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Background: Direction Modulated Brachytherapy (DMBT) enables conformal dose distributions. However, clinicians may face challenges in creating viable treatment plans within a fast‐paced clinical setting, especially for a novel technology like DMBT, where cumulative clinical experience is limited. Deep learning‐based dose prediction methods have emerged as effective tools for enhancing efficiency. Purpose: To develop a voxel‐wise dose prediction model using an attention‐gating mechanism and a 3D UNET for cervical cancer high‐dose‐rate (HDR) brachytherapy treatment planning with DMBT six‐groove tandems with ovoids or ring applicators. Methods: A multi‐institutional cohort of 122 retrospective clinical HDR brachytherapy plans treated to a prescription dose in the range of 4.8–7.0 Gy/fraction was used. A DMBT tandem model was constructed and incorporated onto a research version of BrachyVision Treatment Planning System (BV‐TPS) as a 3D solid model applicator and retrospectively re‐planned all cases by seasoned experts. Those plans were randomly divided into 64:16:20 as training, validating, and testing cohorts, respectively. Data augmentation was applied to the training and validation sets to increase the size by a factor of 4. An attention‐gated 3D UNET architecture model was developed to predict full 3D dose distributions based on high‐risk clinical target volume (CTVHR) and organs at risk (OARs) contour information. The model was trained using the mean absolute error loss function, Adam optimization algorithm, a learning rate of 0.001, 250 epochs, and a batch size of eight. In addition, a baseline UNET model was trained similarly for comparison. The model performance was evaluated on the testing dataset by analyzing the outcomes in terms of mean dose values and derived dose‐volume‐histogram indices from 3D dose distributions and comparing the generated dose distributions against the ground‐truth dose distributions using dose statistics and clinically meaningful dosimetric indices. Results: The proposed attention‐gated 3D UNET model showed competitive accuracy in predicting 3D dose distributions that closely resemble the ground‐truth dose distributions. The average values of the mean absolute errors were 1.82 ± 29.09 Gy (vs. 6.41 ± 20.16 Gy for a baseline UNET) in CTVHR, 0.89 ± 1.25 Gy (vs. 0.94 ± 3.96 Gy for a baseline UNET) in the bladder, 0.33 ± 0.67 Gy (vs. 0.53 ± 1.66 Gy for a baseline UNET) in the rectum, and 0.55 ± 1.57 Gy (vs. 0.76 ± 2.89 Gy for a baseline UNET) in the sigmoid. The results showed that the mean absolute error (MAE) for the bladder, rectum, and sigmoid were 0.22 ± 1.22 Gy (3.62%) (p = 0.015), 0.21 ± 1.06 Gy (2.20%) (p = 0.172), and ‐0.03 ± 0.54 Gy (1.13%) (p = 0.774), respectively. The MAE for D90, V100%, and V150% of the CTVHR were 0.46 ± 2.44 Gy (8.14%) (p = 0.018), 0.57 ± 11.25% (5.23%) (p = 0.283), and ‐0.43 ± 19.36% (4.62%) (p = 0.190), respectively. The proposed model needs less than 5 s to predict a full 3D dose distribution of 64 × 64 × 64 voxels for any new patient plan, thus making it sufficient for near real‐time applications and aiding with decision‐making in the clinic. Conclusions: Attention gated 3D‐UNET model demonstrated a capability in predicting voxel‐wise dose prediction, in comparison to 3D UNET, for DMBT intracavitary brachytherapy planning. The proposed model could be used to obtain dose distributions for near real‐time decision‐making before DMBT planning and quality assurance. This will guide future automated planning, making the workflow more efficient and clinically viable. [ABSTRACT FROM AUTHOR]

Purpose: This study presents a novel and comprehensive framework for evaluating magnetic resonance guided radiotherapy (MRgRT) workflow by integrating the Failure Modes and Effects Analysis (FMEA) approach with Time‐Driven Activity‐Based Costing (TDABC). We assess the workflow for safety, quality, and economic implications, providing a holistic understanding of the MRgRT implementation. The aim is to offer valuable insights to healthcare practitioners and administrators, facilitating informed decision‐making regarding the 0.35T MRIdian MR‐Linac system's clinical workflow. Methods: For FMEA, a multidisciplinary team followed the TG‐100 methodology to assess the MRgRT workflow's potential failure modes. Following the mitigation of primary failure modes and workflow optimization, a treatment process was established for TDABC analysis. The TDABC was applied to both MRgRT and computed tomography guided RT (CTgRT) for typical five‐fraction stereotactic body RT (SBRT) treatments, assessing total workflow and costs associated between the two treatment