GEC ESTRO Research Articles

Five-year results of the very accelerated partial breast irradiation VAPBI phase I-II GEC-ESTRO trial

Background and purposeThe standard partial breast postoperative treatment for early breast carcinomas with multi-catheter interstitial brachytherapy (MIBT) requires 7–8 fractions in 4–5 days as used in the APBI GEC-ESTRO phase III trial. In 2017 the GEC-ESTRO Breast Cancer Working Group started a Phase I-II trial to study if very accelerated partial breast irradiation (VAPBI) using 3–4 fractions could be equivalent. Material81 patients with low-risk invasive carcinomas underwent high dose rate MIBT. Mean age was 68 (51–90); 33 women received 4 fractions of 6.25 Gy in 2–3 days, and 48 subsequent patients 3 fractions of 7.45 Gy in 2 days, 36 perioperatively and 45 postoperatively. ResultsMedian follow-up was 62 months, with 5-year actuarial breast recurrence of 3.4 % (two cases). One patient died due to metastasis. Pigmentation changes in the entrance of tubes remained visible only in 12.3 % in long term (skin G1 toxicity). Fibrosis or slight induration (G1) in 22.2 % and G2 in 9.9 %. No case of telangiectasia has been described. Cosmetic outcome is good or excellent in 95 % and fair in 5 %. Four tumors located in the retroareolar area showed nipple retraction. ConclusionVAPBI with MIBT using four fractions of 6.25 Gy or three fractions of 7.45 Gy in two or three days offers good local control, with a 5-year rate of fibrosis G2 similar to the GEC ESTRO phase III trial. VAPBI in two days is a good choice to decrease the total time of treatment, which is beneficial for the patient and reduces the workload.

Single Dose vs. Fractionated High-Dose Rate Brachytherapy in Localized Prostate Cancer: Long Term Results

To evaluate long-term freedom from biochemical relapse (FFbR) and overall survival (OS) after single-dose high-dose-rate brachytherapy (HDR-BT) compared with 2 or 3 fraction schedules. HDR-BT, delivering 1 × 19 Gy or 1 × 20 Gy (A = 49), 2 × 13 Gy (B = 138) or 3 × 10.5 Gy (C = 106), was given to patients with intermediate or high-risk prostate cancer as their sole treatment. Patients were staged with pelvic MRI and isotope bone scan. Transperineal transrectal ultrasound guided implantation was followed by MRI based CTV definition based on GEC ESTRO guidelines. Biochemical relapse was assessed using the Phœnix definition (PSA nadir plus 2 µg/L). Patients were evaluated prospectively from 6 months after implant and bi-annually thereafter. Estimates of freedom from biochemical relapse, and overall survival (OS) were calculated using the Kaplan-Meier (K-M) method and the log-rank test to test for significance. Univariate and multivariate hazard ratios (HR) were obtained using Cox's proportional hazard model. For multivariate modelling a stepwise reduction method was used. Median follow-up was 123, 116 and 120 months (p = 0.4), (A, B, C, respectively). Neo-adjuvant and adjuvant androgen deprivation treatment was given to 80% of all patients, median duration was 9 months for A and 6 months for B and C. K-M estimates of FFbR, at 8 and 10 years, were 67% and 64% (Group A), 78% and 72% (Group B), and 80% and 76% (Group C). Differences in FFbR between dose groups was not significant (p = 0.2). Similarly, no significant difference was seen in OS. Eight and 10-year estimates were 81% and 75% (A), 85% and 74% (B), and 90% and 83% (C); p = 0.5. Hazard Ratios for risk of biochemical recurrence were significant for ADT administration (yes/no) and overall risk category, in multivariate analyses. Only the latter was significant in univariate analysis for risk of death, Gleason risk (low, intermediate, high), MRI tumor stage risk and overall risk category were significant in univariate analyses. Only tumor stage and Gleason risk were significant in multivariate analyses. Concerns around the efficacy of 19-20 Gy single dose HDR BT as monotherapy, based on early data, may have been unfounded. Long-term outcome data up to 10 years show no significant difference in PSA control and overall survival compared to 2 and 3 fractions of HDR-BT.

