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SU‐E‐T‐290: Dosimetry Comparison of Gating V.S. ITV Approach for Moving Targets in SBRT, Dynamic Treatments
Author(s) -
Alezra D,
Ayun M Ben,
Tsvang L,
Pyatigorsky V,
Dubinsky S
Publication year - 2011
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3612241
Subject(s) - dosimetry , imaging phantom , nuclear medicine , collimator , radiosurgery , contouring , physics , computer science , medicine , radiation therapy , optics , radiology , computer graphics (images)
Purpose: To measure and determined the accuracy of delivered dynamic dose IMRT or RapidArc (RA) in cases of moving targets using gating vs. internal target volumes (ITV) approach for SBRT of lung or any other moving target. Methods: A Varian breathing RPM phantom was attached to a toy wagon for simulating horizontal movements. A 2 slice Perspex phantom was placed on the wagon with option to use mini ion chamber and films for dose measurements. We investigated different setup combinations with different target moving distances 0.5, 0.7, 1.2 and 2.2cm, target sizes and shapes. All setup combinations underwent 4DCT. ITV and gated targets were delineated with ECLIPSE TPS contouring tools for all 4DCT phases. Dynamic SBRT plans ware created (RA, IMRT) with different dose rates (300, 600 MU/min) to be delivered in different number of breathing cycles, and different MLC leaves direction, parallel and perpendicular to target moving direction. Collimator position in 0, 45 and 90 deg.) Point dose and 2D dose distribution were measured and compared to the calculated dose using DVH and Gamma test. Results: The combination of dynamic SBRT and ITV approach may lead in some setup combinations to dosimetric errors of >5% in dose and >5mm in isodose distance. In general Gated SBRT is more accurate from the dosimetry point of view. Conclusions: ITV approach in SBRT dynamic treatments should be used with great caution and every dynamic SBRT protocol should take into account the dosimetry inaccuracy as a result of combination of: target moving distances; target size and shape; dose rate; number of breathing cycles; MLC leaves direction.