Set-up errors of the neck are underestimated using the overall registration frame of head and neck in IMRT for NPC.

BACKGROUND: There is no standardized registration frame of cone beam CT (CBCT) in intensity modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC). The overall registration frame that covers the whole head and neck is the most commonly used CBCT registration frame for NPC patients in IMRT. OBJECTIVE: To compare the set-up errors using different registration frames of CBCT for NPC to assess the set-up errors for different region of the commonly used clinical overall registration frame. METHODS: 294 CBCT images of 59 NPC patients were collected. Four registration frames were used for matching. The set-up errors were obtained using an automatic matching algorithm and then compared. The expansion margin from the clinical target volume (CTV) to the planned target volume (PTV) in the four groups was also calculated. RESULTS: The average range of the isocenter translation and rotation errors of four registration frames are 0.89∼2.41 mm and 0.49∼1.53°, respectively, which results in a significant difference in the set-up errors (p < 0.05). The set-up errors obtained from the overall frame are smaller than those obtained from the head, upper neck, and lower neck frames. The margin ranges of the overall, head, upper neck, and lower neck frames in three translation directions are 1.49∼2.39 mm, 1.92∼2.45 mm, 1.86∼3.54 mm and 3.02∼4.78 mm, respectively. The expansion margins calculated from the overall frame are not enough, especially for the lower neck. CONCLUSION: Set-up errors of the neck are underestimated by the overall registration frame. Thus, it is important to improve the position immobilization of the neck, especially the lower neck. The margin of the target volume of the head and neck region should be expanded separately if circumstances permit.

Calculation of set-up margin in frameless stereotactic radiotherapy accounting for translational and rotational patient positing error.

Context: Rotation corrected set-up margins in stereotactic radiotherapy (SRT). Aims: This study aimed to calculate the rotational positional error corrected set-up margin in frameless SRT. Settings and Design: 6D setup errors for the steriotactic radiotherapy patients were converted to 3D translational only error mathematically. Setup margins were calculated with and without considering the rotational error and compared. Materials and Methods: A total of 79 patients of SRT each received >1 fraction (3-6 fractions) incorporated in this study. Two cone-beam computed tomography (CBCT) scans were acquired for each session of treatment, before and after the robotic couch-aided patient position correction using a CBCT. The postpositional correction set-up margin was calculated using the van Herk formula. Further, a planning target volume_R (PTV_R) (with rotational correction) and PTV_NR (without rotational correction) were calculated by applying the rotation corrected and uncorrected set-up margins on the gross tumor volumes (GTVs). Statistical Analysis Used: General. Results: A total of 380 sessions of pre- (190) and post (190) table positional correction CBCT was analyzed. Posttable position correction mean positional error for lateral, longitudinal, and vertical translational and rotational shifts was (x)-0.01 ± 0.05 cm, (y)-0.02 ± 0.05 cm, (z) 0.00 ± 0.05 cm, and (θ) 0.04° ± 0.3°, (Φ) 0.1° ± 0.4°, (Ψ) 0.0° ± 0.4°, respectively. The GTV volumes show a range of 0.13 cc-39.56 cc, with a mean volume of 6.35 ± 8.65 cc. Rotational correction incorporated postpositional correction set-up margin the in lateral (x), longitudinal (y) and vertical (z) directions were 0.05 cm, 0.12 cm, and 0.1 cm, respectively. PTV_R ranges from 0.27 cc to 44.7 cc, with a mean volume of 7.7 ± 9.8 cc. PTV_NR ranges from 0.32 cc to 46.0 cc, with a mean volume of 8.1 ± 10.1 cc. Conclusions: The postcorrection linear set-up margin matches well with the conventional set-up margin of 1 mm. Beyond a GTV radius of 2 cm, the difference between PTV_NR and PTV_R is ≤2.5%, hence not significant.

Application of Linear Accelerator on Boarding Kilovolt Fan Beam CT and Megavolt Cone Beam CT System on Set-up Errors During Radiation Treatment / 肿瘤防治研究

