A new target localization method for image-guided radiation therapy of prostate cancer

C M Charlie Ma; Guoping Shan; Wei Hu; Robert A Price; Lili Chen

doi:10.1016/j.ejmp.2023.102550

A new target localization method for image-guided radiation therapy of prostate cancer

Phys Med. 2023 Mar:107:102550. doi: 10.1016/j.ejmp.2023.102550. Epub 2023 Mar 3.

Authors

C M Charlie Ma¹, Guoping Shan², Wei Hu³, Robert A Price⁴, Lili Chen⁴

Affiliations

¹ Department of Radiation Oncology, Fox Chase Cancer Center, Philadelphia, PA, United States. Electronic address: charlie.ma@fccc.edu.
² Department of Radiation Physics, Zhejiang Key Lab of Radiation Oncology, Hangzhou, China.
³ Department of Radiation Oncology, Taizhou Central Hospital, Zhejiang, China.
⁴ Department of Radiation Oncology, Fox Chase Cancer Center, Philadelphia, PA, United States.

PMID: 36870203
DOI: 10.1016/j.ejmp.2023.102550

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, D_min, 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, D_min, 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: Image guided radiation therapy (IGRT); In-room CT techniques; Inter-fractional motion; Prostate cancer; Target localization.

MeSH terms

Humans
Male
Prostate
Prostatic Neoplasms* / diagnostic imaging
Prostatic Neoplasms* / radiotherapy
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods
Radiotherapy, Image-Guided* / methods
Radiotherapy, Intensity-Modulated* / methods