Daily setup uncertainty analysis for craniospinal irradiation using helical tomotherapy

PurposeSetup deviations of a craniospinal irradiation (CSI) patient cohort previously treated with helical tomotherapy were used to derive the optimal planning target volume (PTV) margin for CSI patients treated in the supine position.Methods and MaterialsThe daily setup shifts of 27 CSI tomotherapy patients as determined using pretreatment megavoltage computed tomography verification for a total of 454 fractions were evaluated. Translational displacements in the mediolateral (ML), craniocaudal (CC), and anteroposterior (AP) directions were used to assess the systematic and random setup errors, and to derive the PTV margin required when daily image guidance is unavailable.ResultsThe individual patient mean shifts and the corresponding standard deviations in the ML, CC, and AP directions were ? 0.5 ± 2.1 mm, 1.0 ± 2.7 mm, and 0.7 ± 1.1 mm, respectively. The random errors in the corresponding directions were 1.9 mm, 1.9 mm, and 2.2 mm. The PTV margins required in the absence of daily imaging were 3.7 mm to the right, 4.7 mm to the left, 4.4 mm inferior, 6.4 mm superior, 1.6 mm posterior, and 3.0 mm anterior.ConclusionsThe current PTV margin of 3.0 mm is sufficient to ensure clinical target volume coverage for CSI tomotherapy patients treated with daily megavoltage computed tomography imaging. When pretreatment verification imaging is not used to lower the setup uncertainty, a larger PTV margin of up to 6.4 mm in the CC direction will be needed.     

利用CBCT联合六自由度治疗床研究宫颈癌术后放疗摆位误差及CTV外放边界

目的 利用千伏级CBCT联合HexaPOD evo RT六自由度治疗床研究宫颈癌术后盆腔放疗摆位误差,推算CTV外放边界。方法 采用医科达AXESSE^TM直线加速器治疗宫颈癌术后患者17例。所有患者常规摆位后CBCT,治疗床在线校正后再次CBCT,治疗后再次CBCT,分别获得XVI。与计划CT图像配准后,即可获得患者左右、上下、前后方向平移及旋转误差,分析摆位误差及CTV外放边界。采用配对t检验差异。结果 CBCT校正前后均为304次,治疗后68次。所有患者分次间左右、上下、前后方向平移误差和旋转误差经在线校正后均减小,校正前/后绝对值的平均值分别为2.42 mm/0.42 mm、3.55 mm/0.47 mm、3.26 mm/0.27 mm和1.24°/0.24°、0.70°/0.32°、0.57°/0.12°(P=0.036、0.000、0.000、0.002、0.000、0.004)。考虑分次内摆位误差影响,治疗床校正后CTV外扩边界在左右、上下、前后方向上分别为2.24、3.32、2.20 mm。结论 宫颈癌术后患者CBCT联合六维治疗床在线校正可明显减小6个方向分次间摆位误差,且能缩小CTV外放边界。     

Defining the margins in the radical radiotherapy of non-small cell lung cancer (NSCLC) with active breathing control (ABC) and the effect on physical lung parameters.

BACKGROUND: The effectiveness of ABC has been traditionally measured as the reduction in internal margin (IM) within the planning target volume (PTV). Not to overestimate the benefit of ABC, the effect of patient movement during treatment also needs to be taken into account. We determined the IM and set-up error with ABC and the effect on physical lung parameters compared to standard margins used with free breathing. We also assessed interfraction oesophageal movement to determine a planning organ at risk volume (PRV). MATERIALS AND METHODS: Two sequential studies were performed using ABC in NSCLC patients suitable for radical radiotherapy (RT). Twelve out of 14 patients in Study 1 had tumours visible fluoroscopically and had intrafraction tumour movement assessed with and without ABC. Sixteen patients were recruited to Study 2 and had interfraction tumour movement measured using ABC in a moderate deep inspiration breath-hold, of these 7 patients also had interfraction oesophageal movement recorded. Interfraction movement was assessed by CT scan prior to and in the middle and final week of RT. Displacement of the tumour centre of mass and oesophageal borders relative to the first scan provided a measure of movement. Set-up error was measured in 9 patients treated with an in-house lung board adapted for the ABC device. Combining movement and set-up errors determined PTV and PRV margins with ABC. The effect of ABC on mean lung dose (MLD), lung V20 and V13 was calculated. RESULTS: ABC in a moderate deep inspiration breath-hold was tolerated in 25 out of 30 patients (83%) in Study 1 and 2. The random contribution of periodic tumour motion was reduced by 90% in the y direction with ABC compared to free-breathing. The magnitude of motion reduction was less in the x and z direction. Combining the systematic and random set-up error in quadrature with the systematic and random intrafraction and interfraction tumour variations with ABC results in a PTV margin of 8.3mm in the x direction, 12.0mm in the y direction and 9.8mm in the z direction. There was a relative mean reduction in MLD, lung V20 and V13 of 25%, 21% and 18% with the ABC PTV compared to a free-breathing PTV. Oesophageal movement combined with set-up error resulted in an isotropic PRV of 4.7 mm. CONCLUSIONS: The reduction in PTV size with ABC resulted in an 18-25% relative reduction in physical lung parameters. PTV margin reduction has the potential to spare normal lung and allow dose-escalation if coupled with image-guided RT. The oesophageal PRV needs to be considered when irradiating central disease and is of increasing importance with altered RT fractionation and concomitant chemoradiation schedules. Further reductions in PTV and PRV may be possible if patient set-up error was minimised, confirming that attention to patient immobilisation is as important as attempts to control tumour motion.     

