Objective To retrospectively analyze the changes in cerebral blood flow(CBF)of hippocampus before and after radiotherapy(RT)and to explore its relationship with dose for providing a feasible approach for dynamically monitoring hippocampal response after whole brain radiation therapy in patients with brain metastases(BMs).Methods A retrospective analysis was conducted on magnetic resonance(MR)images from 43 BMs patients before and after RT,including T1-weighted imaging(T1WI)and three-dimensional arterial spin labeling(3D-ASL)imaging.Manual segmentation of the hippocampal structures was performed on T1WI to determine hippocampal volume,while CBF within the hippocampus was derived from 3D-ASL images.Patients were categorized into different groups according to the time interval between two MR scans and the dose received by the hippocampus,namely short time interval[<30 d,with an average of(19.74±7.15)d]≤1 Gy,1-30 Gy and≥30 Gy groups;long time interval[>3 months,with an average of(495.50±226.06)d]≤1 Gy,1-30 Gy and≥30 Gy groups.The patterns of changes in hippocampal CBF and volume,as well as the dose-effect relationship following RT were analyzed.Results(1)A total of 86 hippocampi were enrolled,showing reductions of 8.32%in minimum CBF(CBF-min),7.31%in maximum CBF(CBF-max),8.09%in mean CBF(CBF-mean),and 4.11%in hippocampal volume after RT(P<0.05).The decrease rates of CBF-min,CBF-max and CBF-mean were 6.33%,7.01%and 8.23%higher than the reduction rate of hippocampal volume,respectively.(2)With a brief interval between two MR simulation localization scans,hippocampal CBF in the groups receiving≤1 Gy and 1-30 Gy exhibited an increase,with the increase rate positively correlated to the radiation dose absorbed by the hippocampus.Conversely,in the group receiving≥30 Gy,hippocampal CBF decreased.The variations in the rate of hippocampal CBF change across the dose groups were statistically significant,except when comparing≤1 Gy and 1-30 Gy groups(P<0.05).Additionally,the hippocampal volume in all 3 dose groups experienced a slight increase,with the growth rate also positively correlated to the radiation dose received by the hippocampus;however,these differences were not statistically significant(P>0.05).(3)With a long interval between MR simulation localization scans,both hippocampal CBF and volume in all 3 dose groups demonstrated decreasing trends,with the decrease rate positively correlated to the radiation dose received by the hippocampus.Statistically significant differences in the rate of CBF change were noted among the dose groups,except for the comparison between≤1 Gy and 1-30 Gy groups(P<0.05).The reduction rate of hippocampal volume across 3 dose groups was statistically significant(P<0.05).Conclusion The reduction in hippocampal CBF following RT in BMs patients is more sensitive than the reduction in hippocampal volume,exhibiting a pronounced dependence on both time and radiation dose.Consequently,CBF changes should be employed as a standard bioindicator for monitoring the response to hippocampal RT and predicting radiological injuries after whole brain radiotherapy in BMs patients.

Objective To retrospectively analyze the changes in cerebral blood flow(CBF)of hippocampus before and after radiotherapy(RT)and to explore its relationship with dose for providing a feasible approach for dynamically monitoring hippocampal response after whole brain radiation therapy in patients with brain metastases(BMs).Methods A retrospective analysis was conducted on magnetic resonance(MR)images from 43 BMs patients before and after RT,including T1-weighted imaging(T1WI)and three-dimensional arterial spin labeling(3D-ASL)imaging.Manual segmentation of the hippocampal structures was performed on T1WI to determine hippocampal volume,while CBF within the hippocampus was derived from 3D-ASL images.Patients were categorized into different groups according to the time interval between two MR scans and the dose received by the hippocampus,namely short time interval[<30 d,with an average of(19.74±7.15)d]≤1 Gy,1-30 Gy and≥30 Gy groups;long time interval[>3 months,with an average of(495.50±226.06)d]≤1 Gy,1-30 Gy and≥30 Gy groups.The patterns of changes in hippocampal CBF and volume,as well as the dose-effect relationship following RT were analyzed.Results(1)A total of 86 hippocampi were enrolled,showing reductions of 8.32%in minimum CBF(CBF-min),7.31%in maximum CBF(CBF-max),8.09%in mean CBF(CBF-mean),and 4.11%in hippocampal volume after RT(P<0.05).The decrease rates of CBF-min,CBF-max and CBF-mean were 6.33%,7.01%and 8.23%higher than the reduction rate of hippocampal volume,respectively.(2)With a brief interval between two MR simulation localization scans,hippocampal CBF in the groups receiving≤1 Gy and 1-30 Gy exhibited an increase,with the increase rate positively correlated to the radiation dose absorbed by the hippocampus.Conversely,in the group receiving≥30 Gy,hippocampal CBF decreased.The variations in the rate of hippocampal CBF change across the dose groups were statistically significant,except when comparing≤1 Gy and 1-30 Gy groups(P<0.05).Additionally,the hippocampal volume in all 3 dose groups experienced a slight increase,with the growth rate also positively correlated to the radiation dose received by the hippocampus;however,these differences were not statistically significant(P>0.05).(3)With a long interval between MR simulation localization scans,both hippocampal CBF and volume in all 3 dose groups demonstrated decreasing trends,with the decrease rate positively correlated to the radiation dose received by the hippocampus.Statistically significant differences in the rate of CBF change were noted among the dose groups,except for the comparison between≤1 Gy and 1-30 Gy groups(P<0.05).The reduction rate of hippocampal volume across 3 dose groups was statistically significant(P<0.05).Conclusion The reduction in hippocampal CBF following RT in BMs patients is more sensitive than the reduction in hippocampal volume,exhibiting a pronounced dependence on both time and radiation dose.Consequently,CBF changes should be employed as a standard bioindicator for monitoring the response to hippocampal RT and predicting radiological injuries after whole brain radiotherapy in BMs patients.

