Radiation Therapy Planning for Early Stage Hodgkin Lymphoma: Experiences of the International Lymphoma Radiation Oncology Group

Abstract

Early stage Hodgkin lymphoma (HL) is a rare disease and the location of lymphoma varies extensively between patients. This represents a clinical challenge as the quality of radiation therapy (RT) is partly dependent upon the patient volumes and the experience of the treating center. In this study, we evaluate the variability of RT plans by 4 International Lymphoma Radiation Oncology Group (ILROG) centers by field technique, planning parameters and estimated doses to organs at risk (OARs). Nine patients with stage I-II classical HL with masses of different size and location were selected. Based on the clinical information, 4 ILROG centers were asked to fashion RT plans to a prescribed dose of 30.6 Gy in 1.8-2 Gy fractions. A post-chemotherapy CT-scan with a clinical target volume (CTV) adapted from the pre-chemotherapy FDG-PET-CT scan as well as pre-contoured OARs was provided for each patient. The treatment technique and planning methods were chosen according to each center's best practice in 2013. Two patients were stage I, 5 presented with mediastinal disease, and 3 with disease in the neck only. Four patients were male, median age at diagnosis was 35 years (range: 22-74 years). The median CTV was 85.8 cm3 (range: 19.3-462.9 cm3). Of the resulting 36 RT plans, 15 were planned with 3D conformal RT (2 parallel-opposed/angled fields or 3 fields), 15 with IMRT (4-9 fields), 5 with VMAT, and 1 with 3D conformal RT/IMRT. The variations in CTV-to-planning target volume (PTV) margins (1-1.5 cm), field arrangements, maximum tolerated dose, and plan conformity (conformity index = V98%/PTV) were substantial. Five plans did not adhere to current ILROG guidelines. Estimated doses to OARs were comparable between centers. Dose estimates and plan parameters are presented in Table 1. RT planning for HL is challenging due to the heterogeneity in size and location of disease and, additionally, the variation in choice of treatment technique and field arrangements. Despite of the variation between 4 ILROG centers, there was an acceptable and comparable dose to the critical OARs. Adopting ILROG guidelines and implementing universal dose objectives could further standardize treatment techniques and contribute to lower the dose to the surrounding normal tissues.Oral Scientific Abstract 337; Table 1Dose Estimates and Plan Parameters for 9 HL Patients Planned by 4 ILROG CentersCenter 1Center 2Center 3Center 4median (range)median (range)median (range)median (range)Heart mean dose [Gy)1.0 (0-11.6)0.5 (0-9.8)1.2 (0-14.9)0.8 (0-10)Lung mean dose [Gy]6.5 (0-13.9)4.9 (0-11.4)6.5 (0-15.2)6.2 (0-13.5)Breast mean dose [Gy]0.3 (0-8.3)0.3 (0-7.5)0.3 (0-9.2)0.4 (0-8.9)Thyroid mean dose [Gy]14.0 (0.4-28.5)12.3 (0.2-30.4)17.4 (0.5-31.7)14.9 (0.3-31.8)PTV [cm3]500.2 (65.6-1668.4)388.8 (94-1504.6)799.7 (127.9-3056.8)468.4 (94.7-1864.4)Dmax [Gy]32.7 (30.8-34.1)35.4 (30.6-38.6)33.6 (32.8-35)32.8 (32.2-35.2)V30 Gy [cm3]272.3 (8.8-1778.9)427.5 (0.1-1511.3)1224.5 (108.2-5524)450.9 (82.4-2250)Conformity index1.0 (0.1-2.3)1.5 (0-2.3)1.8 (0.8-2.1)0.9 (0.8-1.3) Open table in a new tab