TY - JOUR
T1 - integration between in vivo dosimetry and image guided raditherapy for lung tumors
AU - Piermattei, Angelo
AU - Fidanzio, Andrea
AU - Azario, Luigi
AU - Cilla, Savino
PY - 2009
Y1 - 2009
N2 - The article reports a feasibility study about the potentiality of an in vivo dosimetry method for the
adaptive radiotherapy of the lung tumors treated by 3D conformal radiotherapy techniques 3D
CRTs . At the moment image guided radiotherapy IGRT has been used for this aim, but it requires
taking many periodic radiological images during the treatment that increase workload and patient
dose. In vivo dosimetry reported here can reduce the above efforts, alerting the medical staff for the
commissioning of new radiological images for an eventual adaptive plan. The in vivo dosimetry
method applied on 20 patients makes use of the transit signal St on the beam central axis measured
by a small ion chamber positioned on an electronic portal imaging device EPID or by the EPID
itself. The reconstructed in vivo dosimetry at the isocenter point Diso requires a convolution between
the transit signal St and a dose reconstruction factor C that essentially depends on i tissue inhomogeneities
along the beam central axis and ii the in-patient isocenter depth. The C factors, one
for every gantry angle, are obtained by processing the patient’s computed tomography scan. The
method has been recently applied in some Italian centers to check the radiotherapy of pelvis, breast,
head, and thorax treatments. In this work the dose reconstruction was carried out in five centers to
check the Diso in the lung tumor during the 3D CRT, and the results have been used to detect the
interfraction tumor anatomy variations that can require new CT imaging and an adaptive plan. In
particular, in three centers a small ion chamber was positioned below the patient and used for the St
measurement. In two centers, the St signal was obtained directly by 25 central pixels of an a-Si
EPID, equipped with commercial software that enabled its use as a stable detector. A tolerance
action level of 6% for every checked beam was assumed. This means that when a difference
greater than 6% between the predicted dose by the treatment planning system, Diso,TPS, and the Diso
was observed, the clinical action started to detect possible errors. 60% of the patients examined
presented morphological changes during the treatment that were checked by the in vivo dosimetry
and successively confirmed by the new CT scans. In this work, a patient that showed for all beams
Diso values outside the tolerance level, new CT scans were commissioned for an adaptive plan. The lung dose volume histograms DVHs for a Diso,TPS=2 Gy for fraction suggested the adaptive plan
to reduce the dose in lung tissue. The results of this research show that the dose guided radiotherapy
DGRT by the Diso reconstruction was feasible for daily or periodic investigation on morphological
lung tumor changes. In other words, since during 3D CRT treatments the anatomical lung tumor
changes occur frequently, the DGRT can be well integrated with the IGRT.
AB - The article reports a feasibility study about the potentiality of an in vivo dosimetry method for the
adaptive radiotherapy of the lung tumors treated by 3D conformal radiotherapy techniques 3D
CRTs . At the moment image guided radiotherapy IGRT has been used for this aim, but it requires
taking many periodic radiological images during the treatment that increase workload and patient
dose. In vivo dosimetry reported here can reduce the above efforts, alerting the medical staff for the
commissioning of new radiological images for an eventual adaptive plan. The in vivo dosimetry
method applied on 20 patients makes use of the transit signal St on the beam central axis measured
by a small ion chamber positioned on an electronic portal imaging device EPID or by the EPID
itself. The reconstructed in vivo dosimetry at the isocenter point Diso requires a convolution between
the transit signal St and a dose reconstruction factor C that essentially depends on i tissue inhomogeneities
along the beam central axis and ii the in-patient isocenter depth. The C factors, one
for every gantry angle, are obtained by processing the patient’s computed tomography scan. The
method has been recently applied in some Italian centers to check the radiotherapy of pelvis, breast,
head, and thorax treatments. In this work the dose reconstruction was carried out in five centers to
check the Diso in the lung tumor during the 3D CRT, and the results have been used to detect the
interfraction tumor anatomy variations that can require new CT imaging and an adaptive plan. In
particular, in three centers a small ion chamber was positioned below the patient and used for the St
measurement. In two centers, the St signal was obtained directly by 25 central pixels of an a-Si
EPID, equipped with commercial software that enabled its use as a stable detector. A tolerance
action level of 6% for every checked beam was assumed. This means that when a difference
greater than 6% between the predicted dose by the treatment planning system, Diso,TPS, and the Diso
was observed, the clinical action started to detect possible errors. 60% of the patients examined
presented morphological changes during the treatment that were checked by the in vivo dosimetry
and successively confirmed by the new CT scans. In this work, a patient that showed for all beams
Diso values outside the tolerance level, new CT scans were commissioned for an adaptive plan. The lung dose volume histograms DVHs for a Diso,TPS=2 Gy for fraction suggested the adaptive plan
to reduce the dose in lung tissue. The results of this research show that the dose guided radiotherapy
DGRT by the Diso reconstruction was feasible for daily or periodic investigation on morphological
lung tumor changes. In other words, since during 3D CRT treatments the anatomical lung tumor
changes occur frequently, the DGRT can be well integrated with the IGRT.
KW - in vivo dosimetry
KW - in vivo dosimetry
UR - http://hdl.handle.net/10807/29847
U2 - 10.1118/1.3129158
DO - 10.1118/1.3129158
M3 - Article
SN - 0094-2405
VL - 2009
SP - 2206
EP - 2214
JO - Medical Physics
JF - Medical Physics
ER -