Real time transit dosimetry for the breath-hold radiotherapy technique: an initial experience.
BACKGROUND
The breath-hold is one of the techniques to obtain the dose escalation for lung tumors. However, the change of the patient's breath pattern can influence the stability of the inhaled air volume, IAV, used in this work as a surrogate parameter to assure the tumor position reproducibility during dose delivery.


METHODS
In this paper, an Elekta active breathing coordinator has been used for lung tumor irradiation. This device is not an absolute spirometer and the feasibility study here presented developed (i) the possibility to select a specific range epsilon of IAV values comfortable for the patient and (ii) the ability of a transit signal rate S(t), obtained by a small ion-chamber positioned on the portal image device, to supply in real time the in vivo isocenter dose reproducibility. Indeed, while the selection of the IAV range depends on the patient's ability to follow instructions for breath-hold, the S(t) monitoring can supply to the radiation therapist a surrogate of the tumor irradiation reproducibility.


RESULTS
The detection of the S(t) in real time during breath-hold was used to determine the interfraction isocenter dose variations due to the reproducibility of the patient's breathing pattern. The agreement between the reconstructed and planned isocenter dose in breath-hold at the interfraction level was well within 1.5%, while in free breathing a disagreement up to 8% was observed. The standard deviation of the S(t) in breath-hold observed at the intrafraction level is a bit higher than the one obtained without the patient and this can be justified by the presence of a small residual tumor motion as heartbeat.


CONCLUSIONS
The technique is simple and can be implemented for routine use in a busy clinic.
Piermattei
Angelo
A
Istituto di Fisica, Università Cattolica S. Cuore, Roma, Italy. a.piermattei@rm.unicatt.it
Cilla
Savino
S
Grimaldi
Luca
L
Viola
Pietro
P
Frattarolo
Lorenzo
L
D'Onofrio
Guido
G
Craus
Maurizio
M
Fidanzio
Andrea
A
Azario
Luigi
L
Greco
Francesca
F
Digesu
Cinzia
C
Deodato
Francesco
F
Macchia
Gabriella
G
Morganti
Alessio G
AG
D005240:Feasibility Studies; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D011874:Radiometry / Q000295:instrumentation / Q000379:methods*; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D012119:Respiration; D014057:Tomography, X-Ray Computed