Dosimetric verification of clinical radiotherapy treatment planning system
Abstract
Background/Aim. In the past two decades, we have witnessed the emergence of new radiation therapy techniques, radiotherapy treatment planning system (TPS) with calculating algorithms for the dosage calculation in a patient, units for multislice computed tomography (CT) and image-guided treatment delivery. The aim of the study was investigating the significant difference in dosimetric calculation of radiotherapy TPS in relation to the values obtained by measuring on the linear accelerator (LINAC), and the accuracy of dosimetric calculation between calculating algorithms Analytical Anisotropic Algorithm (AAA) and Acuros XB in various tissues and photon beam energies. Methods. For End-to-End test we used the heterogeneous phantom CIRS Thorax002LFC, which anatomically represents human torso with a set of inserts known as relative electron densities (RED) for obtaining a CT calibration curve, comparable to the “reference” CIRS 062M phantom. For the AAA and Acuros XB algorithms and for 6 MV and 16 MV photon beams in the TPS Varian Eclipse 13.6, four 3D conformal (3DCRT), and one intensity modulated (IMRT) and volumetric modulated arc (VMAT) radiotherapy plans were made. Measurements of the absolute dose in Thorax phantom, by PTW-Semiflex ionization chamber, were carried out on three Varian-DHX LINACs. Results. The difference between “reference” and measured CT conversion curves in the bone area was 3%. For 476 phantom measurements, the difference between measured and TPS calculated dose of 3–6%, was found in 30 (6.3%) cases. According to regression analysis, the standardized Beta coefficient for relative errors, 6 MV vs. 16 MV, was 0.337 (33.7%, p < 0.001). Mean relative errors for AAA and Acuros XB, using Mann-Whitney test, for bones were 1.56% and 2.64%, respectively (p = 0.004). Conclusion. End-to-End test on Thorax002LFC phantom proved the accuracy of TPS dose calculation in relation to the one delivered to a patient by LINAC. There was a significant difference for photon energies relative errors (higher values are obtained for 16 MV vs. 6 MV). A statistically significant minor relative error in AAA vs. Acuros XB was found for the bone.
References
International Atomic Energy Agency (IAEA). Lessons Learned from Accidental Exposures in Radiotherapy, Safety Reports Series No. 17. Vienna: IAEA; 2000.
IAEA. Investigation of an Accidental Exposure of Radiother-apy Patients in Panama. Vienna: IAEA. 2001.
Task Group on Accident Prevention and Safety in Radiation Therapy. Prevention of accidental exposures to patients un-dergoing radiation therapy. A report of the International Commission on Radiological Protection. Ann ICRP 2000; 30(3): 7‒70.
Technical Reports Series No. 430. Commissioning andquality assurance ofcomputerized planningsystems for radiation treatment of cancer. Vienna: International Atomic Energy Agency; 2004.
IAEA-TECDOC-1583. Commissioning of radiotherapy treatment planning systems: testing for typical external beam treatment techniques. Report of the Coordinated Research Project (CRP) on Development of Procedures for Quality As-surance of Dosimetry Calculations in Radiotherapy. Vienna: International Atomic Energy Agency; 2008. (English, Russian)
Mijnheer B, Olszewska A, Florin C, Hartmann G, Knows T, Rosendale JC, et al. ESTRO Booklet No. 7. Quality assurance of treatment planning systems. Practical examples for non-IMRT photon beams. Brussels: ESTRO; 2005.
Fraass B, Doppke K, Hunt M, Kutcher G, Starkschall G, Stern R, et al. American Association of Physicists in Medicine Radia-tion Therapy Committee Task Group 53: quality assurance for clinical radiotherapy treatment planning. Med Phys 1998; 25(10): 1773‒829.
AAPM. Report No. 055 – Radiation Treatment Planning Do-simetry Verification 1995. Alexandria, VA: AAPM American Association of Physicists in Medicine; 1995.
TG-119 IMRT Commissioning Tests Instructions for Plan-ning, Measurement, and Analysis Version 10/21/2009. Alex-andria, VA: AAPM American Association of Physicists in Medicine; 2009.
Schiefer H, Fogliata A, Nicolai G, Cozy L, Selenga W, Born E, et al. The Swiss IMRT dosimetry intercomparison using a thorax phantom. Med Phys 2010; 37(8): 4424‒31.
Gifford K, Followill D, Liu H, Starkschall G. Verification of the accuracy of a photon dose–calculation algorithm. J Appl Clin Med Phys 2002; 3(1): 26–45.
Brittan K, Rather S, Newcomb C, Murray B, Robinson D, Field C, et al. Experimental validation of the Eclipse AAA algorithm. J Appl Clin Med Phys 2007; 8(2): 76‒92.
CIRS Tissue Simulation & Phantom Technology. IMRT Thor-ax phantom Model 002LFC, user guide. Available from: www.cirsinc.com › radiation-therapy
Technical Reports Series No. 398. Absorbed dose determina-tion in external beam radiotherapy. An International Code of Practice for Dosimetry Based on Standards of Absorbed Dose to Water. Vienna: International Atomic Energy Agency; 2000.
Rutonjski L, Petrolia B, Baikal M, Teodorović M, Čudić O, Gersh-kevitsh E, et al. Dosimetric verification of radiotherapy treat-ment planning systems in Serbia: national audit. Radiat Oncol 2012; 7(1): 155.
Thomas SJ. Relative electron density calibration of CT scan-ners for radiotherapy treatment planning. Br J Radiol 1999; 72(860): 781‒6.
Gershkevitsh E, Schmidt R, Velez G, Miller D, Korf E, Yip F, et al. Dosimetric verification of radiotherapy treatment planning systems: results of IAEA pilot study. Radiother Oncol 2008; 89(3): 338‒46.
Knöös T, Wieslander E, Cozzi L, Brink C, Fogliata A, Albers D, et al. Comparison of dose calculation algorithms for treatment planning in external photon beam therapy for clinical situa-tions. Phys Med Biol 2006; 51(22): 5785‒807.