Refining critical structure contouring in STereotactic Arrhythmia Radioablation (STAR): Benchmark results and consensus guidelines from the STOPSTORM.eu consortium.

BACKGROUND AND PURPOSE: In patients with recurrent ventricular tachycardia (VT), STereotactic Arrhythmia Radioablation (STAR) shows promising results. The STOPSTORM.eu consortium was established to investigate and harmonise STAR treatment in Europe. The primary goals of this benchmark study were to standardise contouring of organs at risk (OAR) for STAR, including detailed substructures of the heart, and accredit each participating centre. MATERIALS AND METHODS: Centres within the STOPSTORM.eu consortium were asked to delineate 31 OAR in three STAR cases. Delineation was reviewed by the consortium expert panel and after a dedicated workshop feedback and accreditation was provided to all participants. Further quantitative analysis was performed by calculating DICE similarity coefficients (DSC), median distance to agreement (MDA), and 95th percentile distance to agreement (HD95). RESULTS: Twenty centres participated in this study. Based on DSC, MDA and HD95, the delineations of well-known OAR in radiotherapy were similar, such as lungs (median DSC = 0.96, median MDA = 0.1 mm and median HD95 = 1.1 mm) and aorta (median DSC = 0.90, median MDA = 0.1 mm and median HD95 = 1.5 mm). Some centres did not include the gastro-oesophageal junction, leading to differences in stomach and oesophagus delineations. For cardiac substructures, such as chambers (median DSC = 0.83, median MDA = 0.2 mm and median HD95 = 0.5 mm), valves (median DSC = 0.16, median MDA = 4.6 mm and median HD95 = 16.0 mm), coronary arteries (median DSC = 0.4, median MDA = 0.7 mm and median HD95 = 8.3 mm) and the sinoatrial and atrioventricular nodes (median DSC = 0.29, median MDA = 4.4 mm and median HD95 = 11.4 mm), deviations between centres occurred more frequently. After the dedicated workshop all centres were accredited and contouring consensus guidelines for STAR were established. CONCLUSION: This STOPSTORM multi-centre critical structure contouring benchmark study showed high agreement for standard radiotherapy OAR. However, for cardiac substructures larger disagreement in contouring occurred, which may have significant impact on STAR treatment planning and dosimetry evaluation. To standardize OAR contouring, consensus guidelines for critical structure contouring in STAR were established.

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.

Feasibility and potential advantages using VMAT in SRS metastasis treatments.

BACKGROUND: Utilization of stereotactic radiosurgery (SRS) for brain metastases (BM) has become the technique of choice as opposed to whole brain radiation therapy (WBRT). The aim of this work is to evaluate the feasibility and potential benefits in terms of normal tissue (NT) and dose escalation of volumetric modulated arc therapy (VMAT) in SRS metastasis treatment. A VMAT optimization procedure has therefore been developed for internal dose scaling which minimizes planner dependence. MATERIALS AND METHODS: Five patient-plans incorporating treatment with frame-based SRS with dynamic conformal arc technique (DA) were re-planned for VMAT. The lesions selected were between 4-6 cm3. The same geometry used in the DA plans was maintained for the VMAT cases. A VMAT planning procedure was performed attempting to scale the dose in inner auxiliary volumes, and to explore the potential for dose scaling with this technique. Comparison of dose-volume histogram (DVH) parameters were obtained. RESULTS: VMAT allows a superior NT sparing plus conformity and dose scaling using the auxiliary volumes. The VMAT results were significantly superior in NT sparing, improving both the V10 and V12 values in all cases, with a 2-3 cm3 saving. In addition, VMAT improves the dose coverage D95 by about 0.5 Gy. The objective of dose escalation was achieved with VMAT with an increment of the Dmean and the Dmedian of about 2 Gy. CONCLUSIONS: This work shows a benefit of VMAT in SRS treatment with significant NT sparing. A VMAT optimization procedure, based on auxiliary inner volumes, has been developed, enabling internal dose escalation.

Low-/high-dose-rate brachytherapy boost in patients with intermediate-risk prostate cancer treated with radiotherapy: long-term results from a single institution team experience.

PURPOSE: To compare brachytherapy (BT) boost of low-dose-rate (LDR) and high-dose-rate (HDR) techniques in patients diagnosed with intermediate-risk prostate cancer. MATERIAL AND METHODS: Between January 2005 and February 2018, 142 patients (50 LDR and 92 HDR) with intermediate-risk prostate cancer were treated with a BT boost, and retrospectively analyzed. Prescribed dose was 45 Gy with external beam radiotherapy (EBRT) plus 100-108 Gy with LDR-BT, and 60 Gy with EBRT plus one fraction of 10 Gy with HDR-BT. 99% of patients received androgen deprivation therapy (ADT) for 6 months. Primary endpoint was to compare LDR and HDR boosts in terms of biochemical progression-free survival (bPFS). Secondary endpoint, after re-classifying patients into "favorable" and "unfavorable" sub-groups, was to analyze differences with a similar treatment intensity. RESULTS: Median overall follow-up for the total cohort was 66.5 months (range, 16-185 months). There were no significant differences in bPFS, overall survival, cause specific survival, local failure, lymph node failure, or distant failure when LDR or HDR was employed. bPFS at 90 months was 100% for favorable, and 89% and 85% for unfavorable patients at 60 months and 90 months, respectively (log-rank test, p = 0.017). The crude incidence of genitourinary acute and chronic toxicity grade 3 was 0.7% and 4%, respectively. Twelve patients (8%) had chronic rectal hemorrhage grade 2, in whom argon was applied (4 LDR and 8 HDR). CONCLUSIONS: Combined treatment is an excellent therapeutic option in patients with intermediate-risk prostate carcinoma, with similar results in both LDR and HDR approaches and very low toxicities. Importantly, the current literature has indicated that unfavorable-risk patients belong to a different category, and should be treated as patients with high-risk factors. Therefore, the stratification and identification of both risk groups is extremely relevant.

