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Single-Isocenter Dual-Target Lung SBRT: Dosimetric Sensitivity to Rotational Offsets

Y Yang

Y Yang*, E Subashi , J Duan , F Yin , J Cai , Duke University Medical Center, Durham, NC


SU-I-GPD-T-583 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Treating two lung lesions simultaneously with one isocenter presents a number of potential benefits for lung SRBT such as shorter delivering time and less dose to the lungs. However, precisely correcting rotational deviations for both targets could be challenging. This study aims to evaluate the dosimetric effects of rotational offsets in single-isocenter dual-target lung SBRT.

Methods: Five lung SBRT patients were included in the initial study. Each patient has two lung tumors, separated by 6-14 cm. Treatment plans with simulated three degree rotation in Pitch, Roll, and Yaw were generated with a single-isocenter dual-target VMAT plan and compared with two single-isocenter single-target VMAT plans. Dosimetric metrics including PTV V100%, PTV Dmax, cord Dmax, esophagus Dmax, heart Dmax, and lung V20 were quantitatively evaluated.

Results: Overall, rotational offsets reduced the PTV coverage for both single-isocenter dual-target plans and single-isocenter single-target plans. Of all rotational offsets for the single-isocenter dual-target plans, the maximum change in PTV V100%, PTV Dmax, cord Dmax, esophagus Dmax, heart Dmax, and lung V20 was 28.3%, 2.2%, 7.6%, 10.0%, 8.2%, and 0.4%, respectively. Rotational offsets did not significantly affect PTV Dmax and lung V20. While rotational offsets could cause large percentage dose discrepancy for OARs, 96% of the differences was < 1 Gy.

Conclusion: Rotational offsets may cause large deviation in PTV coverage for single-isocenter dual-target lung SBRT plans. Its effects on other dosimetric parameters are generally small. Extra caution should be made to plan two lesions using a single-isocenter technique for lung SBRT.

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