Highlights
- •Anatomy matching based target localization is problematic due to organ deformation.
- •A new method is proposed to align the target with the prescription-isodose surface.
- •Detailed analyses were based on in-room CT images before and post IMRT treatments.
- •The method can improve localization accuracy and critical structure sparing greatly.
Abstract
In imaged-guided radiation therapy (IGRT), target localization is usually done with
rigid-body registration based on anatomy matching. Problems arise when the target
volume can only be matched partially due to inter-fractional organ motion and deformation,
resulting in deteriorated target coverage and critical structure sparing. A new target
localization method is investigated in which the treatment target volume is aligned
with the prescription isodose surface. Our study included 15 prostate patients previously
treated with intensity-modulated radiation therapy (IMRT). Patient setup and target
localization were performed using a CT-on-rails system before and after the IMRT treatment.
IMRT plans were generated on the original simulation CTs (15) and the same MUs and
leaf sequences were used to compute the dose distributions on post-treatment CTs (98)
with the isocenter adjustments based on either anatomical structure matching or prescription
isodose surface alignment. When patients were aligned with the traditional anatomy
matching method, the dose to 95% of the CTV, D95, received 74.0 – 77.6 Gy and the minimum CTV dose, Dmin, was 61.9 – 71.6 Gy, respectively, in the cumulative dose distributions. The rectal
dose-volume constraints were violated in 35.7% of the treatment fractions. When patients
were aligned using the new localization method, the dose to 95% of the CTV, D95, received 74.0 – 78.2 Gy and the minimum CTV dose, Dmin, was 68.4 – 71.6 Gy, respectively, in the cumulative dose distributions. The rectal
dose-volume constraints were violated in 17.3% of the treatment fractions. Traditional
IGRT target localization based on anatomy matching is effective for population-based
PTV margins but not ideal for those patients with large inter-fractional prostate
rotation/deformation due to large rectal and bladder volume variation. The new method
using the prescription isodose surface to align the target volume could improve the
target coverage and rectal sparing for these patients, which can be implemented clinically
to improve target dose delivery accuracy.
Keywords
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Article info
Publication history
Published online: March 03, 2023
Accepted:
February 18,
2023
Received in revised form:
January 24,
2023
Received:
October 18,
2022
Identification
Copyright
© 2023 Associazione Italiana di Fisica Medica e Sanitaria. Published by Elsevier Ltd. All rights reserved.
