Ambika Sahai Pradhan

Dosimetry of intracavitary applications in carcinoma of the cervix: rectal dose analysis

The International Commission on Radiation Units and Measurements (ICRU), in its Report-38, has given certain recommendations regarding the specifications of bladder and rectal reference points in the intracavitary treatment of carcinoma of the cervix. Conforming to this report, 182 intracavitary applications performed in stage I and II cervix cases were analyzed. In 113 applications, the maximum rectal dose was found to be in a point on the anteroposterior line drawn through the centre of colpostat sources. However, for our type of applications, the point on the anteroposterior line drawn through the lower end of the uterine tube seldom gets maximum dose. In addition, it was observed that there are other dose points than the ICRU reference point receiving doses close to maximum dose. It was concluded that doses to multiple rectal reference points should be recorded, in addition to the ICRU-defined rectal reference point.

A thermoluminescent fast-neutron dosemeter based on pellets of CaSO4:Dy mixed with sulphur

The fast neutron activation reaction 32S(n, p) 32P in CaSO4: Dy has been used in the measurements of fast neutron dose by employing a post-irradiation TL accumulation method. In order to increase the efficiency of the method CaSO4: Dy powder was mixed with sulphur powder in various proportions from which pellets weighing each were made. After neutron irradiation these pellets were each burnt in an aluminium planchette and the phosphor residue with 32P beta activity on it was allowed to undergo self-irradiation for TL accumulation. The fast neutron efficiency of the system employing 10 pellets of 0.1% CaSO4: Dy was found to be about 100 times that of bare CaSO4: Dy powder.

The development of thin CaSO4:Dy Teflon TL dosimeters for beta dosimetry in personnel monitoring

Abstract This paper describes the development of thin (0.1 and 0.2 mm) CaSO4:Dy Teflon dosimeters thermally bonded to thick (0.7 and 0.6 mm respectively) Teflon bases for application to β-dosimetry in personnel monitoring. The composite dosimeters (13 mm dia. and 0.8 mm thick) were found quite rigid and they do not deform during their readout. The TL response of the 0.1 mm TL dosimeter was found to be β-energy independent in the energy range 0.76–2.25 MeV. The TL response of the 0.2 mm dosimeter, however, decreased with decreasing β-energy in this range. The minimum detectable γ-dose with 0.1 mm TL dosimeters was found to be 0.13 mGy. Hence, due to their energy independence, mechanical strength, TL efficiency, and capability in low dose measurements, the 0.1 mm CaSO4:Dy Teflon dosimeters thermally bonded to 0.7 mm Teflon base were found suitable for β-dosimetry in personnel monitoring.

Photothermoluminescence and the behaviour of high-temperature glow peaks in Li2B4O7:Mn and CaSO4:Dy phosphors

Li2B4O7:Mn exhibits a high-temperature glow peak (at ∼ 370°C) in addition to its dosimetric glow peak (at ∼ 210°C) for exposures greater than 105R of 60Co γ-rays. No γ-ray induced sensitization has been observed in the presence of the high-temperature glow peak. Also, this high-temperature glow peak does not exhibit photo-transer in Li2B4O7:Mn. However, CaSo4:Dy, like other phosphors, exhibits γ-ray induced sensitization and photo-transfer in the presence of a high-temperature glow peak. The u.v. sensitivity in Li2B4O7 Mn has been ascribed to the creation of new centres associated with the high-temperature glow peak.

Suggested diagnostic reference levels for paediatric X-ray examinations in India

Exposure of children to ionising radiation is considered to carry higher risk than that of adults; therefore a need to suggest diagnostic reference levels (DRLs) for the common paediatric diagnostic X-ray procedures was recognised for the X-ray machines meeting the requirements of the recently implemented Safety Code for Medical Diagnostic X-ray Equipment and Installations in India. Measurements were carried out for entrance surface air kerma (free in air) in conventional paediatric X-ray diagnostic examinations among four age groups: <1, 1-4, 5-9 and 10-15 y. A total of 2240 air kerma measurements at different fixed focus to skin distances were studied for 7 paediatric diagnostic examinations with 11 different projections on 62 X-ray machines installed in 22 selected hospitals in the country. The third quartile values of air kerma per paediatric examination for the age group of 5-9 y were considered as values of paediatric DRLs. The suggested values of DRLs are 0.2 mGy for chest AP/PA, 0.3 mGy for chest LAT, 0.7 mGy for lumber spine AP, 1.3 mGy for lumber spine LAT, 0.3 mGy for thoracic spine AP, 0.6 mGy for thoracic spine LAT, 0.5 mGy for abdomen AP, 0.7 mGy for pelvis AP, 0.6 mGy for skull PA, 0.5 mGy for skull LAT and 0.8 mGy for hip joints AP.