Objective To quantify the setup errors for the different anatomical sites of patients who received intensity-modulated radiotherapy (IMRT) with linear accelerator on-board kilovolt fan beam CT(kV-FBCT) as non-isocenter IGRT and megavolt cone beam CT (MV-CBCT) as isocenter IGRT. Methods A retrospective analysis was performedon 70 patients who underwent radiotherapy, kV-FBCT, and/or MV-CBCT scans after each routine setup prior to IMRT. The average displacement (M), systematic error (Σ), and random error (б) at different treatment sites in the left-right, anterior-posterior, and cranial-caudal directions were calculated according to the individual displacements. The formula 2.5Σ+0.7б was used to estimate the PTV margin in respective direction. For each single patient, the root mean square in three directions was used as 3D displacement. Results A total of 1130 displacements were recorded in the 70 patients. The PTV margin was estimated to be 1.9-3.1 mm in head and neck cancer, 2.8-5.1 mm in thoracic cancer, 4.6-5.1 mm in breast cancer, 3.0-5.5 mm in upper abdominal cancer, and 3.5-6.8 mm in pelvic tumor. For the 3D mean displacements, the head and neck, thoracic, breast, upper abdominal, and pelvic cancer were 2.4±1.0, 4.0±1.6, 4.1±2.0, 4.6±2.1, and 4.6±2.1 mm, respectively. The average 3D displacement obtained by kV-FBCT and MV-CBCT were 4.1 and 3.4 mm, respectively (P=0.212). Conclusion The quantitative setup-error data can be obtained using linear accelerator on-board FBCT, and the non-isocenter IGRT induced set-up error cannot be negligible.

Dosimetric effect of set-up error in accelerator-based boron neutron capture therapy for head and neck cancer.

The dosimetric effect of set-up error in boron neutron capture therapy (BNCT) for head and neck cancer remains unclear. In this study, we analyzed the tendency of dose error by treatment location when simulating the set-up error of patients. We also determined the tolerance level of the set-up error in BNCT for head and neck cancer. As a method, the distal direction was shifted with an interval of 2.5 mm, from 0.0 mm to +20.0 mm and compared with the dose at the reference position. Similarly, the horizontal direction and vertical direction were shifted, with an interval of 5.0 mm, from -20.0 mm to +20.0 mm. In addition, cases with 3.0 mm and 5.0 mm simultaneous shifts in all directions were analyzed as the worst-case scenario. The dose metrics of the minimum dose of the tumor and the maximum dose of the mucosa were evaluated. From unidirectional set-up error analysis, in most cases, the set-up errors with dose errors within ±5% were Δdistal < +2.5 mm, Δhorizontal < ±5.0 mm and Δvertical < ±5.0 mm. In the simulation of 3.0 mm shifts in all directions, the errors in the minimum tumor dose and maximum mucosal dose were -3.6% ±1.4% (range, -5.4% to -0.6%) and 2% ±1.4% (range, 0.4% to 4.5%), respectively. From these results, if the set-up error was within ±3.0 mm in each direction, the dose errors of the tumor and mucosa could be suppressed within approximately ±5%, which is suggested as a tolerance level.

Exploration of combined application of three Varian OBI image-guided systems in image-guided radiotherapy for nasopharyngeal cancer / 中华放射肿瘤学杂志

Objective:To compare the comprehensive performance of three Varian on-board image (OBI) image systems (KV-CBCT, KV-planar and MV-EPID) and to explore the value of the combined application of these three systems in daily image-guided radiotherapy for nasopharyngeal cancer.Methods:KV-CBCT, KV-planar and MV-EPID scanning and registration were carried out in the left and right/abdominal and back/head and foot direction on human head and neck phantom. The set-up error, registration time, additional radiation dose and image quality of the three systems were compared by F-test.Results:KV-CBCT, kV-planar and MV-EPID were scanned for 55 times, respectively, and the set-up errors in the left and right/abdominal and back/head and foot direction of the three image-guided systems were (0.00±5.43)/(-0.02±5.49)/(0.02±5.58) mm, (0.04±5.49)/(0.02±5.56)/(0.02±5.54) mm, (0.02±5.22)/(0.11±5.34)/(-0.04±5.33) mm, respectively ( P=0.999, 1.000, 0.989). The average time consuming was (200±45) s, (120±36) s and (115±42) s; the additional radiation dose from low to high was kV-planar, KV-CBCT and MV-EPID; the image quality from low to high was MV-EPID, kV-planar and KV-CBCT. Conclusions:Three image-guided systems can meet the requirements of image-guided radiotherapy for nasopharyngeal cancer. Based on the overall performance of the three systems, 1 CBCT+ 4 kV planar per week is recommended and EPID should be used as a backup system in daily image-guided radiotherapy for nasopharyngeal cancer. This scheme makes full use of the high image quality of CBCT and the low radiation of kV planar to realize the regular detection of nasopharyngeal cancer volume change and the implementation of high-precision radiotherapy.