workflows. Results: A total of 279 failure modes were identified, with 31 categorized as high‐risk, 55 as medium‐risk, and the rest as low‐risk. The top 20% risk priority numbers (RPN) were determined for each radiation oncology care team member. Total MRgRT and CTgRT costs were assessed. Implementing technological advancements, such as real‐time multi leaf collimator (MLC) tracking with volumetric modulated arc therapy (VMAT), auto‐segmentation, and increasing the Linac dose rate, led to significant cost savings for MRgRT. Conclusion: In this study, we integrated FMEA with TDABC to comprehensively evaluate the workflow and the associated costs of MRgRT compared to conventional CTgRT for five‐fraction SBRT treatments. FMEA analysis identified critical failure modes, offering insights to enhance patient safety. TDABC analysis revealed that while MRgRT provides unique advantages, it may involve higher costs. Our findings underscore the importance of exploring cost‐effective strategies and key technological advancements to ensure the widespread adoption and financial sustainability of MRgRT in clinical practice. [ABSTRACT FROM AUTHOR]

This systematic review study aims to provide comprehensive data on different radiobiological models, parameters, and endpoints used for calculating the normal tissue complication probability (NTCP) based on clinical data from head and neck cancer patients treated with conformal radiotherapy. A systematic literature search was carried out according to the PRISMA guideline for the identification of relevant publications in six electronic databases of Embase, PubMed, Scopus, and Google Scholar to July 2022 using specific keywords in the paper's title and abstract. The initial search resulted in 1368 articles for all organs for the review article about the NTCP parameters. One hundred and seventy‐eight articles were accepted for all organs with complete parameters for the mentioned models and finally, 20 head and neck cancer articles were accepted for review. Analysis of the studies shows that the Lyman‐Kutcher‐Burman (LKB) model properly links the NTCP curve parameters to the postradiotherapy endpoints. In the LKB model for esophagus, the minimum, and maximum corresponding parameters were reported as TD50 = 2.61 Gy with grade ≥3 radiation‐induced esophagitis endpoints as the minimum TD50 and TD50 = 68 Gy as the maximum ones. nmin = 0.06, nmax = 1.04, mmin = 0.1, and mmax = 0.65, respectively. Unfortunately, there was not a wide range of published articles on other organs at risk like ear or cauda equina except Burman et al. (Fitting of normal tissue tolerance data to an analytic function. Int J Radiat Oncol Biol Phys Ther. 1991;21:123–135). Findings suggest that the validation of different radiobiological models and their corresponding parameters need to be investigated in vivo and in vitro for developing a more accurate NTCP model to be used for radiotherapy treatment planning optimization. [ABSTRACT FROM AUTHOR]

A novel clinical workflow utilizing a direction modulated brachytherapy (DMBT) tandem applicator in combination with a patient-specific, 3D printed vaginal needle-track template for an advanced image-guided adaptive interstitial brachytherapy of the cervix. The proposed workflow has three main steps: (1) pre-treatment MRI, (2) an initial optimization of the needle positions based on the DMBT tandem positioning and patient anatomy, and a subsequent inverse optimization using the combined DMBT tandem and needles, and (3) rapid 3D printing. We retrospectively re-planned five patient cases for two scenarios; one plan with the DMBT tandem (T) and ovoids (O) with the original needle (ND) positions (DMBT + O + ND) and another with the DMBT T&O and spatially reoptimized needles (OptN) positions (DMBT + O + OptN). All retrospectively reoptimized plans have been compared to the original plan (OP) as well. The accuracy of 3D printing was verified through the image registration between the planning CT and the CT of the 3D-printed template. The average difference in D2cc for the bladder, rectum, and sigmoid between the OPs and DMBT + O + OptNs were −8.03 ± 4.04%, −18.67 ± 5.07%, and −26.53 ± 4.85%, respectively. In addition, these average differences between the DMBT + O + ND and DMBT + O + OptNs were −2.55 ± 1.87%, −10.70 ± 3.45%, and −22.03 ± 6.01%, respectively. The benefits could be significant for the patients in terms of target coverage and normal tissue sparing and increase the optimality over free-hand needle positioning. [ABSTRACT FROM AUTHOR]

