Proton Quad Shot RT for Palliation in Patients With Advanced Sarcoma

Abstract

The safety and feasibility of proton quad shot radiation therapy (QS-RT) for patients with sarcoma has not been established. We examine a single institution experience of this treatment approach. Patients treated with proton RT are prospectively registered to an institutional database. We examined advanced sarcoma patients who had QS-RT for progressive lesions beginning 9/2014. Systemic therapy, toxicity and outcome data were obtained by chart review. Twenty-two sarcoma patients were planned for proton QS-RT between 9/2014 and 1/2017. Histology included gastrointestinal stromal tumor (GIST; n=6), leiomyosarcoma (5), spindle cell sarcoma (3), chondrosarcoma (2), synovial sarcoma (2), and liposarcoma, solitary fibrous tumor, uterine sarcoma and follicular dendritic cell sarcoma (1). Most patients (14/22) had target lesions in the abdomen/pelvis while others had lung (6), heart (1), liver (1), or head/neck lesions (1). One patient had treatment to two sites. QS-RT was a median of 3 cycles delivered every 3-4 weeks (range 1-4; cycle = 14.8 CGE in 4 fractions over 2 days). GIST patients had median 5 prior systemic therapies (range 3-6) and 3/6 received concurrent therapy with RT (imatinib, sunitinib and imatinib/sirolimus). The patient on imatinib/sirolimus had TKI held for one week for grade 2 diarrhea. The patient on sunitinib had grade 3 intratumoral bleed, and was changed to imatinib with no further toxicity. Patients with other histologies had median of 5 lines of therapy (range = 2-8). Two chondrosarcoma patients had concurrent pazopanib, while patients with spindle cell sarcoma received concurrent nivolumab (n=2) and pazopanib (n=1) without complication. Censored median survival is 5.9 months in patients who have completed QS-RT (n=13) with 5/13 living at the time of analysis. Of these, 3/5 continue on systemic therapy (range = 1-4 lines), one has stable disease on no systemic therapy, and one has local disease progression. In the set of 7 patients who completed 4 cycles of QS-RT, we found 4 local failures with a median time to failure of 5.2 months (range 2.2 – 8.7 months), and 2 died of disease at 2.2 and 5.8 months after RT. In the remaining patients that completed fewer than 4 cycles, we found 2 local failures at 0.5 and 4.2 months and 6 died of disease at median time of 0.4 months (range 0.5 – 7.0 months). Proton QS-RT appears to be a feasible treatment option for local treatment of sarcoma lesions, allowing for continued systemic treatment in a subset of patients. Patients well enough to complete 4 cycles of QS-RT may benefit from local control, but further prospective analysis will evaluate durability of long-term control, and whether early intervention with QS-RT improves outcome or eligibility for continued systemic therapy.