Integrated multicriterial optimization of beam angles and intensity profiles for coplanar and noncoplanar head and neck IMRT and implications for VMAT.
OBJECTIVE
To quantify improved salivary gland sparing for head and neck cancer patients using intensity-modulated radiotherapy (IMRT) plans based on integrated computerized optimization of beam orientations and intensity profiles. To assess if optimized nonzero couch angles also improve VMAT plans.


METHODS
Our in-house developed algorithm iCycle was used for automated generation of multicriterial optimized plans with optimized beam orientations and intensity profiles, and plans with optimized profiles for preselected beam arrangements. For 20 patients, five IMRT plans, based on one "wish-list," were compared: (i) and (ii) seven- and nine-beam equiangular coplanar plans (iCycle(7equi), iCycle(9equi)), (iii) and (iv) nine-beam plans with optimized coplanar and noncoplanar beam orientations (iCycle(copl), iCycle(noncopl)), and (v) a nine-beam coplanar plan with optimized gantry angles and one optimized couch rotation (iCycle(couch)). VMAT plans without and with this optimized couch rotation were evaluated.


RESULTS
iCycle(noncopl) resulted in the best salivary gland sparing, while iCycle(couch) yielded similar results for 18 patients. For iCycle(7equi), submandibular gland NTCP values were on average 5% higher. iCycle(9equi) performed better than iCycle(7equi). iCycle(copl) showed further improvement. Application of the optimized couch angle from iCycle(couch) also improved NTCP values in VMAT plans.


CONCLUSIONS
iCycle allows objective comparison of competing planning strategies. Integrated optimization of beam profiles and angles can significantly improve normal tissue sparing, yielding optimal results for iCycle(noncopl).
Erasmus MC-Daniel den Hoed Cancer Center, Department of Radiation Oncology, Groene Hilledijk 301, 3075EA Rotterdam, The Netherlands. p.voet@erasmusmc.nl
Peter W J
PW
Voet
Sebastiaan
S
Breedveld
Maarten L P
ML
Dirkx
Peter C
PC
Levendag
Ben J M
BJ
Heijmen
D000465:Algorithms; D001331:Automation; D006258:Head and Neck Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D006801:Humans; D010306:Parotid Gland / Q000528:radiation effects; D011336:Probability; D011878:Radiotherapy / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012469:Salivary Glands / Q000473:pathology; D013363:Submandibular Gland / Q000528:radiation effects; D013997:Time Factors