High dose-rate brachytherapy can be plagued by a multitude of user errors that could result in late toxicities for patients. A common one reported to NRC is wrong treatment length. This error will result in a shifted dose distribution between planned and delivered dose. To automate and verify delivery with correct treatment lengths, Varian released its Bravos remote afterloader which uses the device's dummy wire for accurate pre-treatment applicator measurements. Bravos measurements are compared with the planned lengths and if differences are small, treatment length is adjusted automatically. In this process, dwell positions are kept unchanged relative to the tip of the applicator. In breast interstitial implants, from our clinical experience, we noticed, through these automated measurements a significant catheter lengthening that occurs between the first and second fractions. The first fraction is typically delivered within 2h from implantation and the second fraction is more than 12h later. The catheters length does not seem to change much after that. We seek to quantify the dosimetric impact of such automated adjustments, identify cases and treatment parameters particularly sensitive to these effects and describe the best planning and delivery mitigation strategies to ensure accurate dose delivery. A retrospective cohort of 14 successively treated breast cancer patients using multi-catheter implants were selected for analysis. Actual length measurements were used to create plans simulating the dosimetric impact of making or not making these adjustments. Daily QA for two years shows positional accuracy of 0.3±0.3mm and for the dummy and source wires. In these simulations, it was hypothesized that the target did not change in volume or position relative to breast. In planning these treatments, two targets are used, expansions of the lumpectomy cavity, a CTV1cm and CTV1.5cm for which we try to achieve V95>95% and V90>90% respectively. The max skin dose is limited to <100% Prescription dose regimens included 7.5Gyx3fx=22.5Gy(8/14 patients) and 4.3Gyx7fx=30.1Gy(6/14 patients). Dose inhomogeneity was evaluated using V150% and V200% for breast tissue. The skin contour encompassed an area 5mm from the surface of the breast and the maximum dose was evaluated using D0. 1cc.The change in catheter lengths, as measured by Bravos, were recorded for each fraction of a patient's treatment. The following results show single fraction changes between the original clinically delivered plan and the re-plan which does not consider catheter lengthening by the amount measured by Bravos prior to the second fraction) averaged over all 14 cases. The average reductions in the V95% of the cavity 1.0 and V90% of the cavity 1.5 structures were -0.49±0.99% and -2.93±2.85%, respectively. Negligible changes in normal tissue dose were observed with an average increase in the V200% and V150% for the body of 0.09±0.16% and 0.37±0.48%, respectively. The average change in the skin D0.1cc were 3.37±3.90Gy. The max increase in skin D0.1cc was11.43Gy corresponding to a case in which the lumpectomy cavity abutted the skin surface. In another case, the skin D0.1cc was reduced by 72.3cGy in which the cavity was located distally to the tips of the catheters. The average change in catheter lengths between the first and second fractions amongst all patients was 3.95±1.13mm with a max single catheter lengthening of 6mm. Pre-treatment applicator length measurements are advised when the target is proximal to the skin surface to prevent late toxicities. However, such measurements may be redundant following the first fraction in cases in which the target is located medially or distally to the surface of the breast. Catheter lengthening following implantation generally peaks 24h after the implant. In general, the degree of lengthening increases with increasing lumpectomy cavity (breast) volume. [ABSTRACT FROM AUTHOR]

It is important to have accurate information regarding the dose distribution for treatment planning and to accurately deposit that dose in the tissue surrounding the brachytherapy source. However, the practical measurement of dose distribution for various reasons is associated with several problems. In this study, 6711 I-125, Micro Selectron mHDR-v2r Ir-192, and Flexisource Co-60 sources were simulated using the MCNP5 Monte Carlo method. To simulate the sources, the exact geometric characteristics of each source, the material used in them, and the energy spectrum of each source were entered as input to the program, and finally, the dosimetric parameters including dose rate constant, radial dose function, and anisotropy function were calculated for considered seeds according to AAPM, TG-43 protocol recommendation. Results obtained for dosimetric parameters of dose rate constant, radial dose function, and anisotropy function for I-125, Ir-192, and Co-60 sources agreed with other studies. According to the good agreement obtained between the parameters of TG43 and other studies, now these datasets can be used as input in the treatment planning systems and to validate their calculations. [ABSTRACT FROM AUTHOR]

