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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2025-07-06 15:45 |
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Conference: Bucharest University Faculty of Physics 2025 Meeting
Section: Biophysics; Medical Physics
Title:
Influence of minimum segment-width variation on dose distribution in volumetric modulated arc therapy planning for pelvic cancers
Authors:
Anca BALAN (1), Claudia CHILOM (1), Mirabela DUMITRACHE (2), Mihaela DUMITRACHE (2), Daniela STROE (2)
Affiliation:
1) Facultatea de Fizică, Universitatea din București
2) Spitalul Clinic Colțea
E-mail
ancabalan03@gmail.com
Keywords:
Minimum Segment Width (MSW), Volumetric‐Modulated Arc Therapy (VMAT), Pelvic Malignancies, Planning Target Volume (PTV) Coverage, Conformity Index (CI), Homogeneity Index (HI), Dose‐Distribution Quality, Delivery Reliability, Gamma Analysis
Abstract:
This study investigates how the minimum segment width (MSW) influences dose‐distribution quality and delivery reliability in Volumetric‐Modulated Arc Therapy (VMAT) for pelvic malignancies, specifically cervical, rectal and prostate cancers. Fifteen clinical cases were planned in the Monaco system, generating four VMAT variants per case with MSW values of 0.5 cm, 1.0 cm, 1.5 cm and 2.0 cm, while all other planning parameters remained unchanged.
Dosimetric performance was evaluated by: the percentage of the planning target volume (PTV) receiving at least 95 % of the prescribed dose (V95 %), the conformity index (CI), and the homogeneity index (HI). Exposure of adjacent healthy tissues was assessed using general dose metrics that reflect organ‐protection capacity. Plan delivery was verified with a three‐dimensional phantom and gamma analysis (3 %/3 mm criterion), applying a minimum 95 % pass‐rate threshold.
Results showed that plans with MSW of 0.5 cm and 1.0 cm achieved superior target coverage (over 97 % of the PTV), precise conformity to target contours and uniform dose distribution. In contrast, plans with larger MSW (1.5 cm and 2.0 cm) exhibited slightly reduced coverage (down to 95 %), less accurate conformity and decreased uniformity. Delivery also declined as MSW increased, with gamma pass‐rates falling from 99.9 % at 0.5 cm to 96.2 % at 2.0 cm.
These findings indicate that MSW is a critical parameter in VMAT optimization, directly affecting target coverage, dose conformity and uniformity while safeguarding healthy tissues. Careful evaluation and selection of MSW are therefore essential for each pelvic VMAT plan to maximize therapeutic benefit and ensure reliable treatment delivery.
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