Implementation of online workshops on image-guided adaptive brachytherapy (interventional radiotherapy) in locally advanced cervical cancer: Experience of BrachyAcademy

PURPOSETo provide educational support to brachytherapy users during the COVID-19 pandemic, online workshops were developed and implemented by BrachyAcademy, non-profit peer-to-peer educational initiative in Elekta. METHODS AND MATERIALSIn 2021–2022 two online workshops were organized. Participating teams had to send a clinical case of locally advanced cervical cancer (LACC) including brachytherapy Digital Imaging and Communications in Medicine (DICOM) files and questions to the faculty. During the workshop, feedback was given to each clinical case by five faculty members (two Radiation Oncologists, one Radiologist, two Medical Physicists). Participants competed a post-workshop questionnaire which included combination of qualitative and quantitative questions via yes/no responses, Likert scale, and 1 to 10 scale. RESULTSTwenty-one teams from eight countries (Europe, Asia, Latin America) participated in two online workshops. The total number of participants was 49. The clinical cases represented LACC with The International Federation of Gynecology and Obstetrics (FIGO) stages from IB3 to IVA. During both, Workshop1 (W1) and Workshop 2 (W2) the following areas of improvement were identified: familiarity with the GEC ESTRO and The International Commission on Radiation Units & Measurements, Report 89 (ICRU 89) recommendations for contouring and planning based on clinical drawings and MRI sequencing choice; appropriate applicator selection; experience with interstitial needles; appropriate applicator reconstruction; dose optimization. The participants rated both workshops with overall scores 8,3 for W1, and 8,5 for W2. In 82% participants the training course fully met expectations for W1, and in 76% in W2. CONCLUSIONSWe successfully implemented the online workshops on image-guided adaptive brachytherapy (IGABT) in LACC. Main performance issues and areas for improvement were identified based on multidisciplinary discussion of participant's clinical cases through all steps of the brachytherapy procedure. We encourage teams to consider online workshops in addition to hands-on training.

Feasibility study of defining planning target volume using surgical margins in permanent breast seed implant brachytherapy

PURPOSEThis study investigates the feasibility and potential impacts of utilizing a Groupe Européen de Curiethérapie-European Society for Therapeutic Radiation and Oncology (GEC ESTRO) recommended surgical margin-based planning margin in permanent breast seed implant (PBSI) brachytherapy. METHODS AND MATERIALSSeventy-nine patients were included in this retrospective study. Three margin selections were used for PTV construction: (1) 1.25 or 1.5 cm isotropic margin (PTVPBSI), (2) 2 cm minus surgical margin in each direction as recommended by GEC ESTRO (PTVaniso), and (3) 2 cm minus minimum surgical margin isotropically (PTViso). PTV volume and dose coverage using clinical PBSI plans were compared across three groups. New PBSI plans were constructed on PTVaniso for 20 patients and planning parameters were compared to original plans constructed on PTVPBSI. RESULTSTwenty patients had surgical margins in six directions reported, with a median value of 8 mm anteriorly, and 10 mm in all other directions. PTVaniso (36.3 ± 15.0 cc) was overall smaller than PTVPBSI (55.6 ± 14.3 cc), p value < 0.05. PBSI clinical plans showed satisfactory coverage on PTVaniso, with a median (range) V100 of 97.9% (85.8%–100.0%). Comparing to original treatment plans, new plans constructed on PTVaniso reduced the number of implant seeds and skin dose. CONCLUSIONSClinical PBSI plans provide satisfactory coverage of GEC ESTRO recommended PTVs. In this patient cohort, GEC ESTRO planning margin resulted in smaller target volumes, and therefore, new plans constructed on PTVaniso required fewer implanted seeds and lower skin doses were achieved. However, given PBSI delivery uncertainties, further investigations are required to determine if the GEC ESTRO planning margin will be sufficiently robust.

GEC-ESTRO ACROP prostate brachytherapy guidelines

This is an evidence-based guideline for prostate brachytherapy. Throughout levels of evidence quoted are those from the Oxford Centre for Evidence based Medicine (https://www.cebm.ox.ac.uk/resources/levels-of-evidence/oxford-centre-for-evidence-based-medicine-levels-of-evidence-march-2009).Prostate interstitial brachytherapy using either permanent or temporary implantation is an established and evolving treatment technique for non-metastatic prostate cancer.Permanent brachytherapy uses Low Dose Rate (LDR) sources, most commonly I-125, emitting photon radiation over months. Temporary brachytherapy involves first placing catheters within the prostate and, on confirmation of accurate positioning, temporarily introducing the radioactive source, generally High Dose Rate (HDR) radioactive sources of Ir-192 or less commonly Co-60. Pulsed dose rate (PDR) brachytherapy has also been used for prostate cancer [1] but few centres have adopted this approach. Previous GEC ESTRO recommendations have considered LDR and HDR separately [2–4] but as there is considerable overlap, this paper provides updated guidance for both treatment techniques.Prostate brachytherapy allows safe radiation dose escalation beyond that achieved using external beam radiotherapy alone as it has greater conformity around the prostate, sparing surrounding rectum, bladder, and penile bulb. In addition there are fewer issues with changes in prostate position during treatment delivery. Systematic review and randomised trials using both techniques as boost treatments demonstrate improved PSA control when compared to external beam radiotherapy alone [5–7].