The rise of image guided adaptive brachytherapy (IGABT) in combination with advances in inverse optimization tools has led to improved plan quality via utilization of rich 3D patient-specific anatomical information. The necessity to generate directional "anisotropic" radiation beam for better conformance of dose distributions to target volumes while integrating seamlessly into existing IGABT clinical workflows is apparent. The novel MR-compatible Direction Modulated Brachytherapy (DMBT) tandem applicator accomplishes this by using a six-peripheral-source-channel design. In this study, the authors sought to validate the implementation of 9 unique DMBT tandem models of varying physical dimensions integrated for the first time into the BrachyVision® (v16.1) treatment planning system (BV-TPS). Additionally, the authors quantify the expected improvement in plan quality via organs at risk (OAR) dose reductions from a large cohort of patient cases collected from three institutions. A multi-institutional cohort of 110 retrospective clinical HDR brachytherapy plans (from 42 patients) were re-planned with BV-TPS, using the latest VEGO® inverse optimization algorithm, with dose heterogeneity accounted for through the AcurosBV® model-based dose calculation algorithm. Plans consisted of both intracavitary (77 plans) and interstitial (33 plans) cases with an average prescription dose of 607±113 cGy. The average high-risk clinical target volume (CTV HR) was 26.96±14.95 [range 6.70-69.58] cm3. The 9 DMBT tandem models were designed with a MR-compatible tungsten alloy with thicknesses comparable to those tandems used clinically and ranged between 4-8 mm. During re-planning, the conventional tandems were replaced by one of the 9 DMBT tandem models while leaving ovoids/rings and needles (if present) in place. The two-step inverse optimization was performed such that the lowest possible OAR D2cc doses could be achieved while 1) keeping equivalent target coverage and, at the same time, 2) maintaining the general pear-shape dose distribution of the original plans. For all plans, this process was repeated using each of the 9 DMBT tandem models for a total re-planning of 990 cases. Noteworthy improvements in plan quality were achieved by all 9 DMBT tandem models, which are presented in Figure 1A. In general, irrespective of the DMBT model, about ∼50 cGy reduction in D2cc across all OARs appear feasible. There is also a general trend of D2cc reductions' magnitude getting smaller as the CTV HR volume increased (Figure 1B), as expected, due to the loss of intensity modulation capacity with increasing distance away from the tandem. Additionally, D2cc reductions in terms of EQD2 [Gy] were calculated assuming each re-plan was delivered throughout the course of treatment (Figure 1C), which includes the external beam radiotherapy dose of 45 Gy, and showed significant reductions of -6.29±4.38 Gy, -3.80±2.06 Gy, and -4.86±3.02 Gy for bladder, rectum, and sigmoid, respectively, for the DMBT model #9. These reductions were achieved with an average net increase in total dwell times of 87.99±71.41 seconds, i.e., typically adding 1-2 minutes of treatment time per fraction. We have successfully incorporated 9 DMBT tandem models into a commercial TPS and re-planned 110 cases, to a total of 990 plans. All 9 DMBT tandem models were each able to generate notable D2cc reductions to OARs (∼50 cGy), without compromising target coverage, across plans from multiple institutions with various clinical/optimization practices. The results indicate both a promising impact and smooth integration of DMBT tandem technology into modern clinical IGABT workflow. [ABSTRACT FROM AUTHOR]

There are no standard guidelines for optimal needle insertion/placement during high-dose-rate (HDR) intracavitary-interstitial (IC-IS) brachytherapy of the cervix. Therefore, sophisticated technical skillset must be acquired through repeated practice of inserting IS needles next to IC applicators to enhance dosimetry of improving target coverage while limiting dose to organs at risk (OARs). This study sought to evaluate potential of two direction modulated brachytherapy (DMBT) tandem applicators combined with one DMBT ovoids of unique designs to effectively removing the need for IS needles in a range of IC-IS cases found in multi-institutional clinics via achieving equivalent or better dosimetry. A cohort of 32 retrospective clinical HDR brachytherapy