4D-CBCT reconstruction using MV portal imaging during volumetric modulated arc therapy

Background

Recording target motion during treatment is important for verifying the irradiated region. Recently, cone-beam computed tomography (CBCT) reconstruction from portal images acquired during volumetric modulated arc therapy (VMAT), known as VMAT-CBCT, has been investigated. In this study, we developed a four-dimensional (4D) version of the VMAT-CBCT.

Materials and methods

The MV portal images were sequentially acquired from an electronic portal imaging device. The flex, background, monitor unit, field size, and multi-leaf collimator masking corrections were considered during image reconstruction. A 4D VMAT-CBCT requires a respiratory signal during image acquisition. An image-based phase recognition (IBPR) method was performed using normalised cross correlation to extract a respiratory signal from the series of portal images.

Results

Our original IBPR method enabled us to reconstruct 4D VMAT-CBCT with no external devices. We confirmed that 4D VMAT-CBCT was feasible for two patients and in good agreement with in-treatment 4D kV-CBCT.

Conclusion

The visibility of the anatomy in 4D VMAT-CBCT reconstruction for lung cancer patients has the potential of using 4D VMAT-CBCT as a tool for verifying relative positions of tumour for each respiratory phase.     

Motion-weighted target volume and dose-volume histogram: A practical approximation of four-dimensional planning and evaluation

Background and purpose

In ITV-based 3D-planning, the information of volume occupancy versus respiratory phase is not utilized. We propose a motion-weighted CTV (mwCTV) delineation method, which carries some 4D-information into planning. This method allows plan optimization based on occupancy-weighting and generation of motion-weighted DVH (mwDVH) that approximate the DVHs of full 4D-dose accumulation.

Material and methods

Occupancy information from contours in 4D-CT is incorporated in the mwCTV generation. Higher-occupancy volumes receive higher dosimetric priority in planning. The temporally-weighted mwCTV is converted to a spatially-weighted mwCTV incorporating the temporal-weighting in mwDVH generation using the 3D-dose distribution. The mwDVHs were compared with DVHs of deformable-image-registration (DIR)-based 4D-dose accumulation and 3D-method for 10 cases.

Results

For all the cases, the mwDVH curves are closer to the 4D-calculated DVH than the 3D-DVHs are, indicating a better approximation of the 4D-DVH. The 70 Gy-covered percentage-CTV volume differed by −2.8% ± 0.8% between 3D and 4D, and 0.3% ± 0.7% between mwDVH and 4D-methods. The mean RMS values of the percentage-volume differences for the 4D-3D is 1.7 ± 1.1, while for the 4D-mwDVH is 0.4 ± 0.3.

Conclusion

The mwCTV and mwDVH method, which is simple in implementation and does not require DIR, is a practical approximation of DIR-based 4D-planning and evaluation.     

A novel respiratory motion compensation strategy combining gated beam delivery and mean target position concept - A compromise between small safety margins and long duty cycles

Purpose

To evaluate a novel respiratory motion compensation strategy combining gated beam delivery with the mean target position (MTP) concept for pulmonary stereotactic body radiotherapy (SBRT).

Materials and methods

Four motion compensation strategies were compared for 10 targets with motion amplitudes between 6 mm and 31 mm: the internal target volume concept (plan_ITV); the MTP concept where safety margins were adapted based on 4D dose accumulation (plan_MTP); gated beam delivery without margins for motion compensation (plan_gated); a novel approach combining gating and the MTP concept (plan_gated&MTP).

Results

For 5/10 targets with an average motion amplitude of 9 mm, the differences in the mean lung dose (MLD) between plan_gated and plan_MTP were <10%. For the other 5/10 targets with an average motion amplitude of 19 mm, gating with duty cycles between 87.5% and 75% reduced the residual target motion to 12 mm on average and 2 mm safety margins were sufficient for dosimetric compensation of this residual motion in plan_gated&MTP. Despite significantly shorter duty cycles, plan_gated reduced the MLD by <10% compared to plan_gated&MTP. The MLD was increased by 18% in plan_MTP compared to that of plan_gated&MTP.

Conclusions

For pulmonary targets with motion amplitudes >10-15 mm, the combination of gating and the MTP concept allowed small safety margins with simultaneous long duty cycles.     

