Teletherapy Unit Research Articles

Effect of Field Size Dependence on Dose Rate on Co-60 Teletherapy Unit at BINOR

Background: Cancer, defined as the uncontrolled proliferation of malignant cells, is a serious hazard. Radiotherapy, which employs high-energy radiation, seeks to break cancer cell DNA. Due to the significant consequences involved, accuracy is of utmost importance. Before commencing radiation therapy, thorough quality assurance procedures are carried out. The Percentage Depth Dose (PDD) is employed to ensure accurate dose measurement. The research utilized Cobalt-60 Teletherapy, which produces gamma radiation at energy levels of 1.17 MeV and 1.33 MeV, to assess the various field widths observed in PDD. In this experiment, the percentage depth dose (PDD) was evaluated by using a Farmer chamber, water phantom, PC electrometer, ionization chamber, computer software and barometer. The chamber was used throughout a range of field sizes, which varied from 5x5cm2 to 20x20cm2.The TRS-398 approach was employed to assess the radiation dose. Comparable findings were observed when conducting comparisons with published PDD data for cobalt-60 beams. The accumulation dose zone was found to be located approximately 0.5 cm below the surface, coinciding with the maximum (Zmax) dose site. The absorbed amount of radiation resulted in a decrease in the percentage depth dose (PDD) below the given depth. DOI: https://doi.org/10.52783/pst.643

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.

Clinical Audit of Beam Output of Cobalt-60 Teletherapy Unit at AECH-BINOR

Clinical Audit of Beam Output of Cobalt-60 Teletherapy Unit at AECH-BINOR

Radiotherapy Resources in Latin America and the Caribbean: An International Atomic Energy Agency Analysis of Current and Projected Needs

The inequitable access to radiotherapy (RT) is recognized to be a complex undertaking that will require sustained work identifying gaps and mobilizing efforts to fill in those gaps. Data can support policy-makers as they embark on programs to reduce premature mortality from cancer in their countries and regions. The purpose of this analysis is to identify the current gaps and needs in Latin America and the Caribbean (LAC). We created a database of 41 countries in LAC using open-source data, including data on population size (UN Department of Economic and Social Affairs data), gross national income per capita (GNIPC) (World Bank Data), current and projected cancer incidence and mortality (Globocan 2020). The International Atomic Energy Agency (IAEA) Directory of Radiotherapy Centers (DIRAC) was used to identify the number and operational status of megavoltage (MV) teletherapy machines (Cobalt-60 and Linear Accelerators LINACs) and brachytherapy facilities (HDR and LDR). To calculate current and projected gaps in external beam RT (EBRT) facilities, we matched DIRAC data with Globocan cancer incidence data for 2020 and projections for 2025 and 2030 while applying a 64% optimal EBRT utilization rate (taking into account re-treatment). For brachytherapy, analysis took into account both HDR and LDR capacity and was primarily focused on needs based on current and projected incidence of cervical cancer cases in LAC. EBRT was available in 32 (76%) of 41 countries. There were 742 RT centers in 32 countries with a total of 1131 MV units. Average coverage in 2022 based on an optimal utilization rate of 64% was 64%. LINACs accounted for 87% of the total MV units and Cobalt-60 capacity decreased to 13% of total teletherapy capacity compared to capacity in 2018. Most countries clustered in the same range of GNIPC to teletherapy units per 1000 cases, however outliers were most notable in the Caribbean. The median GNIPC was $6340 and the median MV units per 1000 cancer cases were 1.4. The current deficit in MV units is estimated at 672 megavoltage units and projected to be 2455 units by 2030 representing more than double the current capacity. 28 out of 41 countries (68%) had brachytherapy including 279 installed services, both HDR and LDR. At a 75% optimal utilization rate of brachytherapy in locally advanced cervical cancer, the current brachytherapy capacity in LAC could treat 108,420 patients with cervical cancer/year, which meets the current needs in the region albeit with significant inequity in distribution of resources. There is 15% improvement in the current EBRT capacity in LAC compared to 2018. However, there is still shortage of at least 672 extra units needed. By 2030, the need for MV units will be double the current capacity. The current brachytherapy capacity meets needs albeit with inequitable distribution across the region primarily in the Caribbean.

