Displaying publications 1 - 20 of 72 in total

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  1. Zamaniah WI, Mastura MY, Phua CE, Adlinda A, Marniza S, Rozita AM
    Asian Pac J Cancer Prev, 2014;15(20):8987-92.
    PMID: 25374241
    BACKGROUND: The efficacy of concurrent chemoradiotherapy in the treatment of locally advanced cervical cancer is well established. We aimed to investigate the long-term efficacy of definitive concurrent chemoradiotherapy for cervical cancer in the University of Malaya Medical Centre.

    MATERIALS AND METHODS: A cohort of 60 patients with FIGO stage IB2-IVA cervical cancer who were treated with definitive concurrent chemoradiotherapy with cisplatin followed by intracavitary brachytherapy or external beam radiotherapy (EBRT) boost between November 2001 and May 2008 were analysed. Patients were initially treated with weekly intravenous cisplatin (40 mg/m2) concurrent with daily EBRT to pelvis of 45-50 Gy followed by low dose rate brachytherapy or EBRT boost to tumour. Local control rate, progression free survival, overall survival and treatment related toxicities graded by the RTOG criteria were evaluated.

    RESULTS: The mean age was 56. At the median follow-up of 72 months, the estimated 5-year progression-free survival (PFS) (median PFS 39 months) and the 5-year overall survival (OS) (median OS 51 months) were 48% and 50% respectively. The 5-year local control rate was 67.3%. Grade 3-4 late gastrointestinal and genitourinary toxicity occurred in 9.3% of patients.

    CONCLUSIONS: The 5-year PFS and the 5-year OS in this cohort were lower than in other institutions. More advanced stage at presentation, longer overall treatment time (OTT) of more than fifty-six days and lower total dose to point A were the potential factors contributing to a lower survival.

    Matched MeSH terms: Radiotherapy Dosage
  2. Zaman ZK, Ung NM, Malik RA, Ho GF, Phua VC, Jamalludin Z, et al.
    Phys Med, 2014 Dec;30(8):980-4.
    PMID: 25086486 DOI: 10.1016/j.ejmp.2014.07.002
    Cobalt-60 (Co-60) is a relatively new source for the application of high-dose rate (HDR) brachytherapy. Radiation dose to the rectum is often a limiting factor in achieving the full prescribed dose to the target during brachytherapy of cervical cancer. The aim of this study was to measure radiation doses to the rectum in-vivo during HDR Co-60 brachytherapy. A total of eleven HDR brachytherapy treatments of cervical cancer were recruited in this study. A series of diodes incorporated in a rectal probe was inserted into the patient's rectum during each brachytherapy procedure. Real-time measured rectal doses were compared to calculated doses by the treatment planning system (TPS). The differences between calculated and measured dose ranged from 8.5% to 41.2%. This corresponds to absolute dose differences ranging from 0.3 Gy to 1.5 Gy. A linear relationship was observed between calculated and measured doses with linear regression R(2) value of 0.88, indicating close association between the measured and calculated doses. In general, absorbed doses for the rectum as calculated by TPS were observed to be higher than the doses measured using the diode probe. In-vivo dosimetry is an important quality assurance method for HDR brachytherapy of cervical cancer. It provides information that can contribute to the reduction of errors and discrepancies in dose delivery. Our study has shown that in-vivo dosimetry is feasible and can be performed to estimate the dose to the rectum during HDR brachytherapy using Co-60.
    Matched MeSH terms: Radiotherapy Dosage
  3. Zaini A, Khir A, Doi SA, Chan SP, Paramsothy M, Khoo BH
    J Int Med Res, 1992 Jun;20(3):279-88.
    PMID: 1397673
    To evaluate the effects of simple compensated fixed-dose iodine-131 therapy for thyrotoxicosis, the long-term results for 74 patients treated with a fixed dose of iodine-131 ranging from 5 to 12 mCi (185 to 444 MBq) were evaluated in the first 2 years of a trial. The dose selected was loosely based on the gross size of the thyroid gland. Routine antithyroid drug therapy was given for a minimum of 3 months after iodine-131 therapy. The mean (+/- SD) duration of follow-up was 74.5 +/- 42 months. The results indicated that roughly 25% of patients treated in this way will become hypothyroid after 5 years and that 85% are cured (need no further therapy during the follow-up period) using a single dose of iodine-131. Of those cured using a single iodine-131 dose, 81% were no longer receiving drugs after 6 months and 85% after 1 year. Such a regimen seems currently to be among the best available where prolonged periods of medication-free euthyroidism after therapy are sought.
    Matched MeSH terms: Radiotherapy Dosage
  4. Yu L, Tang TLS, Cassim N, Livingstone A, Cassidy D, Kairn T, et al.
    J Appl Clin Med Phys, 2019 Nov;20(11):189-198.
    PMID: 31613053 DOI: 10.1002/acm2.12726
    PURPOSE: Gamma evaluation is the most commonly used technique for comparison of dose distributions for patient-specific pretreatment quality assurance in radiation therapy. Alternative dose comparison techniques have been developed but not widely implemented. This study aimed to compare and evaluate the performance of several previously published alternatives to the gamma evaluation technique, by systematically evaluating a large number of patient-specific quality assurance results.