GEC ESTRO ACROP consensus recommendations for contact brachytherapy for rectal cancer

PurposeTo issue consensus recommendations for contact X-Ray brachytherapy (CXB) for rectal cancer covering pre-treatment evaluation, treatment, dosimetric issues and follow-up. These recommendations cover CXB in the definitive and palliative setting. MethodsMembers of GEC ESTRO with expertise in rectal CXB issued consensus-based recommendations for CXB based on literature review and clinical experience. Levels of evidence according to the Oxford Centre for Evidence based medicine guidance are presented where possible. ResultsThe GEC ESTRO ACROP consensus recommendations support the use of CXB to increase the chances of clinical complete remission and cure for patients who are elderly with high surgical risk, surgically unfit or refusing surgery. For palliative treatment, the use of CXB is recommended for symptomatic relief and disease control. The use of CXB in an organ-preservation setting in surgically fit patients is recommended within the setting of a clinical trial or registry. ConclusionsThe GEC ESTRO ACROP recommendations for CXB are provided. Recommendations towards standardisation of reporting and prescription are given. Practitioners are encouraged to follow these recommendations and to develop further clinical trials to examine this treatment modality and increase the evidence base for its use. The routine collection of outcomes both clinical and patient-reported is also encouraged.

Optimisation de la curiethérapie utérovaginale de débit pulsé des cancers du col utérin localement évolués : résultats finaux du PHRC Tridicol

PurposeWe present the results of the PHRC Tridicol, a prospective French phase II study whose objective was to increase the dose delivered to the target volume during brachytherapy for locally advanced cervical cancers. Material and methodsEight centers included 48 patients, treated with concomitant radiochemotherapy, then uterovaginal brachytherapy. ResultsThe median follow-up was 63 months. The dose of brachytherapy delivered in biological equivalent dose (EQD2) to 90% of the High Risk CTV (D90 CTV HR) was 80Gy in median dose. The 5-year local control rate (LC) was 84%, close to the hypothesis of 86.7%. The rate of severe complications (grade 3–4) was 23% at 5 years. The rectal dose was correlated with the risk of severe complications. ConclusionHR CTV dose was below the target (85Gy) due to low use of parametrial interstitial needles, as the centers did not always have an adequate applicator, or were at the time at the beginning of their learning curve. The 5-year LC rate was improved compared to that of the comparable STIC PDR group (78%) but lower than the retroEMBRACE cohort of GEC ESTRO (89%). The complication rate was higher than in the comparable group of STIC PDR but close to that of retroEMBRACE. Training brachytherapy teams in interstitial implantation or referring patients to referral centers should help improve the therapeutic index of cervical cancer.

Interstitial multi-catheter breast brachytherapy: Technical aspects and experience feedback in a comprehensive cancer center

PurposeTo focus on technical aspects of the implementation of interstitial high dose rate brachytherapy, with a step-by-step approach. Materials and methodsPatients were selected during multidisciplinary tumor boards, according to inclusion criteria adapted from GEC-ESTRO guidelines. A CT scan was performed a few days before implantation. On pre-implant CT, using surgical scar and clips, surgical and pathological reports, and preoperative images, we delineated the tumor bed to be included in the Clinical Target Volume (CTV), according to GEC ESTRO Recommendations. A 3D virtual implant simulation of the best catheter positions was performed in order to cover the target volume. Implantation was then carried out under local anaesthetic using 3D projections of the catheter inlets and outlets. Dosimetry was performed on post-implantation CT scan. A dose of 34Gy was delivered in 10 fractions. Acute and late side effects, and local control were evaluated 2 and 8 months after treatment. ResultsBetween July 2017 and January 2020, 20 patients were treated with accelerated partial breast irradiation. Dose constraints regarding target volume coverage, overdose, dose homogeneity, conformation index and organs at risk were met in 94.7%, 100%, 63.2%, 0% and 89.5% of the treatment plans, respectively. Grade 1-2 acute adverse events were observed in 21% of patients, with no grade 3-4 events. ConclusionThe first dosimetric results and early clinical tolerance and efficacy achieved by the implementation of breast interstitial multicatheter brachytherapy in routine clinical practice are very encouraging, and confirm the interest of extending this practice.

IBS-GEC ESTRO-ABS recommendations for CT based contouring in image guided adaptive brachytherapy for cervical cancer

MR Imaging is regarded asthe gold standardfor Image Gudied Adaptive Brachytherapy (IGABT) for cervical cancer. However, its wide applicability is limited by its availability, logistics and financial implications. Use of alternative imaging like CTand Ultrasound (US) for IGABT has been attempted. In order to arrive at a systematic, uniform and international approach for CT based definition and contouring of target structures, GEC ESTRO, IBS and ABS agreed to jointly develop such recommendations based on the concepts and terms as published in the ICRU Report 89.The minimum requirements are clinical examination & documentation, CT or MR imaging at diagnosis and at a minimum, CT imaging with the applicator in place. The recommendations are based on (i) assessment of the GTV at diagnosis and at brachytherapy, (ii) categorizing the response to external radiation into different clinical remission patterns, (iii) defining various clinico-radiological environments and (iv) definition & delineation of a target on CT imaging at the time of brachytherapy with the applicator in situ. CT based target contouring recommendations based on 4 remission categories within 8 defined environments, aim at improving the contouring accuracy for IGABT using CT, US and MRI as available. For each clinico-radiological environment, there is an attempt to minimize the specific uncertainties in order to arrive at the best possible contouring accuracy.Evaluating feasibility & reproducibility, to achieve a benchmark towards a gold standard MR IGABT and further clinical research including outcomes with CT Based IGABT will become the next steps.