Breast bracket combined with polyurethane foam improves the accuracy of immobilization in breast cancer radiotherapy / 中华放射肿瘤学杂志

Objective:To compare the difference between breast bracket combined with polyurethane foam and single polyurethane foam in the accuracy of immobilization, providing a better immobilization for breast cancer radiotherapy.Methods:Fifty breast cancer patients who received radiotherapy in Sun Yat-sen University Cancer Center from March 2021 to July 2021 were selected. Among them, 25 patients were immobilized with polyurethane foam (foam group), and the other 25 patients were immobilized with polyurethane foam combined with breast bracket (combination group). All patients were scanned by CBCT once a week to obtain setup errors in the SI, LR and AP directions for t-test. The formula M PTV=2.5 Σ+0.7 σ was used to calculate the margin of the planning target volume(M PTV). Results:The setup errors in the foam group were SI (2.0±3.26) mm, LR (0.88±2.76) mm, AP (1.22±3.55) mm, Rtn -0.24°±0.85°, Pitch 0.16°±1.11°, Roll -0.32°±1.05°, and the M PTV were 6.75 mm, 8.46 mm and 8.73 mm, respectively. The setup errors in the combination group were SI (1.0±3.01) mm, LR (0.62±2.74) mm, AP (1.82±3.21) mm, Rtn 0.64°±0.59°, Pitch 0.71°±1.22°, Roll 0.29°±0.73°, and the M PTV were 6.35 mm, 7.47 mm, and 7.61 mm, respectively. After comparing the setup errors in the three-dimensional directions between two groups, the t value of LR, SI, AP and Rtn, Pitch, Roll was -4.304, -2.681, 1.384, and -9.457, -3.683, -5.323, respectively. And the differences in the LR, SI, Rtn, Pitch and Roll directions were statistically significant (all P<0.05). Conclusions:The immobilization effect of polyurethane foam combined with breast bracket is better and the M PTV is also smaller than those of polyurethane foam alone. Therefore, it is recommended to use polyurethane foam combined with breast bracket for immobilization in breast cancer radiotherapy.

Effect of inter-fractional positional uncertainty on cumulative dose of target volume in intensity-modulated radiotherapy of cervical cancer / 中华放射肿瘤学杂志

Objective:To obtain the inter-fractional set-up errors of intensity-modulated radiotherapy (IMRT) of cervical cancer by cone-beam CT (CBCT), and to analyze the variations of the set-up errors on the cumulative dose deviation of the target volume.Methods:A total of 48 patients with cervical cancer who underwent IMRT were enrolled in this study, and the set-up errors of 696 CBCTs were obtained. The set-up errors were input into the treatment planning system, and the cumulative set-up error dose was obtained by superposing the set-up errors dose. The deviation percentage was calculated by the deviation formula and the standard planning dose.Results:The set-up errors caused the offset of isocenter distance by 0.58(0.36, 0.80) cm. Different statistical differences were noted between the cumulative set-up error dose and the standard planning dose by WilCoxon test. All the dose deviations in the target volume were reduced, and the differential dose volume histogram (DVH) appeared negatively skewed, and the peak value was declined. The DVH diagram shifted to the left with an inverse S-curve and the slope was increased. The HI deviation of the target volume from small to large were: CTV 1, CTV 2, GTV/CTV, CTV 3, CTV n, CTV all, and GTV nd; The HI deviation of the target volume were increased. Conclusions:The effect of set-up errors in IMRT of cervical cancer upon the cumulative doses of the target volume significantly differs. The cumulative dose of the target volume is reduced, and the uniformity of the target volume dose becomes worse. The uncertainty of the inter-fractional position leads to an increase or decrease in the the fractional doses of the target volume. The biological effect on tumor cells and the tumor recurrence remains to be investigated. In IMRT of cervical cancer, the CBCT position calibration is required before each treatment to ensure the dose accuracy of each structure in the target volume.

Dosimetric effects study of set-up error in postoperative intensity modulated radiotherapy of rectal cancer / 中国辐射卫生

