TY - JOUR
T1 - A generalized calibration procedure for in vivo transit dosimetry
using siemens electronic portal imaging devices
AU - Fidanzio, Andrea
AU - Cilla, Savino
AU - Azario, Luigi
AU - Piermattei, Angelo
PY - 2011
Y1 - 2011
N2 - A practical and accurate generalized in vivo
dosimetry procedure has been implemented for Siemens
linacs supplying 6, 10, and 15 MV photon beams, equipped
with aSi electronic portal imaging devices (EPIDs). The in
vivo dosimetry method makes use of correlation ratios
between EPID transit signal, st
0(TPR,w,L), and phantom
mid-plane dose, D0(TPR,w,L), as functions of phantom
thickness, w, square field dimensions, L, and tissue-phantom
ratio TPR20,10. The st
0(TPR,w,L) and D0(TPR,w,L)
values were defined to be independent of the EPID sensitivity
and monitor unit calibration, while their dependence
on TPR20,10 was investigated to determine a set of generalized
correlation ratios to be used for beams with
TPR20,10 falling in the examined range. This way, other
radiotherapy centers can use the method with no need to
locally perform the whole set of measurements in solid
water phantoms, required to implement it. Tolerance levels
for 3D conformal treatments, ranging between ±5 and
±6% according to tumor type and location, were estimated
for comparison purposes between reconstructed isocenter
dose, Diso, and treatment planning system (TPS) computed
dose Diso,TPS. Finally a dedicated software, interfaceable
with record and verify (R&V) systems used in the centers,
was developed to obtain in vivo dosimetry results in less
than 2 min after beam delivery.
AB - A practical and accurate generalized in vivo
dosimetry procedure has been implemented for Siemens
linacs supplying 6, 10, and 15 MV photon beams, equipped
with aSi electronic portal imaging devices (EPIDs). The in
vivo dosimetry method makes use of correlation ratios
between EPID transit signal, st
0(TPR,w,L), and phantom
mid-plane dose, D0(TPR,w,L), as functions of phantom
thickness, w, square field dimensions, L, and tissue-phantom
ratio TPR20,10. The st
0(TPR,w,L) and D0(TPR,w,L)
values were defined to be independent of the EPID sensitivity
and monitor unit calibration, while their dependence
on TPR20,10 was investigated to determine a set of generalized
correlation ratios to be used for beams with
TPR20,10 falling in the examined range. This way, other
radiotherapy centers can use the method with no need to
locally perform the whole set of measurements in solid
water phantoms, required to implement it. Tolerance levels
for 3D conformal treatments, ranging between ±5 and
±6% according to tumor type and location, were estimated
for comparison purposes between reconstructed isocenter
dose, Diso, and treatment planning system (TPS) computed
dose Diso,TPS. Finally a dedicated software, interfaceable
with record and verify (R&V) systems used in the centers,
was developed to obtain in vivo dosimetry results in less
than 2 min after beam delivery.
KW - EPID
KW - in vivo dosimetry
KW - EPID
KW - in vivo dosimetry
UR - http://hdl.handle.net/10807/33070
U2 - 10.1007/s11517-010-0699-6
DO - 10.1007/s11517-010-0699-6
M3 - Article
SN - 1741-0444
VL - 2011
SP - 373
EP - 383
JO - MEDICAL & BIOLOGICAL ENGINEERING & COMPUTING
JF - MEDICAL & BIOLOGICAL ENGINEERING & COMPUTING
ER -