Studies of dose distribution to Lung and Stomach and Estimation of Second Cancer Risk due to Outfeld Dose in Radiotherapy with 60Co Teletherapy Beam

A critical component of the radiation regimen for treating cancer patients is the precise dose delivery to the treatment organ while minimizing the dose to the healthy tissue. This study aims to evaluate in-field organ dose and dose distribution outside the target organs to estimate the excess lifetime risk of second cancer. The study was carried out with a male Alderson Rando Phantom. 20 sets of thermoluminescence dosimeters (MTS-100) were used in this study. The in-field organs absorbed dose was measured by inserting TLDs at different geometrical depths of the left lung, right lung, and stomach, and for peripheral organs skin dose TLDs were placed at the surface of the corresponding organs. Target organs were irradiated at 100 cGy and 200 cGy by a 60Co teletherapy unit, and irradiated TLDs were read out by a RE-2000 TLD reader. For precise dose delivery to the cancerous organs by 60Co teletherapy, the depth dose correction factor for lung cancer treatment is 0.8667 ± 0.01, and for the stomach is 0.7856 ± 0.017. In the case of the treatment for the lung and stomach, the closest organs received significant doses compared to the other distant organs. Thus, the risk of second cancer due to the peripheral dose is obtained. The stomach is at the highest risk when the lung is the target and the liver is at the highest risk when the stomach is the targeted organ.

The Goiânia incident, the semiotics of danger, and the next 10,000 years

The Goiânia Incident In September 1987, two men in Goiânia, Brazil, discovered an abandoned international standard capsule containing less than 100 g of cesium-137 chloride. The material was unguarded, and the warning systems were inadequate and inscrutable. The men took the capsule and sold it for scrap, and within days the city would be contaminated with highly radioactive material. Within weeks, 112,000 individuals would be screened for radioactive contamination, 249 would be exposed to radioactive materials, 46 would receive medical treatment for radioactive contamination, and four would die from acute radiation sickness. The citywide radioactive contamination occurred, in part, due to arbitrary and unfamiliar written warning systems. The individuals who discovered the cesium-137 capsule were illiterate and unfamiliar with the radiation trefoil logo, which was first used in 1946 in California, United States of America. As a result, written language and visual symbols were useless warnings against the dangerous contents of the capsule. Management of cesium-137 exposure in 2023 Cesium-137 enters the body through ingestion or inhalation. This isotope emits beta and gamma radiation, both forms of ionizing radiation which damage living tissues. The radiation dose lethal to 50% of an exposed population within 60 days (LD50/60) is approximately 3.5 to 4 Gray (Gy) without medical intervention. However, this dose increases to around 6-7 Gy when medical support is provided, which typically includes antibiotics, blood transfusions, granulocyte-macrophage colony-stimulating factor, and Prussian blue. Prussian blue binds to cesium, thereby facilitating its elimination from the body. Lessons learned regarding radioactive waste disposal and the next 10,000 years The radiological disaster in Goiânia was due in large part to the failures of various agencies to warn of danger and minimize access to radioactive material. Barriers to risk communication included a lack of a universal semiotic language regarding radioactive hazards, which was compounded by the illiteracy of the scrappers and their inability to recognize the radioactivity warning trefoil. There is no society in which every member understands written language or recognizes every symbol. Given that the teletherapy unit was abandoned in an urban environment, there were no administrative or engineering controls in place to prevent human beings from becoming exposed to radioactive material. Conclusions As little as 100 g of highly radioactive material, such as cesium-137, may lead to massive environmental contamination, fatalities and permanent disability due to acute radiation sickness, wreak havoc, and disrupt society on a scale that is challenging for public health officials to manage. Thousands of tons of radioactive materials from the waste products of nuclear weapons and power plant manufacture will have to be stored for at least 100,000 years to prevent danger to human life and society. Public health officials and governments must build systems to keep humans safe and physically isolated from these radioactive materials for as long as possible.