    METHODS: The agreement indices (or pass rates) for global and local gamma evaluation, maximum allowed dose difference (MADD) and divide and conquer (D&C) techniques were calculated using a selection of acceptance criteria for 429 patient-specific pretreatment quality assurance measurements. Regression analysis was used to quantify the similarity of behavior of each technique, to determine whether possible variations in sensitivity might be present.

    RESULTS: The results demonstrated that the behavior of D&C gamma analysis and MADD box analysis differs from any other dose comparison techniques, whereas MADD gamma analysis exhibits similar performance to the standard global gamma analysis. Local gamma analysis had the least variation in behavior with criteria selection. Agreement indices calculated for 2%/2 mm and 2%/3 mm, and 3%/2 mm and 3%/3 mm were correlated for most comparison techniques.

    CONCLUSION: Radiation oncology treatment centers looking to compare between different dose comparison techniques, criteria or lower dose thresholds may apply the results of this study to estimate the expected change in calculated agreement indices and possible variation in sensitivity to delivery dose errors.

    Matched MeSH terms: Radiotherapy Dosage
  5. Yap LM, Jamalludin Z, Ng AH, Ung NM
    Phys Eng Sci Med, 2023 Sep;46(3):1331-1340.
    PMID: 37470929 DOI: 10.1007/s13246-023-01303-x
    The survey is to assess the current state of adaptive radiation therapy (ART) for head and neck (H&N) cases among radiotherapy centers in Malaysia and to identify any implementation limitations. An online questionnaire was sent to all radiotherapy centers in Malaysia. The 24-question questionnaire consists of general information about the center, ART practices, and limitations faced in implementing ART. 28 out of 36 radiotherapy centers responded, resulting in an overall response rate of 78%. About 52% of the responding centers rescanned and replanned less than 5% of their H&N patients. The majority (88.9%) of the respondents reported the use Cone Beam Computed Tomography alone or in combination with other modalities to trigger the ART process. The main reasons cited for adopting ART were weight loss, changes in the immobilization fitting, and anatomical variation. The adaptation process typically occurred during week 3 or week 4 of treatment. More than half of the respondents require three days or more from re-simulation to starting a new treatment plan. Both target and organ at risk delineation on new planning CT relied heavily on manual delineation by physicians and physicists, respectively. All centers perform patient-specific quality assurance for their new adaptive plans. Two main limitations in implementing ART are "limited financial resources or equipment" and "limitation on technical knowledge". There is a need for a common consensus to standardize the practice of ART and address these limitations to improve the implementation of ART in Malaysia.
    Matched MeSH terms: Radiotherapy Dosage
  6. Yaakob NH, Wagiran H, Hossain MI, Ramli AT, Bradley DA, Ali H
    Appl Radiat Isot, 2011 Sep;69(9):1189-92.
    PMID: 21507665 DOI: 10.1016/j.apradiso.2011.03.039
    We have investigated the thermoluminescent response and fading characteristics of germanium- and aluminium-doped SiO(2) optical fibres. These optical fibres were placed in a solid phantom and irradiated using 6 and 10 MV photon beams at doses ranging from 0.02 to 0.24 Gy delivered using a linear accelerator. In fading studies, the TL measurements were continued up to 14 days post-irradation. We have investigated the linearity of TL response as a function of dose for Ge-, Al-doped optical fibre and TLD-100 obtained for 6 and 10 MV photon irradiations. We have concentrated on doses that represent a small fraction of that delivered to the tumour to establish sensitivity of measurement for peripheral exposures in external beam radiotherapy.
    Matched MeSH terms: Radiotherapy Dosage
  7. Teoh CM, Rohaizak M, Chan KY, Jasmi AY, Fuad I
    Asian J Surg, 2005 Apr;28(2):90-6.
    PMID: 15851360
    This study reviewed the incidence of positive pre-ablative diagnostic scan after total thyroidectomy and the efficacy of the current ablative dose. The predictive factors for outcome using a standard ablative dose and postoperative complications of total thyroidectomy were also examined.
    Matched MeSH terms: Radiotherapy Dosage
  8. Tang D, Peng EW, Giri D, Chowdhary M, Sarkar P
    Br J Hosp Med (Lond), 2009 Apr;70(4):222-4.
    PMID: 19357601 DOI: 10.12968/hmed.2009.70.4.41626
    Mediastinal irradiation for various malignancies can cause radiation injury to mediastinal structures, most importantly the cardiovascular system. This article reviews the effect of radiation on cardiovascular structures and the manifestations of various radiation-induced heart diseases.
    Matched MeSH terms: Radiotherapy Dosage
  9. Tabbakh F, Hosmane NS, Tajudin SM, Ghorashi AH, Morshedian N
    Sci Rep, 2022 Oct 18;12(1):17404.
    PMID: 36258012 DOI: 10.1038/s41598-022-22429-0
    There are two major problems in proton therapy. (1) In comparison with the gamma-ray therapy, proton therapy has only ~ 10% greater biological effectiveness, and (2) the risk of the secondary neutrons in proton therapy is another unsolved problem. In this report, the increase of biological effectiveness in proton therapy has been evaluated with better performance than 11B in the presence of two proposed nanomaterials of 157GdF4 and 157Gd doped carbon with the thermal neutron reduction due to the presence of 157Gd isotope. The present study is based on the microanalysis calculations using GEANT4 Monte Carlo tool and GEANT4-DNA package for the strand breaks measurement. It was found that the proposed method will increase the effectiveness corresponding to the alpha particles by more than 100% and also, potentially will decrease the thermal neutrons fluence, significantly. Also, in this work, a discussion is presented on a significant contribution of the secondary alpha particles in total effectiveness in proton therapy.
    Matched MeSH terms: Radiotherapy Dosage
  10. Syadwa AS, Anita ZB
    Med J Malaysia, 2018 08;73(4):190-196.
    PMID: 30121680 MyJurnal
    AIM: Symptomatic relief following palliative radiotherapy for advanced cancers may take a few weeks up to a few months to achieve. Thus, accurate prognostication is important to avoid harm to these patients with limited lifespan. We conducted a retrospective cohort study to determine the median survival and 30-day mortality (30-DM) and factors associated with these parameters in our centre.

