Evaluation of tumor dynamics and dose delivery techniques for stereotactic lung radiation therapy
Mohatt, Dennis J.
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The primary objectives of this work are to quantify the behavior of pulmonary tumor dynamics and evaluate alternative treatment modalities for stereotactic lung radiation therapy (SLRT). In a retrospective study, we examined lung tumor motion for 65 patients treated for early stage Type I/II NSCLC under abdominal compression. From this clinical study we verified the range of tumor trajectory is anatomic location dependent. Additionally, we found lung tumor mobility to be lobe location dependent as well, generally increasing as we near the base region of the lungs. Our results support the primary mechanism driving lung tumor movement is caused by the diaphragm. In comparison to free breathing studies, abdominal compression is not only highly effective in reducing intrafraction tumor motion, but also ensures a comparatively shorter treatment time. In our phantom study, we compared three dimensional conformal radiation therapy (3DCRT), dynamic conformal arc therapy (DCAT), intensity modulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT) using a TrueBeam STx with flatten filter free (FFF) capability to evaluate the optimal treatment modality for SLRT delivery. In all cases, target conformity was enhanced when switching to FFF mode. The one modality with succeeding best results for all RTOG criterions was VMAT FFF. As compared to 3DCRT, target conformity with VMAT improved by 15-25%. Over a ten-fold reduction in high dose spillage was evaluated when comparing both IMRT and VMAT with 3DCRT. As compared to IMRT, intermediate dose spillage with VMAT was reduced by 16-22%. For 3DCRT and IMRT, delivery efficiency increased by 75% when operating in 10 MV_FFF mode. VMAT treatment efficiency was improved by a factor of 3-4 over IMRT, and up to factor of 7 when compared to 3DCRT. Absolute dose for each modality was verified using ion chamber, and were found to be within 2% agreement with the treatment planning system.
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