Co-60 Machine Research Articles

Radiation-induced dermatitis among breast cancer patients undergoing adjuvant radiotherapy in Ghana

The aim of the study was to investigate radiation-induced epidermal desquamation among breast cancer patients undergoing radiotherapy with 6MV linac and Co-60 teletherapy units. MethodQuantitative data was collected using self-administered closed ended questionnaires addressing the desquamation in relation to some patient-and treatment-related factors. The Radiation Therapy Oncology Group (RTOG) criteria for acute skin toxicity was used to grade the toxicity. Chi square and logistic regression analyses were respectively used to test statistical significance and evaluate the effects of the various factors on radiation induced epidermal desquamation ResultsMajority of the participants had high BMIs (overweight: 39.5 %; obese: 50 %). Patients with BMI ≥ 25 kg/m2 presented with wet desquamation (RTOG grade 2). A chi-square analysis showed a significant difference (p = 0.02) between BMI and severity of desquamation. There was no significant difference between type of treatment machine and cumulative incidence dose of desquamation (p= 0.251). The logistic regression analysis showed that patients who had undergone mastectomy (OR = 0.562) were less likely to develop wet desquamation (RTOG grade 2) on the Co-60 machine within the 20–30 Gy threshold (OR=0.981) compared to those on the linear accelerator. Patients with lower BMI (OR = 0.412,[ < 25 vs ≥30]; OR = 0.286, [25–29.9 vs ≥30]) were also less likely to develop wet desquamation compared to those with higher BMI. ConclusionRadiation-induced epidermal desquamation is a common side effect of breast cancer patients undergoing radiotherapy. BMI has an effect on the severity of desquamation experienced during breast irradiation.

Effect of war on radiotherapy in Ukraine and how to help.

1513 Background: The full-scale Russian invasion of Ukraine on February 24th, 2022 brought the largest humanitarian disaster to the heart of Europe since the World War II. In this work, we describe the impact of the full-scale Russian invasion on the radiation therapy (RT) services in Ukraine and suggest how to help. Methods: We collected the information on operation of RT centers in Ukraine during the war. In addition, in 2023 an annual survey was conducted by Grigoriev Institute for Medical Radiology in Kharkiv for the IAEA DIRAC database. The survey was sent to 41 RT centers in Ukraine requesting information on equipment, staffing, and patient volume. Due to the war conditions the data provided in the survey is limited to the un-occupied territories. Results: After the initial Russian invasion of Ukraine in 2014 and occupation of Crimea and parts of Donbas, Ukraine lost access to 7 RT centers with 18 external beam radiotherapy (EBRT) machines (17% of total). Just before the full-scale invasion in 2022, there were a total of 44 Co-60 machines (57%) and 33 linear accelerators (43%) in the unoccupied territories. As a result of the full-scale invasion of Ukraine in 2022, almost all RT centers suspended operation in the first weeks of war. The most challenging period for RT in Ukraine was in March when Kyiv (where 20 EBRT machines are located) was partially surrounded by the occupiers. Based on the DIRAC survey, compared to 2021 data, in 2022 the number of radiation oncologists decreased on average by 2.9%, medical physicists by 6.7%, and therapists by 6.5% but there was a large variation in staffing levels depending on the region and its proximity to war. The workload in the RT centers close to the combat zone almost halved, while increasing by 10 - 60% in the western and central Ukraine. The total number of patients treated with EBRT decreased by 11% and brachytherapy by 21%. Brachytherapy services sustained the most interruption (47% decrease in LDR and 18% decrease in HDR patient volume) due to inability to perform source exchanges. Overall, approximately 5,500 less patients were treated in 2022 compared to 2021. Despite the ongoing war, Ukrainian cancer centers installed 8 new linear accelerators, with 5 linear accelerators pending installation. In addition, the Ministry of Heath of Ukraine has recently purchased 15 linear accelerators to replace the aging Co-60 machine fleet as the future source exchanges might not be possible. There is an acute need in helping Ukraine transition from Co-60 to modern IMRT/VMAT linear accelerators. Conclusions: Radiotherapy in Ukraine sustained significant damages since the 2014 Russian invasion, which was exacerbated further by the full-scale invasion in 2022. To support the vitality and absorptive capacity of RT services in Ukraine, the democratic world can help by donating equipment, hardware, software, and participating in training of Ukrainian RT professionals as they transition to modern and high-quality RT care for Ukrainian cancer patients.

