Room: Exhibit Hall
Purpose: To compare measured and planned surface dose from helical tomotherapy treatment planning in head and neck case using ultrathin TLDs-100.
Methods: Head and neck anthropomorphic phantom with hypothetical PTVs and normal tissues were planned using Tomotherapy TPS (V 220.127.116.11). The prescribed doses of head and neck plan were 70 Gy and 59.4 Gy in 33 fractions (SIB technique) with spinal cord and parotid sparing. The treatment technique delivered by Tomo-HDTM treatment system (V.2.1.1) with dynamic jaws, field width 2.5 cm, pitch 0.43 and modulation factor 2.5. Ultrathin TLD-100 chips sizes of 3 Î§ 3 Î§ 0.15 mmÂ³ were calibrated with 6 MV photon beams using Varian iX machine for 15Î§15 cmÂ² field size with depth of 1.5cm SAD technique. The TLDs were taped on the phantom surface underneath thermoplastic mask to measure surface dose in 3 locations right side, left side and anterior side of neck respectively. The measurements were repeated 3 times. Mean surface doses were compared to surface doses predicted from treatment planning system on the same measurement areas.
Results: The measured and percent relative surface doses per fraction on the right side, left side and anterior side of phantom were 1.52 Â± 0.02 Gy (71.7 %Â± 0.94% ), 1.47Â±0.06 Gy (69.3% Â± 0.02%) and 1.32 Â± 0.12 Gy (62.26 % Â± 5.6 Gy), Respectively. The planned surface doses on the same areas were 1.69Â±0.08 Gy (79.7% Â±3.8 %), 1.61Â±0.08 Gy (75.9% Â±3.8 %) and 1.43 Â± 0.046 Gy (67.4% Â± 2.2%) respectively.
Conclusion: The surface dose measured by ultrathin TLDs indicated that tomotherapy treatment planning has overestimated surface dose between 5 â€“ 8 %. The skin reaction is a critical part of head and neck treatment. Knowing the efficiency of treatment planning system can reduce the complication effect by applying optimal plan.
TLDs, Tomotherapy, Surface Dose