Teletherapy Unit Research Articles

SU‐GG‐T‐325: The Effects of Neurosurgical Titanium Mesh on Radiation Dose in the Gamma Knife

Purpose: To investigate the impact of titanium neurosurgical mesh and bone cement on Gamma Knife dose distributions. Methods and Materials: Radiation properties of several meshes and bone cement were evaluated using a Theratron Co‐60 teletherapy unit. The mesh that caused the largest perturbation of the beam was then studied in the Leksell Gamma Knife. A head phantom was constructed using a plaster skull and ballistics gel. A section of the skull was removed and replaced with mesh. Two plans were created in the Leksell GammaPlan treatment planning software, one comprising a single 18 mm diameter shot centered at 2 cm below the surface of the phantom, and one 5cm below the surface. The plans were delivered to the phantom with bone and with mesh for a total of four deliveries. Dose profiles were measured in the coronal plane along with surface dose using GafChromic film, analyzed using RIT and ImageJ. Results: For the shallow lesion at 2cm depth, the measured maximum dose with the mesh was 5% less than the measured dose with the intact skull. For the lesion at 5 cm depth, the measured maximum dose with the mesh was 2% less than the measured dose with bone. At the surface immediately above the mesh, there was a 70% increase in dose. Conclusion: This work is significant in evaluating the need to modify a Gamma Knife SRS treatment plan when titanium mesh is present. For shallow lesions near the mesh, there is an associated a 5% reduction in maximum dose, and a 1 mm reduction in the 50% isodose diameter. These values decreased to 2% and 0 mm at 5 cm depth. However, for either depth, the dose at the mesh surface was increased by 68%, due to backscatter from the mesh.

MO‐E‐BRA‐02: Computer Aided Design and Monte Carlo Validation of a Patient‐Specific Co‐60 TBI Treatment Unit

Purpose: To modify and characterize a teletherapy 60Co unit for total body irradiation (TBI) treatments at extended SSD using experiments and a Monte Carlo (MC) model and to propose the design of custom compensators based on MC dose in the patient. Methods and Materials: An existing Eldorado T78 60Co teletherapy unit was stripped from its original collimator and equipped with beam‐defining cerrobend blocks for extended SSD TBI treatments. An acrylic flattening filter was numerically designed based on detailed mapping of the dose distribution of the large open field at 10 cm depth in water and using a primary radiation attenuation calculation. An EGSnrc MC model of the resulting unit was developed and validated. Dose distributions measured using ionization chambers were compared to MC dose distribution in air and phantom. The validated model was used to calculate dose in a whole‐body patient CT image. A compensator, designed to make the patient mid‐plane dose uniform was proposed. Results: The designed filter flattens the beam to within ±2% over an area of 200 × 70 cm2 at patient mid‐plane. The agreement between measured and calculated dose profiles in the open and the filtered beams is at the sub 2% and sub 1% level, respectively. Surface dose in the filtered beam is 78.5% and mean photon energy of the primary fluence is 0.94 MeV independent of position in the field. Patient‐specific calculations show excess dose in lung and the area of neck and extremities relative to prescription dose, by up to 20% and 30%, respectively. These excess doses can be reduced by introducing compensators, designed from the mid‐plane dose distribution, following similar techniques as for the design of the filter. Conclusions: This work shows that extended SSD 60Co irradiation equipment and patient‐specific compensators designed based on realistic dose distributions, can improve TBI delivery.

Evaluation of Dose Distribution Accuracy in HDR Brachytherapy of Esophagus Cancer Based on MRI Normoxic Polymer Gel Dosimetry

