Naoki Hayashi

PURPOSE: 177Lu-DOTATATE-targeted radionuclide therapy (TRT) is effective for patients with somatostatin receptor (SSTR)-positive neuroendocrine tumors; however, radiation safety regulations often necessitate hospitalization, particularly in countries with stringent discharge criteria. This study aimed to identify pretreatment factors predicting outpatient eligibility. METHODS: We retrospectively analyzed 26 patients who underwent their first cycle of 177Lu-DOTATATE TRT with complete data for analysis. The external dose rate at 1 m (EDR-1 m) was measured 6 h after administration. Patients were divided into two groups: EDR-1 m greater than or equal to 18 μSv/h and less than 18 μSv/h. Characteristics, including age, sex, BMI, body surface area, estimated glomerular filtration rate, administered dose, and tumor site, were compared. In addition, the whole-body washout rate from pretreatment SSTR imaging was evaluated as a potential predictor. Logistic regression and receiver operating characteristic (ROC) analyses were conducted. RESULTS: Fourteen of the 26 (53.8%) patients met the discharge criterion at 6 h. No significant differences were observed in demographic or clinical characteristics between groups. The median washout rate was significantly higher in those meeting the criterion (57.6 vs. 35.0%; P < 0.001). The area under the ROC curve for the washout rate was 0.929, indicating excellent predictive ability. An optimal cut-off value of 53.5% predicted same-day discharge with a sensitivity of 92.9% and specificity of 91.7%. CONCLUSION: The whole-body washout rate derived from pretreatment SSTR imaging is a strong, practical predictor for outpatient eligibility following 177Lu-DOTATATE TRT. Incorporating this simple, noninvasive marker into clinical workflow could support individualized discharge planning and improve patient access under strict radiation safety regulations.

The purpose of this study was to evaluate the diffusion of surface-guided radiation therapy (SGRT), implementation of quality control and quality assurance strategies, established clinical workflows and user perceptions regarding the benefits and limitations of SGRT in routine practice. From October to December 2024, we surveyed 880 radiotherapy institutions in Japan regarding institutional characteristics, quality assurance/quality control, computed tomography simulation, treatment procedures and general questions regarding SGRT. The survey was distributed via mailing list and through vendors, and administered via Google Forms. A total of 292 institutions responded, corresponding to a response rate of 33%. Ninety-eight institutions reported introducing SGRT, and 50 institutions had introduced it after 2022. The highest usage rate of SGRT in breast treatment was 87%. Approximately half of the institutions performed daily checks of SGRT and radiation isocenter coincidence, as well as static accuracy, whereas 6% did not perform these checks at all. The primary functions of the SGRT system were patient positioning (94%), respiratory management (78%), patient monitoring (76%) and skin marker-less techniques (69%). Many institutions reduced or eliminated skin marking, citing simplified workflows and reduced setup time. Many respondents observed that SGRT implementation reduced both setup and treatment times for breast/chest, abdomen/pelvis and extremity procedures. SGRT has been widely embraced in Japan, offering notable clinical and workflow benefits. However, because participation in this survey was voluntary, the results may overrepresent institutions with greater awareness or adoption of SGRT. Greater standardization, broader insurance coverage and ongoing technological advancements are essential to fully realize its advantages.

The patient setup using the surface-guided radiation therapy (SGRT) system differs from conventional surface marker procedures. Owing to the abundance of three-dimensional information, there may be operator variability in where to focus during the patient setup. This study aimed to clarify the differences between expert and novice operators in SGRT positioning for head and neck cases by tracking their eye movements, thereby providing data for developing efficient patient setup procedures. Six radiation therapists set up a simulated patient on the SGRT system while recording eye movements on the screen using the QG-PLUS eye-tracking system. The positioning time and number of gaze fixations on the screen were analysed, and the relationship between years of experience with SGRT, positioning time and number of gaze fixations was evaluated. No significant correlation was found between SGRT experience and positioning time (r = -0.67, p = 0.15). However, more experienced radiation therapists exhibited fewer gaze fixations per positioning session (r = -0.81, p < 0.05), indicating that they efficiently identified key positioning points. Additionally, experienced radiation therapists focused more intently on a specific screen during the latter half of positioning, suggesting a refined approach for final patient alignment verification. More experienced radiation therapists showed fewer gaze fixations and demonstrated increased attention to a specific screen during the latter half of the patient setup process, suggesting that eye-tracking technology may provide useful data for standardising patient setup procedures in SGRT patient setups.

To quantify radiation dose reduction in radiotherapy treatment-planning CT (RTCT) using a deep learning-based reconstruction (DLR; AiCE) algorithm compared with adaptive iterative dose reduction (IR; AIDR). To evaluate its potential to inform RTCT-specific diagnostic reference levels (DRLs). In this single-institution retrospective study, 4-part RTCT scans (head, head and neck, lung, and pelvis) were acquired on a large-bore CT. Scans reconstructed with IR (n = 820) and DLR (n = 854) were compared. The 75th-percentile CTDIvol and DLP (CTDIIR, DLPIR vs. CTDIDLR, DLPDLR) were determined per site. Dose reduction rates were calculated as (CTDIDLR - CTDIIR)/CTDIIR × 100% and similarly for DLP. Statistical significance was assessed by the Mann-Whitney U-test. DLR yielded CTDIvol reductions of 30.4-75.4% and DLP reductions of 23.1-73.5% across sites (p < 0.001), with the greatest reductions in head and neck RTCT (CTDIvol: 75.4%; DLP: 73.5%). Variability also narrowed. Compared with published national DRLs, DLR achieved 34.8 mGy and 18.8 mGy lower CTDIvol for head and neck versus UK-DRLs and Japanese multi-institutional data, respectively. DLR substantially lowers RTCT dose indices, providing quantitative data to guide RTCT-specific DRLs and optimize clinical workflows.

BACKGROUND: Accurate absolute dosimetry is essential for achieving high-precision proton beam therapy. Consequently, a comprehensive characterization of the ionization chamber's response properties is necessary. PURPOSE: This study aimed to evaluate the average f Q using Monte Carlo (MC) code PHITS to assess uncertainties among different MC simulation tools. Additionally, P Q values for PTW 30013, NACP-02, and PTW 31013 ionization chambers are calculated using PHITS to provide new reference data for P Q . Furthermore, a new k Q factor for PTW 31013 chamber is established using MC method, contributing to advancements in proton beam dosimetry protocols. METHODS: Monoenergetic proton beams were employed to calculate f Q , k Q , and P Q for Farmer, Semiflex, and plane-parallel chambers. The absorbed dose deposited within the sensitive volume of each chamber was determined via simulations employing PHITS, thereby providing the basis for the estimation of these factors. Computed f Q values were compared with previous reports, while k Q and P Q were benchmarked against literature and Technical Reports Series No. 398 (TRS-398) Rev.1 guideline. RESULTS: Incorporating PHITS-derived f Q values reduced the uncertainty of f ¯ Q P H I T S compared to previous findings. The k Q factor for PTW 31013 followed trends observed in cylindrical chambers with varying sensitive volumes; notably, this study represents the first MC estimation of k Q for this chamber. P Q values for values deviated by up to 1.7% from unity. CONCLUSION: The data generated in this study provide important insights for refining proton beam dosimetry, contributing to the improvement of treatment precision.