plans, from three institutions, were re-planned with Varian's BrachyVision® (v16.1) treatment planning system (BV-TPS), using the latest VEGO® inverse optimization algorithm, with dose heterogeneity accounted for through the AcurosBV® model-based dose calculation algorithm. All plans consisted of IC-IS cases, with a range of 2-4 freehand-loaded needles, with an average prescription dose of 709±53 cGy. The average high-risk clinical target volume (HRCTV) was 36.7±17.1 [range 9.8-69.6] cm3. Two unique DMBT tandem models of 5.4- and 8.0-mm thicknesses along with a novel DMBT ovoids design, introduced for the first time here, with 9 equi-angled grooves and 10-mm-diameter width (30 mm length) were integrated for the first time into the BV-TPS. During re-planning, the conventional tandems, ovoids/rings (20 ovoids & 12 rings cases), and all of the needles were replaced by one of the two DMBT tandem models and the one-and-only DMBT ovoids model. A two-step inverse optimization process was performed such that the lowest possible OAR D2cc doses could be achieved while 1) keeping equivalent target coverage (ΔHRCTV-D90 to within ±0.5%) and, at the same time, 2) maintaining the general pear-shape dose distribution of the original plans. For all plans, this process was repeated using each of the two DMBT tandem-ovoids combinations for a total re-planning of (32×2=) 64 cases. Average ΔHRCTV-D90 was +4.3±2.9 cGy. Significant improvements in plan quality were achieved by combining the DMBT tandem-and-ovoids despite not using the IS needles (Figure 1A). On average, -47.15±29.61 (-40.40±34.90) cGy, -42.98±26.58 (-41.70±27.40) cGy, and -40.47±25.05 (-32.55±25.30) cGy reductions in D2cc across bladder, rectum, and sigmoid, respectively, were achieved for the 8-mm (5.4-mm) DMBT tandem-and-ovoids combinations while maintaining equivalent D90 target coverage as the original IC-IS plans. Additionally, D2cc reductions in terms of EQD2 [Gy] were calculated assuming each re-plan was delivered throughout the course of treatment (Figure 1C), which includes the external beam radiotherapy dose of 45 Gy, and showed significant reductions of -4.05±2.47 (-3.37±2.83) Gy, -2.71±1.79 (-2.59±1.74) Gy, and -3.27±1.96 (-2.65±2.06) Gy for bladder, rectum, and sigmoid, respectively. These reductions were achieved with an average net increase in total dwell times of 241.0±87.6 seconds (i.e., 4-5 minutes) at the luxury of avoiding IS needles to insert. We have successfully incorporated two DMBT tandems and one ovoids models into a commercial TPS and re-planned 32 cases, to a total of 64 plans. According to the results, it is clinically feasible to replace the conventional IC-IS cases, with 2-4 freehand-loaded needles, with the DMBT tandem-and-ovoids technology, effectively avoiding the need for IS needles. [ABSTRACT FROM AUTHOR]

Toxicity from cervical cancer brachytherapy for bladder and rectum has been demonstrated to have positive correlation with the DVH parameter D2cc. Simplified knowledge-based planning with a linear relationship between overlap distance and the D2cc has been demonstrated to predict D2cc and aid optimization for standard cervix brachytherapy. This work demonstrates the feasibility of knowledge-based planning to predict the D2cc, detect suboptimal plans, and improve the plan quality with Direction Modulated Brachytherapy (DMBT) six groove tandem with ovoid (T&O) or ring (T&R) applicators. This study employed the overlap volume histogram (OVH) method to determine the distance for 2cc of overlap between the Organ at Risk (OAR) and High-Risk Clinical Target Volume (CTV HR). Linear plots were utilized to model the OAR D2cc and 2cc overlap distance. Two datasets from 40 patients (110 plans) were used to create two independent models, and the performance of each model was evaluated using fivefold cross-validation. Those plans were randomly divided into 60:40 as training, and testing cohorts respectively. The performance metrics from conventional tandem applicator were calculated and applied as a baseline for direction modulated brachytherapy tandem (DMBT) applicator to predict D2cc. Doses were normalized to ensure consistent CTV HR D90 values. The predicted D2cc was incorporated as the maximum constraints in the inverse planning algorithm for conventional tandem applicator and AcurosBV® model-based dose calculation algorithm (MBDCA) for DMBT applicator in brachy vison treatment planning system. Mean Bladder D2cc decreased by 4.29% and 10.31% for conventional tandem applicator and 4.35%, 3.64% for DMBT tandem applicator from model 1 and model 2 respectively. Mean rectum D2cc decreased by 3.42% and 10.73% for conventional applicator and 2.96%, 4.98% for DMBT tandem