Dosimetric and clinical outcomes of CT based HR-CTV delineation for HDR intracavitary brachytherapy in carcinoma cervix - a retrospective study.

Brachytherapy for carcinoma cervix has moved from Point A based planning to optimization of dose based on HR-CTV. Guidelines have been published by GEC ESTRO on HR-CTV delineation based on clinical gynecological examination and MR sequences. These have given significant clinical results in terms of local control. However, many centers around the country and worldwide still use CT based planning, which restricts HR-CTV delineation, as disease and cervix can rarely be differentiated on a planning CT. Various studies have been done to develop CT based contouring guidelines from the available data, but enough evidence is not available on the clinical outcome when treatment is optimized to HR-CTV contoured on CT images. The purpose of this study is to find out the relation between local control and dosimetry of HR-CTV as delineated on CT images. Patients of locally advanced carcinoma cervix treated radically with EBRT of 50 Gy in 25# and at least 4 cycles of concurrent weekly Cisplatin having a complete or partial response to EBRT were taken for study. All patients had completed CT based Intracavitary brachytherapy to 21 Gy in 3# of 7 Gy per # with dose prescription at point A and optimizing dose to reduce bladder and rectal toxicity. Follow up data on locoregional recurrence was obtained. HR-CTV delineation was done retrospectively on the treatment plan following guidelines by Viswanathan et al. EQD2 doses for EBRT+BT were calculated for point A and HR-CTV D90. The dosimetric data to HR-CTV and to Point A were then compared with patients with locoregional control and with local recurrence. 48 patients were taken, all had squamous cell carcinoma. The median age was 48 years. 33.33% were stage IIA, the rest were stage IIB. Median follow-up was 30 months with 25% developing recurrence of the disease. HR-CTV D90 EQD2 dose was significantly higher in patients with locoregionally controlled disease than in patients with local recurrence (83.97 Gy10 vs. 77.96 Gy10, p = 0.002). Patients with HR-CTV D90 EQD2 dose greater than or equal to 79.75 Gy 10 had better locoregional control than patients receiving dose less than 79.75 Gy10 (p = 0.015). Kaplan Meier plot for PFS showed significantly improved PFS for patients receiving HR-CTV D90 dose of at least 79.75 Gy10 (log-rank p-value = 0.007). Three year progression free survival was 87.1% in patients receiving HR-CTV D90 dose of at least 79.75 Gy10. CT based HR-CTV volume delineation with the help of pre brachytherapy clinical diagrams and MRI imaging may be feasible in a select subgroup of patients with complete or near-complete response to external beam radiation.

3D image guided adaptive brachytherapy in patients with locally advanced cervical cancer: experience and clinical results from a minimum of six years of follow-up

In 2005, individualized 3D image guided brachytherapy was implemented for cervical cancer patients, in accordance with the (GYN) GEC ESTRO recommendation, at St. Olavs Hospital, Trondheim, Norway. This study reports the clinical results of sixty-five consecutive patients treated from 2005 to 2010. The patients were treated with curative intent using external beam radiotherapy, brachytherapy and cisplatin. Results of this treatment are presented, including Kaplan-Meier estimates for overall survival (OS) and cancer specific survival (CSS), as well as biological effective dose normalized to equivalent 2 Gy fractions to tumor, defined as high-risk clinical target volume (CTVH⁢R), and to organs at risk (OARs, here bladder and rectum). Morbidity was prospectively assessed and scored in accordance with the CTCAE 3.0. 92% of the patients achieved treatment response. Local control (LC) remained in all but one patient during follow-up. Five-year OS and CSS were 71% and 80%, respectively. The mean minimum dose to CTVHR for all patients was 80.2 ± 7.3 Gy; 16% and 23% of the patients developed bladder and GI symptoms respectively. 14% of all symptoms were categorized as serious (CTCAE score ≥ 3). A dose-effect relationship was observed for adverse effects of the bladder, and the findings support the more recently recommended lower total dose limit for this OAR.