Comparison of Percentage Depth Doses with the Published Data for Co-60 Radiotherapy Machine at a Regional Cancer Hospital

In external beam radiation therapy, the percentage depth dose (PDD) is a main factor for estimation of patient’s dose and dose distribution in target volume, therefore its accurate estimation is important. The purpose of this article is to compare PDDs with the published PDDs of different authors along central axis at different depths and field sizes for cobalt-60 (Co-60) radiotherapy machine at a regional cancer hospital Pakistan. A dedicated water phantom was used for estimation of PDDs at different depths and different field sizes, for Theratron phoenix Co-60 machine. It was observed that for 10×10 cm2 filed size of Co-60 beam mean percent variation in measured PDDs and published PDDs by different authors was -0.29% to 1.13%, which was within acceptable limit of ± 2%. However, for one author who used semi-empirical equation for PDDs calculation, the mean percent variation between measured PDDs and that of the author was -3.23%, 4.69% and 5.88% for 10×10 cm2, 25×25 cm2 and 30×30 cm2 field sizes of Co-60 beam respectively, which were within acceptable limit of ±10%. A noticeable increase in PDDs was observed with increase of the field size at given depth which shows obvious contribution of secondary scattered radiation. Also measured PDDs were well matched with that of published PDDs of most of the authors i.e. ± 2%, but the measured PDDs were moderately matched with that of PDDs for only one author for some field sizes and some depths i.e. ±10%, which need to be rectified by taking more such data.

Impact of War on Radiotherapy in Ukraine

The full-scale Russian invasion of Ukraine on February 24th, 2022 brought the largest humanitarian disaster to the heart of Europe since the World War II. Ukraine has lost tens of thousands of civilian lives, with approximately a third of the population displaced. The Russian army is deliberately damaging and destroying hospitals and clinics. This study describes the impact of the full-scale Russian invasion on the radiation therapy (RT) services in Ukraine. An annual survey was conducted by Grigoriev Institute for Medical Radiology, Kharkiv for the IAEA DIRAC database. The survey was sent to 41 RT centers in Ukraine requesting information on equipment, staffing, and patient volume. Due to the war conditions the data provided in the survey is limited. The information on operation of RT centers during the war collected by a Ukrainian Association of Medical Physicists representative is reported here as well. After the initial Russian invasion of Ukraine in 2014 and occupation of Crimea and parts of Donbas, Ukraine lost access to 7 RT centers with 18 external beam radiotherapy (EBRT) machines (17% of total). Just before the full-scale invasion in 2022, there were a total of 44 Co-60 machines (57%) and 33 linear accelerators (43%) in the unoccupied territories. As a result of the full-scale invasion of Ukraine in 2022, almost all RT centers suspended operation in the first weeks of war. The most challenging period for RT in Ukraine was in March when Kyiv (where 20 EBRT machines are located) was partially surrounded by the occupiers. The situation improved after Ukrainians liberated approximately half of total occupied territory. Currently, 2 additional RT centers are under occupation; 3 RT centers sustained heavy shelling and equipment damage. The response rate to the survey was 63%. Compared to 2021 data, in 2022, the number of radiation oncologists decreased by 7.8%, medical physicists by 7.3%, and therapists by 10.0%. The workload in the RT centers close to the combat zone almost halved, while increasing by 10 - 60% in the western and central Ukraine. The total number of patients treated with EBRT decreased by 11% and brachytherapy by 21%. Age of the RT equipment in Ukraine is shown in Table 1. Despite the ongoing war, Ukrainian cancer centers installed 3 new linear accelerators, with 14 linear accelerators pending installation. Radiotherapy in Ukraine sustained significant damages since the 2014 Russian invasion, which was exacerbated further by the full-scale invasion in 2022. To support the vitality and absorptive capacity of RT services in Ukraine, the democratic world can help by donating equipment, hardware, software, and participating in training of Ukrainian RT professionals as they transition to modern and high-quality RT care for Ukrainian cancer patients.

Measurement of Absorbed Dose in Water Using Co-60 gamma source Teletherapy Units According to IAEA Dosimetry Protocols

Modern radiotherapy facilities like 3-Dimensional conformal radio therapy (3DCRT), Intensity Modulated Radiotherapy (IMRT), were recently suggested in Co-60 machine with Multi-leaf Collimator (MLC). In this study, two reference chambers NE-2571#1205 and NE2581#537 were used for absolute dose measurement in Equinox accelerator. A comparison of dose measurement by two different IAEA protocols TRS-277 and TRS-398 has been studied. Analyzing TRS-398, a common shaped empirical formula was developed for the four Co-60 units of four Medical Colleges in Bangladesh with fitting parameters. It was found that an average discrepancy in the determination of absorbed dose in water among the two different protocols TRS-277 and TRS-398 were 1.33 % for the chamber NE-2571#1205 and 0.65 % for the chamber NE2581#537 with combined uncertainty ±1.59 % (k=1). A good convergence has been obtained in the concepts and methods in this study.