Effect of patient setup errors on simultaneously integrated boost head and neck IMRT treatment plans

PURPOSE: The purpose of this study is to determine dose delivery errors that could result from random and systematic setup errors for head-and-neck patients treated using the simultaneous integrated boost (SIB)-intensity-modulated radiation therapy (IMRT) technique. METHODS AND MATERIALS: Twenty-four patients who participated in an intramural Phase I/II parotid-sparing IMRT dose-escalation protocol using the SIB treatment technique had their dose distributions reevaluated to assess the impact of random and systematic setup errors. The dosimetric effect of random setup error was simulated by convolving the two-dimensional fluence distribution of each beam with the random setup error probability density distribution. Random setup errors of sigma = 1, 3, and 5 mm were simulated. Systematic setup errors were simulated by randomly shifting the patient isocenter along each of the three Cartesian axes, with each shift selected from a normal distribution. Systematic setup error distributions with Sigma = 1.5 and 3.0 mm along each axis were simulated. Combined systematic and random setup errors were simulated for sigma = Sigma = 1.5 and 3.0 mm along each axis. For each dose calculation, the gross tumor volume (GTV) received by 98% of the volume (D(98)), clinical target volume (CTV) D(90), nodes D(90), cord D(2), and parotid D(50) and parotid mean dose were evaluated with respect to the plan used for treatment for the structure dose and for an effective planning target volume (PTV) with a 3-mm margin. RESULTS: Simultaneous integrated boost-IMRT head-and-neck treatment plans were found to be less sensitive to random setup errors than to systematic setup errors. For random-only errors, errors exceeded 3% only when the random setup error sigma exceeded 3 mm. Simulated systematic setup errors with Sigma = 1.5 mm resulted in approximately 10% of plan having more than a 3% dose error, whereas a Sigma = 3.0 mm resulted in half of the plans having more than a 3% dose error and 28% with a 5% dose error. Combined random and systematic dose errors with sigma = Sigma = 3.0 mm resulted in more than 50% of plans having at least a 3% dose error and 38% of the plans having at least a 5% dose error. Evaluation with respect to a 3-mm expanded PTV reduced the observed dose deviations greater than 5% for the sigma = Sigma = 3.0 mm simulations to 5.4% of the plans simulated. CONCLUSIONS: Head-and-neck SIB-IMRT dosimetric accuracy would benefit from methods to reduce patient systematic setup errors. When GTV, CTV, or nodal volumes are used for dose evaluation, plans simulated including the effects of random and systematic errors deviate substantially from the nominal plan. The use of PTVs for dose evaluation in the nominal plan improves agreement with evaluated GTV, CTV, and nodal dose values under simulated setup errors. PTV concepts should be used for SIB-IMRT head-and-neck squamous cell carcinoma patients, although the size of the margins may be less than those used with three-dimensional conformal radiation therapy.     

热塑头肩模与头颈肩真空垫在肺癌脑转移大分割立体定向放疗中固定效果分析

目的:回顾性分析热塑头肩模单用或联合使用头颈肩真空垫在脑转移瘤大分割立体定向放疗(HFSRT)中的固定效果。方法:纳入2017—2019年间54例非小细胞肺癌脑转移并行HFSRT患者,热塑头肩模固定24例(单模组),热塑头肩模+真空垫固定30例(联合组)。治疗前后分别行在线图像配准,记录疗前分次间误差及疗后分次内误差,...     

