【摘要】 目的 研究使用Bowtie濾線器（F1）后，保證加速器CBCT患者掃描圖像質(zhì)量前提下，如何合理設(shè)置掃描條件，盡量降低輻射劑量。 方法 使用Piranha輻射測量儀測量CBCT在使用F1與未使用F1時(shí)射線的半價(jià)層。設(shè)定不同的掃描模式，使用直徑30 cm的有機(jī)玻璃模體測量掃描劑量，并使用XVI附帶的Catphan503模體測量客觀圖像質(zhì)量。在此基礎(chǔ)上，研究掃描劑量以及圖像質(zhì)量與掃描條件的關(guān)系，提出了適合臨床患者的胸部與腹部不同的掃描條件。 結(jié)果 使用F1后射束的半價(jià)層增加了0.77～0.92 mmAl，掃描劑量明顯減少，中心點(diǎn)減少了22%~29%，邊緣點(diǎn)減少了41%~45%，皮膚劑量減少顯著。圖像質(zhì)量隨著掃描劑量的增大而提高?？臻g分辨力受FOV影響較大，但一般能識(shí)別1～2 mm的物體，完全能夠滿足分辨細(xì)小骨結(jié)構(gòu)與標(biāo)記點(diǎn)的臨床要求。圖像偽影在使用L20時(shí)的大mAs下明顯。胸部低劑量的CBCT圖像如100 kV，M20，0.5 mAs的掃描條件亦可滿足臨床要求。腹部則需要使用較大劑量的掃描模式，CBCT圖像才達(dá)到進(jìn)行配準(zhǔn)的要求。 結(jié)論 F1的使用在改善圖像質(zhì)量的前提下降低了掃描劑量，使用新的掃描序列能平衡二者的關(guān)系。
【Abstract】 Objective To explore the influence of bowtie filtration on absorb dose and half-value layer inaluminum (Al) of cone-beam CT, estimate the image dose under different scan protocol, and establish the relationship between the image quality and the scan protocol after using F1. Methods Piranha was used to measure the HVL. Dose measurements were performed with an 0.6 cc Farmer type ionization chamber with a 30 cm-diam cylindrical shaped water phantoms in 100 and 120 kV with a series of mAs and FOV. CNR, noise and uniformity were measured on the Catphan503 images. Results HVL increased 0.77-0.92 mmAl where XVI generally had more penetrating beams at the similar kV settings. Scanning dose significantly reduced, the center point decreased 22%-29%, the edge with a decrease of 41%-45% which meant a very significant reduction in skin dose. Image quality improved with mAs increase. The spatial resolution mainly changed with FOV. But generally can identify 1-2 mm-diam objects, fully meet the clinical requirements of identify small bone structure and marker. Through this clinical investigation, low-dose CBCT images in chest, such as 100 kV, M20, and 0.5 mAs scanning protocol appeared to be an optimal settings. Abdomen image needed a higher dose to reach the requirements of registration. Conclusion Using F1 under the premise of improving the image quality then reducing the scanning dose and using a new scanning sequence can balance the image quality and scanning dose.
引用本文： 彭光,徐慶豐,陳剛,柏森. 配濾線器的加速器錐形束CT圖像質(zhì)量與掃描劑量的關(guān)系. 華西醫(yī)學(xué), 2010, 25(12): 2151-2155. doi: 復(fù)制
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- 1. Islam MK, Purdie TG. Patient dose from kilo voltage cone beam computed tomography imaging in radiation therapy[J]. Med Phys, 2006, 33(6): 1573-1582.
- 2. Song WY, Kamath S, Ozawa S, et al. A dose comparison study between XVI and OBI CBCT systems[J]. Med Phys, 2008, 35(2): 480-486.
- 3. Moore CJ, Amer A, Marchant T, et al. Developments in and experience of kilovoltage X-ray cone beam image-guided radiotherapy[J]. Br J Radiol, 2006, 27(S1): S66-S78.
- 4. Létourneau D, Wong JW, Oldham M, et al. Cone-beam-CT guided radiation therapy: technical implementation[J]. Radiother oncol, 2005, 75(3): 279-286.
- 5. Mail N, Moseley DJ, Siewerdsen JH, et al. The influence of bowtie filtration on cone-beam CT image quality[J]. Med Phys, 2009, 36(1): 22-32.
- 6. 尹勇, 袁雙虎. 加速器附加錐型束CT圖像質(zhì)量評(píng)價(jià)[J]. 中華放射腫瘤學(xué)雜志, 2007, 16(3): 225-227.
- 7. Amer A, Marchant T, Sykes J. Imaging doses from the Elekta Synergy X-ray cone beam CT system[J]. Br J Radiol, 2007, 80(954): 476-482.
- 8. Bissonnette JP, Moseley DJ, Jaffray DA. A quality assurance program for image quality of cone-beam CT guidance in radiation therapy [J]. Med Phys, 2008, 35(5): 1807-1815.
- 9. McBain CA, Henry AM, Sykes J, et al. X-ray volumetric imaging in image-guided radiotherapy: the new standard in on-treatment imaging[J]. Int J Radiat Oncol Biol Phys, 2006, 64(2): 625-634.
- 10. Smitsmans MH, de Bois J, Sonkes JJ, et al. Automatic prostate localization on cone-beam CT scans for high precision image-guided radiotherapy[J]. Int J Radiat Oncol Boil Phys, 2006, 63(4): 975-984.