Clinical utilization of radiation therapy in Korea between 2017 and 2019.

This study aimed to evaluate the clinical infrastructure and utilization of radiotherapy (RT) services in Korea between 2017 and 2019. We extracted the data of patients who underwent RT between 2017 and 2019 from the Health Insurance Review and Assessment Service. We further analyzed this data according to the diagnosis and treatment modalities of patients diagnosed with International Classification of Disease 10 (ICD-10) diagnostic codes C00-C97 and D00-D48. In addition, we collected statistics on RT facilities in Korea using a nationwide survey. The total number of patients who received RT in 2017, 2018, and 2019 were 77,901, 81,849, and 87,460, respectively. The number of patients diagnosed with ICD 10 C- and D-codes in 2019 was 86,339, of whom 39,467 were men and 46,872 women. The rate of utilization of RT among cancer patients was 30.4% in 2017 and 2018 and 30.9% in 2019. In 2019, the most common types of cancers treated with RT were breast, lung, prostate, colorectal, and liver cancers. Regarding the RT infrastructure in Korea, there were 95 radiation oncology centers, 237 megavoltage (MV) teletherapy units, 35 brachytherapy units, and two proton accelerators in 2019. There were 4.5 MV teletherapy machines per million. The number of patients treated with RT has increased consistently from 2017 to 2019. As the number of patients with cancer increases, it is expected that the RT infrastructure will be further expanded in Korea.

Small fields characterization of teletherapy cobalt-60 photon beam: An experimental and Monte-Carlo study

This research work aims to study small field characteristics of the 60Co source-based teletherapy machine by varying the detector size and source size. Further, the feasibility of clinical use of small fields on 60Co source-based teletherapy unit has been studied. In this study, square fields size varying from 1 × 1 cm2 to 10 × 10 cm2 were used. Two different ionization chambers (SNC125c and Pinpoint) having different sensitive volumes were used for experimental measurements, and the tool for particle simulation (TOPAS) version 3.5 toolkit was used for Monte Carlo (MC) simulations. All the data was measured as per the recommendation of the International Atomic Energy Agency (IAEA) technical report series-483 (TRS-483). Firstly, MC simulated beam data (beam profiles and percentage depth dose) was validated against the experimentally measured beam data and found to be agreed within 2%/2 mm gamma criteria. The SNC125c underestimate the output factors (OFs) by 7% and 5% when compared to MC calculated OFs for small beams of 1 × 1 cm2 and 1.5 × 1.5 cm2, respectively. The full-width half-maxima (FWHM) of all field sizes agreed with the set geometric field size other than 1 × 1 cm2 and 1.5 × 1.5 cm2, for which it was found most deviated, and it shows significant dependency on the size of the source. The present study showed that chamber size significantly impacts the measurement of small fields characteristics, mainly OFs. Further, source size is another parameter that significantly affects the beam profiles that limits the use of 60Co teletherapy machine for field sizes smaller than 3 × 3 cm2.

Assessment of Measured and Calculated Dose Rate of Co-60 Teletherapy Machine: 06 Years’ Experience at NORIN Nawabshah, Pakistan

It is essential to determine the absolute output dose of Co-60 source in the radiation treatment periodically. It is because overdosage may cause radiation hazards whereas under dosage may lead to the unsatisfactory treatment of cancer. The current study is focused on the consistency of monthly dose output verification of the cobalt-60 Teletherapy unit which should be within ±2% as per international standards. In the present study, the measured and calculated dose rate of the Co-60 teletherapy unit at Nuclear Medicine Oncology and Radiotherapy Institute Nawabshah (NORIN) for the last 6 years is analyzed. The dose measurement was done in water phantom 30×30×30 cm3 at 80 cm Source to Surface Distance with 5cm depth by using calibrated electrometer and PTW ionization chamber. The measured output dose rate obtained by actual dosimetry is within ±2% of the dose rate calculated by the decay method and the deviation lies within the permissible limit as prescribed by International Atomic Energy Agency (IAEA), International Commission on Radiological Units and Measurement (ICRUM)and American Association of Physicists in Medicine (AAPM). The variation in measurements obtained is within the tolerable limits according to standard protocols and codes. Thus, our study shows a homogenous trend in the dose rate of the Co-60 teletherapy machine.

