Study of the radiofrequency-induced heating inside the human head with dental implants at 7 T.

Conductive dental implants are commonly used in restorative therapy to replace missing teeth in patients. Ensuring the radiofrequency (RF) safety of these patients is crucial when performing 7 T magnetic resonance scans of their heads. This study aimed to investigate RF-induced heating inside the human head with dental implants at 7 T. Dental implants and their attachments were fabricated and integrated into an anatomical head model, creating different measurement configurations (MCs). Numerical simulations were conducted using a 7 T transmit coil loaded with the anatomical head model, both with and without dental implants. The maximum temperatures inside the head for various MCs were computed using the maximum permissible input powers (MPIPs) obtained without dental implants and compared with published limits. Additionally, the MPIPs with dental implants were calculated for scenarios where the temperature limits were exceeded. The maximum temperatures observed inside the head ranged from 38.4°C to 39.6°C. The MPIPs in the presence of dental implants were 81.9%-97.3% of the MPIPs in the absence of dental implants for scenarios that exceeded the regulatory limit. RF-induced heating effect of the dental implants was not significant. The safe scanning condition in terms of RF exposure was achievable for patients with dental implants. For patients with conductive dental implants of unknown configuration, it is recommended to reduce the input power by 18.1% of MPIP without dental implants to ensure RF safety.

Evaluation of fixed-jaw IMRT and tangential partial-VMAT radiotherapy plans for synchronous bilateral breast cancer irradiation based on a dosimetric study.

PURPOSE: To investigate the fixed-jaw intensity-modulated radiotherapy (F-IMRT) and tangential partial volumetric modulated arc therapy (tP-VMAT) treatment plans for synchronous bilateral breast cancer (SBBC). MATERIALS AND METHOD: Twelve SBBC patients with pTis-2N0M0 stages who underwent whole-breast irradiation after breast-conserving surgery were planned with F-IMRT and tP-VMAT techniques prescribing 42.56 Gy (2.66 Gy*16f) to the breast. The F-IMRT used 8-12 jaw-fixed tangential fields with single (sF-IMRT) or two (F-IMRT) isocenters located under the sternum or in the center of the left and right planning target volumes (PTVs), and tP-VMAT used 4 tangential partial arcs with two isocenters located in the center of the left and right PTVs. Plan evaluation was based on dose-volume histogram (DVH) analysis. Dosimetric parameters were calculated to evaluate plan quality; total monitor units (MUs), and the gamma analysis for patient-specific quality assurance (QA) were also evaluated. RESULTS: For PTVs, the three plans had similar Dmean and conformity index (CI) values. F-IMRT showed a slightly better target coverage according to the V100% values and demonstrated an obvious reduction in V105% and Dmax compared with the values observed for sF-IMRT and tP-VMAT. Compared with tP-VMAT, sF-IMRT was slightly better in terms of V100% , V105% and Dmax . In addition, F-IMRT achieved the best homogeneity index (HI) values for PTVs. Concerning healthy tissue, tP-VMAT had an advantage in minimizing the high dose volume. The MUs of the tP-VMAT plan were decreased approximately 1.45 and 1 times compared with the sF-IMRT and F-IMRT plans, respectively, and all plans passed QA. For the lungs, heart and liver, F-IMRT achieved the smallest values in terms of Dmean and showed a significant difference compared with tP-VMAT. Simultaneously, sF-IMRT was also superior to tP-VMAT. For the coronary artery, tP-VMAT achieved the lowest Dmean , while the value for F-IMRT was 2.24% lower compared with sF-IMRT. For all organs at risk (OARs), tP-VMAT was superior at the high dose level. In contrast, sF-IMRT and F-IMRT were obviously superior at the low dose level. The sF-IMRT and F-IMRT plans showed consistent trends. CONCLUSION: All treatment plans for the provided techniques were of high quality and feasible for SBBC patients. However, we recommend F-IMRT with a single isocenter as a priority technique because of the tremendous advantage of local hot spot control in PTVs and the reduced dose to OARs at low dose levels. When the irradiated dose to the lungs and heart exceed the clinical restriction, two isocenter F-IMRT can be used to maximize OAR sparing. Additionally, tP-VMAT can be adopted for improving cold spots in PTVs or high-dose exposure to normal tissue when the interval between PTVs is narrow.

