A generalized calibration procedure for in vivo transit dosimetry using siemens electronic portal imaging devices.
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, s (t) (0) (TPR,w,L), and phantom mid-plane dose, D (0)(TPR,w,L), as functions of phantom thickness, w, square field dimensions, L, and tissue-phantom ratio TPR(20,10). The s (t) (0) (TPR,w,L) and D (0)(TPR,w,L) values were defined to be independent of the EPID sensitivity and monitor unit calibration, while their dependence on TPR(20,10) was investigated to determine a set of generalized correlation ratios to be used for beams with TPR(20,10) 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, D (iso), and treatment planning system (TPS) computed dose D (iso,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.
Istituto di Fisica, Università Cattolica del Sacro Cuore, Largo F. Vito 1, 00168, Rome, Italy. andrea.fidanzio@rm.unicatt.it
Andrea
A
Fidanzio
Francesca
F
Greco
Laura
L
Gargiulo
Savino
S
Cilla
Domenico
D
Sabatino
Massimo
M
Cappiello
Cinzia
C
Di Felice
Elisabetta
E
Di Castro
Luigi
L
Azario
Mariateresa
M
Russo
Luciano
L
Pompei
Guido
G
D'Onofrio
Angelo
A
Piermattei
D002138:Calibration; D006801:Humans; D019047:Phantoms, Imaging; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D020266:Radiotherapy, Conformal / Q000379:methods