Introduction: The purpose of this work was to study the ability of MRI normoxic polymer gel dosimetry for evaluating the dose distribution in HDR brachytherapy of esophagial cancer at Imam Reza brachytherapy center (Mashhad, Iran). Materials and Methods: Initially, 2liters of normoxic gel (MAGIC) was fabricated and then poured into 12 calibration test tubes and placed in a perspex walled phantom. The gel phantom was irradiated with a brachytherapy remote-afterloader unit using a cobalt-60 brachytherapy source and the test tubes were irradiated with a range of known doses with a cobalt-60 teletherapy unit. Imaging was performed with a multi-spin-echo protocol and a T2 quantitative technique using a Siemens 1.5 T MRI machine. The MRI images were transferred to a computer and then image processing was performed in the MATLAB environment to extract R2 maps of the irradiated area. Results: In this study and at the reference point, the dose deviation between the gel dosimetry and the calculated data was 4.5%. The distance to agreement (DTA) for dose profiles was 2.7 mm. Also, dose sensitivity of the MAGIC gel dosimeter was 0.693 S-1Gy-1 (R2 =0.9376). Conclusion: In this work, the data obtained from TPS calculations were found in very good agreement with the measured results provided by gel dosimetry. It was evaluated using a comparison of isodoses and dose at the reference point, and dose profile verification. It is also concluded that the gel dosimetry systems have proven to be a useful tool for dosimetry in clinical radiotherapy applications.

Trends for the Past 10 Years and International Comparisons of the Structure of Korean Radiation Oncology

Study aims include determination of nationwide structural characteristics of radiation oncology facilities, types of radiation therapy equipment, availability of human resources and trends and comparisons with previous surveys. An annual nationwide survey was conducted to collect the statistics of infrastructure since 1997. All requested questionnaires have been identical for 10 years. The questionnaires included status on basic radiation therapy facilities, human resources and radiation therapy equipment. Journal and statistical data reviews were performed to evaluate the structure of other countries. Radiation oncology facilities have steadily increased for 10 years and reached 60 sites in 2006. Also a steady increase of 1.5 times for linear accelerators, 5.8 times for computed tomography simulators and 3.0 times for radiation treatment planning systems was noted. Meanwhile, cobalt-60 teletherapy units and hyperthermia equipment had steadily deceased for 10 years. The number of human resources has steadily increased for the past 10 years, especially for radiation therapy technologists. However, radiation therapy equipment and human resources per population are relatively low compared with advanced countries. This study will assist preparation of the administrative planning policy of radiation oncology and should be useful to indicate the direction of future development and educational training programs in Korea and possibly in other countries.

Study of the spatial distribution of the absorbed dose in blood volumes irradiated using a teletherapy unit

Blood irradiation can be performed using a dedicated blood irradiator or a teletherapy unit. A thermal device providing appropriate storage conditions during blood components irradiation with a teletherapy unit has been recently proposed. However, the most appropriated volume of the thermal device was not indicated. The goal of this study was to indicate the most appropriated blood volume for irradiation using a teletherapy unit in order to minimize both the dose heterogeneity in the volume and the blood irradiation time using these equipments. Theoretical and experimental methods were used to study the dose distribution in the blood volume irradiated using a linear accelerator and a cobalt-60 therapy machine. The calculation of absorbed doses in the middle plane of cylindrical acrylic volumes was accomplished by a treatment planning system. Experimentally, we also used cylindrical acrylic phantoms and thermoluminescent dosimeters to confirm the calculated doses. The data obtained were represented by isodose curves. We observed that an irradiation volume should have a height of 28 cm and a diameter of 28 cm and a height of 35 cm and a diameter of 35 cm, when the irradiation is to be performed by a linear accelerator and a cobalt-60 teletherapy unit, respectively. Calculated values of relative doses varied from 93% to 100% in the smaller volume, and from 66% to 100% in the largest one. A difference of 5.0%, approximately, was observed between calculated and experimental data. The size of these volumes permits the irradiation of blood bags in only one bath without compromising the homogeneity of the absorbed dose over the irradiated volume. Thus, these irradiation volumes can be recommend to minimize the irradiation time when a teletherapy unit is used to irradiate blood.

