Evaluation of the effectiveness of novel single-intervention adaptive radiotherapy strategies based on daily dose accumulation

Alberto Ciarmatori; Nicola Maffei; Grazia Maria Mistretta; Paola Ceroni; Annalisa Bernabei; Bruno Meduri; Elisa D'Angelo; Alessio Bruni; Patrizia Giacobazzi; Frank Lohr; Gabriele Guidi

doi:10.1016/j.meddos.2019.02.002

Evaluation of the effectiveness of novel single-intervention adaptive radiotherapy strategies based on daily dose accumulation

Med Dosim. 2019;44(4):379-384. doi: 10.1016/j.meddos.2019.02.002. Epub 2019 Mar 12.

Authors

Affiliations

¹ Deptartment of Medical Physics, A.O. Ospedali Riuniti Marche Nord, Pesaro, Italy.
² Department of Medical Physics, A.O. U. di Modena, Modena, Italy; Post Graduate School in Medical Physics, University of Turin, Turin, Italy.
³ Department of Medical Physics, A.O. U. di Modena, Modena, Italy.
⁴ Department of Oncology, A.O. U. di Modena, Radiotherapy Unit, Modena, Italy.
⁵ Department of Medical Physics, A.O. U. di Modena, Modena, Italy. Electronic address: guidi.gabriele@aou.mo.it.

PMID: 30871864
DOI: 10.1016/j.meddos.2019.02.002

Abstract

Parotid gland (PG) shrinkage and neck volume reduction during radiotherapy of head and neck (H&N) cancer patients is a clinical issue that has prompted interest in adaptive radiotherapy (ART). This study focuses on the difference between planned dose and delivered dose and the possible effects of an efficient replanning strategy during the course of treatment. Six patients with H&N cancer treated by tomotherapy were retrospectively enrolled. Thirty daily dose distributions (D_MVCT) were calculated on pretreatment megavoltage computed tomography (MVCT) scans. Deformable Image Registration which matched daily MVCT with treatment planning kilovoltage computed tomography was performed. Using the resulting deformation vector field, all daily D_MVCT were deformed to the planning kilovoltage computed tomography and resulting doses were accumulated voxel per voxel. Cumulative D_MVCT was compared to planned dose distribution performing γ-analysis (2 mm, 2% of 2.2 Gy). Two single-intervention ART strategies were executed on the 18th fraction whose previous data had suggested to be a suitable timepoint for a single replanning intervention: (1) replanning on the original target and deformed organ at risks (OARs) (a "safer" approach regarding tumor coverage) and (2) replanning on both deformed target and deformed OARs. D_MVCT showed differences between planned and delivered doses (3D-γ 2mm/2%-passing rate = 85 ± 1%, p < 0.001). Voxel by voxel dose accumulation showed an increase in average dose of warped PG of 3.0 Gy ± 3.3 Gy. With ART the average dose of warped PG decreased by 3.2 Gy ± 1.7 Gy in comparison to delivered dose without replanning when both target and OARs were deformed. Average dose of warped PG decreased by 2.0 Gy ± 1.4 Gy when only OARs were deformed. Anatomical variations lead to increased doses to PGs. Efficient single-intervention ART-strategies with replanning on the 18th MVCT result a reduced PG dose. A strategy with deformation of both target and OAR resulted in the lowest PG dose, while formally maintaining PTV coverage. Deformation of only OAR nevertheless reduces PG dose and has less uncertainties regarding PTV coverage.

Keywords: Adaptive radiation therapy; Deformable registration; Dose accumulation; Head and neck cancer; Replanning.

Publication types

Evaluation Study

MeSH terms

Adult
Algorithms
Female
Head and Neck Neoplasms / diagnostic imaging
Head and Neck Neoplasms / radiotherapy*
Humans
Male
Middle Aged
Organs at Risk
Parotid Gland / diagnostic imaging
Parotid Gland / radiation effects*
Radiometry
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods
Radiotherapy, Intensity-Modulated
Retrospective Studies
Tomography, X-Ray Computed