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Feasibility of constant dose rate VMAT in the treatment of nasopharyngeal cancer patients.

Yu W, Shang H, Xie C, Han C, Yi J, Zhou Y, Jin X - Radiat Oncol (2014)

Bottom Line: No significant difference in other target coverage parameters was observed.There was no significant difference in OAR sparing among these three planning schemes except for a higher maximum dose (Dmax) on the brainstem for CDR-VMAT.Its plan quality was acceptable but should be thoroughly checked compared with VDR-VMAT and MCO-VMAT in the treatment of NPC.

View Article: PubMed Central - PubMed

Affiliation: Radiation Oncology Department, Quzhou People's Hospital, No. 2 Zhongloudi Street, Quzhou, 324000, China. wlyu1982@aliyun.com.

ABSTRACT

Purpose: To investigate the feasibility of constant dose rate volumetric modulated arc therapy (CDR-VMAT) in the treatment of nasopharyngeal cancer (NPC) patients and to introduce rotational arc radiotherapy for linacs incapable of dose rate variation.

Materials and methods: Twelve NPC patients with various stages treated previously using variable dose rate (VDR) VMAT were enrolled in this study. CDR-VMAT, VDR-VMAT and mutlicriteria optimization (MCO) VMAT plans were generated for each patient on RayStation treatment planning system with identical objective functions and the dosimetric differences among these three planning schemes were evaluated and compared. Non dosimetric parameters of optimization time, delivery time and delivery accuracy were also evaluated.

Results: The planning target volume of clinical target volume (PTV-CTV) coverage of CDR-VMAT was a bit inferior to those of VDR- and MCO-VMAT. The V93 (p=0.01) and V95 (percent volume covered by isodose line) (p=0.04) for CDR-VMAT, VDR-VMAT and MCO-VMAT were 98.74% ± 0.31%, 99.76% ± 0.16%, 99.38% ± 0.43%, and 98.40% ± 0.48%, 99.53% ± 0.28%, 99.07% ±0.52%, respectively. However, the CDR-VMAT showed a better dose homogeneity index (HI) (p=0.01) in PTV-CTV. No significant difference in other target coverage parameters was observed. There was no significant difference in OAR sparing among these three planning schemes except for a higher maximum dose (Dmax) on the brainstem for CDR-VMAT. The brainstem Dmax of CDR-VMAT, VDR-VMAT and MCO-VMAT were 54.26 ± 3.21 Gy, 52.19 ± 1.65 Gy, and 52.79 ± 4.77 Gy, respectively. The average delivery time (p<0.01) and the average percent γ passing rates (p=0.02) of CDR-VMAT, VDR-VMAT and MCO-VMAT were 7.01 ± 0.43 min, 4.75 ± 0.07 min, 4.01 ± 0.28 min, and 95.75% ± 2.57%, 97.65% ± 1.45%, 97.36% ± 2.45%, respectively.

Conclusion: CDR-VMAT offers an additional option of rotational arc radiotherapy for linacs incapable of dose rate variation with a lower initial cost. Its plan quality was acceptable but should be thoroughly checked compared with VDR-VMAT and MCO-VMAT in the treatment of NPC.

No MeSH data available.


Related in: MedlinePlus

Typical target contours for nasopharyngeal cancer patients, green for CTV, red for GTV, pink for right parotid, sky blue for left parotid, and yellow for spinal cord.
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Fig1: Typical target contours for nasopharyngeal cancer patients, green for CTV, red for GTV, pink for right parotid, sky blue for left parotid, and yellow for spinal cord.

Mentions: Target and normal tissue contours have been reported in our previous study and are generalized here [12]. Gross tumor volume (GTV) was delineated as the mass shown in the enhanced computed tomography images or magnetic resonance images or both. The clinical target volume (CTV) was defined as the GTV plus a margin of potential microscopic spread. One typical contour is shown in Figure 1. The planning target volume (PTV) was created by adding a 3 mm margin to the CTV account for setup variability. In order to increase the coverage of the GTV, a PTV-GTV was generated by adding a 2 mm margin to the GTV. Organ at risks (OARs) (brain stem, spinal cord, lens, left and right parotids) were contoured and constrained for optimization.Figure 1


Feasibility of constant dose rate VMAT in the treatment of nasopharyngeal cancer patients.