Radio frequency noise from an MLC: a feasibility study of the use of an MLC for linac-MR systems

Currently several groups are actively researching the integration of a megavoltage teletherapy unit with magnetic resonance (MR) imaging for real-time image-guided radiotherapy. The use of a multileaf collimator (MLC) for intensity-modulated radiotherapy for linac-MR units must be investigated. The MLC itself will likely reside in the fringe field of the MR and the motors will produce radio frequency (RF) noise. The RF noise power spectral density from a Varian 52-leaf MLC motor, a Varian Millennium MLC motor and a brushless fan motor has been measured as a function of the applied magnetic field using a near field probe set. For the Varian 52-leaf MLC system, the RF noise produced by 13 of 52 motors is studied as a function of distance from the MLC. Data are reported in the frequency range suitable for 0.2–1.5 T linac-MR systems. Below 40 MHz the Millennium MLC motor tested showed more noise than the Varian 52-leaf motor or the brushless fan motor. The brushless motor showed a small dependence on the applied magnetic field. Images of a phantom were taken by the prototype linac-MR system with the MLC placed in close proximity to the magnet. Several orientations of the MLC in both shielded and non-shielded configurations were studied. For the case of a non-shielded MLC and associated cables, the signal-to-noise ratio (SNR) was reduced when 13 of 52 MLC leaves were moved during imaging. When the MLC and associated cables were shielded, the measured SNR of the images with 13 MLC leaves moving was experimentally the same as the SNR of the stationary MLC image. When the MLC and cables are shielded, subtraction images acquired with and without MLC motion contains no systematic signal. This study illustrates that the small RF noise produced by functioning MLC motors can be effectively shielded to avoid SNR degradation. A functioning MLC can be incorporated into a linac-MR unit.

Effectiveness of two different HDR brachytherapy regimens with the same BED value in cervical cancer.

PurposeTo analyze the effectiveness of biologically effective dose (BED) in two different regimens of HDR brachytherapy keeping the same total BED to point A and to compare the relationship of overall treatment time in terms of local control and bladder and rectal complications.Material and methodsThe study included two groups comprising a total of 90 cervical cancer patients who underwent external beam radiotherapy (EBRT) followed by HDR intracavitary brachytherapy (ICBT). EBRT treatment was delivered by a Co-60 teletherapy unit to a prescribed dose of 45 Gy with 1.8 Gy per fraction in 25 fractions over a period of five weeks. Parallel opposed anterior–posterior (AP/PA) fields with no central shielding were used, followed by the HDR ICBT dose, to point A, of either two fractions of 9.5 Gy with a gap of 10 days, or three fractions of 7.5 Gy with a gap of 7 days between the fractions. Gemcitabine (dose of 150 mg/m2) was given weekly to all the patients as a radiosensitizer. The calculate BED3 to point A was almost the same in both groups to keep the same late complication rates. The doses, and BED10 and BED3, were calculated at different bladder and rectal point as well as at the lymphatic trapezoid points. During and after treatment patients were evaluated for local control and complications for 24 months.Results and ConclusionsDoses and BEDs at different bladder, rectal and lymphatic trapezoid points, local control, and complications in both HDR ICBT groups did not have statistically significant differences (p > 0.05). Both HDR ICBT schedules are well tolerable and equally effective.

Workload modeling for teletherapy unit

This study aims to derive a radiotherapy workload model using a prospectively collected dataset of patient and treatment information from a teletherapy treatment unit. Information about all individual radiotherapy treatment was collected for two weeks from the Phoenix unit in our department. This information included diagnosis, treatment site, treatment time, fields per fraction, technique, use of blocks and wedges. Data were collected for two weeks (10 working days) in January 2008. During this time, 45 patients were treated with 450 fractions of external beam radiotherapy in Phoenix unit. The mean fraction duration, irradiation time and setup time were 9.55 minutes, 1.84 minutes and 7.66 minutes respectively. A mathematical workload model was derived using the average fraction duration time, total irradiation time and setup time of different types of treatment. A simple software program (Workload Calculation Chart) was also constructed in Microsoft Excel using the derived algorithm. The model based software program was tested and applied for one year and found that it can be used effectively to describe workload of teletherapy unit. Proposed methodology for workload modeling of teletherapy unit and the workload calculation software is very effective to quantitatively plan/calculate the optimal workload which will satisfy both the patient care administrator and radiation therapy technologists.