Micro-invasive surgery combined with intraoperative radiotherapy for the treatment of spinal metastasis.

PURPOSE: This is a retrospective analysis of the strategy and clinical results of surgery combined with intraoperative radiotherapy (IORT) to treat spinal metastases. METHODS: We delivered tumour-conformal IORT in 40 patients with 52 metastatic vertebrae based on our surgical classification system. The strategies were evaluated with respect to neurologic function and spinal stability. The EORTC QLQ-BM22, visual analogue scale (VAS) and the Frankel Scale were used to assess quality of life, pain and neurologic function. Local control was evaluated every 3 months using X-rays and MRI. RESULTS: Micro-invasive IORT was performed in 42 vertebrae (80.8%), and open surgery with IORT was performed in 10 vertebrae (19.2%). Single-level, 2-level and 3-level IORT was performed in 30, 8 and 2 cases, respectively. The delivered dose was 9.2 ± 3.6 Gy (8-15 Gy) with a depth of 10.1 ± 2.1 mm. The actual IORT treatment time was 5 min and 16 s. The follow-up period was 6-23 months (mean: 12.5 months). The local control rate was 92.3%. The EORTC QLQ-BM22 scores showed that patients had significant improvements in pain location, degree and function after treatment (P < 0.01). Thirty-five patients (89.7%) achieved pain relief throughout the follow-up period. VAS scores were significantly reduced by 3.4 points 3 months after treatment. Neurological function was improved in 7 patients (87.5%). No radiation-related complications were observed. CONCLUSIONS: Surgery combined with tumour-conformal IORT can effectively relieve pain, achieve good local control and improve QOL.

Error detection using EPID-based 3D in vivo dose verification for lung stereotactic body radiotherapy.

PURPOSE: To investigate the error detectability limitations of an EPID-based 3D in vivo dosimetry verification system for lung stereotactic body radiation therapy (SBRT). METHODS: Thirty errors were intentionally introduced, consisting of dynamic and constant machine errors, to simulate the possible errors that may occur during delivery. The dynamic errors included errors in the output, gantry angle and MLC positions related to gantry inertial and gravitational effects, while the constant errors included errors in the collimator angle, jaw positions, central leaf positions, setup shift and thickness to simulate patient weight loss. These error plans were delivered to a CIRS phantom using the SBRT technique for lung cancer. Following irradiation of these error plans, the dose distribution was reconstructed using iViewDose™ and compared with the no error plan. RESULTS: All errors caused by the central leaf positions, dynamic MLC errors, Jaw inwards movements, setup shifts and patient anatomical changes were successfully detected. However, dynamic gantry angle and collimator angle errors were not detected in the lung case due to the rotation-symmetric target shape. The results showed that the γmean and γpassrate indicators can detect 13 (81.3%) and 14 (87.5%) of the 16 errors respectively without including the gantry angle error, collimator angle error and output error. CONCLUSIONS: In summary, iViewDose™ is an appropriate approach for detecting most types of clinical errors for lung SBRT. However, the phantom results also showed some detectability limitations of the system in terms of dynamic gantry angle and constant collimator angle errors.

Dosimetric Comparison of Postmastectomy Radiotherapy Plans for Synchronous Bilateral Breast Cancer, Including Regional Lymph Node Irradiation.