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.

Status of cancer treatment by radiotherapy and requirement of radiation oncology medical physicists in Asia Oceania federation of organizations for medical physics region.

Cancer is a major health problem worldwide including Asian-Pacific region. The region hosts over 4.5 billion people, over 60% of the world population and very divergent socioeconomically. The major cancers in the region in male include lung, stomach, liver, colorectal and esophagus and in female breast, lung, cervix, colorectal, and stomach. Over 60% of cancer patients need radiotherapy alone or in combination with surgery and/or chemotherapy, and therefore, radiotherapy is the main and essential modality of cancer treatment. Radiation oncology medical physicists play a pivotal role in efficient implementation of radiotherapy. This study was aimed to assess the status of cancer treatment by radiotherapy and the requirement of radiation oncology medical physicists in the region. To access the status and requirement of radiotherapy machines, availability of radiation oncology physicists in the region of Asia Oceania Federation of Organizations for Medical Physics (AFOMP), we have carried out a survey by sending questioners to AFOMP National Medical Physics Organizations (NMO). We received response from 21 countries, 100% response, regarding availability of teletherapy units, number of medical physicists working in radiotherapy and related information. Using GLOBOCAN cancer incidence data and considering 62.5% of cancer patients need radiotherapy treatment and up to 500 cancer patients can be treated in a year on one teletherapy machine, the gap between the available and required teletherapy machine to treat all the cancer patients requiring radiotherapy is estimated. Further, we estimated the gap between radiotherapy medical physicists available and required as per International Atomic Energy Agency and European Society for Therapeutic Radiology and Oncology guidelines. It was observed that availability of teletherapy machines in AFOMP region is 0.21-14.0 teletherapy machine/million population and radiotherapy medical physicist are 0.82-2.43/teletherapy unit.

Radiotherapy and cancer status in Latin America: economic analysis of investment opportunities up to 2030