The reproducibility of organ position using active breathing control (ABC) during liver radiotherapy

Purpose: To evaluate the intrafraction and interfraction reproducibility of liver immobilization using active breathing control (ABC).

Methods and Materials: Patients with unresectable intrahepatic tumors who could comfortably hold their breath for at least 20 s were treated with focal liver radiation using ABC for liver immobilization. Fluoroscopy was used to measure any potential motion during ABC breath holds. Preceding each radiotherapy fraction, with the patient setup in the nominal treatment position using ABC, orthogonal radiographs were taken using room-mounted diagnostic X-ray tubes and a digital imager. The radiographs were compared to reference images using a 2D alignment tool. The treatment table was moved to produce acceptable setup, and repeat orthogonal verification images were obtained. The positions of the diaphragm and the liver (assessed by localization of implanted radiopaque intra-arterial microcoils) relative to the skeleton were subsequently analyzed. The intrafraction reproducibility (from repeat radiographs obtained within the time period of one fraction before treatment) and interfraction reproducibility (from comparisons of the first radiograph for each treatment with a reference radiograph) of the diaphragm and the hepatic microcoil positions relative to the skeleton with repeat breath holds using ABC were then measured. Caudal-cranial (CC), anterior-posterior (AP), and medial-lateral (ML) reproducibility of the hepatic microcoils relative to the skeleton were also determined from three-dimensional alignment of repeat CT scans obtained in the treatment position.

Results: A total of 262 fractions of radiation were delivered using ABC breath holds in 8 patients. No motion of the diaphragm or hepatic microcoils was observed on fluoroscopy during ABC breath holds. From analyses of 158 sets of positioning radiographs, the average intrafraction CC reproducibility (σ) of the diaphragm and hepatic microcoil position relative to the skeleton using ABC repeat breath holds was 2.5 mm (range 1.8–3.7 mm) and 2.3 mm (range 1.2–3.7 mm) respectively. However, based on 262 sets of positioning radiographs, the average interfraction CC reproducibility (σ) of the diaphragm and hepatic microcoils was 4.4 mm (range 3.0–6.1 mm) and 4.3 mm (range 3.1–5.7 mm), indicating a change of diaphragm and microcoil position relative to the skeleton over the course of treatment with repeat breath holds at the same phase of the respiratory cycle. The average population absolute intrafraction CC offset in diaphragm and microcoil position relative to skeleton was 2.4 mm and 2.1 mm respectively; the average absolute interfraction CC offset was 5.2 mm. Analyses of repeat CT scans demonstrated that the average intrafraction excursion of the hepatic microcoils relative to the skeleton in the CC, AP, and ML directions was 1.9 mm, 0.6 mm, and 0.6 mm respectively and the average interfraction CC, AP, and ML excursion of the hepatic microcoils was 6.6 mm, 3.2 mm, and 3.3 mm respectively.

Conclusion: Radiotherapy using ABC for patients with intrahepatic cancer is feasible, with good intrafraction reproducibility of liver position using ABC. However, the interfraction reproducibility of organ position with ABC suggests the need for daily on-line imaging and repositioning if treatment margins smaller than those required for free breathing are a goal.     

Measurements of intrafraction motion and interfraction and intrafraction rotation of prostate by three-dimensional analysis of daily portal imaging with radiopaque markers