BACKGROUND: To investigate the optimal radiotherapy plans for synchronous bilateral breast cancer (SBBC) patients receiving postmastectomy radiotherapy (PMRT), including regional lymph node irradiation (RNI). METHODS: For 10 SBBC patients who underwent bilateral mastectomy and received bilateral PMRT with RNI, 3 integrally optimized plans with a single isocenter were designed for each patient in this retrospective study: intensity-modulated radiation therapy (IMRT) with 9 fixed beams (9F-IMRT), volumetric-modulated arc therapy (VMAT) with 2 pairs of half arcs (2F-VMAT), VMAT with 2 pairs of outer tangential arcs and 1 pair of 200-degree arcs (3F-VMAT). The paired t-test (in the case of normal variables) and Friedman's test (in the case of nonnormal variables) were applied to compare the planning target volumes (PTVs) and organs at risk (OARs) values of the 3 techniques. RESULTS: The 3 techniques provided adequate target dose coverage and comparable results for PTVs. For OARs, 3F-VMAT yielded the lowest mean or median values of the left lung (15.02 ± 1.57 Gy) and right lung (14.91 ± 1.14 Gy), heart (6.19 (1.96) Gy), coronary artery (15.96 ± 5.76 Gy) and liver (8.10 ± 2.70 Gy) which were significantly different from those of 9F-IMRT and 2F-VMAT. The percentages of volume at various doses (V5, V10, V20, and V30) of 3F-VMAT plans were also lower than or comparable with those of 9F-IMRT and 2F-VMAT. The monitor units (MUs) of 3F-VMAT were 31% higher than those of 9F-IMRT and comparable with those of 2F-VMAT; however, there were time savings and halved beam-on times (BOTs) compared to 9F-IMRT. CONCLUSIONS: The 3F-VMAT plan yielded comparable target coverage compared with 9F-IMRT and 2F-VMAT, was superior in dose sparing of normal tissues and enabled shorter BOTs, improving treatment efficiency. In our research, 3F-VMAT was the optimal radiotherapy technique for SBBC patients receiving PMRT including RNI.

Dosimetric Comparison of Commonly Used Volumetric Modulated Arc Therapy Field Arrangements Based on Flattening Filter-Free Beams for Synchronous Bilateral Breast Carcinoma Radiation Therapy.

PURPOSE: Flattening filter-free (FFF)-based volumetric modulated arc therapy (VMAT) has been shown to be feasible and significantly improves treatment efficiency and lung protection for synchronous bilateral breast irradiation (SBBI). This research compared the commonly used VMAT field arrangements using FFF beams. METHODS: Twenty-eight patients underwent SBBI were retrospectively enrolled to design irradiation plans using tangential arc VMAT (taVMAT), half arc VMAT (haVMAT), and large arc VMAT (laVMAT). Dosimetric and delivery parameters of all designed plans were recorded and compared. RESULTS: Comparable target volume coverage was observed for all field arrangements. taVMAT significantly reduced the dose to spinal cord and the volume covered by 5 Gy (V5Gy) and V7Gy of the lungs while decreasing the conformity index of the target volume. It also increased the volume covered by 105% of the prescription dose (V105%) and V107% of the target volume. haVMAT considerably decreased V20 Gy and V30 Gy of the lungs, mean dose (Dmean) and V30 Gy of the heart and the liver. It also notably reduced Dmean and V40 Gy of the left anterior descending coronary artery while increasing the beam-on time. laVMAT significantly reduced the mean treatment time (range, 113-117 seconds) compared with the other field arrangements. CONCLUSIONS: There were distinct differences in various dosimetric and delivery parameters for different field arrangements, highlighting the importance of selecting the appropriate field arrangement based on specific treatment goals and considerations. This study contributes valuable insights into the use of FFF-based VMAT techniques in SBBI.

Amifostine-Loaded Nanocarrier Traverses the Blood-Brain Barrier and Prevents Radiation-Induced Brain Injury.