Objective To measure set-up errors in intensity modulated radiotherapy of postoperative rectal cancer (IMRTPRC), and analyze the effects of target volumes and normal tissues by set-up errors in IMRTPRC. Methods electrical field device was used to measure the set-up errors of 30 patients in IMRTPRC; we randomly selected 6 patients, and simulated their radiotherapy set-up errors in TPS. Then were counted the dose distribution and analyze relative dosimetrical parameters of target volumes, normal tissues and got the set-up errors effecting on dosimetry. Statistical analysis was performed using an SPSS statistical package(Version 19.0). Results The set-up errors on X, Y and Z direction are (−0.82 ± 2.67) mm, (0.42 ± 2.91) mm and (0.47 ± 1.64) mm respectively. In regard to set-up errors of L5, R7, G8, T5, B6 and A4, most of statistical properties of PTV’s D98%, D95%, D50%, D2%, Hi and Ci are smaller than 0.05, so the differences have statistical values; In L5-Hi, G8-D2%, T5-D50% and B6-D2%, so these differences have not statistical value (P>0.05). In L5, R7, G8, T5, B6 and A4, about half of the statistical properties of normal tissue like bowl, bladder and femur heads, are smaller than 0.05 and have statistical value, and the rest of them are negative. Conclusion The dose of PTV is decreased due toset-up error. Uniformity and conformity is also gone bad. So the dosimetry quantity of PTV can not get reach to the initial design level. However, the dose of normal tissues like bowl, bladder and femur heads, are increased unexpectedly.

IMPACT OF THREE DIFFERENT MATCHING METHODS ON PATIENT SET-UP ERROR IN X-RAY VOLUMETRIC IMAGING FOR HEAD AND NECK CANCER.

Impact of three different matching methods for delivery of Volumetric Modulated Arc Therapy (VMAT) in Cone-beam computed tomography (CBCT) on patient set-up error. As per institutional imaging protocol, 300 CBCT scans of 20 VMAT head and neck cancer patients treated with 60 Gy/30 fractions were chosen for the present study. Approved CT images of the plan were registered as a reference with the CBCT images on board. Grey-scale matching (GM), manual matching (MM), and bone matching (BM) between on-board CBCT and reference CT images were used to assess patient translation errors. Patient positioning verification was evaluated using the Clip-box registration in all three matching methods. Using the GM approach as a reference point, two additional matchings were rendered in offline mode using BM and MM. For analysis, random error (σ), systematic error (∑), maximum error (E) mean set-up error (M), mean displacement vector (R), matching time (Mt), and multiple comparisons using Post hoc Tukey's HSD test were performed. In MM, less random and systematic errors were found than in GM and BM with an insignificant difference (p > 0.05) Compared to BM and GM, the maximum error, mean set-up error, and displacement vector were marginally less in MM (p > 0.05). In MM, an increased Mt relative to BM and GM was observed (p > 0.05). Furthermore, an insignificant difference in set-up error was revealed in a multiple comparison test (p > 0.05). Any of the three matching methods can be used during CBCT to check patient translation errors for the delivery of the VMAT head and neck patients.

The effect of age on skin elasticity and setup error in optical surface image-guided radiotherapy / 中华放射肿瘤学杂志

Objective@#To investigate the correlation between skin elasticity and setup error in optical surface image-guided radiotherapy.@*Methods@#The skin elasticity (R7) data of the head, chest and abdomen were extracted and analyzed its correlation with age by systematic literature review. Fifty-four patients diagnosed with nasopharyngeal carcinoma, breast cancer and cervical cancer were recruited in this study. Firstly, the patients were positioned based on the room laser and markers. Subsequently, the patient position was verified by the Varian On-Board Imager, and then C-Rad Catalyst was adopted to obtain surface images in two states (mask or non-mask) as reference images. In the subsequent fraction treatment, after initial positioning, the local calibration was performed by Catalyst, and setup errors in three directions were recorded. Meanwhile, the patient setup was verified by CBCT twice a week. The Pearson correlation analysis was performed to analyze the correlation between setup error and age.@*Results@#The skin elasticity was negatively correlated with aging (P<0.01). The correlation coefficient between random error and age in head-and-neck cancer were 0.645, 0.624 and 0.866 in the AP, SI and LR directions (all P<0.05) for male patients without mask, respectively. The system error was significantly correlated with age in the LR direction (P<0.05) for male patients, and in the AP direction (P<0.05) for female patients with head-and-neck cancer without mask. The setup error had a significant correlation with skin elasticity in male patients with head-and-neck cancer, and the sequence of absolute value of correlation coefficient was LR>SI>AP.@*Conclusion@#In optical surface-guided radiotherapy of head and neck cancer, skin elasticity may be a significant index for assessing the setup errors in male patients.