PURPOSE: To measure the interfraction and intrafraction motion of the prostate during the course of external beam radiotherapy using a video electronic portal imaging device and three-dimensional analysis. METHODS AND MATERIALS: Eighteen patients underwent implantation with two or three gold markers in the prostate before five-angle/11-field conformal radiotherapy. Using CT data as the positional reference, multiple daily sets of portal images, and a three-dimensional reconstruction algorithm, intrafraction translations, as well as interfraction and intrafraction rotations, were analyzed along the three principal axes (left-right [LR], superoinferior [SI], and AP). The overall mean values and standard deviations (SDs), along with random and systematic SDs, were computed for these translations and rotations. RESULTS: For 282 intrafraction translational displacements, the random SD was 0.8 mm (systematic SD, 0.2) in the LR, 1.0 mm (systematic SD, 0.4) in the SI, and 1.4 mm (systematic SD, 0.7) in the AP axes. The analysis of 348 interfraction rotations revealed random SDs of 6.1 degrees (systematic SD, 5.6 degrees ) around the LR axis, 2.8 degrees (systematic SD, 2.4 degrees ) around the SI axis, and 2.0 degrees (systematic SD, 2.2 degrees ) around the AP axis. The intrafraction rotational motion observed during 44 fractions had a random SD of 1.8 degrees (systematic SD, 1.0 degrees ) around the LR, 1.1 degrees (systematic SD, 0.8 degrees ) around the SI, and 0.6 degrees (systematic SD, 0.3 degrees ) around the AP axis. CONCLUSION: The interfraction rotations observed were more important than those reported in previous studies. Intrafraction motion was generally smaller in magnitude than interfraction motion. However, the intrafraction rotations and translations of the prostate should be taken into account when designing planning target volume margins because their magnitudes are not negligible.     

Understanding the Benefit of Magnetic Resonance-guided Adaptive Radiotherapy in Rectal Cancer Patients: a Single-centre Study

AimsNeoadjuvant chemoradiotherapy followed by surgery is the mainstay of treatment for patients with rectal cancer. Standard clinical target volume (CTV) to planning target volume (PTV) margins of 10 mm are used to accommodate inter- and intrafraction motion of target. Treating on magnetic resonance-integrated linear accelerators (MR-linacs) allows for online manual recontouring and adaptation (MRgART) enabling the reduction of PTV margins. The aim of this study was to investigate motion of the primary CTV (CTVA; gross tumour volume and macroscopic nodes with 10 mm expansion to cover microscopic disease) in order to develop a simultaneous integrated boost protocol for use on MR-linacs.Materials and methodsPatients suitable for neoadjuvant chemoradiotherapy were recruited for treatment on MR-linac using a two-phase technique; only the five phase 1 fractions on MR-linac were used for analysis. Intrafraction motion of CTVA was measured between pre-treatment and post-treatment MRI scans. In MRgART, isotropically expanded pre-treatment PTV margins from 1 to 10 mm were rigidly propagated to post-treatment MRI to determine overlap with 95% of CTVA. The PTV margin was considered acceptable if overlap was >95% in 90% of fractions. To understand the benefit of MRgART, the same methodology was repeated using a reference computed tomography planning scan for pre-treatment imaging.ResultsIn total, nine patients were recruited between January 2018 and December 2020 with T3a-T4, N0–N2, M0 disease. Forty-five fractions were analysed in total. The median motion across all planes was 0 mm, demonstrating minimal intrafraction motion. A PTV margin of 3 and 5mm was found to be acceptable in 96 and 98% of fractions, respectively. When comparing to the computed tomography reference scan, the analysis found that PTV margins to 5 and 10 mm only acceptably covered 51 and 76% of fractions, respectively.ConclusionPTV margins can be reduced to 3–5 mm in MRgART for rectal cancer treatment on MR-linac within an simultaneous integrated boost protocol.     

A randomized comparison of interfraction and intrafraction prostate motion with and without abdominal compression

BACKGROUND AND PURPOSE: To quantify inter- and intrafraction prostate motion in a standard VacLok (VL) immobilization device or in the BodyFix (BF) system incorporating a compression element which may reduce abdominal movement. MATERIALS AND METHODS: Thirty-two patients were randomly assigned to VL or BF. Interfraction prostate motion >3 mm was corrected pre-treatment. EPIs were taken daily at the start and end of the first and last treatment beams. Interfraction and intrafraction prostate motion were measured for centre of mass (COM) and individual markers. RESULTS: There were no significant differences in interfraction (p0.002) or intrafraction (p0.16) prostate motion with or without abdominal compression. Median intrafraction motion was slightly smaller than interfraction motion in the AP (7.0 mm vs. 7.6 mm) and SI direction (3.2 mm vs. 4.7 mm). The final image captured the maximal intrafraction displacement in only 40% of fractions. Our PTV incorporated >95% of total prostate motion. CONCLUSIONS: Intrafraction motion became the major source of error during radiotherapy after online correction of interfraction prostate motion. The addition of 120 mbar abdominal compression to custom pelvic immobilization influenced neither interfraction nor intrafraction prostate motion.     

