Radiotherapy Room Research Articles

Selective contribution of concrete shielding on the equivalent and effective doses in a prostate radiotherapy treatment

Within a radiotherapy room, in addition to the primary beam, there is also secondary radiation that leaks from the accelerator head and scattering caused by surrounding objects, the patient’s body and even the walls of the shielded room itself, designed to protect the external individuals, disregarding effects on the patient. The aim of this work is to study the radiation effect on the patient’s healthy tissues caused by scattering from a concrete shield expressed as equivalent and effective doses. MCNPX simulations of the linear accelerator Varian 2100/2300C/D were performed for a MAX phantom of a patient in a typical radiotherapy room. In addition, calculations were made with and without shielding. It was concluded that the concrete shielding affects in 5% the effective dose absorbed by the patient.

Re-Shielding of Cobalt-60 Teletherapy Rooms for Tomotherapy and Conventional Linear Accelerators using Monte Carlo Simulations

Purpose. Nearly all Cobalt-60 teletherapy machines were removed around the world during the last two decades. The remaining ones are being used for experimental purposes. However, the rooms of these teletherapy machines are valuable because of lack of space in radiotherapy clinics. In order to place a new technology treatment machine in one of these rooms, one should re-shield the room since it was designed only for 1.25 MeV gamma beams on average. Mostly, the vendor of the new machine constructs the new shielding of the room using their experience. However, every radiotherapy room has different surrounding work areas and it would be wise to shield the room considering these special conditions. Also, the shield design goal of the clinic may be much lower than the International Atomic Energy Agency (IAEA) or the local association accepts. The study shows re-shielding of a Cobalt-60 room, specific to the clinic, using Monte Carlo simulations.Materials & Methods. First, a 6 MV Tomotherapy machine, then a 10 MV conventional linear accelerator (LINAC) was placed inside the Cobalt-60 teletherapy room. The photon flux outside the room was simulated using Monte Carlo N-Particle (MCNP6.1) code before and after re-shielding.For the Tomotherapy simulation, flux distributions around the machine were obtained from the vendor and implemented as the source of the model. The LINAC model was more generic with the 10 MeV electron source, the tungsten target, first and secondary collimators. The aim of the model was to obtain the maximum (40x40 cm2 ) open field at the isocenter. Two different simulations were carried out for gantry angles 90o and 270o . The LINAC was placed in the room such that the primary walls were A’ (Gantry 270o ) and C’ (Gantry 90o ) (figure 1).The second part of the study was to model the re-shielding of the room for Tomotherapy and for the conventional LINAC, separately. The aim was to investigate the recommended shielding by the vendors. Left side of the room was adjacent to a LINAC room with 2 meters thick concrete wall (figure 1). No shielding was necessary for that wall. Behind wall A-A’ there was an outdoors forbidden area; behind wall B-B’ was the contouring room for the doctors; and the control room was behind wall C-C’ (figure 1). After some modifications, the final shielding was designed.Results. The photon flux distributions outside the room before and after the re-shielding were compared. The re-shielding of Tomotherapy reduced the flux down to 1.89 % on average with respect to pre-shielding (table 1). For the conventional LINAC case; after re-shielding, the photon flux in the control room -which corresponds to gantry 90°- decreased down to 0.57% with respect to pre-shielding (table 2). The photon flux behind wall A’ -which corresponds to gantry 270°- decreased down to 2.46%. Everybody was all safe behind wall B’ even before re-shielding.

The effect of the presence of the patient on the particles dose estimations in high energy linear accelerator mazes

Purpose: Medical accelerators operating above 10 MV are a source of undesirable neutron radiations which contaminate the therapeutic photon beam. These photo-neutrons which contaminate the therapeutic beam can also generate secondary gamma rays, via inelastic and capture reactions, which increase the undesirable dose to the patient body, the oncology staff and the general public. The purpose of the present work is to investigate, through Monte Carlo simulation, the effect of the presence of the patient on the neutron and gamma rays dose calculations. Methods: To illustrate this effect, the MCNP5 code was used to model a radiotherapy room of a medical linear accelerator operating at 18 MV and to calculate the neutron and the secondary gamma ray energy spectra and the dose equivalent, at various points along the centerline of the maze, in the absence and presence of the patient. Results and Conclusion: The obtained results show a significant change in the neutron energy spectra in the presence of the patient especially in the thermal neutron energy region. The results also indicate that the presence of a patient does not affect the simulated neutron and gamma rays dose equivalents at the maze entrance for mazes greater than 3 m long. A significant change in dose equivalent calculated values was observed when the length of the maze is less than 3 m .

