Brachytherapy Treatment Planning Research Articles

Derivation of in vivo source tracking error thresholds for TRUS-based HDR prostate brachytherapy through simulation of source positioning errors

PurposeThe purpose of this study was to simulate treatment planning source positioning errors in transrectal ultrasound–based real-time high-dose-rate prostate brachytherapy treatments and determine appropriate in vivo source tracking error thresholds. Methods and MaterialsTreatment planning source positioning errors were simulated for 20 patient plans in the brachytherapy treatment planning system by manually adjusting the dwell position coordinates within selected catheters without plan reoptimization. The change in dose-volume histogram (DVH) indices was calculated as a function of the source positioning error. The magnitude of the change in the DVH indices was then used to derive appropriate in vivo source tracking error thresholds. ResultsSource positioning error thresholds to prevent potentially significant changes in prostate (target) DVH metrics ranged from 2 to 5 mm, dependent on the direction of the source positioning error, as well as the relative weight of the dwell position within the plan, and its position relative to the patient anatomy. Source positioning error thresholds to prevent potentially clinically significant changes in organ at risk DVH metrics were found to be complex and patient-dependent. ConclusionsIn vivo source tracking error thresholds for transrectal ultrasound–based real-time high-dose-rate prostate brachytherapy were investigated via the simulation of treatment planning source positioning errors. These error thresholds were found to be dependent not only on the direction of the error, but also on the endpoint. There is still the potential for larger changes in DVH indices to occur for catheter shifts smaller than the proposed threshold levels in this study.

Ultrasound prostate segmentation based on multidirectional deeply supervised V-Net.

Transrectal ultrasound (TRUS) is a versatile and real-time imaging modality that is commonly used in image-guided prostate cancer interventions (e.g., biopsy and brachytherapy). Accurate segmentation of the prostate is key to biopsy needle placement, brachytherapy treatment planning, and motion management. Manual segmentation during these interventions is time-consuming and subject to inter- and intraobserver variation. To address these drawbacks, we aimed to develop a deep learning-based method which integrates deep supervision into a three-dimensional (3D) patch-based V-Net for prostate segmentation. We developed a multidirectional deep-learning-based method to automatically segment the prostate for ultrasound-guided radiation therapy. A 3D supervision mechanism is integrated into the V-Net stages to deal with the optimization difficulties when training a deep network with limited training data. We combine a binary cross-entropy (BCE) loss and a batch-based Dice loss into the stage-wise hybrid loss function for a deep supervision training. During the segmentation stage, the patches are extracted from the newly acquired ultrasound image as the input of the well-trained network and the well-trained network adaptively labels the prostate tissue. The final segmented prostate volume is reconstructed using patch fusion and further refined through a contour refinement processing. Forty-four patients' TRUS images were used to test our segmentation method. Our segmentation results were compared with the manually segmented contours (ground truth). The mean prostate volume Dice similarity coefficient (DSC), Hausdorff distance (HD), mean surface distance (MSD), and residual mean surface distance (RMSD) were 0.92±0.03, 3.94±1.55, 0.60±0.23, and 0.90±0.38mm, respectively. We developed a novel deeply supervised deep learning-based approach with reliable contour refinement to automatically segment the TRUS prostate, demonstrated its clinical feasibility, and validated its accuracy compared to manual segmentation. The proposed technique could be a useful tool for diagnostic and therapeutic applications in prostate cancer.