乳腺托架固定下全乳调强放疗摆位误差兆伏X线验证平片测定分析

目的 用兆伏(MV) X线平片测定乳腺托架固定下全乳放疗摆位误差,探讨自由呼吸状态下临床靶体积(CTV)外扩至计划靶体积(PTV)的边界。
方法 选取2010-2012年本科行保乳术后调强放疗的29例乳腺癌患者,其中17例行全乳照射,12例行全乳和锁骨上淋巴引流区照射。均采用乳腺托架体位固定,利用放疗计划系统数字重建图像与治疗期间拍摄正交MV验证平片比较,确定摆位误差。对接受锁骨上淋巴引流区照射与未照射的误差比较行成组t检验。
结果 全体患者共获得正交MV验证平片图像127套,平均每人(4.4±1.2)套。全组患者左右、上下、前后方向摆位误差分别为(0.9±3.1)、(0.7±3.0)、(1.2±2.1) mm,摆位误差的系统误差分别为3.1、3.0、2.1 mm,随机误差分别为2.7、3.3、3.5 mm;做与未做锁骨上淋巴引流区照射者的摆位误差无差异(t=0.02、0.20、0.20,P=0.98、0.85、0.85)。CTV至PTV边界左右、上下、前后方向分别为9.6、9.8、7.7 mm。
结论 用乳腺托架固定全乳调强放疗的CTV外放PTV在左右、上下、前后方向上应至少分别为9.6、9.8、7.7 mm。     

Clinical evaluation of interfractional variations for whole breast radiotherapy using 3-dimensional surface imaging

PurposeTo evaluate the impact of 3-dimensional (3D) surface imaging on daily patient setup for breast radiotherapy.Materials and MethodsFifty patients undergoing treatment for whole breast radiotherapy were setup daily using an AlignRT system (VisionRT, London, UK) for 3D surface-based alignment. Daily alignments were performed against a reference surface topogram and shifts from skin marks were recorded daily. This investigation evaluated the following: (1) the performance of the surface-based imaging system for daily breast alignment; (2) the absolute displacements between setup with skin marks and setup with the surface-based imaging system; and (3) the dosimetric effect of daily alignments with skin marks versus surface-based alignments.ResultsDisplacements from 1258 treatment fractions were analyzed. Sixty percent of those fractions (749) were reviewed against MV portal imaging in order to assess the performance of the AlignRT system. Daily setup errors were given as absolute displacements, comparing setup marks against shifts determined using the surface-based imaging system. Averaged over all patients, the mean displacements were 4.1 ± 2.6 mm, 2.7 ± 1.4 mm, and 2.6 ± 1.2 mm in the anteroposterior (AP), superoinferior (S/I), and left-right (L/R) directions, respectively. Furthermore, the standard deviation of the random error (σ) was 3.2 mm, 2.2 mm, and 2.2 mm in the A/P, S/I, and L/R directions, respectively.ConclusionsDaily alignment with 3D surface imaging was found to be valuable for reducing setup errors when comparing with patient alignment from skin marks. The result of the surface-based alignments specifically showed that alignment with skin marks was noticeably poor in the anteroposterior directions. The overall dosimetric effect of the interfractional variations was small, but these variations showed a potential for increased dose deposition to both the heart and lung tissues. Although these interfractional variations would not negatively affect the quality of patient care for whole breast radiotherapy, it may require an increase in PTV margin, especially in cases of partial breast irradiation.     

A moving target: Image guidance for stereotactic body radiation therapy for early-stage non-small cell lung cancer

