Calibration system correction factor for measuring the reference air kerma rate (RAKR) applied to high dose rate192Ir sources (HDR).

The aim of this study was to use computer simulation to analyze the impact of the aluminum fixing support on the Reference Air Kerma (RAK), a physical quantity obtained in a calibration system that was experimentally developed in the Laboratory of Radiological Sciences of the University of the State of Rio de Janeiro (LCR-UERJ). Correction factors due to scattered radiation and the geometry of the192Ir sources were also sought to be determined. The computational simulation was validated by comparing some parameters of the experimental results with the computational results. These parameters were: verification of the inverse square law of distance, determination of (RAKR), analysis of the source spectrum with and without encapsulation, and the sensitivity curve of the Sourcecheck 4PI ionization chamber response, as a function of the distance from the source along the axial axis, using the microSelectron-v2 (mSv2) and GammaMedplus (GMp) sources. Kerma was determined by activity in the Reference air, with calculated values of 1.725 × 10-3U. Bq-1and 1.710 × 10-3U. Bq-1for the ionization chamber NE 2571 and TN 30001, respectively. The expanded uncertainty for these values was 0.932% and 0.919%, respectively, for a coverage factor (k = 2). The correction factor due to the influence of the aluminum fixing support for measurements at 1 cm and 10 cm from the source was 0.978 and 0.969, respectively. The geometric correction factor of the sources was ksg= 1.005 with an expanded uncertainty of 0.7% for a coverage factor (k = 2). This value has a difference of approximately 0.2% compared to the experimental values.

Dosimetry of Large Field Valencia applicators for Cobalt-60-based brachytherapy.

BACKGROUND: Non-melanoma skin cancer is one of the most common types of cancer and one of the main approaches is brachytherapy. For small lesions, the treatment of this cancer with brachytherapy can be done with two commercial applicators, one of these is the Large Field Valencia Applicators (LFVA). PURPOSE: The aim of this study is to test the capabilities of the LFVA to use clinically 60Co sources instead of the 192Ir ones. This study was designed for the same dwell positions and weights for both sources. METHODS: The Penelope Monte Carlo code was used to evaluate dose distribution in a water phantom when a 60Co source is considered. The LFVA design and the optimized dwell weights reported for the case of 192Ir are maintained with the only exception of the dwell weight of the central position, that was increased. 2D dose distributions, field flatness, symmetry and the leakage dose distribution around the applicator were calculated. RESULTS: When comparing the dose distributions of both sources, field flatness and symmetry remain unchanged. The only evident difference is an increase of the penumbra regions for all depths when using the 60Co source. Regarding leakage, the maximum dose within the air volume surrounding the applicator is in the order of 20% of the prescription dose for the 60Co source, but it decreases to less than 5% at about 1 cm distance. CONCLUSIONS: Flatness and symmetry remains unaltered as compared with 192Ir sources, while an increase in leakage has been observed. This proves the feasibility of using the LFVA in a larger range of clinical applications.

Determination of the correction factors used in Fricke dosimetry for HDR 192Ir sources employing the Monte Carlo method.

PURPOSE: Fricke dosimetry has shown great potential in the direct measurement of the absolute absorbed dose for 192Ir sources used in HDR brachytherapy. This work describes the determination of the correction factors necessary to convert the absorbed dose in the Fricke solution to the absorbed dose to water. METHODS: The experimental setup for Fricke irradiation using a 192Ir source was simulated. The holder geometry used for the Fricke solution irradiation was modelled for MC simulation, using the PENELOPE. RESULTS: The values of the factors determined for validation purposes demonstrated differences of less than 0.2% when compared to the published values. Four factors were calculated to correct: the differences in the density of the solution (1.0004 ± 0.0004); the perturbations caused by the holder (0.9989 ± 0.0004); the source anisotropy and the water attenuation effects (1.0327 ± 0.0012); and the distance from the center of the detection volume to the source (7.1932 ± 0.0065). CONCLUSION: Calculated corrections in this work show that the largest correction comes from the inverse squared reduction of the dose due to the point of measurement shift from the reference position of 1 cm. This situation also causes the correction due to volume averaging and attenuation in water to be significant. Future versions of the holder will aim to reduce these effects by having a position of measurement closer to the reference point thus requiring smaller corrections.

Monte Carlo simulation of the effect of magnetic fields on brachytherapy dose distributions in lung tissue material.

