Sacrum D30% >38.8Gy3 predicts for insufficiency fracture following pelvic chemo-radiotherapy
PH-0653
Abstract
Sacrum D30% >38.8Gy3 predicts for insufficiency fracture following pelvic chemo-radiotherapy
Authors: Mir|, Romaana(1)*[romaana.mir@nhs.net];Dragan|, Alina(2);Tsang|, Yat(1);Padhani|, Anwar(2);Hoskin|, Peter(1);
(1)Mount Vernon Cancer Centre, Clinical Oncology, Middlesex, United Kingdom;(2)Paul Strickland Scanner Centre, Radiology Department, Middlesex, United Kingdom;
Show Affiliations
Hide Affiliations
Purpose or Objective
Sacral insufficiency fracture (IF) following pelvic concurrent chemo-radiotherapy (cCRT) is a known late toxicity, with incidence between 10 – 89%. Age >50 years, female sex, and osteoporosis are established risk factors. Radiotherapy delivery techniques are advancing, the impact of contemporary techniques and variations in patient anatomy on the development of IF are poorly understood. This study evaluates the impact of fixed field intensity modulated radiotherapy (FF-IMRT), non-adaptive arc (Non-AA), and adaptive arc (AA) treatment delivery on the probability of sacral IF.
Material and Methods
Patients who received radical or adjuvant pelvic cCRT (45–50.2Gy/25–27#) at a single center between 2014-2019 for gynaecological malignancy with or without simultaneous integrated boost (SIB) (60Gy) to positive lymph nodes and high-dose rate brachytherapy were identified. The sacrum was manually contoured on the radiotherapy planning CT along with the site of IF as identified by an experienced radiologist on the routine 3, 12, and 24-month follow-up T1-weighted MRI and STIR sequence. Sacral slope and sacral volume (cc) were recorded. IF were graded for severity on predefined MRI criteria.Dosimetric data (maximum, minimum, mean, D10%–100%, V15Gy–V60Gy) for sacrum and IF were converted to an equivalent dose in 2-Gy fractions (EQD2) using a α/β of 3for bone.Demographic, anatomical, and dosimetric data were analysed for correlation with IF.
Results
115 patients were identified. The median imaging follow-up period was 12.0 months (range 3-47 months). The median age was 54 years (range 21-86 years); 50 patients (43.8%) were pre-menopausal. 57 (49.6%) had an SIB to 60Gy; in 14 instances the SIB planning target volume (PTV) abutted the sacrum, in 10 instances the SIB PTV overlapped the sacral contour. Overall 43 (37.4%) had sacral IF on imaging, with a median of 2 IF per patient (range 1-3); 19/36 (52.8%) with FF-IMRT, 6/26 (23.1%) with Non-AA, and 18/53 (34.0%) with AA. The absolute minimum and maximum radiotherapy dose to contoured IF sites were 28.9Gy (range 11.5-46.3Gy), and 44.1Gy (range 30.2-67.0Gy). On Univariate analysis, age ≤50 years, post-menopause, sacrum V40Gy >37.2%, and sacrum D30% >38.8Gy3 were predictors for sacral IF (table).
Multi-variate analysis demonstrated age ≤50 years HR 0.3 (95% CI 0.15-0.64 p=0.02) and sacrum D30% >38.8Gy3 HR 2.22 (95% CI 1.19-4.14 p=0.01) as independent factors in the development of sacral IF. Sacral volume (p=0.54), sacral slope (p=0.17), radiotherapy delivery technique (p=0.86), and SIB (p=0.84) were not associated with development of sacral IF.
Conclusion
Sacrum D30% >38.8Gy3 along with age >50 years are independent predictors for sacral IF following radical or adjuvant pelvic cCRT for gynaecological cancer. Anatomical variations, radiotherapy delivery technique, and SIB did not impact on the development of IF.