Evaluation of variation of interfraction doses to organs at risk during brachytherapy of cervical cancer

BackgroundTwo-dimensional treatment planning using radiographs or simulator films was the standard in planning brachytherapy for patients with cervical cancer. Three-dimensional (3D) treatment planning has improved treatment efficacy. This retrospective study compares conventional and 3D treatment planning of brachytherapy in patients with cervical cancer and interfraction dose variation to bladder and rectum (D2cc). MethodsThe mean doses to bladder and rectum (D2cc) were computed by computed tomography (CT)–based planning during 100 sessions of intracavitary brachytherapy for carcinoma cervix with the same source configuration as generated for conventional planning, and these estimates were compared with the doses at International Commission on Radiation Units and measurements (ICRU) rectal, bladder points and point A. Interfraction variation of doses to bladder and rectum during various sessions was also analysed. ResultThe mean ICRU bladder dose and D2cc of the bladder for all patients was 3.7 Gy and 7.4 Gy, respectively (p < 0.001). The mean ICRU rectal dose from conventional plan was 4.3Gy and with CT planning, 4.45 Gy (p = 0.04). Interfraction dose variations for D2cc of the bladder were min −5.3 Gy and max 4.8 Gy and those of the rectum were min −1.8 Gy and max 1.72Gy. ConclusionDosimetric evaluation of conventional and 3D CT-based treatment planning for the same brachytherapy sessions demonstrated underestimation of ICRU bladder dose points (p < 0.001) and the rectal ICRU point dose and D2cc (p=0.04). The doses to organs at risk did not show a statistically significant variation between the fractions. However, large variation was noted between the interfractional maximum and minimum doses to bladder and rectum.

A Plan Quality Assurance (QA) Method for HDR Breast Brachytherapy with Multi-Lumen Balloon Applicator and HDR Interstitial Prostate Brachytherapy

A challenge facing the physics community has been quick plan quality checks for high-dose-rate (HDR) brachytherapy treatment planning. This study aims to develop a QA method of manually verifying the planned treatment time from treatment planning system (TPS) for HDR breast brachytherapy using multi-lumen balloon applicators and HDR interstitial prostate brachytherapy.

Dosimetric Verification of HDR Brachytherapy Treatment Plans of Three Different Entities Based on Measurements with a 2D-Array

The aim of this work is to develop a method by which complex HDR brachytherapy treatment plans can be verified dosimetrically. Verification of complex treatment plans is nowadays a standard for teletherapy, so VMAT treatment plans are verified prior to clinical use by a suitable procedure. Often a 2D-Array with ionization chambers is used for this procedure. In HDR brachytherapy, dosimetric verification prior to clinical application is not yet common.

A mixed-integer linear programming optimization model framework for capturing expert planning style in low dose rate prostate brachytherapy

Low dose rate (LDR) brachytherapy is a minimally invasive form of radiation therapy, used to treat prostate cancer, and it involves permanent implantation of radioactive sources (seeds) inside of the prostate gland. Treatment planning in brachytherapy involves a decision making process for the placement of the sources in order to deliver an effective dose of radiation to cancerous tissue in the prostate while sparing the surrounding healthy tissue. Such a decision making process can be modeled as a mixed-integer linear programming (MILP) problem. In this paper, we introduce a novel MILP optimization model framework for interstitial LDR prostate brachytherapy designed to explicitly mimic the qualities of treatment plans produced manually by expert planners. Our approach involves incorporating a unique set of clinically important constraints, called spatial constraints, into the optimization model. Computational results for an initial model reflecting clinical practice at our cancer center show that the treatment plans produced largely capture the spatial and dosimetric characteristics of manual plans created by expert planners.

Study of surgery combined with 125I brachytherapy for adenoid cystic carcinoma of oral and maxillofacial region