    METHODS: Data from 585 eligible patients who received palliative radiotherapy between January 2012 and December 2014 were analysed. Median overall survival was calculated from the commencement of first fraction of the last course of radiotherapy to date of death or when censored. 30-DM was calculated as the proportion of patients who died within 30 days from treatment start date. Kaplan-Meier survival analysis was used to estimate survival. Chi-square test and logistic regression was used to assess the impact of potential prognostic factors on median survival and 30-DM.

    RESULTS: The most common diagnoses were lung and breast cancers and most common irradiated sites were bone and brain. Median survival and 30-DM were 97 days and 22.7% respectively. Primary cancer, age, treatment course, performance status, systemic treatment post radiotherapy and intended radiotherapy treatment completed had an impact on median survival whereas mainly the latter three factors had an impact on 30-DM.

    CONCLUSION: Median survival and factors affecting both survival and 30-DM in our study are comparable to others. However, a 30-DM rate of 22.7% is significantly higher compared to the literature. We need to better select patients who will benefit from palliative radiotherapy in our centre.

    Matched MeSH terms: Radiotherapy Dosage
  11. Suneja G, Brown D, Chang A, Erickson B, Fidarova E, Grover S, et al.
    Brachytherapy, 2017 Jan-Feb;16(1):85-94.
    PMID: 27919654 DOI: 10.1016/j.brachy.2016.10.007
    PURPOSE: Most cervix cancer cases occur in low-income and middle-income countries (LMIC), and outcomes are suboptimal, even for early stage disease. Brachytherapy plays a central role in the treatment paradigm, improving both local control and overall survival. The American Brachytherapy Society (ABS) aims to provide guidelines for brachytherapy delivery in resource-limited settings.