Geometric accuracy of a novel gimbals based radiation therapy tumor tracking system

Purpose

VERO is a novel platform for image guided stereotactic body radiotherapy. Orthogonal gimbals hold the linac-MLC assembly allowing real-time moving tumor tracking. This study determines the geometric accuracy of the tracking.

Materials and methods

To determine the tracking error, an 1D moving phantom produced sinusoidal motion with frequencies up to 30 breaths per minute (bpm). Tumor trajectories of patients were reproduced using a 2D robot and pursued with the gimbals tracking system prototype. Using the moving beam light field and a digital-camera-based detection unit tracking errors, system lag and equivalence of pan/tilt performance were measured.

Results

The system lag was 47.7 ms for panning and 47.6 ms for tilting. Applying system lag compensation, sinusoidal motion tracking was accurate, with a tracking error 90% percentile E_90% < 0.82 mm and similar performance for pan/tilt. Systematic tracking errors were below 0.14 mm. The 2D tumor trajectories were tracked with an average E_90% of 0.54 mm, and tracking error standard deviations of 0.20 mm for pan and 0.22 mm for tilt.

Conclusions

In terms of dynamic behavior, the gimbaled linac of the VERO system showed to be an excellent approach for providing accurate real-time tumor tracking in radiation therapy.     

Evaluation of intra- and inter-fraction movement of the cervix during intensity modulated radiation therapy

Background and purpose

To assess the degree of intra- and inter-fraction cervical motion throughout a course of intensity modulated radiation therapy (IMRT) for cervical cancer patients.

Materials and methods

A retrospective study of 10 women with stage 1B1-3B cervical cancer diagnosed from September 2007 to July 2008 was conducted. All patients were treated with chemoradiation using IMRT followed by intracavitary brachytherapy. Pretreatment, patients had 2 seeds placed at a depth of 10 mm into the cervix. On-Board Imaging (OBI) was used to obtain anterior/posterior (AP) and lateral X-rays before and after each treatment. OBI images were rigidly aligned to baseline digitally reconstructed radiographs (DRRs), and movement of cervical seeds was determined in the lateral, vertical, and AP directions. Mean differences in cervical seed position and standard error of the mean (SEM) were calculated.

Results

A total of 922 images were reviewed, with approximately 90 images per patient. The mean intra-fractional movement in cervical seed position in the lateral, vertical, and AP directions were 1.6 mm (SD ± 2.0), 2.6 mm (SD ± 2.4), and 2.9 mm (SD ± 2.7), respectively, with a range from 0 to 15 mm for each direction. The mean inter-fractional movement in the lateral, vertical, and AP directions were 1.9 mm (SD ± 1.9), 4.1 mm (SD ± 3.2), and 4.2 mm (SD ± 3.5), respectively, with a range from 0 to 18 mm for each direction.

Conclusions

This is the first study to assess intra- and inter-fractional movement of the cervix using daily imaging before and after each fraction. Within and between radiation treatments, cervical motion averages approximately 3 mm in any given direction. However, maximal movement of the cervix can be as far as 18 mm from baseline. This wide range of motion needs to be accounted for when generating planning treatment volumes.     

Shaping ability of reciprocating motion in curved root canals: a comparative study with micro-computed tomography

Introduction

Recently, root canal shaping with reciprocating motion has been postulated to reduce the possibility of unexpected file fractures. However, there has been little information on the shaping capability of this reciprocating motion preparation technique. Therefore, the purpose of this study was to evaluate the shaping ability of reciprocating motion when compared with continuous rotation motion in curved root canals.

Methods

The mesiobuccal and distobuccal canals of 20 extracted maxillary molars with curvatures of 20-45 degrees were instrumented with a series of ProTaper rotary files. The canals in the continuous rotation motion (CM) group (n = 20) were prepared by using continuous rotation with pecking motion, whereas the canals in the reciprocating motion (RM) group (n = 20) were prepared with reciprocating motion (clockwise 140 degrees and counterclockwise 45 degrees). Basic geometric parameters such as curvature, root canal volume, surface area, and structure model index (SMI) before and after canal shaping were evaluated by using micro-computed tomography. The degrees and directions of transportation were also measured, and statistical analysis was carried out with one-way analysis of variance and Tukey post hoc tests.