To retrospectively analyze the results of treatment outcome by surgery combined with 125I brachytherapy and correlative factors of adenoid cystic carcinoma (ACC). In the study, 75 patients with primary ACC of oral and maxillofacial region were treated by surgery combined with 125I seeds brachytherapy. Radical resection or subtotal resection was applied for the tumor. The brachytherapy treatment planning system was used to create implant plans with the prescribed dose of 60 Gy to 120 Gy. The 125I seeds were implanted intraoperatively or postoperatively. The regular follow-up was required. The Kaplan-Meier method was used to assess the tumor control rate and the patients' survival rates. Meanwhile, the Cox regression analysis was used to find out the prognostic factors. Local control rates at the end of 3 and 5 years were as follows: T1-T2, 92.2% and 82.0%; T3-T4, 82.6% and 82.6%; and overall, 90.0% and 78.8%. The disease-free survival rates were 74.9% and 54.3%, respectively. The overall survival rates for all the patients were 86.0% and 79.6%, respectively at the end of 3 and 5 years and were 91.3% and 91.3% for T1-T2 patients vs. 73.9% and 59.7% for T3-T4 patients. Distant metastasis-free survival rates at the end of 3 and 5 years were 84.4% and 76.7%, respectively. The distant metastasis-free survival rates at the end of 3 and 5 years were 83.4% and 79.6% with T1-T2 lesion compared with 86.0% and 67.8% with T3-T4 lesion. According to the COX univariate analysis and multivariate analysis, the risk of local recurrence would be raised by the age. Tumor stage and tumor site were the prognostic factors of the overall survival rates. 125I brachytherapy conducted as an adjuvant therapy postoperatively of ACC of oral and maxillofacial region can acquire satisfactory localregional control, distant metastasis-free survival, disease-free survival and overall survival. Tumors are prone to recur on the older patients. Patients having advanced tumor stage or tumor located in the nasal cavity or sinuses will suffer lower survival rates.

Subdermal injection of hyaluronic acid to decrease skin toxicity from radiation delivered with low-dose-rate brachytherapy for cancer patients.

PurposeTo study the feasibility of hyaluronic acid (HA) injection to increase the distance between skin and radioactive sources, and dose reduction of skin during low-dose-rate (LDR) brachytherapy.Material and methods: A total of 11 patients with subdermal malignant tumors were enrolled in this study. HA was injected after I-125 seed implantation, and dosimetric parameters were calculated by a brachytherapy treatment planning system (BTPS). The distance of the new space between radioactive sources and skin was measured on computed tomography (CT) and magnetic resonance imaging (MRI). Clinical signs were observed and followed up for every patient.ResultsAfter HA injection, the average of newly generated maximum distance was 1.0 cm along the entire length of the tumor. The D90 and V100 did not significantly change for tumors before or after injection (p = 0.39, p = 0.50, respectively). The maximum dose to a relatively small volume (0.1 cc) of the skin (OAR-Max) decreased from 100.66 Gy to 61.20 Gy (p < 0.05), and the mean skin dose (OAR-Mean) decreased from 49.20 Gy to 17.27 Gy (p < 0.05) after injection. On follow-up CT and MRI, HA was quite stable in shape and position for nearly 6 months.ConclusionsOur study results showed that an additional 1.0 cm distance between the radioactive source and skin could be induced by HA injection in patients with subdermal tumor, and this distance could significantly decrease the skin dose in LDR brachytherapy. In addition, no obvious toxicity and side effects were produced by HA injection. Therefore, hyaluronic acid injection is a safe and effective technique.

A dosimetric study of electron beam therapy vs. high-dose-rate mould brachytherapy in adjuvant treatment of non-melanoma skin carcinomas of the head and neck region.

PurposeRadiation for superficial tumours of the head and neck region can be given either by brachytherapy or electrons. Brachytherapy (BT), due to rapid dose fall-off and minor set-up errors, should be superior to external beam radiotherapy (EBRT) for treatment of lesions in difficult locations such as the nose and earlobe. The present study is a dosimetric comparison of computed tomography (CT)-based mould brachytherapy treatment plans with 3D conformal electron beam therapy in the treatment of non-melanoma skin cancers (NMSC).Material and methodsFrom December 2017 to November 2018 10 patients with NMSC of the head and neck region (forehead, nose, cheek) who underwent adjuvant radiation with HDR brachytherapy (BT) with a surface mould individual applicator were enrolled for analysis. We evaluated dose coverage by minimal dose to 90% of planning target volume (PTV, D90), volumes of PTV receiving 90-150% of prescribed dose (PD) (VPTV90-150), conformal index for 90% and 100% of PD (COIN90, COIN100), dose homogeneity index (DHI), dose nonuniformity ratio (DNR), and exposure of organs at risk (OARs) (eyes, lens, underlying bone and skin). Prospectively, we created CT-based treatment plans for electron beam therapy. We compared conformity (COIN90, COIN100), dose coverage of PTV (D90, VPTV90, VPTV100), volumes of body receiving 10-90% of PD (V10-V90), doses to OARs (D0.1cc and D2cc) of BT and electron plans.ResultsWe obtained mean BT-DHI 0.81, BT-DNR 0.608, Electron-DHI 1.25. We observed no significant differences in VPTV90,100 and D90 between BT and electron beam. Mean BT-VPTV125,150 were significantly higher than Electron-VPTV100,125. COIN90 was superior for BT plans.ConclusionsCT-based surface mould brachytherapy results in better conformity of superficial lesions on small, irregular surfaces such as the nose and inner canthus than electrons with a slightly higher skin dose.

