Humanoid Breast Phantom In Radiotherapy Biology Essay

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The aim of this study is to fabricate Rhizophora spp. Particleboard humanoid breast phantom and compare it with perspex phantom, and water phantom in therapy range by using TLD and other detectors to determine the dose in phantom at different depth in different type of phantom using photon and electron beam.

Fabricate Rhizophora spp particle board torso phantom of an adult medium female and compare it with perspex phantom that fabricated by Dr Ahmad Alzoubi (Alzoubi 2009) for the same female in USM labaratory in therapy range.

In radiotherapy, the term phantom is a tissue equivalent material used to measure the dose distribution instead of the patient to correlate the absorbed dose to the tissue .The primary phantom recommended for dosimetry is water phantom, but since it is not always practical to perform dosimetric measurements in water medium, solid homogeneous phantoms such as polystyrene, acrylic and phantoms made from proprietary materials have found considerable popularity (Khan, 1994).

The most recently studies were done on Rhizophora spp Phantom (Tajuddin A.A et al 1996 , Tajuddin & Banjade 2000) . Rhizophora spp is a genus of tropical trees which is difficult to handle, to cut and shape due to it's compact structure, heavy and strong in strength. While fabricated Rhizophora spp. Particle board can overcome this problem by being easily to handle, cut and shape into the required size and shape.

1.1 Literature review

Che Wan Sudin (1993) has studied the composition of Rhizophora spp, finding favourable composition between this medium and water. Further investigation of this wood by Tajuddin et al. (1996), showed Rhizophora spp to have similar scattering and radiographic properties to that of water and modified rubber. Eid (1999) measured dose distribution around brachytherapy sources, showing for dose distributions around 137Cs and 192Ir sources, that there is general agreement between results for Rhizophora spp and water. In D.P. Banjade study (2001) Rhizophora spp was evaluated as a water equivalent phantom medium for high energy photon and electron beams both in terms of depth ionization and energy deposition. The depth-dose distributions in Rhizophora spp phantom have been found to be comparable with those for water, one exception being at depths beyond Rt, for the 12MeV electron beam.

Further study of dose mapping techniques was done by D P Banjade et al (2002) to investigate the dose distribution throughout a planned target volume (PTV) in a humanoid breast phantom exposed to a 6 MV photon beam.

1.2 Problem Statement

While fabricated Rhizophora spp was studies by other researchers as noted in the literature review, but none of these studies used this type of phantom in radiotherapy range. Also this study will design the fabricated Rhizophora spp as humanoid breast phantom and torso phantom of an adult medium female so that the risk effects of radiation during breast cancer radiotherapy treatment can be studied by measuring the dose in the lung, heart and contralateral breast by using this phantom. Furthermore, this study will extend to study the dose mapping technique to investigate the dose distribution throughout a planned target volume (PTV) in a humanoid breast phantom exposed to a 6 MV photon beam.

1.3 Research Objectives

The aims of this study are:

To fabricate Rhizophora spp. Particle board as tissue equivalent phantom

To study the response behavior of thermolominensce (TLD-100) for photon and electron beam by using Rhizophora spp. Particle board phantom .

To shape the fabricated Rhizophora spp. Particle board as humanoid breast phantom and study the dose mapping techniques at 6 MV photon beam

To study the dose in the lung, heart and contralateral breast during radiotherapy treatment.

To compare Rhizophora spp. Particle board with perspex phantom, and water phantom in therapy range.


Procedure of Rhizophora spp Particleboard

The disc of Rhizophora spp. wood is going under chipping process to make it smaller in size like chip-shape. Then, these will be put in grinding machine to produce flakes. Resin will be sprayed over these flakes to strengthen the particleboard. Phenol Formaldehyde (PF) will be used in this study, because it is more weather resistant, better thermal characteristics and extremely durable than other adhesives (e.g. Urea formaldehyde).

Then the mixture of flakes and PF will be put into the mould, after which it will undergo hot pressing. Lastly, particleboard must be cooled, so that it can be carried out from mould without any cracks.

Response Behavior of TLD

Reproducibility: using 100 CGy, 100 cm SSD, 10 x 10 cm2 Field size, TLDs placed at depth (1.5 cm ) and ion camber in Rhizophora spp phantom.

Linearity Response: study the linearity of TLD for different doses using 6 MV X-ray at fixed SSD and field size.

Field Size Response: the output factor will be determined as a ratio of measured doses at different field size to the calculated dose at fixed field size ( 10 x 10 cm2 ).and study the relationship of the output factor and the field size.

Effect of wedge: the wedge correction factor is the ratio between the wedge transmission factor for a 10 x10 cm2 field size measured with the ionizing chamber placed at dmax, and the wedge transmission factor for the same field size, measured with the TLDs placed at the field at dmax, in the phantom. The relationship between the Correction Factor calculated with the wedge angle will be studied.

Dose rate dependence: exposing TLD and ion chamber for different SSD value and reference setting will be used for all measurement.

Percentage Depth Dose Curve ( PDD) by exposing TLDs and ion chamber at different depth in the fabricated phantom, reference setting will be used for all measurement.

Fabricated Rhizophora spp Humanoid Breast and Torso Phantoms

The CT scan of 1 cm slice thickness of a medium built female will be used to produce the actual size and contour of her torso including the lungs.

Flow chart for the methodology

General References:

Alzoubi.A.S.2009.Post-Mastectomy Radiotherapy involving Supraclavical Nodes- Matchline Dose, Tumor Dose and Organs at Risk Dose. School Of Physics , Universiti Sains Malaysia .PHD Thesis.

Khan, F.M., 1994. The Physics of Radiation Therapy, 2nd Edition. Williams and Wilkins, Baltimore.

Tajuddin, A.A., Che Wan Sudin, C.W.A., Bradley, D.A., 1996.Radiographic and scattering investigation on the suitability of Rhizophora spp as tissue equivalent medium for dosimetric study. Radiat. Phys. Chem. 47, 739-740.

Che Wan Sudin, C.W.A., 1993. Kayu tropika sebagai bahantara setaraan tisu untuk kajian dosimetri. M.Sc.Thesis, University of Science Malaysia.

Eid, M.E.A.M., 1999. Radiation dose distribution measurements around brachytherapy sources in water and Rhizophora spp phantom. M.Sc. Thesis, University ScienceMalaysia.

D.P. Banjade et al. 2001. A study of Rhizophora spp wood phantom for dosimetric purposes using high-energy photon and electron beams. Applied Radiation and Isotopes 55 (2001) 297-302

Banjade, D. P. (2002). A novel approach of dose mapping using a humanoid breast phantom in radiotherapy. The British Journal of Radiology. 75: 812-818.

D.P. Banjade et al,2001. Determination of absorbed dose for photon and electron beams from a linear accelerator by comparing various protocols on different phantoms. Applied Radiation and Isotopes 236 55 (2001) 235-243

Shakhreet.B.Z.2006.Attenuation and Scattering Studies of Natural and Fabricated Particleboard of Rhizophora Spp .In the mammographic Energy Range. School Of Physics , Universiti Sains Malaysia .PHD Thesis.

D.P. Banjade 2002. Study On Dose Measurement In Different Phantoms Using Different Protocols and the Applicability of Thermolominescence Dosimetry in Radiotherapy. School Of Physics , Universiti Sains Malaysia .PHD Thesis