    METHODS AND MATERIALS: A panel of clinicians and physicists with expertise in brachytherapy administration in LMIC was convened. A survey was developed to identify practice patterns at the authors' institutions and was also extended to participants of the Cervix Cancer Research Network. The scientific literature was reviewed to identify consensus papers or review articles with a focus on treatment of locally advanced, unresected cervical cancer in LMIC.

    RESULTS: Of the 40 participants invited to respond to the survey, 32 responded (response rate 80%). Participants were practicing in 14 different countries including both high-income (China, Singapore, Taiwan, United Kingdom, and United States) and low-income or middle-income countries (Bangladesh, Botswana, Brazil, India, Malaysia, Pakistan, Philippines, Thailand, and Vietnam). Recommendations for modifications to existing ABS guidelines were reviewed by the panel members and are highlighted in this article.

    CONCLUSIONS: Recommendations for treatment of locally advanced, unresectable cervical cancer in LMIC are presented. The guidelines comment on staging, external beam radiotherapy, use of concurrent chemotherapy, overall treatment duration, use of anesthesia, applicator choice and placement verification, brachytherapy treatment planning including dose and prescription point, recommended reporting and documentation, physics support, and follow-up.
    Matched MeSH terms: Radiotherapy Dosage
  12. Sulieman A, Mayhoub FH, Salah H, Al-Mohammed HI, Alkhorayef M, Moftah B, et al.
    Appl Radiat Isot, 2020 Oct;164:109240.
    PMID: 32819499 DOI: 10.1016/j.apradiso.2020.109240
    Lutetium-177 (DOTATATE) (177Lu; T1/2 6.7 days), a labelled β- and Auger-electron emitter, is widely used in treatment of neuroendocrine tumours. During performance of the procedure, staff and other patients can potentially receive significant doses in interception of the gamma emissions [113 keV (6.4%) and 208 keV (11%)] that are associated with the particle decays. While radiation protection and safety assessment are required in seeking to ensure practices comply with international guidelines, only limited published studies are available. The objectives of present study are to evaluate patient and occupational exposures, measuring ambient doses and estimating the radiation risk. The results, obtained from studies carried out in Riyadh over an 11 month period, at King Faisal Specialist Hospital and Research Center, concerned a total of 33 177Lu therapy patients. Patient exposures were estimated using a calibrated Victoreen 451P survey meter (Fluke Biomedical), for separations of 30 cm, 100 cm and 300 cm, also behind a bed shield that was used during hospitalization of the therapy patients. Occupational and ambient doses were also measured through use of calibrated thermoluminescent dosimeters and an automatic TLD reader (Harshaw 6600). The mean and range of administered activity (in MBq)) was 7115.2 ± 917.2 (4329-7955). The ambient dose at corridors outside of therapy isolation rooms was 1.2 mSv over the 11 month period, that at the nursing station was below the limit of detection and annual occupational doses were below the annual dose limit of 20 mSv. Special concern needs to be paid to comforters (carers) and family members during the early stage of radioisotope administration.
    Matched MeSH terms: Radiotherapy Dosage
  13. Soh HS, Ung NM, Ng KH
    Australas Phys Eng Sci Med, 2008 Jun;31(2):146-50.
    PMID: 18697706
    The advancement of digital imaging has prompted more medical institutions to go filmless. The computed radiography (CR) system is becoming an important tool not only in diagnostic imaging, but also in radiation oncology. A new CR system that was specially designed for the use in radiation oncology, Fuji IP cassette type PII has been introduced to the market in the middle of year 2006. This project aimed to study some basic physical characteristics of this new type of cassette and explore its application for performing quality assurance (QA) tests and portal imaging in radiotherapy. All the images were read by FCR 5000 Plus reader. The image was found to reach its saturation value of 1023 (due to the image was stored in 10 bits data) by depending on the sensitivity value being adjusted. The uniformity test gave the result of 0.12%. The cassette was used to perform the QA tests which were previously performed using film. All the results met the specification as stated in AAPM Task Group 40. The comparison for the portal images of PortalVision contrast-detail phantom showed that the spatial resolution of the images obtained by CR system (Fujifilm Co., Ltd., Tokyo, Japan) were better than the EPID (Varian Medical Systems, Inc., Palo Alto, USA) and film system (Eastman Kodak Co., New York, USA). The IP cassette type PII was found to be suitable as an alternative QA test tool and portal imaging in radiotherapy.
    Matched MeSH terms: Radiotherapy Dosage
  14. Sofian Ibrahim, Chantara Thevy Ratnam, Chai, Chee Keong, Noor Hasni M. Ali, Mohd Noorwadi Mat Lazim, Khairiah Badri
    MyJurnal
    Peroxide pre-vulcanized natural rubber latex prepared by using gamma irradiation technique is an alternative over the conventionally prepared peroxide pre-vulcanized that used activator to promote the peroxide decomposition in natural rubber latex. Through this technique the problems aroused by some activators such as tends to darken the natural rubber latex film during the drying process can also be overcome. For this preliminary study, data obtained from crosslink density and mechanical measurements were used to evaluate the effectiveness of gamma irradiation in the vulcanization process. Increasing the quantity of tert-butyl hydroperoxide (t-BHPO) from 0.1 pphr to 0.3 pphr while the irradiation dose maintain at 12 kGy has successfully delivered peroxide vulcanized natural rubber latex films with average tensile strength, modulus @ 500% and modulus @ 700% around 15.33, 1.01 and 3.42 MPa, respectively. The effective pre-vulcanization irradiation dose with respect to maximum crosslinking density (85.8 %) was observed on film prepared at 0.1 pphr t-BHPO.
    Matched MeSH terms: Radiotherapy Dosage
