Objective To investigate an appropriate megavoltage computed tomography ( MVCT ) protocol to guide helical tomotherapy ( HT) for multiple metastases. Methods According to the location of target volume, 48 patients with multiple metastases undergoing HT were divided into head/chest group ( n=15), head/pelvis group (n=15), and chest/pelvis group (n=18). Each target volume received MVCT scans during the treatment. The obtained MVCT images were registered to CT images and the setup errors were recorded. The CTV?PTV margins were calculated. Comparison was made by paired t test. Results In the head/chest group, there was no significant difference in the setup error in x?axis between the head and chest (-0.15±1?25 vs. -0.21±2?34, P=0?71), while the head had significantly smaller setup errors in y?and z?axis than the chest (0.73±1?22 vs. 1.56±2?54, P=0?00;0.93±1?44 vs. 2.65±1?88, P=0?00). In the head/pelvis group, the head had significantly smaller setup errors in x?, y?, and z?axis than the pelvis (-0.16±1?31 vs. -1.29±3?72, P=0?00;0.81±1?34 vs. 3.20±3?90, P=0?00;1.24±1?75 vs. 5.49±2?80, P=0?00) . In the chest/pelvis group, there were no significant differences in setup errors in x?or y?axis between the chest and pelvis (-0.25± 2?90 vs. -0.22± 3?65, P=0?06;0.35± 3?60 vs. 0.38± 3?78, P=0?87), while the chest had a significantly smaller setup error in z?axis than the pelvis (1.95±2?81 vs. 3.35± 3?05, P=0?00) . In the three groups, the CTV?PTV margins of lower target volume were reduced in three dimensions after the correction of upper target volume, in which y?axis showed the largest reduction of CTV?PTV margins (5?13 vs. 4?01;9?17 vs. 8?30;8?52 vs. 7?13). Conclusions The setup error of individual target volume should not be used for correction of the overall setup error in HT for multiple metastases with isolated target volume. An MVCT protocol that provides image?based guidance for multiple target volumes is recommended.

Objective To discuss the application value of DWI and ADC on predicting therapeutic effect of radiotherapy treatment in NPC. Methods Twenty four local recurrent cases and 38 non-recurrent cases after radiotherapy treatment in NPC were reviewed. MRI and DWI-MRI were performed at pre-radiotherapy and 3, 6, 12 months after treatment, the ADC values of the lesions were analyzed by SPSS 18.0 statistical software. ROC curves based on the ADC values were measured in 3, 6, 12 months after treatment plotted to analyze the threshold ADC value for confirming recurrence. Results The recurrent group and newly diagnosed group showed significantly high signal on DWI, while the non-recurrent group acquired low or mixed signal. The ADC values of the primary tumor in the recurrent group and the non-recurrent group were (0.709 ± 0.078) × 10-3 and (0.693 ± 0.089) × 10-3mm2/s, respectively, t=-0.717,P>0.05, respectively.The ADC values of the primary and recurrent tumor in the recurrent group were (0.730± 0.068) × 10-3mm2/s and (0.709 ± 0.078) × 10-3mm2/s, t=-1.000,P>0.05 , respectively.There were statistical differences between the recurrent group and the non-recurrent group for ADC in 3, 6, 12 months after treatment:(1.128 ± 0.179) × 10-3 and (1.358 ± 0.145) × 10-3mm2/s, t=5.567,P<0.01;(1.164 ± 0.174) and (1.450 ± 0.102) × 10-3mm2/s, t=7.310,P<0.01;(1.107 ± 0.180) × 10-3 and (1.584 ± 0.125) × 10-3mm2/s, t=11.189,P<0.01;respectively. Take 1.29 × 10-3 mm2/s,1.32 × 10-3mm2/s,1.37 × 10-3mm2/s respectively in 3, 6, 12months after treatment as the diagnostic threshold to predict tumor recurrence. The sensitive , specificity, and accuracy were (83.3%, 73.7%, 77.4%), (83.3%, 89.5%, 87.1%), (100.0%, 94.7%, 96.3%).Conclusions Both DWI and ADC value are important for diagnosing and predicting recurrent NPC after radiotherapy treatment, DWI and ADC can be used to regular follow-up after radiotherapy, to further improve the rate of early diagnosis of recurrent NPC.

