Hands-on-training tailored in response to pre-questionnaire-based survey on image-guided brachytherapy effectively reduces anxiety about its implementation

This study assessed the significance of hands-on-training (HoT) and questionnaire-based surveys on 3D image-guided brachytherapy (3D-IGBT) and a combination of intracavitary and interstitial brachytherapy, the so-called 'hybrid' BT (HBT), in uterine cervical cancer. In October 2023, 29 radiation oncologists, nurses, radiologic technologists and medical physicists from 10 Japanese facilities participated in an HoT on 3D-IGBT and HBT. Questionnaires were distributed to each participant before and after the HoT, and feedback was obtained through online channels. The questionnaire response rate was 83% (24/29), with at least one participant responding from each facility. 'Insertion of applicators and needles', 'human resource shortage' and 'pain relief and sedation' were the primary concerns of radiation oncologists. 'Applicator reconstruction', ' optimization of dwell positions', ' treatment planning' and ' human resource shortages ' were the primary concerns of radiological technologists and medical physicists. The HoT content was adjusted according to the results of preliminary surveys. The concerns expressed by the participants were addressed during the lectures and practical training. Significant reductions in anxiety were observed toward all items of the 10-point self-assessment after the HoT, regardless of the profession. The average score on satisfaction with the HoT (on a 10-point scale) was 9.52 (minimum of 8 and maximum of 10). In conclusion, HoT tailored in response to a pre-questionnaire-based survey effectively reduced participants' anxiety regarding the implementation of 3D-IGBT and HBT.

Dosimetric evaluation in Helical TomoTherapy for lung SBRT using Monte Carlo-based independent dose verification software

PURPOSE

To elucidate the dosimetric errors caused by a model-based algorithm in lung stereotactic body radiation therapy (SBRT) with Helical TomoTherapy (HT) using Monte Carlo (MC)-based dose verification software.

METHODS

For 38 plans of lung SBRT, the dose calculation accuracy of a treatment planning system (TPS) of HT was compared with the results of DoseCHECK, the commercial MC-based independent verification software. The following indices were extracted to evaluate the correlation of dosimetric errors: (1) target volume, (2) average computed tomography (CT) value of the planning target volume (PTV) margin, and (3) average CT value of surrounding 2-mm area of the PTV (PTV ring). Receiver operating characteristic (ROC) analyses determined the threshold for 5% of differences in PTV D95%. Then, the 38 plans were classified into two groups using the cutoff values of ROC analysis for these three indices. Dosimetric differences between groups were statistically compared using the Mann-Whitney U test.

RESULTS

TPS of HT overestimated by more than 5% in the PTV D95% in 16 of 38 plans. The PTV ring showed the strongest correlation with dosimetric differences. The cutoff value for the target volume, the PTV margin, and the PTV ring was 14.7 cc, -754 HU, and -708 HU, respectively. The area under the curve (AUC) for the target volume, the PTV margin, and the PTV ring were 0.835, 0.878, and 0.932, respectively. Dosimetric errors more than 5% were observed when the PTV volume was less than 15 cc or when the CT value around the target was less than -700 HU.

CONCLUSION

The TPS of HT might overestimate the PTV dose by more than 5% if any the three indices in this study were below threshold. Therefore, independent verification with an MC-based algorithm should be strongly recommended for lung SBRT in HT.

Critical swallowing functions contributing to dysphagia in patients with recurrent laryngeal nerve paralysis after esophagectomy

BACKGROUND

Recurrent laryngeal nerve paralysis (RLNP) after esophagectomy can cause aspiration because of incomplete glottis closure, leading to pneumonia. However, patients with RLNP often have preserved swallowing function. This study investigated factors that determine swallowing function in patients with RLNP.

METHODS

Patients with esophageal cancer who underwent esophagectomy and cervical esophagogastric anastomosis were enrolled between 2017 and 2020. Videofluoroscopic examination of swallowing study (VFSS) and acoustic voice analysis were performed on patients with suspected dysphagia including RLNP. Dysphagia in VFSS was defined as score ≥ 3 of the 8-point penetration-aspiration scale VFSS and acoustic analysis results related to dysphagia were compared between patients with and without RLNP.

RESULTS

Among 312 patients who underwent esophagectomy, 74 developed RLNP. The incidence of late-onset pneumonia was significantly higher in the RLNP group than in the non-RLNP (18.9 vs. 8.0%, P = .008). Detailed swallowing function was assessed by VFSS in 84 patients, and patients with RLNP and dysphagia showed significantly shorter maximum diagonal hyoid bone elevation (10.62 vs. 16.75 mm; P = .003), which was a specific finding not seen in patients without RLNP. For acoustic voice analysis, the degree of hoarseness was not closely related to dysphagia. The length of oral intake rehabilitation for patients with and without RLNP was comparable if they did not present with dysphagia (8.5 vs. 9.0 days).

