To perform a comprehensive comparative planning study evaluating the utility of the proposed direction modulated brachytherapy (DMBT) tandem applicator against standard applicators, in the setting of ...image guided adaptive brachytherapy of cervical cancer.
A detailed conceptual article was published in 2014. The proposed DMBT tandem applicator has 6 peripheral grooves of 1.3-mm width, along a 5.4-mm-thick nonmagnetic tungsten alloy rod of density 18.0 g/cm(3), capable of generating directional dose profiles. We performed a comparative planning study with 45 cervical cancer patients enrolled consecutively in the prospective observational EMBRACE study. In all patients, MRI-based planning was performed while utilizing various tandem-ring (27 patients) and tandem-ring-needles (18 patients) applicators, in accordance with the Groupe Européen de Curiethérapie-European Society for Radiotherapy and Oncology recommendations. For unbiased comparisons, all cases were replanned with an in-house-developed inverse optimization code while enforcing a uniform set of constraints that are reflective of the clinical practice. All plans were normalized to the same high-risk clinical target volume D90 values achieved in the original clinical plans.
In general, if the standard tandem was replaced with the DMBT tandem while maintaining all other planning conditions the same, there was consistent improvement in the plan quality. For example, among the 18 tandem-ring-needles cases, the average D2cm(3) reductions achieved were -2.48% ± 11.03%, -4.45% ± 5.24%, and -5.66% ± 6.43% for the bladder, rectum, and sigmoid, respectively. An opportunity may also exist in avoiding use of needles altogether for when the total number of needles required is small (approximately 2 to 3 needles or less), if DMBT tandem is used.
Integrating the novel DMBT tandem onto both intracavitary and intracavitary-interstitial applicator assembly enabled consistent improvement in the sparing of the OARs, over a standard "single-channel" tandem, though individual variations in benefit were considerable. Although at an early stage of development, the DMBT concept design is demonstrated to be useful and pragmatic for potential clinical translation.
To demonstrate that utilization of the direction-modulated brachytherapy (DMBT) concept can significantly improve treatment plan quality in the setting of high-dose-rate (HDR) brachytherapy for ...cervical cancer.
The new, MRI-compatible, tandem design has 6 peripheral holes of 1.3-mm diameter, grooved along a nonmagnetic tungsten-alloy rod (ρ = 18.0 g/cm(3)), enclosed in Delrin tubing (polyoxymethylene, ρ = 1.41 g/cm(3)), with a total thickness of 6.4 mm. The Monte Carlo N-Particle code was used to calculate the anisotropic (192)Ir dose distributions. An in-house-developed inverse planning platform, geared with simulated annealing and constrained-gradient optimization algorithms, was used to replan 15 patient cases (total 75 plans) treated with a conventional tandem and ovoids (T&O) applicator. Prescription dose was 6 Gy. For replanning, we replaced the conventional tandem with that of the new DMBT tandem for optimization but left the ovoids in place and kept the dwell positions as originally planned. All DMBT plans were normalized to match the high-risk clinical target volume V100 coverage of the T&O plans.
In general there were marked improvements in plan quality for the DMBT plans. On average, D2cc for the bladder, rectum, and sigmoid were reduced by 0.59 ± 0.87 Gy (8.5% ± 28.7%), 0.48 ± 0.55 Gy (21.1% ± 27.2%), and 0.10 ± 0.38 Gy (40.6% ± 214.9%) among the 75 plans, with best single-plan reductions of 3.20 Gy (40.8%), 2.38 Gy (40.07%), and 1.26 Gy (27.5%), respectively. The high-risk clinical target volume D90 was similar, with 6.55 ± 0.96 Gy and 6.59 ± 1.06 Gy for T&O and DMBT, respectively.
Application of the DMBT concept to cervical cancer allowed for improved organ at risk sparing while achieving similar target coverage on a sizeable patient population, as intended, by maximally utilizing the anatomic information contained in 3-dimensional imaging. A series of mechanical and clinical validations are to be followed.
Purpose:
All forms of past and current high-dose-rate brachytherapy utilize immobile applicators during treatment delivery. The only moving part is the source itself. This paradigm misses an ...important degree of freedom that, if explored, can in some instances produce previously unachievable dose conformality; that is, the dynamic motion of the applicator itself during treatment delivery. Monte Carlo and treatment planning simulations were used to illustrate the potential benefits of moving applicators for rectal cancer applications in particular. This concept is termed dynamic modulated brachytherapy (DMBT).
Methods:
The DMBT system uses a high-density, 18.0 g/cm3, 45 mm long tungsten alloy shield, cylindrical in shape, with a small window on one side to encapsulate a 192Ir source, to create collimation that results in a highly directional beam profile. This shield can be dynamically translated and rotated, using an attached robotic arm, during treatment to create a volumetric modulated arc therapy-type delivery, but from inside the rectal cavity. Monte Carlo simulations and planning optimization algorithms were developed inhouse to evaluate the effectiveness of this new approach using 36 clinical treatment plans comprised of 13 patients each treated using the intracavitary mold applicator (ICMA, Nucletron, The Netherlands) to quantify the potential clinical benefit. The prescription dose was 10 Gy/fx and the group had an average clinical target volume of 9.0 ± 3.5 cm3. Ideal phantom geometries were used to evaluate the impact of various shield dimensions and designs on the resulting plan quality.
