Assessment of the dicentric chromosome assay as a biodosimetry tool for more personalized medicine in a case of a high risk neuroblastoma 131I-mIBG treatment.

PURPOSE: The aims of this study were to estimate the whole - body absorbed - dose with the Dicentric Chromosome Assay (DCA) (biodosimetry) for 131I - metaiodobenzylguanidine (131I - mIBG) therapy for high - risk neuroblastoma, and to obtain an initial correlation with the physical dosimetry calculated as described by the Medical Internal Radiation Dosimetry formalism (MIRD). Together both objectives will aid the optimization of personalized targeted radionuclide therapies. MATERIAL AND METHODS: A 12 year-old child with relapsed high-risk neuroblastoma was treated with 131I-mIBG: a first administration with activity <444 MBq/kg was used as a tracer in order to calculate the activity needed in a second administration to achieve a whole body prescribed dose of ∼4 Gy. Blood samples were obtained before and seven days after each administration to analyze the frequency of dicentrics. Moreover, consequent estimations of retained activity were done every few hours from equivalent dose rate measurements at a fixed position, two meters away from the patient, in order to apply the MIRD procedure. Blood samples were also drawn every 2- to -3 days to assess bone marrow toxicity. RESULTS: For a total activity of 22,867 MBq administered over two phases, both biological and physical dosimetries were performed. The former estimated a whole-body cumulated dose of 3.53 (2.58-4.41) Gy and the latter a total whole-body absorbed dose of 2.32 ± 0.48 Gy. The patient developed thrombocytopenia grade 3 after both infusions and neutropenia grade 3 and grade 4 (based on CTCAE 4.0) during respective phases. CONCLUSION: The results indicate a possible correlation between biodosimetry and standard physical dosimetry in 131I-mIBG treatment for high-risk neuroblastoma. A larger cohort and refinement of the DCA for internal irradiation are needed to define the role of biodosimetry in clinical situations.

Interobserver variability in rectum contouring in high-dose-rate brachytherapy for prostate cancer: A multi-institutional prospective analysis.

PURPOSE: The aim of this study was to evaluate the interobserver variability (IOV) of rectum contouring, and its dosimetric consequences, for high-dose-rate brachytherapy in patients with prostate cancer across multiple institutions. METHODS AND MATERIALS: Five radiation oncologists contoured rectums in 10 patients on transperineal ultrasound image sets after establishing a delineation consensus. The D0.1cc, D1cc, and D2cc rectum volume parameters were determined. The mean, standard deviation, and range of each dose-volume histogram parameter were evaluated for each patient. The IOV was determined using the coefficient of variation, and the dosimetric impacts on the total dose were analyzed by estimating the biologically equivalent dose (EQD2α/ß = 3). RESULTS: The interobserver coefficients of variation (±standard deviation) for the reported D0.1cc, D1cc, and D2cc were 5 ± 1.84%, 4 ± 1.26%, and 4 ± 1.33%, respectively. As for the impact on the total dose, the mean dose differences for D0.1cc, D1cc, and D2cc were 10 Gy, 7.3 Gy, and 6.6 Gy, respectively. CONCLUSIONS: The D2cc is robust as evident by the low IOV (<5%). However, some variability ranges almost overlap with the clinical threshold level, which may present dosimetric and clinical complications. General rectal contouring guidelines for prostate high-dose-rate brachytherapy are desirable to reduce discrepancies in delineation.

High-dose-rate brachytherapy boost for prostate cancer: Analysis of dose-volume histogram parameters for predicting late rectal toxicity.

