Homogeneity Index (HI) is an objective tool to analyz the uniformity of dose distribution in the target volume. Various formulae have been described in literature for its calculation but there is paucity of data regarding the ideal formula and the factors affecting this index. This study was undertaken to analyze HI in our patients using various formulae and to find out the co-relation between HI and prescribed dose, target volume and target location. A retrospective review of 99 patients was performed. HI was calculated using five different formulae (A-E). The patients were divided in five groups each, based on prescribed dose, target volume and target location and mean HI of each group was analysed to find the co-relation between these factors and HI. When there were multiple target volumes the primary target volume was studied. The statistical calculation was done using SPSS version 16.0. Ninety nine patients were found evaluable with 75 males and 24 females. Ninety five patients were treated with radical intent and four with palliative intent. The sites treated were head and neck (46.4%), Pelvis (17.1%), brain (15.1%), abdomen (12.1%), and thorax (6.1%). The mean prescribed dose was 4304 cGy (centiGray) and the mean target volume was 476.2 cc. The mean value of HI was 1.21, 2.08, 30.13, 21.51 and 1.27 with different formulae. There was considerable agreement between HI calculated using various formulae specially the formulae considering prescribed dose (C, D). On statistical analysis, there was no significant co-relation between the location and volume of target but there was a trend toward better HI with increasing prescribed dose. Future studies with more number of patients can confirm our results.

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The evolution of radiotherapy has been ontogenetically linked to medical imaging. Over the years, major technological innovations have resulted in substantial improvements in radiotherapy planning, delivery, and verification. The increasing use of computed tomography imaging for target volume delineation coupled with availability of computer-controlled treatment planning and delivery systems have progressively led to conformation of radiation dose to the target tissues while sparing surrounding normal tissues. Recent advances in imaging technology coupled with improved treatment delivery allow near-simultaneous soft-tissue localization of tumor and repositioning of patient. The integration of various imaging modalities within the treatment room for guiding radiation delivery has vastly improved the management of geometric uncertainties in contemporary radiotherapy practice ushering in the paradigm of image-guided radiation therapy (IGRT). Image-guidance should be considered a necessary and natural corollary to high-precision radiotherapy that was long overdue. Image-guided radiation therapy not only provides accurate information on patient and tumor position on a quantitative scale, it also gives an opportunity to verify consistency of planned and actual treatment geometry including adaptation to daily variations resulting in improved dose delivery. The two main concerns with IGRT are resource-intensive nature of delivery and increasing dose from additional imaging. However, increasing the precision and accuracy of radiation delivery through IGRT is likely to reduce toxicity with potential for dose escalation and improved tumor control resulting in favourable therapeutic index. The radiation oncology community needs to leverage this technology to generate high-quality evidence to support widespread adoption of IGRT in contemporary radiotherapy practice.

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Total body irradiation (TBI) is a special radiotherapy technique, administered prior to bone marrow transplantation. Due to the complex nature of the treatment setup, in vivo dosimetry for TBI is mandatory to ensure proper delivery of the intended radiation dose throughout the body. Lithium fluoride (LiF) TLD-100 chips are used for the TBI in vivo dosimetry. Results obtained from the in vivo dosimetry of 20 patients are analyzed. Results obtained from forehead, abdomen, pelvis, and mediastinum showed a similar pattern with the average measured dose from 96 to 97% of the prescription dose. Extremities and chest received a dose greater than the prescription dose in many instances (more than 20% of measurements). Homogeneous dose delivery to the whole body is checked by calculating the mean dose with standard deviation for each fraction. Reasons for the difference between prescription dose and measured dose for each site are discussed. Dose homogeneity within ±10% is achieved using our in-house TBI protocol.

