Objective: To discuss the influence of different computed tomography (CT) value assignment methods on dose calculation of intensity modulated radiotherapy (IMRT) plan which designed for nasopharyngeal carcinoma (NPC) and the value assignment methods of IMRT plan for NPC based on magnetic resonance (MR) images. Methods: Simulation CT and MR image of 32 NPC patients in Shandong Cancer Hospital from March 2018 to November 2018 were selected for this study. Populate CT values were obtained by contouring and analyzing the simulation CT of patients' tissue, including bone, air, brain, eyeball, optic-nerve, lens, parotid, masseter, skin. Pseudo-CT were generated by different CT value assignment methods: CT1: CT value of all tissues was set to 0HU; CT2: CT value of air cavity was set to populate CT value based on CT1; CT3: CT value of Bone was set to populate CT value based on CT2; CT4: CT value of each soft tissue were set to populate CT value based on CT3. The IMRT plan for NPC as Plan0 was designed base on simulation CT. Then Plan0 was transplanted to four pseudo-CT to recalculate the dose and obtain Plan1, Plan2, Plan3 and Plan4, the differences of dosimetric parameters were compared with Plan0. NPC-IMRT plan was designed base on MR images by using the assignment method with CT value of each tissue were set to populate CT value. Results: In the head and neck CT images, the average populate CT values of bone and cavity were 621 HU and -720 HU, respectively. The populate CT values of other soft tissue ranges from -20 HU to 70 HU. The differences of dosimetric indexes of Plan1, Plan2, Plan3, Plan4 decreased sequentially compare to Plan0, the difference of the dosimetry parameters of Plan4 and Plan0 was the smallest. The differences of PTV D(99), PTV D(95), isocenter dose, D(mean) of all tissues, D(max) of bilateral eye balls, D(max) of bilateral lens, D(max) of bilateral optic nerves, D(mean) of bilateral parotid, V(20) of bilateral parotid, D(50) of bilateral parotid, D(max) of spinal cord, D(max) of brainstem, D(5) of brainstem between Plan4 and Plan0 were all less than 1%. The difference of V(30) in bilateral parotid between Plan4 and Plan0 was less than 1.5%. In the comparison of the pixel dose distribution, the regions of dose distribution difference greater than 1% mainly distributed in the air cavity, bone periphery and the skin. The target area of the IMRT plan for NPC based on MR images met 95% of the prescribed dose, and the dose of each organ at risk was within the dose limit. Conclusions: The assignment method of each tissue and organs set to populate CT value compared with other methods has the least influence on the dose calculation of NPC-IMRT plan, which could meet the clinical requirements. Therefore, it should be the first choice of assignment method when designing NPC-IMRT plan based on MR image.

Background To study the effects of different CT value assignment methods on the dose calculations in radiotherapy plans for brain metastases, this study will provide a reference for radiotherapy planning design based on MR images. Methods All fifty recruited patients underwent CT and MR simulated localization the same day as, but prior to, three dimensional conformal radiation therapy (3D-CRT) or intensity modulated radiation therapy (IMRT) for brain metastases. After rigid registration of both the CT and MR images, the main tissues and organs were delineated on the CT and MR images. The average CT value of each tissue or organ was calculated. Three groups of pseudo-CT were generated by three CT value assignment methods: (I) the whole tissue was assigned 140 HU; (II) cavity, bone and other tissues were assigned −700, 700 and 20 HU, respectively; (III) tissue- and organ-specific CT values were given. The dose distribution was recalculated based on the three groups of pseudo-CT to obtain Plan2, Plan3 and Plan4, accordingly. The resultant radiotherapy plans were considered the original plan (Plan1). Then, the dosimetric differences between these three plans and Plan1 were compared. Results The average pseudo-CT values of bone and cavity were 731.7±69.3 and −725.5±26.1 HU, respectively. The range of average soft-tissue CT values was from −70 to 70 HU. The dose distribution between Plan1 and Plan2, Plan3 or Plan4 showed some differences, and the differences decreased in turn. The differences in the maximum dose of the lenses can reach 5.0%, 1.5% and 1.2%, respectively, while the differences in other dose parameters (maximum dose, mean dose and D98% to the PTV, D5% of the brainstem, and maximum dose of the brainstem, corpus callosum, left eye, right eye) were basically less than 2.0%, 1.2% and 0.8%, respectively. This shows that in the CT value assignment method, the dose calculation error can be greatly reduced by assigning the value to the bone and cavity separately, and if the different soft tissues are distinguished, the error of the dose calculation can be further reduced by more than 30%. In the pixel-by-pixel dosimetric comparison, the areas of more than 1% dose difference between Plan1 and Plan3 as well as Plan4 were mainly distributed near skin while those between Plan1 and Plan2 were mainly distributed at the bone, cavity, bone and soft tissues junction, and the skin near the field. Conclusions In summary, a scheme for assigning specific CT values to MRI-based radiotherapy is established. The scheme will provide patients with a dose-free radiotherapy plan. Through the calculation of the differences between the new plans and the old plan, it is found that our scheme can basically control the dose error below 0.8% to meet the clinical requirements.

