38PD - CT characteristics allow the identification of patient-specific and regional susceptibility for radiation-induced lung damage

Date 16 April 2015
Event ELCC 2015
Session Medical and radiation oncology
Topics Complications of Treatment
Lung and other Thoracic Tumours
Surgery and/or Radiotherapy of Cancer
Presenter Gilles Defraene
Citation Annals of Oncology (2015) 26 (suppl_1): 10-14. 10.1093/annonc/mdv045
Authors G. Defraene1, W. van Elmpt2, W. Crijns1, P. Slagmolen3, D. De Ruysscher1
  • 1Radiation Oncology, University Hospital Leuven/ KU Leuven, 3000 - Leuven/BE
  • 2Radiation Oncology, Maastricht University Medical Centre (MUMC)-MAASTRO clinic, Maastricht/NL
  • 3Electrical Engineering (esat/psi), KU Leuven, 3000 - Leuven/BE

Abstract

Aim/Background

There is a huge difference in radiosensitivity of lungs between patients. The present study aims to identify and quantify patient-specific and regional radiosensitivity based on a single pre-treatment CT scan.

Methods

110 lung cancer patients were studied: 40 stereotactic ablative radiotherapy (SABR) treatments (stage I) and 70 conventional treatments (stage I-IV, 30 from an external dataset). A 3 month-follow-up scan (CT3M) was non-rigidly registered to the planning CT0. Lung volumes, segmented per 5 Gy dose bin, were analysed for their median change in Hounsfield Units (ΔHU = HU3M-HU0). Linear and sigmoidal fits were made for ΔHU versus local 2 Gy equivalent dose. Sigmoidal parameters ΔHUmax (saturation level) and D50 (dose corresponding to 50% of ΔHUmax) were collected. Factors found prognostic for patient-specific dose response were tested within one lung by defining two subvolumes with a presumed sensitivity difference. Dose redistribution plans avoiding high sensitivity subvolumes, while maintaining all original planning constraints, were generated.

Results

Sigmoidal dose response fits outperformed linear fits in all datasets. Distributions of D50 and ΔHUmax reflect a large variation in radiosensitivity (see Table, in per cent of patients). No prognostic factors were found for D50, while a higher baseline (CT0) lung density (p = 0.003) was prognostic for higher ΔHUmax in the SABR group. The difference in ΔHUmax between selected subvolumes was larger than 15 HU in 50% of patients. Redistribution plans could on average decrease the mean dose of high sensitivity subvolumes with 6.6 Gy.

D50 (Gy) 10-20 20-30 30-40 40-50 50-60 >60 Unknown (no effect)
CONV1 10.3 20.7 13.8 6.9 3.4 10.3 31.0
CONV2 10.0 25.0 25.0 5.0 10.0 10.0 15.0
SABR 2.8 19.4 13.9 19.4 8.3 8.3 27.8
ΔHUmax (HU) 10-20 20-30 30-40 40-50 50-60 > 60 Unknown (no effect)
CONV1 13.8 13.8 13.8 13.8 0 13.8 31.0
CONV2 10.0 35.0 15.0 5.0 10.0 10.0 15.0
SABR 25.0 11.1 8.3 11.1 2.8 13.9 27.8

Conclusions

Baseline CT characteristics allow the identification of patient-specific and regional differences in sensitivity for radiation-induced lung damage. This may be used for further treatment individualisation. This project has received funding from the European Union's Seventh Framework Programme under grant agreement no 601826' (REQUITE).

Disclosure

All authors have declared no conflicts of interest.