Objective To verify IMRT plans in point,planar and 3D dose,and to concretely analyze the dose differences of 3D anatomic structure based on Gamma passing rate.Methods Thimble ion-chamber,Matrixx and ArcCheck were separately used to measure six nasopharyngeal carcinoma treatment plans and six lung cancer treatment plans.The dose measurement deviation of the center point was compared as well as the Gamma passing rate of dose verification under the criteria of both 3％/3 mm and 2％/2 mm,the group t-test and one-way ANOVA were also proceeded.3DVH system was used to analyze the dose measurement deviation of target volume (TV) and organ at risk (OAR) through DVH.Results For IMRT and VMAT treatment plans,the mean deviation of point dose was (0.59 ± 1.31) ％ and (-1.00 ± 1.03)％ respectively,and the maximum deviation was less than 3％.Under the criterion of 3％/3 mm,the Gamma passing rate measured by Matrixx,ArcCheck and 3DVH for IMRT plans was 96.28％,97.55％ and 99.02％ respectively,and for VMAT plans,the corresponding results of three different detectors were 97.24％,99.67％ and 98.48％.The results analyzed and compared by 3DVH showed that even under the condition of high Gamma pass rate (more than 95％ for a Gamma criterion of 3％/3 mm),the DVH metrics of both TV and OAR in two cases (account for 16.7％ of the total plan) were significantly different on the clinical parameters,including GTV,spinal cord and brain stem etc.Conclusions The analysis of dose difference of the measurement results based on Gamma pass rate and on anatomic structure of 3D images can more effectively evaluate the influence of dose error to the implementing of clinical plan and the impact to the clinical treatment.

Objective:To analyze the impacts of different registration ranges on the accuracy of multiple metastases treated with helical tomotherapy.Methods:According to the locations of target volumes, 28 patients with multiple metastases were divided into the head/chest group ( n= 15) and the chest/pelvis group ( n= 13). The CT and MVCT images acquired in first fraction were studied and compared in two groups, which were captured and matched with different registration ranges (all targets/the targets in proximity to the head/ the targets in proximity to the foot). The CTV MVCT volume coverage rate (CR) under the matched target volumes, the dice similarity coefficient (DSC) between the CTV CT and CTV MVCT, and the position deviation of the CTV geometric center were compared. Results:We observed similar results in the head/chest group and chest/pelvis group. Specifically, there was no significant difference in the CR, DSC and geometric center deviation between the two target regions when registered with all targets ( P>0.05). Regarding single target region registration, the DSC and geometric center deviation of this target were significantly superior to the other non-registered target ( P< 0.05). To a single target, the CR, DSC, and geometric center deviation obtained with registration presented the best performance, which was significantly greater than these parameters obtained with all targets registration, while the other side target area obtained the worst results ( P< 0.05). Conclusions:Registration of one target region may reduce the accuracy of other non-registered targets. We recommend that the image guidance ranges for multiple metastases treated with tomotherapy should include all target regions or independent registrations for different targets.

Objective To evaluate the effect of helical tomotherapy (HT) megavoltage CT (MVCT) under different acquisition pitch and registration conditions upon the accuracy of radiotherapy for used nasopharyngeal carcinoma,aiming to provide reference for image-guided radiotherapy (IGRT) for nasopharyngeal carcinoma.Methods MVCT scans were performed on an anthropomorphic head& neck phantom which was simulated the positioning errors in the x,y and z direction.The obtained images were registered with the planning CT images.Acquisition pitch was set as the coarse,normal and fine modes.Registration conditions were set as bone registration,bone and soft tissue registration and full-image registration.Registration accuracy was determined by comparing the measured value with the preset value.The accuracy of radiotherapy under different acquisition pitch and registration conditions was statistically compared.Results The 3D errors of bone,bone and soft tissue and full-image registration under different acquisition pitch (coarse,normal and fine) were (1.51±0.47,1.54±0.35,1.81±0.53) mm and (1.41± 0.37,1.53±0.36,1.56±0.39) mm and (1.51±0.27,1.57±0.32,1.73±0.33) mm,respectively.The bone registration yielded the highest accuracy (P＜0.05).When the registration condition was set as bone registration,the accuracy of three acquisition pitch did not significantly differ (all P＞0.05).The fine mode of acquisition pitch possessed the highest stability,whereas required the longest time.Conclusion The acquisition pitch and registration conditions should be selected during HT MVCT based on the clinical requirement of each patient with nasopharyngeal carcinoma.

