Proton Therapy Reirradiation Safe, Effective for Recurrent Thoracic Tumors

The use of reirradiation with intensity-modulated proton therapy (IMPT) yielded strong overall survival with limited toxicity in patients with thoracic tumors, according to a new study, potentially offering a new option in this patient population.

“Local recurrences and local failures are a challenge in lung cancer, and they are common problems,” said Jennifer Ho, MD, of MD Anderson Cancer Center in Houston, during a press briefing at the 2017 Multidisciplinary Thoracic Cancers Symposium in San Francisco. “Historically, patients have not had a lot of treatment options.”

IMPT can target tumors very precisely, and deposit the entire radiation dose inside a tumor with no exit dose, potentially lowering the risk of toxicity to surrounding healthy tissue. Ho presented results of a retrospective study of 27 patients with thoracic tumors who underwent reirradiation with this method between 2011 and 2016 at MD Anderson; 81% of the patients had non–small-cell lung cancer (NSCLC), 81% had centrally located tumors, and they were treated with IMPT a median of 29.5 months after initial radiation therapy. The study’s median follow-up period was 11.2 months.

The median overall survival was 18 months, and the 1-year overall survival rate was 54%. The median progression-free survival was 19.3 months, with a 1-year progression-free survival rate of 51%. The median duration of freedom from local failure was not yet reached, with a 1-year rate of 78%; the same was true of the median duration of freedom from locoregional recurrence, with a 1-year rate of 61%.

Importantly, Ho said there was minimal serious toxicity seen in the study, with no grade 4 or 5 adverse events. There were two grade 3 pulmonary adverse events (7%), and one of fatigue (4%); all other adverse events, including esophagitis, dermatitis, pain, and hemoptysis, were of grade 1 or 2. Other studies of reirradiation have found serious toxicity rates as high as 30%.

Patients who received a reirradiation dose of 66 Gy or higher had better outcomes than those who received a lower dose. The 1-year freedom from local failure was 100% above that threshold and 49% below it (P = .013); a similar result was seen with freedom from locoregional recurrence. For progression-free survival, the 1-year rate above 66 Gy was 76%, compared with 14% below that dose (P = .050). The 1-year overall survival rate was also higher, at 62% vs 46%, respectively, but this did not reach significance (P = .289).

“We conclude that IMPT is an excellent choice for reirradiation,” Ho said. “It’s safe and effective, and it could be particularly useful when giving radiation to more challenging tumors located in complex locations.”

Pranshu Mohindra, MD, of the University of Maryland in Baltimore, moderated the news briefing, and he noted that 60 Gy is the current standard dose for primary radiation of locally advanced NSCLC. “To be able to deliver more than 60 Gy with such high safety is impressive,” he said, adding that at the moment, only a handful of centers around the country are capable of delivering this type of radiation therapy.

Still, he said that these “findings offer hope for patients with the challenging and often incurable diagnosis of recurrent lung cancer.”