The aim of this work was to use TOPAS Monte Carlo simulations to model the effect of magnetic fields on dose distributions in brachytherapy lung treatments, under ideal and clinical conditions. Idealistic studies were modeled consisting of either a monoenergetic electron source of 432 keV, or a polyenergetic electron source using the spectrum of secondary electrons produced by 192Ir gamma-ray irradiation. The electron source was positioned in the center of a homogeneous, lung tissue phantom (ρ = 0.26 g/cm3). Conversely, the clinical study was simulated using the VariSource VS2000 192Ir source in a patient with a lung tumor. Three contoured volumes were considered: the tumor, the planning tumor volume (PTV), and the lung. In all studies, dose distributions were calculated in the presence or absence of a constant magnetic field of 3T. Also, TG-43 parameters were calculated for the VariSource and compared with published data from EGS-brachy (EGSnrc) and PENELOPE. The magnetic field affected the dose distributions in the idealistic studies. For the monoenergetic and poly-energetic studies, the radial distance of the 10% iso-dose line was reduced in the presence of the magnetic field by 64.9% and 24.6%, respectively. For the clinical study, the magnetic field caused differences of 10% on average in the patient dose distributions. Nevertheless, differences in dose-volume histograms were below 2%. Finally, for TG-43 parameters, the dose-rate constant from TOPAS differed by 0.09% ± 0.33% and 0.18% ± 0.33% with respect to EGS-brachy and PENELOPE, respectively. The geometry and anisotropy functions differed within 1.2% ± 1.1%, and within 0.0% ± 0.3%, respectively. The Lorentz forces inside a 3T magnetic resonance machine during 192Ir brachytherapy treatment of the lung are not large enough to affect the tumor dose distributions significantly, as expected. Nevertheless, large local differences were found in the lung tissue. Applications of this effect are therefore limited by the fact that meaningful differences appeared only in regions containing air, which is not abundant inside the human.

Advanced design, simulation, and dosimetry of a novel rectal applicator for contact brachytherapy with a conventional HDR 192Ir source.

PURPOSE: Dose escalation yields higher complete response to rectal tumors, which may enable the omission of surgery. Dose escalation using 50 kVp contact x-ray brachytherapy (CXB) allow the treatment of a selective volume, resulting in low toxicity and organs-at-risk preservation. However, the use of CXB devices is limited because of its high cost and lack of treatment planning tools. Hence, the MAASTRO applicator (for HDR 192Ir sources) was developed and characterized by measurements and Monte Carlo simulations to be a cost-effective alternative to CXB devices. METHODS AND MATERIALS: A cylindrical applicator with lateral shielding was designed to be used with a rectoscope using its tip as treatment surface. Both the applicator and the rectoscope have a slanted edge to potentially allow easier placement against tumors. The applicator design was achieved by Monte Carlo modeling and validated experimentally with film dosimetry, using the Papillon 50 (P50) device as reference. RESULTS: The applicator delivers CXB doses in less than 9 min using a 20375 U source for a treatment area of approximately 20 × 20 mm2 at 2 mm depth. Normalized at 2 mm, the dose falloff for depths of 0 mm, 5 mm, and 10 mm are 130%, 70%, and 43% for the P50 and 140%, 67%, and 38% for the MAASTRO applicator, respectively. CONCLUSIONS: The MAASTRO applicator was designed to use HDR 192Ir sources to deliver a dose distribution similar to those of CXB devices. The applicator may provide a cost-effective solution for endoluminal boosting with clinical treatment planning system integration.

[Image-guided brachyablation for hepatocarcinoma. Report of one case]. / Image-Guided BrachyAblation (IGBA) en hepatocarcinoma. Descripción de la técnica y reporte del primer caso en Chile.

Eighty percent of hepatocarcinomas are inoperable at the moment of diagnosis. Liver transplantation is the treatment of choice in these cases, but local therapies are another alternative. Among these, Image-Guided BrachyAblation is a safe choice. We report a 76-year-old male with a hepatocarcinoma, who was considered inoperable due to the high surgical risk of the patient. A local treatment with Image-Guided BrachyAblation was decided. A brachytherapy needle was placed in the tumor under computed tomography guidance and a 15 Gy single dose was delivered from an Iridium-192 source. The patient had no immediate complications and at one month of follow up he continued without incidents.

Mechanical evaluation of the Bravos afterloader system for HDR brachytherapy.