Objective:To evaluate the cumulative dose of the target volume and organs at risk (OARs) in intensity-modulated radiation therapy (IMRT) for large volume non-small cell lung cancer (NSCLC) based on rigid and deformation registration methods. The dosimetric changes between the initial and second treatment plans were compared.Methods:Thirty patients treated with IMRT for large volume NSCLC with twice 4DCT scans acquired before radiotherapy and after 20 fractions of radiotherapy were recruited. The initial treatment plan (Plan 1) based on the average density projection CT (CT 1-avg) of the first 4DCT images and the second treatment plan (Plan 2) based on the average density projection CT (CT 2-avg) of the second 4DCT images were calculated. Then, the dose distributions of Plan 1 and Plan 2 were accumulated based on rigid and deformation registration methods to obtain Planrig and Plandef, respectively. Finally, the volume changes of gross tumor volume (GTV) and OARs between two CT scans were compared. The dose-volume parameters between Plan 1 and other plans (including Plan 2, Planrig and Plandef) were also statistically compared. Results:Compared with the initial CT scan, the mean volume of GTV and heart on the second CT was decreased by 44.2% and 5.5%, respectively, while the mean volume of ipsilateral lung, contralateral lung and total lung was increased by 5.2%, 6.2% and 5.8%, respectively (all P<0.05). Compared with Plan 1, the D 95%, D 98% and V 100% of target volume IGTV (GTV fusion of 10 4DCT phases) and PTV in Plan 2 did not significantly change (all P>0.05), and those in Planrig and Plandef were decreased (all P<0.05). The dose-volume parameters of spinal-cord, heart, ipsilateral lung and total lung in Plan 2, Planrig and Plandef were significantly lower than those in Plan 1(all P<0.05). Among them, the V 30Gy and D mean of heart were decreased by 27.3%, 16.5%, 15.3% and 15.2%, 6.6%, 5.6%, respectively. The V 20Gy and D mean of total lung were decreased by 15.6%, 4.5%, 3.7% and 15.7%, 6.2%, 5.1%, respectively. Some dose-volume parameters (including D 95% and D 98% of target volume, V 40Gy of heart, V 20Gy and D mean of the ipsilateral lung and the total lung) of Plandef were higher than those in Planrig (all P<0.05). The Dice similarity coefficients (DSCs) of OARs after deformation registration were significantly higher than those after rigid registration ( P<0.05). Conclusions:The dose-volume parameters of OARs significantly differ between Plan 1 and Plan 2. Hence, all these parameters have a large degree of deviation in predicting radiation-induced injury of OARs. Nevertheless, the dose-volume parameters obtained by deformation registration can enhance the prediction accuracy.