Timely access to radiotherapy treatments for cancer in Latin America is hindered by substantial delays in investment. We herein report on the current incidence of the ten most frequent malignancies and on radiotherapy-related logistics across Latin America with the objective of identifying resource gaps and facilitate the planning of health-care investments up to 2030. Data were collected from the International Atomic Energy Agency's (IAEA) Directory of Radiotherapy Centers and matched to open-source databases and individual surveys sent to national scientific societies in participant countries (Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Mexico, Paraguay, Peru, Uruguay, and Venezuela). Demographic, economic, and epidemiological data were gathered from the World Bank and the Global Cancer Observatory registries. The incidence rates of the ten most common cancers treated with radiotherapy in each country were multiplied by the respective radiotherapy use rate according to the IAEA's Time-Driven Activity-Based-Costing model. Country-specific adjustments were made and the following assumptions were factored for the analysis: 240 working days, 60 patients treated per teletherapy unit per day, and 25 external beam radiotherapy fractions required per diagnosis at a cost of US$ 1703·75 or equivalent per full treatment, and four brachytherapy fractions for cervical (75% of total) and endometrial (27%) cancer and one boost fraction for prostate cancer (5%) diagnosis, at a cost of US$ 1426·40 per treatment. These values were adopted from India (for cervix cancer data) and Spain (endometrial cancer data), which are countries with a cancer incidence profile similar to that of Latin America. The prostate brachytherapy use rate was adopted from recently published US data. Human resource requirements were estimated according with the observed annual cancer incidence, keeping with IAEA's recommendations. 10-year incidence and costs projections were calculated according to the estimated demography dynamics and time value of money equation for each country for the period 2020-30. Current and projected cancer incidences and radiotherapy, personnel, and logistic requirements are reported through absolute numeric differences and mean values. Potentially saved lives (equivalent to 50% of newly included patients after increasing radiotherapy capacities to recommended levels) and monetary return, assumed as a mean regional monthly wage multiplied by the rescued life-years, are also reported. Information concerning the 11 most populous countries in Latin America was obtained. As of 2020, a population of 557 213 447 individuals was recorded, accounting for 85% of the Latin American inhabitants and projected to increase to 772 038 620 (an increase of 214 825 173) by 2030. The 2020 overall cancer incidence was 1 055 892 cases and the mean 2020 incidence per country was 95 990 (SD 135 013). The 10-year projection was of 1 460 154 new cases with a mean of 132 741 (SD 188 832) per country, highlighting the high variability in needs across the region. Overall external beam radiotherapy use rate was estimated for 663 236 annual new cases in 2020, versus 916 592 annual new cases by 2030, and overall brachytherapy use was estimated for 90 428 annual new cases in 2020 and 125 152 annual new cases by 2030. The 2020 regional availability of treatment fractions was 11 822 400 for external beam radiotherapy and 216 960 for brachytherapy. Conversely, the 2020 required number of fractions was 13 241 088 (+12·2%) for external beam radiotherapy and 361 672 (+66·7%) for brachytherapy; and the projected required number of fractions in 2030 is 18 324 720 (+55·0%) for external beam radiotherapy and 500 744 (+130·8%) for brachytherapy. If the projected demand was to be covered, an additional 181 622 lives could potentially be saved by 2030, accounting for a 2-year total financial return of US$ 1 963 776 038·20, assuming 50% of additionally treated patients will be reincorporated to the economically active population. Bridging the gap in radiotherapy up to 2030 will save lives and reduce the financial toxicity of cancer management in Latin America. Governmental and private investment in radiotherapy is urgently required to shorten access disparities and reach these goals. None.

Correlation of hypoxia PET tracer uptake with hypoxic radioresistance in cancer cells: PET biomarkers of resistance to stereotactic radiation therapy?

PurposeThe pO2 threshold of an ideal PET hypoxia tracer for radiotherapy planning in cancer would match those observed in clinically and biologically relevant processes such as radioresistance and HIF1α expression. To identify such tracers, we directly compared uptake in vitro of hypoxia PET tracers ([18F]FMISO, [64Cu]CuATSM, and analogues [64Cu]CuATS, [64Cu]CuATSE, [64Cu]CuCTS, [64Cu]CuDTS, [64Cu]CuDTSE, [64Cu]CuDTSM) with levels of radioresistance and HIF1α expression in cultured cancer cells under identical hypoxic conditions ranging from extreme hypoxia to normoxia. Pimonidazole uptake was also compared as a marker of hypoxia. MethodsA custom-built hypoxia apparatus enabled all experiments to be performed under identical hypoxic conditions with constant measurement of pO2 in media using an OxyLab pO2™ probe. HCT116 human colonic carcinoma and MCF-7 human Caucasian breast adenocarcinoma cells were irradiated using a cobalt teletherapy unit. Clonogenic assays were used to assess survival. HIF1α expression was determined by western blotting, tracer uptake by gamma counting and pimonidazole binding by flow cytometry. ResultsRadioresistance, pimonidazole binding and HIF1α expression increased gradually as pO2 decreased between 25 mmHg and 0 mmHg. In contrast, all the PET hypoxia tracers showed a sharp increase in uptake only when pO2 levels fell below 1 mmHg. Above this threshold, tracer uptake was not elevated above that in normoxic cells. ConclusionThis study highlights an important mismatch in pO2 thresholds between these PET tracers and other markers of hypoxia: tracer uptake only occurred at oxygen levels that were well below levels that induced radioresistance, pimonidazole uptake and HIF1α expression. Although their pO2 thresholds do not match the threshold for resistance to conventionally fractionated radiotherapy (pO2 2.5–10 mmHg), their specificity for extreme hypoxia (pO2 ≪ 1 mmHg) suggests these PET tracers may be of particular use to predict outcomes in stereotactic radiation therapy where these maximally resistant cells play a key role in determining the biological effect.