PURPOSE: The Bravos afterloader system was released by Varian Medical Systems in October of 2018 for high-dose-rate brachytherapy with 192Ir sources, containing new features such as the CamScale (a new device for daily quality assurance and system recalibration), channel length verification, and different settings for rigid and flexible applicators. This study mechanically evaluated the Bravos system precision and accuracy for clinically relevant scenarios, using dummy sources. METHODS AND MATERIALS: The system was evaluated after three sets of experiments: (1) The CamScale was used to verify inter- and intra-channel dwelling variability and system calibration; (2) A high-speed camera was used to verify the source simulation cable movement inside a transparent quality assurance device, where dwell positions, dwell times, transit times, speed profiles, and accelerations were measured; (3) The source movement inside clinical applicators was captured with an imaging panel while being exposed to an external kV source. Measured and planned dwell positions and times were compared. RESULTS: Maximum deviations between planned and measured dwell positions and times for the source cable were 0.4 mm for the CamScale measurements and 0.07 seconds for the high-speed camera measurements. Mean dwell position deviations inside clinical applicators were below 1.2 mm for all applicators except the ring that required an offset correction of 1 mm to achieve a mean deviation of 0.4 mm. CONCLUSIONS: Features of the Bravos afterloader system provide a robust and precise treatment delivery. All measurements were within manufacturer specifications.

Image-Guided BrachyAblation (IGBA) en hepatocarcinoma: descripción de la técnica y reporte del primer caso en Chile / Image-guided brachyablation for hepatocarcinoma: report of one case

Eighty percent of hepatocarcinomas are inoperable at the moment of diagnosis. Liver transplantation is the treatment of choice in these cases, but local therapies are another alternative. Among these, Image-Guided BrachyAblation is a safe choice. We report a 76-year-old male with a hepatocarcinoma, who was considered inoperable due to the high surgical risk of the patient. A local treatment with Image-Guided BrachyAblation was decided. A brachytherapy needle was placed in the tumor under computed tomography guidance and a 15 Gy single dose was delivered from an Iridium-192 source. The patient had no immediate complications and at one month of follow up he continued without incidents.

A novel rectal applicator for contact radiotherapy with HDR 192Ir sources.

PURPOSE: Dose escalation to rectal tumors leads to higher complete response rates and may thereby enable omission of surgery. Important advantages of endoluminal boosting techniques include the possibility to apply a more selective/localized boost than using external beam radiotherapy. A novel brachytherapy (BT) rectal applicator with lateral shielding was designed to be used with a rectoscope for eye-guided positioning to deliver a dose distribution similar to the one of contact x-ray radiotherapy devices, using commonly available high-dose-rate 192Ir BT sources. METHODS AND MATERIALS: A cylindrical multichannel BT applicator with lateral shielding was designed by Monte Carlo modeling, validated experimentally with film dosimetry and compared with results found in the literature for the Papillon 50 (P50) contact x-ray radiotherapy device regarding rectoscope dimensions, radiation beam shape, dose fall-off, and treatment time. RESULTS: The multichannel applicator designed is able to deliver 30 Gy under 13 min with a 20350 U (5 Ci) source. The use of multiple channels and lateral shielding provide a uniform circular treatment surface with 22 mm in diameter. The resulting dose fall-off is slightly steeper (maximum difference of 5%) than the one generated by the P50 device with the 22 mm applicator. CONCLUSIONS: A novel multichannel rectal applicator for contact radiotherapy with high-dose-rate 192Ir sources that can be integrated with commercially available treatment planning systems was designed to produce a dose distribution similar to the one obtained by the P50 device.

PROFICIENCY TEST OF THE SSDL-ININ-MEXICO FOR THE CALIBRATION OF WELL-TYPE CHAMBERS WITH HDR 192IR SOURCES USING TWO DIFFERENT DOSIMETRY CODES OF PRACTICE FOR THE DETERMINATION OF REFERENCE AIR KERMA RATE KR.

The results of the comparison between SSDL-ININ and SSDL-CPHR (pilot laboratory) demonstrates the competence of the SSDL-ININ for the performance of the KR in 192Ir. The RININ/CHPR ratio for the calibration coefficients is 0.989 ± 0.005. The comparison uses three SI-HDR 1000-Plus as transfer chambers, series: A02423, A941755 and A973052. CPHR used a secondary standard PTW 3304 chamber, s/n 154, calibrated at PTB and ININ employed a secondary standard SI-90008 s/n A963391, calibrated at NPL. To determine KR, the SSDL-CPHR used the IAEA TEC-DOC-1274 and the SSDL-ININ used the IPEM (UK) code of practice. The latter uses a correction factor by source's geometry, ksg. The results show that both codes are equivalent; however, for the use of well chambers in the highlands or in locations with reduced atmospheric pressure, it is needed to apply an additional factor k'P, or, to design a well chamber with air-equivalent walls for the application of the conventional kPT.