Objective:To investigate the effects of CT images reconstructed using different field of view (FOV) sizes on the automatic segmentation of organs at risk and dose calculation accuracy in radiotherapy after radical mastectomy.Methods:Under the same scanning conditions, CT values-electron density conversion curves were established by reconstructing the original CT images of a phantom placed at the isocenter and extended FOV (eFOV) positions using FOV sizes of 50, 60, 70 and 80 cm. Then, these curves were compared. A standard phantom with a known volume was scanned, and the automatic segmentation result of the phantom on CT images reconstructed using different FOV sizes was compared. A total of 30 patients in Guangdong Second Provincial General Hospital from January 2020 to June 2022 with breast cancer were randomly selected. Through simulated positioning, their CT images were reconstructed using different FOV sizes for the purpose of automatic segmentation of organs at risk, followed by comparison between the outcomes of automatic segmentation and physicians′segmentation. The treatment plan established based on CT images reconstructed using a FOV size of 50 cm (FOV 50 images for short) was applied to CT images reconstructed using FOV sizes of 60, 70 and 80 cm (FOV 60, FOV 70 and FOV 80 images for short) for dose calculation, and the dose calculation result were compared. Results:The CT values - electron density conversion curves derived from CT images reconstructed using different FOV sizes were roughly consistent. At the isocenter, the difference between the segmented volume and actual volume of the standard phantom increased up to a maximum of 6 cm 3 (4.8%) with an increase in the FOV size. As indicated by the automatic segmentation result, the segmentation accuracy of the spinal cord, trachea, esophagus, thyroid, healthy mammary gland, and skin decreased with an increase in the FOV size ( t = -28.43-8.23, P < 0.05). The comparison of dose calculated based on CT images reconstructed using different FOV sizes showed that there was no statistically significant differences( P>0.05) in the dose to target volume ( V95) and the maximum and average doses in the supraclavicular lymph node region, as well as the dose to organs at risk. The coverage for planned target volume decreased with an increase in the FOV size, with a maximum difference of 4.06%. Conclusions:It is recommended that, for radiotherapy after radical mastectomy, FOV 50 images should be selected for the automatic segmentation of organs at risk, CT-values-electron density conversion curves should be established based on the electron density phantom images of the eFOV region, and the eFOV 80 images should be preferred for dose calculation.

Objective:To evaluate the feasibility of delineating subvolume target in radiotherapy for brain tumors using Gd-based contrast clearance difference.Methods:Twenty-six patients with malignant brain tumors were scanned with MRI. The first and second acquisitions of standard T 2-weighted images (T 2WI) and T 1-weighted images (T 1WI) were performed at 5 min and 60 min after injection of contrast agent. Delayed contrast extravasation (DCEM) MRI computed by Brainlab comprised regions of contrast agent clearance representing active tumors and regions of contrast accumulation representing non-tumor tissues. Based on T 2WI images, 14 patients with liquefaction necrosis were divided into group A, and 12 patients without liquefaction necrosis into group B, respectively. Then, gross target volume (GTV) was delineated on T 1WI images. Based on the GTV, active tumor (GTV tumor) and non-tumor regions (GTV non-tumor) were delineated on T 1WI-DCEM fusion images, while liquefaction necrosis (GTV liquefaction) and non-liquefaction (GTV non-liquefaction) were delineated on T 1-T 2WI fusion images. Finally, the differences between different subvolumes were compared by paired t-test. Results:In group A, the GTV non-liquefaction and GTV liquefaction were (13.65±18.15) cm 3 and (6.30±7.57) cm 3. The GTV tumor was (10.40±13.52) cm 3 and the GTV non-tumor was (9.55±14.57) cm 3. The GTV non-liquefaction was significantly increased by 16.3% on average compared with the GTV tumor ( P<0.05). The GTV non-tumor was significantly increased by 16.3% on average compared with the GTV liquefaction ( P<0.05). In group B, The GTV non-tumor was significantly reduced by 68.8% on average compared with the GTV tumor ( P<0.05). Conclusions:Compared with T 2WI, DCEM has advantages in identifying the liquefaction area and can clearly differentiate the subvolume of active tumors from non-liquefaction necrosis. DCEM provides evidence for guiding the delineation of subvolume in primary and metastatic brain tumors.

