Journal of Medical Physics
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   2001| April-June  | Volume 26 | Issue 2  
    Online since April 23, 2009

 
 
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Acceptance Testing And Commissioning Of Ximatron Radiotherapy Simulator
B Paul Ravindran, Rabi Raja I Singh, S Brinda, D Victor Raj
April-June 2001, 26(2):51-59
Though it is well understood that success of radiotherapy involves correct treatment, simulation and accurate patient positioning, the quality assurance of radiotherapy simulator receives little attention. A radiotherapy simulator combines the technology from therapeutic and diagnostic radiology, and hence it needs to be tested for both. In this paper, the authors describe the methods adopted in carrying out the acceptance testing and quality assurance of a Varian Ximatron simulator' prior to its commissioning. Pre-commissioning and quality assurance programs consisted of verification of (i) mechanical and optical parameters, (ii) parameters associated with x-ray beam, (iii) performance of image intensifier, and (iv) parameters related to quality assurance and radiation protection. The check on mechanical and optical parameters included the verification of mechanical and optical read outs, field congruence, isocentre accuracy and accuracy of programmed functions, such as auto-stop. The x-ray beam parameters were verified for kV, MAs, consistency of radiation output and accuracy of timer. The image intensifier performance was checked with respect to resolution, gray image resolution and low contrast sensitivity. The functions of safety interlock for collision were also checked.
[ABSTRACT]   Full text not available  [PDF]
  802 160 -
Scientific Basis For Cancer Chemotherapy And Models Of Tumour Response
Pratik Kumar, M M Rehani, Lalit Kumar
April-June 2001, 26(2):71-81
Chemotherapy is a much more complex mode of cancer treatment than radiotherapy, mainly due to the variety of drugs available for use that differ among themselves in molecular structure, mode of action, pharmacological properties and side effect. The widely accepted tenets of cancer chemotherapy have been largely arrived at with empiricism. Although a number of models for chemotherapeutic effects have been proposed, most of them had no profound impact on practical clinical situations. Again, generally, they have serious limitations in application due to non-availability of treatment and tumour parameters in human cancers. Nevertheless, they do attempt to provide an insight in intricacies of chemotherapy. This paper presents the underlying scientific basis for cancer chemotherapy and a few models. The paper also proposes a clinically applicable model based upon tumour volume known by CT scan films during chemotherapy protocol of Cisplatinum and Cyclophosphamide in 51 patients of epithelial ovarian cancer. Tumour volume regression pattern during treatment was found to follow exponential from. The regression rate could be used to distinguish patients with the risk of shorter survival. Patients with fast regressing tumour (n=29, mean regression constant - 0.026) had median survival of 29.2 months, as opposed to 18.9 months (pc0.05) in case of moderately regressing tumours (n=16, mean regression constant = -0.012). It was also found that if "percent reduction in tumour volume after first cycle of chemotherapy" was less than 15%, the tumour was likely to be inherently resistant to on-going chemotherapy as was the case with 83.3% (5 out of 6 inherently resistant) tumours with median survival of 8.5 months. This may help in identifying such inherently resistant tumours just after the first cycle of chemotherapy and hence save time, money and unnecessary toxicity.
[ABSTRACT]   Full text not available  [PDF]
  565 109 -
Calibration Procedures For Remote Afterloading Selectron (LDR) Unit
Sherly Saju, S S Narayanan, R M Nehru, A Sankar, D D Deshpande
April-June 2001, 26(2):45-50
Remote afterloading machines provide a viable alternate to manual afterloading for brachytherapy, in view of increased radiation safety and of selective source positioning for the given application geometry. Quality assurance program for these machines are essential in terms of accurate dose delivery. As a part of this program, output calibration is to be carried out in a precise manner to evaluate the effective activity of the source being used. In our centre, this is carried out in terms of activity, with Nucletron Source Dosimetry System (NSDS) and in terms of air kerma rate with an air kerma calibrated dosimeter, using a 0.6 cc ion chamber. The effective activity thus arrived at is comparable with the quoted activity by the source manufacturer. This paper describes the calibration procedure for Selectron LDR remote afterloading system.
[ABSTRACT]   Full text not available  [PDF]
  500 94 -
Patient And Staff Doses During Cerebral Angiography
Roshan S Livingstone, L Raghuram, D Victor Raj
April-June 2001, 26(2):60-65
With the advent of "state-of-art" digital subtraction angiography units, there is a need to re-establish the radiation dose related data during procedures performed using such machines. Radiation doses to patients and staff during cerebral angiographic procedures were measured using thermo-luminescent dosimeter and dose-area-product meter. Mean effective dose to patient during cerebral angiogram procedure was found to be 4.6 mSv and that to radiologist was 0.005 mSv. On the basis of these findings, methods to optimize doses received patients during these procedures are discussed.
[ABSTRACT]   Full text not available  [PDF]
  489 102 -
Estimation Of Effective Half-Life In Patients With Graves Disease
G S Pant, Rakesh Kumar, S K Sharma, A K Pandey
April-June 2001, 26(2):66-70
Measurement of effective half-life in individual patients provides accurate means for estimating radiation dose to thyroid gland. However, measurement of this parameter requires a number of visits of patient to the hospital. We suggest a method, which requires less number of visits to the hospital without losing the accuracy. We calculated effective half-life (EHL) in 51 cases by two independent methods. The first one used multiple data points (neck counts) for estimation of EHL, whereas in second, only two data points were obtained, namely, at 24 hr, and 48 hr, 24 hr and 72 hr, 24 hr and 96 hr, 24 hr and 120 hr, respectively. The effective half-lives thus determined from two sets of data points were compared with that obtained from multiple data points. The multiple data points correspond to neck counts at 24 hr, 48 hr, 72 hr, 96 hr, and 120 hr. All these observed values were subjected to statistical analysis to check the agreement between two methods. Measurement of neck counts at 24 hr and at either 96 or 120 hr provides a convenient method for determining EHL in individual patients for the purpose of dosimetry.
[ABSTRACT]   Full text not available  [PDF]
  495 69 -
 
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