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Manufacturing of miniaturized high activity ¹⁹² Ir sources have been made a market preference in modern brachytherapy. The smaller dimensions of the sources are flexible for smaller diameter of the applicators and it is also suitable for interstitial implants. Presently, miniaturized ⁶⁰ Co HDR sources have been made available with identical dimensions to those of ¹⁹² Ir sources. ⁶⁰ Co sources have an advantage of longer half life while comparing with ¹⁹² Ir source. High dose rate brachytherapy sources with longer half life are logically pragmatic solution for developing country in economic point of view. This study is aimed to compare the TG-43U1 dosimetric parameters for new BEBIG ⁶⁰ Co HDR and new microSelectron ¹⁹² Ir HDR sources. Dosimetric parameters are calculated using EGSnrc-based Monte Carlo simulation code accordance with the AAPM TG-43 formalism for microSlectron HDR ¹⁹² Ir v2 and new BEBIG ⁶⁰ Co HDR sources. Air-kerma strength per unit source activity, calculated in dry air are 9.698×10 ^-8 ± 0.55% U Bq ^-1 and 3.039×10 ^-7 ± 0.41% U Bq ^-1 for the above mentioned two sources, respectively. The calculated dose rate constants per unit air-kerma strength in water medium are 1.116±0.12% cGy h ^-1 U ^-1 and 1.097±0.12% cGy h ^-1 U ^-1 , respectively, for the two sources. The values of radial dose function for distances up to 1 cm and more than 22 cm for BEBIG ⁶⁰ Co HDR source are higher than that of other source. The anisotropic values are sharply increased to the longitudinal sides of the BEBIG ⁶⁰ Co source and the rise is comparatively sharper than that of the other source. Tissue dependence of the absorbed dose has been investigated with vacuum phantom for breast, compact bone, blood, lung, thyroid, soft tissue, testis, and muscle. No significant variation is noted at 5 cm of radial distance in this regard while comparing the two sources except for lung tissues. The true dose rates are calculated with considering photon as well as electron transport using appropriate cut-off energy. No significant advantages or disadvantages are found in dosimetric aspect comparing with two sources.

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The organ radiation-absorbed doses have been evaluated for humans in six age groups and both genders based on animal data. After intravenous administration of ⁹⁰ Y-DOTA-Cetuximab to five groups of rats, they were sacrificed at exact time intervals (2, 24, 48, 72, and 96 h) and the percentage of injected dose per gram of each organ was calculated by direct counting from rat data. By using the formulation that Medical Internal Radiation Dose suggests, radiation-absorbed doses for all organs were calculated and extrapolated from rat to human. The total body absorbed dose for all groups was >22 mGy due to pure β-emission of the applied radiopharmaceutical. The effective dose resulting from an intravenously injected activity of 100 MBq is 56.7 mSv for a 60-kg female adult and 60.3 mSv for a 73-kg male adult. The results demonstrated the usefulness of this method for estimation of β-absorbed dose in humans.

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Nepal has a long history of medical radiology since1923 but unfortunately, we still do not have any Radiation Protection Infrastructure to control the use of ionizing radiations in the various fields. The objective of this study was an assessment of the radiation protection in medical uses of ionizing radiation. Twenty-eight hospitals with diagnostic radiology facility were chosen for this study according to patient loads, equipment and working staffs. Radiation surveys were also done at five different radiotherapy centers. Questionnaire for radiation workers were used; radiation dose levels were measured and an inventory of availability of radiation equipment made. A corollary objective of the study was to create awareness in among workers on possible radiation health hazard and risk. It was also deemed important to know the level of understanding of the radiation workers in order to initiate steps towards the establishment of Nepalese laws, regulation and code of radiological practice in this field. Altogether, 203 Radiation workers entertained the questionnaire, out of which 41 are from the Radiotherapy and 162 are from diagnostic radiology. The radiation workers who have participated in the questionnaire represent more than 50% of the radiation workers working in this field in Nepal. Almost all X-ray, CT and Mammogram installations were built according to protection criteria and hence found safe. Radiation dose level at the reference points for all the five Radiotherapy centers are within safe limit. Around 65% of the radiation workers have never been monitored for radiation. There is no quality control program in any of the surveyed hospitals except radiotherapy facilities.

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The purpose of this study is to assess fidelity of radiation delivery between high and low dose rates of the flattening filter free (FFF) modes of a new all-digital design medical linear accelerator (Varian TrueBeam ^TM ), particularly for plans optimized for volumetric modulated arc therapy (VMAT). Measurements were made for the two energies of flattening filter free photon beams with a Varian TrueBeam ^TM linac: 6 MV (6 XFFF) at 400 and 1400 MU/min, and 10 MV (10 XFFF) at 400 and 2400 MU/ min. Data acquisition and analysis was performed with both ionization chambers and diode detector system Delta ⁴ , for square radiation fields and for 8 VMAT treatment plans optimized for SBRT treatment of lung tumors. For the square fields, a percent dose difference between high and low dose rate of the order of 0.3-0.4% for both photon energies was seen with the ionization chambers, while the contribution to the difference from ion recombination was found to be negligible. For both the VMAT and square-field deliveries, the Delta ⁴ showed the same average percent dose difference between the two dose rates of ~0.8% and ~0.6% for 10 MV and 6 MV, respectively, with the lower dose rate values giving the greater measured dose compared to the high dose rate. Thus, the VMAT deliveries introduced negligible dose differences between high and low dose rate. Finally, reproducibility of dose measurements was good for both energies.

