Review on Treatment Planning Systems for Cervix Brachytherapy (Interventional Radiotherapy): Some Desirable and Convenient Practical Aspects to Be Implemented from Radiation Oncologist and Medical Physics Perspectives.

Intracavitary brachytherapy (BT, Interventional Radiotherapy, IRT), plays an essential role in the curative intent of locally advanced cervical cancer, for which the conventional approach involves external beam radiotherapy with concurrent chemotherapy followed by BT. This work aims to review the different methodologies used by commercially available treatment planning systems (TPSs) in exclusive magnetic resonance imaging-based (MRI) cervix BT with interstitial component treatments. Practical aspects and improvements to be implemented into the TPSs are discussed. This review is based on the clinical expertise of a group of radiation oncologists and medical physicists and on interactive demos provided by the software manufacturers. The TPS versions considered include all the new tools currently in development for future commercial releases. The specialists from the supplier companies were asked to propose solutions to some of the challenges often encountered in a clinical environment through a questionnaire. The results include not only such answers but also comments by the authors that, in their opinion, could help solve the challenges covered in these questions. This study summarizes the possibilities offered nowadays by commercial TPSs, highlighting the absence of some useful tools that would notably improve the planning of MR-based interstitial component cervix brachytherapy.

Evaluation of the impact of EMBRACE II protocol in Spanish centers, with a large cohort of patients using a ranking index.

PURPOSE: The aim of this paper was to assess development of high-dose-rate (HDR) cervix brachytherapy (BT) implants in three Spanish institutions before and after introduction of EMBRACE II protocol. MATERIAL AND METHODS: 392 patients from three different institutions, treated between 2009 and 2019 were analyzed. D90 of high-risk clinical target volume (HR-CTV) and D2cc of organs at risk (OARs) of all patients were collected. Statistical distribution was analyzed for two different periods of time: before and after EMBRACE II publication. Index I was applied based on collected dosimetric quantities (D90 and D2cc) to enhance equilibrium between HR-CTV coverage and doses to OARs. Variation in dosimetry and index depending on CTV and technique used (IC vs. IC/IT) were also evaluated. RESULTS: Adaptation of institutions to EMBRACE II protocol resulted in a statistically significant increase of D90 HR-CTV (Institution 1; p < 0.00001) or decrease of D2cc OARs (Institution 2; p < 0.04). Increase in the use of interstitial component showed higher coverage of HR-CTV for Institution 3 (p = 0.03), and lower doses to OARs for the same coverage of HR-CTV at Institution 2 (p-OARs < 0.03). Even though index I was only significantly different between periods for Institution 1 (p < 0.0000001), it was able to show a reduction of dose variability related to higher expertise and higher interstitial component. CONCLUSIONS: Depending on local protocol before EMBRACE II, the adaptation through increasing interstitial component and physician and physicist training, resulted in a significant increase of HR-CTV doses or reduction of OARs doses. Index I was able to describe an evolution of equilibrium between CTV coverage and OARs' sparing.

Phantom development for daily checks in electron intraoperative radiotherapy with a mobile linac.

PURPOSE: IORT with mobile linear accelerators is a well-established modality where the dose rate and, therefore, the dose per pulse are very high. The constancy of the dosimetric parameters of the accelerator has to be checked daily. The aim of this work is to develop a phantom with embedded detectors to improve both accuracy and efficiency in the daily test of an IORT linac at the surgery room. METHODS: The developed phantom is manufactured with transparent polymethyl methacrylate (PMMA), allocating 6 parallel-plate chambers: a central one to evaluate the on-axis beam output, another on-axis one placed at a fixed depth under the previous one to evaluate the energy constancy and four off-axis chambers to evaluate the flatness and symmetry. To analyse the readings a specific application has been developed. RESULTS: For all chambers and energies, the mean saturation and polarization corrections were smaller than 0.7%. The beam is monitored at different levels of the clinical beam. Output, energy constancy and flatness correlate very well with the correspondent values with the complete applicator. During the first six months of clinical use the beam dosimetric parameters showed excellent stability. CONCLUSIONS: A phantom has been developed with embedded parallel plate chambers attached to the upper applicator part of an IORT linac. The phantom allows a very efficient setup reducing the time to check the parameters. It provides complete dosimetric information (output, energy and flatness) with just one shot and using ionization chambers with minimum saturation effect, as this highly pulsed beam requires.

Inter-observer and intra-observer variability in reporting vaginal dose points for cervical cancer in high-dose-rate brachytherapy.

PURPOSE: The ICRU 89 recommends reporting a set of vaginal dose points for cervical cancer treatments in order to quantify the goodness of implant. This vaginal dose reporting method for combined external beam radiotherapy and brachytherapy has been adopted by the EMBRACE II study protocol. Large variations in dose between patients and centers have been reported. The aim of this study was to determine possible discrepancies with consensus observers from the same institution. Therefore, the inter- and intra-observer variability were analyzed. MATERIAL AND METHODS: For five patients, five experienced observers reported dose at the proposed vaginal points twice. The effect of inter- and intra-observer variations on total dose was analyzed by estimating biologically equivalent dose EQD2 (α/ß = 3 Gy). Coefficient of variation (CV) was used to provide a measure of data dispersion as a proportion to the mean. RESULTS: The maximum inter-observer deviation among all patients and all points ranged from 0.5 Gy to 24.1 Gy in EQD2. The higher inter-observer discrepancies were found at points at 3 o'clock and at 6 o'clock, with respect to ovoids. In case of the maximum intra-observer deviation, it ranged from 0.5 Gy to 14.2 Gy, with higher deviation points at 12 o'clock and 9 o'clock, with respect to ovoids. CONCLUSIONS: There is a need to ensure consistency in vaginal points reporting. The impact of the dosimetric inter- and intra-observer variability should also be considered when dealing with dose tolerances and limits due to the potential dose gradient.

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.