Accuracy of Digital Orthodontic Treatment Planning: Assessing Aligner-Directed Tooth Movements and Exploring Inherent Intramaxillary Side Effects.

Background: The attainment of precise posterior occlusion alignment necessitates a deeper understanding of the clinical efficacy of aligner therapy. This study aims to determine whether the treatment goals defined in the virtual planning of aligner therapy are effectively implemented in clinical practice, with a particular focus on the influence of distalization distances on potential vertical side effects. Methods: In this retrospective, non-interventional investigation, a cohort of 20 individuals undergoing Invisalign® treatment was examined. Pre- and post-treatment maxillary clinical and ClinCheck® casts were superimposed utilizing a surface-surface matching algorithm on palatal folds, median palatine raphe, and unmoved teeth as the stable references. The effectivity of planned versus clinical movements was evaluated. Groupings were based on distalization distances, planned vertical movements, and Class II elastic prescription. Statistics were performed with a two-sample t-test and p-value < 0.05. Results: Clinically achieved distalization was significantly lower than virtually planned distalization, regardless of additional vertical movements, where a lack of implementation was contingent upon the extent of distalization, with no mitigating effects observed with the application of Class II elastics. Intriguingly, no adverse vertical side effects were noted; however, the intended intrusions or extrusions, as per the therapeutic plans, remained unattainable regardless of the magnitude of distalization. Conclusions: These findings underscore the imperative for future investigations to delve deeper into the intricacies surrounding translational mesio-distal and vertical movements, thereby enhancing predictability within orthodontic practice. To facilitate successful clinical implementation of vertical and translational movements via aligners, the incorporation of sliders emerges as a promising strategy for bolstering anchorage reinforcement.

Assessment of intrafraction motion and its dosimetric impact on prostate radiotherapy using an in-house developed position monitoring system.

Purpose: To implement an in-house developed position monitoring software, SeedTracker, for conventional fractionation prostate radiotherapy, and study the effect on dosimetric impact and intrafraction motion. Methods: Thirty definitive prostate radiotherapy patients with implanted fiducial markers were included in the study. All patients were treated with VMAT technique and plans were generated using the Pinnacle planning system using the 6MV beam model for Elekta linear accelerator. The target dose of 60 Gy in 20 fractions was prescribed for 29 of 30 patients, and one patient was treated with the target dose of 78 Gy in 39 fractions. The SeedTracker position monitoring system, which uses the x-ray images acquired during treatment delivery in the Elekta linear accelerator and associated XVI system, was used for online prostate position monitoring. The position tolerance for online verification was progressively reduced from 5 mm, 4 mm, and to 3 mm in 10 patient cohorts to effectively manage the treatment interruptions resulting from intrafraction motion in routine clinical practice. The delivered dose to target volumes and organs at risk in each of the treatment fractions was assessed by incorporating the observed target positions into the original treatment plan. Results: In 27 of 30 patients, at least one gating event was observed, with a total of 177 occurrences of position deviation detected in 146 of 619 treatment fractions. In 5 mm, 4 mm, and 3 mm position tolerance cohorts, the position deviations were observed in 13%, 24%, and 33% of treatment fractions, respectively. Overall, the mean (range) deviation of -0.4 (-7.2 to 5.3) mm, -0.9 (-6.1 to 15.6) mm, and -1.7 (-7.0 to 6.1) mm was observed in Left-Right, Anterior-Posterior, and Superior-Inferior directions, respectively. The prostate CTV D99 would have been reduced by a maximum value of 1.3 Gy compared to the planned dose if position deviations were uncorrected, but with corrections, it was 0.3 Gy. Similarly, PTV D98 would have been reduced by a maximum value of 7.6 Gy uncorrected, with this difference reduced to 2.2 Gy with correction. The V60 to the rectum increased by a maximum of 1.0% uncorrected, which was reduced to 0.5%. Conclusion: Online target position monitoring for conventional fractionation prostate radiotherapy was successfully implemented on a standard Linear accelerator using an in-house developed position monitoring software, with an improvement in resultant dose to prostate target volume.

Evaluation of Tooth Movement Accuracy with Aligners: A Prospective Study.

Background. Clear aligners treatment (CAT) is a common solution in orthodontics to treat both simple and complex malocclusions. This study aimed to evaluate the predictability of CAT, comparing the virtually planned and the achieved tooth movement at the end of stage 15, which is often the time of first refinement. Methods. Seventeen patients (mean age: 28.3 years) were enrolled in the study. Torque, tip and rotation were analyzed in 238 maxillary teeth on digital models at Pre-treatment (T0), at the end of stage 15 (T15) and at virtually planned stage 15 (T15i). Prescription, Achieved movement and performance values were calculated to compare the virtually planned and the clinical tooth position. Data were analyzed by means of Student's t test with a level of significance set at p < 0.05. Results. The largest iper-performance was the torque correction of the second molars (+2.3° ± 3.1°), the greatest under-performance was the tip correction of the first molars (−2.3° ± 3.3°), while rotation corrections of all the teeth showed more accurate performance. No significant differences were found between mean Prescription and mean Achieved movement for all the assessed movements (p < 0.05). Conclusions. An accurate evaluation of CAT after the 15th aligner is fundamental in order to individuate the movements that are not matching the digital set-up.