目的 在鼻咽癌调强放疗过程中,靶区和危及器官的体积不断变化,可能导致其实际接受剂量与初次计划剂量不一致.本研究通过形变配准方法获得2次计划的累积剂量,为预测鼻咽癌调强放疗的治疗反应提供参考.方法 收集2014-07-08-2018-05-02山东省肿瘤医院放疗科收治的18例进行同步加量调强放疗的鼻咽癌患者,在定位图像CT1上制定初次放疗计划Plan1,在治疗20～25分次后的复位图像CT2上制定放疗计划Plan2.利用Velocity将Plan2剂量与Plan1剂量分别刚性和形变配准累加得到Plan刚性和Plan形变.比较靶区和危及器官在Plan1、Plan2、Plan刚性和Plan形￡的剂量-体积指标变化.结果 18例鼻咽癌患者CT1和CT2中大体肿瘤靶区(gross tumor volume,GTV)分别为(79.28±49.66)和(64.47±42.39) cm3,Z=-3.724,P＜0.001;左腮腺体积分别为(16.76士4.74)和(10.77士4.07) cm3,Z=-3.724,P＜0.001;右腮腺体积分别为(16.63士4.40)和(10.46±3.99) cm3,Z=-3.724,P＜0.001.形变配准左腮腺(t=5.158,P＜0.001)、右腮腺(t=7.808,P＜0.001)、左视神经(t=2.664,P=0.016)和脊髓(t=4.660,P＜0.001)相似指数与刚性配准比较,差异有统计学意义.Plan2与Plan1相比,左右腮腺的V30以及脑干、左右眼球、左右晶状体、左右视神经的Dmax均下降,平均下降17.0％～60.1％.Plan形￡与Plan1相比,GTV和肿瘤计划靶区(plangross tumor volume,PGTV)的Dmean、D99,腮腺Dmean以及眼球和视神经Dmax变化均＜5％.Plan刚性与Plan1相比,GTV和PGTV的Dmean、D95,腮腺Dmean、v30、D50以及眼球和视神经Dax变化均＜10％.结论 鼻咽癌调强放疗过程中,肿瘤靶区及腮腺体积缩小,形变累加后靶区和危及器官各项剂量-体积指标与初次计划基本相当,因此初次计划的剂量-体积指标可以预测放疗过程中的疗效和放射性损伤.

[Background] With the wide application of radioactive sources and radioactive materials, the probability of losing radioactive source accidents is increasing. [Purpose] This study aims to locate lost radioactive sources by using three gamma ray directional detectors. [Methods] A gamma ray detection system consisting of three NaI(Tl) crystals was designed. The relationship between the full-energy peak ratio of the three NaI (Tl) detectors in the 137Cs radiation field as a function of distance and incident particle direction was studied by simulation and experiment. [Results] The results show that in the case of long-range detection, the full-energy peak ratio method can effectively eliminate the influence of the source-detector spacing on the angular resolution. For the 1.36×106 Bq 137Cs source at the distance of about 2.58 m, maximum angular deviation of measurement is 1.72°or less, and the relative positional deviation is 3.71%. [Conclusions] The designed three NaI(Tl) crystal detector has stable angular resolution in a certain range and can distinguish the incident direction of rays.

Objective To investigate the changes of accumulated dose in target area and organs at risk (OARs) for radiotherapy of left breast cancer by deformable and rigid image registration.Methods A total of 16 left breast cancer patients treated with 6 MV X-ray IMRT were analyzed retrospectively.All targets included the lymph node drainage area and the chest wall.All patients underwent simulation of the primary positioning and repositioning to obtain CT images.Primary and secondary treatment plans were developed using primary positioning CT (CT1) and repositioning CT (CT2),denoted as Plan1 and Plan2 respectively.The dose distribution of Plan2 was mapped to CT1 with rigid and deformable registration from CT2 to CT1 and then added to the dose distribution of Planl to obtain Plan-rigid and Plan-deform,respectively.The dosimetric differences between targets and the OARs of the four plans were compared.Results The CTV volume on CT2 was reduced by 6.64％ from that on CT1.The homogeneity index (HI)increased by 23.05％ after deformation-based accumulation.The Dice similarity coefficients (DSCs) of the heart,left lung and right lung were lower than those before deformable registration (0.94±0.01 vs.0.89± 0.05,0.96±0.01 vs.0.91±0.03,and 0.96±0.01 vs.0.92±0.03,respectively),and the differences were statistically significant (Z =-3.208,-3.533,-3.535,P ＜ 0.05).There were no significant differences in dose-volume indices of heart and left lung between Plan1 with other plans (P＞0.05),while the dose-volume indices in Plan-rigid were higher than that in Plan-deform.Conclusions Rigid registration is recommended in patients undergoing radical resection of left breast cancer with little change in the volume and dose-volume index of the target area and organs at risk.The dose-volume index of the initial intensity modulation plan can basically reflect the dose-volume statistics of both lungs and heart.

