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Improving target coverage and organ-at-risk sparing in intensity-modulated radiotherapy for cervical oesophageal cancer using a simple optimisation method.

Lu JY, Cheung ML, Huang BT, Wu LL, Xie WJ, Chen ZJ, Li DR, Xie LX - PLoS ONE (2015)

Bottom Line: The BDF-based plans provided significantly superior dose homogeneity and conformity compared with both the DCS-based and Original plans.The BDF-based method further reduced the doses delivered to the OARs by approximately 1-3%.All verification tests were passed and no significant differences were found.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiation Oncology, Cancer Hospital of Shantou University Medical College, Shantou, China.

ABSTRACT

Purpose: To assess the performance of a simple optimisation method for improving target coverage and organ-at-risk (OAR) sparing in intensity-modulated radiotherapy (IMRT) for cervical oesophageal cancer.

Methods: For 20 selected patients, clinically acceptable original IMRT plans (Original plans) were created, and two optimisation methods were adopted to improve the plans: 1) a base dose function (BDF)-based method, in which the treatment plans were re-optimised based on the original plans, and 2) a dose-controlling structure (DCS)-based method, in which the original plans were re-optimised by assigning additional constraints for hot and cold spots. The Original, BDF-based and DCS-based plans were compared with regard to target dose homogeneity, conformity, OAR sparing, planning time and monitor units (MUs). Dosimetric verifications were performed and delivery times were recorded for the BDF-based and DCS-based plans.

Results: The BDF-based plans provided significantly superior dose homogeneity and conformity compared with both the DCS-based and Original plans. The BDF-based method further reduced the doses delivered to the OARs by approximately 1-3%. The re-optimisation time was reduced by approximately 28%, but the MUs and delivery time were slightly increased. All verification tests were passed and no significant differences were found.

Conclusion: The BDF-based method for the optimisation of IMRT for cervical oesophageal cancer can achieve significantly better dose distributions with better planning efficiency at the expense of slightly more MUs.

No MeSH data available.


Related in: MedlinePlus

Workflow for generating a BDF-based plan for cervical oesophageal cancer.
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pone.0121679.g001: Workflow for generating a BDF-based plan for cervical oesophageal cancer.

Mentions: To generate a BDF-based plan, the number of fractions of the original plan was modified to 50% of the prescribed number of fractions (from 32 to 16, in our cases) to generate a “base dose plan” with half of the total prescribed dose. Then, the base dose plan was copied to be a “top dose plan”. Afterwards, the top dose plan was re-optimised once based on the base dose plan using Eclipse’s base dose function. At this point, the prescribed dose of the plan sum (the top dose plan plus the base dose plan) was equal to the originally prescribed dose. When the final dose calculation was complete, the number of fractions of the optimised top dose plan was changed from 50% (16 fractions) to 100% (32 fractions) of the prescribed number of fractions, that is, the prescribed dose of the top dose plan was changed from a half dose to the original dose. The resulting optimised top dose plan was referred to as the BDF-based plan. This workflow is depicted in Fig. 1. To generate a DCS-based plan, the isodose of 67.2 Gy (105% of the PTV64 prescription dose) and the 45-Gy isodose in the PRV spinal cord in the original plan were converted into dose-controlling structures, and a cold-spot dose-controlling structure was generated from the PTV64 minus the prescription isodose volume (PIV). Then, the dose-controlling structures for hot and cold spots were assigned new dose objectives. Typically, for the PTV64, the upper dose objective was set to 2% lower than the prescribed dose for the PTV64 hot spots, and the lower dose objective was set to 2% higher than the prescribed dose for the cold spots. The upper dose objective was set to 40–45 Gy for the hot spots of the PRV spinal cord. After one-time re-optimisation and final dose calculation, the DCS-based plan was complete. A distributed calculation framework (DCF) was applied to accelerate the final dose calculation. The one-time re-optimisation time was defined as the time from the beginning of re-optimisation to the completion of the final dose calculation.