Development and Evaluation of a Target-tracking Radiation-therapySystem Using a Multileaf Collimator (MLC) Synchronized with MovingOrgans

A target-tracking radiation-therapy (RT) system that tracks the movement of a treatment target resulting from internal organ movement has been developed, and the system was evaluated for effectiveness. The developed radiation-therapy system determines the limit of the MLC (multileaf collimator) movement range with an acquired maximum displacement value of target movement during the radiotherapy planning stage and moves the MLC to continuously detect and synchronize the displacement of the abdominal by using a CCD camera monitoring system during real-time RT treatment. The system consists of a Co-60 teletherapy unit, an abdominal displacement detection system to correlate the movement of internal organs, and a MLC moving stage synchronized with the abdominal displacement. The effectiveness of the RT system was evaluated by analyzing the beam penumbra from the dose distribution on films (Gafchromic EBT) installed within a moving phantom. Penumbra widths (80%/20%) were measured for the nominal left (perpendicular to leaf motion) and right (parallel to leaf motion) directions of the x-axis and the y-axis for a fixed phantom and fixed MLC (3.3 mm/3.5 mm and 3.7 mm/3.1 mm), a moving phantom and a fixed MLC (9.0 mm/8.2 mm and 9.1 mm/8.8 mm), and a moving phantom and a moving MLC (3.7 mm/3.5 mm and 3.7 mm/3.8 mm). Percent area deviations of the 100% to 80% field of the maximum dose for the exposure condition of a fixed phantom and a fixed MLC were a relatively low value of 0.64% and a relatively high value of 15.04%, as compared to the values for a moving phantom and a fixed MLC and for a moving phantom and a moving MLC. With the method to move the MLC by passive synchronization with organ motion, the target-tracking radiation-therapy system was successfully implemented and was evaluated for performance. In future studies, various verification processes should be performed prior to the application of the system in a clinical situation.

Mapping radiation quality inside photon-irradiated absorbers by means of a twin-chamber method

In photon-beam radiotherapy, the absorbed dose in an irradiated object contains a contribution by energy-degraded photons originating from Compton scatter processes at parts of the treatment head and within the absorber itself. These low-energy spectral components may lead to changes in the response of non-ideally water-equivalent radiation detectors, such as Si diodes and radiographic films, in the water/tissue dose conversion factors and in the relative biological effectiveness (RBE). As a simple means of accounting for these changes in spectral quality, the Monte Carlo calculated fraction of the kerma or absorbed dose contributed by scattered photons with energies not exceeding a certain cut-off value has previously been proposed as a useful parameter. In this paper, we present an equivalent experimental approach, providing a means for the spatial mapping of radiation quality. Its applicability will be demonstrated for the case of 60Co and 6 MV photons. A twin-chamber combination of a Farmer type ionization chamber, equipped with a graphited PMMA outer electrode, and a chamber of the same design, but with an outer electrode made from copper, has been developed. The measured quantity is the signal ratio (SR) of the copper wall and graphited wall chambers. A correlation between the SR and the fraction of the air kerma respectively of the absorbed dose to water, contributed by photons with energies not exceeding 200 keV, has been established at a Theratron 780-C 60Co teletherapy unit and at a Siemens Primus 6 MV linear accelerator. We also describe a two-dimensional version of the twin-chamber method using the PTW 2D-Array 256. Typical trends of parameter SR with depth and off-axis distance in water-equivalent phantoms have been observed. Thereby, a simple experimental method for the space-resolved assessment of the dose fraction attributable to low-energy Compton scattered photons can be presented as an innovative instrument of describing radiation quality in radiotherapy.