Validating Fricke dosimetry for the measurement of absorbed dose to water for HDR 192Ir brachytherapy: a comparison between primary standards of the LCR, Brazil, and the NRC, Canada.

Two Fricke-based absorbed dose to water standards for HDR Ir-192 dosimetry, developed independently by the LCR in Brazil and the NRC in Canada have been compared. The agreement in the determination of the dose rate from a HDR Ir-192 source at 1 cm in a water phantom was found to be within the k = 1 combined measurement uncertainties of the two standards: D NRC/D LCR = 1.011, standard uncertainty = 2.2%. The dose-based standards also agreed within the uncertainties with the manufacturer's stated dose rate value, which is traceable to a national standard of air kerma. A number of possible influence quantities were investigated, including the specific method for producing the ferrous-sulphate Fricke solution, the geometry of the holder, and the Monte Carlo code used to determine correction factors. The comparison highlighted the lack of data on the determination of G(Fe3+) in this energy range and the possibilities for further development of the holders used to contain the Fricke solution. The comparison also confirmed the suitability of Fricke dosimetry for Ir-192 primary standard dose rate determinations at therapy dose levels.

Gynecological brachytherapy for postoperative endometrial cancer: dosimetric analysis (Ir-192 vs Co-60).

INTRODUCTION: Endovaginal brachytherapy treatment dosimetry differences were studied using Ir-192 or Co-60 sources for postoperative endometrial cancer. MATERIALS AND METHODS: A prospective descriptive study was conducted. Thirty-six dosimetry plans of different patients were studied (15 by Ir-192 and 21 by Co-60). Variables studied included D2cc Rectum, D2cc Bladder, D2cc Sigmoid, dose percentage at point 0 (applicator surface on the top of the cylinder) and dose percentage at point 1 (5 mm deep on the top of the cylinder). A comparative analysis was performed of the values obtained from each variable between Ir-192 and Co-60 treatments. We compared average of each variables between Iridium and Cobalt by T Student for independent samples (SPSS 22). RESULTS: There were no significant differences on using Ir-192 or Co-60 by variables, except for dose percentage at point 1 in which we detected significant differences (Table 1). Table 1 The results Variables Sources Iridium 192 Cobalt 60 D2cc Rectum (mean dose) [rank] 6.01 Gy [3.99-7.90] 5.28 Gy [3.87-6,34] D2cc Bladder (mean dose) [rank] 5.82 Gy [4.20-8.38] 5.05 Gy [2.23-6.95] D2cc Sigmoid (mean dose) [rank] 4.43 Gy [1.66-6.67] 2.33 Gy [0.60-4.28] Dose percentage at point 0a (mean) [rank] 210.74% [120.90-234.90] 204.75% [177.10-223] Dose percentage at point 1b (mean) [rank] 93.49% [87.30-100.60] 100.11% [96.70-102] aPoint 0: point to the applicator surface bPoint 1: point to 5 mm applicator surface DISCUSSION: Brachytherapy treatment dosimetry plans are similar using Ir-192 or Co-60, except dose percentage at point 1. In the scientific literature, some differences exist and there are some advantages in using cobalt.

Development of a phantom to validate high-dose-rate brachytherapy treatment planning systems with heterogeneous algorithms.