Co-60 MR Guided Adaptive Radiation Treatment Improves Target Coverage and Organs-At-Risk Sparing: Dosimetric Analysis of 1185 Adaptive Fractions and 5 Years’ Experience

Early data indicate MRI guided online adaptive radiotherapy (MRGRT) spares organs-at-risk (OARs) when inter-fractional motion of tumor targets and critical GI organs is significant. However, these studies were limited in patient numbers. This study systematically assesses all previously adapted treatment fractions of the MR imaging system Co-60 machine at the authors’ institution. The dosimetry metrics on patients’ treatment day anatomy between the adapted plans vs the un-adapted plans are compared. The aims are to determine the reasons (and corresponding rates) necessitating plan adaptations and quantifying improvement in target coverage. All abdominal cancer patients (N = 137) previously treated with MRGRT on the VR Co-60 machine from 2015 to 2019 are included. Treatment sites were pancreas (98), adrenal (11) and not otherwise specified abdomen (28). A total 961 (81.1%) out of 1185 fractions were adapted. Plan adaptation conditions were 1) the target was edited, or 2) any critical OAR constraints were violated, or 3) target coverage was significantly worse (V95%Rx reduction >10% for PTV-PRV) than the one achieved with the previous plan. For each adapted fraction, dose was calculated using a Monte Carlo dose calculation engine previously developed by authors for both 1) the plan before adaptation and 2) the adapted new plan. A suite of computer algorithm programs were developed to 1) process the treatment plan data files exported from TPS, 2) recognize the case-specific target structure and critical OARs, 3) compute treatment-day DVH metrics (V95%Rx and D95% for the targets, and V>constraint for OARs) on the calculated dose volumes, and 4) analyze the results arithmetically and statistically. Data of 961 adapted treatment fractions were processed and analyzed. The analysis shows that 1) critical OARs were edited for 100% cases, 2) tumor targets were edited for 90 (9.4%) cases, 3) critical OAR constraints were violated for 870 (90.5%) cases by the un-adapted plans, 4) plan optimization objectives were edited for 33 (3.4%) cases and 5) all critical OAR constraints were met in all (100%) adapted plans, 6) target coverages were improved for 888 (92.4%) cases with the adapted plans compared to un-adapted plans that were normalized to meet OAR constraints. After more than 5 years and 1100 fractions of experience, results continue to confirm that adapted plans provided significantly better target coverage while preventing violation of critical OAR constraints. Future work is necessary to establish the clinical significance of these data and validate these findings in the VR MRI Linac.

ANALYSIS OF RADIATION THERAPY EQUIPMENT STATUS IN UKRAINE

The subject matter of the article is review and analysis of existing radiation treatment technologies, availability and efficiency of use of modern radiotherapy equipment in regions Ukraine according to European radiotherapy development trends. The goal of the work is to analyze the current status of radiotherapy equipment in Ukraine and to find the ways for extension of its use. The following tasks were solved in the article: the analysis of distribution of radiotherapy machines in Ukraine, estimation of current number of radiotherapy machines per million people for all regions and needs of radiotherapy centers of Ukraine in high precision conformal treatment machines. The following methods used – documentary data analysis, comparison and summarizing. The following results were obtained – estimated that according to requirements of IAEA that necessary number of megavoltage treatment machines in Ukraine should be near 200. Use of 90 machines covers only 45% needs of Ukrainian population in radiation treatment. According to DIRAC data 61 of 65 Co-60 machines in Ukraine are used during more than 20 years, Co-60 sources in 23 these machines now have Dose rate less than 0.4 Gy/min and must be replaced urgently. Conclusions: The main actual aspects of technical status of equipment for External-beam radiation therapy in Ukraine were discussed. Existing radiotherapy facilities were analyzed from the point of view of real needs and possibilities of Ukrainian radiation oncology. As a conclusion, the results of this analysis demonstrate a significant heterogeneity in the access to modern radiotherapy equipment in different regions of Ukraine. The qualitative analyses of used radiotherapy equipment demonstrate its significant technical backwardness. The results of this analysis may be used as technical recommendations for improvement of radiotherapy facilities in Ukraine.

