Image quality for radiotherapy CT simulators with different scanner bore size.

PURPOSE: We compare image quality parameters derived from phantom images taken on three commercially available radiotherapy CT simulators. To make an unbiased evaluation, we assured images were obtained with the same surface dose measured using XR-QA2 model GafChromic™ film placed at the imaging phantom surface for all three CT-simulators. METHODS: Radiotherapy CT simulators GE LS 16, Philips Brilliance Big Bore, and Toshiba Aquilion LB were compared in terms of spatial resolution, low contrast detectability, image uniformity, and contrast to noise ratio using CATPHAN-504 phantom, scanned with Head and Pelvis protocols. Dose was measured at phantom surface, with CT scans repeated until doses on all scanners were within 2%. RESULTS: In terms of spatial resolution, the GE simulator appears slightly better, while Philips CT images are superior in terms of SNR for both scanning protocols. The CNR results show that Philips CT images appear to be better, except for high Z material, while Toshiba appears to fit in between the two simulators. CONCLUSIONS: While the image quality parameters for three RT CT simulators show comparable results, the scanner bore size is of vital importance in various radiotherapy applications. Since the image quality is a function of a large number of confounding parameters, any loss in image quality due to scanner bore size could be compensated by the appropriate choice of scanning parameters, including the exposure and by balancing between the additional imaging dose to the patient and high image quality required in highly conformal RT techniques.

Radiological pulmonary findings after breast cancer irradiation: A prospective study.

The aim of this study was to evaluate radiation-induced pulmonary abnormalities of breast cancer patients. Altogether 202 consecutive patients receiving postoperative radiotherapy entered the study. Plain chest radiographs taken at entry and 3, 6 and 12 months after radiotherapy were evaluated according to modified Arriagada classification. In addition, pulmonary symptoms were recorded. Supplementary high-resolution computed tomography (HRCT) was employed in a subgroup of patients (n?=?15). Plain radiographs were interpreted by a radiologist, and uncertain findings were re-evaluated by a radiologist together with a radiation oncologist. Grade 2 pneumonitis was the most common abnormality. The proportion of patients yielding a grade 2 finding was 22.5%, 28.1%, and 16.0% at three, six, and twelve months, respectively. There were 2 normal findings in HRCTscans, and 8 in plain radiographs of the same patients. Radiological lung abnormalities are common after radiotherapy, but they are usually reversible, and their significance for the patient's well-being is minor. No correlation between symptoms and lung or pleural reactions was seen.

Evaluation of dose-response models and parameters predicting radiation induced pneumonitis using clinical data from breast cancer radiotherapy.

The purpose of this work is to evaluate the predictive strength of the relative seriality, parallel and LKB normal tissue complication probability (NTCP) models regarding the incidence of radiation pneumonitis, in a large group of patients following breast cancer radiotherapy, and furthermore, to illustrate statistical methods for examining whether certain published radiobiological parameters are compatible with a clinical treatment methodology and patient group characteristics. The study is based on 150 consecutive patients who received radiation therapy for breast cancer. For each patient, the 3D dose distribution delivered to lung and the clinical treatment outcome were available. Clinical symptoms and radiological findings, along with a patient questionnaire, were used to assess the manifestation of radiation-induced complications. Using this material, different methods of estimating the likelihood of radiation effects were evaluated. This was attempted by analysing patient data based on their full dose distributions and associating the calculated complication rates with the clinical follow-up records. Additionally, the need for an update of the criteria that are being used in the current clinical practice was also examined. The patient material was selected without any conscious bias regarding the radiotherapy treatment technique used. The treatment data of each patient were applied to the relative seriality, LKB and parallel NTCP models, using published parameter sets. Of the 150 patients, 15 experienced radiation-induced pneumonitis (grade 2) according to the radiation pneumonitis scoring criteria used. Of the NTCP models examined, the relative seriality model was able to predict the incidence of radiation pneumonitis with acceptable accuracy, although radiation pneumonitis was developed by only a few patients. In the case of modern breast radiotherapy, radiobiological modelling appears to be very sensitive to model and parameter selection giving clinically acceptable results in certain cases selectively (relative seriality model with Seppenwoolde et al and Gagliardi et al parameter sets). The use of published parameters should be considered as safe only after their examination using local clinical data. The variation of inter-patient radiosensitivity seems to play a significant role in the prediction of such low incidence rate complications. Scoring grades were combined to give stronger evidence of radiation pneumonitis since their differences could not be strictly associated with dose. This obviously reveals a weakness of the scoring related to this endpoint, and implies that the probability of radiation pneumonitis induction may be too low to be statistically analysed with high accuracy, at least with the latest advances of dose delivery in breast radiotherapy.