SU‐FF‐T‐266: Characterizing a Multi‐Axis Ion Chamber Array

Purpose: To characterize a commercially available multi‐axis ion chamber array for use as a scanning water tank alternative. Method and Materials: The ion chamber array used in this study was the IC Profiler (Sun Nuclear Corporation: Melbourne, FL). We characterized four items of the array: reproducibility, dose linearity, backscatter response, and water tank agreement. Short and long term reproducibility's were established on a 60Co teletherapy unit (Eldorado 6; Atomic Energy of Canada Limited: Mississauga, Canada). The remaining tests were conducted with a Synergy (Elekta: Crawley, UK) linear accelerator (LINAC) operated at a nominal photon energy of 6MV. Results: Over a short time period the array displayed a maximum standard deviation of 0.55% and a mean standard deviation of 0.15%; over a long time period the array displayed a maximum standard deviation of 1.80% and a mean standard deviation of 0.76%. The array was sensitive to startup characteristics of the LINAC when operating in pulsed mode; this affected the dose linearity relative to a Farmer chamber operating under the same geometry. This effect was not observed when the array was operated in continuous mode. Both the array's central axis detector and a Farmer chamber displayed a similar increase in measured signal with increasing backscatter. However, with increasing backscatter (up to 16.6 cm) the arrays in‐beam‐profile shape changed by less than 0.7% relative to a setup with no additional backscatter. The agreement between the array and a scanning water tank differed by less than 1% in the beam. Conclusion: The IC Profiler is a viable option for water tank ‘like’ measurements. The device provides a stable platform with good dose linearity, minimal backscatter response, and uniform profile measurements. Conflict of Interest: This work was supported in part by SBIR Contract No. HHSN261200522014C, the University of Florida, and Sun Nuclear Corporation

Tolerance Doses of Cutaneous and Mucosal Tissues in Ring-necked Parakeets (Psittacula krameri) for External Beam Megavoltage Radiation

Currently used dosages for external-beam megavoltage radiation therapy in birds have been extrapolated from mammalian patients and often appear to provide inadequate doses of radiation for effective tumor control. To determine the tolerance doses of cutaneous and mucosal tissues of normal birds in order to provide more effective radiation treatment for tumors that have been shown to be radiation responsive in other species, ingluvial mucosa and the skin over the ingluvies of 9 ring-necked parakeets (Psittacula krameri) were irradiated in 4-Gy fractions to a total dose of either 48, 60, or 72 Gy using an isocentric cobalt-60 teletherapy unit. Minimal radiation-induced epidermal changes were present in the high-dose group histologically. Neither dose-related acute nor chronic radiation effects could be detected in any group grossly in cutaneous or mucosal tissue over a 9-month period. Radiation doses of 72 Gy in 4-Gy fractions were well tolerated in the small number of ring-necked parakeets in this initial tolerance dose study.

Acute renal failure in patients with rhabdomyolysis

To propose a roadmap and explore the cost implications of establishing a teleradiotherapy network to provide comprehensive cancer care and capacity building in countries without access to radiation therapy.Ten low-income sub-Saharan countries with no current radiation therapy facilities were evaluated. A basic/secondary radiation therapy center (SRTC) with 2 teletherapy, 1 brachytherapy, 1 simulator, and a treatment planning facility was envisaged at a cost of 5 million US dollars (USD 5M). This could be networked with 1 to 4 primary radiation therapy centers (PRTC) with 1 teletherapy unit, each costing USD 2M. The numbers of PRTCs and SRTCs for each country were computed on the basis of cancer incidence, assuming that a PRTC and SRTC could respectively treat 450 and 900 patients annually.An estimated 71,215 patients in these countries will need radiation therapy in 2020. Stepwise establishment of a network with 99 PRTCs and 28 SRTCs would result in 155 teletherapy units and 96% access to radiation therapy. A total of 310 radiation oncologists, 155 medical physicists, and 465 radiation therapy technologists would be needed. Capacity building could be undertaken through telementoring by networking to various international institutions and professional societies. Total infrastructure costs would be approximately USD 860.88M, only 0.94% of the average annual gross domestic product of these 10 countries. A total of 1.04 million patients could receive radiation therapy during the 15-year lifespan of a teletherapy unit for an investment of USD 826.69 per patient. For the entire population of 218.32 million, this equates to USD 4.11 per inhabitant.A teleradiotherapy network could be a cost-contained innovative health care strategy to provide effective comprehensive cancer care through resource sharing and capacity building. The network could also be expanded to include other allied specialties. The proposal calls for active coordination between all national and international organizations backed up by strong geopolitical commitment and action from all stakeholders.