The effect of age on skin elasticity and setup error in optical surface image-guided radiotherapy / 中华放射肿瘤学杂志

Objective To investigate the correlation between skin elasticity and setup error in optical surface image-guided radiotherapy.Methods The skin elasticity (R7) data of the head,chest and abdomen were extracted and analyzed its correlation with age by systematic literature review.Fifty-four patients diagnosed with nasopharyngeal carcinoma,breast cancer and cervical cancer were recruited in this study.Firstly,the patients were positioned based on the room laser and markers.Subsequently,the patient position was verified by the Varian On-Board Imager,and then C-Rad Catalyst was adopted to obtain surface images in two states (mask or non-mask) as reference images.In the subsequent fraction treatment,after initial positioning,the local calibration was performed by Catalyst,and setup errors in three directions were recorded.Meanwhile,the patient setup was verified by CBCT twice a week.The Pearson correlation analysis was performed to analyze the correlation between setup error and age.Results The skin elasticity was negatively correlated with aging (P＜0.01).The correlation coefficient between random error and age in headand-neck cancer were 0.645,0.624 and 0.866 in the AP,SI and LR directions (all P＜0.05) for male patients without mask,respectively.The system error was significantly correlated with age in the LR direction (P＜0.05) for male patients,and in the AP direction (P＜ 0.05) for female patients with head-and-neck cancer without mask.The setup error had a significant correlation with skin elasticity in male patients with head-and-neck cancer,and the sequence of absolute value of correlation coefficient was LR ＞ SI ＞ AP.Conclusion In optical surface-guided radiotherapy of head and neck cancer,skin elasticity may be a significant index for assessing the setup errors in male patients.

Appropriate treatment planning method for field joint dose in total body irradiation using helical tomotherapy.

Total body irradiation (TBI) using helical tomotherapy (HT) has advantages over the standard linear accelerator-based approach to the conditioning regimen for hematopoietic cell transplantation. However, the radiation field has to be divided into two independent irradiation plans to deliver a homogeneous dose to the whole body. A clinical target volume near the skin increases the skin surface dose; therefore, high- or low-dose regions arise depending on the set-up position accuracy because the two radiation fields are somewhat overlapped or separated. We aimed to determine an adequate treatment planning method robust to the set-up accuracy for the field joint dose distribution using HT-TBI. We calculated treatment plans reducing target volumes at the interface between the upper and lower body irradiations and evaluated these joint dose distributions via simulation and experimental studies. Target volumes used for the optimization calculation were reduced by 0, 0.5, 1.0, 2.0, 2.5, and 3.0 cm from the boundary surface on the upper and lower sides. Combined dose distributions with set-up error simulated by modifying coordinate positions were investigated to find the optimal planning method. In the ideal set-up position, the target volume without a gap area caused field junctional doses of up to approximately 200%; therefore, target volumes reduced by 2.0-3.0 cm could suppress the maximum dose to within 150%. However, with set-up error, high-dose areas exceeding 150% and low-dose areas below 100% were found with 2.0 and 3.0 cm target volume reduction. Using the dynamic jaw (DJ) system, dose deviations caused by set-up error reached approximately 20%, which is not suitable for HT-TBI. Moreover, these dose distributions can be easily adjusted when combined with the intensity modulation technique for field boundary regions. The results of a simulation and experimental study using a film dosimetry were almost identical, which indicated that reducing the target volume at the field boundary surface by 2.5 cm produces the most appropriate target definition.

Dosimetric effect of set-up errors on nasal NK/T cell lymphoma based on dose reconstruction / 中华放射肿瘤学杂志

Objective@#To evaluate the dosimetric effects of set-up errors on nasal NK/T cell lymphoma by introducing set-up errors into the radiotherapy planning system for dose reconstruction.@*Methods@#Ten patients with nasal NK/T cell lymphoma were recruited. A non-coplanar volumetric modulated arc therapy plan was designed for CT image and clinical target area of each patient. After the completion of the plan, the set-up errors were introduced into the radiotherapy plan by changing the ISO of the treatment, and dose calculation was performed to reconstruct the dose distribution.@*Results@#With the increase of system set-up errors, the dose of target was decreased and the order affected by set-up errors in different directions was: left-right direction> head-foot direction> front-rear direction. When the translational set-up errors in each direction were -3 mm to 3 mm and the rotating set-up errors were -3° to 3°, the range of dose change in all targets was less than ±3%. When the set-up errors in all directions were ≤ 3 mm, the dose of organ at risk was less than or similar to the prescribed dose. When the set-up errors were> 3 mm, the doses of lens, spinal cord, parotid gland and optic nerve gradually exceeded the prescribed dose. Only when the rotating set-up errors were ≥ 3°, the dose of lens exceeded the prescribed dose. Special attention should be paid to the influence of the greater set-up errors in the left and right direction on lens, spinal cord and parotid gland, as well as on the spinal cord due to the larger set-up errors in the front and rear direction. After the actual set-up errors were introduced from our department, it exerted slight effect on the irradiation dose of GTV and CTV, which was less than ±2%. In a few cases, the dose of organ at risk potentially exceeded the prescribed dose limit, and special attention should be diverted to overdose of the lens and optic nerve.@*Conclusions@#The set-up errors will result in target dose deficiency and overdose of organ at risk in nasal NK/T cell lymphoma, especially upon the set-up errors in the left and right direction. The effect of 3 mm and 3° set-up errors on target and organ at risk is limited. Therefore, it is recommended to maintain the single direction set-up errors within 3 mm and 3°. The actual set-up errors introduced from our department exert little effect on the target dose, but a small number of organs are at risk of exceeding the prescribed dose limit. It is necessary to increase the evaluation of the extension region of organ at risk.

