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M.A. Zajac, R. Chicas-Sett, I. Morales-Orue, J. Castilla Martinez, J. Zafra, J. Blanco, A. Kannemann, M. Lloret Saez-Bravo, P. Lara, Poster: Clinical track: Elderly PO-1272: Immunoradiotherapy induces a rechallenge of the immune response in elderly patients. [Extracted from the article]

Up to 80% of patients under immune checkpoint inhibitors (ICI) face resistance. In this context, stereotactic ablative radiotherapy (SABR) can induce an immune or abscopal response. However, its molecular determinants remain unknown. We present early results of a translational study assessing biomarkers of response to combined ICI and SABR (I-SABR) in liquid biopsy from oligoprogressive patients in a prospective observational multicenter study. Cohort A includes metastatic patients in oligoprogression to ICI maintaining the same ICI due to clinical benefit and who receive concomitant SABR. B is a comparative group of oligometastatic patients receiving only SABR. Blood samples are extracted at baseline (T1), after the first (T2) and last (T3) fraction, two months post-SABR (T4) and at further progression (TP). Response is evaluated by iRECIST and defined by the objective response rate (ORR)-complete and partial responses. We assess peripheral blood mononuclear cells (PBMCs), circulating cell-free DNA (cfDNA) and small RNA from extracellular vesicles. Twenty-seven patients could be analyzed (cohort A: n = 19; B: n = 8). Most were males with non-small cell lung cancer and one progressing lesion. With a median follow-up of 6 months, the last ORR was 63% (26% complete and 37% partial response). A decrease in cfDNA from T2 to T3 correlated with a good response. At T2, CD8+PD1+ and CD8+PDL1+ cells were increased in non-responders and responders, respectively. At T2, 27 microRNAs were differentially expressed. These are potential biomarkers of response to I-SABR in oligoprogressive disease.

Objectives: Naloxegol is a peripherally acting µ-opioid receptor antagonist (PAMORA) for treatment of opioid-induced constipation (OIC). The main objective was to analyse the long-term efficacy, quality of life (QOL) and safety of naloxegol in patients with cancer in a real-world study., Methods: This one-year prospective study included patients older than 18 years, with active oncological disease who were under treatment with opioids for pain control and Karnofsky≥50 and OIC with inadequate response to treatment with laxative (s). All the patients received treatment with naloxegol according to clinical criteria. The main efficacy objectives were measured by the patient assessment of constipation QOL questionnaire (PAC-QOL), the PAC symptoms (PAC-SYM), the response rate at day 15, and months 1-3-6-12, and global QOL (EuroQoL-5D-5L)., Results: A total of 126 patients (58.7% males) with a mean age of 61.5 years (95% CI 59.4 to 63.7) were included. PAC-SYM and PAC-QOL total score and all their dimensions improved from baseline (p<0.0001). At 12 months, 77.8% of the patients were responders to naloxegol treatment. Global QOL was conserved from baseline. A total of 28 adverse reactions, mainly gastrointestinal were observed in 15.1% of the patients (19/126), being 75% (21) mild, 17.9% (5) moderate and 7.1% (2) severe. Most adverse reactions (67.9%) appeared the first 15 days of treatment., Conclusion: The results of this first long-term and real-world-data study in patients with cancer, showed the sustained efficacy and safety of naloxegol for the treatment of OIC in this group of patients., Competing Interests: Competing interests: MC, CB and LC-G received payment from Kyowa Kirin Farmacéutica, S.L. for their participation in the design and coordination of the study. IH, and AS-Y are employees of Kyowa Kirin Farmacéutica, S.L. BSL was contracted by Kyowa Kirin Farmacéutica, S.L. for the design, monitoring and statistical analysis of the study, and for preparation of the manuscript for publication. The rest of the authors declare that they have no conflicts of interest with the study results., (© Author(s) (or their employer(s)) 2023. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Oligometastatic disease (OMD) defines a cancer status that is intermediate between localized and widely spread metastatic disease, and can be treated with curative intent. While diagnostic imaging tools have considerably improved in recent years, unidentified micrometastases can still evade current detection techniques, allowing the disease to progress. The various OMD scenarios are mainly defined by the number of metastases, the biological and molecular tumour profiles, and the timing of the development of metastases. Increasing knowledge has contributed to the earlier and improved detection of OMD, underlining the importance of early disease control. In view of increasing OMD detection rates in current real-world clinical practice and the lack of standardized evidence-based guidelines to treat this cancer status, a board of experts from the Spanish Societies of Radiation Oncology (SEOR) and Medical Oncology (SEOM) organized a series of sessions to update the current state-of-the-art on OMD from a multidisciplinary perspective, and to discuss how results from clinical studies might translate into promising treatment options. This expert review series summarizes what is known and what it is pending clarification in the context of OMD in the scenarios of non-small cell lung cancer and breast cancer (Part I), and prostate cancer and colorectal cancer (Part II), aiming to offer specialists a pragmatic framework to help improve patient management., (© 2022. The Author(s), under exclusive licence to Federación de Sociedades Españolas de Oncología (FESEO).)

