Abstract Book

ESTRO 37

S603

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.

Table 2: Dose results of both techniques, and dose difference (A-P VMAT minus VMAT). N=10.

A-P VMAT

Objective VMAT

Difference

Structure

1 PTV 5030 cGy D95%

98.1% 97.2% - 0.9%

2 PTV 6800 cGy D95%

98.4% 98.7% +0.3%

41.2 Gy 28.8 Gy 19.2 Gy 23.7 Gy 39.5 Gy 48.4 Gy 46.6 Gy 21.4 Gy 47.6 Gy 31.2 Gy

36.7 Gy 21.5 Gy 17.7 Gy 21.8 Gy 36.5 Gy 43.4 Gy 45.1 Gy 21.1 Gy 47.1 Gy 27.3 Gy

3 Spinal Canal

Max Dose

-4.5 Gy

4 Brainstem

Max Dose

-7.3 Gy

Mean Dose Mean Dose Mean Dose Mean Dose Mean Dose Mean Dose Mean Dose Mean Dose

Parotid Gland Left Parotid Gland Right Submandibular Gland Left Submandibular Gland Right

-1.5 Gy

5

-1.9 Gy

6

7

-3.0 Gy

8

-5.0 Gy

9 Larynx

-1.4 Gy

-0.3 Gy

10 Oral Cavity

Pharynx Constrictor

-0.5 Gy

11

12 Esophagus

-3.9 Gy

PO-1073 The effect of PTV margin reduction on out- of-field doses in paediatric radiotherapy of brain tumours E. Lagoni Juhl 1 , A.M.J. Dam 2 , A.R. Beierholm 3 , D.E. Nygaard 4 , J. Hansen 5 1 Copenhagen University Hospital, Department of Oncology, Copenhagen, Denmark 2 Herlev Hospital, Department of Oncology, Herlev, Denmark 3 Danish Health Agency, Radiation Protection, Herlev, Denmark 4 Metropolitan University College, Bachelor’s Degree Programme in Radiography, Copenhagen, Denmark 5 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark Purpose or Objective Radiotherapy techniques such as volumetric-modulated arc therapy (VMAT) and image-guided radiotherapy (IGRT) has increased treatment delivery precision, making it possible to apply smaller margins to reduce doses to healthy tissues. The purpose of this study was to evaluate the effect of PTV margin reduction on the dose to out-of-field organs, for radiotherapy of paediatric brain cancer. Radiotherapy of the brain is associated with a minimal extent of involuntary organ motion. Furthermore, paediatric brain cancer patients generally have a long expected lifetime after radiotherapy, therefore any risk of radiotherapy-induced secondary cancer needs to be carefully evaluated and minimized, if possible. Material and Methods Thermoluminescence dosimeters (TLD-700) were used to measure out-of-field doses to the thyroid, mamma and testes of two CIRS ATOM anthropomorphic phantoms resembling a 1-year and 10–year old child. Coplanar