Activation of Neural Modeling-Related Genes in the Heart of Mice after Gamma Irradiation.

Objective Radiation-induced heart disease (RIHD) is a common sequela of thoracic irradiation. At the same time, nerve remodeling is involved in the progression of heart disease. However, the activation of the nerve remodeling related genes in radiation-induced heart disease is still lacking. Methods In this study, C57BL/J mice was anesthetized by intraperitoneal injection with pentobarbital sodium (2%, 40 mg/kg), and radiation was delivered using a cobalt-60 (60Co) teletherapy unit (Cirus). When the mice were anesthetized, none of them showed the signs of peritonitis, pain, or discomfort. The mice hearts were exposed to a γ-radiation field of 5 mm × 5 mm. The total dose of γ-radiation was 3 Gy/day for each animal for 5 consecutive days. The mice were executed by severed neck, and its limbs were weak. Quantitative Polymerase Chain Reaction (qPCR) and immunohistochemistry were used to explore the possible mechanism of arrhythmia in patients with RIHD. Results Our results demonstrated that Growth-Associated Protein 43 (GAP43) was increased significantly after radioactive heart injury compared with the control group. Moreover, the protein expression of Tyrosine hydroxylase (TH) and Choline acetyl-transferase (CHAT) was significantly decreased compared with the control group and gradually increased with time rend. The nerve growth factor (NGF) was remarkably increased after radiation-induced heart injury compared with the control group. Immunohistochemistry results indicated that the nerve growth factors GAP43 and NGF were significantly increased after radiation-induced heart injury. Conclusions Chest radiotherapy could activate the neural modeling related genes in RIHD. This may provide a new treatment plan for the future treatment of heart problems caused by chest radiotherapy.

Curative-Intent Radiotherapy for Squamous Cell Carcinoma of the Head and Neck in Sri Lanka: The Impact of Radiotherapy Technique on Survival

AimsWe conducted a retrospective analysis of patients with squamous cell carcinoma of the head and neck (SCCHN) treated with curative-intent radiotherapy at the National Cancer Institute of Sri Lanka to determine the impact of the treatment technique on disease-free survival (DFS). Materials and methodsSCCHN patients treated with radical radiotherapy or adjuvant postoperative radiotherapy from 2016 to 2017 were included in the study. Data on the following variables were collected by reviewing clinical and radiotherapy treatment records: age, gender, tumour site, stage, time to delivery of radiotherapy, use of neoadjuvant chemotherapy, use of concurrent radiosensitising chemotherapy and treatment technique. DFS, defined as the time to death, tumour recurrence or loss to follow-up, was the primary end point and outcomes were compared between patients treated with intensity-modulated radiotherapy (IMRT) in linear accelerators and those treated with conventional radiotherapy in cobalt teletherapy units. Univariate and multivariate analyses were carried out on known prognostic variables. ResultsIn total, 408 patients were included in the study, with 138 (34%) being treated with IMRT in the linear accelerator. More than 75% of patients were of stage III or IV at diagnosis. The 2-year DFS of the whole cohort was 25% (95% confidence interval 21–30%). Patients treated with IMRT in the linear accelerator had a superior DFS in comparison with those treated with conventional radiotherapy in the cobalt teletherapy units (P < 0.001, hazard ratio 0.64, 95% confidence interval 0.5–0.82). Higher stage, cobalt treatment and use of neoadjuvant chemotherapy were adversely associated with DFS on multivariate analysis. ConclusionA large proportion of patients with SCCHN treated with curative-intent radiotherapy in Sri Lanka had locally advanced disease and DFS was superior in patients treated with IMRT in the linear accelerator.

