Impact of radiopacified bone cement on radiotherapy dose calculation.

BACKGROUND AND PURPOSE: Radiopacifiers are introduced to bone cements to provide the appearance of bone in kilovoltage (kV) radiographic images. For higher energy megavoltage (MV) radiotherapy treatment beams, however, these radiopacifiers do not cause a bone-like perturbation of dose. This study therefore aimed to determine the impact of the barium-contrasted plastic-based cement materials on radiotherapy dose calculations. MATERIALS AND METHODS: The radiological properties of a physical sample of bone cement were characterised by computed tomography (CT) imaging and transmission measurements. Monte Carlo simulations of percentage depth-dose profiles were performed to determine the possible dose error for MV treatment beams. Dose differences were then investigated for clinical volumetric modulated radiotherapy treatment plans, with and without density overrides applied. RESULTS: Differences of up to 7% were observed at the downstream interface of a 0.6 cm thick bone cement layer, compared to bone. Differences in planning target volume dose-volume metrics varied between -0.5% and 2.0%. CONCLUSION: Before planning radiotherapy treatments for patients who have undergone cranioplasty, every effort should be made to identify whether a radiopacified bone cement has been implanted. Density overrides should be applied to minimise dose calculation errors, whenever bone cement is used.

Non-small cell lung cancer brain metastasis screening in the era of positron emission tomography-CT staging: Current practice and outcomes.

INTRODUCTION: Several clinical guidelines indicate that brain metastasis screening (BMS) should be guided by disease stage in non-small cell lung cancer (NSCLC). We estimate that screening is performed more broadly in practice, and patients undergo brain imaging at considerable cost with questionable benefit. Our aim was to quantify the use and detection rate of BMS in a contemporary cohort staged with 18 F-fluorodeoxyglucose positron emission tomography/computed tomography (PET-CT). METHODS: We conducted a retrospective review of prospectively collected data from three major lung cancer referral centres in Brisbane between January 2011 and December 2015. Patients included had a new diagnosis of NSCLC and had undergone a PET-CT to stage extra-cranial disease. BMS was defined as dedicated brain imaging with contrast-enhanced computed tomography (CE-CT) or magnetic resonance (MR), in the absence of clinically apparent neurological deficits. RESULTS: A total of 1751 eligible cases were identified and of these 718 (41%) underwent BMS. The majority had CE-CT imaging (n = 703). Asymptomatic brain metastases (BM) were detected in 18 patients (2.5%). Of these patients, 12 had concurrent non-brain metastases. Only six patients (0.8%) had BM alone. The rate of detection increased with N-stage (P = 0.02) and overall stage (P < 0.001). It was 0.5%, 1%, 1.6% and 7.3% for stage I, II, III and IV respectively. The overall screening rate increased with T-stage (P = 0.001), N-Stage (P < 0.001) and overall stage (P < 0.001). CONCLUSIONS: Non-small cell lung cancer BMS practices remain at odds with published guidelines. The low number of occult BMs detected supports the existing international recommendations. Rationalising BMS would minimise the burden on patients and the health care system.

A retrospective analysis of survival outcomes for two different radiotherapy fractionation schedules given in the same overall time for limited stage small cell lung cancer.

PURPOSE: To compare survival outcomes for two fractionation schedules of thoracic radiotherapy, both given over 3 weeks, in patients with limited stage small cell lung cancer (LS-SCLC). METHODS AND MATERIALS: At Radiation Oncology Mater Centre (ROMC) and the Royal Brisbane & Women's Hospital (RBWH), patients with LS-SCLC treated with curative intent are given radiotherapy (with concurrent chemotherapy) to a dose of either 40 Gy in 15 fractions ('the 40 Gy/15# group') or 45 Gy in 30 fractions ('the 45 Gy/30# group'). The choice largely depends on institutional preference. Both these schedules are given over 3 weeks, using daily and twice-daily fractionation respectively. The records of all such patients treated from January 2000 to July 2009 were retrospectively reviewed and survival outcomes between the two groups compared. RESULTS: Of 118 eligible patients, there were 38 patients in the 40 Gy/15# group and 41 patients in the 45 Gy/30# group. The median relapse-free survival time was 12 months in both groups. Median overall survival was 21 months (95% CI 2-37 months) in the 40 Gy/15# group and 26 months (95% CI 1-48 months) in the 45 Gy/30# group. The 5-year overall survival rates were 20% and 25%, respectively (P = 0.24). On multivariate analysis, factors influencing overall survival were: whether prophylactic cranial irradiation (PCI) was given (P = 0.01) and whether salvage chemotherapy was given at the time of relapse (P = 0.057). CONCLUSIONS: Given the small sample size, the potential for selection bias and the retrospective nature of our study it is not possible to draw firm conclusions regarding the efficacy of hypofractionated thoracic radiotherapy compared with hyperfractionated accelerated thoracic radiotherapy however hypofractionated radiotherapy may result in equivalent relapse-free survival.