PURPOSE: This work presents the development of a phantom to verify the treatment planning system (TPS) algorithms used for high-dose-rate (HDR) brachytherapy. It is designed to measure the relative dose in a heterogeneous media. The experimental details used, simulation methods, and comparisons with a commercial TPS are also provided. METHODS: To simulate heterogeneous conditions, four materials were used: Virtual Water™ (VM), BR50/50™, cork, and aluminum. The materials were arranged in 11 heterogeneity configurations. Three dosimeters were used to measure the relative response from a HDR (192)Ir source: TLD-100™, Gafchromic(®) EBT3 film, and an Exradin™ A1SL ionization chamber. To compare the results from the experimental measurements, the various configurations were modeled in the penelope/penEasy Monte Carlo code. Images of each setup geometry were acquired from a CT scanner and imported into BrachyVision™ TPS software, which includes a grid-based Boltzmann solver Acuros™. The results of the measurements performed in the heterogeneous setups were normalized to the dose values measured in the homogeneous Virtual Water™ setup and the respective differences due to the heterogeneities were considered. Additionally, dose values calculated based on the American Association of Physicists in Medicine-Task Group 43 formalism were compared to dose values calculated with the Acuros™ algorithm in the phantom. Calculated doses were compared at the same points, where measurements have been performed. RESULTS: Differences in the relative response as high as 11.5% were found from the homogeneous setup when the heterogeneous materials were inserted into the experimental phantom. The aluminum and cork materials produced larger differences than the plastic materials, with the BR50/50™ material producing results similar to the Virtual Water™ results. Our experimental methods agree with the penelope/penEasy simulations for most setups and dosimeters. The TPS relative differences with the Acuros™ algorithm were similar in both experimental and simulated setups. The discrepancy between the BrachyVision™, Acuros™, and TG-43 dose responses in the phantom described by this work exceeded 12% for certain setups. CONCLUSIONS: The results derived from the phantom measurements show good agreement with the simulations and TPS calculations, using Acuros™ algorithm. Differences in the dose responses were evident in the experimental results when heterogeneous materials were introduced. These measurements prove the usefulness of the heterogeneous phantom for verification of HDR treatment planning systems based on model-based dose calculation algorithms.

A feasibility study of Fricke dosimetry as an absorbed dose to water standard for 192Ir HDR sources.

High dose rate brachytherapy (HDR) using 192Ir sources is well accepted as an important treatment option and thus requires an accurate dosimetry standard. However, a dosimetry standard for the direct measurement of the absolute dose to water for this particular source type is currently not available. An improved standard for the absorbed dose to water based on Fricke dosimetry of HDR 192Ir brachytherapy sources is presented in this study. The main goal of this paper is to demonstrate the potential usefulness of the Fricke dosimetry technique for the standardization of the quantity absorbed dose to water for 192Ir sources. A molded, double-walled, spherical vessel for water containing the Fricke solution was constructed based on the Fricke system. The authors measured the absorbed dose to water and compared it with the doses calculated using the AAPM TG-43 report. The overall combined uncertainty associated with the measurements using Fricke dosimetry was 1.4% for k = 1, which is better than the uncertainties reported in previous studies. These results are promising; hence, the use of Fricke dosimetry to measure the absorbed dose to water as a standard for HDR 192Ir may be possible in the future.

A BrachyPhantom for verification of dose calculation of HDR brachytherapy planning system.

PURPOSE: To develop a calibration phantom for (192)Ir high dose rate (HDR) brachytherapy units that renders possible the direct measurement of absorbed dose to water and verification of treatment planning system. METHODS: A phantom, herein designated BrachyPhantom, consists of a Solid Water™ 8-cm high cylinder with a diameter of 14 cm cavity in its axis that allows the positioning of an A1SL ionization chamber with its reference measuring point at the midheight of the cylinder's axis. Inside the BrachyPhantom, at a 3-cm radial distance from the chamber's reference measuring point, there is a circular channel connected to a cylindrical-guide cavity that allows the insertion of a 6-French flexible plastic catheter from the BrachyPhantom surface. The PENELOPE Monte Carlo code was used to calculate a factor, P(sw)(lw), to correct the reading of the ionization chamber to a full scatter condition in liquid water. The verification of dose calculation of a HDR brachytherapy treatment planning system was performed by inserting a catheter with a dummy source in the phantom channel and scanning it with a CT. The CT scan was then transferred to the HDR computer program in which a multiple treatment plan was programmed to deliver a total dose of 150 cGy to the ionization chamber. The instrument reading was then converted to absorbed dose to water using the N(gas) formalism and the P(sw)(lw) factor. Likewise, the absorbed dose to water was calculated using the source strength, Sk, values provided by 15 institutions visited in this work. RESULTS: A value of 1.020 (0.09%, k = 2) was found for P(sw)(lw). The expanded uncertainty in the absorbed dose assessed with the BrachyPhantom was found to be 2.12% (k = 1). To an associated Sk of 27.8 cGy m(2) h(-1), the total irradiation time to deliver 150 cGy to the ionization chamber point of reference was 161.0 s. The deviation between the absorbed doses to water assessed with the BrachyPhantom and those calculated by the treatment plans and using the Sk values did not exceed ± 3% and ± 1.6%, respectively. CONCLUSIONS: The BrachyPhantom may be conveniently used for quality assurance and/or verification of HDR planning system with a priori threshold level to spot problems of 2% and ± 3%, respectively, and in the long run save time for the medical physicist.

