Assessment of intrafractional motion of the cervix-uterus by MR-guided radiotherapy system†.

The uterus is known as one of the moving organs. We evaluated the movement of the uterus during irradiation and the effects of changes in the surrounding organs using a magnetic resonance (MR)-guided radiotherapy system. Seven patients with cervical cancer underwent pre- and posttreatment MR imaging to assess changes in the positioning of the uterus and cervix as well as the alterations in bladder and rectal volume. The study revealed that the movements of the uterus were greater than that of the cervix and showed a tendency to correlate with the bladder rather than the rectum. We also examined whether intrafractional motion could lead to insufficient dose coverage of the clinical target volume (CTV), specifically focusing on the D98% of the CTV in the uterine body and cervix. The impact of intrafractional motion on the D98% varied among patients, with one out of the seven patients experiencing an average dosimetric change of -2.6 Gy in the uterus, although larger planning target volume margins of 1.5 cm were applied, therefore, indicating the need for individualized optimal margins in each case. Online adaptive radiotherapy offers the advantage of modifying the treatment plan when irradiating moving organs, such as the uterus. However, it should be noted that this approach may result in longer overall treatment times compared with the traditional methods. Therefore, we must carefully consider the influence of intrafractional organ motions when opting for such a treatment.

Film measurement and analytical approach for assessing treatment accuracy and latency in a magnetic resonance-guided radiotherapy system.

PURPOSE: We measure the dose distribution of gated delivery for different target motions and estimate the gating latency in a magnetic resonance-guided radiotherapy (MRgRT) system. METHOD: The dose distribution accuracy of the gated MRgRT system (MRIdian, Viewray) was investigated using an in-house-developed phantom that was compatible with the magnetic field and gating method. This phantom contains a simulated tumor and a radiochromic film (EBT3, Ashland, Inc.). To investigate the effect of the number of beam switching and target velocity on the dose distribution, two types of target motions were applied. One is that the target was periodically moved at a constant velocity of 5 mm/s with different pause times (0, 1, 3, 10, and 20 s) between the motions. During different pause times, different numbers of beams were switched on/off. The other one is that the target was moved at velocities of 3, 5, 8, and 10 mm/s without any pause (i.e., continuous motion). The gated method was applied to these motions at MRIdian, and the dose distributions in each condition were measured using films. To investigate the relation between target motion and dose distribution in the gating method, we compared the results of the gamma analysis of the calculated and measured dose distributions. Moreover, we analytically estimated the gating latencies from the dose distributions measured using films and the gamma analysis results. RESULTS: The gamma pass rate linearly decreased with increasing beam switching and target velocity. The overall gating latencies of beam-hold and beam-on were 0.51 ± 0.17 and 0.35 ± 0.05 s, respectively. CONCLUSIONS: Film measurements highlighted the factors affecting the treatment accuracy of the gated MRgRT system. Our analytical approach, employing gamma analysis on films, can be used to estimate the overall latency of the gated MRgRT system.

Identifying risk characteristics using failure mode and effect analysis for risk management in online magnetic resonance-guided adaptive radiation therapy.

Background and purpose: Online magnetic resonance-guided adaptive radiotherapy (MRgART) is a new technology of radiotherapy and requires a new quality control program in many aspects. This study aimed to gain a deeper understanding of risks in online MRgART through the application of failure mode and effect analysis (FMEA) for more enhanced and effective quality assurance (QA) programs. Materials and methods: We present an FMEA conducted by a multidisciplinary team with more than two years of experience. A process map describing the whole process of online MRgART was developed and potential failure modes were identified. High-risk failure modes and their potential causes and corrective measures were also identified. Failure modes were classified into three categories, MRgRT, online ART, and conventional RT, to investigate their features. A comparison with previous studies was also conducted to gain a general perspective. Results: In total, 153 failure modes and 49 high risks were identified. Among all failure modes, 51, 63, and 66 were related to MRgRT, online ART, and conventional RT, respectively. The hazardous processes were structure segmentation, treatment planning, and treatment beam delivery. Lists of failure modes identified in this study and previous studies were presented. Based on the results, characteristics and general aspects of the risks were discussed. Conclusion: Exploring the results of the FMEA enhanced our understanding of risk characteristics to improve QA program of online MRgART.

Performance of a newly designed end-to-end phantom compatible with magnetic resonance-guided radiotherapy systems.