Objective:To evaluate the effect of different reconstruction images on cardiac dose evaluation by comparing the differences between 4D-CT series and special reconstruction images in evaluating the dose-volume index of cardiac structures.Methods:ECG 4D-CT series were scanned in 15 female patients with left breast cancer. The images of 0-95% 20 phases were reconstructed at an interval of 5% cardiac cycle. The maximum intensity projection (MIP), minimum intensity projection (MinIP), average intensity projection (AIP) and sum intensity projection (SIP) images were obtained by special reconstruction of 4D-CT series. Left ventricle (LV) and left anterior descending coronary artery (LADCA) were delineated on 4D-CT and special reconstruction series, respectively. The intensity-modulated radiation therapy plan of the left breast cancer was designed on the basis of 0% phase, and the cumulative dose (Dose-cumulate) of 20 phases was obtained by deformation registration. The doses of 0% phase were deformed and registered to MIP, MinIP, AIP and SIP images to obtain the corresponding dose distribution. The dose-volume indexes of LV and LADCA based on different CT images were compared.Results:In the evaluation of dose-volume index of LV, compared with 4D-CT series, the change rates of V 5Gy, V 30Gy, V 40Gy, D max and D mean on MIP images were 3.8%, 2.0%, 0.9%, 3.8% and 1.7%, respectively. There was significant difference in V 5 and D max between MIP and 4D-CT (both P<0.05). Compared with 4D-CT, the change rates of D max on MinIP, SIP and AIP images were 2.5%, 3.1% and 1.5%, respectively (all P<0.05). In the evaluation of dose-volume index of LADCA, only the change rate of D max on four special reconstructed images was<5%( P<0.05). Conclusions:In the dose-volume evaluation of LV, the V 30Gy, V 40Gy and D mean obtained by MIP are basically equivalent to those obtained by 4D-CT series, which can be used to substitute 4D-CT series to evaluate the dose-volume. The special reconstruction image of LADCA can not replace 4D-CT series.

Objective:To compare the differences in the delineation of the gross tumor volume (GTV) and lymph nodes of nasopharyngeal carcinoma (NPC) patients using computerized tomography (CT), magnetic resonance imaging (MRI), and 18F-fluorodeoxyglucose positron emission tomography/computed tomography ( 18F-FDG PET/CT), and to investigate the optimal standard uptake value (SUV; relative to the MRI-based delineation) for the automatic delineation of GTV using PET. Methods:A total of 53 NPC patients proposing to receive radiotherapy were selected for this study. The CT, MRI, and PET images of each patient were obtained before radiotherapy. Then GTV and positive lymph nodes were delineated on these three types of images. They were individually named GTV MRI, GTV CT, GTV PET2.5 (SUV=2.5), Lymph MRI, Lymph CT, and Lymph PET2.5 and compared. The GTV ∩2.5 (overlapped GTV) was obtained through the alignment of MRI and PET/CT images. Meanwhile, GTV was delineated on PET images using thresholds of SUV=4.0, 4.5, 5.0, and 5.6, obtaining GTV PET4.0, GTV PET4.5, GTV PET5.0, and GTV PET5.6. Then their volume and Dice similarity coefficients (DSCs) were compared. Results:Compared to GTV MRI, GTV CT decreased by 1.73% ( P>0.05) and GTV PET2.5 increased by 21.34% ( t=-3.52, P < 0.05) in the three types of images. The volume of Lymph PET2.5 was 1.61 and 1.87 times the volume of Lymph MRI and Lymph CT, respectively ( t=-4.12, -5.18; P< 0.05). The volume of high-SUV lymph nodes was 4.07 times the volume of lymph nodes with low SUVs or SUV=0 ( t=5.50, P< 0.05) on PET images. The DSC between GTV PET4.0and GTV MRI was 0.78 ± 0.27, which was lower than that between GTV PET2.5 and GTV MRI (0.84 ± 0.18). However, GTV PET4.0 approximated to GTV ∩2.5 ( P>0.05). Conclusions:Compared to CT and 18F-FDG PET/CT, MRI shows more accurate boundaries of GTV and lymph nodes. When 18F-FDG PET/CT was adopted to automatically delineate GTV, the GTV delineated using SUV=4.0 was closer to GTV MRI.

