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Sci—Sat AM(1): Planning — 08: Estimating Planning Target Volume Margins for Fractionated Stereotactic Radiotherapy on Perfexion
Author(s) -
Ruschin M,
Craig T,
Nayebi N,
Li W,
Tamerou M,
Cho YB,
Ménard C,
Jaffray D
Publication year - 2010
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3476208
Subject(s) - radiosurgery , nuclear medicine , margin (machine learning) , radiation therapy , medicine , population , radiation treatment planning , stereotactic radiotherapy , mathematics , computer science , radiology , environmental health , machine learning
The purpose of this study was to estimate planning target volume (PTV) margins for frame‐based Perfexion (PFX) SRT using the eXtend™ system's relocatable head frame (RHF). Patients with large brain metastases are currently undergoing hypofractionated (3 fractions) SRT on PFX enrolled on a phase 1 dose‐escalation clinical trial. In prior investigation, the performance of the RHF was quantified using cone‐beam CT (CBCT) in fourteen patients undergoing linac‐based SRT (median: 30 treatment fractions). Standard performance metrics — group mean (μ), systematic (Σ) and random (σ) uncertainties — were determined for frame‐guided positioning and intra‐fraction motion. A published margin‐determination formula (2.5*Σ) +0.7*σ) was used to estimate the PTV margin. An additional factor of (σ/√3) was added to the systematic component of the formula when initially designing the PTV for 3 fractions in PFX‐SRT. To more accurately account for PFX dose distributions and only 3 treatment fractions, a population‐based stochastic modeling approach is being developed to refine the PTV margin for hypofractionated PFX‐SRT. For frame‐guided SRT (30 fractions), the post‐correction positioning performance estimates were μ(position) = {0.1,−0.2,−0.6}mm, Σ(position) = {0.2;0.8;0.6}mm, and σ(position) = {0.3;0.6;0.4}mm in {Right; Superior;Anterior}. For intra‐fraction motion, μ(motion) = {−0.1;−0.1;0.0}mm, Σ(motion) = {0.2;0.2;0.1}mm, and σ(motion)={0.2;0.4;0.2}mm. The margin formula indicated an expansion of {1.0;2.6;1.8}mm and {1.6;3.1;2.3}mm for 30 fractions and 3 fractions, respectively. For three patients treated to date on PFX, μ(position) = (0.2mm;−0.9mm;−0.8mm). To ensure that the GTV receives the prescription dose, PTV margins have been calculated to account for the geometric uncertainties present in PFX‐SRT. The margins will be reviewed as more data are collected, RHF refinements are made, and stochastic‐based modeling is used.