Results:
Simulations of ideal phantom geometries found that shields as small as 10 mm in diameter can produce high quality plans. For the clinical patient cases, compared to the ICMA, for equal prescription tumor coverage, the DMBT plans provided >30% decrease in D5 (high dose volume) resulting in a ∼40% decrease in dose heterogeneity index. In addition, mean dose and D98 showed a reduction (typically 40%–60%) on all critical structures evaluated. However, for a 10 Gy prescribed dose there was an increase in total treatment time on average from 7.6 to 20.8 min for a source with an air-kerma strength of 40.25 kU (10 Ci).
Conclusions:
Dosimetric properties of a novel DMBT system have been described and evaluated. Comparison with the ICMA commercial applicator has shown it to be a prospective step forward in high-dose-rate brachytherapy192Ir technology. Dynamic motion of an applicator during treatment, for any applicator and site in general, can provide additional degrees of freedom that, if properly considered, can potentially increase the plan quality significantly.
Purpose
To investigate the dose modulation capability of a novel MRI‐compatible direction modulated brachytherapy (DMBT) tandem applicator design with various high‐density shielding materials for ...brachytherapy treatment of cervical cancer. The shield materials that have been evaluated are tantalum (Ta), pure tungsten (W), gold (Au), rhenium (Re), osmium (Os), platinum (Pt), iridium (Ir), and W′ tungsten alloy (95%W, 3.5%Ni, 1.5%Cu).
Materials and methods
The recently proposed six‐channel DMBT tandem is composed of nonmagnetic tungsten alloy (W′) rod with diameter of 5.4 mm and coated with 0.3‐mm thick bio‐safe plastic sheath. The tandem shielding material can, however, be individually replaced with various other shields to create directional radiation. Monte Carlo N‐Particle (MCNP) code was used to calculate the three‐dimensional (3D) dose distributions in a water phantom for an HDR 192Ir (mHDR‐v2) source inside each DMBT tandem with various shields and a plastic conventional tandem (Con.T). Then, the 3D dose distributions were imported into an in‐house‐coded inverse planning optimization algorithm to obtain optimal plans for 12 clinical cases chosen at random from the international RetroEMBRACE dataset involving conventional tandem and ring (Con.T&R) applicators. All plans generated by the DMBT tandem and ring (DMBT&R) with the tungsten alloy DMBT(W′)&R were compared with the corresponding Con.T&R plans, to generate benchmark results. These benchmark results were then considered as reference plans for other shields performances. Plans were normalized to receive the same high‐risk clinical target volume (CTVHR) D90. The D100, D10, and V100 for CTVHR, and D2cm3 for organs at risk (OARs) of bladder, sigmoid, and rectum were calculated and compared.
Results
Transmission factor (TF), that is, the dose in the backside of the DMBT shield over that in the front opening, at a 5 cm distance, were 36.6%, 34.8%, 31.9%, 28.9%, 27.9%, 26.2%, 26.2%, and 25.5%, for Ta, W′, W, Re, Au, Os, Pt, and Ir shields, respectively. On average, the CTVHR values for D100, V100, D10 were not significantly different across all DMBT&R shields and the Con.T&R plans (P > 0.219). For the D2cm3, the benchmark results showed significant reductions (P < 0.03), that is, on average, −8.3% for bladder, −10.7% for rectum, and −10.1% for sigmoid, compared to the Con.T&R plans. However, the various shields showed little improvement from the tungsten alloy (W′), where on average, rectum (bladder) sigmoid D2cm3 were reduced by −1.32% (−0.85%) −1.01%, −1.25% (−0.78%) −0.91%, −1.22% (−0.75%) −0.86%, −0.94% (−0.60%) −0.70%, −0.84% (−0.51%) −0.59%, and −0.38% (−0.24%) −0.23% for Ir, Pt, Os, Au, Re, and W shields, relative to the benchmark W′ DMBT plans, respectively. These corresponding values for Ta increased by +0.28% (+0.08%) +0.25%, respectively.
Conclusion
The Ir, Pt, Os, Au, Re, and W shielding materials, respectively, in descending order, lead to better OAR sparing than the DMBT(W′)&R plans. However, the amount of improvement is limited and clinically insignificant. This finding suggests that the initial W′ shield remains a suitable choice given the proven MR compatibility, for use in MR‐guided adaptive brachytherapy of cervical cancer.
Background
Technological advancements have made it possible to improve patient outcomes in radiotherapy, sparing both normal tissues and increasing tumour control. However, these advancements have ...resulted in an increase in the number of software systems used, which each require data inputs to function. For institutions with multiple vendors for their treatment planning systems and oncology information systems, the transfer of data between them is potentially error prone and can lead to treatment errors.
Purpose
The goal of this work was to determine the frequency of errors in data transfers between the Varian Eclipse treatment planning system and the Elekta Mosaiq oncology information system.
Methods
An in‐house program was used to quantify the number of errors for 2700 unique plans over an 8‐month period. Using this information, the frequency of the errors were calculated. A risk priority number was calculated using the calculated frequencies to determine the impact on the clinic.
Results
The most common errors discovered were backup timer settings (10.7%), Field label (8.5%), DRR associations (3.3%), imaging field types (3.1%), dose rate (1%), Field Id (0.8%), imaging isocenter (0.7% and SSD (0.7%). Based on the risk priority numbers, the DRR association error was ranked as having the highest potential impact on the patient.
Conclusions
The results of the work show that the most effort should be focused on checking the manual steps performed in the transfer process, while items that are imported directly from DICOM‐RT without modification are highly likely to be transferred accurately. The data can be used to help guide the implementation of future automated tools and process improvement in the clinic.
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