A randomized prospective study comparing concomitant chemoradiotherapy using paclitaxel-carboplatin with concomitant chemoradiotherapy using etoposide-cisplatin in inoperable or nonresectable locally advanced non-small cell lung cancer

Context: Several randomized trials have established that the best survival can be achieved in patients with locally advanced non-small cell lung cancer (NSCLC) with concurrent chemoradiation (CRT). In this study, we have compared different chemotherapy regime along with radiation in locally advanced NSCLC. Aims: Compare the disease response, toxicity, quality of life (QoL) and overall survival in concomitant CRT using paclitaxel-carboplatin versus cisplatin-etoposide for the radical treatment of NSCLC. Subjects and Methods: In this randomized study, 36 patients were enrolled. In study arm, patients were treated with injection cisplatin-etoposide along with external beam radiotherapy (EBRT) to a total dose of 60 Gy, using CO-60 machine. In study arm, patients were treated with injection paclitaxel-carboplatin along with EBRT. QoL was evaluated using QLQ–LC13 questionnaire. Results: The median age of patients was 65 years. Complete response was obtained in two patients in control and two patients in the study arm. Partial response was obtained in 11 patients in the control arm and 13 patients in the study arm. The observation was statistically insignificant. When Grade ≥III toxicities are analyzed, the total number of events in the control arm were three (16.7%) and in the study arm were five (27.8%) which is statistically insignificant. Statistical Analysis Used: The data were analyzed using Chi-square and t-test, and P values were calculated. Conclusion: The response rates and disease progression are similar between the two arms. The other endpoints are also similar between the two arms. However, larger studies are needed to establish comparability.

Assessment of Radiotherapy Treatment Field on Portal Film Using Image Processing

Many factors contribute to the accuracy of delivered dose to patients in external-beam radiotherapy (EBRT). Although some of these factors can be checked by implementing suitable quality control procedures, the main aim was to assess the radiotherapy treatment filed on portal film using image processing technique in order to increase the accuracy of treatment delivery to the tumor by measuring the actual F/S, dose uniformity and penumbra size using portal film. This research is conducted at radiation therapy department, Khartoum Oncology Center (RICK), Khartoum state, Sudan, from July-2014 up to December-2014. The field size of each type of radiotherapy Co60 is measured as (9.4 × 9.4) cm and (9.1 × 9.1) cm, for linear accelerator machines it was 10 × 10 cm exactly as the reference field size, and there is no area reduced in linacs. The penumbra size for the two types of Co60 machine was measured also and it was 1.2 cm and 1.0 cm, and penumbra size of the linear accelerator machines was found to be 4 mm. The area of the field that received radiation by 100% was measured and it was 94.1% and 91.1% in Co60 and 100% for linear accelerator machine and that means linacs deliver the 100% of the dose to the useful field size. The dose percentage in the field for Co60 was 98.0% and 94.1% and thus the dose in the border of field 83.1% and 89.0% and it’s different in linacs because the dose percentage in the field was 78.4% and 78.4% and there is no measurable dose outside its field. Penumbra Co60 machines are relatively large which increase radiation dose to normal tissue and reduce the TCP, so calculation and accuracy of such calculation are necessary to the patient in term of NTCP.

Abstract ID: 89 Investigation of conformal arc therapy utilizing Cobalt 60 beams

Purpose The trend today in modern radiation therapy is toward conformal therapy with segmented or moving field techniques. Generally, this requires multifield irradiation or the use of arc/rotation therapy. Many authors have pointed out in literature that if the Co-60 machines were modernized with state of the art devices, it may be able to provide similar quality of radiation therapy as provided by linacs. Co-60 units will have the advantage of having more simple and robust design, and minimal maintenance and technical expertise to operate the machine as compared to the technologically complex linacs. Thus, in this work we conduct a dosimetric comparison between conformal arc utilizing Co-60 beams and that utilizing 6MV beam energy. Material and methods CT scans was unarchived for patient previously treated by SBRT in our department. We selected lung, breast, and head and neck cases. All of these cases were previously planned on Eclipse planning system (Varian, Palo Alto, Medical Systems). We regenerated treatment plans using conformal arcs with the arc being modeled by delivery of multiple conformal beams. Dose distributions for all plans were calculated using Monte Carlo simulation for both 6MV and Co-60 beam energies. Results As the number of fields increases, advantage of higher energies over lower radiation energies decreases. In all studied cases, conformal arc plans utilizing Co-60 beam was achieving almost same conformity when compared to the 6Mv plans. Isodose distributions were tailored similarly around the PTV. On reviewing the minimum and maximum dose reaching all targets, it was shown that both Co-60 and 6Mv plans was achieving our clinical acceptation criteria for the target coverage. The DVH of Co-60 plans were showing slightly lower dose to critical structures however the difference was small in most cases. Conclusion Our results have shown the potential for newly designed Co-60 machines as a modality that could treat a good fraction of cancer patients. The overall performance seen in the conformal arcs using Co-60 beams was encouraging as being compared to the 6MV conformal arcs. There was no significant superiority detected for the 6MV plans over the Co-60 plans for SBRT cases.