Characteristic evaluation of photoneutron in radiotherapy room usingMCNPX

Linear accelerators are now playing a pivotal role in radiotherapy and high energy photon beams of a strength exceeding 8 MV have recently been mainly used. However, when using high energy photons, neutron contamination due to photonuclear reaction develops. This study focused on the dose distribution of photoneutrons emitted from a linear accelerator using Monte Carlo MCNPX code. MCNPX was used to simulate transportation of photoneutrons in the linear accelerator and the entire space of the radiotherapy room and is useful for calculating the flux, spectrum and absorbed dose. As result of the simulation, we could know that the neutron absorbed dose was as less as negligible when comparing to the photon absorbed dose in radiotherapy room. And it was found that the photoneutron flux increased substantially starting from 10 MV while the absorbed dose rose sharply between 10 MV and 12 MV. It was observed that although the ratio of thermal neutrons to fast neutrons was not altered as the energy increased, it was found that as the distance from the source increased the ratio of thermal neutrons rose markedly.

Monte Carlo Simulation of Photoneutron Dose in Radiotherapy Room as A Function of Gantry Angles

Monte Carlo Simulation of Photoneutron Dose in Radiotherapy Room as A Function of Gantry Angles

Risk factors for surgical site infection after posterior fixation surgery and intraoperative radiotherapy for spinal metastases.

Posterior surgery with intraoperative radiotherapy for spinal metastases offers effective therapy, as we have reported previously. However, the procedure involves transfer from the operating room to the radiotherapy room, and as these patients are somewhat immunocompromised, the risk of postoperative surgical site infection (SSI) may be increased. The aim of our study was to identify risk factors and patient characteristics associated with postoperative SSI following posterior fixation surgery and intraoperative radiotherapy for spinal metastases. Participants comprised 279 patients who underwent IORT for the treatment of spinal metastases between August 2004 and June 2013. Patients who suffered SSI within 1 month after surgery were categorized as infected, and all others were categorized as non-infected. We compared factors of age, sex, use of pre-operative corticosteroid, medical history of diabetes, prognosis scores (Tomita, Tokuhashi, and Katagiri), pre- and postoperative Frankel scale scores, site of tumor origin, administration of pre-operative radiotherapy, operation time, intraoperative blood loss, intraoperative irradiation dose, and pre- and postoperative performance status between groups. SSI occurred in 41 patients (14.7%). Katagiri's and Tokuhashi's prognostic scores (P < 0.05 each), postoperative Frankel scale score (P < 0.01), administration of pre-operative radiotherapy (P < 0.05), and postoperative performance status (P < 0.05) all correlated significantly with occurrence of SSI. Multivariate analysis using those factors revealed administration of pre-operative radiotherapy as a factor independently associated with SSI (P < 0.05). Patient prognosis, postoperative ambulatory function, and pre-operative radiotherapy were risk factors for SSI in patients with spinal metastases. Duration of surgery and intraoperative blood loss were not associated with occurrence of SSI.

Dose reduction of scattered photons from concrete walls lined with lead: Implications for improvement in design of megavoltage radiation therapy facility mazes.