Radiation-induced brain injury (RIBI) is a severe, irreversible, or even life-threatening cerebral complication of radiotherapy in patients with head and neck tumors, and there is no satisfying prevention and effective treatment available for these patients. Amifostine (AMF) is a well-known free radical scavenger with demonstrated effectiveness in preventing radiation-induced toxicity. However, the limited permeability of AMF across the blood-brain barrier (BBB) when administered intravenously reduces the effectiveness of AMF in preventing RIBI. Herein, we construct a nanoparticle (NP) platform for BBB delivery of AMF. AMF is conjugated with 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-n-[poly(ethylene glycol)]-hydroxy succinamide [DSPE-PEG-NHS, PEG M 2000], and the product is DSPE-PEG-AMF. Then, the nanoparticles (DAPP NPs) were formed by self-assembly of poly(lactic-co-glycolic acid) (PLGA), DSPE-PEG-AMF, and polysorbate 80 (PS 80). PEG shields the nanoparticles from blood clearance by the reticuloendothelial system and lengthens the drug circulation time. PS 80 is used to encapsulate nanoparticles for medication delivery to the brain. The results of our study showed that DAPP NPs were able to effectively penetrate the blood-brain barrier (BBB) in healthy C57BL/6 mice. Furthermore, in a well-established mouse model of X-knife-induced brain injury, treatment with DAPP NPs (corresponding to 250 mg/kg AMF) was found to significantly reduce the volume of brain necrosis compared to mice treated with AMF (250 mg/kg). Importantly, the use of DAPP NPs was also shown to significantly mitigate the effects of radiation-induced neuronal damage and glial activation. This work presents a convenient brain-targeted AMF delivery system to achieve effective radioprotection for the brain, providing a promising strategy with tremendous clinical translation potential.

Synchronous bilateral breast carcinoma irradiation: A comparative investigation between flattened and unflattened beams.

Synchronous bilateral breast carcinoma (SBBC) radiotherapy is a very complicated and time-consuming process. Considering the advantages of unflattened (FFF) beams at a high dose rate, this work investigated the feasibility of FFF beam application in SBBC radiotherapy and compared the advantages between FFF and flattened (FF) beams. CT images of 13 patients with SBBC were retrospectively collected to design intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) plans using FF and FFF beams. Dosimetric verification was applied for each plan. The target volume metrics, dose received by organs at risk (OARs), and delivery parameter of the plans were documented. All plans met the universal tolerance limits in dosimetric verification. FFF decreased the volume to receive 5 Gy (V5Gy), V7Gy, and mean dose of the left lung but slightly increased the V30Gy of the liver for VMAT and decreased the V17Gy and V20Gy of the right lung for IMRT. No remarkable differences between FF and FFF were found in the other investigated OARs and all the investigated target volume metrics. The mean treatment times of FFF were 66 and 45 s shorter than those of FF for IMRT and VMAT, respectively. FFF beams were feasible and had advantages in reducing treatment time and protecting the lung while maintaining the target volume metrics in SBBC irradiation.

Contouring the accessory parotid gland and major parotid glands as a single organ at risk during nasopharyngeal carcinoma radiotherapy.

Background and purpose: No research currently exists on the role of the accessory parotid gland (APG) in nasopharyngeal carcinoma (NPC). We thereby aimed to assess the effects of APG on the dosimetry of the parotid glands (PGs) during NPC radiotherapy and evaluate its predictive value for late xerostomia. Material and methods: The clinical data of 32 NPC patients with radiological evidence of the APG treated at Sun Yat-sen Memorial Hospital between November 2020 and February 2021 were retrospectively reviewed. Clinically approved treatment plans consisted of only the PGs as an organ at risk (OAR) (Plan1), while Plan2 was designed by considering the APG as a single organ at risk (OAR). The APG on Plan1 was delineated, and dose-volume parameters of the PGs alone (PG-only) and of the combined structure (PG+APG) were analyzed in both plans. The association of such dosimetric parameters in Plan1 with xerostomia at 6-9 months post-radiotherapy was further explored. Results: Fifty APGs were found, with a mean volume of 3.3 ± 0.2 ml. Significant differences were found in all dosimetric parameters between Plan1 and Plan2. The mean dose and percentage of OAR volumes receiving more than 30 Gy significantly reduced in Plan1 itself (PG-only vs. PG+APG, 39.55 ± 0.83 Gy vs. 37.71 ± 0.75 Gy, and 62.00 ± 2.00% vs. 57.41 ± 1.56%, respectively; p < 001) and reduced further in Plan2 (PG+APG, 36.40 ± 0.74 Gy, and 55.54 ± 1.61%, respectively; p < 0.001). Three additional patients met the dose constraint in Plan1, which increased to seven in Plan2. With APG included, the predictive power of the dosimetric parameters for xerostomia tended to improve, although no significant differences were observed. Conclusion: APG is anatomically similar to the PGs. Our findings suggest the potential benefits of treating the APG and PGs as a single OAR during radiotherapy (RT) of NPC by improving PG sparing.