Carotid dosimetry after re-irradiation with 131Cs permanent implant brachytherapy in recurrent, resected head and neck cancer.

PurposePermanent seed implant cesium-131 (131Cs) brachytherapy provides highly localized radiation for patients with recurrent head and neck cancer (HNC), who may be ineligible for external beam radiation therapy due to a high-risk of toxicity. As carotid blowout is a concern in the setting of re-irradiation, a dose to the carotid artery was examined for 131Cs brachytherapy implants.Material and methodsEleven patients were implanted with 131Cs adjacent to carotid at the time of resection for recurrent HNC. Vascularized tissue flaps were used in some patients. The carotid artery was contoured on the post-implant brachytherapy treatment plan, and the maximum carotid point dose and minimum carotid-seed distances are reported. The incidence of carotid blowout in the follow-up period was also measured.ResultsThe maximum carotid dose was 77 ±52 Gy (range, 3-158 Gy). The closest seed to the carotid artery was 0.8 ±0.8 cm (range, 0.2-2.6 cm). One patient without a flap experienced carotid blowout, which was attributed to a non-healing wound rather than to high radiation doses.ConclusionsCarotid artery doses from 131Cs are reported. Vascularized tissue flaps should be considered when planning 131Cs brachytherapy.

Hybrid optimization based on non-coplanar needles for brachytherapy dose planning.

PurposeAn ideal dose distribution in a target is the ultimate goal of preoperative dose planning. Furthermore, avoiding vital organs or tissues such as blood vessels or bones during the puncture procedure is significant in low-dose-rate brachytherapy. The aim of this work is to develop a hybrid inverse optimization method based on non-coplanar needles to assist the physician during conformal dose planning, which cannot be properly achieved with a traditional coplanar template.Material and methodsThe hybrid inverse optimization technique include two novel technologies: an inverse optimization algorithm and a dose volume histogram evaluation method. Brachytherapy treatment planning system was designed as an experimental platform. Left lung adenocarcinoma case was used to test the performance of the method in non-coplanar and coplanar needles, and malignant tumor of spine case was involved to test the practical application of this technique. In addition, the optimization time of every test was also recorded.ResultsThe proposed method can achieve an ideal dose distribution, avoiding vital organs (bones). In the first experiment, 13 non-coplanar needles and 24 seeds were used to get an ideal dose distribution to cover the target, whereas 11 coplanar needles and 23 seeds were used to cover the same target. In the second experiment, the new method used 22 non-coplanar needles and 65 seeds to cover the target, while 63 seeds and 22 needles were used in the actual operation. In addition, the computation time of the hybrid inverse optimization method was 20.5 seconds in the tumor of 94.67 cm3 by using 22 needles, which was fast enough for clinical application.ConclusionsThe hybrid inverse optimization method achieved high conformity in the clinical practice. The non-coplanar needle can help to achieve a better dose distribution than the coplanar needle.

