.4, and 0.9%, respectively.

Conclusion:

The DMBT tandem is able to generate closely similar dosimetric characteristics as that of the single‐channel conventional tandem if needed (with the source occupying all six holes), at the same time, generate directional radiation profile(s) for favorably enabling 3D dose sculpting capability.
SU‐F‐T‐33: Air‐Kerma Strength and Dose Rate Constant by the Full Monte Carlo Simulations
Authors: Tsuji S , Oita M , Narihiro N
Published: July 2016

Purpose:

In general, the air‐kerma strength (Sk) has been determined by the energy weighting the photon energy fluence and the corresponding mass‐energy absorption coefficient or mass‐energy transfer coefficient. Kerma is an acronym for kinetic energy released per unit mass, defined as the sum of the initial kinetic energies of all the charged particles. Monte Carlo (MC) simulations can investigate the kinetic energy of the charged particles after photo interactions and sum the energy. The Sk of 192Ir source is obtained in the full MC simulation and finally the dose rate constant Λ is determine.

Methods:

MC simulations were performed using EGS5 with the microSelectron HDR v2 type of 192Ir source. The air‐kerma rate obtained to sum the electron kinetic energy after photoelectric absorption or Compton scattering for transverse‐axis distance from 1 to 120 cm with a 10 m diameter air phantom. Absorbed dose in water is simulated with a 30 cm diameter water phantom. The transport cut‐off energy is 10 keV and primary photons from the source need two hundred and forty billion in the air‐kerma rate and thirty billion in absorbed dose in water.

Results:

Sk is multiplied by the square of the distance in air‐kerma rate and determined by fitting a linear function. The result of Sk is (2.7039±0.0085)*10‐−11 µGy m2 Bq−1 s−1. Absorbed dose rate in water at 1 cm transverse‐axis distance D(r0, θ0) is (3.0114±0.0015)*10−11 cGy Bq−1 s−1.

Conclusion:

From the results, dose rate constant Λ of the microSelectron HDR v2 type of 192Ir source is (1.1137±0.0035) cGy h−1 U−1 by the full MC simulations. The consensus value conΛ is (1.109±0.012) cGy h−1 U−1. The result value is consistent with the consensus data conΛ.
SU‐F‐T‐35: Optimization of Bladder and Rectal Doses Using a Multi‐Lumen Intracavitary Applicator for Gynecological Brachytherapy
Authors: Laoui S , Dietrich S , Sehgal V , Al‐Ghazi M
Published: July 2016

Purpose:

Radiation dose delivery for endometrial cancer using HDR techniques is limited by dose to bladder and rectum. A dosimetric study was performed using Varian Capri vaginal brachytherapy applicator to determine the optimal channel configuration which minimizes dose to bladder and rectum, while providing good target coverage.

Methods:

A total of 17 patients, 63 plans clinically delivered, and 252 simulated plans using Varian BrachyVision planning system were generated to investigate optimal channel configuration which results in minimum dose to bladder and rectum while providing adequate target coverage. The Capri applicator consists of 13 lumens arranged in two concentric rings, one central lumen and six lumens per ring. Manual dose shaping is invariably required to lower the dose to critical organs. Three‐dimensional plans were simulated for 4 channel arrangements, all 13 channels, channel 12 o'clock (close to bladder) and 6 o'clock (close to rectum) deactivated, central channel deactivated, and central channel in addition to 12 o'clock and 6 o'clock deactivated. A relationship between V100, the volume that receives the prescribed dose, and the amount of curie‐seconds required to deliver it, was established.

Results:

Using all 13 channels results in maximum dose to bladder and rectum. Deactivating central channel in addition to 12 o'clock and 6 o'clock resulted in minimizing bladder and rectum doses but compromised target coverage. The relationship between V100, the volume that receives the prescribed dose, and the curie seconds was found to be linear.

Conclusion:

Deactivating channels 12 o'clock and 6 o'clock was shown to be the optimal configuration leading to minimum dose to bladder and rectum without compromising target coverage. The linear relationship between V100 and the curie‐ seconds can be used as a verification parameter.
SU‐F‐T‐37: Dosimetric Evaluation of Planned Versus Decay Corrected Treatment Plans for the Treatment of Tandem‐Based Cervical HDR Brachytherapy
Authors: Goyal M , Manjhi J , Kehwar T , Rai D , Barker J , Heintz B , Shide K
Published: July 2016

Purpose:

This study evaluated dosimetric parameters for actual treatment plans versus decay corrected treatment plans for cervical HDR brachytherapy.

