The brachytherapy applicator was implanted under analgosedation. Routinely, the Rotte applicator was used, if feasible. Alternatively, individual flexible catheters, the ring applicator, or a colpostate with intrauterine tube were applied. A treatment-planning CT scan using a 64-slice CT scanner with uniform slice thickness of 1.5/3.0 mm was performed with the patient in supine position. Treatment planning was performed using PLATO (Nucletron, Veenendaal, The Netherlands) until 2010 and Oncentra Brachy (Nucletron, now Elekta AB, Stockholm, Sweden) afterwards. The entire uterus and cervix were contoured as the clinical target volume (CTV). Organs-at-risks (OARs) were delineated, including the rectum and bladder, as well as the sigmoid and bowel, if required. An HDR-brachytherapy afterloading system with Iridium-192 (microSelectron, Nucletron, now Elekta until 2017 and Flexitron, Elekta afterwards) was utilized for treatment delivery. Dose was prescribed to an isodose line that covered the uterine serosa and cervix.
Flexitron
Manufactured by Elekta
The Flexitron is a high-dose-rate (HDR) brachytherapy afterloader produced by Elekta. It is designed to deliver targeted radiation therapy to treat various types of cancer. The Flexitron is used to remotely control and position a radioactive source for the delivery of brachytherapy treatments.
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Lab products found in correlation
5 protocols using flexitron
1
HDR Brachytherapy Procedural Protocol for Cervical Cancer
2
Brachytherapy Dosimetry in Rat Model
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Rats were irradiated using brachytherapy. The radioactive source (Ir-192) was connected to an afterloader system (Elekta Flexitron), which places the source in the right position inside the rat for a short time. The correct positioning of the catheter implanted in the rats with regard to the target region was verified using a computed tomography (CT) scan (Siemens Sensation 16).
The scanning protocol is shown inTable 1 :
The CT images (Figure S3 ) were used to design a treatment plan to give the desired radiation dose to the target zone, minimizing dose application to non-target sites, by using specically designed software (Oncentra v4.5.2). This program calculates the stop positions and the time spent with the source to reach the required dose radiation distribution in the target zone and the rest of the body. The plan was designed to give at least 8 Gy to the target volume delimited in the CT. Once the treatment design was finished, all the necessary data were digitally transferred to the afterloader system. On the day of irradiation, the catheter implanted in the rat was connected to this system and the treatment was begun.
The scanning protocol is shown in
The CT images (
3
Vaginal Brachytherapy Dose and Technique
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Vaginal applicator diameter ranged from 2.0 to 3.5 cm (median 3 cm). OncentraBrachy treatment planning system and MicroSelectron (Elekta, Stockholm, Sweden) device with a 192-Ir source were used to plan and treat the first cohort of patients (cohort 1–C1), respectively. The proximal third of the vagina was irradiated with a HDR-IRT schedule based on 21 Gy in three weekly fractions (7 Gy) prescribed 0.5 cm from the applicator surface. OncentraBrachy treatment planning system and a Flexitron (Elekta, Stockholm, Sweden) device with a 192-Ir source were used to treat the second cohort of patients (cohort 2 – C2). The upper 3 cm of the vagina was irradiated by a HDR-IRT schedule of 6 Gy per fraction/weekly (total dose 24 Gy) prescribed 0.5 cm from the applicator surface.
4
Quantifying HDR Source Air Kerma Strength
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The air‐Kerma strength parameter that is updated within the TPS (Oncentra Prostate) reflects the source strength measured under the conditions of the calibration at the time of the source exchange. Any source or applicator differences from the initial calibration setup could lead to discrepancies in the dose rate. Therefore, the impact of the stainless steel interstitial needles on the resulting air Kerma strength was quantified relative to the measured air‐Kerma strength within a plastic catheter, which is the conventional applicator that is used to measure the source strength at the time of a source exchange.
The air‐Kerma strength of the 192IrHDR source was measured using the Flexitron (Elekta AB, Inc.) afterloader and current Flexisource 192Ir source (Elekta AB, Inc.) using the conventional plastic catheter and interstitial needle. Measurements were carried out using an HDR 1000 Plus well‐type ionization chamber (Standard Imaging, Inc.) and a CDX‐2000B electrometer (Standard Imaging, Inc.). Sweet spot determinations were initially carried out for each catheter by displacing the source position within the chamber to map out the sensitivity profile. Temperature, pressure, electrometer, and calibration coefficients were applied to the final current readings to determine the measured air‐Kerma strength of the source delivered among the two applicators.
The air‐Kerma strength of the 192IrHDR source was measured using the Flexitron (Elekta AB, Inc.) afterloader and current Flexisource 192Ir source (Elekta AB, Inc.) using the conventional plastic catheter and interstitial needle. Measurements were carried out using an HDR 1000 Plus well‐type ionization chamber (Standard Imaging, Inc.) and a CDX‐2000B electrometer (Standard Imaging, Inc.). Sweet spot determinations were initially carried out for each catheter by displacing the source position within the chamber to map out the sensitivity profile. Temperature, pressure, electrometer, and calibration coefficients were applied to the final current readings to determine the measured air‐Kerma strength of the source delivered among the two applicators.
5
Intraluminal HDR Brachytherapy for Rectal Cancer
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A week after completion of external beam RT, patients received 192Ir source HDR-BRT with two fractions of 4 Gy prescribed to a 0.5 cm depth from the mucosal surface weekly. Patients were sedated with 2 mg midazolam before each treatment session. Brachytherapy was done in the lateral decubitus position, and digital rectal exam was performed to evaluate the location of tumor and to select the best diameter for intra-luminal cylinder. A rigid single-channel cylinder with 2 or 2.5 cm diameter was chosen according to patient’s anatomy and comfort. The length of cylinder was determined following pre-treatment MRI or EUS staging, with a 2 cm proximal and distal margin. The length and width of the cylinder in both fractions were the same. All treatment planning was performed with the aid of Flexiplan (ELEKTA AB, Stockholm, Sweden). Moreover, all patients were treated using the same brachytherapy unit (Flexitron, ELEKTA, AB, Stockholm, Sweden).
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