Preliminary study on CT imaging of polymer gel radiation dosimetry

BackgroundNew radiotherapy techniques such as stereotactic radiotherapy (SRT) stereotactic radiosurgery (SRS), three dimensional conformal radiotherapy (3DCRT) and intensity modulated radiation therapy (IMRT) aim to deliver a high dose to the tumour while sparing the surrounding normal healthy tissues. As a result of these complicated treatment techniques there is a need for a 3-dimensional (3D) dose verification system. However, currently available dosimeters such as ion chambers, diodes, thermoluminescent dosimeters and films are limited to point (or) planar measurement. Multiple measurements are required to obtain the 3-dimensional dose distribution using the above dosimeters. Hence volumetric measurements are not feasible without multiple detectors (or) multiple measurements. Gel dosimetry attempts to meet the requirements of 3D radiation dose distribution. Gel dosimetry is tissue equivalent [1] and it acts as a phantom as well as dosimeter so there is no need for dose perturbation correction.AimRadiation-induced polymerization in polymer gel dosimeters gives rise to a change in CT number which can be measured with X-ray computed tomography (CT). The aim of this study is to assess the feasibility of using the X-ray CT scanner for the evaluation of dose distribution in polymer gel dosimetry.Materials/MethodsPolymer gel called PAGAT (Polyacrylamide Gelatin and Tetrakis hydroxymethyl phosphonium) consisting of 3.5% (w/w) BIS, 3.5% (w/w) acrylamide, 5% (w/w) gelatin, 10 mM Tetrakis hydroxymethyl phosphonium (THP) and 88% (w/w) water was manufactured in normal atmospheric conditions. The gel was irradiated using a Siemens Primus linear accelerator. The radiation-induced change in CT number was evaluated using a Siemens Somatom Emotion CT scanner. The percentage depth doses and profiles were deduced. The same study was carried out using radiation field analyzer RFA-200 with RK-ion chamber and film and compared with polymer gel measurements.ResultsPolymer gel dosimetry measurement was in agreement with ion chamber and film measurements except for a slight deviation in the build-up region. Discrepancies found were due to analysis of image without image averaging and background subtraction.ConclusionsThis preliminary study was conducted to evaluate the feasibility of using X-ray CT-based polymer gel dosimetry for clinical use. The results of this study encourage further use of X-ray CT in conjunction with polymer gel for 3D radiation dose measurements

Modulation of docetaxel-induced apoptosis and cell cycle arrest by all- trans retinoic acid in prostate cancer cells

We report that all- trans retinoic acid (ATRA) enhanced the toxicity of docetaxel against DU145 and LNCaP prostate cancer cells, and that the nature of the interaction between ATRA and docetaxel was highly synergistic. Docetaxel-induced apoptotic cell death was associated with phosphorylation and hence inactivation of Bcl-2. ATRA enhanced docetaxel-induced apoptosis and combined treatment with ATRA and docetaxel resulted in down-regulation of Bcl-2. Docetaxel caused phosphorylation and hence inactivation of cdc2 kinase result ing in G2/M arrest. ATRA inhibited docetaxel-induced phosphorylation of cdc2 resulting in activation of cdc2 kinase and partial reversal of the G2/M arrest. ATRA also inhibited docetaxel-induced activation of MAPK indicating that the effects of docetaxel and ATRA on cdc2 phosphorylation are dependent on MAPK. We conclude that ATRA synergistically enhances docetaxel toxicity by down-regulating Bcl-2 expression and partially reverses the docetaxel-induced G2/M arrest by inhibiting docetaxel-induced cdc2 phosphorylation in a pathway that is dependent on MAPK. © 2001 Cancer Research Campaign http://www.bjcancer.co

Measurements of peripheral dose for multileaf collimator based linear accelerator