Results

There were no significant differences between the 2 groups in canal curvature, volume, surface area, and SMI categories measured before preparation (P > .05). Changes in curvature, root canal volume, surface area, and SMI were not affected by the instrumentation technique used (P > .05). There were no significant differences in the degrees and directions of transportation between CM and RM groups (P > .05).

Conclusions

The application of reciprocating motion during instrumentation did not result in increased apical transportation when compared with continuous rotation motion, even in the apical part of curved canals. Reciprocating motion might be an attractive alternative method to prevent procedural errors during root canal shaping.     

Effect of Lateral Pressure Motion on the Torsional Behavior of Rotary ProTaper Universal Instruments

Introduction

The purpose of this study was to evaluate the torsional behavior of rotary ProTaper Universal instruments after multiple clinical uses with and without lateral pressure motion.

Methods

Thirty sets of ProTaper Universal instruments were divided into 3 groups (n = 10): control group (CG) involving new instruments tested in torsion on the basis of ISO 3630-1, lateral pressure (LP) group involving instruments that were clinically used on 5 molars by using the shaping instruments S1 and S2 with lateral pressure motion, and no lateral pressure (NLP) group involving instruments that were clinically used on 5 molars without lateral pressure motion. The instruments in the LP and NLP groups were subsequently tested in torsion. Data were analyzed by using analysis of variance (α = 0.05).

Results

Multiple clinical uses caused a reduction in the maximum torque in the analyzed instruments. When the effect of using lateral pressure motion with the shaping instruments was assessed, a tendency of reduction in the maximum torque for the S1 and S2 instruments and of increase for the F1 and F2 instruments was observed in the group with lateral pressure motion.

Conclusions

The use of lateral pressure motion with the shaping instruments S1 and S2 tended to produce smaller decreases in the torsional resistance of the finishing instruments F1 and F2.     

辅助性治疗手套在手外伤后功能康复中的应用*

目的:观察自制辅助性治疗手套对外伤后手功能障碍患者手部关节主、被动屈曲度的影响,并探讨手套的安全性及临床推广价值。方法:30例患者被随机分为治疗组与对照组。两组患者均接受每日1次、每周5d的常规康复治疗,疗程为4周;治疗组患者每次另增加佩戴辅助性治疗手套15min。分别于治疗开始前和治疗结束后的次日,重点对患者功能活动受限的手指进行包括掌指关节(MP)、近端指间关节(PIP)和远端指间关节(DIP)在内的主、被动关节活动度测量。结果:经治疗,治疗组患者食、中、环、小指各关节的被动屈曲度的增加值较对照组有显著性差异(P<0.05),且食、中、环三指掌指关节的被动屈曲度的增加值较对照组有非常显著的差异(P<0.01);治疗组患者食、中、环、小指各关节的主动屈曲度的增加值虽均大于对照组,但差异无显著性意义(P>0.05)。结论:辅助性治疗手套对外伤后手功能障碍患者食、中、环、小指各关节的被动屈曲度有独立的改善作用,尤其是食、中、环三指的掌指关节。     

Low back pain status affects pelvis-trunk coordination and variability during walking and running

Background

The purpose of this study was to compare pelvis–trunk coordination and coordination variability over a range of walking and running speeds between three groups of runners; runners with low to moderate low back pain; runners who had recovered from a single bout of acute low back pain; and runners who had never experienced any symptoms of low back pain.

Methods

Pelvis and trunk kinematic data were collected as speed was systematically increased on a treadmill. Coordination between pelvis and trunk in all three planes of motion was measured using continuous relative phase, and coordination variability was defined as the standard deviation of this measure.

Findings

Oswestry Disability Index indicated the low back pain group was high functioning (mean 7.9% out of 100%). During walking, frontal plane coordination was more in-phase for the low back pain group compared to controls (P = 0.029), with the resolved group showing an intermediate coordination pattern (P = 0.064). During running, both low back pain (P = 0.021) and resolved (P = 0.025) groups showed more in-phase coordination in the transverse plane than the control group. The low back pain group also showed reduced transverse plane coordination variability compared to controls (P = 0.022).

Interpretation

Coordination and coordination variability results showed a continuum of responses between our three groups. Taken together, the data lend insight into increased injury risk and performance deficits associated with even one bout of low back pain, and suggest that clinicians need to look beyond the resolution of pain when prescribing rehabilitation for low back pain.