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Radiother Oncol. 2013 Dec;109(3):344-9. doi: 10.1016/j.radonc.2013.09.012. Epub 2013 Oct 31.

Treatment simulations with a statistical deformable motion model to evaluate margins for multiple targets in radiotherapy for high-risk prostate cancer.

Author information

1
Department of Medical Physics, Aarhus University Hospital, Denmark; Department of Oncology, Aarhus University Hospital, Denmark. Electronic address: sarathoe@rm.dk.

Abstract

BACKGROUND AND PURPOSE:

Deformation and correlated target motion remain challenges for margin recipes in radiotherapy (RT). This study presents a statistical deformable motion model for multiple targets and applies it to margin evaluations for locally advanced prostate cancer i.e. RT of the prostate (CTV-p), seminal vesicles (CTV-sv) and pelvic lymph nodes (CTV-ln).

MATERIAL AND METHODS:

The 19 patients included in this study, all had 7-10 repeat CT-scans available that were rigidly aligned with the planning CT-scan using intra-prostatic implanted markers, followed by deformable registrations. The displacement vectors from the deformable registrations were used to create patient-specific statistical motion models. The models were applied in treatment simulations to determine probabilities for adequate target coverage, e.g. by establishing distributions of the accumulated dose to 99% of the target volumes (D99) for various CTV-PTV expansions in the planning-CTs.

RESULTS:

The method allowed for estimation of the expected accumulated dose and its variance of different DVH parameters for each patient. Simulations of inter-fractional motion resulted in 7, 10, and 18 patients with an average D99 >95% of the prescribed dose for CTV-p expansions of 3mm, 4mm and 5mm, respectively. For CTV-sv and CTV-ln, expansions of 3mm, 5mm and 7 mm resulted in 1, 11 and 15 vs. 8, 18 and 18 patients respectively with an average D99 >95% of the prescription.

CONCLUSIONS:

Treatment simulations of target motion revealed large individual differences in accumulated dose mainly for CTV-sv, demanding the largest margins whereas those required for CTV-p and CTV-ln were comparable.

KEYWORDS:

Margin expansion; PCA; Pelvic lymph nodes; Seminal vesicles; Statistical deformable motion model

PMID:
24183863
DOI:
10.1016/j.radonc.2013.09.012
[Indexed for MEDLINE]
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