This study explores the possibility of using lead to cover part of the radiation therapy facility maze walls in order to absorb low energy photons and reduce the total dose at the maze entrance of radiation therapy rooms. Experiments and Monte Carlo simulations were utilized to establish the possibility of using high-Z materials to cover the concrete walls of the maze in order to reduce the dose of the scatteredphotons at the maze entrance. The dose of the backscatteredphotons from a concrete wall was measured for various scattering angles. The dose was also calculated by the FLUKA and EGSnrc Monte Carlo codes. The FLUKA code was also used to simulate an existing radiotherapy room to study the effect of multiple scattering when adding lead to cover the concrete walls of the maze. Monoenergetic photons were used to represent the main components of the x ray spectrum up to 10 MV. It was observed that when the concrete wall was covered with just 2 mm of lead, the measured dose rate at all backscattering angles was reduced by 20% for photons of energy comparable to Co-60 emissions and 70% for Cs-137 emissions. The simulations with FLUKA and EGS showed that the reduction in the dose was potentially even higher when lead was added. One explanation for the reduction is the increased absorption of backscatteredphotons due to the photoelectric interaction in lead. The results also showed that adding 2 mm lead to the concrete walls and floor of the maze reduced the dose at the maze entrance by up to 90%. This novel proposal of covering part or the entire maze walls with a few millimeters of lead would have a direct implication for the design of radiation therapy facilities and would assist in upgrading the design of some mazes, especially those in facilities with limited space where the maze length cannot be extended to sufficiently reduce the dose.

Using Monte Carlo Simulation to Calculate The Dose Reduction at The Maze Entrance of A Radiotherapy Room

The aim of this study was to introduce a method to reduce the dose of the backscattered photons from a linear accelerator at the maze entrance of a radiotherapy room (RR). For this purpose a typical RR was designed and simulated using FLUKA Monte Carlo Code (version 2011.2b.1). The maze of a RR was the main focus for the study. Its walls including, floor and ceiling were lined with thin sheets of lead and stainless steel of 2 mm and 4 mm thicknesses respectively to find the most effective material and thickness for dose reducing. It was found that 2 mm lead sheet was able to reduce the dose at the maze entrance by more than 60 % and 4 mm 70 %. Whereas, 2 mm of stainless steel was able to reduce about 30% of the dose and 4 mm was able to reduce about 35%.

SU‐E‐J‐184: Stereo Time‐Of‐Flight System for Patient Positioning in Radiotherapy

Purpose:The objective of this work is to test the advantage of using the surface acquired by two stereo Time‐of‐Flight (ToF) cameras in comparison of the use of one camera only for patient positioning in radiotherapy.Methods:A first step consisted on validating the use of a stereo ToFcamera system for positioning management of a phantom mounted on a linear actuator producing very accurate and repeatable displacements. The displacements between two positions were computed from the surface point cloud acquired by either one or two cameras thanks to an iterative closest point algorithm. A second step consisted on determining the displacements on patient datasets, with two cameras fixed on the ceiling of the radiotherapy room. Measurements were done first on voluntary subject with fixed translations, then on patients during the normal clinical radiotherapy routine.Results:The phantom tests showed a major improvement in lateral and depth axis for motions above 10 mm when using the stereo‐system instead of a unique camera (Fig1). Patient measurements validate these results with a mean real and measured displacement differences in the depth direction of 1.5 mm when using one camera and 0.9 mm when using two cameras (Fig2). In the lateral direction, a mean difference of 1 mm was obtained by the stereo‐system instead of 3.2 mm. Along the longitudinal axis mean differences of 5.4 and 3.4 mm with one and two cameras respectively were noticed but these measurements were still inaccurate and globally underestimated in this direction as in the literature. Similar results were also found for patient subjects with a mean difference reduction of 35%, 7%, and 25% for the lateral, depth, and longitudinal displacement with the stereo‐system.Conclusion:The addition of a second ToF‐camera to determine patient displacement strongly improved patient repositioning results and therefore insures better radiation delivery.

Physician‐Commanded Six‐DOF Robotic Manipulation for Target Localization in Conformal Radiotherapy

AbstractTo effectively improve treatment precision in conformal radiotherapy, ultrasound sensing is employed to detect tumors in real time. In order to implement this new configuration, the physician operating the ultrasound probe must not stay in the radiotherapy room. This motivates the development of a physician‐commanded robotic manipulation system for target localization in conformal radiotherapy. The proposed robotic control system is in eye‐to‐hand configuration with binocular vision and force sensing. The ultrasound probe mounted on the end‐effector of the manipulator is controlled to follow the pose commanded by the physician. Based on the measurements from a six‐axis force sensor, the probe can be controlled further to maintain the desired contact force against the possibly‐deforming treatment surface. The proposed hybrid force and vision‐based control approach has been validated by experimenting with a six‐degrees‐of‐freedom industrial manipulator to allow clear ultrasound images.

