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Dosimetric Accuracy of Delivering Cu-ATSM PET Dose Painting Plans with Tomotherapy

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T Bradshaw

T Bradshaw*, M Henzler, L Forrest, R Jeraj, University of Wisconsin, Madison, WI

SU-E-T-369 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
Unlike conventional IMRT plans, PET-based dose painting plans can include high dose modulation and steep dose gradients within target volumes; these can be challenging for some therapy systems to deliver. The purpose of this study was to assess tomotherapy's ability to accurately deliver PET-based dose painting plans.

Methods:
Five canine patients with sinonasal tumors were imaged with [⁶¹Cu]Cu-ATSM PET/CT prior to treatment. Dose painting prescriptions were created with the following parameters: 1) PTV = 42 Gy, 2) GTV voxel doses were linearly related to Cu-ATSM SUV, and 3) GTV voxel doses had a lower limit of 42 Gy, an upper limit of 100 Gy, and a mean GTV dose of 50 Gy. Plans were split into 10 fractions. Voxel dose prescriptions were converted into 8 contours representing dose levels and imported into tomotherapy TPS for optimization. One fraction from each optimized plan was delivered to the tomotherapy phantom. Absolute and relative measurements were performed with ion chamber and EDR2 film, respectively.

Results:
Maximum voxel doses varied between patients, ranging from 69 Gy to 100 Gy, depending on Cu-ATSM uptake patterns. Good conformity was obtained between optimized plans and voxel prescriptions: on average 89% of voxels received +/-10% of their prescribed dose. Absolute dose measurements were within 3% of dose plans for all patients, with an average difference of -1.4%. Film dosimetry showed tomotherapy was capable of delivering the highly modulated plans. Gamma analysis (3%/3mm) showed that plans on average had only 0.1% of gamma values greater than 1.

Conclusion:
Tomotherapy was able to deliver dose painting treatment plans for all five of the test patients with a high degree of accuracy. Despite high dose modulation within planning structures, PET-based dose painting is feasible with tomotherapy.

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