Radiotherapy for non-malignant shoulder syndrome: Is there a risk for radiation-induced carcinogenesis?

PURPOSE: To estimate the organ-specific probability for carcinogenesis following radiotherapy for non-malignant shoulder syndrome. METHODS: Photon-beam radiation therapy to 6 Gy for shoulder syndrome was simulated with a Monte Carlo code. An androgynous computational phantom representing a typical adult was used to calculate the radiation dose to out-of-field organs having a predilection for carcinogenesis. The organ-specific lifetime attributable risk (LAR) for out-of-field cancer induction was estimated by the organ dose calculations and the proper risk factors introduced by the BEIR-VII report. The average dose (Dav) and organ equivalent dose (OED) of lung, which was partially included within the treatment volume, was found from 3d-conformal radiotherapy plans. The Dav and OED were used to estimate the lung cancer risk with a linear and mechanistic models, respectively. All risk assessments were made for 50- and 60-year-old male and female patients. RESULTS: Monte Carlo simulations resulted in an out-of-field organ dose range of 0.7-48.4 mGy. The LARs for out-of-field cancer induction were (1.4 × 10-4)% to (2.8 × 10-2)%. These probabilities were at least 403 times lower than the respective lifetime intrinsic risk (LIR) values. The Dav and OED of lung was up to 164.9 and 142.3 mGy, respectively. The LAR for developing lung malignancies varied from 0.11 to 0.18% by the model used and the patient's age and gender. The lung cancer risks were 36-64 times smaller than the LIRs. CONCLUSIONS: The estimated probabilities for developing malignancies due to radiotherapy for non-malignant shoulder syndrome are minor relative to the natural cancer occurrence rates.

Accuracy of multislice CT angiography for the assessment of in-stent restenoses in the iliac arteries at reduced dose: a phantom study.

OBJECTIVE: We investigated the potential of low-dose CT angiography for accurate assessment of in-stent restenoses (ISRs) of the iliac artery. METHOD: A Rando anthropomorphic phantom (Alderson Research Labs, Stanford, CA), custom-made wax simulating hyperplastic tissue and a nitinol stent were used to simulate a patient with clinically relevant iliac artery ISRs. The cylindrical lumen was filled with a solution of iodine contrast medium diluted in saline, representing a patient's blood during CT angiography. The phantom was subjected to standard- and low-dose angiographic exposures using a modern multidetector (MD) CT scanner. The percentage of ISR was determined using the profile along a line normal to the lumen axis on reconstructed images of 2 and 5 mm slice thickness. Percentage ISRs derived using the standard- and low-dose protocols were compared. In a preliminary study, seven patients with stents were subjected to standard- and low-dose MDCT angiography during follow-up. The resulting images were assessed and compared by two experienced radiologists. RESULTS: The accuracy in measuring the percentage ISR was found to be better than 12% for all simulated stenoses. The differences between percentage ISRs measured on images obtained at 120 kVp/160 mAs and 80 kVp/80 mAs were below 6%. Patient image sets acquired using low-exposure factors were judged to be of satisfactory diagnostic quality. The assessment of ISR did not differ significantly between image sets acquired using the standard factors and those acquired using the low-exposure factors, although the mean reduction in patient effective dose was 48%. CONCLUSION: A reduction in exposure factors during MDCT angiography of the iliac artery is possible without affecting the accuracy in the determination of ISRs.

Determination of the weighted CT dose index in modern multi-detector CT scanners.

The aim of the present study was to (a) evaluate the underestimation in the value of the free-in-air (CTDI(air)) and the weighted CT dose index (CTDI(w)) determined with the standard 100 mm pencil chamber, i.e. the CTDI(100) concept, for the whole range of nominal radiation beam collimations selectable in a modern multi-slice CT scanner, (b) estimate the optimum length of the pencil-chamber and phantoms for accurate CTDI(w) measurements and (c) provide CTDI(w) values normalized to free-in-air CTDI for different tube-voltage, nominal radiation beam collimations and beam filtration values. The underestimation in the determination of CTDI(air) and CTDI(w) using the CTDI(100) concept was determined from measurements obtained with standard polymethyl-methacrylate (PMMA) phantoms and arrays of thermoluminescence dosimeters. The Monte Carlo N-Particle transport code was used to simulate standard CTDI measurements on a 16-slice CT scanner. The optimum pencil-chamber length for accurate determination of CTDI(w) was estimated as the minimum chamber length for which a further increase in length does not alter the value of the CTDI. CTDI(w)/CTDI(air) ratios were determined using Monte Carlo simulation and the optimum detector length for all selectable tube-voltage values and for three different values of beam filtration. To verify the Monte Carlo results, measured values of CTDI(w)/CTDI(air) ratios using the standard 100 mm pencil ionization chamber were compared with corresponding values calculated with Monte Carlo experiments. The underestimation in the determination of CTDI(air) using the 100 mm pencil chamber was less than 1% for all beam collimations. The underestimation in CTDI(w) was 15% and 27% for head and body phantoms, respectively. The optimum detector length for accurate CTDI(w) measurements was found to be 50 cm for the beam collimations commonly employed in modern multi-detector (MD) CT scanners. The ratio of CTDI(w)/CTDI(air) determined using the optimum detector length was found to be independent of beam collimation. Percentage differences between measured and calculated corresponding CTDI(w)/CTDI(air) ratios were always less than 8% for head and less than 5% for body PMMA phantoms. In conclusion, the CTDI(air) of MDCT scanners may be measured accurately with a 100 mm pencil chamber. However, the CTDI(100) concept was found to be inadequate for accurate CTDI(w) determination for the wide beam collimations commonly used in MDCT scanners. Accurate CTDI(w) determination presupposes the use of a pencil chamber and PMMA phantoms at least 50 cm long.