Determination of transit dose profile for a (192)Ir HDR source.

PURPOSE: Several studies have reported methodologies to calculate and correct the transit dose component of the moving radiation source for high dose rate (HDR) brachytherapy planning systems. However, most of these works employ the average source speed, which varies significantly with the measurement technique used, and does not represent a realistic speed profile, therefore, providing an inaccurate dose determination. In this work, the authors quantified the transit dose component of a HDR unit based on the measurement of the instantaneous source speed to produce more accurate dose values. METHODS: The Nucletron microSelectron-HDR Ir-192 source was characterized considering the Task Group 43 (TG-43U1) specifications. The transit dose component was considered through the calculation of the dose distribution using a Monte Carlo particle transport code, MCNP5, for each source position and correcting it by the source speed. The instantaneous source speed measurements were performed in a previous work using two optical fibers connected to a photomultiplier and an oscilloscope. Calculated doses were validated by comparing relative dose profiles with those obtained experimentally using radiochromic films. RESULTS: TG-43U1 source parameters were calculated to validate the Monte Carlo simulations. These agreed with the literature, with differences below 1% for the majority of the points. Calculated dose profiles without transit dose were also validated by comparison with ONCENTRA(®) Brachy v. 3.3 dose values, yielding differences within 1.5%. Dose profiles obtained with MCNP5 corrected using the instantaneous source speed profile showed differences near dwell positions of up to 800% in comparison to values corrected using the average source speed, but they are in good agreement with the experimental data, showing a maximum discrepancy of approximately 3% of the maximum dose. Near a dwell position the transit dose is about 22% of the dwell dose delivered by the source dwelling 1 s and reached 104.0 cGy per irradiation in a hypothetical clinical case studied in this work. CONCLUSIONS: The present work demonstrated that the transit dose correction based on average source speed fails to accurately correct the dose, indicating that the correct speed profile should be considered. The impact on total dose due to the transit dose correction near the dwell positions is significant and should be considered more carefully in treatments with high dose rate, several catheters, multiple dwell positions, small dwell times, and several fractions.

Ultrasound-assisted endocavitary HDR-Ir(192) brachytherapy for unresectable locally advanced uterine cervix carcinoma: retrospective analysis focusing the efficacy and tolerability.

PURPOSE: To evaluate the impact of uterine cavity's ultrasound to final selected length of intracavitary tandem. The efficacy and tolerability of external beam radiation plus HDR-Ir(192) brachytherapy in our cohort of patients were also estimated. MATERIALS AND METHODS: 48 women with locally advanced unresectable uterine cervix carcinoma were treated by HDR-Ir(192) endocavitary brachytherapy between January 2007 and January 2009. The median age was 63 (range 38-74). The distribution according to Federation of Gynaecology and Obstetrics (FIGO) staging system was as follows: Stage IIB, 54.16 %; IIIA, 10.4 %; IIIB, 27.0 %; and IVA, 8.3 %. HDR intracavitary brachytherapy was given weekly, beginning at the last week of whole pelvis irradiation, with a dose of 7 Gy to point A for three to four fractions. The median overall treatment time was 50 days (range 42-73 days). The median follow-up time was 2.7 years (range 3 months to 4.9 years). Multivariate analysis was performed using the Cox regression proportional hazards model. RESULTS: The complete remission rate after radiotherapy was 93.75 % (45/48). The 5-year actuarial major complication rates (Grade 3 or above) were 6.3 % overall (2.1 % proctitis, 2.1 % cystitis and 2.1 % enteritis). Estimation of the length of uterine cavity by ultrasound helped decisively in the proper placement of the intrauterine tandem inserted. CONCLUSIONS: Prior knowledge of the length of uterine cavity can facilitate the decisions regarding the proper insertion length of the tandem. Results of cervical cancer treatment with external beam radiation and HDR intracavitary brachytherapy in our hospital are encouraging.

Twenty-year experience in the management of squamous cell anal canal carcinoma with interstitial brachytherapy.

