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A modified VMAT adaptive radiotherapy for nasopharyngeal cancer patients based on CT-CT image fusion.

Jin X, Han C, Zhou Y, Yi J, Yan H, Xie C - Radiat Oncol (2013)

Bottom Line: The volume of other OARs did not shrink very much.Patients with NPC undergoing VMAT have significant anatomic and dosimetric changes to parotids.Repeat CT as an anatomic changes reference and re-optimization in the iCT based on CT-CT image fusion was accurate enough to identify the volume changes and to ensure safe dose to parotids.

View Article: PubMed Central - HTML - PubMed

Affiliation: Radiotherapy and Chemotherapy, Department of the 1st Affiliated Hospital of Wenzhou Medical University, No,2 Fuxue Lane, Wenzhou 325000, China. billy07@wzhospital.cn.

ABSTRACT

Background: To investigate the feasibility and benefits of a modified adaptive radiotherapy (ART) by replanning in the initial CT (iCT) with new contours from a repeat CT (rCT) based on CT-CT image fusion for nasopharyngeal cancer (NPC) patients underwent volumetric modulated arc radiotherapy (VMAT).

Materials and methods: Nine NPC patients underwent VMAT treatment with a rCT at 23rd fraction were enrolled in this study. Dosimetric differences for replanning VMAT plans in the iCT and in the rCT were compared. Volumetric and dosimetric changes of gross tumor volume (GTV) and organs at risk (OARs) of this modified ART were also investigated.

Results: No dosimetric differences between replanning in the iCT and in the rCT were observed. The average volume of GTV decreased from 78.83 ± 38.42 cm3 in the iCT to 71.44 ± 37.46 cm3 in the rCT, but with no significant difference (p = 0.42).The average volume of the left and right parotid decreased from 19.91 ± 4.89 cm3 and 21.58 ± 6.16 cm3 in the iCT to 11.80 ± 2.79 cm3 and 13.29 ± 4.17 cm3 in the rCT (both p < 0.01), respectively. The volume of other OARs did not shrink very much. No significant differences on PTVGTV and PTVCTV coverage were observed for replanning with this modified ART. Compared to the initial plans, the average mean dose of the left and right parotid after re-optimization were decreased by 62.5 cGy (p = 0.05) and 67.3 cGy (p = 0.02), respectively, and the V5 (the volume receiving 5 Gy) of the left and right parotids were decreased by 7.8% (p = 0.01) and 11.2% (p = 0.001), respectively. There was no significant difference on the dose delivered to other OARs.

Conclusion: Patients with NPC undergoing VMAT have significant anatomic and dosimetric changes to parotids. Repeat CT as an anatomic changes reference and re-optimization in the iCT based on CT-CT image fusion was accurate enough to identify the volume changes and to ensure safe dose to parotids.

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DVH comparisons between replanning based on the initial planning CT with propagated new contours from the rCT and replanning based on the rCT.
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Figure 3: DVH comparisons between replanning based on the initial planning CT with propagated new contours from the rCT and replanning based on the rCT.

Mentions: Dosimetric comparisons between replanning VMAT plans based on the iCT with SOr-to-iCT and replanning plans based on the rCT with SOrCT were shown in Figure 3 and Table 3. Figure 3 shows the DVH curves of targets and OARs of one NPC patient optimized in two CT sets with identical objective settings and parameters. The curves from two replanning VMAT plans were very close. Detailed average dosimetric characteristics were presented in Table 3. The V95 (percent volume covered by 95% prescription dose) of PTVGTV for replanning in the iCT and in the rCT were 91.8 ± 7.2 and 93.0 ± 5.4 (p = 0.66), respectively. The V95 of PTVCTV in these two replanning plans were 98.4 ± 1.3 and 98.7 ± 1.2 (p = 0.24), respectively. No significant dosimetric difference between replanning in the iCT and in the rCT was observed.


