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SU‐GG‐T‐366: Evaluation of Effects of Cable Exposure on the Scanning Data for MV Linear Accelerator
Author(s) -
Kurokawa C,
Fox C,
Ozawa S,
Sugimoto S,
Karasawa K,
Palta J,
Liu C
Publication year - 2010
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3468763
Subject(s) - ionization chamber , linear particle accelerator , polarity (international relations) , polarity symbols , energy (signal processing) , signal (programming language) , ion , detector , optics , materials science , field (mathematics) , physics , voltage , analytical chemistry (journal) , atomic physics , nuclear medicine , electrical engineering , chemistry , mathematics , ionization , engineering , computer science , breakdown voltage , cell , beam (structure) , biochemistry , quantum mechanics , programming language , medicine , chromatography , pure mathematics
Purpose : To evaluate the effects of cable exposure on the scanning data for MV linear accelerators Method and Materials : Profiles and PDDs from 10 × 10 cm 2 to 30 × 30 cm 2 field sizes for 6 and 18 MV photons were measured using a 3D automated scanning system (IBA, blue tank and OmniPro 6.5 Accept, Tennessee) and CC04 and CC13 ion chambers (IBA, Tennessee) of volume 0.04 and 0.13 cm 3 . The measurements were made at ±300V for each detector Results : The cable effect induced a positive change in the measured signal resulting in a reduction in the measured signal for negative polarity measurements and an increase with a positive polarity. The effect is significant for low energy, deep depth and large field size. Although it makes the difference in the GT profiles, the measured field sizes agreed within 0.13 % and 0.07 % for CC04 and CC13 ion chambers. For PDD measurements, the data with a +300V was found to be elevated at the shallow depth (d < d max ) due to the small amount of the cable length in the field. This is consistent with the results of the profile measurements. Although the effect does not change the location of d max , the measured PDDs of 10×10 and 30×30 cm 2 with both voltage, which are normalized at 10cm depth, have 0.3% and 1.2% differences at the d max , respectively. Conclusion : The effect of cable exposure is significant for low energy, deep depth and large field size measured with the small volume chamber. Ideally, profile and PDD measurements should be acquired as an average of positive and negative bias to remove the effects of cable effects on the measurements.