PURPOSE: In this study, we report on our proposed phantom based on the new end-to-end (E2E) methodology and its results. In addition, we verify whether the proposed phantom can replace conventional phantoms. METHODS: The hexagonal-shaped newly designed phantom has pockets on each side for a film dosimeter of size 80 × 90 mm2 , which is easily removable, considering the 60 Co penumbra. The new phantom comprises water, shell, and auxiliary shell phantoms. The shell and auxiliary shell materials are Solid Water HE. A mock tumor (aluminum oxide) was attached by a single prop in the water phantom and placed at the center of the new phantom. The results of a conventional E2E test were compared with those of the novel E2E test using the newly designed phantom. The irradiated film dosimeter in the novel E2E test was scanned in a flatbed scanner and analyzed using an in-house software developed with MATLAB. The irradiated field center, laser center, and mock tumor center were calculated. In the novel image-matching E2E (IM-E2E) test, image matching is performed by aligning the laser center with ruled lines. In the novel irradiation-field E2E (IF-E2E) test, the displacement of the irradiation-field center was defined as its distance from the laser center. In the composite E2E test, the overall displacement, which included the accuracy of the irradiated field and image matching, was defined as the distance between the irradiated field center and mock tumor center. In addition, using the newly designed phantom, the overall irradiation accuracy of the machine was evaluated by calculating the three-dimensional (3D) center of the irradiated field, phantom, and laser. The composite E2E test could be performed using the newly designed phantom only. RESULTS: In the IM-E2E test, the results of the conventional and novel IM-E2E tests were significantly different in each direction (left-right direction: p-value < < 0.05, anterior-posterior direction: p-value = 0.002, and superior-inferior direction: p-value = 0.002). The displacement directions were the same in both the conventional and novel IM-E2E tests. In the analysis of the IF-E2E test, no significant difference was evident between the results in each direction. Moreover, the displacement directions were the same in the conventional and novel IF-E2E tests, except for the left-right lateral direction of head three. In addition, the 3D analysis results of the novel IF-E2E test were less than 1 mm in all directions. In the analysis of the composite E2E test, the maximum displacement was 1.4 mm in all directions. In addition, almost all results of 3D analysis for the composite E2E test were less than 1 mm in all directions. CONCLUSION: The newly designed E2E phantom simplifies the E2E test for MRIdian, and is a possible alternative to the conventional E2E test. Furthermore, we can perform the previously unfeasible composite E2E tests that include the entire treatment process.

Dosimetric effect of the intestinal gas of online adaptive stereotactic body radiotherapy on target and critical organs without online electron density correction for pancreatic cancer.

OBJECTIVE: This study aimed to assess the dosimetric effect of intestinal gas of stereotactic magnetic resonance (MR)-guided adaptive radiation therapy (SMART) on target and critical organs for pancreatic cancer without online electron density correction (EDC). METHODS: Thirty pancreatic cancer patients who underwent online SMART were selected for this study. The treatment time of each stage and the total treatment time were recorded and analyzed. The concerned dose-volume parameters of target and organs-at-risk (OAR) were compared with and without an intestinal gas EDC using the Wilcoxon-signed rank test. Analysis items with p value < 0.05 were considered statistically significant. The relationships between dosimetric differences and intestinal gas volume variations were investigated using the Spearman test. RESULTS: The average treatment time was 82 min, and the average EDC time was 8 min, which accounted for 10% of the overall treatment time. There were no significant differences in CTV (GTV), PTV, bowel, stomach, duodenum, and skin (p > 0.05) with respect to dose volume parameters. For the Dmax of gastrointestinal organs (p = 0.03), the mean dose of the liver (p = 0.002) and kidneys (p = 0.03 and p = 0.04 for the left and right kidneys, respectively), there may be a risk of slight overestimation compared with EDC, and for the Dmax of the spinal cord (p = 0.02), there may be a risk of slight underestimation compared with EDC. A weak correlation for D95 in the PTV and D0.5 cc in the duodenum was observed. CONCLUSION: For patients with similar inter-fractional intestinal gas distribution, EDC had little dosimetric effects on the D0.5 cc of all GI organs and dose volume parameters of target in most plans. ADVANCES IN KNOWLEDGE: By omitting the EDC of intestinal gas, the online SMART treatment time can be shortened.

Establishment of postal audit system in intensity-modulated radiotherapy by radiophotoluminescent glass dosimeters and a radiochromic film.

We developed an efficient postal audit system to independently assess the delivered dose using radiophotoluminescent glass dosimeters (RPLDs) and the positional differences of fields using EBT3 film at the axial plane for intensity-modulated radiotherapy (IMRT). The audit phantom had a C-shaped target structure as a planning target volume (PTV) with four measurement points for the RPLDs and a cylindrical structure as the organ at risk (OAR) for one measurement point. The phantoms were sent to 24 institutions. Point dose measurements with a 0.6 cm3 PTW farmer chamber were also performed to justify glass dosimetry in IMRT. The measured dose with the RPLDs was compared to the calculated dose in the institution's treatment planning system (TPS). The mean ±â€¯1.96σ of the ratio of the measured dose with the RPLDs to the farmer chamber was 0.997 ±â€¯0.024 with no significant difference (p = .175). The investigations demonstrated that glass dosimetry was reliable with a high measurement accuracy comparable to the chamber. The mean ±â€¯1.96σ for the dose differences with a reference of the TPS dose for the PTV and the OAR was 0.1 ±â€¯2.5% and -2.1 ±â€¯17.8%, respectively. The mean ±â€¯1.96σ for the right-left and the anterior-posterior direction was -0.9 ±â€¯2.8 and 0.5 ±â€¯1.4 mm, respectively. This study is the first report to justify glass dosimetry for implementation in IMRT audit in Japan. We demonstrate that our postal audit system has high accuracy with a high-level criterion of 3%/3 mm.