CONCLUSIONS

Impaired hyoid bone elevation is a specific dysphagia factor in patients with RLNP, suggesting compensatory epiglottis inversion by hyoid bone elevation is important for incomplete glottis closure caused by RLNP.

Efficacy and safety of FDG-PET for determining target volume during intensity-modulated radiotherapy for head and neck cancer involving the oral level

PURPOSE

To determine the efficacy and safety of target volume determination by 18F-fluorodeoxyglucose positron emission tomography-computed tomography (PET-CT) for intensity-modulated radiation therapy (IMRT) for locally advanced head and neck squamous cell carcinoma (HNSCC) extending into the oral cavity or oropharynx.

METHODS

We prospectively treated 10 consecutive consenting patients with HNSCC using IMRT, with target volumes determined by PET-CT. Gross tumor volume (GTV) and clinical target volume (CTV) at the oral level were determined by two radiation oncologists for CT, magnetic resonance imaging (MRI), and PET-CT. Differences in target volume (GTVPET, GTVCT, GTVMRI, CTVPET, CTVCT, and CTVMRI) for each modality and the interobserver variability of the target volume were evaluated using the Dice similarity coefficient and Hausdorff distance. Clinical outcomes, including acute adverse events (AEs) and local control were evaluated.

RESULTS

The mean GTV was smallest for GTVPET, followed by GTVCT and GTVMRI. There was a significant difference between GTVPET and GTVMRI, but not between the other two groups. The interobserver variability of target volume with PET-CT was significantly less than that with CT or MRI for GTV and tended to be less for CTV, but there was no significant difference in CTV between the modalities. Grade ≤ 3 acute dermatitis, mucositis, and dysphagia occurred in 55%, 88%, and 22% of patients, respectively, but no grade 4 AEs were observed. There was no local recurrence at the oral level after a median follow-up period of 37 months (range, 15-55 months).

CONCLUSIONS

The results suggest that the target volume determined by PET-CT could safely reduce GTV size and interobserver variability in patients with locally advanced HNSCC extending into the oral cavity or oropharynx undergoing IMRT. Trial registration UMIN, UMIN000033007. Registered 16 jun 2018, https://center6.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000037631.

Safe dose escalation and reduction of the fraction number of uterine cervical brachytherapy using a gel spacer in the rectovaginal and vesicouterine septum: A planning study

PURPOSE

To evaluate the possibility of dose escalation and reduction of fraction number in cervical brachytherapy using a gel spacer.

MATERIAL AND METHODS

Twenty patients with uterine cervical cancer treated with image-guided adaptive brachytherapy (IGABT) were selected. Hyaluronic acid gel injection (HGI) was performed in the rectovaginal and vesicouterine septum for 10 patients. The other ten patients were not with HGI. Both groups were treated with IGABT involving tandem/ovoid or cylindrical applicators along with additional interstitial needles. Dose distributions approved by radiation oncologists were retrospectively analyzed, and a dose summation of 45 Gy/25 of external beam radiation therapy and IGABT was performed. Dose constraints for D2cc of bladder, rectum, and sigmoid were 80, 70, and 70 Gy, respectively. Equivalent dose in 2-Gy fractions calculations used α/β = 10 Gy for high-risk clinical target volume (CTVHR) D90 and α/β = 3 Gy for organs at risks (OARs). As a planning study, dose distribution rescaling was conducted to deliver as much dose to CTVHR D90 as possible within the dose constraint limitation for OARs when IGABT was performed for four, three, and two fractions in both groups.

RESULTS

The median CTVHR D90 was >80 Gy in the non-HGI group and >85 Gy in the HGI group for virtual two and three fractions. Rectum D2cc was significantly lower in the HGI group for three fractions (p < 0.01).

CONCLUSIONS

In the HGI group, adequate dose delivery to CTVHR could be achieved with a reduced IGABT fraction number while meeting the dose constraints of OARs.

