148
INVESTIGATE DIFFERENCES IN ELECTRON BEAMS WITH A 10 X 10 CM 2
OPEN CONE, A 10 X 10 CM 2 CONE WITH 5 CM DIAMETER CIRCULA R
CUTOUT, AND A 5 CM DIAMETER OP EN CONE FOR 12 MEV LI NAC
Mu-Tai L iu ',
Jao-Pe rn g Lin
Sung- Yen L iri '" ,
I
l 2
. ,
T ie h-Ch i C h u
Shen g-S ang H ua ng ' ,
2
,
Kui -Hua Lin' " ,
C hi-Yuan Ye h
l
Department of Radiation Oncology. Chang Hua Christian Hospital.
J
Department ofAtomic Science. National I sing HI/o University.
Introdu ction: When e lectron beam s are used for rad iot herapy, the treatm ent po rta ls are often shaped to fit the
treatment area . In so me cli nica l app licat ion, a larger nominal gap is necessar y. For these different applica tor
effects, we must de termine em pirically these effects for the applicator sys tem employe d.
Materials al/d Methods: In this paper, a lO x 10 cm 2 open co ne, a lO x 10 co ne with 5 cm d iameter circ ular
cutout. and a 5 cm diameter open co ne for 12 MeV, 80 MU e lec tro ns wi ll be studie d. Cha nge the ai r ga p
betwee n the co llima tor and the phantom surface from 0 cm to 10 em. We measure parameters and co mpa re
these d ifferences.
J
Results: Wh en applicato r is a lO x 10 cm open co ne resu lting in larger X-ra y back ground , larger D ma" Go and
flat ness is better. If the app licat or is a I0 x 10 cnl co ne with 5 ern d iam ete r c irc ular c uto ut, the X-ray backgro und is sma lle r. As the ai r ga p bet ween the co llimator and the phantom surface inc rea ses the pen umb ra
2
increases, X-ray back groun d and sca tters increase, too . We a lso find that the lO x 10 cm ope n co ne for the
effec t of the air gap is larger.
2
Conclusion : Electro n beams with a lO x 10 cm open co ne ca n be used to treat larger tumors. To treat sma ller
tumors, a l O x 10 em' cone wit h 5 em dia me ter circ ular cutout wi ll be better. Th e flatness and effective treat2
ment size of e lectron beams with a lO x 10 cm co ne wit h 5 em d iam eter cir cular cuto ut are better than with a 5
cm d iam eter open co ne .
fTherapeut Radi al Onco l 1998; 5: 143 - 148
1
Key words: Electron beam , Electro n co ne, Air ga p. Flatness