International Journal of Radiation Oncology*Biology*Physics
Clinical InvestigationAdding Ipsilateral V20 and V30 to Conventional Dosimetric Constraints Predicts Radiation Pneumonitis in Stage IIIA–B NSCLC Treated With Combined-Modality Therapy
Introduction
In the overall treatment strategy for non–small-cell lung cancer (NSCLC) patients, the pulmonary toxicity is an important limiting factor. Several authors have previously explored the role of dosimetric predictive factors, such as the percentage of total lung volume exceeding a defined dose (Vdose) and mean lung dose (MLD), to plan for an optimized strategy to reduce radiation pneumonitis (RP) and/or escalate radiation dose. Among these, Graham et al.(1) and Hernando et al.(2) have correlated the value of percentage of lung volume exceeding 20 Gy (V20), percentage of lung volume exceeding 30 Gy (V30), and MLD stratifying the risk of RP developing.
Their data have been widely used by the community and have improved the way in which curative radiation doses are delivered. This applies, as well, in patients receiving concurrent chemoradiation (3).
Nevertheless, the role of concurrent chemotherapy to radiation in treating locally advanced NSCLC has been gaining substantial value in the recent years, and this has encouraged some authors to review their data and report the RP rate in patients receiving a multimodality treatment (4).
Paradoxically, the Vdose and MLD referring to both lungs as a single functional unit do not take into account the possible chances of an imbalance among the doses to the lung with the primary tumor and the contralateral lung; substantially, the final value of each dosimetric parameter is just a mean value for the total lung parenchyma. So, an extreme case could be characterized by no dose to the contralateral lung by concentrating the radiation beams on one lung.
The focus of this trial is to assess the relevance of ipsilateral dosimetric parameters on RP. We report the results of our experience in patients treated with concurrent chemoradiotherapy for NSCLC obtained by analyzing the value of adding ipsilateral V20 (V20ipsi), ipsilateral V30 (V30ipsi), and ipsilateral MLD (MLDipsi) to total lung volume constraints.
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Methods and Materials
Between June 2002 and December 2006, after Institutional Review Board approval, 97 consecutive patients with locally advanced NSCLC underwent concomitant radiochemotherapy indicated and applied with radical or neoadjuvant (inductive) intent.
The patients' characteristics, tumor stage, and radiation dose delivered are shown in Table 1. Minimum follow-up was 6 months.
In all patients a history was obtained and physical examination and staging studies were performed. These included chest, upper
Results
After a median follow-up period of 29 months (range, 6–45 months), 14 of the 97 patients had RP of Grade 2 or higher, yielding a mean rate of 14.4% (Table 2). In the group of surgically resected patients, the incidence was 8.7% (4 of 46), whereas in the nonresected patients, it was 19.6% (10 of 51) (p = 0.15).
For the entire cohort, the lung injury arose after a median period of 79 days from the beginning of radiotherapy; in the surgical and nonsurgical groups, the median time was 123 and 55
Discussion
A review of published studies shows that the ideal dose–volume histogram metric for the prediction of the risk of RP has not yet been identified (14). However, it has been established with certainty that adding chemotherapy to radiation therapy will cause a rise in toxicity rate (4).
In the study of Graham et al.(1) half of the patients were treated with radiotherapy and half with radiochemotherapy. The incidence of pneumonitis was up to 20% at 24 months but just 7% if the V20 value was 31% or
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Conflict of interest: none.