The output factor correction as function of the photon beam field size – direct measurement and calculation from the lateral dose response functions of gas-filled and solid detectors

A three dimensional treatment planning system has been installed in the Oncology Center, Bangladesh. This system is based on the Anisotropic Analytical Algorithm (AAA). The aim of this study is to verify the validity of photon dose distribution which is calculated by this treatment planning system by comparing it with measured photon beam data in real water phantom. To do this verification, a quality assurance program, consisting of six tests, was performed. In this program, both the calculated output factors and dose at different conditions were compared with the measurement. As a result of that comparison, we found that the calculated output factor was in excellent agreement with the measured factors. Doses at depths beyond the depth of maximum dose calculated on-axis or off-axis in both the fields or penumbra region were found in good agreement with the measured dose under all conditions of energy, SSD and field size, for open and wedged fields. In the build up region, calculated and measured doses only agree (with a difference 2.0%) for field sizes > 5 × 5 cm2 up to 25 × 25 cm2. For smaller fields, the difference was higher than 2.0% because of the difficulty in dosimetry in that region. Dose calculation using treatment planning system based on the Anisotropic Analytical Algorithm (AAA) is accurate enough for clinical use except when calculating dose at depths above maximum dose for small field size.DOI: http://dx.doi.org/10.3329/bjmp.v4i1.14686 Bangladesh Journal of Medical Physics Vol.4 No.1 2011 43-49

Download Full-text

Percentage depth dose fragmentation for investigating and assessing the photon beam dosimetry quality

Journal of Radiotherapy in Practice ◽

10.1017/s1460396918000687 ◽

2018 ◽

Vol 18 (03) ◽

pp. 280-284 ◽

Cited By ~ 4

Author(s):

Mohamed Bencheikh ◽

Abdelmajid Maghnouj ◽

Jaouad Tajmouati

Keyword(s):

Exponential Decay ◽

Target Volume ◽

Photon Beam ◽

Field Size ◽

Photon Beams ◽

Energy Agency ◽

Percentage Depth Dose ◽

Depth Dose ◽

Beam Dosimetry

AbstractAimThe purpose of this study is to introduce a new approach to assess the dosimetry quality of photon beam with energy and irradiation field size. This approach is based on percentage depth dose (PDD) fragmentation for investigating the dosimetry quality.Materials and methodsFor the investigation of the dosimetry quality of 6 and 18 MV photon beams, we have proceeded to fragment the PDD at different field sizes. This approach checks the overall PDD and is not restricted to the exponential decay regions, as per the International Atomic Energy Agency Technical Reports Series No 398 and the American Association of Physicist in Medicine Task Group 51 recommendations.Results and discussionThe 6 MV photon beam deposited more energy in the target volume than the 18 MV photon beam. The dose delivered by the 6 MV beam is greater by a factor of 1·5 than that delivered by the 18 MV beam in the build-up region and the dose delivered by the 6 MV beam is greater by a factor of 2·6 than that delivered by the 18 MV beam in the electronic equilibrium and the exponential decay regions.ConclusionThe dose measured at different points of the beam is higher for 6 MV than for 18 MV photon beam. Therefore, the 6 MV beam is more dosimetrically efficient than the 18 MV beam. Using the proposed approach, we can assess the dosimetry quality by taking into account overall PDD not only in the exponential decay region but also in the field.

Download Full-text

Study of dosimetric characteristics of a commercial optically stimulated luminescence system

Journal of Radiotherapy in Practice ◽

10.1017/s1460396917000346 ◽

2017 ◽

Vol 16 (4) ◽

pp. 461-475 ◽

Cited By ~ 1

Author(s):

Gourav K. Jain ◽

Arun Chougule ◽

Ananth Kaliyamoorthy ◽

Suresh K. Akula

Keyword(s):