Evaluation of Radio-Protective Effects of N-Acetylcysteine on Radiation-Induced Lethality in Mice

Introduction It has long been known that ionizing radiation can lead to detrimental effects in normal cells. In this light, Radioprotective chemicals have been used to decrease morbidity or mortality caused by ionizing irradiation. This study aimed to evaluate the radio-protective effect of N-acetylcysteineagainst radiation-induced mortality in male mice. Materials and Methods 52 healthy male mice were divided into four groups including NAC before irradiation (1), irradiation (2), NAC after irradiation (3) NAC before irradiation (4) and control. Three groups were treated orally with 100 mg/ kg of NAC. Gamma irradiation was performed at 8 Gy using a Co-60 machine. Kaplan-Meier method and the log-rank test were performed, using SPSS version 16. The significance level was considered to be 0.05. Results The statistical analysis revealed a significant difference between the test and control groups (P<0.05). The percentage of survival after 30 days was 46.2% for the irradiation group (1). In addition, the percentage of decreased lifespan was calculated at 5.90%, 23.60% and 17.93% for the first-third groups, respectively. Conclusion Results revealed lack of effectiveness of treatment with NAC after lethal dose. These results suggested that application of NAC for mice before irradiation protected them from the lethal effects of whole-body irradiation.

P2.05-026 Postoperative Radiotherapy in Non-Small Cell Lung Cancer: 20 Years' Experience in a Single Center: Topic: Multimodality Treatment

The purpose of this study is to evaluate the long term outcomes of postoperative radiotherapy (PORT) in patients with NSCLC. A total of 130 patients with resected NSCLC who were treated with PORT between January 1994 and December 2014 were respectively evaluated. Among the whole group 86 patients (66%) were treated with Co60 machines till 2005, and 44 patients (34%) with 6-10 MV photons with linear accelerators. Median RT dose was 54 Gy(range, 48-66 Gy) with 2 Gy daily fractions. the treatment fileds covered the bronchial stump, ipsilateral hilum and mediastinum in 109 patients (83.8%); bronchial stump, ipsilateral hilum, mediastinum and supraclavicular nodes in 15 patients (11.5%); and bronchial stump and ipsilateral hilum in 6 patients (4.6%). Cisplatinum-based chemotherapy was administered to 69 (53%) patients. Chemoterapy was applied preoperatively in 22 patients (17%), concomitantly in 27 patients (21%), and after PORT in 20 patients (15%). Overall (OA) survival, locoregional-free (LRF) survival and distant-metastasis free (DMF) survival were calculated using the Kaplan-Meier method. The median age of the patients was 59 years (range 35-75 years). The most frequently performed surgical procedure was lobectomy (64.6%), followed by pneumonectomy (19.2%), wedge resection (10%), and bilobectomy (6.2%). Stages included I (19.2%), II (42.3%), IIIA (30.8%), and IIIB (6,9%). Neoadjuvant chemotherapy was applied to 62% of stage III patients.The median overall survival was 48 months. The 5-year OA, LRF and DMF survival rates for whole group were 43%, 75%, and 63% respectively. Significant prognostic factors for OA survival were indicated in the table. Acute and subacute toxicities were Grade I to II esophagitis in 48 patients (37%), anemia in 11 patients (8%), pulmonary infection in 11 patients (8%), and Grade ≥II radiation pneumonitis in 11 patients (8%) Radiation-induced late toxicities including radiologic Grade I to II fibrosis were recorded in 22 patients (17%).Tabled 1The Prognostic Factors for Overall SurvivalCharacteristics5-yearOA survivalUnivariateAnalysis (Log-rank p value)Multivariate Analysis(Cox regression p value)Age(Years) <59 >=5955 320.0120.000KPS 70-80 90-10035 480.0280.003Laterality Left Right31 540.0110.005Stage T1-T2 T3-T455 280.0010.050Dose <54 >=5455 360.0370.006 Open table in a new tab Unfavorable prognostic factors for PORT were RT dose > 54 Gy, advanced T stage, poor Karnofsky performance status, advanced age, and left sided tumors. When irradiating left-sided tumors cardiac toxicity must be kept in mind.

