ESTRO 37 Abstract book

ESTRO 37

S603

Results

Purpose or Objective To create an Auto-Planning (A-P) VMAT technique for irradiation of head and neck tumors, that generates conformal and homogeneous treatment plans, with adequate coverage of the target volume and optimal sparing of the organs at risk (OARs), as good as but preferably superior to operator-driven VMAT treatment plans. Secondary aim was to reduce planning-hands-on- time. Material and Methods Ten H&N-cancer patients treated with VMAT were selected for dosimetric comparison with an A-P VMAT technique. All patients underwent a CT-scan with 3 mm slice thickness. The following organs at risk were contoured: parotid glands, submandibular glands, larynx, oral cavity, mandible, esophageal inlet, pharynx constrictor, spinal canal and brainstem. CTV’s were delineated based on EORTC 1219 H&N study protocol. A margin of 3 mm was used to generate the PTV. Treatment plans were created in the Pinnacle 3 treatment planning system V.9.10 using 2 full-arc 6 MV photon beams. A SIB technique was used to deliver 50.3 Gy to the elective and 68 Gy to the boost volume in 34 fractions, 5 times a week. For the new technique the A-P module in Pinnacle was used. Table 1 shows the set-up parameters of this new technique. Treatment was delivered on an Elekta linac with Agility collimator. PTV coverage and dose to the OARs were analyzed to compare the planning techniques. Results As can be seen in figure 1 and table 2, the A-P VMAT technique reduces the spinal canal and brainstem maximum dose and the mean dose to the other OARs. The A-P VMAT technique saves at least 50% planning- hands-on-time (up to 2 hours). Conclusion We developed an Auto-Planning VMAT technique for irradiation of head and neck tumors, which creates treatment plans with adequate PTV coverage and comparable or lower dose to the OARs relative to the currently used VMAT technique while planning-hands-on- time is significantly reduced.

The statistical results showed no significance in all the parameters of PTV and OARs, except for V20 of whole lung. Relatively DJ2.5 and DJ5.0 had the best and the worst dosimetric quality respectively in term of dose- volume specifications of PTV and OARs among 3 modes. Larynx and liver, sited superior and inferior to PTV, were the only OARs giving a relatively lower dose in DJ5.0 than FJ2.5. For other OARs, including heart and lung, FJ2.5 showed a better OARs sparing than DJ5.0. Radiobiologically, NTCP of heart and lung for all plans were close to 0, while those of DJ2.5 were calculated to be the lowest. The delivery time and actual MF were found to have statistical significance. The average delivery time of DJ5.0 was significantly lower than DJ2.5 and FJ2.5 by almost 40%. The actual MF was significantly higher in FJ2.5 than DJ2.5.

Conclusion No statistical significance was found in those dosimetric and radiobiological parameters among 3 modes while the delivery time has greatly reduced by using DJ5.0. A shorter treatment time can minimize intra-fractional error and better the patient’s experience during treatment. Therefore, DJ5.0 is suggested to be the optimization mode in HT for left-breast cancer patient with SCF nodal involvement. PO-1072 Head & Neck VMAT Auto-Planning in Pinnacle. A class solution. P.G.M. Van Kollenburg 1 , L.C.W. Bouwmans 1 , J.M.A.M. Kusters 1 , E.J.L. Brunenberg 1 , M.C. Kunze-Busch 1 , T. Dijkema 1 , J.H.A.M. Kaanders 1 1 UMC St Radboud Nijmegen, Dept. of radiation oncology 874, Nijmegen, The Netherlands