Subcutaneous spacer injection to reduce skin toxicity in breast brachytherapy: A pilot study on mastectomy specimens

PurposeAccelerated partial breast irradiation is a treatment option for selected patients with early-stage breast cancer. Some accelerated partial breast irradiation techniques lead to skin toxicity with the skin dose as a main risk factor. Biodegradable spacers are effective and safe in prostate brachytherapy to protect the rectum. We hypothesize that a subcutaneous spacer injection reduces the skin dose in breast brachytherapy. Methods and MaterialsUltrasound-guided spacer injections, either hyaluronic acid (HA) or iodined polyethylene glycol (PEG), were performed on fresh mastectomy specimens. Success was defined as a spacer thickness of ≥5 mm in the high-dose skin area. Usability was scored using the system usability scale. Pre and postinjection CT scans were used to generate low-dose-rate seed brachytherapy treatment plans after defining a clinical target volume. Maximum dose to small skin volumes (D0.2cc) and existence of hotspots (isodose ≥90% on 1 cm2 of skin) were calculated as skin toxicity indicators. ResultsWe collected 22 mastectomy specimens; half had HA and half had PEG injection. Intervention success was 100% for HA and 90.9% for PEG (p = NS). Hydrodissection was feasible in 81.8% with HA and 63.6% with PEG. Median system usability scale score was 97.5 for HA and 82.5 for PEG (p < 0.001). Mean D0.2cc was 80.8 Gy without spacer and 53.7 Gy with spacer (p < 0.001). Skin hotspots were present in 40.9% without spacer but none with spacer (p < 0.001). ConclusionsA spacer injection in mastectomy specimens is feasible. An extra 5 mm space is always achieved, thereby potentially reducing the skin dose dramatically in low-dose-rate seed breast brachytherapy.

Dosimetric Parameters Estimation of I-125 Brachytherapy Source in fat phantom using GATE8.0 code

Introduction: Brachytherapy is one type of internal radiation therapy where radiation sources, which are usually encapsulated, are placed as close as possible to the tumor site or inside the patient's body. In this technique, it is important to determine dose distribution around the brachytherapy capsule to create optimal treatment plant. In this way, dosimetric parameters are estimated according to TG-43U1 protocol in the water phantom as reference medium while the attenuation coefficient of the sources in the water phantom is different from that of different tissues. The purpose of this study is to investigate the effects of the fat phantom materials on the TG-43U1 dosimetery parameters of the I-125 brachytherapy source using GATE 8.0 Monte Carlo code. Materials and Methods: In this work, we used GATE_v8.0 (Geant4 Application for Emission Tomography) to calculate of dosimetric parameters of the I-125 brachytherapy source model 2301. At first, validation of the GATE platform was performed by some criteria such as dose rate constant, radial dose function, 2D anisotropy function inside liquid water according to the AAPM TG-43. Then, the Monte Carlo simulated dosimetric parameters of the 2301 I-125 were calculated in fat phantom. The TG-43 dosimetry parameters of the brachytherapy source were compared with those of the fat phantom. Results: Dosimetric parameters of simulated I-125 brachytherapy capsule show good consistency compared with the other study of the Monte Carlo simulation of I-125 source. The maximum deviation was about 9%. The maximum relative deviation of radial dose function of the fat tissue compared with water medium were about 13% at distances below 1cm. These differences increased, when the distance from the source increased. At the distance of 5cm from the source, it approximately reached to 55.67%. The maximum relative deviation of the anisotropy parameter of the fat phantom was observed about 6.7% compared with the water phantom. Conclusion: There was a good agreement between the results of this work and other study in calculation of dosimetric parameters of brachytherapy I-125 (model 2301) brachytherapy base on the recommendations of TG-43U1 protocole, using GATE Monte Carlo simulation method. Acquired results show that the obtained data can be used to develop GATE code for treatment plan of brachytherapy I- 125 brachytherapy source. Furthermore, In the clinical application of the I-125 brachytherapy source, which is contracted in the treatment of the adjacent tumors to the fat tissues, the correction factors of the fat tissues must be applied after dosimetric parameters calculation in water phantoms in the treatment planning to estimate accurate results for brachytherapy treatment planning.