SU-GG-T-371: Monte Carlo Neutron Shielding Evaluation of Treatment Vaults Built to NCRP 49 Or NCRP 151 Recommendations

Purpose: To use MCNP5 to compare and contrast the recommendations found in NCRP 49 and NCRP 151 pertaining to neutron shielding. Method and Materials: An Elekta SL25 accelerator head with nominal peak energy of 18MV was modeled in MCNP5 and verified against known measured beam characteristics.Neutron angular and energy distributions produced by the Elekta SL25 were calculated using the photoneutron production feature of MCNP5. These neutron distributions were then used as source terms for shielding calculations in simulated treatment vaults designed to either NCRP 49 or NCRP 151 standards. Results: The neutron penetration calculations indicate that shielding for megavoltage teletherapy units, i.e. those with energies greater than 10MV, should include materials designed to prevent neutron leakage. A quantitative assessment of neutron dose contributions to personnel outside of the treatment vaults will be presented. Conclusion: Although the phenomenon of photoneutron production has been well known for some time recommendations for shielding these neutrons in megavoltage teletherapy settings are relatively recent. This study may be used by those institutions considering upgrading existing units to ones with higher energies or by new sites to justify the added expense of incorporating shielding aimed at preventing neutron leakage.

Dosimetry quality audit of high energy photon beams in greek radiotherapy centers

Background and purpose Dosimetry quality audits and intercomparisons in radiotherapy centers is a useful tool in order to enhance the confidence for an accurate therapy and to explore and dissolve discrepancies in dose delivery. This is the first national comprehensive study that has been carried out in Greece. During 2002 – 2006 the Greek Atomic Energy Commission performed a dosimetry quality audit of high energy external photon beams in all (23) Greek radiotherapy centers, where 31 linacs and 13 Co-60 teletherapy units were assessed in terms of their mechanical performance characteristics and relative and absolute dosimetry. Materials and Methods The quality audit in dosimetry of external photon beams took place by means of on-site visits, where certain parameters of the photon beams were measured, calculated and assessed according to a specific protocol and the IAEA TRS 398 dosimetry code of practice. In each radiotherapy unit (Linac or Co-60), certain functional parameters were measured and the results were compared to tolerance values and limits. Doses in water under reference and non reference conditions were measured and compared to the stated values. Also, the treatment planning systems (TPS) were evaluated with respect to irradiation time calculations. Results The results of the mechanical tests, dosimetry measurements and TPS evaluation have been presented in this work and discussed in detail. This study showed that Co-60 units had worse performance mechanical characteristics than linacs. 28% of all irradiation units (23% of linacs and 42% of Co-60 units) exceeded the acceptance limit at least in one mechanical parameter. Dosimetry accuracy was much worse in Co60 units than in linacs. 61% of the Co60 units exhibited deviations outside ±3% and 31% outside ±5%. The relevant percentages for the linacs were 24% and 7% respectively. The results were grouped for each hospital and the sources of errors (functional and human) have been investigated and discussed in details. Conclusion This quality audit proved to be a useful tool for the improvement of quality in radiotherapy. It succeeded to disseminate the IAEA TRS-398 protocol in nearly all radiotherapy centers achieving homogenization and consistency of dosimetry within the country. Also, it detected discrepancies in dosimetry and provided guidance and recommendations to eliminate sources of errors. Finally, it proved that quality assurance programs, periodic quality control tests, maintenance and service play an important role for achieving accuracy and safe operation in radiotherapy.

