Program Information
The Dosimetric Impact of Moving Small Size Lung Tumor Using Helical Tomotherapy
P Tu1*, H Nien2 , H Lee1 , C Wu2 , C Lin1 , C Lin1 , (1) Department of Radiation Oncology,Sijhih Cathay General Hospital, Taiwan, New Taipei City, New Taipei City (2) Department of Radiation Oncology, Cathay General Hospital, Taiwan, Taipei
Presentations
SU-E-T-729 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose:Respiration during radiotherapy irradiation causes dose delivery uncertainty to the lung tumor. This phantom study was designed to investigate the dosimetric impact of tumor motion during respiration with TomoTherapy treatment.
Methods:Dynamic thorax phantom (CIRS. Inc, Norfolk, VA), was used to mimic small size lung tumors (1, 2, and 3cm in diameter) motion during respiration. CT images of tumors under static condition were imported into TomoTherapy Hi-Art system. Plans were calculated with different jaw sizes for each size of tumor. Dose measurement was performed under both static and respiratory simulation produced by dynamic thorax phantom. Our respiratory simulation setting was chosen due to more compatible with clinical breathing cycle pattern including 1cm amplitude movement in SI direction, 4s breathing period and cos6 breathing pattern. Two-dimensional dose of DQA plans were measured by EBT3 films. The point dose was measured in the center of each tumor using A1SL ion chamber.
Results:The point dose of 1 cm motion tumor was 9% higher than plan dose, and decreased variation by increasing jaw size. The point dose of 1 cm and 2 cm motion tumors were greater than static tumors, but the results of 3 cm tumor were in contrast. Dose coverage was improved by increasing tumor size and jaw size. The width of 50% dose level of motion tumors on horizontal 2D dose profile were similar with widths of static tumor, but dose distribution shifted toward inferior direction. The widths of 60% dose level of motion tumors were smaller than widths of static tumor and difference decreased by increasing tumor and jaw size.
Conclusion:Small size motion tumor has greater dose difference than bigger tumors. Large jaw size leads to more penumbra but provides better dose coverage. Larger margin was suggested at the longitudinal superior direction to compensate the dose distribution deviation during respiration.
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