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Before clinical use of a brachytherapy source, regulations or recommendations by medical physics societies require an independent measurement of its air kerma strength by a qualified medical physicist. Currently, in addition to Ir-192, also HDR-Co-60 sources are increasingly coming into operation. However, the existing dosimetry protocols do not provide any guidelines for Co-60 sources. The purpose of this work was therefore to compare air kerma rate measurements as recommended by different dosimetry protocols for Ir-192 HDR sources and to test their applicability to Co-60 sources. Dosimetric verification of HDR afterloading source specification was performed according to three protocols, DIN 6809-2 (1993) in combination with DGMP-Report 13 (2006), IAEA-TECDOC-1274 (2002) and AAPM Report 41 (1993) for the nuclides Ir-192 and Co-60. Measurements of the sources reference air kerma rate were performed with 3 different methods (with a cylindrical chamber both in a solid phantom and in free air, and with a well chamber) and evaluated using all three protocols for each type of source and method of measurement. The measurements with all protocols and methods show deviations from the certified specification smaller than about 1.2% for Ir-192 and 2.5% for Co-60-Sources. The measurements with the well chamber showed the lowest deviations from the certificate value. Air kerma rate measurements for Co-60 HDR sources using the existing protocols are possible with accuracy sufficient to verify source calibration as provided by the source certificate. However, extension of the protocols by correction factors for measurement with Co-60 sources would be helpful.

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In order to evaluate two-dimensional radiation dose distributions, an algorithm called the Gamma function has recently been modified. The current study concentrates on modification of the gamma function as a three-dimensional dose distribution evaluation tool, and includes the recognition of over-dose/under-dose areas. Using a sign term, the conventional gamma function separates the disagreed areas into two parts: over-dose and under-dose areas. The new gamma function was modified using an extension of the dose difference criterion, ΔD, from two dimensions into three dimensions. In order to provide two-dimensional dose maps for analysis, several images were acquired for a range of regular and irregular radiation fields using a Scanning Liquid Ionization Chamber Electronic Portal Imaging Device. The raw images were then converted into two-dimensional transmitted dose maps using an empirical method. They were utilized as reference dose maps. Translational and rotational manipulations were performed on the reference dose distribution maps to provide evaluated dose maps. The reference and evaluated dose maps were then compared using conventional and modified gamma tools. The results indicated that the modified algorithm is able to enhance the over- and under-dose regions. In addition, a slight increase of the agreement percentage for reference and evaluated dose maps were observed by the extension of ΔD to three dimensions. It is concluded that the modified method is more realistic and applicable for the evaluation of both two-dimensional and three-dimensional dose distributions.

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Inversely planned intensity-modulated radiotherapy (IMRT) and stereotactic small field radiotherapy should be verified before treatment execution. A second verification is carried out for planned treatments in IMRT and 3D conformal radiotherapy (3D-CRT) using a monitor verification commercial dose calculation management software (DCMS). For the same reference point the ion-chamber measured doses are compared for IMRT plans. DCMS (Diamond) computes dose based on modified Clarkson integration, accounting for multi-leaf collimators (MLC) transmission and measured collimator scatter factors. DCMS was validated with treatment planning system (TPS) (Eclipse 6.5 Version, Varian, USA) separately. Treatment plans computed from TPS are exported to DCMS using DICOM interface. Doses are re-calculated at selected points for fields delivered to IMRT phantom (IBA Scanditronix Wellhofer) in high-energy linac (Clinac 2300 CD, Varian). Doses measured at central axis, for the same points using CC13 (0.13 cc) ion chamber with Dose 1 Electrometer (Scanditronix Wellhofer) are compared with calculated data on DCMS and TPS. The data of 53 IMRT patients with fields ranging from 5 to 9 are reported. The computed dose for selected monitor units (MU) by Diamond showed good agreement with planned doses by TPS. DCMS dose prediction matched well in 3D-CRT forward plans (0.8 ± 1.3%, n = 37) and in IMRT inverse plans (−0.1 ± 2.2%, n = 37). Ion chamber measurements agreed well with Eclipse planned doses (−2.1 ± 2.0%, n = 53) and re-calculated DCMS doses (−1.5 ± 2.6%, n = 37) in phantom. DCMS dose validation is in reasonable agreement with TPS. DCMS calculations corroborate well with ionometric measured doses in most of the treatment plans.

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