Monte Carlo simulation of TLD response function: Scattered radiation field application

Summary Aim Thermoluminescent dosimeters (TLDs) have various applications in non-primary beam dosimetry. Monte Carlo simulation of TLD response was done in low energy beams to improve its clinical use in scattered beam dosimetry. Materials/Methods TLD material made from LiF doped with Mg and Ti sized 3.1×3.1×1mm 3 was used for experimental measurements as well as modelling by MCNP-4c Monte Carlo simulation. TLDs were irradiated for different doses of beam qualities ranging from 120, 180, 200, 250 to 300kVp x-rays generated from an orthovoltage machine and 1.25MeV gamma rays from a Co-60 teletherapy unit at reference depth in a water phantom. The simulation conditions were the same as experimental conditions. The calibration factor, (CF)q, and its quality dependence factor, ( F C X o ), were defined as: ( C F ) q = Calibration Dose / T L , ( F c o X ) = T L ( X ) / D m e d ( X ) T L ( X ) / D m e d ( C o ) Results The normalized values of measured quality dependence factors for different x-ray beams were 1.28, 1.24, 1.16, 1.07 and 1.03 for different beam qualities, respectively. Comparatively, the MCNP simulated findings were 1.134, 1.96, 1.139, 1.052 and 1.034. The change of calibration factor with energy followed the equation CF = B 0 + B 1 E + B 2 E 2 + B 3 E 3 , where CF and E are calibration factor and energy (keV), respectively. B 0 , B 1 , B 2 , B 3 are constants. Conclusions Our findings showed significant deviation of true dose value when TLDs are calibrated at different beam qualities. The greatest deviation was 19.9±2.1% in beam quality of 120kVp. Obtaining a dose response curve may be helpful to calculate the calibration factor with more precision.

Quality control of blood irradiation with a teletherapy unit: damage to stored red blood cells after cobalt‐60 gamma irradiation

Previous publications have documented the damage caused to red blood cells (RBCs) irradiated with X-rays produced by a linear accelerator and with gamma rays derived from a 137Cs source. The biologic effects on RBCs of gamma rays from a 60Co source, however, have not been characterized. This study investigated the effect of 3000 and 4000 cGy on the in vitro properties of RBCs preserved with preservative solution and irradiated with a cobalt teletherapy unit. A thermal device equipped with a data acquisition system was used to maintain and monitor the blood temperature during irradiation. The device was rotated at 2 r.p.m. in the irradiation beam by means of an automated system. The spatial distribution of the absorbed dose over the irradiated volume was obtained with phantom and thermoluminescent dosimeters (TLDs). Levels of Hb, K+, and Cl(-) were assessed by spectrophotometric techniques over a period of 45 days. The change in the topology of the RBC membrane was investigated by flow cytometry. Irradiation caused significant changes in the extracellular levels of K+ and Hb and in the organizational structure of the phospholipid bilayer of the RBC membrane. Blood temperature ranged from 2 to 4 degrees C during irradiation. Rotation at 2 r.p.m. distributed the dose homogeneously (92%-104%) and did not damage the RBCs. The method used to store the blood bags during irradiation guaranteed that all damage caused to the cells was exclusively due to the action of radiation at the doses applied. It was demonstrated that prolonged storage of 60Co-irradiated RBCs results in loss of membrane phospholipids asymmetry, exposing phosphatidylserine (PS) on the cells' surface with a time and dose dependence, which can reduce the in vivo recovery of these cells. A time- and dose-dependence effect on the extracellular K+ and plasma-free Hb levels was also observed. The magnitude of all these effects, however, seems not to be clinically important and can support the storage of irradiated RBC units for at last 28 days.

Current Status of the Infrastructure and Characteristics of Radiation Oncology in Korea

