[Stereotactic radiotherapy with linear accelerators. Dosage considerations on collimators and photon beam energy].
The small X-ray beam profiles produced by linear accelerators and used in stereotactic radiosurgery were studied. Circular focusing and not-focusing beams outlined by additional collimators (diameter ranging 10 to 30 mm) and square field outlined by the jaws (field size 10 to 30 mm) were measured. 6 and 18-MV X-ray beams from a dual energy accelerator and 6 and 15-MV X-ray beams produced by 2 single-energy accelerators were used. Measurements were carried out with Kodak X Omat V films in a perspex phantom in the same conditions for all the fields. To study the profile characteristics we introduced the V80/V20 = (R80/R20)3 ratio where R80 and R20 are respectively the mean distance of the 80% and 20% isodose lines from the beams axis. Measurement results show that 6-MV X-ray beams have a higher V80/V20 ratio than the ones obtained with the other energies. There is no significant difference between the beams produced with focused collimators and those produced with not-focused collimators. Square fields outlined by the jaws have a V80/V20 ratio greatly dependent on the accelerator used. This ratio is generally worse than the ones obtained with beams outlined by additional collimators.
Somigliana
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Istituto Nazionale per lo Studio e la Cura dei Tumori di Milano.
Filice
S
S
Stucchi
C
C
Gramaglia
A
A
Villa
S
S
Pasqualotto
C
C
Brusa
A
A
Crippa
M
M
Casolino
D
D
Scorsetti
M
M
D017785:Photons / Q000627:therapeutic use*; D011829:Radiation Dosage; D016634:Radiosurgery / Q000379:methods*