Irradiating Residual Disease to 30 Gy with Proton Therapy in Pediatric Mediastinal Hodgkin Lymphoma

BACKGROUND: Local relapse is a predominant form of recurrence among pediatric patients with Hodgkin lymphoma (PHL). Although PHL radiotherapy doses have been approximately 20 Gy, adults with Hodgkin lymphoma receiving 30 to 36 Gy experience fewer in-field relapses. We investigated the dosimetric effect of such a dose escalation to the organs at risk (OARs). MATERIALS AND METHODS: Ten patients with PHL treated with proton therapy to 21 Gy involved-site radiation therapy (ISRT(21Gy)) were replanned to deliver 30 Gy by treating the ISRT to 30 Gy (ISRT(30Gy)), delivering 21 Gy to the ISRT plus a 9-Gy boost to postchemotherapy residual volume (rISRT(boost)), and delivering 30 Gy to the residual ISRT target only (rISRT(30Gy)). Radiation doses to the OARs were compared. RESULTS: The ISRT(30Gy) escalated the dose to the target by 42% but also to the OARs. The rISRT(boost) escalated the residual target dose by 42%, and the OAR dose by only 17% to 26%. The rISRT(30Gy) escalated the residual target dose by 42% but reduced the OAR dose by 25% to 46%. CONCLUSION: Boosting the postchemotherapy residual target dose to 30Gy can allow for dose escalation with a slight OAR dose increase. Treating the residual disease for the full 30Gy, however, would reduce the OAR dose significantly compared with ISRT(21Gy). Studies should evaluate these strategies to improve outcomes and minimize the late effects.