Dosimetric comparison of four-dimensional computed tomography based internal target volume against variations in respiratory motion during treatment between volumetric modulated arc therapy and three-dimensional conformal radiotherapy in lung stereotactic body radiotherapy

This study focused on the dosimetric impact of variations in respiratory motion during lung stereotactic body radiotherapy (SBRT). Dosimetric comparisons between volumetric modulated arc therapy (VMAT) and three-dimensional conformal radiotherapy (3DCRT) were performed using four-dimensional computed tomography (4DCT)-based internal target volumes (ITV). We created retrospective plans for ten patients with lung cancer who underwent SBRT using 3DCRT and VMAT techniques. A Delta4 Phantom + (ScandiDos, Uppsala, Sweden) was used to evaluate the dosimetric robustness of 4DCT-based ITV against variations in respiratory motion during treatment. We analyzed respiratory motion during treatment. Dose-volume histogram parameters were evaluated for the 95% dose (D95%) to the planning target volume (PTV) contoured on CT images obtained under free breathing. The correlations between patient respiratory parameters and dosimetric errors were also evaluated. In the phantom study, the average PTV D95% dose differences for all fractions were - 2.9 ± 4.4% (- 16.0 - 1.2%) and - 2.0 ± 2.8% (- 11.2 - 0.7%) for 3DCRT and VMAT, respectively. The average dose difference was < 3% for both 3DCRT and VMAT; however, in 5 out of 42 fractions in 3DCRT, the difference in PTV D95% was > 10%. Dosimetric errors were correlated with respiratory amplitude and velocity, and differences in respiratory amplitude between 4DCT and treatment days were the main factors causing dosimetric errors. The overall average dose error of the PTV D95% was small; however, both 3DCRT and VMAT cases exceeding 10% error were observed. Larger errors occurred with amplitude variation or baseline drift, indicating limited robustness of 4DCT-based ITV.

Maximum phonation time: an independent predictor of late-onset pneumonia after esophageal cancer surgery

Dysphagia after esophagectomy is a major risk factor for aspiration pneumonia, thus preoperative assessment of swallowing function is important. The maximum phonation time (MPT) is a simple indicator of phonatory function and also correlates with muscle strength associated with swallowing. This study aimed to determine whether preoperative MPT can predict postoperative aspiration pneumonia. The study included 409 consecutive patients who underwent esophagectomy for esophageal cancer between 2017 and 2021. Pneumonia detected by routine computed tomography on postoperative days 5-6 was defined as early-onset pneumonia, and pneumonia that developed later (most often aspiration pneumonia) was defined as late-onset pneumonia. The correlation between late-onset pneumonia and preoperative MPT was investigated. Patients were classified into short MPT (<15 seconds for males and <10 seconds for females, n = 156) and normal MPT groups (≥15 seconds for males and ≥10 seconds for females, n = 253). The short MPT group was significantly older, had a lower serum albumin level and vital capacity, and had a significantly higher incidence of late-onset pneumonia (18.6 vs. 6.7%, P < 0.001). Multivariate analysis showed that short MPT was an independent risk factor for late-onset pneumonia (odds ratio: 2.26, P = 0.026). The incidence of late-onset pneumonia was significantly higher in the short MPT group (15.6 vs. 4.7%, P = 0.004), even after propensity score matching adjusted for clinical characteristics. MPT is a useful predictor for late-onset pneumonia after esophagectomy.

MucoUp® as a spacer in brachytherapy for uterine cervical cancer: A first-in-human experience

We first used MucoUp®, a hyaluronic acid used in endoscopic resection, as a spacer in brachytherapy. In five cervical cancer patients, MucoUp® insertion increased a 90% dose of the high-risk CTV to over 80 Gy while decreasing the dose of organs at risk. No related adverse events were observed.

Effective clinical applications of Monte Carlo-based independent secondary dose verification software for helical tomotherapy

PURPOSE

To investigate the scope of the effective clinical application of Monte Carlo (MC)-based independent dose verification software for helical tomotherapy.

METHODS

DoseCHECK was selected as the MC-based dose calculation software. First, the dose calculation accuracy of DoseCHECK was evaluated with film and chamber measurements in a water-equivalent phantom. Second, the dose calculation accuracy was examined in several heterogeneous materials. Finally, dosimetric comparisons between DoseCHECK and the treatment planning system (TPS) were performed for clinical patient plans. Prostate IMRT, head and neck IMRT (HN), total body irradiation (TBI), and brain stereotactic radiotherapy (SRT) were evaluated.

RESULT

The DoseCHECK calculations agreed with the chamber and film measurements in the homogenous phantom. For heterogeneous phantom cases, the dose differences between DoseCHECK and TPS were within 3 %, except in air, in which large dose differences of 20 % were observed. In clinical patient plans, the median dose differences between the lung D_mean in TBI cases and the normal brain D_mean in brain SRT cases were significantly >3 %. For HN and brain SRT cases, the median target dose differences were >3 %.