applicator, mean sigmoid D2cc decreased by 3.07% and 6.85% in case of conventional applicator and 3.17% and 5.89% in case of DMBT tandem applicator for model1 and model 2 respectively. In addition, mean point dose for recto-vaginal decreased by 14.04% and 16.49% in the case of conventional tandem applicator,1.39% and 6.26% in case of DMBT tandem applicator from model 1 and 2 respectively. Similarly, for posterior-inferior border of symphysis (PIBS), PIBS+2, PIBS+1, PIBS-1, PIBS-2 decreased in the range of (11-16) % and (9-13) % in case of conventional tandem applicator, (1-3) % and (1-4)% for DMBT applicator from model 1 and model 2 respectively. A simplified knowledge-based planning method was used to predict D2cc and was able to automate optimization of brachytherapy plans for locally advanced cervical cancer. The proposed model demonstrates the feasibility of predicting D2cc, detect suboptimal plans, and improve the plan quality. This becomes particularly crucial for a novel technology like DMBT where there is lack of cumulative clinical experience. [ABSTRACT FROM AUTHOR]

Direction modulated brachytherapy creates anisotropic dose distribution from an isotropic source. Every dwell position has a unique dose distribution. This study aims to develop a truncated conditional value at risk optimization algorithm for Direction Modulated Brachytherapy (DMBT) six groove tandem with ovoid (T&O) or ring (T&R) applicators. This study employed the new optimization algorithm that uses mean dose of the DVH metrics tails. The mean dose approach is called conditional value at risk (CvaR), and unfortunately produces worse DVH metrics. The improved upon the CvaR approach so called Truncated CvaR (TCVaR) was used, by excluding the hottest and coldest voxels in the structure from the calculation of the mean dose of the tail. A library of plans was created to span Pareto surfaces over 15% ranges of doses in each of the four DVH metrics for cervical treatment site. The cervix treatment site, with 66 dwells, included HRCTV D90%, bladder, rectum, and sigmoid D2cc metrics, and the surface dose for the cervix ovoid structure was constrained to at most 200% of the prescription dose. The initial plan was used to initialize the construction of the pareto surface as a clinically delivered treatment. The clinical plan was created in a commercial treatment planning system, with AcurosBV® model-based dose calculation algorithm (MBDCA) in brachy vison treatment planning system (BVTPS). Thus, the new optimization algorithm gives the HRCTV D90% 7.76Gy, D2cc bladder 3.96 Gy, D2cc Rectum 0.82 Gy, and D2cc Sigmoid 2.04 Gy, in comparison with the BVTPS HRCTV D90% 5.12 Gy, D2cc bladder 2.97 Gy, D2cc rectum 0.49 Gy and D2cc sigmoid 1.44 Gy. A new optimization algorithm for DMBT applicator may produce plans with superior DVH metrics compared with BVTPS. The algorithm may be computationally efficient and has potential applications to DMBT applicator which has anisotropic dose distribution. [ABSTRACT FROM AUTHOR]

There are no standard guidelines for optimal needle insertion/placement during high dose-rate (HDR) intracavitary-interstitial (IC-IS) brachytherapy of the cervix. Therefore, sophisticated technical skillset must be acquired through repeated practice of inserting IS needles next to IC applicators to enhance dosimetry of improving target coverage while limiting dose to organs at risk (OARs). This study sought to evaluate potential of nine direction modulated brachytherapy (DMBT) tandem applicator models of unique designs to effectively removing the need for IS needles in a range of IC-IS cases found in multi-institutional clinics via achieving equivalent or better dosimetry. A cohort of 33 retrospective clinical HDR brachytherapy plans, from three institutions, were re-planned with Varian's BrachyVision® (v16.1) treatment planning system (BV-TPS), using the latest VEGO® inverse optimization algorithm, with dose heterogeneity accounted for through the AcurosBV® model-based dose calculation algorithm. All plans consisted of IC-IS cases, with a range of 2-4 freehand-loaded needles, with an average prescription dose of 706±54 cGy. The average high-risk clinical target volume (HRCTV) was 36.0±17.4 [range 9.8-69.6] cm3. Nine unique DMBT tandem models of varying physical dimensions were integrated for the first time into the BV-TPS, with thicknesses comparable to those tandems used clinically and ranged between 4-8 mm. During re-planning, the conventional tandems and all of the needles were replaced by one of the 9 DMBT tandem models while leaving the ovoids/rings in place. A two-step inverse optimization process was performed such that the lowest possible OAR D2cc doses could