RapidBrachyMCTPS: a Monte Carlo-based treatment planning system for brachytherapy applications

Despite being considered the gold standard for brachytherapy dosimetry, Monte Carlo (MC) has yet to be implemented into a software for brachytherapy treatment planning. The purpose of this work is to present RapidBrachyMCTPS, a novel treatment planning system (TPS) for brachytherapy applications equipped with a graphical user interface (GUI), optimization tools and a Geant4-based MC dose calculation engine, RapidBrachyMC. Brachytherapy sources and applicators were implemented in RapidBrachyMC and made available to the user via a source and applicator library in the GUI. To benchmark RapidBrachyMC, TG-43 parameters were calculated for the microSelectron v2 (192Ir) and SelectSeed (125I) source models and were compared against previously validated MC brachytherapy codes. The performance of RapidBrachyMC was evaluated for a prostate high dose rate case. To assess the accuracy of RapidBrachyMC in a heterogeneous setup, dose distributions with a cylindrical shielded/unshielded applicator were validated against film measurements in a Solid WaterTM phantom. TG-43 parameters calculated using RapidBrachyMC generally agreed within 1%–2% of the results obtained in previously published work. For the prostate case, clinical dosimetric indices showed general agreement with Oncentra TPS within 1%. Simulation times were on the order of minutes on a single core to achieve uncertainties below 2% in voxels within the prostate. The calculation time was decreased further using the multithreading features of Geant4. In the comparison between MC-calculated and film-measured dose distributions, at least 95% of points passed the 3%/3 mm gamma index criteria in all but one case. RapidBrachyMCTPS can be used as a post-implant dosimetry toolkit, as well as for MC-based brachytherapy treatment planning. This software is especially well suited for the development of new source and applicator models.

P223] Treatment planing in brachytherapy HDR based on three-demensional images

Purpose Treatment planning in High Dose Rate (HDR) brachytherapy based on three-dimensional (3D) imaging allows for prearranging and realization optimal treatment process. This process consists of procedure planning, the choice of applicators, adjusting the appropriate implantation technique, and planning of three-dimensional distribution of dose in computerized treatment planning system. 3D images used in treatment planning in HDR brachytherapy allows for choosing the most appropriate application technique. This in turn allows for the best area coverage by reference dose with simultaneous protection of critical organs. Treatment planning on 3D images assures individual planning of dose dispersion in target area. Methods Several techniques will be presented based on 3D imaging in location such as lung, skin cancer, breast, and prostate cancer. For each location, relative cases will be provided where different applicators and techniques were applied. These examples are going to present images from before and after performed application along with the pictures from computer treatment planning system. In each of described locations, relative advice and rules of conducting accurate application will be provided. Results Differences between Monaco TPS and Dolphin in SRS/SRT plans, PTV1: 5.1%, PTVaverage: 8.1% and PTV99: 9.2%. Differences between Compass and Dolphin in SRS/SRT plans, PTV1: 2.9%, PTVaverage: 4.8% and PTV99: 6.5%. Differences between Monaco TPS and Dolphin in lung SBRT plans, PTV1: 3.5%, PTVaverage: 2.2% and PTV99: 2.6%. Differences between Compass and Dolphin in Lung SBRT plans, PTV1: 2.7%, PTVaverage: 2% and PTV99: 2.6%. Differences between Monaco TPS and Dolphin in spine SBRT plans, PTV1: −1.9%, PTVaverage: −5.8% and PTV99: −6.8%. Differences between Compass and Dolphin in spine SBRT plans, PTV1: 3.3%, PTVaverage: −0.47% and PTV99: −1.1%. When average gamma values are examined in the regions formed with 1, 2, 3, 4 cm margins in SRS/SRT/SBRT plans: 3–3 mm 0.34–0.6, 2%–2 mm 0.51–0.83, 1%–1 mm 0.92–1.15, 3%–1 mm 0.36–0.86. In 2D gamma analysis, SRS/SRT was 96%, lung SBRT was 88% and spine SBRT was 84.1% according to the criteria of 2–2 mm. SRS/SRT was 93%, lung SBRT was 83% and spine SBRT was 72.4% according to the criteria of 3–1 mm. Conclusions Computer tomography allows for establishing individual treatment solutions that provide optimal approach to every patient as in skin cancer. With more and easier access to threedimensional imaging, new ways of applying HDR brachytherapy open in new location as well as in form of radical treatment. With the use of imaging, we are now able to introduce catheters precisely into the tumor area with putting the patient at risk of posttreatment complications. It allows the treatment of people that no more qualify for other forms of treatment (radiotherapy). Because of the high gradient dose in HDR brachytherapy and patients with internal intracranial implants, i.e., pacemaker or cardioverter-defibrillator, we know exactly the dose the device will receive, so we can perform the procedures without exposing the patient to additional risk. Thanks to different optimization forms based on 3D images, HDR brachytherapy is applied not only in palliative treatment but also in new ways of radical treatment, i.e., in case of APBI.