Feasibility and Significance of Dose Adaptation via Linear Couch Translations to Correct for Rotational Shifts During Frameless Brain Radiosurgery with the Gamma Knife Icon™.

OBJECTIVE: The present study aimed to examine the technical feasibility and effectiveness of adapting the radiation dose distributions with three-dimensional (3D) linear couch translations in contrast to full six-dimensional couch maneuvers to correct for rotational shifts during frameless radiosurgical treatment with the Gamma Knife Icon™ (Elekta AB; Stockholm, Sweden). METHODS: The original magnetic resonance images used for radiosurgery treatment planning (15 targets) were digitally processed to simulate rotational shifts of ±1, ±2, ±3, ±5, and ±10 degrees in the transverse plane and imported back into Leksell GammaPlan® (Elekta AB), creating "uncorrected" treatment plans. In addition, geometrically optimized 3D translation shifts were consequently applied to each isocenter in all "uncorrected" treatment plans to account for systematically introduced rotational shifts and to produce "corrected" treatment plans. The differences in the dose distribution between the original treatment plans and the "uncorrected" and "corrected" treatment plans were calculated and compared at each rotational shift position. RESULTS: The "uncorrected" treatment plans resulted in a significant deterioration in target coverage (by 8-72%) and selectivity (by 2-42%), with some targets being missed completely with rotations of ±3 or more degrees. In contrast, in all "corrected" treatment plans, the average decreases in target coverage and selectivity were only 1% (maximum values 4-5%). CONCLUSION: Applications of 3D linear couch translations successfully overcome gross uncertainties in dose distributions caused by up to ±10 degrees of rotational shifts in a target. As a result, rapid dose adaptation with 3D couch translations is unique and effective for frameless radiosurgery with the Gamma Knife Icon™.

Accuracy of automatic structure propagation for daily magnetic resonance image-guided head and neck radiotherapy.

BACKGROUND AND PURPOSE: Deformable image registration (DIR) and contour propagation are used in daily online adaptation for hybrid MRI linac (MRL) treatments. The accuracy of the propagated contours may vary depending on the chosen workflow (WF), affecting the amount of required manual corrections. This study investigated the impact of three different WFs of contour propagations produced by a clinical treatment planning system for a high-field MRL on head and neck cancer patients. METHODS: Seventeen patients referred for curative radiotherapy for oropharyngeal cancer underwent standard CT-based dose planning and MR scans in the treatment position for planning (pMR), and at the 10th (MR10), 20th (MR20) and 30th (MR30) fraction (±2). The primary tumour, a metastatic lymph node and 8 organs at risk were manually delineated on each set of T2 weighted images. Delineations were repeated one month later on the pMR by the same observer to determine the intra-observer variation (IOV). Three WFs were used to deform images in the treatment planning system for the high-field MRL: In WF1, only the planning image and contours were used as a reference for DIR and propagation to MR10,20,30. The most recently acquired image set prior to the daily images was deformed and uncorrected (WF2) versus manually corrected (WF3) structures propagated to the session image. Dice similarity coefficient (DSC), mean surface distance (MSD) and Hausdorff distance (HD) were calculated for each structure in each model. RESULTS: Population median DSC, MSD and HD for WF1 and WF3 were similar and slightly better than for WF2. WF3 provided higher accuracy than WF1 for structures that are likely to shrink. All DIR workflows were less accurate than the IOV. CONCLUSIONS: WF1 and WF3 provide higher accuracy in structure propagation than WF2. Manual revision and correction of propagated structures are required for all evaluated workflows.

Neurological outcome and memory performance in patients with 10 or more brain metastases treated with frameless linear accelerator (LINAC)-based stereotactic radiosurgery.