Methods:

125 plans of 25 patients, who received 5 fractions of HDR brachytherapy, were evaluated in this study. Dose was prescribed to point A (ICRU‐38) and High risk clinical tumor volume (HR‐CTV) and organs at risk (OAR) were, retrospectively, delineated on original CT images by treating physician. First HDR plan was considered as reference plan and decay correction was applied to calculate treatment time for subsequent fractions, and was applied, retrospectively, to determine point A, HR‐CTV D90, and rectum and bladder doses.

Results:

The differences between mean point A reference doses and the point A doses of the plans computed using decay times were found to be 1.05%±0.74% (−2.26% to 3.26%) for second fraction; −0.25%±0.84% (−3.03% to 3.29%) for third fraction; 0.04%±0.70% (−2.68% to 2.56%) for fourth fraction and 0.30%±0.81% (−3.93% to 2.67%) for fifth fraction. Overall mean point A dose difference, for all fractions, was 0.29%±0.38% (within ± 5%). Mean rectum and bladder dose differences were calculated to be −3.46%±0.12% and −2.47%±0.09%, for points, respectively, and −1.72%±0.09% and −0.96%±0.06%, for D2cc, respectively. HR‐CTV D90 mean dose difference was found to be −1.67% ± 0.11%. There was no statistically significant difference between the reference planned point A doses and that calculated using decay time to the subsequent fractions (p<0.05).

Conclusion:

This study reveals that a decay corrected treatment will provide comparable dosimetric results and can be utilized for subsequent fractions of cervical HDR brachytherapy instead of actual treatment planning. This approach will increase efficiency, decrease workload, reduce patient observation time between applicator insertion and treatment delivery. This would be particularly useful for institutions with limited resources or large patient populations with limited access to care.
SU‐F‐T‐43: Prediction of Dose Increments by Brain Metastases Resection Cavity Shrinkage Model with I‐125 and Cs‐131 LDR Seed Implantations
Authors: Han D , Braunstein S , Sneed P , McDermott M , Ma L
Published: July 2016

Purpose:

This work aims to determine dose variability via a brain metastases resection cavity shrinkage model (RC‐SM) with I‐125 or Cs‐131 LDR seed implantations.

Methods:

The RC‐SM was developed to represent sequential volume changes of 95 consecutive brain metastases patients. All patients underwent serial surveillance MR and change in cavity volume was recorded for each patient. For the initial resection cavity, a prolate‐ellipsoid cavity model was suggested and applied volume shrinkage rates to correspond to 1.7, 3.6, 5.9, 11.7, and 20.5 months after craniotomy. Extra‐ring structure (6mm) was added on a surface of the resection volume and the same shrinkage rates were applied. Total 31 LDR seeds were evenly distributed on the surface of the resection cavity. The Amersham 6711 I‐125 seed model (Oncura, Arlington Heights, IL) and the Model Cs‐1 Rev2 Cs‐131 seed model (IsoRay, Richland, WA) were used for TG‐43U1 dose calculation and in‐house‐programed 3D‐volumetric dose calculation system was used for resection cavity rigid model (RC‐RM) and the RC‐SM dose calculation.

Results:

The initial resection cavity volume shrunk to 25±6%, 35±6.8%, 42±7.7%, 47±9.5%, and 60±11.6%, with respect to sequential MR images post craniotomy, and the shrinkage rate (SR) was calculated as SR=56.41Xexp(−0.2024Xt)+33.99 and R‐square value was 0.98. The normal brain dose as assessed via the dose to the ring structure with the RC‐SM showed 29.34% and 27.95% higher than the RC‐RM, I‐125 and Cs‐131, respectively. The dose differences between I‐125 and Cs‐131 seeds within the same models, I‐125 cases were 9.17% and 10.35% higher than Cs‐131 cases, the RC‐RM and the RC‐SM, respectively.

