[Winston-lutz test and acquisition of flexmap using rotational irradiation].
OBJECTIVE
IGRT (image guided radiation therapy) is a useful technique for implementing precisely targeted radiation therapy. Quality assurance and quality control (QA/QC) medical linear accelerators with a portal imaging system (electronic portal imaging device: EPID) are the key to ensuring safe IGRT. The Winston-Lutz test (WLT) provides an evaluation of the MV isocenter, which is the intersection of radiation, collimator, and couch isocenters. A flexmap can indicate a displacement of EPID from the beam center axis as a function of gantry angles which can be removed from the images. The purpose of this study was to establish a novel method for simultaneously carrying out WLT and acquiring a flexmap using rotational irradiation. We also observed long-term changes in flexmaps over a period of five months.


METHODS
We employed rotational irradiation with a rectangular field (30×30 mm). First, the displacement of EPID from the beam center axis, indicated by the ball bearing (BB) center, was evaluated using an in-house program. The location of the BB center was then modified according to WLT. Second, a second irradiation was used to acquire a flexmap. We performed this examination regularly and evaluated long-term changes in the flexmap.


CONCLUSIONS
It proved feasible to perform WLT and flexmap measurements using our proposed methods. The precision of WLT using rotational irradiation was 0.1 mm. In flexmap analysis, the maximum displacement from the mean value for each angle was 0.4 mm over five months.


CONCLUSIONS
We have successfully established a novel method of simultaneously carrying out WLT and flexmap acquisition using rotational irradiation. Maximum displacement from the mean in each angle was 0.4 mm over five months.
Toshikazu
T
Imae
Akihiro
A
Haga
Naoya
N
Saotome
Shigeharu
S
Takenaka
Yukari
Y
Okano
Katutake
K
Sasaki
Makoto
M
Nedu
Shigeki
S
Saegusa
Takashi
T
Shiraki
Keiichi
K
Yano
Keiichi
K
Nakagawa
Kuni
K
Ohtomo
D011785:Quality Assurance, Health Care; D011786:Quality Control; D061089:Radiotherapy, Image-Guided / Q000295:instrumentation / Q000379:methods*