The effect of z overscanning on patient effective dose from multidetector helical computed tomography examinations.

z overscanning in multidetector (MD) helical CT scanning is prerequisite for the interpolation of acquired data required during image reconstruction and refers to the exposure of tissues beyond the boundaries of the volume to be imaged. The aim of the present study was to evaluate the effect of z overscanning on the patient effective dose from helical MD CT examinations. The Monte Carlo N-particle radiation transport code was employed in the current study to simulate CT exposure. The validity of the Monte Carlo simulation was verified by (a) a comparison of calculated and measured standard computed tomography dose index (CTDI) dosimetric data, and (b) a comparison of calculated and measured dose profiles along the z axis. CTDI was measured using a pencil ionization chamber and head and body CT phantoms. Dose profiles along the z axis were obtained using thermoluminescence dosimeters. A commercially available mathematical anthropomorphic phantom was used for the estimation of effective doses from four standard CT examinations, i.e., head and neck, chest, abdomen and pelvis, and trunk studies. Data for both axial and helical modes of operation were obtained. In the helical mode, z overscanning was taken into account. The calculated effective dose from a CT exposure was normalized to CTDI(free in air). The percentage differences in the normalized effective dose between contiguous axial and helical scans with pitch = 1, may reach 13.1%, 35.8%, 29.0%, and 21.5%, for head and neck, chest, abdomen and pelvis, and trunk studies, respectively. Given that the same kilovoltage and tube load per rotation were used in both axial and helical scans, the above differences may be attributed to z overscanning. For helical scans with pitch = 1, broader beam collimation is associated with increased z overscanning and consequently higher normalized effective dose value, when other scanning parameters are held constant. For a given beam collimation, the selection of a higher value of reconstructed image slice width increases the normalized effective dose. In conclusion, z overscanning may significantly affect the patient effective dose from CT examinations performed on MD CT scanners. Therefore, an estimation of the patient effective dose from MD helical CT examinations should always take into consideration the effect of z overscanning.

Pegulated liposomal doxorubicin and cisplatin given concurrently with conventional radiotherapy: a phase I dose-escalation trial for patients with squamous cell carcinoma of head and neck and lung.

This is a phase I study of concurrent chemoradiation with pegulated liposomal doxorubicin (PLDH) and cisplatin for patients with squamous non-small cell lung cancer (NSCLC) and head and neck carcinoma (SCCHN). Nine patients with NSCLC and 9 with SCCHN were recruited in two phase I dose-escalation trials. The starting dose of PLDH was 7 mg/m2 once a week and was increased by 5 mg/m2 dose increments for every 3 patients. The standard dose of cisplatin was 20 mg/m2 once a week for 6.5-7 weeks of conventional external irradiation. The total tumor dose was 64 and 70 Gy for NSCLC and SCCHN patients respectively. The maximum tolerated dose of PLDH was 12 mg/m2 for the two cohorts of patients. Grade 3 mucositis was the dose limiting toxicity for NSCLC and SCCHN patients, at the 17 mg/m2 dose level. Three chemoradiation delays of 7 days were confirmed. The median time of follow-up was 17.9 months (range 3-36 months). Four patients died due to local-regional failure combined with distant metastases (3 patients) and pericardial effusion (1 patient). In total, there were 6/18 (33%) CRs (95% confidence interval, 11-55%), and 10/18 (55%), PRs (95% confidence interval, 32-78%). The recommended phase II PLDH dose combined to cisplatin and external irradiation is 12 mg/m2/week. The incorporation of PLDH in concomitant chemoradiation regimens for future treatment of squamous cell carcinoma of the lung and head and neck is warranted.