Intensity-modulated radiotherapy improves target coverage, spinal cord sparing and allows dose escalation in patients with locally advanced cancer of the larynx

Abstract

Background and purpose: An investigation has been carried out into the potential of intensity-modulated radiotherapy (IMRT) to improve the coverage of the targets and the sparing of the spinal cord (SC) in radiotherapy treatment of the larynx and bilateral cervical lymph nodes, in patients with advanced larynx cancer.

Patients and methods: Conventional radiotherapy (CRT) and IMRT plans were produced for six patients to treat the larynx (PTV1) and lymph nodes (PTV2) to 50 Gy (phase 1). A second plan was created to treat the PTV1 to 65 Gy and PTV2 to 50 Gy (phases 1 and 2). The potential to escalate the dose to both the larynx (to 67 Gy) and the nodes (to 56 Gy) was investigated for the IMRT plans.

Results: The phase 1 treatment gave average minimum doses (dose received by 99% volume) of 38.1 (+/-8.2) and 48.5 (+/-0.2)Gy for PTV1, treated by CRT and IMRT, respectively, and 35.9 (+/-2.9) and 46.2 (+/-1.8)Gy for PTV2. For the two phase treatment the average minimum doses to PTV1 were 51.6 (+/-8.2) (CRT) and 62.1 (+/-0.7)Gy (IMRT) (p=0.028) and for PTV2 were 36.2 (+/-2.9) (CRT) and 46.8 (+/-0.5)Gy (IMRT) (P=0.0004). The average maximum doses (dose received by 1% volume) to the SC were 42.5 (+/-1.9) (CRT) and 37.9 (+/-1.4)Gy (IMRT) (P=0.01). For the dose escalated IMRT plans the minimum dose to PTV1 was 64.6 (+/-0.5) and 50.8 (+/-1.8)Gy to PTV2. The average SC maximum was 41.5 (+/-1.6)Gy.

Conclusions: IMRT offers improved target homogeneity and reduces irradiation of the SC. This sparing of normal tissue structures is sufficient that significant dose escalation of both the larynx and lymph nodes may be possible.