Factors associated with set-up errors in intensity-modulated radiotherapy after breast conserving surgery / 中华放射医学与防护杂志

Objective To evaluate the difference of set-up errors between thermoplastic mask and breast bracket in patients receiving intensity-modulated radiotherapy after breast conserving surgery,and the impact of clinical factors associated with set-up errors.Methods A total of 34 patients treated with intensity-modulated radiotherapy after breast conserving surgery from January 2016 to June 2018 were reviewed.Eighteen patients were fixed with thermoplastic mask,and sixteen were with breast bracket.Weekly CBCT scan records were used to analyze set-up errors,and group systematic and random errors were computed.The influence of clinical factors on set-up errors was also analyzed.Results The immobilization technique with thermoplastic mask showed great superior in comparison with breast bracket;however,only in the Ty(translation) and Ry(rotation),the differences had significance.Based on group systematic and random errors,PTV margins in Tx,Ty and Tzwere 2.65,4.36 and 2.87 mm in thermoplastic mask group,as well as 5.71,6.07 and 4.20 mm in breast bracket group,respectively.Multi-factor regression analysis showed that BMI was independent factors affecting set-up errors.Conclusions Compared with breast bracket,the immobilization technique with thermoplastic mask has the potential of reducing set-up errors and PTV margins in patients receiving intensity-modulated radiotherapy after breast conserving surgery,especially in patients with high BMI.

Comparison of imbolization accuracy between styrofoam and breast carrier in intensity-modulated radiotherapy after breast conservative surgery for breast cancer patients / 中华放射肿瘤学杂志

Objective To investigate the difference of styrofoam and breast carrier in postposition fixation of intensity-modulated radiotherapy after breast conservative surgery for breast cancer patients.Methods From February 2018 to August 2018,tweenty-four patients with breast cancer in Sun Yet-Sen Memorial Hospital of Sun Yet-sen University were selected for this study,who underwent hypofactionationed radiotherapy after breast conservative surgery with total dose 42.56 Gy/16Fractions.They were randomized into styrofoam test group and breastcarrier control group.Cone beam CT as used to record the positioning error under the directions of left and right (x),head and foot (y),abdomen and back (y) within two groups at the first,third,fifth,seventh,eleventh time before irradiation.Furthermore,the PTV extension margin was calculated and the positioning time of two groups was recorded.Two sets of pendulum errors were analyzed by independent sample T-test,and the outspread value of inter-fractional set up error of the PTV was calculated.Results The errors of the test group and the control group in the direction of x,y,z were as follows:(2.36±1.89) and (2.56±2.05) mm (P=0.49),(1.76± 1.78) and (3.28±2.79) mm (P＜0.05),(1.47± 1.49) and (1.73± 1.81) mm (P=0.28).The extension values of inter-fractional set up error of CTV to PTV were 2.97,2.92,2.21 mm and 3.41,4.09,2.59 mm respectively.The time of single positioning was (3.4± 1.1) and (5.5 ± 3.1) min respectively (P=0.01).Conclusion Styrofoam has better positioning accuracy and efficiency compared with breast carrier.

Study of significance of head fixation in the chest wall field combined with supraclavicular field radiotherapy for breast cancer / 中华放射肿瘤学杂志

