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Introduction: In vivo dosimetry (IVD) can be used for source tracking (ST), i.e., estimating source positions, during brachytherapy. The aim of this study was to exploit IVD-based ST to perform 3D dose reconstruction for high-dose-rate prostate brachytherapy and to evaluate the robustness of the treatments against observed geometric variations., Materials and Methods: Twenty-three fractions of high-dose-rate prostate brachytherapy were analysed. The treatment planning was based on MRI. Time-resolved IVD was performed using a fibre-coupled scintillator. ST was retrospectively performed using the IVD measurements. The ST identified 2D positional shifts of each treatment catheter and thereby inferred updated source positions. For each fraction, the dose was recalculated based on the source-tracked catheter positions and compared with the original plan dose using differences in dose volume histogram indices., Results: Of 352 treatment catheters, 344 had shifts of less than 5 mm. Shifts between 5 and 10 mm were observed for 3 catheters, and shifts greater than 10 mm for 2 catheters. The ST failed for 3 catheters. The maximum relative difference in clinical target volume (prostate + 3 mm isotropic margin) D 90% was 5%. In one fraction, the bladder D 2cm 3 dose increased by 18% (1.4 Gy) due to a single source position being inside the bladder rather than nearby as planned. The max increase in urethra dose was 1.5 Gy (15%)., Conclusion: IVD-based 3D dose reconstruction for high-dose-rate prostate brachytherapy is feasible. The dosimetric impact of the observed catheter shifts was limited. Dose reconstruction can therefore aid in determining the dosimetric impact of geometric variations and errors in brachytherapy., Competing Interests: Conflict of interest Nothing to report., (Copyright © 2022. Published by Elsevier B.V.)

Purpose: To characterize and report on dosimetric outcomes of image guided adaptive brachytherapy (IGABT) using intracavitary and interstitial (IC/IS) applicators including oblique needles (O-needles) in locally advanced cervical cancer (LACC)., Methods and Materials: Twenty LACC patients treated with radio-chemotherapy and offered IC/IS-IGABT including O-needles were analyzed. An in-house 3D-printed vaginal template was used to steer the needles parallel and obliquely in relation to the tandem, supplemented with free-hand needles if needed. Implant characteristics and loading patterns were analyzed. Using the equivalent dose in 2Gy-fractions (EQD2) concept, cumulative (EBRT+BT) V85, V75, V60Gy, targets/OARs doses and high dose volumes (150%, 200% and 300% (100% = 85 Gy EQD2 10 )) were evaluated., Results: Median(range) tumor width at diagnosis was 5.5(3.6; 7.5)cm; CTV HR volume was 45(23; 136)cm 3 with maximum distance from tandem to CTV HR border of 3.4(2.5; 4.8)cm. T-stage distribution was IIB/III/IVA in 6(30%)/9(45%)/5(25%) of patients. At BT, 13(65%) patients had distal parametrial/pelvic wall infiltration. Median(range) number of needles per patient was 11(8-18). Average distribution of intrauterine, vaginal and interstitial dwell times were 31%, 25% and 44%, respectively. Median(range) dwell-time per dwell position was 11(2-127)% of average point-A based standard loading. Median V 85Gy /V 150% /V 200% /V 300% were 85(38; 171)/41(21; 93)/22(12; 41)/7(4; 19) cm 3 ; CTV HR D 90% was 93(83; 97)Gy EQD2 10 ; bladder/rectum/sigmoid/bowel D 2cm3 were 78(64; 104)/65(52; 76)/59(53; 69)/61(47; 76)Gy EQD2 3 ., Conclusions: The use of O-needles in patients with large and/or unfavorable tumors resulted in excellent target coverage and OARs sparing. Intrauterine and vaginal loadings were reduced compared to standard loading and almost half of the loading was shifted into IS needles. This was achieved with gentle loading in the majority of dwell positions., (Copyright © 2021 American Brachytherapy Society. All rights reserved.)

Purpose: To report on the accuracy of an in vivo dosimetry (IVD)-based source tracking (ST) method for high dose rate (HDR) prostate brachytherapy (BT)., Methods: The ST was performed on a needle-by-needle basis. A least square fit of the expected to the measured dose rate was performed using the active dwell positions in the given needle. Two fitting parameters were used to determine the position of each needle relative to the IVD detector: radial (away or toward the detector) and longitudinal (along the axis of the treatment needle). The accuracy of the ST was assessed in a phantom where the geometries of five HDR prostate BT treatments previously treated at our clinic were reproduced. For each of the five treatment geometries, one irradiation was performed with the detector placed in the middle of the implant. Furthermore, four additional irradiations were performed for one of the geometries where the detector was retracted caudally in four steps of 10-15 mm and up to 12 mm inferior of the most inferior active dwell position, which represented the prostate apex. The time resolved dose measurements were retrieved at a rate of 20 Hz using a detector based on an Al 2 O 3 :C radioluminescence crystal, which was placed inside a standard BT needle. Individual calibrations of the detector were performed prior to each of the nine irradiations., Results: Source tracking could be applied in all needles across all nine irradiations. For irradiations with the detector located in the middle region of the implant (a total of 89 needles), the mean ± standard deviation (SD, k = 1) accuracy was -0.01 mm ± 0.38 mm and 0.30 mm ± 0.38 mm in the radial and longitudinal directions, respectively. Caudal retraction of the detector did not lead to reduced accuracy as long as the detector was located superior to the most inferior active dwell positions in all needles. However, reduced accuracy was observed for detector positions inferior to the most inferior active dwell positions which corresponded to detector positions in and inferior to the prostate apex region. Detector positions in the prostate apex and 12 mm inferior to the prostate resulted in mean ± SD (k = 1) ST accuracy of 0.7 mm ± 1 mm and 2.8 mm ± 1.6 mm, respectively, in radial direction, and -1.7 mm ± 1 mm and -2.1 mm ± 1.1 mm, respectively, in longitudinal direction. The largest deviations for the configurations with those detector positions were 2.6 and 5.4 mm, respectively, in the radial direction and -3.5 and -3.8 mm, respectively, in the longitudinal direction., Conclusion: This phantom study demonstrates that ST based on IVD during prostate BT is adequately accurate for clinical use. The ST yields submillimeter accuracy on needle positions as long as the IVD detector is positioned superior to at least one active dwell position in all needles. Locations of the detector inferior to the prostate apex result in decreased ST accuracy while detector locations in the apex region and above are advantageous for clinical applications., (© 2021 American Association of Physicists in Medicine.)

