Introduction: Conventional radiotherapy (RT) based on photons has achieved its physical limits. Proton beam offers promising dosimetric benefits compared to photons, due to its potential to decrease unintended healthy tissue irradiation. Mediastinal proton RT can be safely provided with the awareness of targeting to a moving structure. The technological progress in proton RT allows solving this issue. It can be reasonably managed via pencil beam scanning technique with repainting and/or the use of deep inspiration breath hold method. We present our preliminary clinical experience with this technique. Methods: Between May 2013 and June 2016, 39 patients (pts) with Hodgkin lymphoma (HL) underwent mediastinal proton RT. Pencil beam scanning technique was used in all pts. Overall 33 of 39 pts were evaluable for acute toxicity and early response. Proton RT was indicated in the first-line treatment in 30 pts, 3 pts were re-irradiated after previous photon RT. Median age at the time of RT was 32 years (range, 13-59 years). RT volume definition: involved field 9 pts, residual disease 10 pts, involved site 14 pts. RT to PET negative disease was indicated in 23 pts as a part of combined modality of treatment after chemotherapy. RT to PET positive disease after chemotherapy was performed in 10 pts. Median total dose was 30 GyE (range, 19.8-40 GyE). Overall 17 pts underwent RT in deep inspiration breath hold, the rest of pts received RT in free breathing after 4D control of mediastinal structures movement. Results: Of evaluable pts, 31 are in complete remission. Two pts with multiple sites of progression achieved a local control of disease. Acute and subacute RT toxicity was mild (pharyngeal mucositis gr. 2 in 3 pts, leukopenia gr.3 in 1 pt, leukopenia gr 2 in 1 pt, radiodermatitis gr.2 in 1 pt). No case of radiation pneumonitis or Lhermitte sign was observed. No pt required growth factor application or hemosubstitution during RT. Conclusion: Proton RT offers promising and safe option for most pts indicated for mediastinal RT. Proton irradiation has low acute toxicity profile and a potential to decrease the risk of significant late toxicity. Proton RT should be considered in all HL patients indicated for mediastinal RT or re-irradiation.
This work was supported by grant awarded by AZV 16-29857A, Ministry of Health in Czech Republic and Research project P 27/2012 awarded by Charles University in Prague, 3rd Faculty of Medicine, Prague, Czech Republic