CONCLUSION

Our results show that independent dose verification with the MC algorithm can detect systematic errors caused by the lack of heterogeneity correction in the TPS. In particular, MC-based independent dose verification is required for HN, TBI, and brain SRT cases in helical tomotherapy.

Generation of ozone during irradiation using medical linear accelerators: an experimental study

Background

Some patients have noted a foul odor during radiation therapy sessions, but the cause of the odor remains unknown. Since we suspected that this phenomenon is due to ozone generated by ionizing radiation, this experimental study measured ozone concentrations in the treatment room and in a coiled polyvinyl chloride (PVC) tube placed within the radiation field.

Methods

We measured ozone concentrations using an ultraviolet absorption method and an ozone monitor. A PVC tube (inner diameter 7 mm, outer diameter 10 mm) was used to mimic the environment of the nasal cavity. The tube (790 cm) was coiled and set between two 4-cm-thick (for X-rays) or 2-cm-thick (for electron beams) water-equivalent solid phantoms. The sampling tube of the ozone monitor was inserted into the PVC tube, and the joint was sealed to prevent environmental air contamination. To measure ozone concentrations in the atmosphere, the sampling tube supplied with the unit was used. A linac was used on a full-sized treatment field (40 cm × 40 cm at a source-to-axis distance of 100 cm). The effect of an electron beam on ozone concentrations was also evaluated with a full-sized treatment field (40 cm × 40 cm at a source-to-surface distance of 100 cm).

Results

Ozone levels in the treatment room were undetectable before the start of daily treatment but reached 0.008 parts per million (ppm) or more at 1 h after the start of treatment. Concentrations then remained nearly constant at 0.010–0.015 ppm throughout the day. The maximum ozone concentration in the PVC tube was only 0.006 ppm, even when it was irradiated at 2400 monitor units/min. Depending on the X-ray dose rate, the concentration increased to a maximum of 0.010 ppm with oxygen flowing into the other end of the tube at 1.5 L/min. Ozone concentrations in the PVC tube did not differ significantly between X-ray and electron-beam irradiation.

Conclusions

Only traces of ozone were found in the PVC tube that was used to mimic the nasal passages during radiation, these concentrations were too low for human perception. However, ozone concentrations did reach potentially detectable levels in the treatment room.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13014-022-02005-6.

Intrafraction stability using full head mask for brain stereotactic radiotherapy

Purpose

We investigated the immobilization accuracy of a new type of thermoplastic mask—the Double Shell Positioning System (DSPS)—in terms of geometry and dose delivery.

Methods

Thirty‐one consecutive patients with 1–5 brain metastases treated with stereotactic radiotherapy (SRT) were selected and divided into two groups. Patients were divided into two groups. One group of patients was immobilized by the DSPS (n = 9). Another group of patients was immobilized by a combination of the DSPS and a mouthpiece (n = 22). Patient repositioning was performed with cone beam computed tomography (CBCT) and six‐degree of freedom couch. Additionally, CBCT images were acquired before and after treatment. Registration errors were analyzed with off‐line review. The inter‐ and intrafractional setup errors, and planning target volume (PTV) margin were also calculated. Delivered doses were calculated by shifting the isocenter according to inter‐ and intrafractional setup errors. Dose differences of GTV D_99% were compared between planned and delivered doses against the modified PTV margin of 1 mm.

Results

Interfractional setup errors associated with the mouthpiece group were significantly smaller than the translation errors in another group (p = 0.03). Intrafractional setup errors for the two groups were almost the same in all directions. PTV margins were 0.89 mm, 0.75 mm, and 0.90 mm for the DSPS combined with the mouthpiece in lateral, vertical, and longitudinal directions, respectively. Similarly, PTV margins were 1.20 mm, 0.72 mm, and 1.37 mm for the DSPS in the lateral, vertical, and longitudinal directions, respectively. Dose differences between planned and delivered doses were small enough to be within 1% for both groups.

Conclusions

The geometric and dosimetric assessments revealed that the DSPS provides sufficient immobilization accuracy. Higher accuracy can be expected when the immobilization is combined with the use of a mouthpiece.

