加速器MVCBCT扫描图像在自适应放疗中应用的可行性研究

目的 探讨加速器成像射束影像系统（IBL）的全扇形束和大射野（EFOV）两种模式扫描得到的兆伏级锥形束断层（MV CBCT）图像可否用于剂量计算。方法 利用大孔径CT和在IBL的全扇形束和EFOV模式下对CIRS 062M型电子密度模体进行扫描,在Pinnacle计划系统中分别建立电子密度曲线。用CT和加速器MV级CBCT模式扫描头颈、胸、腹盆腔部仿真模体,利用CT图像制作调强计划,并将计划移植于MV CBCT的图像中,利用相应的电子密度曲线计算剂量,比较靶区及危及器官剂量分布。结果 MV CBCT图像中剂量分布比参考计划剂量偏低,并且在头颈、胸、腹盆腔模体中偏差依次增大。与参考计划相比,头颈部靶区剂量和危及器官剂量分布一致,偏差均在3%以内。胸部和腹盆腔靶区和危及器官的剂量分布均有大幅度的降低,偏差分别达到5%和10%,超出了临床接受范围。结论 在加速器IBL中全扇形束模式条件下,头颈部患者扫描得到的MV CBCT图像可在自适应放疗中用于剂量计算,胸、腹盆腔部位在EFOV模式下仅可用于图像引导,不能用于剂量计算。     

四种剂量探测器对放疗加速器常用剂量率的响应特性分析

目的 探讨4种剂量探测器对放疗加速器常用剂量率的响应特性。方法 在100~600 cGy/min的剂量率范围内,分别测量PTW的0.6 cm³电离室、0.015 cm³电离室以及Matrixx Evolution 二维电离室矩阵和MapCHECK 二维半导体矩阵在同一测量条件和剂量下的剂量率响应;测量和分析0.6 cm³电离室在不同能量和工作电压下的剂量率响应特性。结果 PTW的0.6 cm³电离室、0.015 cm³电离室以及Matrixx Evolution 二维电离室矩阵在6 MV X射线能量下都表现一定的剂量率依赖性,差异均<1%,在15 MV X射线能量下,无剂量率依赖性。MapCHECK 二维半导体矩阵在6 MV X射线和15 MV X射线能量下都显示了较强剂量率依赖性,响应差异在2%左右。结论 依据剂量率变化治疗技术的放疗加速器的剂量测量,需要对测量设备进行剂量率响应测试和分析,以保证日常刻度和剂量验证的精度。     

鼻咽癌调强放疗中实施同一计划对剂量的影响

目的 探讨鼻咽癌调强放疗过程中实施同一治疗计划的可行性。方法 选10例采用调强放射治疗的鼻咽癌患者,用Pinnacle³制定IMRT计划。在患者放疗中期重新行CT定位扫描,把基于初次定位CT图像所做的IMRT计划复制到重新定位CT图像上,使得照射野参数保持一致,测得基于两套图像计划中的肿瘤靶区、脊髓、脑干和腮腺的受量。统计在整个放疗过程中如果实施同一计划,患者靶区及各器官的剂量变化率。结果 两组计划相比,等中心层面外轮廓左右和前后长度平均缩小8%、3%。靶区PTV₁(D₉₅)减少0.6%~5.3%;放疗中期和放疗前相比右侧和左侧腮腺体积分别缩小13.1%~41.4%、12.0%~49.0%;右侧和左侧腮腺平均剂量增加5.6%~45.1%、3.3%~32.2%;脊髓最大剂量变化为-4.1%~13.9%;脑干剂量变化为-3.9%~9.3%。结论 对于采用鼻咽癌调强放射治疗的患者,在不考虑摆位误差的影响因素下,由于靶区及正常组织显著变化等因素影响有重新定位修改计划的必要性。     