Oligometastatic disease (OMD) defines a status of cancer that is intermediate between localized and widely spread metastatic disease, and can be treated with curative intent. While imaging diagnostic tools have considerably improved in recent years, unidentified micrometastases can still escape from current detection techniques allowing disease to progress. The variety of OMD scenarios are mainly defined by the number of metastases, the biological and molecular tumour profiles, and the timing of the development of metastases. Increasing knowledge has contributed to the earlier and improved detection of OMD, underlining the importance of an early disease control. Based on increasing detection rates of OMD in the current real clinical practice and the lack of standardized evidence-based guidelines to treat this cancer status, a board of experts from the Spanish Societies of Radiation Oncology (SEOR) and Medical Oncology (SEOM) organized a series of sessions to update the current state-of-the-art on OMD from a multidisciplinary perspective, and to discuss how results from clinical studies may translate into promising treatment options. This experts' review series summarizes what is known and what it is pending clarification in the context of OMD in the scenarios of Non-Small Cell Lung Cancer and Breast Cancer (Part I), and Prostate Cancer and Colorectal Cancer (Part II), aiming to offer specialists a pragmatic framework that might contribute to the improved management of patients., (© 2022. The Author(s), under exclusive licence to Federación de Sociedades Españolas de Oncología (FESEO).)

The advent of targeted therapy has transformed the treatment paradigm and survival of patients with metastatic non-small cell lung cancer (NSCLC) with driver mutations. The development of acquired resistances during treatment with tyrosine kinase inhibitors (TKIs) impedes a prolonged survival in many patients. This fact is leading to the use of locally ablative therapies such as stereotactic ablative radiotherapy (SABR) to counter these resistances. SABR is a non-invasive treatment that can be delivered in multiple locations and has already proven effective in oligometastatic disease. Clinical evidence suggests that the combination of SABR with TKIs prolongs progression-free survival (PFS) in metastatic NSCLC patients with mutations in epidermal growth factor receptor (EGFR), with international guidelines recommending their use in unfavorable scenarios such as oligoprogressive disease. In this publication, we have reviewed the available evidence on EGFR-TKIs resistance mechanisms and the combination of SABR with TKI in metastatic NSCLC with EGFR mutations. We also describe the utility and clinical recommendations of this combination in oligometastatic and oligoprogressive disease., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Chicas-Sett, Castilla Martinez, Hernández Blanquisett, Zafra and Pastor-Peidro.)

