Impact of head and neck intensity modulated radiation therapy on CT numbers of primary and nodal Gross tumour volume

CT number (CTN) for the gross tumour volumes (GTV) can change with radiation therapy which could be an early indicator for radiation response. This study investigates the correlation of radiation induced changes in volume and CTN in GTV of primary and nodal tumour during the course of intensity modulated radiation therapy (IMRT) in head and neck cancers (HNC).

Re-CT scans were acquired at 4 weeks for 71 patients with stage II-IVb HNC treated with chemoradiation. The changes in volumes and CTN of the GTV primary and GTV node at 4 weeks of radiation were observed. Pearsons's correlation were used to assess any correlation between CTN change and volume reduction of the GTVs.

The volumes of the GTV Primary and GTV Node were reduced during the course of the radiation therapy after 4 weeks with mean volume shrinkage of 26.30±7.66(p<0.0001) and 32.09±37.2(p<0.04) respectively and the mean CTN reduced by 2.50±5.4 and 1.79±4.12HU's respectively. The CTN and GTV volume decreases were found to be positively correlated (GTVP >GTV N) though the relationship is weak.

The CTN changes in GTV P and GTV N during delivery of radiation for HNC is measurable and are patient specific. The volume reduction is observed more in GTV N where as CTN reduction is noticed in both GTVs with a reasonable correlation between the mean CTN and volume reductions in GTVs.