The following is a summary of “Impact of dosimetric compromises on early outcomes of chordomas and chondrosarcomas treated with Image-guided pencil beam scanning proton beam therapy,” published in the July 2024 issue of Oncology by Chilukuri et al.

This study critically examines the clinical factors, dosimetry, and their correlation with early outcomes in patients with chordomas and chondrosarcomas treated with pencil beam scanning proton beam therapy (PBS-PBT).

Researchers analyzed data from 64 consecutive patients diagnosed with chordoma or chondrosarcoma treated at the center. They recorded patient, tumor, and treatment-related factors, including dosimetry. Early and late toxicities and early outcomes were evaluated and correlated with clinical and dosimetric factors using standard statistical tools.

The median age of the patients was 39 years (range: 4-74 years). The most common tumor site was the skull base (47%), followed by the sacrum (31%) and mobile spine (22%). The median prescription dose for the high-risk CTV was 70.4 CGE (Cobalt Gray Equivalent) for chordomas and 66 CGE at 2.2 CGE per fraction for chondrosarcomas. At the time of presentation to the center, 55% of the patients had recurrence/progression, with 17% having received prior radiation and 32% experiencing significant neural compression. At the time of PBS-PBT, 25% of patients had suboptimal neural separation. Three-fourths of patients had at least acceptable target coverage. However, 11% experienced a tier-1 compromise (GTV D98 < 90%), and 14% had a tier-2 compromise (GTVD9328<59 CGE).

With a median follow-up of 27.5 months, the 2-year local control and progression-free survival (PFS) rates were 86.7% and 81.8% for chordomas, and 87.5% and 77.1% for chondrosarcomas, respectively. On multivariate analysis, a residual GTV > 25 cc and a tier-2 dosimetric compromise were associated with inferior local control (HR = 0.19, p = 0.019; HR = 0.061, p = 0.022, respectively) and PFS (HR = 0.128, p = 0.014; HR = 0.194, p = 0.025, respectively). Despite multiple surgeries, a majority of recurrent diseases, and prior radiation treatments, grade-3 acute and late toxicities were limited and comparable to existing literature.

Achieving adequate neural separation remains challenging despite multiple surgeries. Severe dosimetric compromise (GTVD98<59CGE) led to inferior early outcomes. Ensuring sufficient neural separation is crucial to avoid dosimetric compromise and achieve optimal local control.

Source: sciencedirect.com/science/article/pii/S2452109424001453