湖北省调强放疗多叶光栅野光子线束吸收剂量和二维剂量分布验证研究

目的 用热释光剂量计（TLD）和放射性免冲洗胶片测量调强放疗（IMRT）多叶光栅（MLC）野光子线束吸收剂量并验证二维剂量分布。方法 选择湖北省7家三级甲等医院的7台不同型号医用直线加速器,使用国际原子能机构（IAEA）提供的15 cm×15 cm×15 cm聚苯乙烯专用模体,TLD和放射性免冲洗胶片,在源皮距90 cm,照射深度10 cm,照射野5 cm×5 cm,6 MV X射线,6 Gy吸收剂量照射条件下制定IMRT计划并实施照射,比较TLD和胶片吸收剂量测量值与放疗计划系统（TPS）预估剂量之间的偏差。同时,使用医院配备的30 cm×30 cm均质固体模体,在模体表面下5 cm处放置25 cm×25 cm放射性免冲洗胶片,并将IMRT计划中单个射野移植到模体中胶片层面上并实施照射,通过胶片剂量分析系统验证二维剂量分布。结果 所检医用直线加速器中,1号加速器TLD吸收剂量相对偏差和胶片吸收剂量相对偏差分别为-8.5%和-1.9%;7号加速器TLD吸收剂量相对偏差和胶片吸收剂量相对偏差分别为5.4%和0.5%;其余加速器TLD和胶片吸收剂量相对偏差均在±5%范围以内。所有加速器的二维剂量分布通过率均在90%以上。结论 TLD和胶片核查调强放疗剂量质量方法,操作简单,科学性强,TLD和胶片便于邮件方式寄送,该方法可运用于对放疗机构调强放疗剂量大范围的质量核查。     

局部晚期鼻咽癌诱导化疗后原发病灶靶区勾画的探讨

目的 探讨局部晚期鼻咽癌诱导化疗后原发病灶(GTVnx)靶区勾画。方法 选择2012-2013年收治的52例局部晚期鼻咽癌患者,诱导化疗2~3周期后行CT定位、标记及图像采集;同期采取相同体位行鼻咽部MRI平扫及增强扫描,采集T₁W₁增强图像;分别在CT图像及MRI图像进行GTV_nx勾画;转移淋巴结、CTV1、CTV2及正常组织均在CT图像进行勾画;通过放疗计划系统进行MRI/CT图像GTV_nx靶区融合;两套靶区给予相同处方剂量及正常组织限量,物理师进行调强放疗计划设计。比较不同图像下诱导化疗后GTV_nx、各靶区照射体积及剂量、正常组织受量变化。结果 在局部晚期鼻咽癌诱导化疗后GTV_nx勾画中,MRI图像勾画靶体积大于CT图像[(43.14±28.40)、(40.09±27.04)cm³,t=3.791,P<0.001];MRI图像勾画靶体积与诱导化疗前原发病灶体积差值[(27.90±11.86)cm³]小于CT图像勾画体积差值[(30.64±11.86)cm³](t=3.948,P<0.001)。两套计划原发病灶靶区照射体积比较,融合靶区计划(41.71±26.86)cm³大于CT图像计划[(38.65±25.66)cm³](t=4.098,P<0.001),但靶区剂量及正常组织受量差异无统计学意义。结论 采用MRI图像进行局部晚期鼻咽癌诱导化疗后原发病灶靶区勾画、MRI/CT靶区图像融合进行放疗计划设计,增加原发灶靶区体积及照射体积,可能减少诱导化疗后放射治疗靶区勾画漏靶发生。     

三种双剂量计法估算介入术者有效剂量比较

目的 比较3种双剂量计算法估算介入术者有效剂量的优劣。方法 在仿真人体模内布放热释光剂量片并将体模置于介入术者位置,在体模外穿戴铅防护衣、铅围脖和铅帽,并在铅衣内左前胸和铅围脖外左侧放置个人剂量计,在手术台上放置散射模体,分别为CIRS放疗调强体模和CT剂量检测模体,模拟介入手术曝光条件曝光一定时间,通过器官组织吸收剂量估算有效剂量;以3种双剂量计法计算有效剂量并与体模法结果进行比较。结果 得到两组各4个有效剂量结果,即使用CIRS放疗调强体模时,体模法、NCRP法、Niklason法和Boetticher法分别为0.138、0.097、0.161和0.173 mSv;使用CT剂量检测模体时分别为0.018、0.013、0.019和0.026 mSv。其中,Niklason法与体模法最为接近。结论 对于估算介入术者的有效剂量,Niklason法更为准确和实用。     