BackgroundIn radiation therapy, peripheral dose (PD), or the dose outside the geometrical boundaries of the radiation field, is of clinical importance when anatomical structures such as foetus in pregnant women, gonads, and lenses of the eye, with low dose tolerances are involved. Even a small percentage of the total treatment dose might cause injury in such cases. The sources of peripheral dose are leakage from the treatment unit, scatter from the secondary collimators and beam modifiers such as wedges and blocks, and internal scatter originating in the patient.AimTo determine the peripheral dose (PD) for multileaf collimator (MLC) based linear accelerator in water equivalent slab phantom for open and wedged fields.Materials/MethodsPD measurements were carried out for 6 and 15 MV photons using a 0.4cc parallel plate chamber in the slab phantom. Measurements were performed for different field sizes at different depths (Dmax, 5 cm and 10 cm) and up to a maximum distance of 30 cm beyond the field edges. PD was measured using wedge filters also. PD was further computed using a three-dimensional treatment planning system (3D TPS).ResultsFor 6 MV photon beams, the maximum PD for open beams at 5 cm distance from the field edge was 3.42% and the minimum PD at 20 cm distance was 0.11%. For 15 MV, the maximum PD for open beam at 5 cm distance was 3.07% and the minimum PD was 0.14%. For wedge filters, the maximum PD measured at 5 cm distance for 6 and 15 MV photons were 5.56% (60° Wedge) and 5.03% (45° wedge). The TPS PD values showed minimal variation from the measured values.ConclusionsThe PD due to MLC and beam modifiers would definitely be helpful to assess the doses received by the relevant critical structures outside the treatment field

Analyzing the variability parameters of the landraces and varieties of little millet (Panicum sumatrense Roth ex Roem. & Schult.)

Little millet is one of the underutilized crops among the cereals, which is being cultivated by farmers of tribal agriculture. The landraces under cultivation possess excellent variability presenting good opportunities for selection. In view of this, the current study was carried out with 17 little millet landraces for 10 quantitative and nine qualitative traits. The study revealed the preponderance of additive gene action for all the 10 traits and hence effective selection could be done for their improvement. Higher to moderate ranges for PCV and GCV with minimum ECV for genetic variability for all the traits were observed. Among the nine qualitative traits, there were significant variations observed for inflorescence shape and panicle compactness. Hence, these traits could be utilized as major DUS descriptors in differentiating the little millet landraces in future. Further the PCA analysis exhibited three reliable principal components contributing to an overall variation of 74.54%. The traits such as days to 50% flowering, peduncle length and flag leaf length were the major positive contributors for variability across all the eigen vectors. These traits were found to exhibit a higher variability among the population and thus a rewarding selection and hybridization for improving these traits could be effected in future breeding programs. Among all the landraces and varieties chittan samai, perunsamai, ATL 1, CO 4 (samai), paakulam karunjamai and vellai samai could be further identified as desirable donors for improving the yield parameters in little millet breeding programs in future

Cancer effects of formaldehyde: a proposal for an indoor air guideline value

Formaldehyde is a ubiquitous indoor air pollutant that is classified as “Carcinogenic to humans (Group 1)” (IARC, Formaldehyde, 2-butoxyethanol and 1-tert-butoxypropanol-2-ol. IARC monographs on the evaluation of carcinogenic risks to humans, vol 88. World Health Organization, Lyon, pp 39–325, 2006). For nasal cancer in rats, the exposure–response relationship is highly non-linear, supporting a no-observed-adverse-effect level (NOAEL) that allows setting a guideline value. Epidemiological studies reported no increased incidence of nasopharyngeal cancer in humans below a mean level of 1 ppm and peak levels below 4 ppm, consistent with results from rat studies. Rat studies indicate that cytotoxicity-induced cell proliferation (NOAEL at 1 ppm) is a key mechanism in development of nasal cancer. However, the linear unit risk approach that is based on conservative (“worst-case”) considerations is also used for risk characterization of formaldehyde exposures. Lymphohematopoietic malignancies are not observed consistently in animal studies and if caused by formaldehyde in humans, they are high-dose phenomenons with non-linear exposure–response relationships. Apparently, these diseases are not reported in epidemiological studies at peak exposures below 2 ppm and average exposures below 0.5 ppm. At the similar airborne exposure levels in rodents, the nasal cancer effect is much more prominent than lymphohematopoietic malignancies. Thus, prevention of nasal cancer is considered to prevent lymphohematopoietic malignancies. Departing from the rat studies, the guideline value of the WHO (Air quality guidelines for Europe, 2nd edn. World Health Organization, Regional Office for Europe, Copenhagen, pp 87–91, 2000), 0.08 ppm (0.1 mg m−3) formaldehyde, is considered preventive of carcinogenic effects in compliance with epidemiological findings