Dose volume histogram constraints in patients with head and neck cancer treated with surgery and adjuvant HDR brachytherapy: A proposal of the head and neck and skin GEC ESTRO Working group

BackgroundThe Head and Neck and Skin (HNS) Working group of the GEC-ESTRO acknowledges the lack of widely accepted Dose Volume Histogram (DVH) constraints in adjuvant head and neck brachytherapy and issues recommendations to minimize mandibular Osteoradionecrosis (ORN) and Soft Tissue Necrosis (STN). MethodsA total of 227 patients with the diagnosis of head and neck cancer treated with surgery and adjuvant HDR brachytherapy alone or combined with other treatment modalities during the period 2000–2018 were analyzed. ResultsSTN was observed in 28 out of 227 cases (12.3%) with an average time to appearance of 4.0 months. In previously unirradiated cases, there was a positive correlation between CTV size and STN (p = 0.017) and a trend towards significance between Total EQD2-DVH TV100 dose and STN (p = 0.06). The risk of STN in the absence of both factors (i.e, CTV < 15 cm3 and Total EQD2-DVH TV100 dose < 87 Gy) was 2%, with one factor present 15.7% and with both factors 66.7% (p = 0.001). ORN was observed in 13 out of 227 cases (5.7%) with an average time to appearance of 26.2 months. In unirradiated cases, ORN correlated with Total Physical Dose to Mandible2cm3 (p = 0.027). Patients receiving Total Physical Doses greater than 61 Gy had a 20-fold increased risk of ORN. ConclusionsIn Unirradiated patients the panel recommends to avoid implantation of postoperative CTVs exceeding 15 cm3 at Total EQD2-DVH TV100 doses in excess of 87 Gy as well as to limit the irradiation of the Mandible2cm3 to 61 Gy. In previously irradiated patients the panel cannot make a recommendation based on the available results.

Outcomes of freehand interstitial brachytherapy in advanced gynecologic malignancies

PurposeThe purpose of the study is to present the first results of freehand interstitial brachytherapy (ISBT) used to treat patients with carcinoma of the cervix and the vagina. Methods and MaterialsPatients diagnosed with carcinoma of the cervix or carcinoma of the vagina who were not suitable for intracavitary brachytherapy were treated with freehand ISBT. The implant was performed transperineally using C arm or transrectal ultrasound guidance. Patients received an external beam radiotherapy dose of 50 Gy in 25 fractions. The dose delivered by high-dose-rate ISBT was 18 Gy in three fractions, 6 Gy per fraction, 6 h apart. The brachytherapy dose volume parameters were analyzed after CT-based planning using GEC ESTRO image-guided brachytherapy-based guidelines. ResultsFrom June 2018 till November 2018, 14 patients were treated with freehand ISBT. The mean dose received by 90% of the high-risk clinical target volume (D90) was 82 Gy EQD210 for patients with carcinoma of the cervix and 80 Gy EQD210 for patients with carcinoma of the vagina. The mean dose received by 2 cc volume of the bladder and rectum was 80 Gy EQD23 and 70 Gy EQD23 for patients with carcinoma of the cervix and 75 Gy EQD23 and 72 Gy EQD23 for patients with carcinoma of the vagina, respectively. The mean dose received by 2 cc of the sigmoid was 65 Gy EQD23 for cervical carcinoma and 58 Gy EQD23 for vaginal carcinoma, respectively. At a median followup of 14 months, 2 patients developed local recurrence. Two patients developed Grade 2 gastro intestinal toxicity, and 1 patient developed Grade 2 genitourinary toxicity. None of the patients developed Grade 3 or 4 toxicities. ConclusionA freehand interstitial implant is feasible in resource limited settings and provides acceptable local control with minimal acute toxicity.

Differences Between MRI- and CT-Based Delineation of Target Volume and Organs at Risk in High-Dose-Rate Brachytherapy of Cervix

With superior soft tissue imaging characteristics, MRI is better than CT in determining the local disease extent during intracavitary brachytherapy of carcinoma cervix. The aim of the study is to evaluate the differences in dimensions and volumes of the target and organs at risk and the subsequent changes in dosimetry between MRI- and CT-based plans. MRI and CT datasets of 34 locally advanced cervical cancer patients taken up for intracavitary brachytherapy between January and September 2017 were analyzed. The target volumes and organs at risk, namely bladder, rectum and sigmoid, were contoured by the same radiation oncologist on both the MRI and CT images as per the GEC ESTRO guidelines. The dimensions of HRCTV, the dose volume parameters of the target and OAR were recorded for the CT and MRI plans. CT image significantly overestimated the width (p = 0.000) and thickness (p = 0.009) of HRCTV. The volumes of HRCTV (p = 0.000) and IRCTV (p = 0.041) were larger with CT image compared to MRI. There was no statistically significant difference between rectal (p = 0.107) and sigmoid (p = 0.365) volumes on CT and MRI. There was statistically significant difference (all p 0.05) in the dose received by rectum and sigmoid on CT and MR plans. MRI-based brachytherapy planning has shown considerable improvements in tumor control and reductions in normal tissue toxicity. However, the high cost of MRI and non-availability of MRI preclude its use in many centers. CT, on the other hand, is widely available, but it can lead to overestimation of the target, at the time of brachytherapy. Hence, it is important to identify the subset of patients who will benefit from MRI-based planning at the time of brachytherapy.

