Implementation of compensator-based intensity modulated radiotherapy with a conventional telecobalt machine using missing tissue approach

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Abstract

Objectives: The present study aimed to generate intensity-modulated beams with compensators for a conventional telecobalt machine, based on dose distributions generated with a treatment planning system (TPS) performing forward planning, and cannot directly simulate a compensator.

Materials and Methods: The following materials were selected for compensator construction: Brass, Copper and Perspex (PMMA). Boluses with varying thicknesses across the surface of a tissue-equivalent phantom were used to achieve beam intensity modulations during treatment planning with the TPS. Beam data measured for specific treatment parameters in a full scatter water phantom with a 0.125 cc cylindrical ionization chamber, with a particular compensator material in the path of beams from the telecobalt machine, and that without the compensator but the heights of water above the detector adjusted to get the same detector readings as before, were used to develop and propose a semi-empirical equation for converting a bolus thickness to compensator material thickness, such that any point within the phantom would receive the planned dose. Once the dimensions of a compensator had been determined, the compensator was constructed using the cubic pile method. The treatment plans generated with the TPS were replicated on the telecobalt machine with a bolus within each beam represented with its corresponding compensator mounted on the accessory holder of the telecobalt machine.

Results: Dose distributions measured in the tissue-equivalent phantom with calibrated Gafchromic EBT2 films for compensators constructed based on the proposed approach, were comparable to those of the TPS with deviation less than or equal to ± 3% (mean of 2.29 ± 0.61%) of the measured doses, with resultant confidence limit value of 3.21. Conclusion: The use of the proposed approach for clinical application is recommended, and could facilitate the generation of intensity-modulated beams with limited resources using the missing tissue approach rendering encouraging results.

[1] Tagoe SNA, Mensah SY, Fletcher JJ, Sasu E. Telecobalt Machine Beam Intensity Modulation with Aluminium Compensating Filter Using Missing Tissue Approach. Iraj J Med Phys. 2018;15(1):48-61.

[2] Schlegel W, Bortfeld T, Grosu A. New technologies in radiation oncology. Springer-Verlag Berlin Heidelberg, Germany. 2006.

[3] Khan FM. The physics of radiation therapy. Fourth Edition. Lippincott William and Wilkins. 2010.

[4] Vaarkamp J, Adams EJ, Warrington AP, Dearnaley DP. A comparison of forward and inverse planned conformal, multi segment and intensity modulated radiotherapy for the treatment of prostate and pelvic nodes. Radiother Oncol. 2004;73(1):65-72.

[5] Shepard DM, Earl MA, Li XA, et al. Direct aperture optimization: A turnkey solution for step-and-shoot IMRT. Med Phys. 2002:29(6): 1007-1018.

[6] Van de Werf E, Verstraete J, Lievens Y. The cost of radiotherapy in a decade of technology evolution. Radiother Oncol. 2012;102(1): 148-153.

[7] Chang S. Compensating filter-intensity-modulated Radiotherapy – A Traditional Tool for Modern Application. European Oncological Disease. 2006;1(2):82-87.

[8] International Atomic Energy Agency (IAEA). Technical report series 398. Absorbed dose determination in external beam radiotherapy. IAEA. 2000.

[9] Podgorsak EB. Radiation oncology physics: A handbook for teachers and students. International Atomic Energy Agency (IAEA). 2005.

[10] Canadian Nuclear Safety Commission. Certified Transport Packages and Special Form Radioactive Material. Canadian Nuclear Safety Commission. 2012.

[11] Nelms B, Markman J. Implementation of ‘solid IMRT’: modulator design, fabrication, dose delivery, and quality assurance. Australas Phys Eng Sci Med. 2001;24(4):223-224.

[12] Prowess Inc. Prowess Panther treatment planning system user manual. Prowess Inc., USA. 2003.

[13] Earl MA, Afghan MKN, Yu CX, et al. Jaws-only IMRT using direct aperture optimization. Med Phys. 2007:34(1):307-314.

[14] Sasaki K, Obata Y. Dosimetric characteristics of a cubic-block-piled compensator for intensity-modulated radiation therapy in the Pinnacle radiotherapy treatment planning system. J Appl Clin Med Phys. 2007;8(1):85-100.

[15] van Battum LJ, Hoffmans D, Piersma H, Heukelom S. Accurate dosimetry with GafChromic EBT film of a 6 MV photon beam in water: what level is achievable? Med Phys. 2008;35(2):704-716.

[16] Kassaee A, Bloch P, Yorke E, et al. Beam spoilers versus bolus for 6 MV photon treatment of head and neck cancers. Med Dosim. 2000;25(3):127-131.

[17] Amin NAB, Zukhi J, Kabir NA, Zainon R. Determination of effective atomic numbers from mass attenuation coefficients of tissue-equivalent materials in the energy range 60 keV-1.33 MeV. IOM Conf Series: Journal of Physics: Conference Series. 2017;851(1):012018.

[18] van der Merwe D, Van Dyk J, Healy B, et al. Accuracy requirements and uncertainties in radiotherapy: a report of the International Atomic Energy Agency. Acta Oncol. 2017;56(1):1-6.

Polish Journal of Medical Physics and Engineering

The Journal of Polish Society of Medical Physics

Journal Information


CiteScore 2017: 0.19
ICV 2017 = 103.49

SCImago Journal Rank (SJR) 2017: 0.104
Source Normalized Impact per Paper (SNIP) 2017: 0.233

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