K Huang*, P Das, D Fuentes, A Olanrewaju, D Hancock, D Rhee, L Court, U.T. M.D. Anderson Cancer Ctr, Houston, TX

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  K Huang

(Saturday, 3/26/2022)   [Central Time (GMT-5)]

Purpose: To develop an adaptive automated field-in-field (FIF) technique for rectal cancer 3DCRT treatments.

Methods: We created an algorithm that automates the clinical workflow for creating field-in-field plans. The algorithm automatically identifies a hotspot volume, creates a subfield, calculates dose, and optimizes beam weight without user intervention. This process is repeated until the hotspot is sufficiently reduced. Configurable parameters include the definition of hotspot, the target volume, the maximum number of subfields, the minimum MU per field, and the optimization solver. The beam weights are optimized based on user-configured physical constraints for DVH coverage and least-squared cost functions. The following configurations were tested on 12 rectal patients treated with 3-field 3DCRT: (A) lateral fields with 45-deg wedges, FIF optimized to minimize 107% volumes, (B) lateral fields with 60-deg wedges, FIF optimized to minimize 107% volumes, and (C) laterals fields with 45-deg wedge and FIF optimized to minimize 106% volumes. All plans were normalized so that 99% of the PTV was covered with the prescription dose.

Results: All configurations successfully generated plans with the specified dose coverage. 34/36 plans achieved final hotspot dose of less than 110%. The FIF reduced the average hotspot doses to 107.9%, 107.3%, and 107.2% for configuration A, B, and C respectively. The average number of subfields added were 4.5, 2.8, and 4.2, respectively. It took approximately 13 minutes to calculate and add each field. Qualitative evaluations of the plans showed that the automated FIF process was more effective when the density of large air volumes was set to water. Generally, 60-deg wedge plans were preferred compared with plans with 45-deg wedges. Covering 106% hotspot occasionally caused small cold spots in the PTV.

Conclusion: We have automated the clinical workflow for generating FIF to reduce hotspots in 3-field 3D conformal plans for rectal cancer.

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• 174-60656-16021654-182524-1668570980.pdf (K Huang)

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