Dosimetric comparison of 60Co and 192Ir high dose rate source used in brachytherapy treatment of cervical cancer.

The study purpose included dosimetric comparison of cobalt 60 (60Co) and iridium 192 (192Ir) high dose rate (HDR) source used in brachytherapy treatment of cervical cancer. Computed tomography (CT) scans for 15 patients of carcinoma of uterine cervix using 3-mm slice thickness were considered for the study The contouring of high-risk clinical target volume (HRCTV), bladder, and rectum on CT images was done as per the GEC ESTRO guidelines with the help of magnetic resonance imaging images in the treatment planning system. All parameters were kept the same for 60Co (3.5 mm active length, 0.5 mm active dia, Bebig) and 192Ir (3.5 mm active length, 0.6 mm active dia, Bebig) HDR source with 2.5-mm step size and dose prescription to Point A. As per the International Commission on Radiation Unit (ICRU)-89 guidelines, the dose-volume parameters such as D50(Gy), D90(Gy), and D98(Gy) for HRCTV and D0.1cc (Gy), D1cc (Gy), D2cc (Gy), and D5cc (Gy) to the bladder and rectum were calculated for both the HDR sources. The difference in dose-volume histogram parameters such as D50,D90,and D98 of HRCTV was 3.19%, 1.13%, and 0.50%, respectively, for the two radioisotopes. The difference in dose values of D0.1cc, D1cc, D2cc, D5cc, and ICRU reference points of bladder was -0.58%, -0.67%, -0.99%, -0.94%, and -1.75%, respectively. On the other hand, dose difference for D0.1cc, D1cc, D2cc, D5cc, and ICRU reference points of rectum was 0.67%, 0.26%, 0.56%, 0.63%, and -0.33%, respectively. The present study results show that all the dose parameters of HRCTV, bladder, and rectum with 60Co were comparable with those of 192Ir HDR source. The isodose distribution is more bulge out for 60Co in cranial-caudal direction compared to that of 192Ir. However, these differences can be reduced by treatment planning optimization techniques. The clinical plan evaluation in each slice and plane is necessary to explore the logistic and financial benefits of miniaturized 60Co source over 192Ir HDR source.

Dose and Volume Parameters for MRI-Guided Cervix Cancer Brachytherapy in the Embrace Trial

The international study on MRI-guided Brachytherapy in locally Advanced Cervical cancer (EMBRACE, www.embracestudy.dk) is a prospective observational study of treatment and clinical outcome data of 1416 patients with locally advanced cervical cancer from 23 centers, who were treated with radiochemotherapy (EBRT and image-guided brachytherapy (IGBT), between 2008 and 2016. EMBRACE data reflect the implementation of MRI-based IGBT through a variety of institutional protocols. The aim of this analysis was to report on the overall status of the implementation of this technique and to analyze dose-volume parameters according to GEC ESTRO recommendations. There were 1300 patients with complete treatment data records were included in this analysis. The distribution of implant types (intracavitary [ic] or intracavitary/interstitial [ic/is]), and dose rate schedules (high/pulsed dose rate [HDR/PDR]) was analyzed. Total treatment doses including EBRT and IGBT were converted to biologically equieffective dose in 2Gy fractions (EQD2) using the linear quadratic model, and dose reporting parameters for high-risk CTV (CTVHR) and organs at risk according to ICRU89 and GEC-ESTRO recommendations. A subgroup analysis was performed for different target volumes. Almost all patients were treated with EBRT of 45-50.4 Gy to the elective PTV, with 3D conformal (58%) or IMRT (42%) techniques. HDR BT (57%) was delivered mostly in 3 (20%), 4 (73%) or 5 (7%) fractions; PDR BT (42%) in 1 or 2 fractions (50%/50%). Most BT treatments were delivered with ring applicators (58%), followed by ovoids (27%), vaginal molds (12%) or cylinders (1%). IC applicators were exclusively used in 56% of patients, 44% were treated with ic/is only, or a combination of techniques. In ic/is implants the mean number of active needles per patient was 4.1±2.8. The mean overall treatment time for EBRT (including any sequential nodal boosts) and BT was 46.5±6.5 days. BT was administered after delivery of at least 45Gy of EBRT in 58% of patients, while 39% of BT treatments started after 30-45 Gy EBRT. The FIGO stage distribution was 19% 1B, 5% 2A, 52% 2B, 1% 3A, 15% 3B, 3% 4A, and 5% 4B. The median CTVHR volume was 28.7 cm3 (mean 34.5±21.5 cm3). The mean CTVHR D90 was 89.7±8.8 Gy EQD210. For ic treatments, the mean point A dose was 74.1±7.6 Gy EQD210. For ic and ic/is groups, with mean CTVHR volumes of 26.5 and 44.8 cm3, the mean CTVHR D90 were 90.5/88.7 Gy EQD210. Overall, for CTVHR volumes </> 30cm3, the mean D90 was 92.5/86.5 Gy EQD210, mean D2cm3 was 73.8/79.4 for bladder, and 61.1/64.3 Gy EQD23 for rectum. In total 76% of all patients received a CTVHR D90>85 Gy EQD210, 92% had a bladder D2cm3 <90 Gy EQD3, and 95% had a rectum D2cm3 <75Gy EQD3. The prospective EMBRACEII protocol will further promote the implementation of IGBT with ic/is technique. Further improvement of target coverage and organ sparing is expected.