be achieved while 1) keeping equivalent target coverage (ΔHRCTV-D90 to within ±0.5%) and, at the same time, 2) maintaining the general pear-shape dose distribution of the original plans. For all plans, this process was repeated using each of the 9 DMBT tandem models for a total re-planning of (33×9=) 297 cases. Average ΔHRCTV-D90 was +2.8±3.1 cGy. Reductions in D2cc for the OARs for most of the plans were achieved by all 9 DMBT tandem models, which are shown in Figure 1A, with the magnitude increasing with the DMBT tandem thickness (from #1-9). The performance of the thickest DMBT model (#9, with 8 mm) was the best in terms of achieving the lowest D2cc for all OARs. For this particular model, 31 out of 33 plans (94%) had achieved lower D2cc doses for all three OARs. The two cases where the D2cc doses could not be lowered, compared to the original plans, had HRCTV volumes of about 50 cm3 and 60 cm3 (Figure 1b-c). Additionally, D2cc reductions in terms of EQD2 [Gy] were calculated assuming each re-plan was delivered throughout the course of treatment (Figure 1C), which includes the external beam radiotherapy dose of 45 Gy, and showed significant reductions of -2.64±2.67 Gy, -1.65±1.97 Gy, and -2.80±2.20 Gy for bladder, rectum, and sigmoid, respectively, for the DMBT model #9. These reductions were achieved with an average net increase in total dwell times of 173.8±58.5 seconds (i.e., 3-4 minutes) at the luxury of avoiding IS needles to insert. We have successfully incorporated 9 DMBT tandem models into a commercial TPS and re-planned 33 cases, to a total of 297 plans. According to the results, it is clinically feasible to replace the conventional IC-IS cases, with 2-4 freehand-loaded needles, with the DMBT tandem technology, effectively avoiding the need for IS needles. [ABSTRACT FROM AUTHOR]

In brachytherapy, there are inherent risks and challenges due to patient anatomical changes and inaccuracies in radiation source placement, leading to dose deviations from the planned dose. Observed discrepancies in dose delivery can range from minor variations to significant overages of more than 100%. The introduction of plastic and inorganic scintillators in our project, with their high readout frequency, realizes real-time in-vivo dosimetry, enabling the immediate identification and correction of dose delivery errors. Our study employed the TG-43 protocol for dose calculation in brachytherapy. The proof-of-concept experimental setup involved the Exradin W2MR Scintillator System (Standard Imaging; Madison, WI, USA), a cubic phantom with parallel cylindrical holes at varying distances, the BRAVOS™ afterloader system (Varian, Palo Alto, California, U.S.), and threaded female hub closed-end disposable needles (Alpha-Omega services, Inc; Bellflower, CA, USA). Preliminary phantoms, featuring 20% PLA infill density, were designed with parallel spiral channels in Autodesk Fusion 360 (Figure 1B). This design specifically aimed to prevent air gaps between the detector and source channels. They were printed using an in-house 3D printer, the 3D40 (Dremel; Mount Prospect, IL, USA), as shown in Figure 1A. Two treatment plans were created using Varian TPS software (Varian Medical Systems, Inc., Palo Alto, CA, USA). The first plan involved a single 5-second dwell at the nearest point within a channel 8mm from the detector, while the second plan consisted of 5-second dwells every 5mm at the same channel. The first plan aimed to capture sufficient signal, while the second focused on recording a staircase signal to determine dwell times and positions. The measurements were conducted in an HDR procedure room, with the W2MR detector inserted into its channel and connected to the Max SD device, and the afterloader connected to a needle inserted in a channel 8mm away. The detector registered a charge of 308.08 pC over 5.83s. This measurement's limitation was the Extradin W2MR System's trigger setting, which records the signal before the source reaches and after it leaves the dwell position. Another limitation of the detector is its inability to record instantaneous charge rates, hindering the capture of the staircase signal. Our experimental setup proved the feasibility of capturing relevant dosimetric data for the upcoming measurements with the BluePhysics detector. Although the limitations identified in our proof-of-concept setup, specifically the detector's inability to record instantaneous charge rates, prevented us from extracting the dwell times and positions from the staircase signal, the groundwork has been laid for further developments. With this foundation, the BluePhysics detector is poised to enhance the precision of our measurements. [ABSTRACT FROM AUTHOR]