Effects of positioning uncertainty and breathing on dose delivery and radiation pneumonitis prediction in breast cancer.

The quality of the radiation therapy delivered in the treatment of breast cancer is susceptible to setup errors and organ motion uncertainties. For 60 breast cancer patients (24 resected with negative node involvement, 13 resected with positive node involvement and 23 ablated) who were treated with three different irradiation techniques. these uncertainties are simulated. The delivered dose distributions in the lung were recalculated taking positioning uncertainty and breathing effects into account. In this way the real dose distributions delivered to the patients are more closely determined. The positioning uncertainties in the anteroposterior (AP) and the craniocaudal (CC) directions are approximated by Gaussian distributions based on the fact that setup errors are random. Breathing is assumed to have a linear behavior because of the chest wall movement during expiration and inspiration. The combined frequency distribution of the positioning and breathing distributions is obtained by convolution. By integrating the convolved distribution over a number of intervals, the positions and the weights of the fields that simulate the original 'effective fields' are calculated. Opposed tangential fields are simulated by a set of 5 pairs of fields in the AP direction and 3 such sets in the CC direction. Opposed AP + PA fields are simulated by a set of 3 pairs of fields in the AP direction and 3 such sets in the CC direction. Single frontal fields are simulated by a set of 5 fields. In radiotherapy for breast cancer, the lung is often partly within the irradiated volume even though it is a sensitive organ at risk. The influence of the deviation in the dose delivered by the original and the adjusted treatment plans on the clinical outcome is estimated by using the relative seriality model and the biologically effective uniform dose concept. Radiation pneumonitis is used as the clinical endpoint for lung complications. The adjusted treatment plans show larger lung complication probabilities than the original plans. This means that the true expected complications are often underestimated in clinical practice. The lung density variation during breathing is calculated from the maximal change in average density during tidal breathing. The change in density in the lung due to breathing is shown to have almost no influence on the dose distribution in the lung. The proposed treatment-plan adjustments taking positioning uncertainty and breathing effects into account indicate significant deviations in the dose delivery and the predicted lung complications.

Early skin and lung reactions in breast cancer patients after radiotherapy: prospective study.

PURPOSE: The association between early radiological lung reactions consequent upon radiotherapy and patients' symptoms is not well established. This prospective study examined the association between symptoms experienced by the patient, clinical findings observed by the physician and reactions visible in chest X-ray as interpreted by a radiologist, as well as the association between skin or breast symptoms and lung symptoms induced by radiotherapy after different methods of surgery. METHODS: Altogether 207 consecutive breast cancer patients entered the trial between 1st October 1997 and 31st December 1998. Chest X-rays were taken at entry and 3, 6 and 12 months after radiotherapy. The frequency and intensity of symptoms as well as clinical and chest X-ray findings were assessed over time. RESULTS: Skin and breast symptoms were common after radiotherapy but seldom severe (9%). Lung reactions were seen in chest X-ray in 47% of patients in re-evaluation by a radiologist at 3 months. The frequency of lung or skin symptoms did not correlate with chest X-ray findings, but there was a significant correlation between skin and lung symptoms. Radiotherapy after conservative surgery for node-positive breast cancer caused lung reactions seen in chest X-ray more often than after mastectomy when using other techniques. The reactions were most common at the 6 month evaluation (P=0.01). Concomitant adjuvant chemo- or endocrine therapy did not significantly increase the incidence of lung reactions. CONCLUSIONS: Skin, breast and lung symptoms were frequent after radiotherapy, but there was no real association between lung or skin symptoms and chest X-ray findings. The only correlation noted was between skin or breast symptoms and lung symptoms experienced by patients. Radiotherapy after conservative surgery was more frequently linked to chest X-ray findings than radiotherapy after mastectomy. We conclude that routine chest X-ray after radiotherapy gives no more clinically relevant information than the symptoms of the patient and we do not recommend routine chest X-rays for that reason.