Proton-based radiotherapy for unresectable or incompletely resected osteosarcoma.

Background: A study was undertaken to assess clinical outcome and the role of proton therapy for local control of osteosarcoma (OSA).

Methods: All patients who received proton therapy or mixed photon-proton radiotherapy from 1983 to 2009 at the Massachusetts General Hospital were reviewed. Criteria for proton therapy were the need for high dose in the context of highly conformal radiotherapy of unresected or partially resected OSA, positive postoperative margins, postoperative imaging studies with macroscopic disease, or incomplete resection as defined by the surgeon. The primary endpoint was local control of the site treated; secondary endpoints were disease-free survival (DFS), overall survival (OS), long-term toxicity, and prognostic factors associated with clinical outcome.

Results: Fifty-five patients with a median age of 29 years (range, 2-76 years) were offered proton therapy. The mean dose was 68.4 gray (Gy; standard deviation, 5.4 Gy). Of the total dose, 58.2% (range, 11%-100%) was delivered with protons. Local control after 3 and 5 years was 82% and 72%, respectively. The distant failure rate was 26% after 3 and 5 years. The 5-year DFS was 65%, and the 5-year OS was 67%. The extent of surgical resection did not correlate with outcome. Risk factors for local failure were ≥ 2 grade disease (P < .0001) and total treatment length (P = .008). Grade 3 to 4 late toxicity was seen in 30.1 % of patients. One patient died from treatment-associated acute lymphocytic leukemia, and 1 from secondary carcinoma of the maxilla.

Conclusions: Proton therapy to deliver high radiotherapy doses allows locally curative treatment for some patients with unresectable or incompletely resected OSA.