Objective To explore the importance of head fixation in chest wall field combined with supraclavicular field radiotherapy for breast cancer by comparing the displacement error and dosimetric differences caused by multi-functional body board and breast bracket.Methods Thirty patients with breast cancer were randomly divided into groups A and B.In group A,patients were fixed with multi-functional body board and head thermoplastic film.In group B,patients were fixed with traditional breast brackets.Each patient received CBCT scan before and after radiotherapy.Both setup errors and intra-fractional displacements in the x-,y-and z-axis,V100 and V95 were calculated.Statistical analyses were performed using the independent sample t-test.Results The displacement errors in groups A and B before and after radiotherapy were (1.24± 0.42),(1.71± 0.61) and (2.25± 1.04) mm vs.(3.67± 2.05),(3.78± 1.74),(4.65±2.66) mm in the x-,y-and z-axis,respectively (P=0.033,0.027,0.020).The intra-fractional displacements in groups A and B were (1.10±0.66),(1.13±0.59),(1.11 ±0.62) mm vs.(2.48±0.88),(2.21 ±0.98),(3.53±2.01) mm in the x-,y-and z-axis,respectively (P=0.030,0.021,0.013).The V100 in groups A and B were (94.27± 3.20) ％ and (99.08± 0.60) ％ (P =0.065),and (89.48± 4.70) ％ and (96.53± 2.50) ％ for V95 (P =0.002),respectively.Conclusion The risk of displacement error is significantly reduced using multi-functional body board,which enhances the accuracy of radiation dose in chest wall and supraclavicular fields of breast cancer patients.

Analysis of influencing factors of intrafractional positioning errors in the hypofractionated radiotherapy for pulmonary tumors / 中华放射肿瘤学杂志

Objective Image-guided radiation therapy(IGRT)was performed to investigate the intrafractional body motion and identify the relevant influencing factors during hypofractionated radiotherapy for malignant pulmonary tumors. Methods A total of ninety-six patients with malignant pulmonary tumors receiving hypofractionated radiotherapy in Jiangsu Cancer Hospital were enrolled in this clinical trial. The kilo-voltage cone beam CT(kV-CBCT)was acquired prior to each fraction and matched to the planning CT images to correct the set-up errors. CBCT was performed immediately after the end of treatment to evaluate the intrafractional variation in the mediolateral,anteroposterior and craniocaudal dimensions.The relationship between relevant influencing factors and intrafractional variation was analyzed using multivariate linear regression. Results In the anteroposterior and craniocaudal directions,the intrafractional positioning errors were reduced along with the increase of ordinal number of fraction(P= 0.000). In the mediolateral direction, the intrafractional positioning errors were increased along with the longer duration of hypofractionated radiotherapy(P=0.010).The intrafractional positioning errors were decreased over larger body weight(P=0.003).The intrafractional positioning errors were significantly increased when vacuum bag and thermoplastic film were utilized for fixation(P= 0.009). Conclusions Certain intrafractional positioning errors occur during hypofractionated radiotherapy. Relevant influencing factors differ in different directions. Relevant influencing factors should be modified to reduce intrafractional positioning variation and improve the treatment accuracy.

Application of combined body position fixation in radiation therapy of lung cancer / 中华放射医学与防护杂志

Objective To explore the CTV to PTV external expansion boundary and the effect of the dose of normal lung tissue under different fixed modes by a comparative analysis of combined body position and thermoplastic film fixed set-up error of radiation therapy for lung cancer. Methods From October 2016 to March 2018, the patients who received chest radiology at the Tangshan people's hospital were enrolled as subjects retrospectively divided into two groups, including 50 patients with lung cancer radiotherapy with combined body position fixation, and 40 patients with lung cancer with thermoplastic film fixation. The two groups of patients drew the target areas in accordance with the unified standard, and the set-up error of left and right, up and down, front and rear ( x, y, z axis) were recorded respectively after 1 time/week cone CT( CBCT) matched with the planned CT image and analyzed by t test. According to the MPTV =2. 5Σ+0. 7δ, CTV to PTV external expansion boundary in the combined body position group were calculated. And the V5、V20 and V30 of two groups of patients were calculated and analyzed by TPS system. Results The set-up error of the combined body position group and thermoplastic film group were respectively (1. 00 ± 0. 58) mm and (3. 28 ± 0. 43) mm on the x axis, (1. 42 ± 0. 28) mm on the y axis and (4. 03 ± 0. 41) mm, (1. 06 ± 0. 44) mm and (3. 18 ± 0. 34) mm on the z axis. The set-up errors of the two groups were statistically significant on x, y and z axis( t= -20. 740, -35. 596, -25. 015,P<0. 05). There was no significant difference in set-up errors between the central and peripheral lung cancer patients and between left and right lung cancer patients(P>0. 05). Through the MPTV =2. 5Σ+0. 7δ, CTV to PTV external expansion boundary in the combined body position fixation group was 2. 906 , 3. 746 and 2. 958 mm on x, y and z axis respectively. The comparison between group A and B showed that the mean values of V5 , V20 and V30 in group B were reduced by 1. 5％, 3. 1％ and 4. 8％ respectively compared with group A. Conclusions The combined body position technique can improve the accuracy of lung cancer patients after radiation therapy,and further reduce the boundary of CTV to PTV, which is of certain value to reduce the occurrence of radiation pneumonitis.