Improving target coverage and organ-at-risk sparing in intensity-modulated radiotherapy for cervical oesophageal cancer using a simple optimisation method.

Lu JY, Cheung ML, Huang BT, Wu LL, Xie WJ, Chen ZJ, Li DR, Xie LX - PLoS ONE (2015)

Workflow for generating a BDF-based plan for cervical oesophageal cancer.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4358965&req=5

pone.0121679.g001: Workflow for generating a BDF-based plan for cervical oesophageal cancer.
Mentions: To generate a BDF-based plan, the number of fractions of the original plan was modified to 50% of the prescribed number of fractions (from 32 to 16, in our cases) to generate a “base dose plan” with half of the total prescribed dose. Then, the base dose plan was copied to be a “top dose plan”. Afterwards, the top dose plan was re-optimised once based on the base dose plan using Eclipse’s base dose function. At this point, the prescribed dose of the plan sum (the top dose plan plus the base dose plan) was equal to the originally prescribed dose. When the final dose calculation was complete, the number of fractions of the optimised top dose plan was changed from 50% (16 fractions) to 100% (32 fractions) of the prescribed number of fractions, that is, the prescribed dose of the top dose plan was changed from a half dose to the original dose. The resulting optimised top dose plan was referred to as the BDF-based plan. This workflow is depicted in Fig. 1. To generate a DCS-based plan, the isodose of 67.2 Gy (105% of the PTV64 prescription dose) and the 45-Gy isodose in the PRV spinal cord in the original plan were converted into dose-controlling structures, and a cold-spot dose-controlling structure was generated from the PTV64 minus the prescription isodose volume (PIV). Then, the dose-controlling structures for hot and cold spots were assigned new dose objectives. Typically, for the PTV64, the upper dose objective was set to 2% lower than the prescribed dose for the PTV64 hot spots, and the lower dose objective was set to 2% higher than the prescribed dose for the cold spots. The upper dose objective was set to 40–45 Gy for the hot spots of the PRV spinal cord. After one-time re-optimisation and final dose calculation, the DCS-based plan was complete. A distributed calculation framework (DCF) was applied to accelerate the final dose calculation. The one-time re-optimisation time was defined as the time from the beginning of re-optimisation to the completion of the final dose calculation.

Bottom Line: The BDF-based plans provided significantly superior dose homogeneity and conformity compared with both the DCS-based and Original plans.The BDF-based method further reduced the doses delivered to the OARs by approximately 1-3%.All verification tests were passed and no significant differences were found.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiation Oncology, Cancer Hospital of Shantou University Medical College, Shantou, China.

ABSTRACT

Purpose: To assess the performance of a simple optimisation method for improving target coverage and organ-at-risk (OAR) sparing in intensity-modulated radiotherapy (IMRT) for cervical oesophageal cancer.

Methods: For 20 selected patients, clinically acceptable original IMRT plans (Original plans) were created, and two optimisation methods were adopted to improve the plans: 1) a base dose function (BDF)-based method, in which the treatment plans were re-optimised based on the original plans, and 2) a dose-controlling structure (DCS)-based method, in which the original plans were re-optimised by assigning additional constraints for hot and cold spots. The Original, BDF-based and DCS-based plans were compared with regard to target dose homogeneity, conformity, OAR sparing, planning time and monitor units (MUs). Dosimetric verifications were performed and delivery times were recorded for the BDF-based and DCS-based plans.

Results: The BDF-based plans provided significantly superior dose homogeneity and conformity compared with both the DCS-based and Original plans. The BDF-based method further reduced the doses delivered to the OARs by approximately 1-3%. The re-optimisation time was reduced by approximately 28%, but the MUs and delivery time were slightly increased. All verification tests were passed and no significant differences were found.

Conclusion: The BDF-based method for the optimisation of IMRT for cervical oesophageal cancer can achieve significantly better dose distributions with better planning efficiency at the expense of slightly more MUs.

No MeSH data available.


Related in: MedlinePlus