Multileaf collimators (mlc) are now commonly used to shape treatment ﬁelds for conformal radiotherapy. In some of the clinical applications, a large area of extended leaves is uncovered. Such ﬁelds can be assumed to be mlc only deﬁned ﬁelds. Percentage surface dose (psd), build up region, percentage depth dose (pdd), penumbra width (P80/20), central axis absorbed dose (caad) and total scatter factor (Scp) for radiation ﬁelds deﬁned by jaw collimators (jc) only, jc and mlc together (jc + mlc), and mlc only were measured to quantify the diﬀerences in these parameters due to deﬁnition of ﬁelds by diﬀerent combinations of jc/mlc. Measurements were carried out on a Varian Clinac 2100C medical linear accelerator and a Varian 80 leaf mlc with 6 (quality index, QI = TPR20,10 = 0.66) and 18 MV (QI = 0.78) photon beams. Radiation transmitted through jc alone, jc + mlc and mlc alone were also determined. psd and dose in build up region for mlc only ﬁelds are higher than jc/jc + mlc ﬁelds. Diﬀerences in psd of mlc only and jc/jc+mlc ﬁelds depend on beam energy and ﬁeld size. These three types of ﬁelds have the same pdd while mlc penumbra (P80/20) is about 1 mm larger than jc penumbra. caad of mlc only ﬁeld is also higher than jc/jc + mlc ﬁeld and the diﬀerence in caad of these ﬁelds depend on ﬁeld size, beam energy and distance of jaw collimators from mlc ﬁeld boundary. Scp of mlc only ﬁeld for ﬁeld sizes greater than 10 × 10 cm2 are comparatively smaller than jc ﬁeld. Radiation transmitted through mlc alone at 18 MV is 2.66%, which is about 6 times higher than transmission through either of the jaw collimators (≤ 0.44%).
|Data di pubblicazione:||2004|
|Titolo:||Comparative dosimetric analysis of Varian MLC only and jaw collimator shaped fields|
|Codice identificativo ISI:||WOS:000225351500002|
|Codice identificativo Scopus:||2-s2.0-8444225501|
|Parole Chiave:||Multileaf Collimator; Jaw Collimator; Conformal Radiotherapy; Dosimetry.|
|Appare nelle tipologie:||Articolo su Rivista|