Experimental verification of the Acuros XB and AAA dose calculation adjacent to heterogeneous media for IMRT and RapidArc of nasopharygeal carcinoma
- Department of Oncology, Princess Margaret Hospital, Kwai Chung, Hong Kong Special Administrative Region and Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong Special Administrative Region (Hong Kong)
- Department of Oncology, Princess Margaret Hospital, Kwai Chung, Hong Kong Special Administrative Region (Hong Kong)
- Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong Special Administrative Region (Hong Kong)
Purpose: To compare the doses calculated by the Acuros XB (AXB) algorithm and analytical anisotropic algorithm (AAA) with experimentally measured data adjacent to and within heterogeneous medium using intensity modulated radiation therapy (IMRT) and RapidArc{sup Registered-Sign} (RA) volumetric arc therapy plans for nasopharygeal carcinoma (NPC). Methods: Two-dimensional dose distribution immediately adjacent to both air and bone inserts of a rectangular tissue equivalent phantom irradiated using IMRT and RA plans for NPC cases were measured with GafChromic{sup Registered-Sign} EBT3 films. Doses near and within the nasopharygeal (NP) region of an anthropomorphic phantom containing heterogeneous medium were also measured with thermoluminescent dosimeters (TLD) and EBT3 films. The measured data were then compared with the data calculated by AAA and AXB. For AXB, dose calculations were performed using both dose-to-medium (AXB{sub Dm}) and dose-to-water (AXB{sub Dw}) options. Furthermore, target dose differences between AAA and AXB were analyzed for the corresponding real patients. The comparison of real patient plans was performed by stratifying the targets into components of different densities, including tissue, bone, and air. Results: For the verification of planar dose distribution adjacent to air and bone using the rectangular phantom, the percentages of pixels that passed the gamma analysis with the {+-} 3%/3mm criteria were 98.7%, 99.5%, and 97.7% on the axial plane for AAA, AXB{sub Dm}, and AXB{sub Dw}, respectively, averaged over all IMRT and RA plans, while they were 97.6%, 98.2%, and 97.7%, respectively, on the coronal plane. For the verification of planar dose distribution within the NP region of the anthropomorphic phantom, the percentages of pixels that passed the gamma analysis with the {+-} 3%/3mm criteria were 95.1%, 91.3%, and 99.0% for AAA, AXB{sub Dm}, and AXB{sub Dw}, respectively, averaged over all IMRT and RA plans. Within the NP region where air and bone were present, the film measurements represented the dose close to unit density water in a heterogeneous medium, produced the best agreement with the AXB{sub Dw}. For the verification of point doses within the target using TLD in the anthropomorphic phantom, the absolute percentage deviations between the calculated and measured data when averaged over all IMRT and RA plans were 1.8%, 1.7%, and 1.8% for AAA, AXB{sub Dm} and AXB{sub Dw}, respectively. From all the verification results, no significant difference was found between the IMRT and RA plans. The target dose analysis of the real patient plans showed that the discrepancies in mean doses to the PTV component in tissue among the three dose calculation options were within 2%, but up to about 4% in the bone content, with AXB{sub Dm} giving the lowest values and AXB{sub Dw} giving the highest values. Conclusions: In general, the verification measurements demonstrated that both algorithms produced acceptable accuracy when compared to the measured data. GafChromic{sup Registered-Sign} film results indicated that AXB produced slightly better accuracy compared to AAA for dose calculation adjacent to and within the heterogeneous media. Users should be aware of the differences in calculated target doses between options AXB{sub Dm} and AXB{sub Dw}, especially in bone, for IMRT and RA in NPC cases.
- OSTI ID:
- 22130554
- Journal Information:
- Medical Physics, Vol. 40, Issue 3; Other Information: (c) 2013 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-2405
- Country of Publication:
- United States
- Language:
- English
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61 RADIATION PROTECTION AND DOSIMETRY
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ACCURACY
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COMPARATIVE EVALUATIONS
COMPUTERIZED TOMOGRAPHY
DENSITY
DISTRIBUTION
DOSES
DOSIMETRY
FILMS
IMAGE PROCESSING
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PATIENTS
PHANTOMS
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