Predictors of Hypothyroidism in Hodgkin Lymphoma Survivors after Intensity-Modulated versus 3-Dimensional Radiation Therapy

Publication date: Available online 14 March 2018
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Chelsea C. Pinnix, Laura Cella, Therese Y. Andraos, Zeina Ayoub, Sarah A. Milgrom, Jillian Gunther, Sonali Thosani, Christine Wogan, Manuel Conson, Vittoria D'Avino, Yasuhiro Oki, Michelle Fanale, Hun J. Lee, Sattva Neelapu, Luis Fayad, Frederick Hagemeister, M. Alma Rodriguez, Loretta J. Nastoupil, Yago Nieto, Wei Qiao, Roberto Pacelli, Bouthaina Dabaja
PurposeTo identify predictors of hypothyroidism after chemoradiation for Hodgkin lymphoma (HL) and to compare outcomes after intensity-modulated radiation therapy RT (IMRT) with those after 3-dimensional conformal RT (3D-CRT).Patients and MethodsNinety patients given involved-site IMRT in 2009–2014 were evaluated for treatment-induced hypothyroidism, defined as elevated thyroid-stimulating hormone (TSH) or decreased free thyroxine (fT4) levels or both. Receiver operating characteristic curve analysis identified individuals at low vs. high risk based on dosimetric variables. Dosimetric cutoff points were verified with an external dataset of 50 patients given 3D-CRT.ResultsMost patients given IMRT (75 [83%]) had stage II HL and the median prescribed dose was 30.6 Gy; in the 3D-CRT group 32 (64%) had stage II HL and the median prescribed dose was 32.0 Gy. No differences were found in proportions of patients with bilateral (P=0.982) or unilateral neck involvement (P=0.074) between either group. Hypothyroidism rates were marginally higher in the IMRT group, with estimated 3-year rates of freedom from hypothyroidism of 56.1% for the 3D-CRT group and 40% for the IMRT group (P=0.057). Univariate analysis showed that smaller thyroid volume and higher thyroid dose were associated with hypothyroidism in both groups (P<0.05). In the IMRT group, V25 and the absolute volume of thyroid spared from 25 Gy (VS25Gy) were the strongest predictors of hypothyroidism (P=0.001 and P<0.001). Cutoff points of 63.5% (V25) and 2.2 mL (VS25Gy) classified patients as high-risk (80%-82%) or low-risk (37%-44%) (P<0.001). Use of a thyroid avoidance structure reduced the incidence of hypothyroidism (P<0.05) in the IMRT group.ConclusionsThe percentage of thyroid receiving 25 Gy and the volume of thyroid spared from 25 Gy predicted risk of hypothyroidism after either IMRT or 3D-CRT for HL. IMRT may confer a higher risk than 3D-CRT unless a treatment avoidance structure is used during planning.

Teaser

In this comprehensive evaluation of risk factors associated with hypothyroidism after IMRT and involved-site RT for HL, identified variables included thyroid V25 and V30 and both absolute thyroid volume (cut point 11.2 mL) and volume spared from ≥25 Gy (≥2.2 mL). We further recommend contouring the thyroid and using thyroid avoidance structures in treatment planning when they do not compromise target coverage.


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