【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(cè)量?jī)x測(cè)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(cè)量掃描劑量，并使用XVI附帶的Catphan503模體測(cè)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?！〗Y(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。空間分辨力受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?！〗Y(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.
【摘要】 目的 分析重力因素對(duì)二維探測(cè)器陣列驗(yàn)證靜態(tài)調(diào)強(qiáng)計(jì)劃的影響，判斷機(jī)架角度歸為0°的測(cè)量方法是否安全可靠?！》椒ā≡?°機(jī)架角和實(shí)際治療機(jī)架角分別測(cè)量靜態(tài)調(diào)強(qiáng)計(jì)劃的劑量分布，以3 mm范圍內(nèi)偏差lt;3%(3% 3 mm)標(biāo)準(zhǔn)進(jìn)行γ分析，獲得相對(duì)于參考劑量分布的通過率，分析通過率變化規(guī)律。分析兩種方法測(cè)量的等中心點(diǎn)絕對(duì)劑量的差異。 結(jié)果 通過率的變化呈隨機(jī)分布，96.9%的照射野偏差lt;2.5%。所有計(jì)劃的85.7%絕對(duì)劑量偏差lt;2%，最大偏差為4.75%。 結(jié)論 使用二維探測(cè)器陣列在0°角進(jìn)行調(diào)強(qiáng)計(jì)劃的日常驗(yàn)證是安全可靠的。【Abstract】 Objective To analyze impacts of gravity on the verification of IMRT plans with 2-Dimensional detector arrays and to evaluate the reliability of the measurements in vertical direction (gantry angle=0). Methods The dose distributions for each beam in IMRT plans were measured with 0 degree gantry angle and actual gantry angle respectively. The γ percentage pass rate (according to 3% 3 mm) for each beam under each angle condition was obtained by the comparison between the measured dose distribution and the calculated dose map from the treatment planning system which was treated as the reference distribution. Then the absolute dose at the isocenter for each plan was measured at each angle condition and was analyzed. Results The variations of γ percentage pass rates between the two types of measurements were randomly distributed, and the deviations for 96.9% beams were less than±2.5%. The differences between absolute doses for 85.7% beams were less than±2% and the biggest deviation was -4.75%. Conclusion Verification of IMRT plans for the radiotherapy quality assurance using 2-Dimensional detector arrays in 0 degree gantry angle is safe and reliable.