Feasibility of dose painting using volumetric modulated arc optimization and delivery.
OBJECTIVE
Dose painting strategies are limited by optimization algorithms in treatment planning systems and physical constraints of the beam delivery. We investigate dose conformity using the RapidArc optimizer and beam delivery technique. Furthermore, robustness of the plans with respect to positioning uncertainties are evaluated.


METHODS
A head & neck cancer patient underwent a [(61)Cu]Cu-ATSM PET/CT-scan. PET-SUVs were converted to prescribed dose with a base dose of 60 Gy, and target mean dose 90 Gy. The voxel-based prescription was converted into 3, 5, 7, 9, and 11 discrete prescription levels. Optimization was performed in Eclipse, varying the following parameters: MLC leaf width (5 mm and 2.5 mm), number of arcs (1 and 2) and collimator rotation (0, 15, 30 and 45 degrees). Dose conformity was evaluated using quality volume histograms (QVHs), and relative volumes receiving within ±5% of prescribed dose (Q(0.95-1.05)). Deliverability was tested using a Delta4(®) phantom. Robustness was tested by shifting the isocenter 1 mm and 2 mm in all directions, and recalculating the dose.


RESULTS
Good conformity was obtained using MLC leaf width 2.5 mm, two arcs, and collimators 45/315 degrees, with Q(0.95-1.05)=92.8%, 91.6%, 89.7% and 84.6%. Using only one arc or increasing the MLC leaf width had a small deteriorating effect of 2-5%. Small changes in collimator angle gave small changes, but large changes in collimator angle gave a larger decrease in plan conformity; for angles of 15 and 0 degrees (two arcs, 2.5 mm leaf width), Q(0.95-1.05) decreased by up to 15%. Consistency between planned and delivered dose was good, with ∼90% of gamma values <1. For 1 mm shift, Q(0.95-1.05) was decreased by 5-15%, while for 2 mm shift, Q(0.95-1.05) was decreased to 55-60%.


CONCLUSIONS
Results demonstrate feasibility of planning of prescription doses with multiple levels for dose painting using RapidArc, and plans were deliverable. Robustness to positional error was low.
Korreman
Stine S
SS
University of Wisconsin School of Medicine and Public Health, Department of Human Oncology, Clinical Sciences Center, Madison, Wisconsin, USA. stine.korreman@rh.regionh.dk
Ulrich
Silke
S
Bowen
Steve
S
Deveau
Michael
M
Bentzen
Søren M
SM
Jeraj
Robert
R
D002138:Calibration; D002294:Carcinoma, Squamous Cell / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D054893:Cone-Beam Computed Tomography / Q000295:instrumentation / Q000379:methods*; D056831:Coordination Complexes; D004307:Dose-Response Relationship, Radiation; D005240:Feasibility Studies; D006801:Humans; D009942:Organometallic Compounds / Q000493:pharmacokinetics; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000295:instrumentation / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods* / Q000592:standards; D013882:Thiosemicarbazones / Q000493:pharmacokinetics; D014062:Tongue Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*
D056831:Coordination Complexes; D009942:Organometallic Compounds; D013882:Thiosemicarbazones; C089548:copper (II) diacetyl-di(N(4)-methylthiosemicarbazone)