Priming Low-Dose Gamma Irradiation Increases Cellular Radioadaptation Response through the Induction of Hsp70 and SOD2

Exposure to low-dose radiation has been demonstrated to stimulate increased cell protection when receiving subsequent challenge dose in what is known as radioadaptation response. Hsp70 and SOD, especially SOD2, are cytoprotectors against superoxide radicals generated by radiation exposure. This study aims to measure the expressions of Hsp70 and SOD2 in parotid salivary gland acinar cells as an indicator of radioadaptation response stimulated by low-dose gamma irradiation. The study used 24 male Rattus norvegicus that are divided into four groups: normal control, positive control, with 50-mGy priming irradiation, and with 100-mGy priming irradiation. The animals were immobilized without anesthetics with special tools designed especially for this study. Irradiation was carried out using a cobalt-60 (gamma ray) teletherapy unit (Philips XK-100) directed to the dorsa of the animals’ heads . High-dose gamma irradiation (2 Gy) was administered 5 hours after priming irradiation. The expression of Hsp70 and SOD2 was measured through immunohistochemical technique on the parotid salivary gland acinar cells and observed using a light microscope with 1000× magnification. Data obtained was analyzed with one-way ANOVA test ( α = 0.05). The results showed that Hsp70 and SOD2 expressions in the priming irradiation groups were higher than those in control groups. The conclusion of this study: priming irradiation with low-dose gamma radiation before challenge irradiation with high-dose gamma radiation increases the radioadaptation response of salivary gland acinar cells through induction of Hsp70 and SOD2.

Ablative radiotherapy for liver tumors using stereotactic MRI-guidance: A prospective phase I trial

Background and purposeTo prospectively determine the feasibility, safety, and efficacy of stereotactic body radiation therapy (SBRT) to primary and secondary liver tumors with MR-guided radiation therapy (MRgRT). Materials and methodsTreatment plans with a conventional CT-guided linear accelerator and a MRI-guided tri-60Co teletherapy unit (MR-Co) were generated and compared for patients undergoing liver-directed SBRT from 2015 to 2017. If dosimetric parameters were met on MR-Co, patients were treated with MRgRT. The highest priority constraint was >1000 cc or >800 cc of normal liver receiving <15 Gy for single- or multiple-lesion treatments, respectively. Treatment was delivered every other day. ResultsOf 23 patients screened, 20 patients (8 primary, 12 secondary) and 25 liver tumors underwent MR-guided SBRT to a median dose of 54 Gy (range 11.5–60) in a median of 3 fractions (range 1–5). With a median follow up of 18.9 months, the 1- and 2-year estimate of local control were 94.7% and 79.6%, respectively. A difference in local control between single and multiple lesions or BED ≥ 100 Gy10 and BED < 100 Gy10, respectively, was observed. The 2-year estimate of overall survival (OS) was 50.7% with a median OS of 29 months. There were no acute grade ≥ 3 toxicities and one late grade 3/4 toxicity from a single patient whose plan exceeded an unrecognized dose constraint at the time. ConclusionMR-guided SBRT is a viable and safe option in the delivery of ultrahypofractionated ablative radiation treatment to primary and secondary liver tumors resulting in high rates of local control and very favorable toxicity profiles.

A Malaysian Secondary Standard Dosimetry Laboratory participation in the IAEA/WHO Postal Dose Quality Audit: Data Analysis 2009 – 2019

Participation of Secondary Standard Dosimetry Laboratory (SSDL) of Malaysia in the IAEA/WHO Postal Dose Quality Audit Service is very important in confirming the traceability of absorbed dose measurements provided to the radiotherapy centres. In the audit, the SSDL was supplied with a set of dosimeter for irradiation with absorbed dose to water of 200 cGy in reference conditions using 60Co teletherapy or medical linear accelerator. In the period of 2009 to 2019, a total of 10 photon beams from 60Co teletherapy unit, 6 MV X-ray and 10 MV X-ray produced by medical linear accelerator have been audited. The results of the audit demonstrate that the mean of percentage deviations between the SSDL and the IAEA measurements was -0.35% with standard deviation of 0.86%. The deviations vary between a minimum percentage relative deviation of -2.5% and a maximum of 0.6%. These results were considered satisfactory in which complied with the IAEA’s acceptance limit of ± 3.5%.