Radiological safety status and quality assurance audit of medical X-ray diagnostic installations in India

We conducted a radiological safety and quality assurance (QA) audit of 118 medical X-ray diagnostic machines installed in 45 major hospitals in India. The main objective of the audit was to verify compliance with the regulatory requirements stipulated by the national regulatory body. The audit mainly covered accuracy check of accelerating potential (kVp), linearity of tube current (mA station) and timer, congruence of radiation and optical field, and total filtration; in addition, we also reviewed medical X-ray diagnostic installations with reference to room layout of X-ray machines and conduct of radiological protection survey. A QA kit consisting of a kVp Test-O-Meter (ToM) (Model RAD/FLU-9001), dose Test-O-Meter (ToM) (Model 6001), ionization chamber-based radiation survey meter model Gun Monitor and other standard accessories were used for the required measurements. The important areas where there was noncompliance with the national safety code were: inaccuracy of kVp calibration (23%), lack of congruence of radiation and optical field (23%), nonlinearity of mA station (16%) and timer (9%), improper collimator/diaphragm (19.6%), faulty adjustor knob for alignment of field size (4%), nonavailability of warning light (red light) at the entrance of the X-ray room (29%), and use of mobile protective barriers without lead glass viewing window (14%). The present study on the radiological safety status of diagnostic X-ray installations may be a reasonably good representation of the situation in the country as a whole. The study contributes significantly to the improvement of radiological safety by the way of the steps already taken and by providing a vital feed back to the national regulatory body.

Dosimetric aspects of physical and dynamic wedge of clinac 2100C linear accelerator

AimTo investigate variation of wedge factors on field size and depth for physical and dynamic wedges of identical wedge angles for Clinac 2100C linear accelerator and its clinical implementation.Material and MethodsA computer controlled water phantom dosimetric system is used to generate profile data for physical wedges, whereas a 0.6 cm3 ion chamber is used for generation of profiles for dynamic wedge and wedge factors for both types of wedges. The method has been discussed to handle the dynamic wedge dosimetry in absence of linear array of detectors or film densitometer.ResultsA systematic dependence on wedge factor is observed for physical wedge, with respect to depth and wedge angle but not depending on field size. Whereas dynamic wedge shows strong dependence on field size and is not systematic because the dynamic wedge is controlled by segmented treatment tables depending on field size and energy and no significant variation is observed on depth for various wedge angles. The handling of beam data in a commercially available treatment planning system is discussed and a comparison has been made for isodoses of both types of wedges.ConclusionThe dynamic wedge isodose curves shows rather straight lines than physical wedge but larger hot spots at thin edge which needs careful consideration during planning.ZusammenfassungZielEs werden die Keilfilterfaktoren für physikalische und dynamische Keilfilter des Clinac 2100C in Abhängigkeit von Feldgröße und Phantomtiefe untersucht.Material und Methode nDie Dosisprofile der physikalischen Keile werden in einem automatischen Wasserphantom erfaßt, während eine Ionisationskammer von 0,6 cm3 sowohl für die physikalischen als auch die dynamischen Keile in Einsatz kommt. Es ist eine Methode, die es erlaubt, dynamische Keile auch ohne Linear-Array-Detektoren oder Filmdosimetrie zu dosimetrieren.ErgebnisseFür die physikalischen Keile ist eine systematische Abhängigkeit der Keilfaktoren von Keilwinkel und Phantomtiefe, aber nicht von der Feldgröße zu beobachten. Dynamische Keile dagegen zeigen eine starke Abhängigkeit der Keilfaktoren von der Feldgröße, während keine signifikante Abhängigkeit von der Phantomtiefe für verschiedene Keilwinkel zu beobachten ist. Die Feldgrößenabhängigkeit ist nicht systematisch, da die Dynamik der Keile aufgrund segmentierter Tabellen für die Output-Faktoren, die die Feldgrößenunabhängigkeit enthalten, gesteuert wird. Die Handhabung der Daten mit einem kommerziellen Planungssystem wird diskutiert, und es werden die Isodosen beider Keilfilterarten verglichen.SchlußfolgerungDie Isodosenverteilungen unter dynamischen Keilen zeigen viel geradere Flanken als jene unter physikalischen Keilen. Dadurch ergben sich höhere Maxima (hot spots) hinter den dünnen Enden, was bei der Planung sorgfältig bedacht werden muß.

Some dosimetric parameters of MgB4O7:Dy sintered pellets and CaSO4:Dy Teflon discs—A comparative study

Abstract The effect of u.v. and sunlight exposures on MgB 4 O 7 :Dy and CaSO 4 :Dy have been studied. Both phosphors are found to have intrinsic sensitivity to u.v. radiation and their γ ray induced TL fades faster if exposed to sunlight. The intrinsic TL response for an u.v. (253.7 nm) exposure of 1500 Jm −2 was found equivalent to that caused by 1 and 5 mGy of 60 Co γ rays for MgB 4 O 7 :Dy and CaSO 4 :Dy, respectively. The fading caused by 48000 lx of sunlight exposure was 99.7% and 56% in MgB 4 O 7 :Dy pellets and CaSO 4 :Dy Teflon TLD discs respectively. MgB 4 O 7 :Dy pellets did not exhibit any added advantage over CaSO 4 :Dy Teflon discs except its near tissue equivalence.

Photon energy dependence of CaSO4: Dy embedded teflon TLD discs

Abstract The photon energy dependence of CaSo 4 : Dy TLD phosphor embedded in Teflon in various proportions has been studied and results are compared with calculated energy dependence for such mixtures. It is found that the energy response of a high effective Z TL phosphor could not be reduced by simply embedding it into a low effective Z binding matrix. The discrepancies in experimental and calculated values are explained.

Dose dependence of photo-transfer thermoluminescence in CaSO4:Dy

Photo-transfer thermoluminescence (PTTL) has been found to be highly dependent on gamma ray dose. The PTTL and the reduction in residual thermoluminescence intensity ( Delta RTL) suggest that transfer originates not only from the residual thermoluminescent (RTL) traps but also from other radiation-induced nonluminescent centres.