PURPOSE: To assess the neurocognitive function and neurological toxicity of frameless linear accelerator (LINAC)-based stereotactic radiosurgery (SRS) in patients with 10 or more brain metastases (BM). PATIENTS AND METHODS: Forty consecutive adult patients who received SRS for ten or more 10 BM < 3 cm in maximum size were evaluated. All plans were generated using a single-isocenter multiple-target (SIMT) SRS technique with doses of 22 Gy for lesions < 2 cm and 16-18 Gy for those ≥ 2 cm in size. Survival analyses were estimated by Kaplan-Meier method from the date of SRS. Neurocognitive function using the Hopkins verbal learning test-revised (HVLT-R) and activity of daily living scale (ADLS) were collected prospectively at baseline and at 3,6 and 12-month follow-up. Toxicity was assessed by the National Cancer Institute Common Toxicity Criteria for Adverse Events (Version 5.0). RESULTS: With a median follow-up of 10.8 months, 1-year survival and local control rates were 65% and 86%, respectively. Grade 2 or 3 toxicity occurred in eleven patients, being associated with radiological changes suggestive of radiation necrosis in seven patients. Three months after SRS, the mean relative decline was 14.2% for HVLT-R delayed recall, 12.3% for HVLT-R recognition, and 9.8% for HVLT-R total recall. A significant deterioration of HVLT-R scores ranged from 5.5 to 18.7% of patients at different time points. ADLS scores declined over time, but changes were not significant. CONCLUSIONS: SRS is an effective and safe approach for patients with 10 or more BM able to maintain the pretreatment neurocognitive function in the majority of patients.

Advantages of tracking no less than three gold markers in radiotherapy with CyberKnife / 中华放射肿瘤学杂志

Objective To analyze the differences between CyberKnife radiotherapy with different numbers of gold markers.Methods A total of 424 patients undergoing CyberKnife with gold markers from 2013 to 2014 were enrolled and analyzed.In these patients,330 patients with no less than 3 gold markers were assigned to observation group and 94 patients with less than 3 gold markers were assigned to control group.The setup error and treatment error were recorded and analyzed for each patient.Results The mean setup error and mean treatment error were 0.031 mm and 0.314 mm in the observation group and 0.057 mm and 1.122 mm in the control group,respectively.Conclusion Tracking no less than 3 gold markers can substantially improve the accuracy and quality of treatment.

A comprehensive evaluation of treatment accuracy, including end-to-end tests and clinical data, applied to intracranial stereotactic radiotherapy.

BACKGROUND AND PURPOSE: A methodology is presented to quantify the uncertainty associated with linear accelerator-based frameless intracranial stereotactic radiotherapy (SRT) combining end-to-end phantom tests and clinical data. METHODS AND MATERIALS: The following steps of the SRT chain were analysed: planning computed tomography (CT) and magnetic resonance (MR) scans registration, target volume delineation, CT and cone beam CT (CBCT) registration and intrafraction-patient displacement. The overall accuracy was established with an end-to-end test. The measured uncertainties were combined, deriving the total systematic (ΣT) and random (σT) error components, to estimate the GTV-PTV margin. RESULTS: The uncertainty in the MR-CT registration was on average 0.40mm (averaged over AP, CC and LR directions). Rotational variations were smaller than 0.5° in all directions. Interobser variation in GTV delineation was on average 0.29mm. The uncertainty in the CBCT-CT registration was on average 0.15mm. Again, rotational variations were smaller than 0.5° in all directions. The systematic and random intrafraction displacement errors were on average 0.55mm and 0.45mm, respectively. The systematic and random positional errors from the end-to-end test were on average 0.49mm and 0.53mm, respectively. Combining these uncertainties resulted in an average ΣT=0.9mm and σT=0.7mm and an average GTV-PTV margin of 2.8mm. CONCLUSION: This comprehensive methodology including end-to-end tests enabled a GTV-PTV margin calculation considering all sources of uncertainties. This generic method can also be used for other treatment sites.

Detection and correction of the accuracy of gamma knife treatment positioned by MRI / 中华放射肿瘤学杂志

Objective To investigate MRI localization the accuracy and correct the deviation for gamma knife treatment.Methods With 25-point-matrix tank,the deviation of MRI localization and its regularities could be identified after the comparison between the coordinates of MRI localization and the ones which have already been verified by CT within the deviation of 0.5 mm.Then the original MRI coordinates will be corrected by the acquired mean deviation and the geometric distortion of images.Afterwards the corrected coordinates will be compared with the standard ones and finally validated by exposure film.Results There are no significant deviations on x-and z-axis after measurement in three hospitals,y-axis,however,bears deviation of (1.94 ±0.45) mm for hospital A,(-2.22 ±0.29) mm for hospital B,(-1.25 ±0.21) mm for hospital C,respectively.Furthermore there also exists geometric distortion of 1％ on y-axis in hospital A.The corrected coordinates on y-axis (Yc) will be calculated from the formula:Yc =(Y-M) + GD (Y0-Y) (Y:the original coordinates on y-axis,M:the mean of deviation on y-axis,GD:the geometric distortion,Y0:the coordinate on y-axis of the central point among the 25-point matrix).Once completed,the corrected coordinates of MRI localization is of no significant difference with the standard coordinates verified by CT.Even the deviation of focal spot on validation film is within 0.5 mm.Conclusions The 25-point-matrix tank in the multi-point measurement of the accuracy and the correction of deviation for gamma knife treatment is feasible to determine whether MRI can be utilized in the localization for head gamma knife treatment.