Conclusion:

A realistic RC‐SM should be considered during LDR brain seed implementation and post‐implement planning to prevent potential overdose. The RC‐SM calculation shows that Cs‐131 is more advantageous in sparing normal brain as the resection cavity volume changes with the LDR seeds implementation.
SU‐F‐T‐45: Dosimetric Effects of Saline Filled Balloons During IORT Using Xoft Electronic Brachytherapy
Authors: Redler G , Templeton A , Turian J , Chu J , Bernard D , Zhen H , Liao Y
Published: July 2016

Purpose:

The portability of Xoft Axxent Electronic Brachytherapy (EBx) System has made it a viable option for intraoperative radiation therapy (IORT) treatment of early‐stage breast cancer. The low energy (50kVp) of the X‐ray source makes the shielding easy, but also means its dose distribution is sensitive to the medium's composition. Current treatment planning systems (TPS) typically assume homogenous water for brachytherapy dose calculations, including the pre‐calculated atlas plans for the Xoft IORT cases. However, Xoft recommends using saline to fill the balloon applicator. This study investigates the dosimetric difference due to the increased effective atomic number (Zeff) from water (7.42) to saline (7.56).

Methods:

The diameter of the balloon applicators ranges from 3–6cm, with 4cm being most frequently used. For the 4‐cm and 6‐cm diameter applicators, MCNP Monte Carlo program was used to calculate the dose at the surface (Ds) of the middle section of the balloon and 1 cm away (D1cm) for water‐ and saline‐filled balloons: one plan with a single dwell at the center and another with multiple dwells as in the atlas plans. The single dwell plan is a simple estimation of the dosimetry, while the atlas plan is representative of the actual dose distribution.

Results:

The single‐dwell plan showed a 5.1% and 6.1% decrease in Ds for the 4‐ and 6‐cm applicators, respectively, due to the saline. The atlas plan showed similar

Results:

4.8% and 6.4% decrease, respectively. The decrease in D1cm is 4.3%–5.2% and 3.3%–5.3s% in the single‐dwell and atlas plans, respectively, for the 4‐ and 6‐cm applicator.

Conclusion:

The dosimetric effect introduced by saline is on the order of 5%. This effect should be taken into account during both treatment planning and patient outcome studies.
SU‐F‐T‐48: Clinical Implementation of Brachytherapy Planning System for COMS Eye Plaques
Authors: Ferreira C , Islam M , Ahmad S , De La Fuente Herman T
Published: July 2016

Purpose:

To commission the Brachytherapy Planning (BP) system (Varian, Palo Alto, CA) for the Collaborative Ocular Melanoma Study (COMS) eye plaques by evaluating dose differences against original plans from Nucletron Planning System (NPS).

Methods:

NPS system is the primary planning software for COMS‐plaques at our facility; however, Brachytherapy Planning 11.0.47 (Varian Medical Systems) is used for secondary check and for seed placement configurations not originally commissioned. Dose comparisons of BP and NPS plans were performed for prescription of 8500 cGy at 5 mm depth and doses to normal structures: opposite retina, inner sclera, macula, optic disk and lens. Plans were calculated for Iodine‐125 seeds (OncoSeeds, Model 6711) using COMS‐plaques of 10, 12, 14, 16, 18 and 20 mm diameters. An in‐house program based on inverse‐square was utilized to calculate point doses for comparison as well.

Results:

The highest dose difference between BP and NPS was 3.7% for the prescription point for all plaques. Doses for BP were higher than doses reported by NPS for all points. The largest percent differences for apex, opposite retina, inner sclera, macula, optic disk, and lens were 3.2%, 0.9%, 13.5%, 20.5%, 15.7% and 2.2%, respectively. The dose calculated by the in‐house program was 1.3% higher at the prescription point, and were as high as 42.1%, for points away from the plaque (i.e. opposite retina) when compared to NPS.

Conclusion:

Doses to the tumor, lens, retina, and optic nerve are paramount for a successful treatment and vision preservation. Both systems are based on TG‐43 calculations and assume water medium tissue homogeneity (ρe=1, water medium). Variations seen may result from the different task group versions and/or mathematical algorithms of the software. BP was commissioned to serve as a backup system and it also enables dose calculation in cases where seeds don't follow conventional placement configuration.