Intensity-modulated radiotherapy does not induce volumetric changes of the Bichat fat pad in nasopharyngeal cancer.

Abstract

To evaluate morphological and functional changes in the Bichat fat pad (BFP) after curative concurrent chemoradiotherapy in nasopharyngeal cancer (NPC) patients. We retrospectively analyzed the volumetric, metabolic, and dosimetry parameters of BFPs in 7NPC patients who underwent intensity-modulated radiotherapy (IMRT) between 2015 and 2020. Inclusion criteria were i)histologically confirmed diagnosis of NPC, ii)follow-up period of at least 12months, iii)no history of previous irradiation or surgery in the maxillofacial area, and ìv)availability of pre- and posttreatment MRI and 18F‑FDGPET-CT performed in our Institution. All patients had stageIII-IVA disease (n = 7) and received platinum-based chemotherapy. Planned doses in 30daily fractions/5days per week were 66 Gy (2.2 Gy/die 5days/week) to the gross tumor volume, 66 Gy (2.1-2.2 Gy/die 5days/week) to the gross nodal volume, 60 Gy (2 Gy/die 5days week) to clinical target volume (CTV)1, and 54 Gy (1.8 Gy/die 5days/week) to CTV2. All patients completed the planned radiotherapy course in amedian time of 42days (range 42-43). Relationships between BFP volumes and the following DVH parameters were evaluated: mean dose, maximum dose (Dmax), and percentage of BFP volume receiving more than 5to 65 Gy (V5to V65). The pre-RT volumes of the left and right BFPs were 12.24cc (range 6.51-20.01cc) and 11.55cc (range 5.78-17.53cc), respectively. The mean volumes of left BFPPRE and BFPPOST were 12.24cc (range6.51-20.01cc) and 13.85cc (range7.54-20.21 cc), respectively, with no significant statistical differences (P > 0.05). No statistically significant correlations were found between dosimetry features and BFP volumetric changes (all P > 0.05). Our original results showed that chemoradiotherapy does not induce significant volumetric changes of the BFP. Further investigations are needed to evaluate the effects of higher radiation doses on BFP. This is the first real-world study on this issue.