SU‐E‐T‐866: IMRT Dose Optimization in the Limit of Large Number of Incident Beams

H. Kim, L. Zhu, T. Kim, L. Xing

Research output: Contribution to journalArticlepeer-review


Purpose: Recently proposed algorithm with total‐variation regularization greatly contributes to simplifying fluence‐map in IMRT inverse planning. In practice, however, there exist several cases where fluence‐map cannot be simplified as PTV may be complicated and critical structures are close to PTV, requiring high dose conformality. To overcome these difficulties, this study proposes increasing the number of beams so that it could achieve improvement in the quality of planning with similar or smaller number of beam segments. Methods: High number of beams is arranged at the uniform angular distance. For optimizing a fluence‐map, a new L1‐solver, TFOCS, was used due to many benefits for IMRT optimization. As a criterion to assess the dose conformality of PTV, conformation number (CN) was adopted for all cases with different number of beams. Other factors any other than beam number, such as the way of determining weighting factors and the prescribed residues on PTV and OAR, should be determined in the same way for fair comparisons. To validate the method, head and neck patient data having a complicated and large target volume is used for 7, 15 and 30 beamsResults: The result shows that the increase in the number of beams results in higher conformation number. In terms of the required number of segments, 7 beams requires the most, while 15 beams and 30 beams need less number of segments to be deliverable. The planning with 30 beams turns out to be somewhat better protection for healthy tissue nearby PTV than that with 15 beams. Significantly, higher number of beams is also beneficial from reducing the beamlet intensity required for treatment. Conclusions: Increasing the number of beams in IMRT inverse planning based upon total‐variation can offer better quality of planning, represented by CN, with similar or less number of beam segments.

Original languageEnglish
Pages (from-to)3691
Number of pages1
JournalMedical physics
Issue number6
StatePublished - Jun 2011


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