72P - Occurrence of significant tumor volume changes during stereotactic body radiation therapy for lung cancer

Date 17 April 2015
Event ELCC 2015
Session Poster lunch
Topics Non-Small-Cell Lung Cancer, Early Stage
Surgery and/or Radiotherapy of Cancer
Presenter Florian Charlier
Citation Annals of Oncology (2015) 26 (suppl_1): 18-23. 10.1093/annonc/mdv048
Authors F. Charlier, L. Moretti, Y. Jourani, T. de Brouwer, P. Van Houtte
  • Radiation Oncology, Institute Jules Bordet, 1000 - Brussels/BE

Abstract

Aim/Background

This study aimed to evaluate the importance of interfraction variations in tumor volume during stereotactic body radiotherapy (SBRT) for stage I lung cancer patients.

Methods

Forty seven consecutive patients undergoing SBRT were analyzed (group 1: n = 35, 48 Gy in 4 fractions; group 2: n = 12, 60 Gy in 8 fractions). Cone-Beam Computed Tomography (CBCT) imaging was taken for registration at each treatment fraction. Each tumor volume was delineated on a total of 236 CBCTs by one young physician, and was then reviewed by an experienced radiation oncologist. Statistical analysis was performed using TANAGRA software. To compare differences between independent samples, the Mann-Whitney U test or t-test were used for non-normal continuous variables and the χ2 test for proportions within each SBRT group. Wilcoxon test was also used to assess changes in volume and tumor localization. All significance tests were two-tailed and p < 0.05 was considered significant.

Results

Median treatment times were 8 and 19.5 days for 4 and 8 fractions SBRT groups, respectively. Unexpectedly, tumor volume was significantly bigger at the 2nd fraction (p = 0.003 for group 1 and p = 0.049 for group 2) compared to the 1st CBCT. Volume changes were not significantly different at the 3rd fraction compared to initial volume (p = 0.60 for group 1 and p = 0.209 for group 2). In group 1, tumor volume significantly decreases at the 4th fraction compared to the 2nd (p = 0.047). In group 2, the significant decrease in volume occurs at the 6th fraction (p = 0.026). There was no association between the overall treatment time and tumor volume variations. Taken individually (n = 47) 83% of tumors have at least one occurrence of a greater than 15% volume change during SBRT compared to the 1st CBCT. Variations of more than 20%, 30% and even 40% were observed in ∼60%, 40%, and 17% of treatments, respectively. No factor that would predict a significant volume change during SBRT for the patients analyzed could be identified.

Conclusions

Tumor volume changes were larger and more frequent than initially expected for patients undergoing lung SBRT. Whether these results impact treatment and/or patient outcome remains to be investigated in prospective clinical trials.

Disclosure

All authors have declared no conflicts of interest.