  15. Singam P, Ho C, Hong GE, Mohd A, Tamil AM, Cheok LB, et al.
    Asian Pac J Cancer Prev, 2010;11(2):503-6.
    PMID: 20843141
    Renal cancer is rare and its incidence is 1.9 per 100,000 in the Malaysian population, which consists of three major ethnic groups (Malay, Chinese and Indians). A retrospective study was her conducted to identify clinical characteristics and ethnic background influences on presentation. The study included all renal cancer patients from a single medical institution over ten years, with a total of 75 cases. Seventy-three patients underwent surgery while 2 received only radiotherapy or chemotherapy. The male to female ratio was 2.75:1. Incidence was equal among the Malay (49.3%) and Chinese ethnic groups (45.3%). Mean age of patients were 57.1 (18-93) years old. There were 26 (37.4%) patients with Stage I disease, 14 (18.7%) at Stage II, 23 (30.7%) at Stage III and 12 (16%) at Stage IV. The Chinese race presented at mean older age (p= 0.02) and later stage of disease (p= 0.046). Patients above 40 years old had more advanced stage disease (p= 0.023). Tumour histology were clear cell (72%), urothelial cell (13.3%), sarcomatoid cell and nephroblastoma each contributed 2.7%. The mean tumour size was 8.1 (2-20) cm. There was substantial agreement between the pre and post operative staging (kappa 0.691). In conclusion we observed significant influences of age and race in the clinical presentation of renal cancer in our institution based population. There was larger male to female ratio and mean tumour size as compared to previous epidemiology studies.
    Matched MeSH terms: Radiotherapy Dosage
  16. Sim GS, Wong JH, Ng KH
    J Appl Clin Med Phys, 2013 Jul 08;14(4):4182.
    PMID: 23835383 DOI: 10.1120/jacmp.v14i4.4182
    Radiochromic and radiographic films are widely used for radiation dosimetry due to the advantage of high spatial resolution and two-dimensional dose measurement. Different types of scanners, including various models of flatbed scanners, have been used as part of the dosimetry readout procedure. This paper focuses on the characterization of the EBT2 film response in combination with a Microtek ScanMaker 9800XL scanner and the subsequent use in the dosimetric verification of a 3D conformal radiotherapy treatment. The film reproducibility and scanner uniformity of the Microtek ScanMaker 9800XL was studied. A three-field 3D conformal radiotherapy treatment was planned on an anthropomorphic phantom and EBT2 film measurements were carried out to verify the treatment. The interfilm reproducibility was found to be 0.25%. Over a period of three months, the films darkened by 1%. The scanner reproducibility was ± 2% and a nonuniformity was ±1.9% along the direction perpendicular to the scan direction. EBT2 measurements showed an underdose of 6.2% at high-dose region compared to TPS predicted dose. This may be due to the inability of the treatment planning system to predict the correct dose distribution in the presence of tissue inhomogeneities and the uncertainty of the scanner reproducibility and uniformity. The use of EBT2 film in conjunction with the axial CT image of the anthropomorphic phantom allows the evaluation of the anatomical location of dose discrepancies between the EBT2 measured dose distribution and TPS predicted dose distribution.
    Matched MeSH terms: Radiotherapy Dosage
  17. Sharma DN, Gairola M, Mohanti BK, Rath GK
    Med J Malaysia, 1999 Jun;54(2):210-5.
    PMID: 10972031
    From June 1993 to September 1995, 132 case files of patients who received palliative radiotherapy (RT) for skeletal metastases were reviewed. Majority of the patients (75/132) was in the age range of 41-60 years. Common sites of metastases were the vertebrae (86 patients) and the pelvic bones (40 patients). The major primary tumors encountered were as follows: multiple myeloma (30), breast cancer (25) and prostate cancer (20). Pain was the commonest symptom of presentation. Doses of palliative RT ranged from 8-40 Gy in different fractionation schedules. Ninety-four patients showed more than 50% symptomatic response, 26 had no response and 12 were lost to follow up immediately after the treatment. Single fraction treatments resulted in almost similar responses compared to various multiple fraction treatments. To conclude, short course radiation therapy regimes are optimum in our local circumstances where RT resources are limited and patients have to travel long distances to attend hospital.
    Matched MeSH terms: Radiotherapy Dosage
  18. Selambakkan, Sarala, Khomsaton Abu Bakar, Jamaliah Shariff, Suhairi Alimon
    MyJurnal
    This paper studies about water obtained from fish pond of fisheries research centre. Usual water
    quality parameters such as pH, COD, Turbidity and Ammonia content were analyzed before and
    after irradiation. Electron beam irradiation was used to irradiate the water with the dose 100 kGy,
    200 kGy and 300 kGy. Only high dose was applied on this water as only a limited amount of
    samples was supplied. All the parameters indicated a slight increase after irradiation except for the
    ammonia content, which showed a gradual decrease as irradiation dose increases. Sample
    condition was changed before irradiation in order to obtain more effective results in the following
    batch. The water sample from fisheries was diluted with distilled water to the ratio of 1:1.This was
    followed with irradiation at 100 kGy, 200 kGy and 300 kGy. The results still showed an increase in
    all parameters after irradiation except for ammonia content. For the following irradiation batch,
    the pH of the sample was adjusted to pH 4 and pH 8 before irradiation. For this sample the
    irradiation dose selected was only 100 kGy. A higher value of ammonia was observed for the
    sample with pH 4 after irradiation. Other parameters were almost the same as the first two batches
    Matched MeSH terms: Radiotherapy Dosage
  19. Sathasivam HP, Davies GR, Boyd NM
    Head Neck, 2018 Jan;40(1):46-54.
    PMID: 29149496 DOI: 10.1002/hed.24907
    BACKGROUND: Osteoradionecrosis of the jaw (ORNJ) is a well-recognized complication of radiotherapy. The purpose of this study was to assess predictive factors for the development of ORNJ.

