CT densimetry for graduating subcutaneous fibrosis after photon/neutron therapy

Background: To evaluate alternative treatment regimen e. g. neutron therapy determination of treatment efficacy as well as side effects is important. Sensitivity of computed tomography (CT) in detecting changes of connective tissue after neutron therapy was examined. Patients and Methods: In the course of their follow-up period (median 45 mo nths) 12 patients with malignant salivary gland tumors who had postoperativ ely received neutron (1/12) or photon/neutron therapy (11/12) were examined by means of CT densimetry on 3 representative scans in the area of radioth erapy. In 3 ROI (regions of interest) in subcutaneous fatty tissue the dens ity at the irradiated and the non-irradiated side was determined according to Hounsfield units (HU) and the average density was calculated. The averag e density of both sides was compared and correlated with the clinical grade of fibrosis according to LENT SOMA. Results: All CT measurements (216 ROI, 18 ROI per patient) showed higher de nsity levels on the irradiated side than on the non-irradiated side. The av erage density on the irradiated side was -57.7 +/- 4.7 HU and on the non-ir radiated side -69.4 +/- 5.8 HU (p = 0.002). In 3/12 patients a clinical fib rosis was not seen; however, the relative density measured on the irradiate d and non-irradiated side deviated by up to 8%. This could have been caused by minimal changes not being noticed by either patient and examiner. In pa tients with determined fibrosis Grade 1 (8/12) the relative density deviati on was 4 to 39%. In 1/12 patients with determined fibrosis Grade 2 the rela tive density deviation was 50% (Figures la and Ib). Fibrosis Grade 3 and 4 did not occur (Table 1). Conclusions: Fibrosis is correlated with an increasing value of HU of the t issue density in CT. With the described method it is possible to graduate r adiation induced subcutaneous fibrosis in correlation to the clinical fibro sis grade according to LENT SOMA. In the patients we examined subcutaneous fibroses after photon/neutron therapy were moderate. Especially in characte rising subclinical or slight changes of connective tissue after radiotherap y computed tomography is of value.