Proton therapy for adults with mediastinal lymphomas: the International Lymphoma Radiation Oncology Group guidelines

Abstract

Among adult lymphoma survivors, radiation treatment techniques that increase the excess radiation dose to organs at risk (OARs) put patients at risk for increased side effects, especially late toxicities. Minimizing radiation to OARs in adults patients with Hodgkin and non-Hodgkin lymphomas involving the mediastinum is the deciding factor for the choice of treatment modality. Proton therapy may help to reduce the radiation dose to the OARs and reduce toxicities, especially the risks for cardiac morbidity and second cancers. Because proton therapy may have some disadvantages, identifying the patients and the circumstances that may benefit the most from proton therapy is important. We present modern guidelines to identify adult lymphoma patients who may derive the greatest benefit from proton therapy, along with an analysis of the advantages and disadvantages of proton treatment.

Figure 1.

Robustness analysis based on DVHs showing multiple scenarios representative of different uncertainties and their resulting effect on the dose distribution for a specific organ at risk or target.

Figure 2.

Three scenarios of the relation between mediastinal disease and the heart. (A) Showing how to use the takeoff of the left main stem coronary artery (outlined in pink) to determine the upper and lower mediastinal locations. (B) Scenario 1: coronal CT images of a 28-year-old man with primary mediastinal lymphoma before (i) and after (ii) 6 cycles of rituximab, cyclophosphamide, doxorubicin, vincristine, prednisone (RCHOP) chemotherapy presenting for consolidation with radiation. (Biii) Axial, coronal, and sagittal views of an IMRT plan (upper panels) and a proton plan (lower panels). (Biv) Corresponding mean doses to critical structures using IMRT vs protons. (C) Scenario 2: coronal CT images of a 25-year-old man with Hodgkin lymphoma before (i) and after (ii) 4 cycles of doxorubicin, bleomycin, vinblastine, and dacarbazine (ABVD) chemotherapy presenting for consolidation with radiation. (Ciii) Axial, coronal, and sagittal views of an IMRT plan (upper panels) and a proton plan (lower panels). (Civ) Corresponding mean doses to critical structures using IMRT vs protons. (D) Scenario 3: coronal CT images of a 30-year-old man with recurrent Hodgkin lymphoma as shown in the coronal images of a PET/CT scan (i-ii) presenting for definitive radiation. (Diii) Axial, coronal, and sagittal views of an IMRT plan (upper panels) and a proton plan (lower panels). (Div) Corresponding mean doses to critical structures using IMRT vs protons.

Figure 3.

Axillary involvement at presentation. (A) Axial, coronal, and sagittal views of a proton plan (left) and an IMRT plan (right) for a patient presenting with axillary involvement. Use of proton therapy in this case spares the left breast. (B) Regardless of which treatment modality is chosen, IMRT (left panel) and proton (right panel), limiting the volume exposed to radiation should include attention to avoiding a low-dose bath. (C) Limiting lung dose. If avoiding the lung is the primary objective in a given patient, especially if the patient has received pulmonary toxic chemotherapy (eg, any combination of bleomycin, busulfan, gemcitabine, brentuximab, etc.), proton therapy may better spare the lungs by reducing the low-dose bath seen with photons.

Figure 4.

An example of an approach using 2 anterior fields with proton therapy, which can better spare the heart and esophagus (right) compared with an anterior/posterior approach (left).

Figure 5.

Plans for PBSPT with a single-field uniform dose and a gradient match, with anterior and posterior beams used to treat disease that involves the bilateral upper neck and the mediastinum (disease anterior to the right heart).

Figure 6.

Scans for a young woman in whom the target included mediastinal, left parasternal, and left axillary regions. One anterior field was used for the mediastinum, and a separate posterior field was used for the axillary region.

Figure 7.

Use of DIBH can help to manage some of the uncertainties associated with the use of proton therapy. Compared with free breathing (right panel), DIBH expands the lungs, moves the heart downward, and causes the mediastinum to become thinner (left panel).