OBJECTIVES: The aim of this study was to retrospectively evaluate clinical characteristics, local control, acute and late toxicity, and prognostic factors of patients with anal canal carcinoma treated with brachytherapy. METHODS: From 1989 to 2009, 38 patients were treated with iridium 192 low-dose-rate (N = 26) or pulsed-dose-rate (N = 12) interstitial brachytherapy at a single institution. The median age was 62 years (range, 38-86 years). The TNM classification was as follows: 10 T1, 22 T2, 5 T3 and 1 T4; 32 N0, 3 N1 and 3 N2. Most patients (32/38) received either a first course of radiochemotherapy (N = 22) or radiotherapy alone (N=10) consisting of a total delivered dose of 45 Gy to the pelvis (range, 32-50) followed by a boost a median of 18 days later of 15-35 Gy (median 20 Gy) to the anal canal. The remaining 6 cases were treated with brachytherapy alone (dose range, 60-65 Gy). RESULTS: With a median follow-up of 30 months (range, 4-200), 2- and 5-year local control rates were 91% and 87%, respectively. Preservation of the anal sphincter was achieved in 32 patients (84%). Three patients experienced incontinence after brachytherapy. Only 2 patients showed chronic mucositis grade 3/4. Age proved to be a statistically significant prognostic factor for overall survival in the univariate (p = 0.033) and multivariate analyses (p = 0.018). Concurrent chemotherapy with external beam radiotherapy was a statistically significant prognostic factor for disease-free survival in the univariate and multivariate analyses (p = 0.007 and p = 0.044, respectively). CONCLUSIONS: Interstitial brachytherapy appears to be an effective and well tolerated treatment for anal carcinoma offering both high local tumour control and anal sphincter preservation.

Numerical dosimetric reconstruction of a radiological accident in South America in April 2009.

A severe irradiation accident involving a victim occurred in April 2009 in South America. The victim has found a (192)Ir source fallen from a gammagraphy device and has put it in the left pocket of his pants. Very quickly, an erythema and a blister appeared on the left leg of the victim involving hospitalisation. Following the request of the IAEA assistance, the Ionizing Radiation Dosimetry Laboratory of IRSN was asked to perform a numerical dosimetric reconstruction. A personalised voxel phantom of the victim has been constructed thanks to the Simulation of External Source Accident with Medical images tool developed by the laboratory, and a calculation of the dose with the MCNPX computer code allowed to determine the boundary of the necrotic dose at 25 Gy. On the basis of these calculations, the physicians have performed exeresis of the necrotic region on the left leg on 4 May 2009. Associated with mesenchymal stem cell injection, the leg of the victim was healthy on December 2009.

Direct measurement of instantaneous source speed for a HDR brachytherapy unit using an optical fiber based detector.

PURPOSE: Several attempts to determine the transit time of a high dose rate (HDR) brachytherapy unit have been reported in the literature with controversial results. The determination of the source speed is necessary to accurately calculate the transient dose in brachytherapy treatments. In these studies, only the average speed of the source was measured as a parameter for transit dose calculation, which does not account for the realistic movement of the source, and is therefore inaccurate for numerical simulations. The purpose of this work is to report the implementation and technical design of an optical fiber based detector to directly measure the instantaneous speed profile of a 192Ir source in a Nucletron HDR brachytherapy unit. METHODS: To accomplish this task, we have developed a setup that uses the Cerenkov light induced in optical fibers as a detection signal for the radiation source moving inside the HDR catheter. As the 192Ir source travels between two optical fibers with known distance, the threshold of the induced signals are used to extract the transit time and thus the velocity. The high resolution of the detector enables the measurement of the transit time at short separation distance of the fibers, providing the instantaneous speed. RESULTS: Accurate and high resolution speed profiles of the 192Ir radiation source traveling from the safe to the end of the catheter and between dwell positions are presented. The maximum and minimum velocities of the source were found to be 52.0 +/- 1.0 and 17.3 +/- 1.2 cm/s. The authors demonstrate that the radiation source follows a uniformly accelerated linear motion with acceleration of [a] = 113 cm/s2. In addition, the authors compare the average speed measured using the optical fiber detector to those obtained in the literature, showing deviation up to 265%. CONCLUSIONS: To the best of the authors' knowledge, the authors directly measured for the first time the instantaneous speed profile of a radiation source in a HDR brachytherapy unit traveling from the unit safe to the end of the catheter and between interdwell distances. The method is feasible and accurate to implement on quality assurance tests and provides a unique database for efficient computational simulations of the transient dose.