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To Validate Dose Delivery in Static Field Stereotactic Body Radiation Therapy (SBRT) of Lung Cancer

C Joshi

C P Joshi1,2*, L Garcia3, T Olding1,2, K Alexander2, T Owen1,2, A Kerr1,2, (1) Cancer Centre of South Eastern Ontario, Kingston General Hospital, Kingston, ON, Canada (2) Departments of Oncology and Physics, Queen's University, Kingston, ON, Canada (3) RS McLaughlin Durham Regional Cancer Centre, Oshawa, ON,Canada

SU-E-T-419 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

To validate dose delivery in static field stereotactic body radiation therapy (SBRT) of lung cancer

An Exradin A16 0.007cc ion chamber, EBT3 Gafchromic film and Fricke-Xylenol-Orange-Gelatin (FXG) gel dose measurements were performed providing measurements for point, planar and volumetric dose comparisons. CT images (GE Lightspeed RT16 CTSIM) of a Quasar respiratory motion phantom (Modus Medical) with stationary and moving inserts were acquired. Respiratory motion was recorded using a Varian RPM system. Standard cedar inserts with 3cm diameter solid tumors for the ion chamber and film, and an in-house fabricated custom insert for FXG gel were used. Internal target volumes (ITV) were obtained from 4DCT scans. A typical 15BPM, 20mm amplitude peak-to-peak breathing pattern for ion chamber; and sinusoidal 15BPM/10mm respiratory cycles for film and gel dosimetry were used. Nine-field SBRT plans using 6MV beams were calculated on Eclipse treatment planning system (v10.0; Varian). CBCT scans were used to reproduce the treatment setup; and irradiations were performed on a Trilogy (Varian) linear accelerator. Percentage dose difference and gamma analysis for 3% dose difference and 3mm distance-to-agreement were used to compare measured and calculated dose distributions.

Measured vs. calculated point dose differences (at a point inside the ITV) for the moving insert geometry were -2.1%, -1.5% and -0.5% for the ion chamber, film and gel measurements, respectively. The planar and volumetric gamma analysis of measured and calculated dose distributions for moving insert geometry showed 99.9% agreements for both EBT3 film and FXG gel dosimetry. Similar comparisons for a stationary insert geometry showed 100% and 98.5% agreements for film and gel measurements, respectively.

A consistent level of agreement observed between measured and calculated doses for the point, planar and volumetric dose measurements validates the lung SBRT dose delivery.

Funding Support, Disclosures, and Conflict of Interest: Research funding support provided by the Canadian Institutes of Health Research (CIHR)

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