Objective To comparatively analyze the acute adverse reactions of helical tomotherapy ( HT) and intensity-modulated radiation therapy ( IMRT) for nasopharyngeal carcinoma ( NPC) . Methods A total of 100 NPC patients treated with radiotherapy were selected and divided into the HT group ( n=50) and IMRT group ( n=50) . All patients were treated with concurrent chemoradiotherapy. The prescription dose of radiotherapy was DT 68.2-73.8 Gy/30-34F. The severity of acute adverse reactions of skin, oral mucosa, salivary glands and esophagus was evaluated with the established RTOG criteria. The differences between two groups were evaluated by paired t-test. Results The dose of organs at risk ( OARs) in the HT group was significantly lower than that in the IMRT group ( P<0.05) , whereas the dose of target area of PTVnx, PTVnd ( left) and PTVnd ( right) did not significantly differ between two groups ( all P>0.05) . In the HT group, the incidence rate of grade 0-3 acute adverse reactions in the skin, oral mucosa, salivary glands and esophagus were ( 14%, 68%, 18%, 0%) , ( 10%, 54%, 36%, 0%) , ( 0%, 74%, 26%, 0%) and ( 10%, 60%, 28%, 2%) , respectively. In the IMRT group, the corresponding results were ( 0%, 52%, 48%, 0%) , ( 0%, 58%, 42%, 0%) , ( 0%, 28%, 72%, 0%) and ( 0, 40%, 60%, 0%) , respectively. The severity of acute adverse reactions of skin, salivary glands and esophagus in the HT group was slighter than those in the IMRT group ( all P<0.05) , the acute adverse reactions in the oral mucosa were similar between two groups ( P>0.05) . In the HT group, the onset time of acute adverse reactions in the skin was later than that in the IMRT group ( P<0.05) , and the onset time of other adverse reactions was similar between two groups ( all P>0.05) . Conclusions Both HT and IMRT can meet the requirements of the dose distribution in the target area for NPC, whereas HT is superior to IMRT in terms of the protection of OARs protection, the severity and onset time of acute adverse reactions.

Objective:To study the change pattern of neck diameter and relevant factors in nasopharyngeal carcinoma (NPC) patients treated with helical tomotherapy, aiming to provide reference for clinical practice.Methods:Fifteen NPC patients treated with helical tomotherapy at Sun Yat-Sen University Cancer Center from November 2020 to February 2021 were enrolled in this study. The transverse diameters of NPC patients' neck contours and body weight of all patients during radiotherapy were recorded weekly. We used descriptive statistics to explore the distribution of transverse diameters of NPC patients' neck contours during radiotherapy. And Spearman correlation analysis was used to assess the association between weight loss and changes in neck contour transverse diameter.Results:During radiotherapy, the distribution of transverse diameters of NPC patients' neck contours was completely different from the initial values. Specifically, the transverse diameters were significantly reduced at the 4th week of the radiotherapy. Moreover, the reduction of transverse diameter of neck contour was highly correlated with the weight loss ( r=0.803, P<0.05), and moderately correlated with gender ( r=0.523, P<0.05). However, there was no statistical correlation between the alteration of neck diameter and age, TNM stage, and the mean dose of GTV nd-L, GTV nd-R, PTV nd-L and PTV nd-R (all P>0.05). Conclusions:The neck contours of NPC patients are altered regularly during helical tomotherapy, which are narrowed the most obviously in the 4th week. Extensive attention should be paid to the changes of neck contour during radiotherapy in clinical practice.

Objective:To analyze the related factors affecting the dose to the small intestine exposure to preoperative radiotherapy for rectal cancer, aiming to provide reference for alleviating the adverse reactions of radiotherapy for rectal cancer.Methods:Medical record data and radiotherapy plan information of 138 rectal cancer patients who received intensity-modulated arc radiotherapy at Sun Yat-sen University Cancer Center from May 2021 to February 2023 were retrospectively analyzed. Tumor staging, tumor location, gender, age, planned bladder volume, body mass index (BMI), and small intestine irradiation dose volume were subject to Spearman correlation analysis. Further grouping and comparison were conducted based on the correlation results. Independent sample non parametric tests were used for inter group comparison.Results:The main factors related to the small intestine irradiation dose volume were tumor location, gender, planned bladder volume, and BMI. Tumor location was weakly correlated with the small intestine V 5 Gy-V 45 Gy. Gender was weakly correlated with the small intestine V 30 Gy-V 45 Gy. Planned bladder volume was weakly negatively correlated with the small intestine V 20 Gy-V 45 Gy. BMI was weakly negatively correlated with the small intestine V 10 Gy-V 45 Gy. Grouping comparison analysis showed that the small intestine V 5 Gy-V 45 Gy of rectal cancer patients in the low position group was significantly smaller than those in the middle and high position groups (both P<0.05), and there was no significant difference between the middle and high position groups ( P>0.05). Female rectal cancer patients had higher V 30 Gy-V 45 Gy levels than male counterparts ( P<0.05). The small intestine V 20 Gy and V 25 Gy levels in the planned bladder volume <200 ml group were significantly higher than those in the 200-400 ml and >400 ml groups (all P<0.05), whereas there was no difference between the 200-400 ml and >400 ml groups ( P>0.05). The small intestine V 30 Gy-V 45 Gy levels in the 200-400 ml group were significantly lower than those in the <200 ml group, but higher than those in the >400 ml group, and the differences were statistically significant (all P<0.05). Regarding BMI comparison among groups, the small intestine V 15 Gy-V 45 Gy in the low body weight group was significantly higher than those in the other three groups (all P<0.05). There were no significant differences among the normal, overweight, and obese groups (all P>0.05). Conclusion:In preoperative radiotherapy for rectal cancer, more attention should be paid to the dose to the small intestine in patients with middle and high position rectal cancer, female patients, and patients with low body weight.