Identifying an indoor air exposure limit for formaldehyde considering both irritation and cancer hazards

Formaldehyde is a well-studied chemical and effects from inhalation exposures have been extensively characterized in numerous controlled studies with human volunteers, including asthmatics and other sensitive individuals, which provide a rich database on exposure concentrations that can reliably produce the symptoms of sensory irritation. Although individuals can differ in their sensitivity to odor and eye irritation, the majority of authoritative reviews of the formaldehyde literature have concluded that an air concentration of 0.3 ppm will provide protection from eye irritation for virtually everyone. A weight of evidence-based formaldehyde exposure limit of 0.1 ppm (100 ppb) is recommended as an indoor air level for all individuals for odor detection and sensory irritation. It has recently been suggested by the International Agency for Research on Cancer (IARC), the National Toxicology Program (NTP), and the US Environmental Protection Agency (US EPA) that formaldehyde is causally associated with nasopharyngeal cancer (NPC) and leukemia. This has led US EPA to conclude that irritation is not the most sensitive toxic endpoint and that carcinogenicity should dictate how to establish exposure limits for formaldehyde. In this review, a number of lines of reasoning and substantial scientific evidence are described and discussed, which leads to a conclusion that neither point of contact nor systemic effects of any type, including NPC or leukemia, are causally associated with exposure to formaldehyde. This conclusion supports the view that the equivocal epidemiology studies that suggest otherwise are almost certainly flawed by identified or yet to be unidentified confounding variables. Thus, this assessment concludes that a formaldehyde indoor air limit of 0.1 ppm should protect even particularly susceptible individuals from both irritation effects and any potential cancer hazard

Preliminary study on CT imaging of polymer gel radiation dosimetry

SummaryBackgroundNew radiotherapy techniques such as stereotactic radiotherapy (SRT) stereotactic radiosurgery (SRS), three dimensional conformal radiotherapy (3DCRT) and intensity modulated radiation therapy (IMRT) aim to deliver a high dose to the tumour while sparing the surrounding normal healthy tissues. As a result of these complicated treatment techniques there is a need for a 3-dimensional (3D) dose verification system. However, currently available dosimeters such as ion chambers, diodes, thermoluminescent dosimeters and films are limited to point (or) planar measurement. Multiple measurements are required to obtain the 3-dimensional dose distribution using the above dosimeters. Hence volumetric measurements are not feasible without multiple detectors (or) multiple measurements. Gel dosimetry attempts to meet the requirements of 3D radiation dose distribution. Gel dosimetry is tissue equivalent [1] and it acts as a phantom as well as dosimeter so there is no need for dose perturbation correction.AimRadiation-induced polymerization in polymer gel dosimeters gives rise to a change in CT number which can be measured with X-ray computed tomography (CT). The aim of this study is to assess the feasibility of using the X-ray CT scanner for the evaluation of dose distribution in polymer gel dosimetry.Materials/MethodsPolymer gel called PAGAT (Polyacrylamide Gelatin and Tetrakis hydroxymethyl phosphonium) consisting of 3.5% (w/w) BIS, 3.5% (w/w) acrylamide, 5% (w/w) gelatin, 10 mM Tetrakis hydroxymethyl phosphonium (THP) and 88% (w/w) water was manufactured in normal atmospheric conditions. The gel was irradiated using a Siemens Primus linear accelerator. The radiation-induced change in CT number was evaluated using a Siemens Somatom Emotion CT scanner. The percentage depth doses and profiles were deduced. The same study was carried out using radiation field analyzer RFA-200 with RK-ion chamber and film and compared with polymer gel measurements.ResultsPolymer gel dosimetry measurement was in agreement with ion chamber and film measurements except for a slight deviation in the build-up region. Discrepancies found were due to analysis of image without image averaging and background subtraction.ConclusionsThis preliminary study was conducted to evaluate the feasibility of using X-ray CT-based polymer gel dosimetry for clinical use. The results of this study encourage further use of X-ray CT in conjunction with polymer gel for 3D radiation dose measurements