Is proton treatment better than radiation therapy for anal cancer?

Intensity modulated proton therapy (IMPT) leads to a reduction in bone marrow doses but not to a lower haematologic toxicity when compared to intensity modulated radiation therapy (IMRT) in patients with anal cancer, reveals a recent study.

A team of investigators compared patients enrolled in a prospective feasibility trial assessing the use of IMPT for anal cancer with contemporaneous patients treated with IMRT. They obtained blood counts during chemoradiation and graded haematologic events using the Common Terminology Criteria for Adverse Events version 5.0.

Pelvic bone marrow (PBM) and positron emission tomography-defined active bone marrow (ABM) were defined and contoured for each patient. The investigators then compared toxicity rates, PBM, and ABM dose metrics between groups.

Forty-one patients who underwent definitive chemoradiation for anal cancer between 2015 and 2021 were analysed. Of these, 14 were treated with IMPT and 27 with IMRT.

Patients in the IMPT group had lower PBM dose metrics. They also had significantly lower ABM mean dose when compared with patients receiving IMRT (1,996 vs 3,073 Gy; p<0.01).

However, no statistically significant between-group difference was noted in haematologic toxicity. More patients in the IMPT group experienced at least one grade ≥3 haematologic event than did those in the IMRT group (86 percent vs 70 percent; p=0.48).