Dosimetric Risk Estimation of Chest Wall Pain Following 5-Fraction Lung Stereotactic Body Radiotherapy

Abstract

Development of chest wall pain (CWP) following lung stereotactic body radiotherapy (SBRT) is a known toxicity, particularly for peripheral lesions. While CW V30 has been most consistently associated with development of post-SBRT CWP, existing series included heterogeneous dose-fractionation regimens, most commonly 48-54 Gy in 3-4 fractions. The present study aims to identify clinical and dosimetric variables associated with development of CWP among patients treated with 5 fraction lung SBRT. Intradepartmental quality assurance database of SBRT patients was queried to identify lung targets treated to a minimum of 45 Gy in 5 fractions. Retrospective chart and plan reviews were performed on these cases to collect patient, tumor, and treatment-related data, selecting for patients with peripheral lesions (any histology), and recording presence or absence of CWP during or following SBRT. Patients with less than 6 months of post-SBRT clinical follow-up were excluded. The CW was defined as a 2 cm expansion of the ipsilateral lung (inclusive of intercostal musculature, ribs, and superficial soft tissue). Logistic regression analyses were performed on continuous and nominal data to determine statistically significant (p<0.05) correlations between clinical (age, gender, known osteopenia/osteoporosis, diabetes, prior thoracic radiotherapy, lesion distance to CW), treatment (interval of SBRT delivery, dose prescribed), and dosimetric (Dose to 0.1/1/5/10cc; V30, V40) factors with CWP. Between February 2011 and January 2022, 93 patients were identified for inclusion in the present analysis, treated to 100 total lesions in 99 courses of treatment. Median patient age was 75 years (range 34-90), 48 (52%) were female, and 29 (of 99 treatment courses; 29%) had received prior thoracic radiotherapy. Median SBRT dose was 50 Gy (45-60), delivered over a median of 9 days (4-18). At a median post-SBRT follow-up of 21 months, 11 patients developed CWP at a median of 9 months post-SBRT (0-32). Statistically significant correlations were identified between CWP and known pre-existing osteopenia or osteoporosis, target distance to CW, and CW D0.1cc, D1cc, D5cc, and D10cc, but not CW V30 or V40. Crude risk of CWP for selected clinically practical dose-volume thresholds are presented in Table 1: CONCLUSION: For patients treated with lung SBRT in 5 fractions, dose to CW volume thresholds appears to correlate more closely than V30 or V40 for CWP estimation. Further investigation and validation of optimal CW volume thresholds, as well as integration of pre-existing condition clinical factors in risk estimation, appears warranted.