Effect of external shielding for neutrons during radiotherapy for prostate cancer, considering the 2300 CD linear accelerator and voxel phantom

Photoneutron production occurs when high energy photons, greater than 6.7MeV, interact with linear accelerator head structures. In Brazil, the National Cancer Institute, one of the centers of reference in cancer treatment, uses radiation at 4 angles (0°, 90°, 180° and 270°) as treatment protocol for prostate cancer. With the objective of minimizing the dose deposited in the patient due to photoneutrons, this study simulated radiotherapy treatment using MCNPX, considering the most realistic environment; simulating the radiotherapy room, the Linac 2300 head, the MAX phantom and the treatment protocol with the accelerator operating at 18MV. In an attempt to reduce the dose deposited by photoneutrons, an external shielding was added to the Linac 2300. Results show that the equivalent dose due to photoneutrons deposited in the patient diminished. The biggest reduction was seen in bone structures, such as the tibia and fibula, and mandible, at approximately 75%. Besides that, organs such as the brain, pancreas, small intestine, lungs and thyroid revealed a reduction of approximately 60%. It can be concluded that the shielding developed by our research group is efficient in neutron shielding, reducing the dose for the patient, and thus, the risk of secondary cancer, and increasing patient survival rates.

Calculation of Dose in Healthy Organs, during Radiotherapy 4-Field Box 3D Conformal for Prostate Cancer, Simulation of the Linac 2300, Radiotherapy Room and MAX Phantom

In men, prostate cancer is one of the most frequent types, and radiotherapy is adopted as a form of treatment. Although there are efforts to minimize the dose in the healthy organ and tissues adjacent to the tumor during radiotherapy, these organs are affected by the secondary scattered and leakage radiation originating from the therapeutic beam and these doses deposited in the healthy organs, can induce the appearance of new focal points of cancer. The aim of this study is to calculate the equivalent and effective doses, due to photons and neutrons, in healthy organs of a patient submitted to radiotherapy treatment for prostate cancer. Computed simulation of radiotherapy treatment for prostate cancer was used to perform the dose calculations, adopting the treatment protocol used at INCA (Brazilian National Cancer Institute). The MCNPX code was employed in the simulation radiation transport while the male voxel MAX phantom was used to represent the patient's human anatomy. The results obtained in this study indicate that the organs close to the irradiated region are predominantly affected by the dose due to photons, with an impact on organs from different systems of the body, such as the bladder, colon, and testicles, besides bone structures such as the femur, pelvis and spinal column. The results obtained from the doses deposited due to neutrons suggest that tibia and fibula, mandible, cranium, brain and thyroid, had the highest dose deposited due to neutrons in relation to photons. The result obtained from the effective dose was 31.47 mSv due to photons, while the dose due to neutrons was 0.42 mSv. Note that the effective dose due to photons is significantly higher than the effective dose due to neutrons. The values calculated in this study were compared with the experimental values obtained in the literature, presenting reasonable concordance. Additionally, as described in the literature, it was verified that the dose due to photons decreases considerably with the increase in the distance of the target organ, while the dose due to neutrons is distributed homogeneously in the organs. It is concluded that the contribution of neutrons to the appearance of secondary cancers is more relevant in the organs furthest from the target volume, and that organs close to the tumor, are affected predominantly by the dose due to photons.

Sci-Fri PM: Delivery - 02: CT image guidance strategies for dose-adaptive IMRT of the prostate.

