A study of dosimetric characteristics for in vivo dosimetry with cylindrical n-type Isorad diode

Abstract

Background and purpose: The objective was to determine diode characteristics before actual dose verification on human phantom and patients. Materials and methods:The reliability and stability of equipment, signal stability, precision, dose response linearity, field flatness, perturbation of radiation dose, plastic to water conversion factor (K pl ), ionisation chambers (ICs) and diode calibration were determined. Correction factors for tray (CF tray ), wedge (CF wedge ), field size (CF FS ), SSD (CF SSD ), angle (CF angle ) and block (CF block ) were found. Patient dose monitor, Isorad diode (n-type) and IC (PTW Frieburg), Co-60 unit (Theratron), ATOM Adult male human phantom (Model 701-D, CIRS) were used.Results and conclusion: Good signal stability, precise data, and linear dose response, variation of 0?500% and 5?000% in field flatness and perturbation tests, respectively, were noted. K pl was 1?006 for IC PTW Frieburg TW30013, 0114. The diode calibration factor was 0?989. CF tray , CF FS , CF SSD , CF angle , CF block were 1?001, 1?001, 0?997, 1?006 and 0?990, respectively. CF wedge were 1?024, 1?030 and 1?038 for 308, 458 and 608 wedges, respectively. The verification of above correction factors (CFs) on Nasopharynx and lung of human phantom was also done.

Effect of correction/calibration factors on accuracy of in vivo dose delivery with cylindrical n-type Isorad diode in conventional radiotherapy

“…In vivo dosimetry is a tool of independent dose verification and quality assurance in radiotherapy which may be helpful not only to improve the quality of procedure but also the treatment 1 , 2 . Being the first use of Isorad diode in radiation therapy unit, for in vivo dosimetry, a list of correction factors were calculated including certain preliminary tests, based upon this data the accuracy of in vivo dose results were determined 3 . This dosimetry is a requirement of a busy radiotherapy department in order to formulate action levels for radiation treatment of patients 4 – 6 .…”

“…1,2 Being the first use of Isorad diode in radiation therapy unit, for in vivo dosimetry, a list of correction factors were calculated including certain preliminary tests, based upon this data the accuracy of in vivo dose results were determined. 3 This dosimetry is a requirement of a busy radiotherapy department in order to formulate action levels for radiation treatment of patients. [4][5][6] Diode dosimeter with its electrometer generates signal in order to record the dose delivered to human phantom/patient.…”