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Evaluating the therapeutic dose distribution of intensity-modulated radiation therapy for head and neck with cone-beam computed tomography image: a methodological study.

Zhang GS, Huang SM, Chen C, Xu SK, Zhang DD, Deng XW - Biomed Res Int (2014)

Bottom Line: Also setup deviations were simulated to evaluate the ability of the CBCT-based calculation for detecting the dose errors caused by positioning deviation.The gamma comparison between CBCT- and FBCT-based dose computations showed that the pass rates of (2%, 2 mm) criteria were better than 97.60 ± 0.83% and 97.74 ± 2.08% in the phantom and 10 NPC cases.When setup deviation was introduced into CBCT-based dose calculation, the gamma pass rate significantly decreased while the volumetric doses of the targets and some normal organs exhibited different changes compared to the original plan.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiation Oncology, Sun Yat-Sen University Cancer Center, State Key Laboratory of Oncology in Southern China, Collaborative Innovation Center for Cancer Medicine, 651 Dong Feng Road East, Guangzhou 510060, China.

ABSTRACT
An approximate correction method for the CT value-electron density curve of CBCT was established, through comparison and fitting with FBCT images, and applied to evaluate the therapeutic dose of IMRT. The precision of using CBCT for plan calculation was validated by comparing the dose distribution between CBCT- and FBCT-based IMRT plans. Also setup deviations were simulated to evaluate the ability of the CBCT-based calculation for detecting the dose errors caused by positioning deviation. The gamma comparison between CBCT- and FBCT-based dose computations showed that the pass rates of (2%, 2 mm) criteria were better than 97.60 ± 0.83% and 97.74 ± 2.08% in the phantom and 10 NPC cases. When setup deviation was introduced into CBCT-based dose calculation, the gamma pass rate significantly decreased while the volumetric doses of the targets and some normal organs exhibited different changes compared to the original plan. Our results validated the above CT value-electron density correction which reduced the difference between CBCT- and FBCT-based IMRT plan calculation for NPC to less than 2%. Online CBCT-based dose calculation can be used to reflect and evaluate the dose distribution discrepancy caused by setup deviation and structure changes during the treatment, ensuring more effective quality control of IMRT treatment.

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Related in: MedlinePlus

The isodose line (left), gamma (2%, 2 mm) comparison (right) on the transversal plane, and DVH changes for the simulation condition with a −3 mm positioning deviation along the A-P direction. The upper row is the result of correct positioning and the second row is the result with positioning deviation.
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fig3: The isodose line (left), gamma (2%, 2 mm) comparison (right) on the transversal plane, and DVH changes for the simulation condition with a −3 mm positioning deviation along the A-P direction. The upper row is the result of correct positioning and the second row is the result with positioning deviation.

Mentions: One case of NPC IMRT plan and the CBCT images with the first treatment setup were randomly selected and the above-mentioned method was used to simulate setup deviations of 1 mm, 2 mm, and 3 mm in three directions (superior-inferior S-I, anterior-posterior A-P, and left-right L-R). The comparison between the CBCT-based dose calculation with the introduction of the setup deviation and the original treatment plan showed that when the setup deviation was in the range of 1 mm-2 mm, the change in the gamma (3%, 3 mm) pass rate was small, while the change in the gamma (2%, 2 mm) pass rate was significant. When the setup deviation reached ±3 mm, the gamma (3%, 3 mm) pass rate was still over 95% but the gamma (2%, 2 mm) pass rate was reduced to approximately 75% (Table 3). When the deviation of patient positioning at the anterior-posterior direction reached 3 mm, the CBCT-based dose recalculation showed that the DVH of the target and certain normal organs changed significantly. The dose received by the target volume was reduced (3 mm setup deviation towards the anterior direction) or the maximum dose of the spinal cord significantly increased (3 mm setup deviation towards the posterior direction), as shown in Figure 3.


