Clinical dose-volume histogram analysis in predicting radiation pneumonitis in Hodgkin’s lymphoma

Purpose: To quantify the incidence of radiation pneumonitis (RP) in a modern Hodgkin’s lymphoma (HL) cohort, and to identify any clinically relevant parameters that may influence the risk of RP.

Methods and Materials: Between January 2003 and February 2005, 64 consecutive HL patients aged 18 years or older receiving radical mediastinal radiation therapy (RT) were retrospectively reviewed. Symptomatic cases of radiation pneumonitis were identified. Dose–volume histogram parameters, including V13, V20, V30, and mean lung dose (MLD), were quantified.

Results: At a median follow-up of 2.1 years, the actuarial survival for all patients was 91% at 3 years. There were 2 (2/64) cases of Radiation Therapy Oncology Group (RTOG) Grade 2 RP (incidence 3.1%). Both index cases with corresponding V20 values of 47.0% and 40.7% were located in the upper quartile (2/16 cases), defined by a V20 value of ≥36%, an incidence of 12.5% (p = 0.03). Similarly for total MLD, both index cases with values of 17.6 Gy and 16.4 Gy, respectively, were located in the upper quartile defined by MLD ≥14.2 Gy, an incidence of 11.8% (2/17 cases, p = 0.02).

Conclusions: Despite relatively high V20 values in this study of HL patients, the incidence of RP was only 3%, lower compared with the lung cancer literature. We suggest the following clinically relevant parameters be considered in treatment plan assessment: a V20 greater than 36% and an MLD greater than 14 Gy, over and above which the risk of RTOG Grade 2 or greater RP would be considered clinically significant.
 

The ability to predict and quantify the risk of radiation pneumonitis (RP) has clear benefits both in reducing normal tissue complications, as well as maximizing tumor control probability. To our knowledge no prior studies have focused specifically on the incidence of, and predictive factors for, radiation pneumonitis in Hodgkin’s lymphoma (HL). The majority of predictive measures have been extrapolated from the lung cancer setting, where the incidence of clinically symptomatic cases is estimated to range from 13–37%

Although a variety of specific volumetric predictors, including V13 and V30, have been reported, the V20 (the volume of lung receiving greater than 20 Gy) and total mean lung dose (MLD) remain the most widely accepted and currently applied metrics in the clinical practice and management of lung cancer. Graham reviewed 99 patients with non–small-cell lung cancer (NSCLC) treated radically with three-dimensional conformal radiotherapy and reported that the V20, as well as the MLD, were significantly correlated with RTOG Grade 2 or greater pneumonitis. Despite the use of comparably lower radiation doses in a typically younger patient population in HL, pulmonary toxicity remains an important issue in the management of supradiaphragmatic disease. Furthermore, the relative importance of the contributing factors to RP for HL are likely different from that of lung cancer patients.

The objectives of this study were to firstly quantify the incidence of RP in a modern Hodgkin’s lymphoma cohort, and secondly to identify clinically relevant parameters that may influence the risk of radiation pneumonitis.