Medical Physics Challenges for the Implementation of Quality Assurance Programmes in Radiation Oncology

The importance of quality assurance in radiation therapy, as well as its positive consequences on patient treatment outcome, is well known to radiation therapy professionals. In low- and middle-income countries, the implementation of quality assurance in radiation therapy is especially challenging, due to a lack of staff training, a lack of national guidelines, a lack of quality assurance equipment and high patient daily throughput. According to the International Atomic Energy Agency (IAEA) Directory of Radiotherapy Centres, the proportion of linear accelerators compared with Co-60 machines has increased significantly in recent years in low- and middle-income countries. However, this increase in the proportion of relatively more demanding technology is not always accompanied with the necessary investment in staff training and quality assurance. The IAEA provides supports to low- and middle-income countries to develop and strengthen quality assurance programmes at institutional and national level. It also provides guidance, through its publications, on quality assurance and supports implementation of comprehensive clinical audits to identify gaps and makes recommendations for quality improvement in radiation therapy. The new AAPM TG100 report suggests a new approach to quality management in radiation therapy. If implemented, it will lead to improved cost-effectiveness of radiation therapy in all income settings. Low- and middle-income countries could greatly benefit from this new approach as it will help direct their scarce resources to areas where they can produce the optimum impact on patient care, without compromising patient safety.

SU-F-T-375: Optimization of a New Co-60 Machine for Intensity Modulated Radiation Therapy: A Monte Carlo Characterization Study

Purpose: To provide a wide range of dose output for intensity modulation purposes while minimizing the beam penumbra for a new rotating cobalt therapy system. The highest dose rate needs to be maximized as well. Methods: The GEPTS Monte Carlo system is used to calculate the dose distribution from each tested Co-60 head for a wide range of field sizes (1×1 to 40×40 cm2). This includes the transport of photons (and secondary electrons) from the source through the collimation system (primary collimator, Y and × jaws, and MLCs) and finally in the water phantom. Photon transport includes Compton scattering (with electron binding effect), Rayleigh scattering, Photoelectric effect (with detailed simulation of fluorescence x-rays). Calculations are done for different system designs to reduce geometric penumbra and provide dose output modulation. Results: Taking into account different clinical requirements, the choice of a movable head (SAD = 70 to 80 cm) is made. The 120-leaf MLC (6-cm thick) entrance is at 32 cm from the bottom of the source (to reduce penumbra while allowing larger patient clearance). Three system designs (refereed here as S1–3) were simulated with different effective source sizes (2mm, 10mm and 17mm diameter). The effective point source is at mid-height of the 25-mm-long source. Using a 12000-Ci source, the designed Co-60 head can deliver a wide range of dose outputs (0.5 − 4 Gy/mn). A dose output of 2.2 Gy/mn can be delivered for a 10cm × 10cm field size with 1-cm penumbra using a 10mm effective source. Conclusion: A new 60Co-based VMAT machine is designed to meet different clinical requirements in term of dose output and beam penumbra. Outcomes from this study can be used for the design of 60Co machines for which a renewed interest is seen.

