Proton Therapy Shows Potential For Hodgkin’s Lymphoma

For patients with Hodgkin’s lymphoma, proton therapy may offer a toxicity-sparing form of radiotherapy

medwireNews: Proton therapy may help reduce the radiation dose required by patients with Hodgkin’s lymphoma (HL) who have completed chemotherapy, US researchers suggest after reviewing findings from patients treated within two registries and a tracked protocol.

“Early results with proton therapy demonstrate excellent relapse-free survival with a favorable acute toxicity profile including very low rates of pneumonitis”, say Bradford Hoppe, from the University of Florida College of Medicine in Jacksonville, USA, and colleagues.

“These results are encouraging and support continued treatment of patients with HL with proton therapy in a registry setting, which permits long-term follow-up and potential confirmation of decreased late toxicity.”

As published in the Annals of Oncology, the team looked at the characteristics and outcomes of 138 HL patients who received consolidative proton therapy between 2008 and 2015, finding the patients to be generally young (median age 20 years, range 6–57 years), with 42% aged 18 years or younger.

The majority of patients had stage I–II disease and 27% had stage III–IV disease; 96% had mediastinal involvement and 57% had bulky disease, with 37% showing B symptoms.

The patients had all completed chemotherapy before being treated with proton therapy, with the paediatric patients given a median dose of 21.0 Gy and the adult patients a median dose of 30.6 Gy.

After a median of 32 months, the 3-year relapse-free survival (RFS) rate was 92% and the rate did not significantly differ between paediatric and adult patients, at 87% versus 96%. Nor did the 3-year RFS rate differ among patients with favourable early-stage, unfavourable early-stage and advanced-stage disease, at 97%, 88% and 92%, respectively, and this remained true when comparing these subgroups by age.

“Although these results are preliminary, they represent excellent 3-year outcomes, especially considering most patients (70%) had unfavorable early-stage or advanced-stage disease”, remark Bradford Hoppe et al.

“Despite the adverse risk factors in our cohort of proton therapy patients (i.e., risk group, [positron emission/computed tomography] PET/CT response, bulky disease, and B symptoms), our results compare favorably to the only three published clinical outcomes studies of IMRT [intensity-modulated radiation therapy] for [HL], which altogether comprise 140 patients treated with IMRT”, they add.

But patients who had achieved a partial response to chemotherapy, as determined by PET/CT, had significantly poorer 3-year RFS than those who had achieved a complete or unknown response, at 78% versus 94%.

Nevertheless, the authors emphasize that of these patients with a partial response, “many remained in remission following proton therapy and avoided salvage regimens and stem cell transplant, and their associated toxicities.”

The investigators say there were no reports of grade 3 toxicity, adding that the absence of grade 2 pneumonitis during follow-up was “surprising” given it has previously been reported in 7% of mediastinal lymphoma patients given IMRT.

“[T]he absence of a low-dose proton bath may mitigate the risk of clinically meaningful pneumonitis,” they suggest. “Overall, the lack of clinically significant toxicity in this proton cohort is encouraging.”

And while acknowledging that their observational study does not report on the impact of proton therapy on late toxicity outcomes, the researchers cite earlier research indicating that proton therapy may also reduce the risk of secondary tumours compared with photon radiation.

Reference

Hoppe BS, Hill-Kayser CE, Tseng YD, et al. Consolidative proton therapy after chemotherapy for patients with Hodgkin lymphoma. Ann Oncol; Advance online publication 13 August 2017. doi: https://doi.org/10.1093/annonc/mdx287

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