PurposePrecise patient positioning is critical due to the large fractional doses and small treatment margins employed for thoracic stereotactic body radiation therapy (SBRT). The goals of this study were to evaluate the following: (1) the accuracy of kilovoltage x-ray (kV x-ray) matching to bony anatomy for pretreatment positioning; (2) the magnitude of intrafraction tumor motion; and (3) whether treatment or patient characteristics correlate with intrafraction motion.Methods and MaterialsEighty-seven patients with lung cancer were treated with SBRT. Patients were positioned with orthogonal kV x-rays matched to bony anatomy followed by cone-beam computed tomography (CBCT), with matching of the CBCT-visualized tumor to the internal gross target volume obtained from a 4-dimensional CT simulation data set. Patients underwent a posttreatment CBCT to assess the magnitude of intrafraction motion.ResultsThe mean CBCT-based shifts after initial patient positioning using kV x-rays were 2.2 mm in the vertical axis, 1.8 mm in the longitudinal axis, and 1.6 mm in the lateral axis (n = 335). The percentage of shifts greater than 3 mm and 5 mm represented 39% and 17%, respectively, of all fractions delivered. The mean CBCT-based shifts after treatment were 1.6 mm vertically, 1.5 mm longitudinally, and 1.1 mm laterally (n = 343). Twenty-seven percent and 10% of shifts were greater than 3 mm and 5 mm, respectively. Univariate and multivariable analysis demonstrated a significant association between intrafraction motion with weight and pulmonary function.ConclusionsKilovoltage x-ray matching to bony anatomy is inadequate for accurate positioning when a conventional 3-5 mm margin is employed prior to lung SBRT. Given the treatment techniques used in this study, CBCT image guidance with a 5-mm planning target volume margin is recommended. Further work is required to find determinants of interfraction and intrafraction motion that may help guide the individualized application of planning target volume margins.     

胸段食管癌三维适形放疗摆位误差研究

目的 应用电子射野影像装置(EPID)测量胸段食管癌三维适形放疗(3DCRT)的摆位误差,推算PTV与CTV之间的间隙.方法 对41例胸段食管癌患者每周拍摄1次正侧位EPI,通过比较EPI和数字重建影像(DRR)的差异来测量摆位误差.根据公式计算出PTV与CTV之间的间隙.采用自身配对设计对22例接受根治性放疗患者应用不同PTV与CTV的间隙值分别设计两套模拟治疗计划,A组x、y和z轴均为10 mm,B组采用本研究结果 的间隙值.应用配对t检验或Wilcoxon符号秩检验来比较两套计划间的差异.结果 x、y、z轴的PTV与CTV的间隙值分别为8.72、10.50、5.62 mm.两套模拟计划间的脊髓最高照射剂量不同,A计划为(4638.7±1449.6)cGy,B计划为(4310.2±1528.7)cGy(t=5.48,P=0.000);脊髓并发症概率也不同,A计划为4.82%±5.99%,B计划为3.64%±4.70%(Z=-2.70,P=0.007).结论 笔者单位胸段食管癌接受3DCRT时在x,y和z轴上的PTV与CTV之间的间隙值分别为8.72、10.50、5.62 mm;与3个轴均为10 mm的间隙值相比应用本研究结果 制定治疗计划可更有效地保护脊髓.     

Comparison of setup accuracy and intrafraction motion using stereotactic frame versus 3-point thermoplastic mask-based immobilization for fractionated cranial image guided radiation therapy

PurposeProspectively compare patient setup accuracy and intrafraction motion of a standard 3-point thermoplastic mask with the Gill-Thomas-Cosman relocatable stereotactic frame, during fractionated cranial radiation therapy using the ExacTrac system (Brainlab AG Feldkirchen, Germany) for daily online correction.Methods and MaterialsThe number of fractions with all postcorrection and post-treatment errors < 2 mm was assessed in 21 patients undergoing fractionated stereotactic radiation therapy (13 frame setup, 8 mask setup) using daily online correction. Achievable patient setup accuracy and total intrafraction motion were evaluated. The relative contributions of movement during floor rotation and patient movement to intrafraction motion were calculated.ResultsWith daily online correction, patient setup margins can be reduced from 1, 5, and 4 mm in the lateral, longitudinal, and vertical axes for mask setup and from 1-2, 2, and 1 mm, respectively, for frame setup to < 1 mm isotropically for either immobilization system. Intrafraction movement was small for frame setup (mean [SD], ? 0.3 [0.3], ? 1.1[0.4], and ? 0.2 [0.6] in lateral, longitudinal and vertical axes, respectively; maximum, ? 2.7 mm [longitudinal axis]), and mask-setup (mean [SD], ? 0.4 [0.5], ? 0.8 [0.7], and 0.0 [0.3], respectively; maximum, ? 2.0 mm [longitudinal axis]) and is mainly due to floor rotation. Postcorrection and post-treatment errors were all < 2 mm in 95% and 99% of fractions in the mask and frame, respectively, meeting the criteria for a 3-mm clinical target volume-planning target volume margin for either immobilization method.ConclusionsDaily online correction can compensate for less precise immobilization and permits stereotactic margins to be used for standard thermoplastic masks without the need for specialized mask systems.     

