2Dokuz Eylül University, Department of Radiation Oncology (DEUDRO), Izmir, Turkey
3AstraZeneca, Alderley Park, UK OBJECTIVES
To evaluate set-up errors using Electronic Portal Imaging (EPI) for Three Dimensional Conformal Radiotherapy (3D CRT) protocol for head and neck carcinoma in Dokuz Eylül University Department of Radiation Oncology (DEUDRO).
METHODS
Ten patients between July 2004 - September 2005 were included.
Seven EPIs/5 weeks per patient were planned to
evaluate by two independent observers. Differences between
Digitally Reconstructed Radiography (DRR) images and EPIs
measured in cranio-caudal (CC), anterior-posterior (AP) and
medio-lateral (ML) directions. Random (σ) and the systematic
(Σ) errors were calculated and used in van Herk margin formula
(2.5 x Σ + 0.7 x σ) for PTV margin.
RESULTS
Ninety three EPIs with 186 [93 (50%) CC, 78 (42%) AP and
15 (8%) ML] measurements were evaluated. The σ were AP:
2.6 mm, CC: 2.9 mm, ML: 1 mm. The Σ AP: 3.9 mm, CC: 1.8
mm, ML: 1.9 mm. PTV margins calculated were AP: 11.7 mm,
CC: 6.6 mm, ML: 5.8 mm.
CONCLUSION
3DCRT protocol for head and neck cancer was amended using
these PTV margins. These maybe wide especially for IMRT,
and can reduce with better immobilization systems.