利用3D打印颅脑辐射等效体模进行个性化适形放疗的剂量验证

目的 建立利用3D打印颅脑辐射等效体模对患者进行个性化放疗剂量验证的方法,为三维适形放射治疗安全提供一种可靠的剂量保证手段。方法 采集两例患者（患者1和患者2）的CT图像数据,基于患者1的图像数据,重建其颅骨与脑组织,制作颅脑体模,验证颅骨与脑组织的等效材料。基于患者2的图像数据,根据3D图像重建并选用组织等效材料重建完全的头颅结构,采用3D打印技术制作全头颅体模。通过对目标区域插入电离室剂量仪并行放射治疗方案,获得头颅体模病灶部的剂量,验证和校准实际放疗计划的安全性。结果 对所获两个体模分别进行DR、CT成像,颅脑体模的等效骨骼与患者1骨骼的X射线灰度值差异为13 721,颅脑体模的等效脑组织与患者1的脑组织的CT值差异为35~40 HU,全头颅体模等效颞肌与患者2的颞肌组织的CT值差异为18~28 HU,影像数据表明体模材质的辐射等效性与人体组织近似,并且等效剂量分布符合常规治疗范围,体模的剂量验证可以有效验证放疗计划系统的准确性。结论 基于3D打印和组织等效技术所设计的个性化放疗体模,可应用于个性化放射治疗验证。体模制作方法简单快速,个性化程度高,为三维适形放射治疗安全提供一种可靠的剂量保证手段。     

射波刀影像追踪中X射线曝光条件对脊柱追踪错误节点及辐射剂量的影响

目的 研究和探讨射波刀脊柱追踪影像引导放疗中X射线曝光条件与错误节点比率的关系。方法 利用脊柱追踪放疗计划,采用不同X射线曝光条件对体模进行影像引导定位,观察脊柱追踪错误节点比率及体模表面吸收剂量的变化规律,确定X射线曝光条件与脊柱追踪错误节点比率之间是否存在优化曝光剂量。结果 脊柱追踪错误节点比率随着X射线曝光条件增加而降低,初期明显,但随着曝光条件的增加到一定水平,脊柱追踪错误节点比率不再降低;体模表面吸收剂量随着X射线曝光条件增加而增加;在≤5%的错误节点标准范围内,当平均错误节点为2.77%、1.07%、1.0%时,体模表面吸收剂量分别为0.11、0.26、0.31~0.46 mGy,相差1~3倍。结论 在射波刀影像引导放疗中,X射线曝光条件与脊柱追踪错误节点之间存在优化曝光剂量,使用最优X射线影像曝光剂量可大幅降低患者辐射剂量,对放疗患者的辐射防护具有非常重要的意义。     

二维电离室矩阵探测器的光子剂量学性能测试

目的 研究二维电离室矩阵探测器的剂量学特性,初步建立对其质量控制检测方法.方法 参照IEC 60731-2011报告对电离室剂量学指标的要求,在光子束(⁶⁰Co γ射线,6、10和15 MV X射线)下,对二维矩阵探测器剂量测量重复性、稳定性、剂量率依赖性、剂量响应线性和电离室间响应一致性等剂量学指标进行测试.结果 二维矩阵探测器在不同能量射线下测量重复性<0.3%,在⁶⁰Co γ射线下测量6个月的稳定性< 0.5%;在不同能量X射线下,加速器出束10~250 cGy和⁶⁰Co γ射线下剂量响应线性< 0.5%;在剂量率为200~600 MU/min下测量值最大偏差为0.87%;不同电离室间剂量响应偏差< 1%.结论 二维电离室矩阵探测器具有良好的剂量学特性;初步建立的质量控制检测方法具有可行性,并为放疗质量控制体系的建立提供理论依据.     

河南省调强放疗光子线束吸收剂量和二维剂量分布验证研究

目的 用热释光剂量计（TLD）和胶片测量调强放疗（IMRT）光子线束吸收剂量和二维剂量分布。方法 采用非概率抽样方法,在河南省选择5家三级甲等医院的8台可开展IMRT的医用加速器,TLD放入国家原子能机构（IAEA）提供的聚苯乙烯固体模体（15 cm×15 cm×15 cm）中,经CT扫描,影像传给放射治疗计划系统（TPS）制定放疗计划,源皮距90 cm,深度10 cm,照射野5 cm×5 cm,6 MV X射线,计算吸收剂量6 Gy和相应的监督单位（MU）,实施IMRT计划照射模体,测量TLD吸收剂量,同样方法测量胶片吸收剂量。医院的均质固体模体,尺寸30 cm×30 cm,厚度20 cm,25 cm×25 cm的胶片放在模体中,源皮距95 cm,深度5 cm,实施IMRT计划。结果 调查的8台医用加速器中,有7台加速器的TLD吸收剂量相对偏差符合要求,1台加速器不符合要求;胶片吸收剂量相对偏差全部符合要求;7台加速器的二维剂量分布通过率符合要求,1台加速器不符合要求。结论 TLD和胶片用于核查调强放疗多叶光栅野吸收剂量和二维剂量分布,方法简单,可操作性强,适合在我省医院大范围实施IMRT剂量质量核查。     