Tolerance range of breast cancer patients with set?up errors after volume modulated radiotherapy / 中华放射医学与防护杂志

Objective To predict the tolerance range of set-up errors in clinical practice by predicting the virtual set-up errors of postoperative radiotherapy patients for breast cancer. Methods A retrospective analysis was made of the patients who underwent radiotherapy after breast cancer surgery in recent 3 years. According to different treatment method, 10 cases of breast cancer after modified radical mastectomy and 10 cases after breast conserving radical mastectomy were selected. The target area was delineated, the volume modulated radiation therapy plan was made, the virtual moving error of the center point of the plan was moved, and the maximum moving error was 5 mm by 1 mm step. After recalculating the dose, the corresponding data including the clinical target areas ( CT ) , CTV ( V50 ) , average heart volume, V20 of the affected lung and CTV volume were recorded. SPSS 19. 0 software was used for statistical analysis, and repeated measurement of variance analysis was used to analyze the changes of the actual dose in the target area after moving the center point. Linear regression analysis method was used to analyze the correlation between the CTV volume and the dose change after the CTV moving midline. Results The virtual set-up error had little influence on the axis direction of the approximate mammary tangent direction, while the vertical direction of the approximate mammary tangent direction had greater influence. After moving more than 3 mm on the vertical axis, the CTV ( V50 ) decreased to below 90％, which was lower than the general requirement for the target area of CTV. Statistical analysis of set-up errors in all directions showed that there was significant difference in dosimetric changes ( F=34. 182, 12. 877, 16. 443, 9. 846, 46. 829, 10. 122, 57. 931, P <0. 05) in all directions except the B direction of left breast set-up errors (P>0. 05). Between breast conserving surgery and modified radical mastectomy, there was little effect on target movement. Through correlation analysis, it was found that the volume of CTV in the target area of breast cancer patients was linearly related to the errors caused by the movement of B, C and B directions of left breast and right breast(F=5. 733, 18. 496, 6. 630, P<0. 05). Conclusions In postoperative radiotherapy for breast cancer, the errors perpendicular to the section of breast should be paid special attention to whether left or right breast. When the error of this direction exceeds 3 mm, CTV is obviously less than V50 below 83. 85％. The effect of set-up error on the dose of CTV was not related to the operation mode of breast cancer and there was no obvious correlation with the volume of the target area.

Potential proton and photon dose degradation in advanced head and neck cancer patients by intratherapy changes.

PURPOSE: Evaluation of dose degradation by anatomic changes for head-and-neck cancer (HNC) intensity-modulated proton therapy (IMPT) relative to intensity-modulated photon therapy (IMRT) and identification of potential indicators for IMPT treatment plan adaptation. METHODS: For 31 advanced HNC datasets, IMPT and IMRT plans were recalculated on a computed tomography scan (CT) taken after about 4 weeks of therapy. Dose parameter changes were determined for the organs at risk (OARs) spinal cord, brain stem, parotid glands, brachial plexus, and mandible, for the clinical target volume (CTV) and the healthy tissue outside planning target volume (PTV). Correlation of dose degradation with target volume changes and quality of rigid CT matching was investigated. RESULTS: Recalculated IMPT dose distributions showed stronger degradation than the IMRT doses. OAR analysis revealed significant changes in parotid median dose (IMPT) and near maximum dose (D1ml ) of spinal cord (IMPT, IMRT) and mandible (IMPT). OAR dose parameters remained lower in IMPT cases. CTV coverage (V95% ) and overdose (V107% ) deteriorated for IMPT plans to (93.4 ± 5.4)% and (10.6 ± 12.5)%, while those for IMRT plans remained acceptable. Recalculated plans showed similarly decreased PTV conformity, but considerable hotspots, also outside the PTV, emerged in IMPT cases. Lower CT matching quality was significantly correlated with loss of PTV conformity (IMPT, IMRT), CTV homogeneity and coverage (IMPT). Target shrinkage correlated with increased dose in brachial plexus (IMRT, IMPT), hotspot generation outside the PTV (IMPT) and lower PTV conformity (IMRT). CONCLUSIONS: The study underlines the necessity of precise positioning and monitoring of anatomy changes, especially in IMPT which might require adaptation more often. Since OAR doses remained typically below constraints, IMPT plan adaptation will be indicated by target dose degradations.