P241] Factors affecting urethral dose in intracavitary brachytherapy using multichannel vaginal applicator

Purpose In intracavitary brachytherapy (ICBRT) performed with multichannel vaginal applicators (MVA), there is scarce data on the factors affecting urethral dose. In this study it was aimed to define the factors influencing urethral dose in patients with vaginal involvement treated with external beam radiotherapy (EBRT) and ICBRT using tandem + Miami applicators (MA). Methods Five consecutive gynecological cancer patients (4 with cervical and 1 with vaginal cancer) given 3-D conformal ICBRT using tandem + MA were included in this retrospective dosimetric study. The patients’ disease stage was II in 2, and III in 3 of them. EBRT total dose was 4500–5050 cGy while brachytherapy total dose dose was 1950–2600 cGy delivered with 400–700 cGy fraction dose in 3–5 fractions. Angulated tandem was used in all patients. The diameter of the MA ranged between 3 and 4 cm. Mean HR CTV D90 (as percentage of the prescribed dose) was 86% (77.6%-99.3%) in all patients. For this study urethra was contoured retrospectively by a radiation oncology specialist and controlled by a radiation oncology lecturer. Brachytherapy urethra D0.1 cc (as percentage of the prescribed dose) was obtained from the DVHs in brachytherapy treatment planning system. Patients were divided into two groups according to the diameter of MA used (diameter = 4 cm vs diameter ≥ 0.6 vs ratio 0.6). Mann Whitney test was used to compare groups with respect to urethra D0.1 cc. Results Brachytherapy mean urethra D0.1 cc was 99.8% (43.3%-134.9%) of the prescribed dose. Mean values were 113.9%, and 78.5% for high and low anterior loading groups, respectively (p = 0.564). Also, mean values were 120.4%, and 68.9% for large and small diameter applicator groups, respectively. Although mean urethra D0.1 cc was higher in the patients with large diameter MA, this difference didn’t reach statistical significance (p = 0.083). This may be due to the small number of patients in the study. Conclusions Larger and prospective studies are needed in order to determine factors affecting urethral dose when using MVAs.

Verification of the dose distribution calculated by the treatment planning system in high dose rate brachytherapy

For HDR brachytherapy, there is still no clear optimum method used to measure dosimetric accuracy. For brachytherapy, there is a steep dose fall off with distance which can make dosimetric measurements more challenging when compared with external beam radiation therapy (EBRT). It is important that as HDR brachytherapy continues to develop that quality control measures develop also. The aim of this study is to verify the dose distribution for HDR brachytherapy using Gafchromic film. This was done by verifying the treatment dose for three brachytherapy applicators; the cylinder, fletcher and flap applicators. Each applicator was placed in a water phantom with calibrated Gafchromic film placed at known locations. The phantoms were scanned and planned on the brachytherapy treatment planning system (TPS), and the dose to the film noted. After irradiation the Gafchromic film was scanned and analysed. The results showed that the cylinder applicator had the largest percentage difference between the TPS dose and calculated dose with a difference of 11.93%. Smaller differences of 7.99% and 6.07% were seen for the fletcher and flap applicators respectively. However, uncertainties in these results were seen for each of the applicators and should be taken into account. It was observed that the Gafchromic film overestimated the dose for the three applicators, however provided steps were taken to reduce these uncertainties Gafchromic film does have the potential to be used as a QA tool to measure the dose distribution for HDR brachytherapy which this study set out to do.