Dosimetric Evaluation Between Megavoltage Cone-Beam Computed Tomography and Body Mass Index for Intracranial, Thoracic, and Pelvic Localization

The aim of this study was to evaluate radiation dose for organs at risk (OAR) within the cranium, thorax, and pelvis from megavoltage cone-beam computed tomography (MV-CBCT). Using a clinical treatment planning system, CBCT doses were calculated from 60 patient datasets using 27.4 × 27.4 cm² field size and 200° arc length. The body mass indices (BMIs) for these patients range from 17.2–48.4 kg/m². A total of 60 CBCT plans were created and calculated with heterogeneity corrections, with monitor units (MU) that varied from 8, 4, and 2 MU per plan. The isocenters of these plans were placed at defined anatomical structures. The maximum dose, dose to the isocenter, and mean dose to the selected critical organs were analyzed. The study found that maximum and isocenter doses were weakly associated with BMI, but linearly associated with the total MU. Average maximum/isocenter doses in the cranium were 10.0 (± 0.18)/7.0 (± 0.08) cGy, 5.0 (± 0.09)/3.5 (± 0.05) cGy, and 2.5 (± .04)/1.8 (± 0.05) cGy for 8, 4, and 2 MU, respectively. Similar trends but slightly larger maximum/isocenter doses were found in the thoracic and pelvic regions. For the cranial region, the average mean doses with a total of 8 MU to the eye, lens, and brain were 9.7 (± 0.12) cGy, 9.1 (± 0.16) cGy, and 7.2 (± 0.10) cGy, respectively. For the thoracic region, the average mean doses to the lung, heart, and spinal cord were 6.6 (± 0.05) cGy, 6.9 (± 1.2) cGy, and 4.7 (± 0.8) cGy, respectively. For the pelvic region, the average mean dose to the femoral heads was 6.4 (± 1.1) cGy. The MV-CBCT doses were linearly associated with the total MU but weakly dependent on patients' BMIs. Daily MV-CBCT has a cumulative effect on the total body dose and critical organs, which should be carefully considered for clinical impacts.     

Measuring absorbed dose for i-CAT CBCT examinations in child,adolescent and adult phantoms

Objectives:

Design and construct child and adolescent head phantoms to measure the absorbed doses imparted during dental CBCT and compare with the absorbed dose measured in an adult phantom.

Methods:

A child phantom was developed to represent the smallest patients receiving CBCT, usually for craniofacial developmental concerns, and an adolescent phantom was developed to represent healthy orthodontic patients. Absorbed doses were measured using a thimble ionization chamber for the custom-built child and adolescent phantoms and compared with measurements using a commercially available adult phantom. Imaging was performed with an i-CAT Next Generation (Imaging Sciences International, Hatfield, PA) CBCT using two different fields of view covering the craniofacial complex (130 mm high) or maxilla/mandible (60 mm high).

Results:

Measured absorbed doses varied depending on the location of the ionization chamber within the phantoms. For CBCT images obtained using the same protocol for all phantoms, the highest absorbed dose was measured in all locations of the small child phantom. The lowest absorbed dose was measured in the adult phantom.

Conclusions:

Images were obtained with the same protocol for the adult, adolescent and child phantoms. A consistent trend was observed with the highest absorbed dose being measured in the smallest phantom (child), while the lowest absorbed dose was measured in the largest phantom (adult). This study demonstrates the importance of child-sizing the dose by using dedicated paediatric protocols optimized for the imaging task, which is critical as children are more sensitive to harmful effects of radiation and have a longer life-span post-irradiation for radiation-induced symptoms to develop than do adults.     

Evaluation of incidental testicular dose with thermoluminescence dosimetry during prostate radiotherapy

