SU-E-T-178: Experimental Study of Acceptable Movement Conditions for SBRT Lung Treatments
- Hospital de la Santa Creu i Sant Pau, Barcelona, Barcelona (Spain)
Purpose: To experimentally study the acceptable movement conditions for SBRT lung treatments we quantified with film dosimetry the change in dose distributions due to periodic movements of 5 different amplitudes and 4 respiratory gating duty cycles on a SBRT treatment plan. Methods: We planned a SBRT treatment plan for the QUASAR™ (Modus Medical) phantom equipped with the respiratory motion device. We placed a 3 mm water-equivalent sphere simulating a tumour inside the lung-equivalent insert. This sphere is divided in two hemispheres that allow placing films in between. We used radiochromic EBT2™ (Ashland) films. We oriented the lung insert in such a way that sagittal dose distributions could be measured. We applied a sinusoidal movement with 3 s period for 5 different amplitudes of 0(static), 5, 7, 10, 15 and 20 mm without gating. For the 20 mm amplitude we studied the gating technique with 4 duty cycles of 20, 40, 60 and 80% of the respiratory cycle. Each situation was irradiated in a Clinac 2100 linac (Varian) equipped with the RPM™ system. FilmQA Pro™ (Ashland) software together with an Expression 10000XL scanner (EPSON) were used to analyze and compare the measured dose distributions with those planned by the Eclipse™ TPS v. 8.9 (Varian) by means of gamma analysis with 6 criteria: 5%/3mm, 5%/2mm, 5%/1mm, 3%/3mm, 3%/2mm and 2%/2mm (threshold of 10%). Results: Movements with amplitude of less than 7mm do not significantly modified the dosimetry. Gating duty cycles of less than 40% yielded also acceptable results for a 2 cm amplitude movement. Conclusion: To safely perform daily accurate SBRT treatments, movements have to be restricted to 7 mm amplitude (±3.5 mm). Otherwise, a gating strategy should be considered.
- OSTI ID:
- 22339925
- Journal Information:
- Medical Physics, Vol. 41, Issue 6; Other Information: (c) 2014 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-2405
- Country of Publication:
- United States
- Language:
- English
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