Current status of radiation oncology facilities in Nigeria

Background: An analysis of the current radiation oncology facilities status in Nigeria was conducted to establish a comprehensive baseline. Nigeria is the most populated African country with a population of at least 160 million people based on 2006 population census and average annual growth rate of 3.1%. It is also one of the least developed countries as regards radiation oncology resources with inadequate radiotherapy facilities. Many of the patients have little or no access to safe and modern radiation therapy. Purpose: To obtain a better understanding of the status of radiation oncological practices in Nigeria and to help sensitize the Nigerian government and its developmental partners on the way forward. Materials and Methods: The data were obtained mainly through surveys on the availability of major items of equipment and personnel which were conducted in September 2011. The study included only commissioned and functioning public radiotherapy facilities which are 5 in the country. Data were related to number and types of megavoltage machines, trained manpower (Radiation Oncologists, Medical Physicists, Oncology Nurses, Radiotherapy technologists, maintenance engineers and mould room Technicians), treatment planning systems TPS, Brachytherapy equipment, CT Simulator and Conventional simulators. Results: Of over 50 Tertiary Health Institutions (Teaching Hospitals and Federal Medical Centers) in the country, only 5 has Radiation Therapy facilities with 1 megavoltage machine each, 2 located in the north, 2 in the south and 1 in the Federal Capital Territory. The population served by each megavoltage machine ranges from 20 to 40 million per machine based on 2006 census. Most patients have little or no access to radiation oncology services. Some differences in equipment and personnel amongst centers were demonstrated and the shortage of radiation therapy resources was grossly evident. There are 18 Radiation Oncologists, 8 Medical physicists, 18 Radiotherapy technologists, 26 Oncology Nurses, 3 linear accelerators, 2 Co-60 machines, 2 orthovoltage therapy machines, 2 conventional simulators, 2 CT simulators, 2 centers with 3D TPS, 3 LDR and 1 HDR brachytherapy machines and 2 mould rooms. Some centers were found to treat patients without simulators or treatment planning system. Conclusion: A large deficiency exists for radiation oncological services in Nigeria. There are significant deficiencies in the availability of all components of radiation therapy in the analysed centers. Cognisance should be taken of the specific short falls in each centre to ensure that there is expansion of existing centers and creation of new centers especially in every geopolitical zone and major teaching hospitals in the country.

Fabrication and Optimization of a PAGATA Gel Dosimeter: Increasing the Melting Point of the PAGAT Gel Dosimeter with Agarose Additive

Introduction: The PAGAT polymer gel dosimeter melts at 30 ˚C and even at room temperature during the summer, so it needs to be kept in a cool place such as a refrigerator. To increase the stability of the PAGAT gel, different amounts of agarose were added to the PAGAT gel composition and the PAGATA gel was manufactured. Material and Methods: The PAGATA gel vials were irradiated using a Co-60 machine. Then, the samples were evaluated using a 1.5 T Siemens MRI scanner. The ingredients of the PAGATA normoxic gel dosimeter were 4.5% N-N' methylen-bis-acrylamide, 4.5% acrylamide, 4.5% gelatine, 5 mM tetrakis (THPC), 0.01 mM hydroquinone (HQ), 0.5% agarose and 86% de-ionized water (HPLC). Results: Melting point and sensitivity of the PAGAT gel dosimeter with addition of 0.0, 0.3, 0.5, 1.0, 1.5 and 2.0% of agarose were measured, in which the melting points were increased to 30, 82, 86, 88, 89 and 90°C and their sensitivities found to be 0.113, 0.1059, 0.125, 0.122, 0.115 and 0.2 respectively. Discussion and Conclusions: Adding agarose increased the sensitivity and background R2 of the evaluated samples. The optimum amount of agarose was found to be 0.5% regarding these parameters and also the melting point of the gel dosimeter. A value of 0.5% agarose was found to be an optimum value considering the increase of sensitivity to 0.125 and melting point to 86°C but at the expense of increasing the background R2 to 4.530.

SU-GG-T-608: Modeling Scatter-To-Primary Dose Ratio for Megavoltage Photons

Purpose: In radiation oncology, measured x-ray dose (TPR or PDD) at central axis are usually tabulated and used for clinical dose calculation. An efficient technique to examine these datasets whether contain systematic or random errors can be useful to maintain the accuracy of the data and improve patient treatment. An optimization routine employing a newly developed scatter-to-primary dose ratio (SPR) can be used to examine the accuracy of clinical beam data. The SPR formula proposed in this study is more accurate than that published previously, especially for low energy beams, because the effect of backscattered photon is taken into account. Method and Materials: A formula, involving three fitting parameters, is formulated to express the SPR. Because of absence of measurement error and the ability separating scattering and primary dose component, Monte Carlo (MC) data is used to extract these parameters. Based on the results of fitting MC data, we are able to obtain a set of empirical expression for the fitting parameters as a function of photon beam attenuation coefficients. These empirical expressions are implemented into our optimization routine, used to match measured beam data. Results: In terms of fitting accuracy for MC, the new SPR formula outperforms the previously published form. For clinical data study, our optimization routine successfully fits the measured photon beam data with depth and field size up to 40 cm for a large variety of linear accelerators (6 to 25 MV) and Co60 machine from different manufactures. The maximum error among these fits is 2.8 % for Co60 and better than 2 % for all other energies. Conclusion: Because of the high fitting accuracy, our optimization routine, incorporating the new SPR form, can serve as a tool performing quality control of x-ray beam data in a fast-pace clinical environment.