Purpose: The percentage of patients with metastatic non-small cell lung cancer (NSCLC) and melanoma who benefit from anti-programmed cell death protein 1 (anti-PD-1) is low owing to resistance mechanisms. SABR has a role in oligoprogressive disease and can improve responses to anti-PD-1. This multicenter prospective observational study aimed to determine whether concomitant anti-PD-1 and SABR to oligoprogressive sites enhance tumor response in metastatic NSCLC and melanoma., Methods and Materials: Patients with metastatic NSCLC or melanoma in progression to anti-PD-1 but continuing the same line owing to clinical benefit were referred for palliative SABR. All patients received concomitant pembrolizumab or nivolumab and SABR to 1 to 5 lesions, maintaining anti-PD-1 until further progression, unacceptable toxicity, or medical/patient decision. Objective response rate-complete responses and partial responses-was evaluated during all follow-up according to Response Evaluation Criteria in Solid Tumors 1.1. The abscopal response was evaluated 8 weeks after SABR as a ≥30% reduction in 1 to 2 predefined nonirradiated lesions., Results: Of the 61 patients enrolled, 50 could be analyzed. With a median follow-up of 32.8 months, objective response rate was 42% (30% complete responses and 12% partial responses). Median progression-free survival was 14.2 months (95% confidence interval, 6.9-29 months). Median overall survival since SABR was 37.4 months (95% confidence interval, 22.9 months-not reached). Abscopal response was 65%, evaluated in 40 patients who fulfilled the criteria., Conclusions: Combined anti-PD-1 and SABR in oligoprogressive metastatic NSCLC or melanoma can achieve high rates of response and extend the clinical benefit of immunotherapy by delaying further progression and a new systemic therapy. This approach should be assessed in larger randomized trials., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Non-small cell lung cancer (NSCLC) is a heterogeneous disease accounting for approximately 85% of all lung cancers. Only 17% of patients are diagnosed at an early stage. Treatment is multidisciplinary and radiotherapy plays a key role in all stages of the disease. More than 50% of patients with NSCLC are treated with radiotherapy (curative-intent or palliative). Technological advances-including highly conformal radiotherapy techniques, new immobilization and respiratory control systems, and precision image verification systems-allow clinicians to individualize treatment to maximize tumor control while minimizing treatment-related toxicity. Novel therapeutic regimens such as moderate hypofractionation and advanced techniques such as stereotactic body radiotherapy (SBRT) have reduced the number of radiotherapy sessions. The integration of SBRT into routine clinical practice has radically altered treatment of early-stage disease. SBRT also plays an increasingly important role in oligometastatic disease. The aim of the present guidelines is to review the role of radiotherapy in the treatment of localized, locally-advanced, and metastatic NSCLC. We review the main radiotherapy techniques and clarify the role of radiotherapy in routine clinical practice. These guidelines are based on the best available evidence. The level and grade of evidence supporting each recommendation is provided., Competing Interests: Conflict-of-interest statement: Rodríguez De Dios N reports personal fees from AstraZeneca, and Siemens Healthcare outside the submitted work. Couñago F reports personal fees from Astellas Pharma and AstraZeneca outside the submitted work. All other authors declare no competing interests., (©The Author(s) 2022. Published by Baishideng Publishing Group Inc. All rights reserved.)

Stereotactic ablative body radiotherapy (SABR) is an effective technique comparable to surgery in terms of local control and efficacy in early stages of non-small cell lung cancer (NSCLC) and pulmonary metastasis. Several fractionation schemes have proven to be safe and effective, including the single fraction (SF) scheme. SF is an option cost-effectiveness, more convenience and comfortable for the patient and flexible in terms of its management combined with systemic treatments. The outbreak of the severe acute respiratory syndrome coronavirus 2 pandemic has driven this not new but underutilized paradigm, recommending this option to minimize patients' visits to hospital. SF SABR already has a long experience, strong evidence and sufficient maturity to reliably evaluate outcomes in peripheral primary NSCLC and there are promising outcomes in pulmonary metastases, making it a valid treatment option; although its use in central locations, synchronous and recurrencies tumors requires more prospective safety and efficacy studies. The SABR radiobiology study, together with the combination with systemic therapies, (targeted therapies and immunotherapy) is a direction of research in both advanced disease and early stages whose future includes SF., Competing Interests: Conflict-of-interest statement: The authors declare having no conflicts of interests related to this article., (©The Author(s) 2022. Published by Baishideng Publishing Group Inc. All rights reserved.)