On-line CT imaging in the radiotherapy room has become the norm for targeted intensity-modulated radiotherapy (IMRT), enabling precise adjustments of the daily patient setup based on soft tissue visualization. Corrections for plasticity of the anatomy and dose deformation are within technological reach but will require more on-line resources. We have developed a computer model that allows exploration of "what if" scenarios for assessing the benefits of Image Guidance strategies in terms of the multi-fraction dose distribution and DVH metrics (Target D95 and rectum V70). In this work we report on changes in anatomy and resultant dose distribution as observed in 35 daily megavoltage CT (MVCT) scans of the pelvis during prostate therapy for 13 patients. Our goal is to assess the effectiveness and efficiency of various adaptive strategies involving imaging schedule with and without dose re-planning of 5-field IMRT with 18 MV x-rays. Our research questions are: To what extent do radiation dose distributions delivered to individual patients (in vivo) diverge from the planned dose distributions (in silico)? Is there a robust schedule of CT image guidance, with or without dose re-planning that will mitigate discrepancies? For prostate IMRT, we conclude that image guidance schedule can be relaxed when generous GTV margins (10/7mm) are used. Tighter margins (isotropic 5 mm) reduce the dose to the rectum as expected. However, daily re-planning may be required to maintain adequate target coverage as planned when tighter margins are used.

방사선 치료실의 실내 구조와 산란선 측정에 관한 연구

This research aims at examining the amount of scattered radiation generated during irradiation by adhering structures with different sizes of aluminum prominence and depression to the inside of a radiotherapy room. The irregular aluminum structures were stuck to the wall of a radiotherapy room, and the scattered radiation generated during irradiation was measured. The sizes of the aluminum prominence and depression were 1.5×1.5, 3×3, and 5×5 cm2 with the width of 60 cm and the height of 60 cm. The distance between TLD and the wall of the radiotherapy room to measure scattered radiation was 310 cm, and the used radiation energy was 6 MV and 15 MV generated from a linear accelerator. The research result showed that the irradiation amount at 6 MV was 100, and at 300 cGy the scattered radiation decreased by the installation of the structure with aluminum prominence and depression, but at 200 cGy, only the scattered radiation of the uneven structure of 5×5 cm2 decreased. At 15 MV, the irradiation amount was 200 cGy, and at 300 cGy, the scattered radiation was reduced when the rugged aluminum structure was set up, but at 100 cGy, similar result values were produced regardless of the uneven structure. Consequently, installation of an additional structure with aluminum prominence and depression in the present interior structure can decreased the stochastic effect of the scattered radiation generated from the wall of a radiotherapy room and patients.

The evaluation of neutron and gamma ray dose equivalent distributions in patients and the effectiveness of shield materials for high energy photons radiotherapy facilities

In this study, the MCNP5 code was used to model radiotherapy room of a medical linear accelerator operating at 18MV and to evaluate the neutron and the secondary gamma ray fluences, the energy spectra and the dose equivalent distributions inside a liquid tissue-equivalent (TE) phantom. The obtained results were compared with measured data published in the literature. Moreover, the shielding effects of various neutron material shields on the radiotherapy room wall were also investigated. Our simulation results showed that paraffin wax containing boron carbide presents enough effectiveness to reduce both neutron and secondary gamma ray doses.

Neutron and photon doses in high energy radiotherapy facilities and evaluation of shielding performance by Monte Carlo method

Medical accelerators operating above 10 MV are a source of undesirable neutron radiations which contaminate the therapeutic photon beam. These photoneutrons can also generate secondary gamma rays which increases undesirable dose to the patient body and to personnel and general public. In this study, the Monte Carlo N-Particle MCNP5 code has been used to model the radiotherapy room of a medical linear accelerator operating at 18 MV and to calculate the neutron and the secondary gamma ray energy spectra and the dose equivalents at various points inside the treatment room and along the maze. To validate our Monte Carlo simulation we compared our results with those evaluated by the recommended analytical methods of IAEA Report No. 47, and with experimental and simulated values published in the literature. After validation, the Monte Carlo simulation has been used to evaluate the shielding performance of the radiotherapy room. The obtained results showed that the use of paraffin wax containing boron carbide, in the lining of the radiotherapy room walls, presents enough effectiveness to reduce both neutron and gamma ray doses inside the treatment room and at the maze entrance. Such evaluation cannot be performed by the analytical methods since room material and wall surface lining are not taken into consideration.