Evaluating the therapeutic dose distribution of intensity-modulated radiation therapy for head and neck with cone-beam computed tomography image: a methodological study.

Zhang GS, Huang SM, Chen C, Xu SK, Zhang DD, Deng XW - Biomed Res Int (2014)

The isodose line (left), gamma (2%, 2 mm) comparison (right) on the transversal plane, and DVH changes for the simulation condition with a −3 mm positioning deviation along the A-P direction. The upper row is the result of correct positioning and the second row is the result with positioning deviation.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4150500&req=5

fig3: The isodose line (left), gamma (2%, 2 mm) comparison (right) on the transversal plane, and DVH changes for the simulation condition with a −3 mm positioning deviation along the A-P direction. The upper row is the result of correct positioning and the second row is the result with positioning deviation.
Mentions: One case of NPC IMRT plan and the CBCT images with the first treatment setup were randomly selected and the above-mentioned method was used to simulate setup deviations of 1 mm, 2 mm, and 3 mm in three directions (superior-inferior S-I, anterior-posterior A-P, and left-right L-R). The comparison between the CBCT-based dose calculation with the introduction of the setup deviation and the original treatment plan showed that when the setup deviation was in the range of 1 mm-2 mm, the change in the gamma (3%, 3 mm) pass rate was small, while the change in the gamma (2%, 2 mm) pass rate was significant. When the setup deviation reached ±3 mm, the gamma (3%, 3 mm) pass rate was still over 95% but the gamma (2%, 2 mm) pass rate was reduced to approximately 75% (Table 3). When the deviation of patient positioning at the anterior-posterior direction reached 3 mm, the CBCT-based dose recalculation showed that the DVH of the target and certain normal organs changed significantly. The dose received by the target volume was reduced (3 mm setup deviation towards the anterior direction) or the maximum dose of the spinal cord significantly increased (3 mm setup deviation towards the posterior direction), as shown in Figure 3.

Bottom Line: Also setup deviations were simulated to evaluate the ability of the CBCT-based calculation for detecting the dose errors caused by positioning deviation.The gamma comparison between CBCT- and FBCT-based dose computations showed that the pass rates of (2%, 2 mm) criteria were better than 97.60 ± 0.83% and 97.74 ± 2.08% in the phantom and 10 NPC cases.When setup deviation was introduced into CBCT-based dose calculation, the gamma pass rate significantly decreased while the volumetric doses of the targets and some normal organs exhibited different changes compared to the original plan.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiation Oncology, Sun Yat-Sen University Cancer Center, State Key Laboratory of Oncology in Southern China, Collaborative Innovation Center for Cancer Medicine, 651 Dong Feng Road East, Guangzhou 510060, China.

ABSTRACT
An approximate correction method for the CT value-electron density curve of CBCT was established, through comparison and fitting with FBCT images, and applied to evaluate the therapeutic dose of IMRT. The precision of using CBCT for plan calculation was validated by comparing the dose distribution between CBCT- and FBCT-based IMRT plans. Also setup deviations were simulated to evaluate the ability of the CBCT-based calculation for detecting the dose errors caused by positioning deviation. The gamma comparison between CBCT- and FBCT-based dose computations showed that the pass rates of (2%, 2 mm) criteria were better than 97.60 ± 0.83% and 97.74 ± 2.08% in the phantom and 10 NPC cases. When setup deviation was introduced into CBCT-based dose calculation, the gamma pass rate significantly decreased while the volumetric doses of the targets and some normal organs exhibited different changes compared to the original plan. Our results validated the above CT value-electron density correction which reduced the difference between CBCT- and FBCT-based IMRT plan calculation for NPC to less than 2%. Online CBCT-based dose calculation can be used to reflect and evaluate the dose distribution discrepancy caused by setup deviation and structure changes during the treatment, ensuring more effective quality control of IMRT treatment.

Show MeSH
Related in: MedlinePlus