The aim of this study was to investigate incidental testicular doses during intensity modulated radiation therapy (IMRT) in patients treated with prostate radiotherapy only (PORT) and whole pelvis radiotherapy (WPRT). A total of 34 prostate cancer patients with intermediate and high risk were included in this prospective study. Each patient in the intermediate risk group received a total of 78 Gy in 39 fractions for prostate and seminal vesicles. In patients in the high risk group, 2 Gy daily fraction dose for pelvic lymphatics was given to 50 Gy, and then 78 Gy was given to prostate and seminal vesicles volumes. Treatment plans were created for all patients using the IMRT technique with 6MV. Testicular doses were measured for WPRT and PORT by thermoluminescence dosimetry (TLD) detectors placed on testis surface. Testicular doses measured for WPRT and PORT were compared. The isocenter to testicular distance for WPRT and PORT was 16.83-cm (13.20 to 18.80-cm) and 11.15 cm (9.10 to 13.00-cm), respectively. The mean testicular dose measurements of TPS and TLD per fraction during PORT were 2.41 cGy (1.95 to 3.60 cGy) and 3.70 cGy (2.80 to 5.10 cGy), respectively (p = 0.00). In WPRT irradiation, mean testicular dose values of TPS and TLD per fraction were measured as 3.85 cGy (2.00 to 5.70 cGy) and 5.85 cGy (4.25 to 7.55 cGy), respectively (p = 0.00). The cumulative mean scattered dose for PORT irradiation of 78 Gy in 39 fractions was 144.30 cGy. The mean cumulative dose received by the testis for the high-risk prostate patient was 228.15 cGy. There was a significant difference in testicular dose between WPRT and PORT irradiation. Testicular doses decreased significantly with increasing isocenter-testis distance. Incidental testicular dose during prostate radiotherapy can be significantly detrimental to spermatogenesis. Therefore, the testicles should be contoured as an organ at risk for the estimation of absorbed doses. The use of in vivo dosimetry is recommended for accurate measurement of testicular dose in radiotherapy of prostate cancer for men desiring continued fertility.     

加速器机载kV锥形束CT有效剂量的分析

目的 分析医用直线加速器机载kV锥形束CT扫描过程中患者的有效剂量随扫描条件的变化。方法 用PTW TM30009电离室分别在T40017头模和T40016躯干模体中,改变XVI锥形束CT的管电压、毫安秒、准直器以及机架旋转范围等参数测量加权CT剂量指数,计算相应的剂量长度乘积和有效剂量。结果 kV锥形束CT的加权剂量指数和有效剂量随管电压呈二次方变化,随毫安秒线性变化,与准直器以及机架旋转范围密切相关。临床常用条件下,kV锥形束CT单次扫描的剂量长度乘积和有效剂量低于参考剂量水平。结论 锥形束CT扫描过程中患者接受的有效剂量与扫描条件密切相关。锥形束CT扫描时,应该根据患者的解剖部位合理选择成像参数,最大限度减少患者接受剂量。     

江苏省8台加速器调强放疗靶体积和危及器官剂量及二维剂量分布验证方法研究

目的用热释光剂量计(TLD)及免冲洗胶片(film)测量调强放射治疗靶体积(TPV)、危及器官(OAR)剂量和二维剂量分布验证方法。方法选择8台医用直线加速器(瓦里安、医科达、西门子),国际原子能机构(IAEA)提供的聚苯乙烯专用模体,经CT扫描,影像传给放射治疗计划系统(TPS)制定治疗计划,勾画PTV,OAR的处方剂量,计算相应的监督单位(MU),能量6 MV X射线束,对模体实施调强放疗(IMRT)照射。照射后的TLD和胶片邮寄至中国疾病预防控制中心辐射防护与核安全医学所二级标准剂量学实验室测量和估算。结果按IAEA要求,对于靶体积和危及器官剂量,TLD测量剂量值与TPS计划剂量值的相对偏差为±7.0%。靶体积结果表明,8台加速器的TLD测量值与TPS计划值的相对偏差为0.6%~5.9%,符合要求。危及器官结果表明,8台加速器的TLD测量值与TPS计划值相对偏差为-0.6%~7.0%,符合要求。按IAEA要求,二维剂量分布3 mm/3%通过率为90%。8台加速器的胶片测量与TPS计划二维剂量分布通过率为90.2%~100.0%,符合要求。结论用TLD和放射性免冲洗胶片验证调强放射治疗靶体积、危及器官和二维剂量分布通过率,方法可行,可推广大范围运用到质量核查中,也可用于医院内部核查。     

Radiopaque drug-eluting embolisation beads as fiducial markers for stereotactic liver radiotherapy

