Adaptive Radiotherapy with Dose Fractionation Painting

Document Type

Conference Proceeding

Publication Date

10-2023

Publication Title

International Journal of Radiation Oncology, Biology, Physics

Abstract

Purpose/Objective(s): Efficacy of dose fractionation is dependent on tumor radiosensitivity. However, due to intra-tumoral dose response heterogeneity, the advantage of fractionation cannot be fully utilized. FDGPET/CT has been used to assess intra-tumoral dose response during the treatment course. Thus, radiosensitivity of different sub-volumes within the individual tumors can be assessed and used to design dose fractionation. Materials/Methods: For each patient, the pre-treatment FDG-PET/CT and a feedback FDG-PET/CT obtained within the 3rd week of the chemoradiotherapy for HN cancer were used to construct tumor voxel dose response matrix, DRM. Biologically equivalent dose EQD2 was determined using the DRM and assuming relative stability of the radiation double-hit effect, meanwhile normal tissue EQD2 was determined assuming the corresponding a/b = 3.0. Tumor voxel EQD2 ratio was calculated with a given limitation of normal tissue EQD2 and used to determine tumor voxel fractionation (Table). Tumor was divided into few sub-volumes based on ranges of the tumor voxel DRM value. Different fractionation doses, but same number of fractions, were selected to ensure that the planning dose distribution can be simultaneously delivered. Results: Table shows the EQD2 of tumor voxel DRM for each given fractionation and normal tissue dose limitation. The treatment dose efficiency increases exponentially as increasing dose per fraction for those of resistant tumor voxels, i.e., DRM > = 0.7. The 2 Gy per fraction was used within the first 3 treatment weeks before tumor voxel dose response assessed. After the 15 fractions, tumor voxel dose fractionation will be adjusted with respect to its DRM and the expected treatment dose. Typically, 3 sub-volumes for each resistant tumor were segmented and designed with 3 fractionation regimens. With respect to normal tissue EQD2 constraint < = 70 Gy, the corresponding EQD2 was 55 » 73 Gy for tumor sub-volume with DRM = 0.1 » 0.6; 77 » 90 Gy for tumor sub-volume with DRM = 0.65 » 0.75; > 101 Gy for tumor sub-volume with DRM > = 0.8 respectively. For very resistant tumor cells i.e., DRM > 0.9, the EQD2 > 160 Gy can be achieved or > 244 Gy if the normal tissue EQD2 constraint can be relaxed to 90 Gy for the small resistant tumor sub-volume. For the study patients, tumor sub-volume with DRM > 0.9 = 0.128 » 7.4cc. Conclusion: Adaptive dose fractionation painting can be achieved followed by the dose response assessment. Dependent on the size and location of resistant tumor sub-volumes, tumor EQD2 could be largely improved without increasing normal tissue dose

Volume

117

Issue

2 Suppl.

First Page

e739

Comments

American Society for Radiation Oncology 65th Annual Meeting ASTRO 2023, October 1-4, 2023, San Diego, CA

DOI

10.1016/j.ijrobp.2023.06.2270

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