Abstract P088

Individualizing Consolidative Radiotherapy in Intermediate-Stage Hodgkin Lymphoma: A PET-Residual Re-Planning Analysis of Patients from the GHSG HD17 Trial

Background: In intermediate-stage Hodgkin lymphoma, consolidative radiotherapy (RT) is increasingly challenged by chemotherapy-only strategies. In the GHSG HD17 trial, patients with PET-positive residuals after chemotherapy received involved-node radiotherapy (INRT) with 30 Gy. However, further limitation of RT field to focal RT to PET+ residuals has not been tested, yet. We therefore performed an exploratory post-hoc re-planning analysis comparing standard INRT with focal PET-residual RT.

Methods: Overall, 21 patients (16 female, 5 male) from the GHSG HD17 trial were evaluated. For each patient, the original INRT plan was compared with a focal PET-based re-plan using the PET/CT after four cycles of chemotherapy (2x eBEACOPP followed by 2x ABVD). Focal target volumes included PET-positive residual sites with a small anatomy-adapted margin of approximately 0.8–1.2 cm. Dose-volume histogram endpoints were assessed for target volume and organs at risk, including heart, lungs, esophagus, thyroid, spinal canal, liver and, where applicable, female breast. Paired comparisons used a two-sided Wilcoxon signed-rank test. Relapse patterns were reviewed in relation to the original and focal fields.

Results: Focal PET-based re-planning reduced mean PTV from 1194.0 cm3 to 87.0 cm3, corresponding to a 92.7% reduction (p<0.001). Organ-at-risk exposure was significantly reduced, including mean heart dose from 9.6 Gy to 1.5 Gy, esophageal dose from 20.9 Gy to 4.0 Gy, thyroid dose from 22.7 Gy to 2.9 Gy, spinal canal maximum dose from 29.1 Gy to 11.3 Gy, and mean total lung dose from 9.4 Gy to 2.3 Gy (all p<0.001). Total lung V20 decreased from 46.1% to 11.2% (p<0.001). In female patients, total breast mean dose decreased from 4.1 Gy to 0.6 Gy (p=0.016). Two patients later relapsed: one in-field relapse two months after therapy completion, which would have been covered by the focal PTV, and one abdominal relapse outside the thoracic irradiation field after one year.

Conclusion: In patients from the GHSG HD17 trial, focal PET-based radiotherapy re-planning reduced target volume by 90% and relevant organ-at-risk dose. There was no recurrence adjacent to the involved regions which would have been covered by INRT but missed by focal RT-only. PET-residual fields therefore merit prospective evaluation as a potential RT de-escalation strategy, with mature relapse-pattern data required before clinical implementation.