Clinical benefits of a swallowing intervention for esophageal cancer patients after esophagectomy

Dysphagia after esophagectomy is the main cause of a prolonged postoperative stay. The present study investigated the effects of a swallowing intervention led by a speech-language-hearing therapist (SLHT) on postoperative dysphagia. We enrolled 276 consecutive esophageal cancer patients who underwent esophagectomy and cervical esophagogastric anastomosis between July 2015 and December 2018; 109 received standard care (control group) and 167 were treated by a swallowing intervention (intervention group). In the intervention group, swallowing function screening and rehabilitation based on each patient's dysfunction were led by SLHT. The start of oral intake, length of oral intake rehabilitation, and length of the postoperative stay were compared in the two groups. The patient's subgroups in the 276 patients were examined to clarify the more effectiveness of the intervention. The start of oral intake was significantly earlier in the intervention group (POD: 11 vs. 8 days; P = 0.009). In the subgroup analysis, the length of the postoperative stay was also significantly shortened by the swallowing intervention in patients without complications (POD: 18 vs. 14 days; P = 0.001) and with recurrent laryngeal nerve paralysis (RLNP) (POD: 30 vs. 21.5 days; P = 0.003). A multivariate regression analysis identified the swallowing intervention as a significant independent factor for the earlier start of oral intake and a shorter postoperative stay in patients without complications and with RLNP. Our proposed swallowing intervention is beneficial for the earlier start of oral intake and discharge after esophagectomy, particularly in patients without complications and with RLNP. This program may contribute to enhanced recovery after surgery.

Trajectory log analysis and cone-beam CT-based daily dose calculation to investigate the dosimetric accuracy of intensity-modulated radiotherapy for gynecologic cancer

This study evaluated unexpected dosimetric errors caused by machine control accuracy, patient setup errors, and patient weight changes/internal organ deformations. Trajectory log files for 13 gynecologic plans with seven‐ or nine‐beam dynamic multileaf collimator (MLC) intensity‐modulated radiation therapy (IMRT), and differences between expected and actual MLC positions and MUs were evaluated. Effects of patient setup errors on dosimetry were estimated by in‐house software. To simulate residual patient setup errors after image‐guided patient repositioning, planned dose distributions were recalculated (blurred dose) after the positions were randomly moved in three dimensions 0–2 mm (translation) and 0°–2° (rotation) 28 times per patient. Differences between planned and blurred doses in the clinical target volume (CTV) D_98% and D_2% were evaluated. Daily delivered doses were calculated from cone‐beam computed tomography by the Hounsfield unit‐to‐density conversion method. Fractional and accumulated dose differences between original plans and actual delivery were evaluated by CTV D_98% and D_2%. The significance of accumulated doses was tested by the paired t test. Trajectory log file analysis showed that MLC positional errors were −0.01 ± 0.02 mm and MU delivery errors were 0.10 ± 0.10 MU. Differences in CTV D_98% and D_2% were <0.5% for simulated patient setup errors. Differences in CTV D_98% and D_2% were 2.4% or less between the fractional planned and delivered doses, but were 1.7% or less for the accumulated dose. Dosimetric errors were primarily caused by patient weight changes and internal organ deformation in gynecologic radiation therapy.

Utilization of native oxygen in Eu(RE)-doped GaN for enabling device compatibility in optoelectronic applications

The detrimental influence of oxygen on the performance and reliability of V/III nitride based devices is well known. However, the influence of oxygen on the nature of the incorporation of other co-dopants, such as rare earth ions, has been largely overlooked in GaN. Here, we report the first comprehensive study of the critical role that oxygen has on Eu in GaN, as well as atomic scale observation of diffusion and local concentration of both atoms in the crystal lattice. We find that oxygen plays an integral role in the location, stability, and local defect structure around the Eu ions that were doped into the GaN host. Although the availability of oxygen is essential for these properties, it renders the material incompatible with GaN-based devices. However, the utilization of the normally occurring oxygen in GaN is promoted through structural manipulation, reducing its concentration by 2 orders of magnitude, while maintaining both the material quality and the favorable optical properties of the Eu ions. These findings open the way for full integration of RE dopants for optoelectronic functionalities in the existing GaN platform.

Pathway for the Production of Neutron-Rich Isotopes around the N=126 Shell Closure

Absolute cross sections for isotopically identified products formed in multinucleon transfer in the (136)Xe+(198)Pt system at ∼8  MeV/nucleon are reported. The isotopic distributions obtained using a large acceptance spectrometer demonstrated the production of the "hard-to-reach" neutron-rich isotopes for Z<78 around the N=126 shell closure far from stability. The main contribution to the formation of these exotic nuclei is shown to arise in collisions with a small kinetic energy dissipation. The present experimental finding corroborates for the first time recent predictions that multinucleon transfer reactions would be the optimum method to populate and characterize neutron-rich isotopes around N=126 which are crucial for understanding both astrophysically relevant processes and the evolution of "magic" numbers far from stability.