A modified VMAT adaptive radiotherapy for nasopharyngeal cancer patients based on CT-CT image fusion.

Jin X, Han C, Zhou Y, Yi J, Yan H, Xie C - Radiat Oncol (2013)

DVH comparisons between replanning based on the initial planning CT with propagated new contours from the rCT and replanning based on the rCT.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4222034&req=5

Figure 3: DVH comparisons between replanning based on the initial planning CT with propagated new contours from the rCT and replanning based on the rCT.
Mentions: Dosimetric comparisons between replanning VMAT plans based on the iCT with SOr-to-iCT and replanning plans based on the rCT with SOrCT were shown in Figure 3 and Table 3. Figure 3 shows the DVH curves of targets and OARs of one NPC patient optimized in two CT sets with identical objective settings and parameters. The curves from two replanning VMAT plans were very close. Detailed average dosimetric characteristics were presented in Table 3. The V95 (percent volume covered by 95% prescription dose) of PTVGTV for replanning in the iCT and in the rCT were 91.8 ± 7.2 and 93.0 ± 5.4 (p = 0.66), respectively. The V95 of PTVCTV in these two replanning plans were 98.4 ± 1.3 and 98.7 ± 1.2 (p = 0.24), respectively. No significant dosimetric difference between replanning in the iCT and in the rCT was observed.

Bottom Line: The volume of other OARs did not shrink very much.Patients with NPC undergoing VMAT have significant anatomic and dosimetric changes to parotids.Repeat CT as an anatomic changes reference and re-optimization in the iCT based on CT-CT image fusion was accurate enough to identify the volume changes and to ensure safe dose to parotids.

View Article: PubMed Central - HTML - PubMed

Affiliation: Radiotherapy and Chemotherapy, Department of the 1st Affiliated Hospital of Wenzhou Medical University, No,2 Fuxue Lane, Wenzhou 325000, China. billy07@wzhospital.cn.

ABSTRACT

Background: To investigate the feasibility and benefits of a modified adaptive radiotherapy (ART) by replanning in the initial CT (iCT) with new contours from a repeat CT (rCT) based on CT-CT image fusion for nasopharyngeal cancer (NPC) patients underwent volumetric modulated arc radiotherapy (VMAT).

Materials and methods: Nine NPC patients underwent VMAT treatment with a rCT at 23rd fraction were enrolled in this study. Dosimetric differences for replanning VMAT plans in the iCT and in the rCT were compared. Volumetric and dosimetric changes of gross tumor volume (GTV) and organs at risk (OARs) of this modified ART were also investigated.

Results: No dosimetric differences between replanning in the iCT and in the rCT were observed. The average volume of GTV decreased from 78.83 ± 38.42 cm3 in the iCT to 71.44 ± 37.46 cm3 in the rCT, but with no significant difference (p = 0.42).The average volume of the left and right parotid decreased from 19.91 ± 4.89 cm3 and 21.58 ± 6.16 cm3 in the iCT to 11.80 ± 2.79 cm3 and 13.29 ± 4.17 cm3 in the rCT (both p < 0.01), respectively. The volume of other OARs did not shrink very much. No significant differences on PTVGTV and PTVCTV coverage were observed for replanning with this modified ART. Compared to the initial plans, the average mean dose of the left and right parotid after re-optimization were decreased by 62.5 cGy (p = 0.05) and 67.3 cGy (p = 0.02), respectively, and the V5 (the volume receiving 5 Gy) of the left and right parotids were decreased by 7.8% (p = 0.01) and 11.2% (p = 0.001), respectively. There was no significant difference on the dose delivered to other OARs.

Conclusion: Patients with NPC undergoing VMAT have significant anatomic and dosimetric changes to parotids. Repeat CT as an anatomic changes reference and re-optimization in the iCT based on CT-CT image fusion was accurate enough to identify the volume changes and to ensure safe dose to parotids.

Show MeSH
Related in: MedlinePlus