Thermoplastic immobilizing masks have dosimetric effects on the patient’sskin dose. The thermoplastic percentage depth dose
(PDD), equivalent thickness of water for the masks and surface doses
were determined. The surface dose factors due to the thermoplastic
mask was found to be 1.7949, 1.9456,2.0563, 2.1967, 2.3827, 2.5459 and
2.6565 for field sizes of 5×5, 8 × 8,
10 × 10, 12 × 12, 15
× 15, 18 × 18 and 20×20 cm2 respectively which shifted thepercentage depth dose curve to lower
values. The physical thermoplastic thickness was measured to be between 2.30 and 1.80 mm, and the equivalent thicknesses of water, de, were determined to be between 1.2 and 1.00 mm. This meant that, as the mask thickness decreased, its water equivalent
thickness also decreased. The presence of the mask material increased the skin
dose to a factor of 1%. The thermoplastic mask factor was also found to be 0.99.
References
[1]
What Are Thermoplastics? (2007). http://www.scottstool.com/thermoplastic.htm
[2]
Sweeney, R.B.S., Bale, R.M.D., Vogele, M., Nevinny-Sticke, M., Bluhm, A.R.T.T., Auer, T.B.S. and Lukas, P.M. (1998) Repositioning Accuracy: Comparison of a Noninvasive Head Holder with Thermoplastic Mask for Fractionated Radiotherapy and a Case Report. International Journal of Radiation Oncology-Biology-Physics, 41, 475-483. https://doi.org/10.1016/S0360-3016(98)00064-9
[3]
International Commission on Radiation Units and Measurements (1976) Determination of Absorbed Dose in a Patient Irradiated by Beams of X or Gamma Rays in Radiotherapy Procedures. ICRU Report No. 24, International Commission on Radiation Units and Measurements, Bethesda.
[4]
Gilbeau, L., Octave-Prignot, M., Loncol, T., Renard, L., Scalliet, P. and Gregoire, V. (2001) Comparison of Setup Accuracy of Three Different Thermoplastic Masks for the Treatment of Brain and Head and Neck Tumors. Radiotherapy and Oncology, 58, 155-162. https://doi.org/10.1016/S0167-8140(00)00280-2
[5]
Sharp, L., Lewin, F., Johansson, H., Payne, D., Gerhardsson, A. and Rutqvist, L.E. (2005) Randomized Trial on Two Types of Thermoplastic Masks for Patient Immobilization during Radiation Therapy for Head-and-Neck Cancer. International Journal of Radiation Oncology-Biology-Physics, 61, 250-256. https://doi.org/10.1016/j.ijrobp.2004.04.047
[6]
Fuss, M., Salter, B.J., Cheek, D., Sadeghi, A., Hevezi, J.M. and Herman, T.S. (2004) Repositioning Accuracy of a Commercially Available Thermoplastic Mask System. Radiotherapy and Oncology, 71, 339-345. https://doi.org/10.1016/j.radonc.2004.03.003
[7]
Bogdanov, B. (2003) Isometric Crystallization of Stretched Poly (E-Caprolactone). Sheets for Medical Applications. Journal of Thermal Analysis and Calorimetry, 72, 667-674. https://doi.org/10.1023/A:1024502421970
[8]
Mijnheer, B.J., Battermann, J.J. and Wambersie, A. (1987) What Degree of Accuracy Is Required and Can Be Achieved in Photon and Neutron Therapy. Radiotherapy and Oncology, 8, 237-252. https://doi.org/10.1016/S0167-8140(87)80247-5
[9]
Brahme, A. (1984) Dosimetric Precision Requirements in Radiation Therapy. Acta Radiologica: Oncology, 23, 379-391. https://doi.org/10.3109/02841868409136037
[10]
Bentzen, S. (2004) High-Tech in Radiation Oncology. International Journal of Radiation Oncology-Biology-Physics, 58, 320-330. https://doi.org/10.1016/j.ijrobp.2003.09.057
[11]
Almond, P.R., Biggs, P.J., Coursey, B.M., Hanson, W.F., Huq, M.S., Nath, R. and Rogers, D.W. (1999) AAPM’s TG-51 Protocol for Clinical Reference Dosimetry of High-Energy Photon and Electron Beams. Medical Physics, 26, 1847-1870. https://doi.org/10.1118/1.598691
[12]
Grills, I.S., Hugo, G., Kestin, L.L., Galerani, A.P., Chao, K.K., Wloch, J. and Yan, D. (2008) Image-Guided Radiotherapy via Daily Online Cone-Beam CT Substantially Reduces Margin Requirements for Stereotactic Lung Radiotherapy. International Journal of Radiation Oncology-Biology-Physics, 70, 1045-1056. https://doi.org/10.1016/j.ijrobp.2007.07.2352
[13]
Rotondo, R.L., Sultanem, K., Lavoie, I., Skelly, J. and Raymond, L. (2008) Comparison of Repositioning Accuracy of Two Commercially Available Immobilization Systems for Treatment of Head-and-Neck Tumors Using Simulation Computed Tomography Imaging. International Journal of Radiation Oncology-Biology-Physics, 70, 1389-1396. https://doi.org/10.1016/j.ijrobp.2007.08.035
[14]
Hadley, S.W., Kelly, R. and Lam, K. (2005) Effects of Immobilization Mask Material on Surface Dose. Journal of Applied Clinical Medical Physics, 6, 1-7. https://doi.org/10.1120/jacmp.v6i1.1957
[15]
Półtorak, M., Fujak, E. and Kukołowicz, P. (2016) Effect of the Thermoplastic Masks on Dose Distribution in the Build-up Region for Photon Beams. Polish Journal of Medical Physics and Engineering, 22, 1-4. https://doi.org/10.1515/pjmpe-2016-0001
[16]
Yadav, G., Yadav, R. and Kumar, A. (2009) Skin Dose Estimation for Various Beam Modifiers and Source-to-Surface Distances for 6 MV Photons. Journal Medical Physics, 34, 87-92. https://doi.org/10.4103/0971-6203.51935
