S23
Brachytherapy - Gastro-intestinal, paediatric brachytherapy, miscellaneous
ESTRO 2026
≤ 5cm, and lymph nodes ≤ 8mm. Patients were treated with chemoradiotherapy (25x1.8Gy) and MAASTRO Rectal Applicator boost (3x30Gy). Primary endpoint was clinical feasibility, assessed using predefined criteria evaluating tumor visualization, applicator positioning and fixation, and dose delivery. MAASTRO Rectal Applicator treatment was considered feasible if ≥ 7/10 treatment series met all criteria. Secondary endpoints included acute toxicity ≥ G2. Endorectal ultrasound tumor thickness measurements were performed before each brachytherapy procedure and used to calculate GTV D90% estimates. Results: Between August 2024 and July 2025, 10 patients were included. All tumors were ≥ 2.5cm and received chemoradiotherapy first. 8/10 MAASTRO Rectal Applicator treatment series and 27/30 procedures (90%) met all checklist criteria. In 3 procedures, post- treatment assessment revealed that the tumor was no longer centrally aligned within the applicator, prompting procedural improvements (Table 1). Pain management evolved from full anesthesia to a local perianal lidocaine block over the course of the trial. ≥ G2 adverse events due to boosting within one week post-treatment included pain (n=2), tiredness (n=1) and diarrhea (n=1). No ≥ G3 adverse events occurred. The median estimated GTV D90% per boost fraction was 15.8Gy (range 3.5-24.4Gy), resulting in a median total EQD2 ( α / β =10) GTV dose (including EBRT) of 141.3Gy (range 87.9-191.2Gy).
Mini-Oral 2636
Enabling HDR contact therapy in rectal cancer: rectal cancer boosting using the MAASTRO Rectal Applicator is clinically feasible Anne C Valkenburg 1 , Evert Van Limbergen 1 , Frank Verhaegen 1 , Murillo Bellezzo 1 , Gabriel Paiva Fonseca 1 , Jan-Erik Palmgren 1 , Robert Voncken 1 , Jarno Melenhorst 2 , Geerard L Beets 2 , Liselot Valkenburg-van Iersel 3 , Tim G.A. Calon 3 , Jeroen W.A. Leijtens 4 , Henricus J Belgers 5 , Joop L.M. Konsten 6 , Brigitte Reniers 7 , Jeroen Buijsen 1 , Britt J.P. Hupkens 1 , Maaike Berbée 1 1 Department of Radiation Oncology (Maastro), GROW Research Institute for Oncology and Reproduction, GROW Research Institute for Oncology and Reproduction, Maastricht, Netherlands. 2 Department of Surgery, Maastricht University Medical Centre+, Maastricht, Netherlands. 3 Department of Medical Oncology, Maastricht University Medical Centre+, Maastricht, Netherlands. 4 Department of Surgery, Laurentius Hospital Roermond, Roermond, Netherlands. 5 Department of Surgery, Zuyderland Medical Centre, Sittard-Geleen, Netherlands. 6 Department of Surgery, Viecuri, Venlo, Netherlands. 7 Research group NuTeC, Centre for Environmental Sciences, Hasselt University, Diepenbeek, Belgium Purpose/Objective: Rectal cancer treatment is shifting towards organ preservation. Endoluminal radiation boosting improves complete response rates and may allow omission of surgery, but its use is limited by the cost and availability of 50 kV contact x-ray brachytherapy (CXRT) equipment, and by suboptimal dose profiles and complex treatment procedures of current HDR applicators. The newly developed MAASTRO Rectal Applicator (Varian, a Siemens Healthineers company) allows non-image-based treatment with a 50 kV- equivalent dose profile, while being compatible with standard HDR afterloaders (figure 1) [1]. We introduced this method in the clinical setting and aimed to confirm feasibility of the MAASTRO Rectal Applicator treatment procedure. This abstract reports on the early endpoints regarding feasibility and acute toxicity.
Conclusion: Endoluminal boosting using the MAASTRO Rectal Applicator is clinically feasible with limited acute toxicity. Like CXRT, MAASTRO HDR boosting enables dose escalation to EQD2 GTV dose levels significantly higher than existing HDR and EBRT techniques. Clinical implementation of the MAASTRO Rectal Applicator is expected to enhance the accessibility of safe and cost- effective high-dose endoluminal radiotherapy, supporting rectal organ preservation. Keywords: Rectal contacttherapy, HDR, clinical trial
Material/Methods: We conducted a clinical feasibility study based on the OPERA treatment regimen [2] in 10 patients with cT2- 3bN0-1M0 rectal adenocarcinoma, tumor diameter
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