Dose Response ◽

Response Curve ◽

Light Exposure ◽

Dose Range ◽

Optically Stimulated Luminescence ◽

Dose Response Curve ◽

Field Size ◽

In Vivo Dosimetry ◽

Detector Response

AbstractBackgroundOptically stimulated luminescence dosimeters (OSLDs) have a number of advantages in radiation dosimetry making them an excellent dosimeter for in vivo dosimetry. The study aimed to study the dosimetric characteristics of a commercial optically stimulated luminescence (OSL) system by Landauer Inc., before using it for routine clinical practice for in vivo dosimetry in radiotherapy. Further, this study also aimed to investigate the cause of variability found in the literature in a few dosimetric parameters of carbon-doped aluminium oxide (Al2O3:C).Materials and methodsThe commercial OSLD system uses Al2O3:C nanoDotTM as an active radiation detector and InLightTM microStar® as a readout assembly. Inter-detector response, energy, dose rate, field size and depth dependency of the detector response were evaluated for all available clinical range of photon beam energies in radiotherapy.ResultsInter-detector variation in OSLD response was found within 3·44%. After single light exposure for the OSL readout, detector reading decreased by 0·29% per reading. The dose linearity was investigated between dose range 50–400 cGy. The dose response curve was found to be linear until 250 cGy, after this dose, the dose response curve was found to be supra-linear in nature. OSLD response was found to be energy independent for Co60 to 10 MV photon energies.ConclusionsThe cause of variability found in the literature for some dosimetric characteristics of Al2O3:C is due to the difference in general geometry, construction of dosimeter, geometric condition of irradiation, phantom material and geometry, beam energy. In addition, the irradiation history of detector used and difference in readout methodologies had varying degree of uncertainties in measurements. However, the large surface area of the detector placed in the phantom with sufficient build-up and backscatter irradiated perpendicularly to incident radiation in Co60 beam is a good method of choice for the calibration of a dosimeter. Understanding the OSLD response with all dosimetric parameters may help us in estimation of accurate dose delivered to patient during radiotherapy treatment.

Download Full-text

On the statistical evaluation of dose-response functions

Radiation and Environmental Biophysics ◽

10.1007/bf01323095 ◽

1974 ◽

Vol 11 (1) ◽

pp. 1-13 ◽

Cited By ~ 29

Author(s):

A. M. Kellerer ◽

J. Brenot

Keyword(s):

Dose Response ◽

Statistical Evaluation ◽

Response Functions

Download Full-text

Improvement of the ISO classification system based on dose-response functions describing the corrosivity of outdoor atmospheres

Outdoor Atmospheric Corrosion ◽

10.1520/stp10884s ◽

2009 ◽

pp. 73-73-15 ◽

Cited By ~ 6

Author(s):

J Tidblad ◽

V Kucera ◽

AA Mikhailov ◽

D Knotkova

Keyword(s):

Dose Response ◽

Classification System ◽

Response Functions

Download Full-text

Khảo sát một số đặc tính bức xạ của buồng ion hóa CC13 và diode bán dẫn razor đối với các chùm photon kích thước nhỏ trên máy gia tốc tuyến tính xạ trị Clinac IX

Journal of Clinical Medicine- Hue Central Hospital ◽

10.38103/jcmhch.2020.66.15 ◽

2020 ◽

Author(s):

Tu Vu Ngoc

Keyword(s):

Radiation Field ◽

Dose Response ◽

Dose Distribution ◽

Ionization Chamber ◽

Field Size ◽

Photon Beams ◽

Silicon Diode ◽

Depth Dose ◽

The Difference

Purpose: Compare percent depth dose (PDD) and off-center ratio (OCR) measured by the CC13 ionization chamber and the RAZOR silicon diode in small photon beams. Method and Materials: Some dosimetric characteristics, such as PDD, OCR, penumbra and radiation field size, were considered in this study for 2x2, 3x3, and 4x4 cm2 field sizes. We used the CC13 ionization chamber and the RAZOR silicon diode to measure dose distribution with depth along the axis and off-center of the beam. From the results obtained, the team investigated the differences in radiation parameters measured by the two types of probes above. Results: There are significant differences in the radiation parameters investigated for the CC13 ionization chamber and the RAZOR silicon diode, especially the width of penumbra. For PDD curves, the difference is less than 5% from dmax to 30 cm, however the difference becomes greater in the build-up region, which reaches to 33% at the water phatom surface. The width of penumbra measured by CC13 is always larger than that of RAZOR, the ratio of the penumbra width between two detectors is 1.8 and 1.3 for energies of 6 MV and 15 MV, respectively. Conclusion: The RAZOR silicon diode has better dose response than the CC13 ionization chamber for measuring the PDD and the OCR in small photon beams.

Download Full-text