Yu W, Shang H, Xie C, Han C, Yi J, Zhou Y, Jin X - Radiat Oncol (2014)

Typical target contours for nasopharyngeal cancer patients, green for CTV, red for GTV, pink for right parotid, sky blue for left parotid, and yellow for spinal cord.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4222390&req=5

Fig1: Typical target contours for nasopharyngeal cancer patients, green for CTV, red for GTV, pink for right parotid, sky blue for left parotid, and yellow for spinal cord.
Mentions: Target and normal tissue contours have been reported in our previous study and are generalized here [12]. Gross tumor volume (GTV) was delineated as the mass shown in the enhanced computed tomography images or magnetic resonance images or both. The clinical target volume (CTV) was defined as the GTV plus a margin of potential microscopic spread. One typical contour is shown in Figure 1. The planning target volume (PTV) was created by adding a 3 mm margin to the CTV account for setup variability. In order to increase the coverage of the GTV, a PTV-GTV was generated by adding a 2 mm margin to the GTV. Organ at risks (OARs) (brain stem, spinal cord, lens, left and right parotids) were contoured and constrained for optimization.Figure 1

Bottom Line: No significant difference in other target coverage parameters was observed.There was no significant difference in OAR sparing among these three planning schemes except for a higher maximum dose (Dmax) on the brainstem for CDR-VMAT.Its plan quality was acceptable but should be thoroughly checked compared with VDR-VMAT and MCO-VMAT in the treatment of NPC.

View Article: PubMed Central - PubMed

Affiliation: Radiation Oncology Department, Quzhou People's Hospital, No. 2 Zhongloudi Street, Quzhou, 324000, China. wlyu1982@aliyun.com.

ABSTRACT

Purpose: To investigate the feasibility of constant dose rate volumetric modulated arc therapy (CDR-VMAT) in the treatment of nasopharyngeal cancer (NPC) patients and to introduce rotational arc radiotherapy for linacs incapable of dose rate variation.

Materials and methods: Twelve NPC patients with various stages treated previously using variable dose rate (VDR) VMAT were enrolled in this study. CDR-VMAT, VDR-VMAT and mutlicriteria optimization (MCO) VMAT plans were generated for each patient on RayStation treatment planning system with identical objective functions and the dosimetric differences among these three planning schemes were evaluated and compared. Non dosimetric parameters of optimization time, delivery time and delivery accuracy were also evaluated.

Results: The planning target volume of clinical target volume (PTV-CTV) coverage of CDR-VMAT was a bit inferior to those of VDR- and MCO-VMAT. The V93 (p=0.01) and V95 (percent volume covered by isodose line) (p=0.04) for CDR-VMAT, VDR-VMAT and MCO-VMAT were 98.74% ± 0.31%, 99.76% ± 0.16%, 99.38% ± 0.43%, and 98.40% ± 0.48%, 99.53% ± 0.28%, 99.07% ±0.52%, respectively. However, the CDR-VMAT showed a better dose homogeneity index (HI) (p=0.01) in PTV-CTV. No significant difference in other target coverage parameters was observed. There was no significant difference in OAR sparing among these three planning schemes except for a higher maximum dose (Dmax) on the brainstem for CDR-VMAT. The brainstem Dmax of CDR-VMAT, VDR-VMAT and MCO-VMAT were 54.26 ± 3.21 Gy, 52.19 ± 1.65 Gy, and 52.79 ± 4.77 Gy, respectively. The average delivery time (p<0.01) and the average percent γ passing rates (p=0.02) of CDR-VMAT, VDR-VMAT and MCO-VMAT were 7.01 ± 0.43 min, 4.75 ± 0.07 min, 4.01 ± 0.28 min, and 95.75% ± 2.57%, 97.65% ± 1.45%, 97.36% ± 2.45%, respectively.

Conclusion: CDR-VMAT offers an additional option of rotational arc radiotherapy for linacs incapable of dose rate variation with a lower initial cost. Its plan quality was acceptable but should be thoroughly checked compared with VDR-VMAT and MCO-VMAT in the treatment of NPC.

No MeSH data available.


Related in: MedlinePlus