1064 - Beyond Involved-Site Radiotherapy: NRG, COG, Alliance, ECOG-ACRIN, SWOG and CCTG Consensus Nomenclature for Radiation Targets on NCTN Lymphoma Trials

O. Saifi¹, C. C. Pinnix², L. K. Ballas³, C. R. Kelsey⁴, S. A. Milgrom⁵, S. A. Terezakis⁶, N. B. Figura⁷, R. R. Parikh⁸, J. C. Grecula⁹, J. P. Plastaras¹⁰, D. Hodgson¹¹, and B. S. Hoppe¹; ¹Department of Radiation Oncology, Mayo Clinic, Jacksonville, FL, ²Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, ³Department of Radiation Oncology, Cedars-Sinai Medical Center, Los Angeles, CA, ⁴Duke University Medical Center, Department of Radiation Oncology, Durham, NC, ⁵University of Colorado, Department of Radiation Oncology, Aurora, CO, ⁶University of Minnesota: Department of Radiation Oncology, Minneapolis, MN, ⁷H. Lee Moffitt Cancer Center and Research Institute, Department of Radiation Oncology, Tampa, FL, ⁸Department of Radiation Oncology, Rutgers Cancer Institute of New Jersey, New Brunswick, NJ, ⁹Department of Radiation Oncology, James Cancer Hospital, The Ohio State University, Columbus, OH, ¹⁰Department of Radiation Oncology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, ¹¹Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada

Purpose/Objective(s): Contemporary cooperative group lymphoma trials have developed smaller radiation (RT) fields based on interim (i) or end-of-systemic therapy (EST) PET scans. These fields are used as a “boost” following standard-of-care involved site RT (ISRT) or to replace ISRT entirely. These fields lack standardized nomenclature, complicating comparison of RT approaches across studies. Materials/

Methods: The NRG hematologic working group convened a forum of radiation oncology lymphoma leaders from the National Clinical Trials Network (NCTN) groups (NRG Oncology, COG, SWOG, Alliance for Clinical Trials in Oncology (Alliance), ECOG-ACRIN, CCTG). The forum’s objective was to establish standardized nomenclature for contemporary lymphoma RT target volumes. This nomenclature was developed through a comprehensive review of RT volumes utilized in 6 NCTN group lymphoma protocols after 2012 that included non-standard ISRT fields. A classification was developed based on the different fields described in the protocols and nomenclature was chosen to represent the fields.

Results: Analysis of the protocols (Table) revealed 5 non-mutually exclusive RT volumes, defined by our group as: ISRT, residual site radiotherapy (RSRT), and 3 PET-directed radiotherapy (PD-RT) types. ISRT considers post-chemo anatomic changes in the axial dimension only, and generally includes the full cranial-caudal extent of pre-chemo disease. RSRT targets only the post-chemo CT-anatomical mass, regardless of its PET avidity and irrespective of pre-chemo disease extent. ISRT and RSRT are independent of EST PET imaging. Conversely, PD-RT is only feasible with EST PET or iPET, and exclusively targets PET-positive disease. The 3 PD-RT types include: PET-directed involved site radiotherapy (pISRT), PET-directed residual site radiotherapy (pRSRT), and PET-directed residual PET radiotherapy (pRPRT). The pISRT target volume includes and follows the superior-inferior aspect of the pre-chemo involved disease site(s) that remain(s) PET-avid on post-treatment imaging. pRSRT target volume includes only the post-systemic therapy CT-anatomical residual mass that contains the PET-avid lesion on EST +/- iPET imaging, without including sites that achieved complete metabolic response. pRPRT target volume includes only the PET-avid focus, irrespective of the corresponding adjacent non-PET-avid CT-anatomical disease surrounding it. Detailed target delineation and concept illustrations will be presented at the meeting.

Conclusion: NRG Oncology, COG, SWOG, Alliance, ECOG-ACRIN, and CCTG propose a consensus nomenclature for contemporary RT target volumes to be used on lymphoma protocols. Recommendations for using these target volumes are beyond the scope of this work and require comparative studies and/or in-depth analysis of patterns of relapse.

Study	RT Indications	RT Type
		ISRT	pISRT	pRSRT	pRPRT
AHOD 1331	Prechemo LMA	X
	SER / PR		X		X
S1826	PR			X	X
ANHL 1931	RCHOP	X		X
	PR
AHOD 2131	SER / PR	X		X
AHOD 1822	ABVD	X		X
	PR
AHOD 1721	R1 cohort	X