An analysis of radiotherapy infrastructure in Korea was performed in 2006 to collect data on treatment devices, the work force and new patients for future development plans. The survey included radiotherapy centers, their major equipment and personnel. The centers were categorized into four levels: level 0 (stand-alone teletherapy units); level 1 (teletherapy, brachytherapy, treatment planning system, and at least the part-time service of a medical physicist); level 2 (level 1 plus individual customized radiotherapy block and full-time medical physicist); and level 3 [level 2 plus intensity-modulated radiation therapy (IMRT), intra-operative radiation therapy or stereotactic radiotherapy]. A total of 61 facilities delivered radiation therapy with 104 megavoltage devices, which included 96 linear accelerators, two cobalt 60 units, three Tomotherapy, two CyberKnife units and one proton accelerator. There were 28,789 new radiotherapy patients in 2004. Personnel included 132 radiation oncologists, 50 radiation oncology residents, 64 physicists, 130 nurses and 369 radiation therapy technologists. Thirty-two percent (20 facilities) used a CT-simulator, 66% (40) used a PET or PET-CT scanner, and 35% (22) had the capacity to implement IMRT. Centers were also divided into four levels: 41% were included in level 3, 31% in level 2, 25% in level 1 and 3% in level 0. There is a shortage of human resources. The distribution of megavoltage units per million inhabitants over the country was inadequate; geographic disparities were noted. Furthermore, the necessity of quality assurance for recent high-technology radiation therapy is increasing.

SU‐FF‐T‐93: Beam Characterization of the Equinox Cobalt‐60 Treatment Unit

Purpose: Beam penumbra, symmetry, flatness and surface dose have been measured for the Equinox cobalt‐60 external beam therapy system using both source to surface distance (SSD) and source to axes distance (SAD) setups. Method and Materials: All data were measured using a 100 cm Equinox teletherapy unit manufactured by MDS Nordion. This newly designed unit features asymmetric jaw capability and has a source to diaphragm distance of 50 cm. The unit was installed with a 2.0 cm diameter C‐146 source. Beam data were measured using a Scanidtronix / Wellhofer Blue Phantom water tank equipped with a p‐type Silicon detector (PFD3G) or a CC13 ion chamber. OmniPro Accept software, version 6.2, was used to manipulate the data and to calculate penumbra, flatness and symmetry according to IEC 976 definitions. Surface dose measurements were independently confirmed with GafChromic film and MOSFETs. Results: Percent depth dose measurements were compared to BJR Supplement 25 data with good agreement for field sizes up to 12×12 cm and reasonable agreement for larger field sizes and depths. Relative surface dose measurements indicated that the IEC 60601‐2‐11 criteria of 90% for the maximum field size may be exceeded when an 80 cm SSD setup is used. Beam flatness, symmetry and penumbra parameters have changed little from previously manufactured units and are reported for square field sizes ranging from 1 cm to 40 cm. Conclusion: This investigation demonstrates that the beam characteristics of the Equinox unit do not differ significantly from previous units. In order to reduce surface dose to IEC stated levels; it is recommended that an electron filter be utilized on the 80 cm machine for field sizes exceeding 900 square cm. Conflict of Interest: MDS Nordion provided financial support for this project.

SU-FF-T-06: 4D In-Vivo Dosimetry in Radiotherapy

Purpose: To present a novel concept of 4D in-vivo dosimetry in radiotherapy. Method and Materials: A prototype of a new system capable of simultaneous measurement of dose and spatial position has been developed. The device, controlled by a computer, consists of a probe combining two technologies: MOSFET radiation detector coupled with a magnetic positioning device. Special software that allows sampling position and dose in user defined time intervals has been developed. The preliminary tests of the new device have been performed. The tests included measurements of spatial position accuracy as well as a dosimetric evaluation of the device in beam from a Theratron teletherapy unit. In addition, some tests were performed in a 6 MV beam from a Siemens linear accelerator to assess if the electromagnetic field from the linac interferes with the performance of the 4D dosimeter system. Results: Measurements of the angular response of the probe over 3600 range in a beam have been found isotropic within +/− 7%. Measurements of dose profiles in air in a beam have been performed. They agree very well with the measurements performed using RFA300 dosimeter system and a high quality photon diode. Tests conducted in a 6 MV beam indicate that there is no interference from the linac electromagnetic field on the performance of this new 4D dosimeter system. Conclusion: The results of the preliminary tests indicate that the device can be used for in-vivo dosimetry in a and high energy beams from linear accelerators. Future work will involve technical improvements to the device, experiments in a 4D phantom and finally patient in-vivo dosimetry. This project has been supported by HTX-OCE-IRAP grant.