Dosimetric feasibility of an anthropomorphic three-dimensional PRESAGE® dosimeter for verification of single entry hybrid catheter accelerated partial breast brachytherapy

AbstractPurposeTo determine the feasibility of an anthropomorphic breast polyurethane-based three-dimensional (3D) dosimeter with cavity to measure dose distributions and skin dose for a commercial strut-based applicator strut-adjusted volume implant (SAVI™) 6–1.Materials and methodsAn anthropomorphic breast 3D dosimeter was created with a cavity to accommodate the SAVI™ strut-based device. 2 Gy was prescribed to the breast dosimeter having D95 to planning target volume evaluation (PTV_EVAL) while limiting 125% of the prescribed dose to the skin. Independent dose distribution verification was performed with GAFCHROMIC® EBT2 film. The dose distribution from the 3D dosimeter was compared to the distributions from commercial brachytherapy treatment planning system (TPS) and film. Point skin doses, line profiles and dose–volume histogram (DVHs) for the skin and PTV_EVAL were compared.ResultsThe maximum difference in skin dose for TPS and the 3D dosimeter was 4% whereas 41% between the TPS and EBT2 film. The maximum dose difference for line profiles between TPS, 3D dosimeter, and film was 4·1%. DVHs of skin and PTV_EVAL for TPS and 3D dosimeter differed by a maximum of 4% at 5 mm depth and skin differed by a maximum 1·5% between TPS and 3D dosimeter. The criterion for gamma analysis comparison was 92·5% at ±5%±3 mm criterion. The TPS demonstrated at least ±5% comparability in predicting dose to the skin, PTV_EVAL and normal breast tissue.Conclusions3D anthropomorphic polyurethane dosimeter with cavity gives comparable results to the TPS dose predictions and GAFCHROMIC® EBT2 film results in the context of HDR brachytherapy.

Brachytherapy organ dose estimation using Monte Carlo simulations of realistic patient models.

Radiation Therapy Planning Systems (RTPS) currently used in hospitals contain algorithms based on deterministic simplifications that do not properly consider electrons lateral transport in the areas where there are changes of density, and as a result, erroneous dose predictions could be produced. According to this, the present work proposes the use of Monte Carlo method in brachytherapy planning systems, which could affect positively on the radiotherapy treatment planning, since it provides results that are more accurate and takes into account the in homogeneities density variations. This paper presents a Monte Carlo (MC) simulation of a brachytherapy prostate treatment with I-125 seeds, using the latest version of MCNP, v.6.1.1. To that, a 3D model of the anatomy of a real anonymized patient is created from the segmentation of Computed Tomography (CT) images. Treatment over this 3D model is simulated and the dose given to each organ is obtained. These doses are compared with those calculated by deterministic planning system used in hospital demonstrating the effectiveness of MC method in the planning of brachytherapy treatments, because of not only the results precision but also regarding the affordable computing times.

Comparison of Two Commercially Available Model Based Dose Calculation Algorithms and TG-43 for APBI Brachytherapy

Brachytherapy dose calculation algorithms that account for heterogeneous patient geometries have recently become commercially available. However, it is as yet unknown how the treatment plans produced by these new algorithms will compare to the current clinical standard, TG-43 algorithm when applied to patients. Ten clinical APBI brachytherapy treatment plans were randomly chosen from our clinical database. These plans were recomputed with the Oncentra® Advanced Collapsed Cone Engine (ACE) version 4.5 and Acuros™ BV version 13 and compared to the current standard TG-43-based algorithms treated at our institution with a Strut-Adjusted Volume Implant (SAVI).