Objective:To evaluate the feasibility of magnetic resonance (MR) perfusion imaging for sub-region segmentation of brain metastases (BMs), and to provide reference for individualized radiotherapy based on blood flow perfusion heterogeneity in BMs patients.Methods:96 BMs patients were selected, including 55 patients with necrosis and 41 without necrosis. Each patient was scanned with CT simulation and MR simulation before radiotherapy. MIM Maestro 6.8.8 software was used to delineate the gross tumor volume (GTV) and necrosis GTV (GTV N) from enhanced T 1W images and T 2 Propeller images, respectively, and the solid GTV (GTV S) was obtained by the subtraction of the two. Then, the cerebral blood flow map of three dimensional arterial spin labeling (3D-ASL) was employed to determine the high perfused GTV (GTV H) and low perfused GTV (GTV L). The volume and proportion of sub-regions were counted and compared between two groups and the correlation of each sub-region was analyzed. Results:The volume of GTV in the necrosis and non-necrosis groups was 19.56 and 7.34 cm 3, respectively. Besides, the AUC of the ROC between GTV volume and necrosis was 0.749. In the necrosis group, the ratio of GTV N, GTV S, GTV H and GTV L to GTV was 20.47%, 79.53%, 33.03% and 46.50%, respectively (all P<0.05). Among them, the r value between GTV S and GTV was 0.963, 0.849 for GTV L and GTV, and 0.840 for GTV L and GTV S, significantly higher than 0.683 for GTV H and GTV and 0.764 for GTV H and GTV S (all P<0.05). In the non-necrosis group, the ratio of GTV H to GTV was higher than that in the necrosis group (58.95% vs. 33.03%, P<0.05). In addition, the ratio of GTV L to GTV was slightly lower than that in the necrosis group (41.05% vs. 46.50%, P>0.05). The r value between GTV H and GTV was 0.776, significantly higher than 0.574 between GTV L and GTV ( P<0.05). Conclusion:MR-3D-ASL can quantitatively analyze the heterogeneous blood perfusion of BMs, which could guide the sub-region segmentation and local dose escalation of tumors.

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.

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.

Objective: To study the effects of different CT values assignment methods on the dose calculation of radiotherapy plan for brain metastases, which will provide a reference for radiotherapy treatment planning based on MR images. Methods: A total of 35 patients treated with radiotherapy for brain metastases were selected, with pre-treatment CT and MR simulated positioning performed at the same day. Based on the simulation CT images, three dimensional conformal radiation therapy (3D-CRT) or intensity modulated radiation therapy (IMRT) plans were calculated as the original plan (Plan1). The CT and MR images were rigidly registered and then the main tissues and organs were delineated on CT and MR images. The average CT values of each tissue and organ were calculated. Three groups of pseudo CT were generated by three CT values assignment methods based on the CT images: whole tissue was assigned 140 HU; cavity, bone and other tissues were assigned -700 HU, 700 HU and 20 HU, respectively; different tissues and organs were assigned corresponding CT values. The dose distribution of Plan1 was recalculated on three groups of pseudo-CT to obtain Plan2, Plan3 and Plan4, respectively. Finally, the dosimetric difference between Plan1 and other plans (including Plan2, Plan3 and Plan4) were compared. Results: The average CT values of bone and cavity were (735.3±68.0) HU and (-723.9±27.0) HU, respectively. The average CT values of soft tissues was mostly distributed from -70 to 70 HU. The dosimetric differences between Plan2, Plan3, Plan4, and Plan1 decreased in turn. The differences of maximum dose of lens were the biggest, which can reach more than 5.0%, 1.5%-2.0% and 1.0%-1.5%, respectively, and the differences of other dose parameters were basically less than 2.0%, 1.2% and 0.8%, respectively. In the pixelwise dosimetric comparison, the areas with more than 1% difference in the local target cases were mainly distributed in the skin near the field. On the other hand, those in the whole brain target cases were mainly distributed at the bone, cavity, bone and soft tissues junction, and the skin near the field. In addition, the dose calculation error of CT value assignment methods in 3D-CRT plan was slightly larger than that in IMRT plan, and that in whole brain target cases were significantly larger than that in local target cases. Conclusions Different CT value assignment methods have a significant effect on the dose calculation of radiotherapy for brain metastases. When appropriate CT values are given to bone, air cavity and soft tissue, respectively, the deviation of dose calculation can be basically controlled within 1.2%. And by assigning mass CT values to various tissues and organs, the deviation can be further controlled within 0.8%, which can meet the clinical requirements.