Grafted Neural Stem Cells Show Lesion-Specific Migration in Radiation-Injured Rat Brains.

Neural stem cells (NSCs) exhibit preferential homing toward some types of brain lesion, but their migratory property during radiation brain injury (RBI) remains unexplored. Here, we use the superparamagnetic iron oxide (SPIO)-labeled magnetic resonance imaging (MRI) technology to determine the migration of transplanted NSCs in two partial RBI models in real time, created by administering 30-55 Gy of radiation to the right or posterior half of the adult rat brain. SPIO-labeled NSCs were stereotactically grafted into the uninjured side one week after RBI. The migration of SPIO-labeled NSCs in live radiation-injured brains was traced by MRI for up to 28 days after engraftment and quantified for their moving distances and speeds. A high labeling efficiency (>90%) was achieved by incubating NSCs with 100µg/ml of SPIO for 12-24 hours. Upon stereotactic transplantation into the healthy side of the brain, SPIO-labeled NSCs were distinctively detected as hypointense signals on T2-weighted images (T2WI), showed sustained survival for up to 4 weeks, and exhibited directional migration to the radiation-injured side of the brain with a speed of 86-127 µm/day. The moving kinetics of grafted NSCs displayed no difference in brains receiving a high (55 Gy) vs. moderate (45 Gy) dose of radiation, but was slower in the right RBI model than in the posterior RBI model. This study shows that NSCs can be effectively labeled by SPIO and traced in vivo by MRI, and that grafted NSCs exhibit directional migration toward RBI sites in a route-dependent but radiation dose-independent manner.

New Clinical Features and Dosimetric Predictor Identification for Symptomatic Radiation Pneumonitis after Tangential Irradiation in Breast Cancer Patients.

Background: Tangential irradiation is the most popular postoperative radiotherapy technique for breast cancer. However, irradiation has been related to symptomatic radiation pneumonitis (SRP), which decreases the quality of life of patients. This study investigated the clinical features and dosimetric parameters related to SRP of the ipsilateral lung to identify risk factors for SRP in breast cancer patients after three-dimensional conformal radiation therapy (3D-CRT) with tangential fields. Material and Methods: A total of 515 breast cancer patients were evaluated and divided into two groups: the local-regional irradiation group (259 patients) and the simple local irradiation group (256 patients). Clinical symptoms were registered and patient data collected. The relationship between the incidence of SRP and dosimetric parameters for the ipsilateral lung was assessed within 6 months after 3D-CRT. Dosimetric parameters were compared using t tests. The dosimetric predictors for SRP were estimated using a logistic regression model and receiver operating characteristic curve analysis. Results: In total, 19 patients (3.7%) developed grade 2 SRP. In the local-regional irradiation group, the probability of SRP in the lung body was greater than that in the lung apex (3.9% vs. 1.5%). V20 and V30 were independent predictors for SRP in the local-regional irradiation group (odds ratio = 1.152 and 1.439, both p = 0.030), whereas only V20 was an independent predictor of SRP in the simple local irradiation group (odds ratio = 1.351, p = 0.001). With 39.8% as the optimal threshold for V20 and 25.7% for V30 for local-regional irradiation, SRP could be predicted with an accuracy of 80.3% and 79.9%, a sensitivity of 61.5% and 69.2%, and a specificity of 81.3% and 80.5%, respectively. With 20.2% as the optimal V20 threshold for simple local irradiation, SRP could be predicted with an accuracy of 88.7%, a sensitivity of 83.3% and a specificity of 89.6%. Conclusions: SRP has become a rare complication with mild symptoms and occurs mainly in the lung body. V20 and V30 may be useful dosimetric predictors to evaluate SRP risk of the ipsilateral lung in breast cancer.