Purpose: This paper presents a method to verify dwell times during High Dose Rate (HDR) Brachytherapy (BT) by means of in vivo dosimetry (IVD), and reports on an afterloader's stability in dwell time control., Methods: In vivo dosimetry was performed during 20 HDR prostate cancer treatments using a point detector based on a radio-luminescence crystal (Al 2 O 3 :C) coupled to a fiber-optic cable. The dose rate was recorded at either 10 Hz or 20 Hz during the treatments. The "time of transit" when the source moved between two dwell positions was identified using the difference in count rate between two measurements. The dwell times were then determined by subtracting two adjacent times of transit. The measured dwell times were matched with the planned dwell times and categorised into two groups: Dwell times matching a single dwell position (identified) and dwell times matching the sum of multiple dwell positions (unidentified). Deviations between measured and planned dwell times were calculated for the identified dwell positions., Results: A total of 3518 dwell positions were analysed. The amount of identified dwell positions were 82%, which increased to 89% if the short dwell times (<1 s) were omitted in the analysis. The largest deviation was -0.4 s seen for a single dwell position, and in 97.1% of the cases, the deviations were <0.15 s., Conclusion: The dwell times in BT are well controlled by the afterloader. It is shown that IVD facilitates the detection of dwell time offsets that could have a clinical impact., (Copyright © 2019 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)

Purpose: The purpose of this article is to demonstrate that brachytherapy source tracking can be realized with in vivo dosimetry. This concept could enable real-time treatment monitoring., Methods: In vivo dosimetry was incorporated in the clinical routine during high-dose-rate prostate brachytherapy at Aarhus University Hospital. The dosimetry was performed with a radioluminescent crystal positioned in a dedicated brachytherapy needle in the prostate. The dose rate was recorded every 50-100 ms during treatment and analyzed retrospectively. The measured total delivered dose and dose rates for each dwell position with dwell times >0.7 s were compared with expected values. Furthermore, the distance between the source and dosimeter, which was derived from the measured dose rates, was compared with expected values. The measured dose rate pattern in each needle was used to determine the most likely position of the needle relative to the dosimeter., Results: In total, 305 needles and 3239 dwell positions were analyzed based on 20 treatments. The measured total doses differed from the expected values by -4.7 ± 8.4% (1SD) with range (-17% to 12%). It was possible to determine needle shifts for 304 out of 305 needles. The mean radial needle shift between imaging and treatment was 0.2 ± 1.1 mm (1SD), and the mean longitudinal shift was 0.3 ± 2.0 mm (1SD)., Conclusion: Time-resolved in vivo dosimetry can be used to provide geometric information about the treatment progression of afterloading brachytherapy. This information may provide a clear indication of errors and uncertainties during a treatment and, therefore, enables real-time treatment monitoring., (Copyright © 2017 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.)

Purpose: To investigate the reproducibility of virtually planned needles, changes in DVH parameters and clinical feasibility of combined intracavitary/interstitial (IC/IS) pulsed dose rate brachytherapy (PDR-BT) for locally advanced cervical cancer based on 3D MRI preplanning., Material and Methods: Fifty-eight consecutively patients accrued in the EMBRACE study were included. Treatment was initiated with external beam radiotherapy and cisplatin. Three BT implants and MRI with the applicator in situ were performed in all patients, i.e. week 5 (BT0), week 6 (BT1) and week 7 (BT2) of the treatment. BT0 was only used for preplanning of subsequent implantations, whereas BT1 and BT2 comprised 2 equal sized fractions of PDR BT., Results: Based on BT0, 24 patients (41%) were selected for a combined IC/IS implant at BT1 and BT2. Patients treated with IC/IS BT had significantly larger tumours compared with patients treated with IC BT only (p<0.03). Additional time in general anaesthesia for the IC/IS component was on average 16 min. The number of preplanned virtual needles was 5.3±2.7 compared to 5.3±2.9 and 5.4±3.0 needles implanted at BT1 and BT2, respectively (p=0.72). Planned needle implantation depth was 33±15 mm compared to 30±10 mm at BT1 and 29±11 mm at BT2 (p=0.04). In the 24 patients selected for IC/IS BT both the virtual IC/IS plan (BT0) and the actually delivered plan (BT1+BT2) significantly increased D90 and D100 for HR CTV (p<0.01) and reduced D2cc for sigmoid (p<0.01) and bowel (p=0.04) compared to the optimised IC preplan (BT0). IC/IS BT was only associated with minor morbidity, which was resolved at a 3-month follow up., Conclusion: Combined IC/IS BT based on full 3D MRI preplanning is clinically feasible. The virtual preplanned needle positions are reproducible at subsequent BT applications leading to significantly improved DVH parameters and a clinically feasible and fast implant procedure., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)