BACKGROUND:To evaluate the cumulative dose to the target volumes and organs at risk (OARs) after replanning during intensity-modulated radiation therapy (IMRT) for large volume non-small cell lung cancer (NSCLC) based on rigid registration and deformation registration technologies. METHODS:Thirty patients with large volume NSCLC who were treated with IMRT were selected, and two four-dimensional computed tomography (4DCT) scans were acquired before radiotherapy and after 20 fractions of radiotherapy. The initial treatment plan (Plan1) based on the average density projection CT (CT1-avg) of the first 4DCT images and the second treatment plan (Plan2) based on CT2-avg of the second 4DCT images were calculated. Then, the dose distributions of Plan2 and Plan1 were accumulated based on rigid and deformation registration technologies to obtain Planrig and Plandef, respectively. Finally, the volume changes of the gross tumor volume (GTV) and OARs between the two CT scans, and the dose-volume parameters among Plan1, Plan2, Planrig and Plandef were compared. RESULTS:Compared with those on the first CT, the mean GTV and heart volume on the second CT decreased by 44.2% and 5.5%, respectively, while the mean volumes of the ipsilateral lung, contralateral lung and total lung increased by 5.2%, 6.2% and 5.8%, respectively. The differences in the above volume parameters between the two CT scans were statistically significant (P<0.05). Compared with those in Plan1, the D95, D98 and V100% values of the IGTV (GTV fusion of 10 CT phases) and planning target volume (PTV) in Plan2 did not change significantly (P>0.05), and those of Planrig and Plandef decreased slightly (P<0.05). The dose-volume parameters of the spinal cord, heart, ipsilateral lung and total lung in Plan2, Planrig and Plandef were significantly lower than those in Plan1 (P<0.05). Among these parameters, V30 and the mean dose to the heart in Plan2, Planrig and Plandef decreased by 27.3%, 16.5%, and 15.3% and 15.2%, 6.6%, and 5.6% compared to those in Plan1, respectively; V20 and the mean dose to the total lung in Plan2, Planrig and Plandef decreased by 15.6%, 4.5%, and 3.7% and 15.7%, 6.2%, and 5.1% compared to those in Plan1, respectively. Some dose-volume parameters (including D95 and D98 to the target volume, V40 of the heart, V20 and the mean dose to the ipsilateral lung and the total lung) of Plandef were slightly higher than those in Planrig (P<0.05). The Dice similarity coefficients (DSCs) of the OARs after deformation registration were significantly higher than those after rigid registration (P<0.05). CONCLUSIONS:The dose-volume parameters of OARs in Plan2 were noticeably different from those in Plan1, so all of these parameters have large deviations in evaluating the actual dose to the OARs. And, the dose-volume parameters obtained by deformation registration can better predict the actual dose than those obtained by rigid registration.

BACKGROUND:During intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC), the volume of the target volume and the organs at risk (OARs) will change constantly, which may lead to differences between the actual dose received and the initial planned dose. In this study, the cumulative dose of the two plans was obtained by deformable registration. This study provides an approach to evaluate the dose volume of IMRT for the NPC objective.METHODS:From July 2014 to May 2018, eighteen NPC patients who accepted simultaneous integrated boost IMRT were enrolled. All patients underwent simulation CT (CT1) and replanning CT (CT2) scans after 20-25 fractions of radiation therapy. The treatment plans were designed on CT1 and CT2 with the name of Plan1 and Plan2, respectively. The Planreg and Plandef were obtained after registering from CT2 to CT1 using rigidity and deformation technology by Velocity. Then the dose-volume indices of the tumor target volumes and OARs at Plan1, Plan2, Planrig and Plandef were compared.RESULTS:The gross tumor volume (GTV) and the left and right parotid gland volumes decreased by 20.8% (P<0.001), 36.8% (P<0.001) and 37.5% (P<0.001), respectively, from CT1 to CT2. There was no significant difference in the dose-volume index on the GTV and plan gross tumor volume (PGTV) between Plan1 and Plan2. The V30 of the left and right parotid gland and the Dmax of the brainstem, left and right eyeballs, left and right lens, and left and right optic nerves were all lower in Plan2 than in Plan1 (the average decrease was 17.0% to 60.1%). The differences in some dose-volume parameters (including Dmean, D99 of the GTV and PGTV, Dmean of the parotid glands, Dmax of the lens and optic nerves) between Plandef and Plan1 were less than 5%. The differences in some dose-volume parameters (including Dmean, D95 of the GTV and PGTV, Dmean, D50 and V30 of the parotid glands, Dmax of lens and optic nerves) between Planrig and Plan1 were less than 10%. The Dyce Similarity Coefficient of the target volume and OARs after deformation registration were higher than that after rigid registration.CONCLUSIONS:The volume of the GTV and parotid glands were decreased during the IMRT for NPC. The dose-volume indices of the GTV and the OARs in Plandef were similar to those in Plan1. Therefore, the dose-volume indices of Plan1 can be used to evaluate the efficacy of radiotherapy and to predict radioactive damage.