Evaluation of clinical target volume expansion required for involved site neck radiotherapy for lymphoma to account for the absence of a pre-chemotherapy PET-CT in the radiotherapy treatment position.

BACKGROUND AND PURPOSE

Involved site radiotherapy clinical target volume (CTV) for lymphoma requires an expansion to account for the absence of radiotherapy treatment-position pre-chemotherapy imaging, which is not widely implemented. This prospective imaging study aims to quantify CTV expansion required for neck radiotherapy.

MATERIALS AND METHODS

10 patients from a prospective single centre imaging study underwent a pre-chemotherapy FDG-PET-CT in both the diagnostic and radiotherapy treatment position, and subsequently received neck radiotherapy post-chemotherapy. CTV and CTV were delineated on the planning CT, following co-registration of the radiotherapy position PET-CT and side-by-side assessment of diagnostic PET-CT respectively.

RESULTS

Intra-observer variability was limited, with delineation of CTV highly reproducible and slightly lower for CTV (mean DICE 0.88 and 0.8 respectively). Superiorly, CTV varied by -10 to +15mm from CTV. Inferiorly, CTV varied by -18 to +6mm from CTV. Comparing CTV and CTV in the axial plane, the mean DICE was 0.74. Mean sensitivity index was 0.75 (range 0.59-0.91), showing that on average 75% of the CTV was encompassed by the CTV.

CONCLUSIONS

In the absence of treatment-position PET-CT, CTV expansion cranially and caudally by 10mm and 18mm respectively, along with generous contouring in the axial plane, was required to encompass pre-chemotherapy disease.