S2799
RTT - RTT contouring, target definition, and treatment planning
ESTRO 2026
superior, 3mm anterior-posterior and 3mm left-right. Contralateral vocal cord, arytenoids and carotid arteries on both sides were considered organs-at-risk (OARs). During optimization, voxels within PTV were assignedto a minimum relativeelectron density of 0.5 using Monaco’s Fill-ED option. After optimization, plan robustness wasevaluated forpossible changes in the target byusing the original CT-values (no Fill-ED) and a Fill-ED of 1.0simulating swelling. All plans were evaluated on targetand OAR doses.Statistical significancedifferenceswereassessed using t-test with p-value <0.05.For each plan, treatment delivery time (e.g., beam-on-time and gantry-travel-time) was recorded.QA measurements were done with Octavius phantom/SRS1000 array (PTW) and compared with Monaco calculations using a gamma criterion of 3%/3 mm. A gamma pass-rate >90% was used. Results: The targetcoverage of VMAT- plans was 98.7±0.4% and comparable to that of IMRT- plans(98.7±0.5%), VMAT-plans resulted in lower Dmean values to the contralateral vocalcord in all cases (41.3±3.8 Gy in IMRT vs 37.3±3.4 Gy in VMAT, p<0.05).For the contralateral arytenoid, the dose was reduced in 9/10 cases for VMAT (24.6±2.4 Gy in IMRT vs 21.3 ±1.4 Gy in VMAT,p<0.01).Dose in the ipsilateral arytenoid was comparable between the two techniques. For all VMATand IMRT-plans OAR constraints were always met;in both carotid arteries Dmean was lower in IMRT- plans (see figure).Plan robustness simulation showed an increasein V107% of 1.3% [0.1-5.2%]in VMAT-plans compared to 0.4% [0-1.8%] in IMRT- plans.Mean delivery time for VMAT plans was46.6 seconds[39.7 - 49.1], versus more than 4 minutes with IMRT. The gamma pass rate was on average 97.8% [95.6–99.4%].
21498 mm ³ ), and maintained equivalent dosimetric performance to virtual boluses. Skin toxicity was Grade I in all patients without differences between groups. Conclusion: With its visual cavity design and excellent skin adhesion, the bolus provides great convenience in clinical application. Additionally, research indicates that the visualized thermosensitive color-changing personalized bolus offers superior dosimetric performance in target coverage, homogeneity, and conformity. References: 1.Early Breast Cancer Trialists’ Collaborative Group (EBCTCG), Darby S, McGale P, et al. Effect of radiotherapy after breast-conserving surgery on 10- year recurrence and 15-year breast cancer death: meta-analysis of individual patient data for 10,801 women in 17 randomised trials.Lancet. 2011;378(9804):170716. https://doi.org/10.1016/S0140-6736(11)61629-22. Lobo D, Banerjee S, et al. Influence of air gap under bolus in the dosimetry of a clinical 6 MV photon beam. J Med Phys. 2020;45(3):175– 81.https://doi.org/10.4103/jmp.JMP_53_203.Dahn HM, Boersma LJ, et al. The use of bolus in postmastectomy radiation therapy for breast cancer: A systematic review. Crit Rev Oncol Hematol. 2021;163:103391. https:/ /doi.org/10.1016/j.critrevonc Keywords: Bolus, , Thermosensitive, Color-changing Digital Poster 4420 Fast VMAT replaces IMRT for single vocal cord radiotherapy treatment Aileen Booij-van der Kooij, Abdul Wahab M. Sharfo, Stefan L.S. Kwa, Lisa Tans, Joan J. Penninkhof Radiotherapy, Erasmus MC cancer institute, Rotterdam, Netherlands
Purpose/Objective: To evaluate if flatteningfilter free
(FFF) Volumetric ModulatedArc Therapy (VMAT) is a suitable alternative for Intensity Modulated Radiothera py Treatment (IMRT) for patients treated on a single vocal cord (SVC), to reduce treatmenttime andthus improve patient comfort. Material/Methods: For 10 patients, VMAT plans were retrospectively optimizedusing a single-partial- arc of 145 degreesusing 6 MVFFF and compared with the clinicallyused IMRT-plansbased on5beams6 MV. All plans were created in Elekta Monaco 6.00.01, andthe prescribed dose was 58.08 Gy in 16 fractions. CTV-to-PTV margins were5mminferior-
Conclusion: FFF VMAT can replace IMRT in SVC treatment. This will decrease treatment time by80%, thus increasing patient comfort and enhancing department throughput. This approach is considered as the treatmentoptionin our department. References: [1]Tans L, Al-Mamgani A, Kwa SLS, et al. Single vocal cord irradiation for early-stage glottic cancer: Excellent
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