Immunotherapy has represented one of the main medical revolutions of recent decades, and is currently a consolidated treatment for different types of tumors at different stages and scenarios, and is present in a multitude of clinical trials. One of the diseases in which it is most developed is non-small cell lung cancer. The combination of radiotherapy and immunotherapy in cancer in general and lung cancer in particular currently represents one of the main focuses of basic and clinical research in oncology, due to the synergy of this interaction, which can improve tumor response, resulting in improved survival and disease control. In this review we present the biochemical and molecular basis of the interaction between radiotherapy and immunotherapy. We also present the current clinical status of this interaction in each of the stages and cases of non-small cell lung cancer, with the main results obtained in the different studies both in terms of tumor response and survival as well as toxicity. Finally, we mention the main studies underway and the challenges of this interaction in the coming years, including how these treatments should be combined to achieve the greatest efficacy with the fewest possible side effects (dose, type of radiotherapy and drugs, sequence of treatments)., Competing Interests: Conflict-of-interest statement: No conflict of interest., (©The Author(s) 2021. Published by Baishideng Publishing Group Inc. All rights reserved.)

Objectives: Opioid-induced constipation (OIC) can affect up to 63% of all patients with cancer. The objectives of this study were to assess quality of life as well as efficacy and safety of naloxegol, in patients with cancer with OIC., Methods: An observational study was made of a cohort of patients with cancer and with OIC exhibiting an inadequate response to laxatives and treated with naloxegol. The sample consisted of adult outpatients with a Karnofsky performance status score ≥50. The Patient Assessment of Constipation Quality of Life Questionnaire (PAC-QOL) and the Patient Assessment of Constipation Symptoms (PAC-SYM) were applied for 3 months., Results: A total of 126 patients (58.2% males) with a mean age of 61.3 years (range 34-89) were included. Clinically relevant improvements (>0.5 points) were recorded in the PAC-QOL and PAC-SYM questionnaires (p<0.0001) from 15 days of treatment. The number of days a week with complete spontaneous bowel movements increased significantly (p<0.0001) from 2.4 to 4.6 on day 15, 4.7 after 1 month and 5 after 3 months. Pain control significantly improved (p<0.0001) during follow-up. A total of 13.5% of the patients (17/126) presented some gastrointestinal adverse reaction, mostly of mild (62.5%) or moderate intensity (25%)., Conclusions: Clinically relevant improvements in OIC-related quality of life, number of bowel movements and constipation-related symptoms were recorded as early as after 15 days of treatment with naloxegol in patients with cancer and OIC, with a good safety profile., Competing Interests: Competing interests: MCD, CBZ and LCG received payment from Kyowa Kirin Farmacéutica, S.L.U. for their participation in the design and coordination of the study. AJJL, IHG and ASY are employees of Kyowa Kirin Farmacéutica, S.L.U. BSL was contracted by Kyowa Kirin Farmacéutica, S.L.U. for the design, monitoring and statistical analysis of the study, and for preparation of the manuscript for publication., (© Author(s) (or their employer(s)) 2021. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Opinion Statement: Management of chronic pain is crucial to improve the quality of life of cancer and palliative care patients. Opioid-based treatments used to control pain can be prolonged over time. Unfortunately, constipation is one of the most disturbing adverse effects of long-term use of opioids. Opioid-induced constipation (OIC) occurs when opioids bind to the specific receptors present in the gastrointestinal (GI) tract, and can affect any patients receiving chronic opioid therapy, including cancer patients. The limited efficacy of laxatives to treat OIC symptoms prompted the search for new therapeutic strategies. Peripherally acting μ-opioid receptor antagonists (PAMORAs) have recently emerged as new effective drugs for OIC management due to their specific binding to enteric μ-receptors. Little information is available on the use of PAMORAs in real-life practice for OIC treatment in cancer patients. In this paper, a panel of experts specializing in cancer and palliative care pools their clinical experience with PAMORAs in cancer patients presenting OIC and highlights the importance of timing and choice of therapy in achieving prompt OIC management and benefitting patients.