Impact of MR geometric distortion on brachytherapy in cervical cancer

Introduction Volumetric imaging and in particular magnetic resonance (MR) has replaced the 2D imaging for brachytherapy treatment planning. However it is recognized that MR images suffer from geometric distortions which can have an impact on target and OARs DVH parameters due to high dose gradient in brachytherapy applications. Objective To assess the potential dosimetric impact of MR geometric distortion on the brachytherapy treatment planning for cervical cancer. Materials and methods MR dataset for 15 cervical cancer patients were acquired based on GEC ESTRO recommendations. Structures were delineated on the paraaxial images and treatment plans were generated using Oncentra™ TPS. In-house software was developed to calculate the deformable registration between CT and MR images of a control point based phantom and to derive a distortion map of the MR system. Geometrically corrected images were then generated by applying the inverse of the distortion map. Structures were copied and adapted to the corrected datasets and the treatment plans recomputed. Dose Volume Histograms (DVH) were evaluated for High Risk CTV (HRCTV), bladder, rectum, and sigmoid. Results Mean geometric distortions were less than 0.5 mm over a Field Of View (FOV) of 350 mm. Differences in D100 and D90 were less than 2% for HRCTV. Differences in D2cc were less than 4% for bladder, rectum, and sigmoid. Preliminary results showed that, for all organs, less than 4% of deviation was observed for D100 and D90. Conclusions For an FOV of 350 mm, MR geometric distortion has no significant dosimetric impact on DVH parameters in brachytherapy for cervical cancer. Disclosure Authors have nothing to disclose.

A volumetric analysis of GTVD and CTVHR as defined by the GEC ESTRO recommendations in FIGO stage IIB and IIIB cervical cancer patients treated with IGABT in a prospective multicentric trial (EMBRACE)

PurposeTo quantify the gross tumor volume at diagnosis (GTVD) and high-risk clinical target volume (CTVHR) at brachytherapy (BT) and describe subgroups of patients with different patterns of response to chemoradiotherapy (CRT) in patients with FIGO stage IIB and IIIB cervical cancer treated with image-guided adaptive brachytherapy (IGABT). Additionally, to evaluate the feasibility of IGABT achieving adequate target coverage in these groups. Materials and methodsPatients with FIGO stage IIB and IIIB cervical cancer enrolled in the EMBRACE study were analyzed. T2-weighted MRI scans were obtained at diagnosis and at BT. GTVD and CTVHR were defined as per the GEC ESTRO recommendations. Patients were classified taking into account that initial tumor volume and response to CRT represented by the volume of residual disease (CTVHR) and extent of residual parametrial disease are all major factors determining local dose delivery by BT, local control, and overall disease outcome. These factors were quantified applying the following criteria: (1) volume of the GTVD relative to the median volume of the GTVD; (2) the ratio (R) of CTVHR to GTVD for each patient; (3) the extent of residual parametrial disease at the time of BT. Accordingly, patients were classified into six groups (G1–G6): stage IB1-like tumors (G1), tumors with good response and any size (G2), small tumors with moderate response (G3), large tumors with moderate response (G4), tumors with poor response (G5) and those with progressive disease (G6). Tumor and treatment characteristics were then compared among the first five groups (only 3 patients were allocated to G6). ResultsA total of 481 patients were evaluated. The number of patients in the 6 groups were 55, 78, 123, 147, 75 and 3, respectively. The mean (SD) GTVD was 43.6 (32.8)cm3 and the mean (SD) CTVHR was 31.6 (16.1)cm3. The mean GTVD and CTVHR were 12.6cm3 and 23.7cm3 in G1 (R>1.1), 47.5cm3 and 25.3cm3 in G2 (R<0.9), 23.9 cm3 and 29.9cm3 in G3 (R 0.9–1.1), 73.4cm3 and 38.5cm3 in G4 (R 0.9–1.1), 79.4cm3 and 59.5cm3 in G5 (R>1.1), respectively. Parametrial disease extent at BT was as follows: no involvement in G1 and G2, proximal at most in G3 and G4, distal or to the pelvic wall in G5, progressive in G6. The use of interstitial needles was progressively higher among the groups (mean 0, 0, 2, 3, 6 in G1–5, P<0.001). The mean GTVBT D100 in G1-5 was 103.1Gy, 91.8Gy, 93.5Gy, 88.3Gy and 87.1Gy. The mean CTVHR D90 in G1-5 was 95.1Gy, 92.1Gy, 92.6Gy, 87.6Gy and 88.4Gy. ConclusionsIn patients with FIGO stage IIB and IIIB disease, intra-FIGO stage heterogeneity and overlap between the two stages exist with respect to tumor volume, treatment response and extent of parametrial disease at BT. Taking into account GTVD, parametrial disease at BT and the ratio of CTVHR/GTVD, five major groups exist. These enable prediction of GTVBT and CTVHR dose coverage through BT. IGABT, as performed in EMBRACE, accommodates to a considerable degree for the different variants of tumor regression in these groups through adaptation of the treatment technique including the use of needles. However, major variations remain at present with regard to dose to GTVBT and to CTVHR, which are most pronounced in G4 and G5. This new classification will be validated in future in regard to clinical outcome in EMBRACE.

