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4D Vs 3D Dose Calculations for Non-Small-Lung-Cancer: A Comparison Using Tumor Control Probability (TCP)

G Valdes

G Valdes1*, J Lamb2, D Low3, P Lee4, K Iwamoto5, (1) UCLA, Los Angeles, CA, (2) University of California, Los Angeles, Los Angeles, CA, (3) UCLA, Los Angeles, CA, (4) UCLA, Los Angeles, California, (5) UCLA, Los Angeles, California

SU-E-T-414 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To investigate the utility of four dimensional (4D) dose calculations for design and optimization of stereotactic lung radiotherapy treatment plans.

Methods: Radiotherapy plans for stage I-II lung cancer were created for 8 patients. Clinically acceptable treatment plans were created with dose calculated on the end-exhale 4D-CT phase, using a Monte Carlo algorithm. Dose was then projected onto the remaining 9 phases of 4D-CT using the Monte Carlo algorithm and accumulated onto the end-exhale phase using commercially available deformable registration software. The resulting DVHs of the gross tumor volume (GTV), planning tumor volume (PTV), and PTVsetup were compared according to target coverage and dose. The PTVsetup was defined as a volume including the GTV and a margin for setup uncertainties but not for respiratory motion. Tumor control probabilities (TCP) resulting from these DVHs were estimated using a wide range of alphas, betas, and tumor cell densities.

Results:Differences of up to 5 Gy were observed in dosimetric indices related to the tumor between 3D and 4D calculations. When the TCP was calculated using the resulting DVHs for fractionation schedules typically used in stereotactic body radiation therapy (SBRT), the TCP differed at most by 5% between 4D and 3D cases, and in most cases differed less than 1%.

Conclusion:In some cases moderate dosimetric differences may be obtained between 3D and 4D dose calculations. Even when dosimetric differences exist between 3D and 4D calculations, the resulting TCPs do not differ greatly for commonly-used SBRT dose prescriptions.

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