Lung cancer is one of the main causes of cancer-related mortality worldwide. Over the years, different therapeutic modalities have been adopted depending on tumor stage and patient characteristics, such as surgery, radiotherapy (RT), and chemotherapy. Recently, with the development of immune-checkpoint inhibitors (ICI), the treatment of metastatic and locally advanced non-small cell lung cancer (NSCLC) has experienced a revolution that has resulted in a significant improvement in overall survival with an enhanced toxicity profile. Despite this paradigm shift, most patients present some kind of resistance to ICI. In this setting, current research is shifting towards the integration of multiple therapies, with RT and ICI being one of the most promising based on the potential immunostimulatory synergy of this combination. This review gives an overview of the evolution and current state of the combination of RT and ICI and provides evidence-based data that can improve patient selection. The combination in lung cancer is a safe therapeutic approach that improves local control and progression-free survival, and it has the potential to unleash abscopal responses. Additionally, this treatment strategy seems to be able to re-sensitize select patients that have reached a state of resistance to ICI, further enabling the continuation of systemic therapy.

Breast cancer (BC) is the principal cause of cancer-related death in women. Metastatic patients are usually treated with a systemic therapy, but clinical results are limited. Oligometastatic subjects can benefit from high-precision radiotherapy techniques to potentially achieve a complete response. Currently, there is limited evidence of stereotactic ablative radiotherapy (SABR) treatments in elderly oligometastatic cancer patients. A review of the medical literature was performed in PubMed database to assess the current role of SABR in the treatment of breast oligometastases in elderly patients. SABR represents a feasible and safe therapeutic approach in oligometastatic elderly BC patients. Further studies are required to establish the optimum patient selection and treatment scheme., Competing Interests: Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at http://dx.doi.org/10.21037/tcr.2019.08.29). The series “Radiotherapy for Breast Cancer in Advanced Age” was commissioned by the editorial office without any funding or sponsorship. The authors have no other conflicts of interest to declare., (2020 Translational Cancer Research. All rights reserved.)

Background: Immune checkpoint inhibitors (ICI) have represented a revolution in the treatment of non-small-cell lung cancer (NSCLC). To improve these results, combined approaches are being tested. The addition of stereotactic ablative radiotherapy (SABR) to ICI seems promising. A systematic review was performed in order to assess the safety and efficacy of SABR-ICI combination. Material and Methods: MEDLINE databases from 2009 to March 3, 2019 were reviewed to obtain English language studies reporting clinical outcomes of the combination of ICI-SABR in NSCLC. 18 out of the 429 initial results fulfilled the inclusion criteria and were selected for review. Results: Eighteen articles, including six prospective studies, describing 1736 patients treated with an ICI-SABR combination fulfilled the selection criteria. The reported mean rates for local control and distant/abscopal response rates were 71% and 41%, respectively. Eleven studies reported progression-free survival and overall survival, with a mean of 4.6 and 12.4 months, respectively. Toxicity rates were consistent with the ones attributable to ICI treatment alone. Conclusions: The ICI-SABR combination has a good safety profile and achieves high rates of local control and greater chances of obtaining abscopal responses than SABR alone, with a relevant impact on PFS. More studies are needed to improve patient selection for an optimal benefit from this approach.

Over the last decade, immunotherapy has emerged as a hopeful alternative in cancer therapy. Different drugs are used to stimulate the immune system and block negative immune regulatory pathways, known as "immune checkpoint inhibitors (ICI)". Although clinical studies have reported efficacy and safety with the use of ICI, only a small group of patients have obtained a clinical benefit. Because of this, immunomodulation based on immunogenic cell death produced by radiotherapy (RT) has been well positioned as an alternative to increase the clinical effect on the primary neoplasm, but also in distant tumours, a phenomenon known as the "abscopal effect". Early clinical outcomes with RT-ICI combination are promising, but the rate of abscopal responses remains low. These developments have opened a path to evaluate the use of nanotechnology as antigen-capturing nanoparticles (AC-NPs) for improving clinical outcomes in metastatic disease treated with RT-ICI. In this review, we aim to highlight the basic characteristics of nanoparticles and its application in oncology, focusing on their potential to enhance abscopal responses.

