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P C Philip

Publications and source records attributed to P C Philip.

7 recordsLinked to original sources
PubMed1988

Uniform analysis of dose distribution in interstitial brachytherapy dosimetry systems.

In brachytherapy, articles are published with dose and homogeneity specifications using different systems which are hard to compare. For the same "stated dose", the dose delivered, volume treated and activity chosen are not the same in different systems, due to the fact that the source placement rules are different. In this article, the authors have circumvented this problem by the use of an approach not applied hitherto, viz. by determining the value of the Uniformity index (UI) of an implant using different systems. This value takes into account the integral dose within the treatment volume and is compared with an idealized implant, where the dose is uniform and the target and treatment volumes are the same. This method of evaluation has been applied for single plane, multiple plane and cylindrical volume implants using the Manchester, Quimby and Paris systems. Although the results obtained are different, the degree of closeness of these values are striking, with some minor exceptions. Thus, it is possible to combine all the brachytherapy parameters, such as: dose, homogeneity, treatment volume within a single value to determine the quality of an implant.

Brachytherapy↗
PubMedDate not supplied

AAPM Task Group 21 protocol: dosimetric evaluation.

The AAPM Task Group 21 protocol is the latest amongst the protocols introduced in recent years covering the dosimetry of high-energy x-ray and electron beams used in radiotherapy. We have found that the C lambda value for 15-MV x rays requires 1.6% upward adjustment, whereas the CE values for electrons in the range 7-18 MeV require downward adjustment of 1%-3% compared to our previous values. The adjustment values given in this paper pertain to the specific measuring systems and high-energy beams considered here and would not necessarily be applicable to other systems. The dose to medium, calculated for different modalities, was verified by thermoluminescent dosimetry and the results were found to be consistent. These values of C lambda and CE have also been compared with those derived using other protocols, particularly the Nordic Association of Clinical Physics 80 and 81, and the discrepancies discussed.

Biophysical Phenomena↗
PubMedDate not supplied

Comparison between continuous and discrete sources in the Paris system of implants.

Since the Paris system of interstitial brachytherapy is based on iridium wires, the consequences resulting from the substitution of discrete point sources in afterloading ribbons have been analyzed. The results are presented in this article for single ribbons, single plane implants of thicknesses 0.5 and 1.0 cm, and biplanar implants of both equal and unequal areas of sizes most frequently used clinically in the thickness range 1.5-3.0 cm. These results indicate changes in the quality of implants using wires and point sources up to the maximum spacing of 1.5 cm. The quality of the implants is judged on the basis of a parameter, the uniformity index, which takes into account both the size of the treatment volume for a given target volume and the homogeneity within the treatment volume as determined from the integral dose. Other implant parameters such as total activity, treatment volume, total volume receiving greater than twice the stated dose rate, average dose rate, and variation of basal dose rate, etc., are also provided to indicate quality of the implants. The results with the customary seed spacing of 1 cm are compatible with those using wires and are found to have improved quality in many cases.

Brachytherapy↗