PURPOSE: To determine the significance of dose-volume histogram parameters for predicting late rectal toxicity (LRT) after single-fraction high-dose-rate brachytherapy (HDRBT) boost and external beam radiotherapy (EBRT) in prostate cancer. MATERIALS AND METHODS: Three hundred patients with intermediate- or high-risk prostate cancer were included between August 2010 and March 2015. Treatment comprised a single-fraction HDRBT boost of 15.0 Gy plus EBRT (46.0 Gy delivered in 23 fractions) or an HDRBT boost of 9.5 Gy plus EBRT (60.0 Gy delivered in 30 fractions) if the seminal vesicles were infiltrated using real-time transrectal ultrasound-based planning. LRT was evaluated every 3 months after the end of the combined treatment using the Common Terminology Criteria for Adverse Events, version 4.0. The minimum dose received by the most exposed 0.1 and 2.0 cm3 volume of the rectum (D0.1 cc/D2cc) was analyzed by estimating the biologically equivalent rectal dose according to the recommendations of the Groupe Européen de Curiethérapie/European Society for Radiotherapy and Oncology and an ordinal regression analysis was performed. RESULTS: LRT was observed in 62 patients (20.7%) at a median followup of 33 (range, 2-68) months. Twenty patients (6.7%) developed grade 2 and 3 patients (1%) developed grade 3 LRT. A significant association was observed between D2cc and the probability of developing grade 1-3 LRT (p = 0.04). CONCLUSIONS: D2cc is associated with the occurrence of LRT in HDRBT-treated prostate cancer patients. The dose constraints proposed and recommended by experienced HDRBT centers must be investigated to determine the threshold dose through long-term and prospective studies.

Evaluation of the shielding in a treatment room with an electronic brachytherapy unit.

Esteya® (Elekta Brachytherapy, Veenendaal, The Netherlands) is an electronic brachytherapy (eBT) system based on a 69.5 kVp x-ray source and a set of collimators of 1 to 3 cm in diameter, used for treating non-melanoma skin cancer lesions. This study aims to estimate room shielding requirements for this unit. The non-primary (scattered and leakage) ambient dose equivalent rates were measured with a Berthold LB-133 monitor (Berthold Technologies, Bad Wildbad, Germany). The latter ranges from 17 mSv h-1 at 0.25 m distance from the x-ray source to 0.1 mSv h-1 at 2.5 m. The necessary room shielding was then estimated following US and some European guidelines. The room shielding for all barriers considered was below 2 mmPb. The dose to a companion who, exceptionally, would stay with the patient during all treatment was estimated to be below 1 mSv if a leaded apron is used. In conclusion, Esteya shielding requirements are minimal.

Failure mode and effects analysis of skin electronic brachytherapy using Esteya® unit.

PURPOSE: Esteya® (Nucletron, an Elekta company, Elekta AB, Stockholm, Sweden) is an electronic brachytherapy device used for skin cancer lesion treatment. In order to establish an adequate level of quality of treatment, a risk analysis of the Esteya treatment process has been done, following the methodology proposed by the TG-100 guidelines of the American Association of Physicists in Medicine (AAPM). MATERIAL AND METHODS: A multidisciplinary team familiar with the treatment process was formed. This team developed a process map (PM) outlining the stages, through which a patient passed when subjected to the Esteya treatment. They identified potential failure modes (FM) and each individual FM was assessed for the severity (S), frequency of occurrence (O), and lack of detection (D). A list of existing quality management tools was developed and the FMs were consensually reevaluated. Finally, the FMs were ranked according to their risk priority number (RPN) and their S. RESULTS: 146 FMs were identified, 106 of which had RPN ≥ 50 and 30 had S ≥ 7. After introducing the quality management tools, only 21 FMs had RPN ≥ 50. The importance of ensuring contact between the applicator and the surface of the patient's skin was emphasized, so the setup was reviewed by a second individual before each treatment session with periodic quality control to ensure stability of the applicator pressure. Some of the essential quality management tools are already being implemented in the installation are the simple templates for reproducible positioning of skin applicators, that help marking the treatment area and positioning of X-ray tube. CONCLUSIONS: New quality management tools have been established as a result of the application of the failure modes and effects analysis (FMEA) treatment. However, periodic update of the FMEA process is necessary, since clinical experience has suggested occurring of further new possible potential failure modes.