Observation of apoptosis and bone lamella structures in the human mastoid.

HYPOTHESIS: To investigate the localization of apoptotic cells and the lamellar bone structure in mastoid bone tissue, focusing on the mechanism of the development of mastoid pneumatization in humans. BACKGROUND: The biological mechanism of poor development of the mastoid air cells found in patients with otitis media (OM) has not yet been fully clarified, as there have been few immunohistochemical research studies to examine the cell biology involved. METHODS: We evaluated the localization of apoptotic cells and the lamellar bone structure in 112 human mastoid bones harvested during various ear surgeries from 57 patients with OM and 55 patients without OM. We used the TdT-mediated dUTP nick end-labeling (TUNEL) method and a polarizing microscope for observing the apoptotic cells and lamellar bone structure, respectively. RESULTS: The TUNEL-positive cell ratio in an arbitrary 500 cells in the specimen (apoptotic index: AI) was 13.8 in the healthy group and 1.2 in the OM group (Mann-Whitney U test, p < 0.001). From their localization, these apoptotic cells were considered to be osteocytes. The observation of lamellar structures revealed many eroded surfaces in the circumference of the appositional bone in the healthy group. In contrast, apposition of bone without an eroded surface was evident in the bone circumference in the OM group. CONCLUSION: Apoptosis of osteocytes was significantly suppressed in the mastoid bone of the OM patients. Apoptotic osteocytes may be one of the signals of bone resorption in the process of development of the mastoid air cells. The lamellar structure of the mastoid bone suggested that poor development of the mastoid air cells was caused by decreased resorption of the appositional bone.

Subjective visual vertical test in patients with chronic dizziness without abnormal findings in routine vestibular function tests.

CONCLUSION: The subjective visual vertical (SVV) test can detect abnormality of the otolithic organs and the graviceptive pathways present in a considerable number of patients having dizziness but presenting no abnormal findings in conventional vestibular function tests. OBJECTIVE: To evaluate whether the SVV test can detect dysfunction of the otolithic organs and perception of gravity in patients with dizziness having no abnormal finding on routine tests for the vestibular system. PATIENTS AND METHODS: Forty-four patients who complained of chronic dizziness but had no abnormal finding on routine tests for vestibular system and on brain MRI studies were selected between 2004 and 2006. SVV tests were performed on these patients. Patients with chronic dizziness caused by apparent psychogenic disorders, such as depression, were excluded. RESULTS: Among the 44 patients, 3 showed abnormal tilts of SVV. The latter three patients had deep white matter hyperintensities on their MRI, probably due to aging.

A case with posterior fossa epidermoid cyst showing audiovestibular symptoms caused by insufficiency of anterior inferior cerebellar artery--usefulness of free DICOM image viewing and processing software.

A 58-year-old Japanese man suddenly suffered from vertigo. On physical examination, left-beating horizontal torsional spontaneous nystagmus was observed; the direction did not change with gaze. Other neurotological examinations revealed findings within normal limits except the left side sensorineural hearing loss of approximately 32 dB on average. Diffusion-weighted MRI revealed no infarction in the brain, but demonstrated an epidermoid cyst in the left cerebello-pontine cistern region. Using free digital imaging and communications in medicine (DICOM) image viewing and processing software, it was found that the epidermoid cyst clearly compressed the left anterior inferior cerebellar artery (AICA). Therefore, we speculated that insufficiency of the left AICA caused his audiovestibular symptoms. This new technique used in the present study was considered useful when the site responsible for vertigo is suspected in the cerebello-pontine angle, where anatomic relationships between the nerves and the vessels are complicated.

Subjective visual vertical in acute attacks of Ménière's disease.

OBJECTIVES: To investigate whether or not and how often there is otolith dysfunction in an acute attack of Ménière's disease. PATIENTS: Twenty-two definite cases of unilateral Ménière's disease diagnosed in accordance with the 1995 criteria of the American Academy of Otolaryngology-Head and Neck Surgery for Ménière's disease. INTERVENTION: Subjective visual vertical (SVV) test was performed before, at, and after acute attacks on 22 patients with unilateral Ménière's disease who showed normal tilts of SVV before acute attacks. MAIN OUTCOME MEASURE: Abnormal tilts of SVV. RESULTS: Of 22 cases, 14 (63.6%) with unilateral Ménière's disease showed abnormal tilts of SVV in acute attacks. The tilts were toward the side of the affected ear in 13 (92.9%) of them. Abnormal tilts returned to normal within a few weeks after the acute attacks in 12 (85.7%) of the 14 cases with unilateral Ménière's disease. CONCLUSION: Otolith dysfunction occurred in acute attacks in a considerable number of patients with Ménière's disease. Subjective visual vertical can be used as a good tool for the evaluation of otolith dysfunction at acute attacks in patients with Ménière's disease.