Design of a Treatment Room for an 18-MV Linac

This work studies the design of the treatment room for an 18-MV linac to ensure radiation protection and safety of hospital staff and patients. The walls’ thickness, the door, and the maze were designed according to the National Council on Radiation Protection and Measurements Report 151 recommendations. The results of this work are contrasted with the Monte Carlo calculations performed with the MCNP5 code where dose equivalents due to neutrons and neutron spectra estimated at different points inside and outside the radiotherapy room verify that the shielding thicknesses obtained are enough to reduce the dose level permitted by Mexican regulation.

Physical and mechanical properties of concrete containing hematite as aggregates

Radiation limits above permission limit have harmful effects on living bodies (i.e., carcinogenic, etc.). Heavyweight concrete is used in facilities such as nuclear power plant and radiotherapy room where radioactive impermeability is required. Aggregate and cement play an essential role in both the shielding performance and the structural behavior of concrete. Concretes with 0% (control), 15%, 30%, 45% and 60% of conventional aggregate replaced by hematite aggregate for each control concrete, were fabricated with 300, 350, 400 and 450 kg/m3cement contents. Water-cement ratio was kept constant at 0.40. In addition to investigation of the mineralogical structure of hematite, physical and mechanical experiments were carried out on the concrete produced. The results show that slump and compressive strength, like other mechanical properties, increase as the hematite aggregate replacement volume increase.

Photoneutron and capture gamma dose calculations for a radiotherapy room made of high density concrete

Neutron and capture gamma ray dose equivalent along the maze and entrance door of a radiation therapy room made of high density concrete was calculated using analytical and Monte Carlo methods. The room geometry and the 18 MV photon beam of a Varian 2100C/D linac were simulated using MCNPX MC code. Four analytical methods including Kersey, French, McCall, and Wu-McGinley methods were used in the current study. Average difference of 13-30% was seen between analytical and MC methods along the maze for photoneutron calculations. The difference between Wu-McGinley and MC methods was about 17% for capture gamma ray calculations. It was concluded that the analytical methods overestimate both neutron and capture gamma ray dose equivalents compared to MC. Moreover, it was shown that the analytical methods can be used as conservative estimators for neutron and capture gamma calculations.

SU‐GG‐T‐315: Single Event Effects in Radiotherapy

Introduction A single event effect (SEE) is a change of state of a microelectronic device caused by a single energetic particle. Single event upsets (SEUs) is one kind of SEEs. A SEU on a Siemens Linac has been reported in a SRAM of PLC. With more and more integrated circuits in modern Linacs and treatment head, such as MLC, the probability of SEEs becomes larger. The consequences of the SEEs in radiotherapy, especially of safety functions and considerations, need further investigation. Method and materials A Linac with high energy (15MV) mode (Varian, Palo Alto, CA) was investigated. Integrated circuits used inside treatment room were identified. Of interest wert those CMOS and FPGA. The SEE rates were estimated based on published papers. Further estimation was made with Monte Carlo code and data from NASA's SEE test reports. SEEs in beam delivery and MLC control were also scrutinized. Results SEU rate of 0.047 events⋅MiB−1⋅MU−1 for Varian 15 MV photons has been derived. If the response of the ICs is linear, a radiotherapy room with 32 patients/day, 1/8 patients treated with high energy, and 200 MU/patient, the SEUs will be 38 SEUs⋅MiB−1⋅day−1. If somewhat arbitrary one megabyte is taken for memory size in use, the SERs will be 38 events per day. Thus, there is a significant potential for quite a few SEEs in radiotherapy. Conclusion The SEE is well known phenomena of increased importance. SEE is a critical to electronic reliability in certain environment like radiotherapy. The SEE characteristics of electronics should be tested further and evaluated for clinical application. Further knowledge on their impact to radiotherapy, especially to under‐dose or over‐dose delivery, and control of parts like MLC, should be investigated. Care should be taken by the manufacturer to use ICs which are immune of SEEs.