TH‐AB‐BRA‐04: Dosimetric Evaluation of MR‐Guided HDR Brachytherapy Planning for Cervical Cancer

Purpose:To perform a retrospective study on 16 patients that had both CT and T2‐weighted MR scans done at first fraction using the Utrecht CT/MR applicator (Elekta Brachytherapy) in order to evaluate uncertainties associated with an MR‐only planning workflow.Methods:MR‐workflow uncertainties were classified in three categories: reconstruction, registration and contouring. A systematic comparison of the CT and MR contouring, manual reconstruction and optimization process was performed to evaluate the impact of these uncertainties on the recommended GEC ESTRO DVH parameters: D90% and V100% for HR‐CTV as well as D2cc for bladder, rectum, sigmoid colon and small bowel. This comparison was done using the following four steps: 1. Catheter reconstruction done on MR images with original CT‐plan contours and dwell times. 2. OAR contours adjusted on MR images with original CT‐plan reconstruction and dwell times. 3. Both reconstruction and contours done on MR images with original CT‐plan dwell times. 4. Entire MR‐based workflow optimized dwell times reimported to the original CT‐plan.Results:The MR‐based reconstruction process showed average D2cc deviations of 4.5 ± 3.0%, 1.5 ± 2.0%, 2.5 ± 2.0% and 2.0 ± 1.0% for the bladder, rectum, sigmoid colon and small bowels respectively with a maximum of 10%, 6%, 6% and 4%. The HR‐CTV's D90% and V100% average deviations was found to be 4.0 ± 3.0%, and 2.0 ± 2.0% respectively with a maximum of 10% and 6%. Adjusting contours on MR‐images was found to have a similar impact. Finally, the optimized MR‐based workflow dwell times were found to still give acceptable plans when re‐imported to the original CT‐plan which validated the entire workflow.Conclusion:This work illustrates a systematic validation method for centers wanting to move towards an MR‐only workflow. This work will be expanded to model based reconstruction, PD‐weighted images and other types of applicators.

Recommendations from GEC ESTRO Breast Cancer Working Group (II): Target definition and target delineation for accelerated or boost partial breast irradiation using multicatheter interstitial brachytherapy after breast conserving open cavity surgery

ObjectiveTo prepare guidelines for target definition and delineations after open cavity breast conserving surgery in accelerated partial breast irradiations or boost treatments using multicatheter interstitial brachytherapy based on the consensus of the Breast Working Group of GEC-ESTRO. MethodFollowing a study on interobserver variations of target volume delineation in multicatheter breast brachytherapy after open cavity surgery and a number of discussions in consensus meetings these guidelines were worked out by experts on the field. Proposed recommendations(1) Consistent windowing has to be used for proper cavity visualization. (2) The cavity visualization score has to be at least 3 in order to minimize the interobserver variations of target definition. (3) At delineation of surgical cavity only the homogeneous part of the postoperative seroma has to be included in the contours and protrusions or sharp irregularities have to be excluded. When surgical clips are present, they have to be surrounded by the contour with close contact. (4) CTV is created from the outlined surgical cavity with a nonisotropic geometrical extension. In each direction the safety margin is calculated by taking into account the size of the free resection margin. The total size of safety margin is always 20mm which is the sum of the surgical and added safety margins. CTV is limited to chest wall/pectoral muscles and 5mm below the skin surface. ConclusionFollowing these guidelines the target volume definition in breast brachytherapy after open cavity surgery is expected to be accomplished in more consistent way with low interobserver variations.