Evaluation of respiratory movement during gated radiotherapy using film and electronic portal imaging

PURPOSE: To evaluate the effectiveness of a commercial system(1) in reducing respiration-induced treatment uncertainty by gating the radiation delivery. METHODS AND MATERIALS: The gating system considered here measures respiration from the position of a reflective marker on the patient's chest. Respiration-triggered planning CT scans were obtained for 8 patients (4 lung, 4 liver) at the intended phase of respiration (6 at end expiration and 2 at end inspiration). In addition, fluoroscopic movies were recorded simultaneously with the respiratory waveform. During the treatment sessions, gated localization films were used to measure the position of the diaphragm relative to the vertebral bodies, which was compared to the reference digitally reconstructed radiograph derived from the respiration-triggered planning CT. Variability was quantified by the standard deviation about the mean position. We also assessed the interfraction variability of soft tissue structures during gated treatment in 2 patients using an amorphous silicon electronic portal imaging device. RESULTS: The gated localization films revealed an interfraction patient-averaged diaphragm variability of 2.8 +/- 1.0 mm (error bars indicate standard deviation in the patient population). The fluoroscopic data yielded a patient-averaged intrafraction diaphragm variability of 2.6 +/- 1.7 mm. With no gating, this intrafraction excursion became 6.9 +/- 2.1 mm. In gated localization films, the patient-averaged mean displacement of the diaphragm from the planning position was 0.0 +/- 3.9 mm. However, in 4 of the 8 patients, the mean (over localization films) displacement was >4 mm, indicating a systematic displacement in treatment position from the planned one. The position of soft tissue features observed in portal images during gated treatments over several fractions showed a mean variability between 2.6 and 5.7 mm. The intrafraction variability, however, was between 0.6 and 1.4 mm, indicating that most of the variability was due to patient setup errors rather than to respiratory motion. CONCLUSIONS: The gating system evaluated here reduces the intra- and interfraction variability of anatomy due to respiratory motion. However, systematic displacements were observed in some cases between the location of an anatomic feature at simulation and its location during treatment. Frequent monitoring is advisable with film or portal imaging.     

Setup Management for Stereotactic Body Radiation Therapy of Patients With Pancreatic Cancer Treated via the Breath-Hold Technique

PurposeActive Breathing Coordinator (Elekta AB, Crawley, UK) is a motion management strategy for radiation treatment. During setup, aligning the patient to the bony spine alone does not necessarily lead to an accurate alignment to soft tissue targets, and further adjustment is necessary. Determining a safe range of values for such adjustments is an important quality assurance measure and was the purpose of this study, with focus on stereotactic body radiation therapy in patients with pancreatic cancer.Methods and MaterialsThe retrospective study included 19 previously treated patients. For each fraction, a free-breathing cone beam computed tomography scan was registered to a reference breath-hold computed tomography for alignment to the spine. Two perpendicular breath-hold kV projection images were then acquired and compared with corresponding reference digitally reconstructed radiographs for additional alignment with a surrogate fiducial marker. By comparing the breath-hold kV projection images from subsequent treatment fractions with those from the first fraction, we derived the 3-dimensional variability of the fiducial position with respect to the reference image.ResultsWe observed intrafraction setup error to be within 2.0 mm. For interfraction, we observed average reproducibility of 1.7 ± 0.8 mm, 2.0 ± 1.4 mm, and 3.2 ± 2.5 mm in the left–right (LR), anterior–posterior (AP), and superior–inferior (SI) directions, respectively. The average excursion values from free breathing spine to breath-hold fiducial alignment were 1.5 ± 1.4 mm, 2.0 ± 1.9 mm, and 3.0 ± 2.0 mm in the LR, AP and SI directions, respectively. The observed ranges of average excursions among all patients were 0.2 to 5.1 mm, 0.1 to 5. 9 mm, and 0.6 to 7.8 mm in the LR, AP, and SI directions, respectively.ConclusionsThis study demonstrates that intrafraction targeting errors can be within 2 mm, and interfraction shifts from free-breathing spine to Active Breathing Coordinator breath-hold target can be as high as 8 mm. Values that deviate significantly would need further investigation to rule out factors such as local progression, bowel gas, or fiducial shift before treatment.     