    METHODS: A retrospective study of 325 patients with head and neck squamous cell carcinoma (HNSCC) treated at one institution between January 1, 1999, and December 31, 2008, was conducted. Outcome measure was the presence/absence of ORNJ. Time to event was recorded and Cox proportional hazard regression analysis was used to determine statistically significant predictive factors.

    RESULTS: Fifty-nine patients had ORNJ. Statistical analysis using Cox regression analysis identified several statistically significant variables: dentoalveolar surgery; peri-resective surgery of the jaw; continued tobacco usage after radiotherapy, diabetes mellitus type 2 (DM2); and total radiation dose.

    CONCLUSION: Patients at greater risk of developing ORNJ can be identified and measures can be instituted to reduce its incidence and expedite management when it does occur.

    Matched MeSH terms: Radiotherapy Dosage
  20. Samat SB, Evans CJ, Kadni T, Dolah MT
    Br J Radiol, 2000 Aug;73(872):867-77.
    PMID: 11026863
    A cylindrical gamma-ray 60Co source of activity alpha is predicted to produce an exposure rate X at a distance d in vacuum, given by X = gamma(T)(alpha/d2), where gamma(T) is the specific gamma-ray constant. It has been documented that this formula may be used to approximate X with an accuracy of 1% from a source of length l, provided that d/l > or = 5. It is shown that the formula is accurate to 0.1% under these conditions, provided that the distance is measured from the centre of the source. When absorption in the source and scattering in the collimator are considered, the position of the origin d = 0 can shift by a distance of the order of centimetres. Absorption in air between the source and the ionization chamber adds an exponential factor to the formula. It is shown that even when these modifications are included the discrepancy in the results, although generally less than 1%, is still large compared with the measurement errors. Some suggestions are made for the origin of this discrepancy.
    Matched MeSH terms: Radiotherapy Dosage
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