Abstract
Purpose: Acuros XB (AXB) dose calculation algorithm is available for external beam photon dose calculations in Eclipse treatment planning system (TPS). The AXB can report the absorbed dose in two modes: dose-to-water (D w ) and dose-to-medium (D m ). The main purpose of this study was to compare the dosimetric results of the AXB_D m with that of AXB_D w on real patient treatment plans. Methods: Four groups of patients (prostate cancer, stereotactic body radiation therapy (SBRT) lung cancer, left breast cancer, and right breast cancer) were selected for this study, and each group consisted of 5 cases. The treatment plans of all cases were generated in the Eclipse TPS. For each case, treatment plans were computed using AXB_D w and AXB_D m for identical beam arrangements. Dosimetric evaluation was done by comparing various dosimetric parameters in the AXB_D w plans with that of AXB_D m plans for the corresponding patient case. Results: For the prostate cancer, the mean planning target volume (PTV) dose in the AXB_D w plans was higher by up to 1.0%, but the mean PTV dose was within ±0.3% for the SBRT lung cancer. The analysis of organs at risk (OAR) results in the prostate cancer showed that AXB_D w plans consistently produced higher values for the bladder and femoral heads but not for the rectum. In the case of SBRT lung cancer, a clear trend was seen for the heart mean dose and spinal cord maximum dose, with AXB_D w plans producing higher values than the AXB_D m plans. However, the difference in the lung doses between the AXB_D m and AXB_D w plans did not always produce a clear trend, with difference ranged from -1.4% to 2.9%. For both the left and right breast cancer, the AXB_D m plans produced higher maximum dose to the PTV for all cases. The evaluation of the maximum dose to the skin showed higher values in the AXB_D m plans for all 5 left breast cancer cases, whereas only 2 cases had higher maximum dose to the skin in the AXB_D m plans for the right breast cancer. Conclusion: The preliminary dosimetric results from our clinical study showed that the selection of either D m or D w in AXB is less likely to produce significant dosimetric differences in the clinical environment. However, the difference between the AXB_D m and AXB_D w calculations depends on the disease site, and even for the same type of disease (e.g., lung cancer), the results are patient specific.
Highlights
In conventional radiation therapy treatment planning systems (TPS), photon dose calculation algorithms typically report the absorbed dose as dose-to-water (Dw)
The preliminary results from the clinical cases in this study showed that the differences in dosimetric results between the AXB_Dm and AXB_Dw plans depend on the tumor type
The results presented in this study demonstrated that the difference between the AXB_Dm and AXB_Dw calculations is dependent on the tumor type, and even for the same type of tumor, the results are patient specific
Summary
In conventional radiation therapy treatment planning systems (TPS), photon dose calculation algorithms typically report the absorbed dose as dose-to-water (Dw). Dose calculation algorithms employed in the TPS aim to best match the computed results with the measurements, which are performed in water phantoms. Siebers et al.[1] suggested that the conversion of Dm to Dw may be desirable in some of the situations when MC-based calculations are used in external beam photon radiation therapy. Dosimetric calibration protocols of external beam photon radiation therapy[2, 3] are based on the Dw mode, and the use of either Dm or Dw (after the conversion of Dm to Dw) for MC-based photon dose calculations remains a debating topic.[4]
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