乳腺托架固定下全乳调强放疗CBCT测定摆位误差的研究

目的 探讨乳腺癌保乳术后乳腺托架固定下全乳调强放疗的摆位误差和影响因素,明确临床靶体积外扩至计划靶体积的边界。方法 选取肿瘤医院2016-2017年间乳腺癌保乳术后接受全乳大分割调强放疗的患者30例,其中左侧乳腺癌患者15例,右侧乳腺癌患者15例。所有患者均采用乳腺托架体位固定。比较放疗计划系统图像与放射治疗期间锥形束CT的位移,确定摆位误差,并计算临床靶体积外扩至计划靶体积的边界。不同情况的摆位误差比较采用t检验。结果 全组患者共拍摄锥形束CT图像151套,平均每人(5.0±1.3)套。全组患者摆位误差在x、y、z轴的位移分别为(2.2±1.7)、(3.1±2.5)、(3.3±2.3) mm,CTV至PTV外扩边界分别为6.39、10.00、8.57 mm。放疗第1周摆位误差与后续治疗摆位误差在z轴方向有统计学差异[(3.7±2.5) mm和(2.6±1.6) mm,P=0.002],体重指数超重比正常患者在z轴方向摆位误差显著增大[(3.9±2.6) mm和(2.9±2.0) mm,P=0.033]。结论 乳腺癌保乳术后乳腺托架固定行全乳调强放疗时,推荐CTV至PTV的外扩边界为6~10 mm。建议增加放疗第1周的影像验证频率。     

Image-guided radiotherapy via daily online cone-beam CT substantially reduces margin requirements for stereotactic lung radiotherapy

PURPOSE: To determine treatment accuracy and margins for stereotactic lung radiotherapy with and without cone-beam CT (CBCT) image guidance. METHODS AND MATERIALS: Acquired for the study were 308 CBCT of 24 patients with solitary peripheral lung tumors treated with stereotactic radiotherapy. Patients were immobilized in a stereotactic body frame (SBF) or alpha-cradle and treated with image guidance using daily CBCT. Four (T1) or five (T2/metastatic) 12-Gy fractions were prescribed to the planning target volume (PTV) edge. The PTV margin was >or=5 mm depending on a pretreatment estimate of tumor excursion. Initial daily setup was according to SBF coordinates or tattoos for alpha-cradle cases. A CBCT was performed and registered to the planning CT using soft tissue registration of the target. The initial setup error/precorrection position, was recorded for the superior-inferior, anterior-posterior, and medial-lateral directions. The couch was adjusted to correct the tumor positional error. A second CBCT verified tumor position after correction. Patients were treated in the corrected position after the residual errors were 相似文献   

Set-up errors and planning target volume margins in head and neck cancer radiotherapy: a clinical study of image guidance with on-line cone-beam computed tomography

Background

Set-up errors represent a source of uncertainty in head and neck (H&N) cancer radiotherapy. The present study evaluated set-up accuracy with the use of cone-beam computed tomography (CBCT) in order to establish the proper clinical target volume (CTV) to planning target volume (PTV) margins to be adopted.

Methods

Local set-up accuracy was analysed for 44 H&N cancer patients since the implementation of CBCT. An on-line correction protocol was adopted, with the first 3 scans used to correct systematic errors with a 3-mm action level. The overall mean displacement (M), the population systematic (Σ) and random (σ) errors and the 3D vector length were calculated. PTV margins were calculated according to the van Herk formula (2.5Σ + 0.7σ).

Results

A total of 420 CBCT scans were analysed. A systematic correction was needed in 43% of patients. The value of M was <1 mm in all directions; the values of Σ and σ ranged over 1–1.2 and 1.4–1.9 mm, respectively. Pre-correction PTV margins were 3.48, 4.08 and 4.33 mm along the 3 axes. The PTV margins calculated after online correction were <2.5 mm in all directions.

Conclusions

Kilovoltage CBCT is effective in evaluating set-up accuracy in H&N patients. CTV–PTV margins of 5 mm are safe and are currently adopted at our centre; however, some special situations, such as re-irradiation or the close proximity of organs at risk and high-dose regions, could benefit from daily image registration and lower (i.e., 3 mm) margins.     

Carbon Fiducial Image Guidance Increases the Accuracy of Lumpectomy Cavity Localization in Radiation Therapy for Breast Cancer

Purpose

We investigated the feasibility and accuracy of using carbon fiducials to localize the lumpectomy cavity with 2-dimensional kV imaging for early stage breast cancer radiation therapy.