Does 5 + 5 Equal Better Radiation Treatment Plans in Head and Neck Cancers?
Does 5 + 5 Equal Better Radiation Treatment Plans in Head and Neck Cancers?
Blog Article
read more Purpose: Accurate contouring in head and neck cancer (HNC) is critical.International consensus guidelines recommend the 5 + 5 mm rule for expansions around the primary tumor, wherein high- and low-dose clinical target volumes (CTV-P1 and CTV-P2, respectively) are created using successive 5 mm expansions on the gross tumor volume.To our knowledge, the necessity of a low-dose CTV-P2 has never been assessed; therefore, we evaluated the dosimetric impact of adding a CTV-P2 expansion using the 5 + 5 mm rule compared with contouring with a high-dose CTV-P1 alone.
Methods and materials: A retrospective study of clinically delivered (chemo)radiation therapy treatment plans for HNC was conducted.All patients were treated with 70 Gy in 35 fractions using volumetric modulated arc therapy in a single phase.CTV-P2 was retrospectively contoured per guidelines as a 5 mm expansion on CTV-P1 from the clinical plan, carving off specified barriers to spread.
We used a 5 mm planning target volume (PTV) expansion.Our primary outcome was whether 95% of the volume of the PTV for the CTV-P2 contour (ie, PTV-P2) received at least 56 Gy.To assess dose falloff, the coverage of a PTV ring structure was created by subtracting PTV-P1 from PTV-P2.
Results: Twenty-seven patients from 4 HNC subsites (base of tongue, tonsil, hypopharynx, and supraglottic larynx) were included.In all 108 treatment plans, at least 95% of the PTV-P2 structure received at least 56 Gy.The minimum volume of the PTV-P2 structure receiving at least 56 Gy was 97.
4%.Eight of 108 treatment plans had borderline coverage of the PTV ring substructure alone.Conclusions: Adding a CTV-P2 structure using the 5 + 5 mm rule had no dosimetric impact, adds usc trojans snapback hat contouring time, adds treatment planning complexity, and could potentially introduce errors.
The 5 + 5 mm rule may have value in other settings, such as when smaller PTV margins are used, and warrants further evaluation with prospective or randomized studies.