Objective:To determine the feasibility of using radiopaque (RO) beads as direct tumour surrogates for image-guided radiotherapy (IGRT) in patients with liver tumours after transarterial chemoembolisation (TACE).Methods:A novel vandetanib-eluting RO bead was delivered via TACE as part of a first-in-human clinical trial in patients with either hepatocellular carcinoma or liver metastases from colorectal cancer. Following TACE, patients underwent simulated radiotherapy imaging with four-dimensional computed tomography (4D-CT) and cone-beam CT (CBCT) imaging. RO beads were contoured using automated thresholding, and feasibility of matching between the simulated radiotherapy planning dataset (AVE-IP image from 4D data) and CBCT scans assessed. Additional kV, MV, helical CT and CBCT images of RO beads were obtained using an in-house phantom. Stability of RO bead position was assessed by comparing 4D-CT imaging to CT scans taken 6–20 days following TACE.Results:Eight patients were treated and 4D-CT and CBCT images acquired. RO beads were visible on 4D-CT and CBCT images in all cases and matching successfully performed. Differences in centre of mass of RO beads between CBCT and simulated radiotherapy planning scans (AVE-IP dataset) were 2.0 mm mediolaterally, 1.7 mm anteroposteriorally and 3.5 mm craniocaudally. RO beads in the phantom were visible on all imaging modalities assessed. RO bead position remained stable up to 29 days post TACE.Conclusion:RO beads are visible on IGRT imaging modalities, showing minimal artefact. They can be used for on-set matching with CBCT and remain stable over time.Advances in knowledge:The role of RO beads as fiducial markers for stereotactic liver radiotherapy is feasible and warrants further exploration as a combination therapy approach.     

湖北省7台加速器调强放疗靶体积和危及器官剂量及二维剂量分布验证方法研究

目的研究用热释光剂量计(TLD)和胶片(film)测量调强放疗(IMRT)靶体积(PTV)、危及器官(OAR)和二维剂量分布方法。方法选择湖北省7家三甲医院的7台不同型号医用直线加速器,国际原子能机构(IAEA)提供的聚苯乙烯专用模体,TLD和放射性免冲洗胶片(EPT3),经CT模拟定位机扫描模体,影像传输至治疗计划系统(TPS),分别勾画PTV、OAR处方剂量和相应的监督单位(MU),能量6 MV X射线束,对模体实施IMRT照射,照射后的TLD和胶片邮寄至中国疾病预防控制中心辐射防护与核安全医学所二级标准剂量学实验室测量和估算。结果按IAEA要求,OAR和PTV的TLD测量值与TPS计划处方剂量的相对偏差为±7.0%。7台加速器PTV的TLD测量值与TPS计划值相对偏差在-5.4%~6.5%范围内,均符合IAEA的要求;5台加速器的OAR的TLD测量值和TPS计划值相对偏差在-2.2%~6.7%范围内,2台加速器相对偏差为-8.6%和8.2%,超出IAEA的要求。按IAEA要求,二维剂量分布3 mm/3%通过率为90%。7台加速器的二维剂量分布通过率在90.3%~98.9%范围内,均符合IAEA要求。结论使用TLD和胶片做IMRT剂量验证,科学性强,操作简单,TLD和胶片便于邮件寄送,该方法可运用于今后对放疗机构调强放疗剂量大范围的质量核查。     

Dose reduction in maxillofacial imaging using low dose Cone Beam CT

Objectives(a) To measure the absorbed dose at certain anatomical sites of a RANDO phantom and to estimate the effective dose in radiographic imaging of the jaws using low dose Cone Beam computed tomography (CBCT) and (b) to compare the absorbed and the effective doses between thyroid and cervical spine shielding and non-shielding techniques.Study designThermoluminescent dosimeters (TLD-100) were placed at 14 sites in a RANDO phantom, using a Cone Beam CT device (Newtom, Model QR-DVT 9000, Verona, Italy). Dosimetry was carried out applying two techniques: in the first, there was no shielding device used while in the second one, a shielding device (EUREKA!, TRIX) was applied for protection of the thyroid gland and the cervical spine. Effective dose was estimated according to ICRP₆₀ report (E_ICRP). An additional estimation of the effective dose was accomplished including the doses of the salivary glands (E_SAL). A Wilcoxon Signed Ranks Test was used for statistical analysis.ResultsIn the non-shielding technique the absorbed doses ranged from 0.16 to 1.67 mGy, while 0.32 and 1.28 mGy were the doses to the thyroid and the cervical spine, respectively. The effective dose, E_ICRP, was 0.035 mSv and the E_SAL was 0.064 mSv. In the shielding technique, the absorbed doses ranged from 0.09 to 1.64 mGy, while 0.18 and 0.95 mGy were the respective values for the thyroid and the cervical spine. The effective dose, E_ICRP, was 0.023 mSv and E_SAL was 0.052 mSv.ConclusionsThe use of CBCT for maxillofacial imaging results in a reduced absorbed and effective dose. The use of lead shielding leads to a further reduction of the absorbed doses of thyroid and cervical spine, as well as the effective dose.