EVALUATION OF THE RTDOSEPLAN TREATMENT PLANNING SYSTEM USING RADIOCHROMIC FILM AND MONTE CARLO SIMULATION

Introduction: GafChromic EBT films are one of the self-developing and modern films commercially available for dosimetric verification of treatment planning systems (TPSs). Their high spatial resolution, low energy dependence and near-tissue equivalence make them suitable for verification of dose distributions in radiation therapy. This study was designed to evaluate the dosimetric parameters of the RtDosePlan TPS such as PDD curves, lateral beam profiles, and isodose curves measured in a water phantom using EBT Radiochromic film and EGSnrc Monte Carlo (MC) simulation. Methods and Materials: A Microtek color scanner was used as the film scanning system, where the response in the red color channel was extracted and used for the analyses. A calibration curve was measured using pieces of irradiated films to specific doses. The film was mounted inside the phantom parallel to the beam's central axis and was irradiated in a standard setup (SSD = 80 cm, FS = 10×10 cm2) with a 60Co machine. The BEAMnrc and the DOSXYZnrc codes were used to simulate the Co-60 machine and extracting the voxel-based phantom. The phantom's acquired CT data were transferred to the TPS using DICOM files. Results: Distance-To-Agreement (DTA) and Dose Difference (DD) among the TPS predictions, measurements and MC calculations were all within the acceptance criteria (DD=3%, DTA=3 mm). Conclusion: This study shows that EBT film is an appropriate tool for verification of 2D dose distribution predicted by a TPS system. In addition, it is concluded that MC simulation with the BEAMnrc code has a suitable potential for verifying dose distributions.

VIABILITAS INOKULAN DALAM BAHAN PEMBAWA GAMBUT, KOMPOS, ARANG BATOK DAN ZEOLIT YANG DISTERIL DENGAN IRADIASI SINAR GAMMA Co-60 DAN MESIN BERKAS ELEKTRON

Carrier is one of the important factor to determine the quality of biofertilizer. The inoculant carriers should contain no or less microbial contaminant. The purpose of this research was to investigate viability of Azospirillum, Azotobacter and Phosphate Solubilizing Fungi inoculants in carrier material that were sterilized by Gamma Irradiation Co-60 and Electron Beam Machine (EBM). Each inoculants was injected to the sterilized peat, compost, coconut shell charcoal and zeolite. Viability of inoculants in steriled carrier was evaluated at 0, 7, 14, 42 and 70 days after preparation. The stirage was done in incubator at 25ºC. The result of viability of Azospirillum, Azotobacter and Phosphate Solubilizing Fungi inoculants on sterilized carrier material by Gamma Irradiation Co-60, EBM and autoclave tended to decline during storage 70 days at room temperature (250C). Viability of Azospirillum inoculants in zeolite sterilized by Gamma Irradiation Co-60 and autoclave gave the highest numbres of viable cells. Storage of these inoculants at 25ºC for 70 days only reduce the number of viable cells by 11.1%. Viability of Phosphate Solubilizing Fungi inoculants in coconut shell charcoal or compost sterilized by Gamma Irradiation Co-60 went down by 99.8% after 70 days. The sterilization of carriers by using autoclave or Gamma Irradiation Co-60 were better than EBM sterilization. . Keywords: Carrier, Electron Beam Machine, Gamma Irradiation Co-60, sterilization, viability

Design of mini phantom and measurement of cobalt-60 beam data parameters

Low cost mini phantoms were fabricated indigenously with different water equivalent material such as polymethyl methacrylate and Bee's wax of different shapes (with dome top surface and flat top surface). The beam parameters of the Co-60 machine, such as head scatter correction factor (Sh), phantom scatter correction factor (SP), total scatter correction factor (SC,P), collimator exchange effect were measured. Output ratio measurements were taken for both mini phantom and water phantom for different square and rectangular field sizes. Normalized output ratios were compared with ESTRO published values and (Storchi and Van Gasteren) S and G data. The percentage of variation between the measured and the literature values is about 0.7%. Collimator exchange effect were measured for water and mini phantom for different field size, were compared with ESTRO value. This was found to be 0.5% and 1.0% respectively. Phantom scatter correction factors were calculated for square and rectangular filed sizes; this was compared with ESTRO values, found to be 0.7% for square and 1.0% for rectangular filed size. It was also noted that there were no appreciable variation observed in ion chamber readings of different materials of mini phantoms for dome and flat surfaces. Mini phantom measurements were done for all types of phantoms and the measured values were compared with the existing data and they were in good agreement with the published values.