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Importance of 4DCT for Target Volume Definition in Stereotactic Lung Radiotherapy

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E Goksel

E Goksel1*, D Cone1 , E Tezcanli2 , H Kucucuk1 , O Senkesen1 , M Yilmaz1 , M Garipagaoglu2 , I Aslay1 , M Sengoz2 , (1) Acibadem Kozyatgi Hospital, Istanbul, (2) Acibadem University, Istanbul,

Presentations

SU-E-J-75 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: We aimed to investigate the importance of 4DCT for lung tumors treated with SBRT and whether maximum intensity projection (MIP) and free breathing (FB) images can compansate for tumor movement.

Methods: Six patients with primary lung cancer and 2 patients with lung metastasis with a median age of 69.5 (42-86) were included. Patients were positioned supine on a vacuum bag. In addition to FB planning CT images, 4DCT images were obtained at 3 mm intervals using Varian RPM system with (Siemens Somatom Sensetion 64). MIP series were reconstructed using 4DCT images. PTV-FB and PTV-MIP (GTV+5mm) volumes were contoured using FB and MIP series, respectively. GTVs were defined on each of eight different breathing phase images and were merged to create the ITV. PTV-4D was generated with a 5 mm margin to ITV. PTV-MIP and PTV-4D contours were copied to FB CT series and treatment plans for PTV-MIP and PTV-FB were generated using RapidArc (2 partial arc) technique in Eclipse (version 11, AAA algorithm). The prescription dose was 5600cGy in 7 fractions. ITV volumes receiving prescription dose (%) and V95 for ITV were calculated for each treatment plan.

Results: The mean PTV-4B, PTV-MIP and PTV-FB volumes were 23.2 cc, 15.4cc ve 11cc respectively. Median volume of ITV receiving the prescription dose was 34.6% (16.4-70 %) and median V95 dose for ITV was 1699cGy (232cGy-5117cGy) in the plan optimized for PTV-FB as the reference. When the plan was optimized for PTV-MIP, median ITV volume receiving the prescription dose was 67.15% (26-86%) and median V95 dose for ITV was 4231cGy (1735cGy-5290cGy).

Conclusion: Images used in lung SBRT are critical for treatment quality; FB and MIP images did not compensate target movement, therefore 4DCT images should be obtained for all patients undergoing lung SBRT or the safety margins should be adjusted.


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