Strategies to Maximize Available Resources With Minimum Cost Escalation for Improving Radiation Therapy Accessibility in the Post–Coronavirus Disease 2019 Era: An Analysis for Asia

PurposeThere is widespread accord among economists that the coronavirus disease 2019 (COVID-19) pandemic will have a severe negative effect on the global economy. Establishing new radiation therapy (RT) infrastructure may be significantly compromised in the post–COVID-19 era. Alternative strategies are needed to improve the existing RT accessibility without significant cost escalation. The outcomes of these approaches on RT availability have been examined for Asia. Methods and MaterialsThe details of RT infrastructures in 2020 for 51 countries in Asia were obtained from the Directory of Radiotherapy Centers of the International Atomic Energy Agency. Using the International Atomic Energy Agency guidelines, the percent of RT accessibility and the additional requirements of teletherapy (TRT) units were computed for these countries. To maximize the utilization of the existing RT facilities, 5 options were evaluated, namely, hypofractionation RT (HFRT) alone, with/without 25% or 50% additional working hours. The effect of these strategies on the percent of RT access and additional TRT unit requirements to achieve 100% RT access were estimated. ResultsIn 46 countries, 4617 TRT units are available. The mean percent of RT accessibility is 62.4% in 43 countries (TRT units = 4491) where the information on cancer incidence was also available, and these would need an additional 6474 TRT units for achieving 100% RT accessibility. By adopting HFRT alone, increasing the working hours by 25% alone, 25% with HFRT, 50% alone, and 50% with HFRT, the percent of RT access could improve to 74.9%, 78%, 90.5%, 93.7%, and 106.1%, respectively. Correspondingly, the need for additional TRT units would progressively decrease to 4646, 4284, 3073, 2820, and 1958 units. ConclusionsThe economic slowdown in the post–COVID-19 period could severely impend establishment of new RT facilities. Thus, maximal utilization of the available RT infrastructure with minimum additional costs could be possible by adopting HFRT with or without increased working hours to improve the RT coverage.

COLLIMATOR EXCHANGE EFFECT OF MEGAVOLTAGE PHOTON BEAMS AND ITS IMPACT ON CLINICAL DOSIMETRY

AIM To determine the Collimator Exchange Effect (CEE) for telecobalt unit (Bhabhatron -II TAW) and Linear accelerator unit (Varian Trilogy). MATERIALS AND METHOD The study was carried out in Bhabhatron-II TAW Telecobalt machine and Varian Trilogy Linear Accelerator. The study was done to find the collimator scatter factor (S¬c) for rectangular fields at 5 and 10gm/cm2 depths using indigenously designed mini phantom. Three sets of electrometer reading were noted for the irradiation of each field size and the average was taken for calculation. Sc values for different rectangular fields were then calculated from these data sets and the CEE at two depths (5 and 10 gm/cm2) for the 6MV and 15MV photon and Co-60 gamma beam were calculated. RESULTS The values of Sc obtained for the rectangular fields as alternatively defined by X &amp; Y jaws are different for high energy photon beams indicating CEE. The maximum percentage difference between the Sc of the corresponding collimator settings for the Bhabhatron-II TAW unit for depths 5 and 10gm/cm2 were found to be 0.42% and 0.5% respectively. Sc values for 6MV and 15MV photon beams were found to be higher when Y-jaw (upper jaw) acts as the longer side of the rectangular field. The maximum percentage difference between the Sc values of the corresponding collimator settings for 6MV at depths 5 and 10gm/cm2 were 2.74% and 2.87% respectively whereas for 15 MV the differences were 3% and 2.99%. CONCLUSION The CEE of Cobalt Teletherapy units can be ignored in clinical dosimetry. However, the CEE of Linear Accelerators having energies 6MV &amp; 15MV should be taken into consideration. A two dimensional table of Sc should be generated for rectangular fields during MU calculations in Linear Accelerators. For TPS based calculations, the generated data should be incorporated during beam modeling for accurate dose delivery in clinical dosimetry.