Development of shielding evaluation and management program for O-ring type linear accelerators.

The shielding parameters can vary depending on the geometrical structure of the linear accelerators (LINAC), treatment techniques, and beam energies. Recently, the introduction of O-ring type linear accelerators is increasing. The objective of this study is to evaluate the shielding parameters of new type of linac using a dedicated program developed by us named ORSE (O-ring type Radiation therapy equipment Shielding Evaluation). The shielding evaluation was conducted for a total of four treatment rooms including Elekta Unity, Varian Halcyon, and Accuray Tomotherapy. The developed program possesses the capability to calculate transmitted dose, maximum treatable patient capacity, and shielding wall thickness based on patient data. The doses were measured for five days using glass dosimeters to compare with the results of program. The IMRT factors and use factors obtained from patient data showed differences of up to 65.0% and 33.8%, respectively, compared to safety management report. The shielding evaluation conducted in each treatment room showed that the transmitted dose at every location was below 1% of the dose limit. The results of program and measurements showed a maximum difference of 0.003 mSv/week in transmitted dose. The ORSE program allows for the shielding evaluation results to the clinical environment of each institution based on patient data.

Development of open access tool for automatic use factor calculation using DICOM-RT patient data.

Our study recalculated the use factor of linear accelerators (LINACs) by using an in-house program based on Digital Imaging and Communications in Medicine radiation therapy (DICOM-RT). We considered the impact of advancements and changes in treatment trends, including modality, technology, and radiation dose, on the use factor, which is one of the shielding parameters. In accordance with the methodology described in the NCRP 151 report, we computed the use factor for four linear accelerators (LINACs) across three hospitals. We analyzed the results based on the treatment techniques and treatment sites for three-dimensional conformal radiation therapy (3D-CRT) and intensity modulated radiation therapy or volumetric modulated arc therapy. Our findings revealed that the use factors obtained at 45° and 90° were 14.8% and 13.5% higher than those of the NCRP 151 report. In treatment rooms with a high 3D-CRT ratio, the use factor at a specific angle differed by up to 14.6% relative to the NCRP 151 report value. Our results showed a large difference in the use factor for specific sites such as the breast and spine, so it is recommended that each institution recalculate the use factor using patient's data.

Metodología para la evaluación de la idoneidad de las barreras en Medicina Nuclear / Assessing methodology for nuclear medicine barrier suitability

Este documento presenta una exhaustiva verificación de los sistemas de blindaje en un servicio de terapias radiometabólicas, ubicada en el cuarto piso del edificio de Medicina Nuclear. En esta área, se llevan a cabo terapias con I 131 , Lu177 y Ra223 al menos tres veces por semana, atendiendo a un promedio de 60 pacientes al mes, de los cuales aproximadamente 15 son tratados con terapias de baja actividad. Todo esto se realiza en estricto cumplimiento de los límites de dosis establecidos para la zona, los horarios de ocupación, los puntos de control y el equipo de medición correspondiente. La metodología propuesta está diseñada para abordar las necesidades prácticas de los centros de terapias radiometabólicas en su funcionamiento diario, considerando las condiciones reales de exposición. Los resultadosconfirman la idoneidad de los sistemas de blindaje, adaptados específicamente a las actividades desarrolladas en estas instalaciones

This document presents an exhaustive verification of shielding systems in a radiometabolic therapy service, located on the fourth floor of the Nuclear Medicine building. In this area, therapies with I 131, Lu177 and Ra223 are carried out at least three times a week, serving an average of 60 patients per month, of which approximately 15 are treated with low-activity therapies. All this is carried out in strict compliance with the dose limits established for the zone, the occupation times, the control points and the corresponding measurement equipment. The proposed methodology is designed to address the practical needs of radiometabolic therapy centers in their daily operation, considering real exposure conditions. The results confirm the suitability of the shielding systems, specifically adapted to the activities carried out in these installations

Evaluation of a conventionally shielded proton treatment room for FLASH radiotherapy.

PURPOSE: FLASH radiotherapy (FLASH-RT) is the potential for a major breakthrough in cancer care, as preclinical results have shown significantly reduced toxicities to healthy tissues while maintaining excellent tumor control. However, FLASH conditions were not considered in the current proton facilities' shielding designs. The purpose of this study is to validate the adequacy of conventionally shielded proton rooms used for FLASH-RT. METHODS: Clinical FLASH irradiations typically take place in a few 100 ms, orders of magnitude shorter than the response time of the wide-energy neutron detector (WENDI-II). The nozzle beam current (representing the dose rate) dependence of the WENDI-II detector response was empirically determined to stabilize with a beam current of ≤10 nA at the measurement point with the highest dose rate. A large, predefined proton transmission FLASH plan (250 MeV, 7 × 20 cm2 , 8 Gy at isocenter) was commissioned as part of a FLASH clinical trial. For purpose of this study, that field was adjusted from 250 to 244 MeV, allowing a lower beam current of 10 nA to provide reliable detector response. Radiation surveys were performed for the proton beams with/without extra beam stopper (30 × 30 × 40-cm3 solid water slabs) at 0°, 90°, 180°, and 270° gantry angles. RESULTS: Ambient doses were recorded at seven different locations. A 170-nA beam current, commonly used for clinical FLASH plans, was chosen to normalize the average ambient dose rate to FLASH conditions. Assuming 200-Gy/h workload (25 FLASH beams, 8 Gy/beam), annual occupational dose at controlled areas was calculated. For all gantry angles, ≤0.4 mSv/year is expected at treatment room door. The highest ambient dose, 2.46 mSv/year, ∼5% of the maximum annual permissible occupational dose, was identified at the isocenter of the adjacent treatment room with 90° gantry. CONCLUSION: These survey results indicate that our conventionally shielded proton rotating gantry rooms result in acceptable occupational and public doses when the transmission FLASH beams delivered at four cardinal gantry angles based on 200-Gy/h workload assumption. These findings support that FLASH clinical trials in our conventionally shielded proton facilities can be safely implemented.