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.

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.

Detector for monitoring potential bleeding during electron intraoperative radiotherapy.

PURPOSE: The aim of this work is to develop a bleeding detector integrated into the acrylic circular applicators for specific mobile linacs. Thus, a bleeding detector has been developed based on a capacitive sensor to be used with plastic applicators, as in the case of LIAC HWL from Sordina IORT Technologies SpA. According to the clinical impact, we have selected 0.5 cm as the minimum depth of fluid that should be detected. METHODS: An experiment was developed using water-simulating blood. Two setups were considered: non-beveled applicators with 7 cm and 10 cm diameter. Measurements were done for applicators 0° and 45° tilted, both with respect to the horizontal surface, in order to mimic the worst clinical scenario according to the irradiation gantry and applicator bevel angle. The behavior of the detector under irradiation was analyzed and the impact of the stray radiation on the detector was also evaluated. RESULTS: The detector was able to distinguish the presence of liquid at a minimum height of 0.5 cm. A linear behavior was obtained for both setups. We have also verified that the LIAC HWL radiation does not affect the measurements nor does the detector interfere with the stray radiation. The bleeding detector is a quasi-digital capacitive sensor with low-cost, high linearity, and easy to install. CONCLUSIONS: With this detector it is possible to perform a continuous monitoring of the liquid measurements even during the irradiation phase. Thus, it can operate not only as a pre-treatment detector but also as a continuous one.

Permanent seed implant brachytherapy in low-risk prostate cancer: Preoperative planning with 145 Gy versus real-time intraoperative planning with 160 Gy.

AIM: The present retrospective study was to compare toxicity and survival outcomes in a group of low-risk PCa patients treated with either the preoperative planning technique (145 Gy) or the real-time IoP technique (160 Gy). BACKGROUND: The two most common permanent seed implantation techniques are preoperative planning (PP) with 145 Gy and real-time intraoperative planning (IoP) with 160 Gy. Although IoP has largely replaced PP at many centres in recent years, few studies have directly compared these two techniques. MATERIALS AND METHODS: Retrospective study of 408 patients with low-risk PCa treated with permanent seed implant brachytherapy at our institution between October 2003 and December 2014. Of these, 187 patients were treated with PP at a dose of 145 Gy while 221 received real-time IoP with 160 Gy. RESULTS: At a median follow up of 90 months, 5- and 8-year rates of biochemical relapse-free survival (BRFS) were 94.8% and 86% with the IoP technique versus 90.8% and 83.9%, respectively, with PP. The maximum dose to the urethra was <217 Gy with both techniques. Despite the higher dose, IoP did not cause any significant increase in toxicity (p = 0.11). CONCLUSIONS: The present study shows that real-time intraoperative brachytherapy at a dose of 160 Gy yield better biochemical control than preoperative planning at 145 Gy. In addition, urinary toxicity did not increase, despite the dose escalation, probably because the dose constraints to the urethra were met despite the increased dose escalation. These findings support the use of real-time IoP.

Novel simple templates for reproducible positioning of skin applicators in brachytherapy.

PURPOSE: Esteya and Valencia surface applicators are designed to treat skin tumors using brachytherapy. In clinical practice, in order to avoid errors that may affect the treatment outcome, there are two issues that need to be carefully addressed. First, the selected applicator for the treatment should provide adequate margin for the target, and second, the applicator has to be precisely positioned before each treatment fraction. In this work, we describe the development and use of a new acrylic templates named Template La Fe-ITIC. They have been designed specifically to help the clinical user in the selection of the correct applicator, and to assist the medical staff in reproducing the positioning of the applicator. These templates are freely available upon request. MATERIAL AND METHODS: Templates that were developed by University and Polytechnic Hospital La Fe (La Fe) and Hospital Clínica Benidorm (ITIC) in cooperation with Elekta, consist of a thin sheet made of transparent acrylic. For each applicator, a crosshair and two different circles are drawn on these templates: the inner one corresponds to the useful beam, while the outer one represents the external perimeter of the applicator. The outer circle contains slits that facilitate to draw a circle on the skin of the patient for exact positioning of the applicator. In addition, there are two perpendicular rulers to define the adequate margin. For each applicator size, a specific template was developed. RESULTS: The templates have been used successfully in our institutions for more than 50 patients' brachytherapy treatments. They are currently being used for Esteya and Valencia applicators. CONCLUSIONS: The template La Fe-ITIC is simple and practical. It improves both the set-up time and reproducibility. It helps to establish the adequate margins, an essential point in the clinical outcome.