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 D 0.1cc , D 1cc , and D 2cc 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 (EQD 2α/β = 3 )., Results: The interobserver coefficients of variation (±standard deviation) for the reported D 0.1cc , D 1cc , and D 2cc 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 D 0.1cc , D 1cc , and D 2cc were 10 Gy, 7.3 Gy, and 6.6 Gy, respectively., Conclusions: The D 2cc 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., (Copyright © 2017 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.)

Background: In the last years, limited studies have described that radiotherapy could produce important distant responses in unirradiated sites, the so-called "abscopal effect". Recent evidence suggests that radiotherapy induces antigen release from tumor, in this way activating the immune system. However, radiotherapy alone is rarely enough to induce the systemic response requested for control of the metastases. With the advent of immunotherapy, the immune checkpoint inhibitors (ICI) have demonstrated impressive efficacy in various metastatic cancers. Currently, preclinical and clinical studies have reported a significant increase of abscopal responses in patients treated with the combination of radiotherapy and ICI. The purpose of this review was summarizing the clinical studies combining radiotherapy and ipilimumab (ipi), particularly focusing on abscopal responses., Methods and Materials: Databases of Medline (via Pubmed) from 2009 to June 2, 2017 were reviewed to obtain English language studies reporting clinical abscopal effect in the combination of radiotherapy with exclusive ipi in metastatic melanoma cancers. Included studies reported the abscopal effect as a primary endpoint, and as secondary endpoint included overall survival and toxicity., Results: A total of 16 studies met the inclusion criteria. These studies included a total of 451 patients, and in 5/16 studies the patients were treated on research protocols and followed-up prospectively. The median reported abscopal effect and OS were 26.5% and 19 months, respectively. The median toxicity ≥ Grade 3 was 18.3% ranged from 10% to 20%., Conclusion: Early clinical outcomes reports suggest that the combination of ipilimumab and RT may improve survival in metastatic melanoma patients. The abscopal responses become a clinically relevant effect of such combination and should be studied in controlled randomized trials.

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 cm 3 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., (Copyright © 2017 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.)

Purpose: Groupe Européen de Curiethérapie (GEC) and European Society for Radiotherapy & Oncology (ESTRO) has proposed a rectal dose constraint of the most exposed 2-cc volume (D2cc of ≤ 75 Gy EQD2α/β = 3) during external-beam plus high-dose-rate brachytherapy (HDR-BT) in localized prostate cancer patients. This study aimed to evaluate D2cc for rectal contouring via interobserver variability., Material and Methods: Four blinded observers contoured rectums of 5 patients. Rectal contouring anatomical limits were determined through previous consensus. Dose-volume histogram (DVH) dosimetric parameters (D0.1cc, D1cc, and D2cc) were analyzed according to GEC/ESTRO recommendations and subjected to intra- and interobserver comparisons. Latter comparisons involved coefficients of variation. For each parameter, the mean, standard deviation (SD), and range were evaluated. The effect of interobserver variation on total dose was analyzed by estimating the biologically equivalent rectal dose (EQD2α/β = 3)., Results: Interobserver coefficients of variation for D0.1cc, D1cc, and D2cc were 5.7%, 4.5%, and 4%, respectively. The highest interobserver rectal delineation variation yielded a rectal dose difference up to 5.8 Gy EQD2. Estimated intraobserver variation for the reported D2cc was 5.5% in the worst-case scenario (non-significant)., Conclusions: We observed acceptable interobserver variability in EQD2 for D2cc, with strong impacts on clinical threshold levels (D2cc ≤ 75 Gy EQD2) in some cases. This small, single-center analysis will be extended in a multicenter study.