Patient centring and scan length: how inaccurate practice impacts on radiation dose in CT colonography (CTC).

OBJECTIVE: The aim of this study was to acknowledge errors in patients positioning in CT colonography (CTC) and their effect in radiation exposure. MATERIALS AND METHODS: CTC studies of a total of 199 patients coming from two different referral hospitals were retrospectively reviewed. Two parameters have been considered for the analysis: patient position in relation to gantry isocentre and scan length related to the area of interest. CTDI vol and DLP were extracted for each patient. In order to evaluate the estimated effective total dose and the dose to various organs, we used the CT-EXPO® software version 2.2. This software provides estimates of effective dose and doses to the other various organs. RESULTS: Average value of the patients' position is found to be below the isocentre for 48 ± 25 mm and 29 ± 27 mm in the prone and supine position. It was observed that the increase in CTDI and DLP values for patients in Group 1, due to the inaccurate positioning, was estimated at about 30% and 20% for prone and supine position, respectively, while in Group 2, a decrease in CTDI and DLP values was estimated at about 16% and 18% for prone and supine position, respectively, due to an average position above isocentre. A dose increase ranging from 4 up to 13% was calculated with increasing the over-scanned region below anal orifice. CONCLUSION: Radiographers and radiologists need to be aware of dose variation and noise effects on vertical positioning and over-scanning. More accurate training need to be achieved even so when examination protocol varies from general practice.

Dosimetric implications of inter- and intrafractional prostate positioning errors during tomotherapy : Comparison of gold marker-based registrations with native MVCT.

INTRODUCTION: For high-dose radiation therapy (RT) of prostate cancer, image-guided (IGRT) and intensity-modulated RT (IMRT) approaches are standard. Less is known regarding comparisons of different IGRT techniques and the resulting residual errors, as well as regarding their influences on dose distributions. PATIENTS AND METHODS: A total of 58 patients who received tomotherapy-based RT up to 84 Gy for high-risk prostate cancer underwent IGRT based either on daily megavoltage CT (MVCT) alone (n = 43) or the additional use of gold markers (n = 15) under routine conditions. Planned Adaptive (Accuray Inc., Madison, WI, USA) software was used for elaborated offline analysis to quantify residual interfractional prostate positioning errors, along with systematic and random errors and the resulting safety margins after both IGRT approaches. Dosimetric parameters for clinical target volume (CTV) coverage and exposition of organs at risk (OAR) were also analyzed and compared. Interfractional as well as intrafractional displacements were determined. RESULTS: Particularly in the vertical direction, residual interfractional positioning errors were reduced using the gold marker-based approach, but dosimetric differences were moderate and the clinical relevance relatively small. Intrafractional prostate motion proved to be quite high, with displacements of 1-3 mm; however, these did not result in additional dosimetric impairments. CONCLUSION: Residual interfractional positioning errors were reduced using gold marker-based IGRT; however, this resulted in only slightly different final dose distributions. Therefore, daily MVCT-based IGRT without markers might be a valid alternative.

Setup errors in patients with head-neck cancer (HNC), treated using the Intensity Modulated Radiation Therapy (IMRT) technique: how it influences the customised immobilisation systems, patient's pain and anxiety.

BACKGROUND: In patients with head-neck cancer treated with IMRT, immobility of the upper part of the body during radiation is maintained by means of customised immobilisation devices. The main purpose of this study was to determine how the procedures for preparation of customised immobilisation systems and the patients characteristics influence the extent of setup errors. METHODS: A longitudinal, prospective study involving 29 patients treated with IMRT. Data were collected before CT simulation and during all the treatment sessions (528 setup errors analysed overall); the correlation with possible risk factors for setup errors was explored using a linear mixed model. RESULTS: Setup errors were not influenced by the patient's anxiety and pain. Temporary removal of the thermoplastic mask before carrying out the CT simulation shows statistically borderline, clinically relevant, increase of setup errors (+24.7%, 95% CI: -0.5% - 55.8%). Moreover, a unit increase of radiation therapists who model the customised thermoplastic mask is associated to a -18% (-29.2% - -4.9%) reduction of the errors. The setup error is influenced by the patient's physical features; in particular, it increases both in patients in whom the treatment position is obtained with 'Shoulder down' (+27.9%, 2.2% - 59.7%) and in patients with 'Scoliosis/kyphosis' problems (+65.4%, 2.3% - 164.2%). Using a 'Small size standard plus customized neck support device' is associated to a -52.3% (-73.7% - -11.2%) reduction. The increase in number of radiation therapists encountered during the entire treatment cycle does not show associations. Increase in the body mass index is associated with a slight reduction in setup error by (-2.8%, -5% - -0.7%). CONCLUSION: The position of the patient obtained by forcing the shoulders downwards, clinically significant scoliosis or kyphosis and the reduction of the number of radiation therapists who model the thermoplastic mask are found to be statistically significant risk factors that can cause an increase in setup errors, while the use of 'Small size' neck support device and patient BMI can diminish them.

Quantification and Assessment of Interfraction Setup Errors Based on Cone Beam CT and Determination of Safety Margins for Radiotherapy.

INTRODUCTION: To quantify interfraction patient setup-errors for radiotherapy based on cone-beam computed tomography and suggest safety margins accordingly. MATERIAL AND METHODS: Positioning vectors of pre-treatment cone-beam computed tomography for different treatment sites were collected (n = 9504). For each patient group the total average and standard deviation were calculated and the overall mean, systematic and random errors as well as safety margins were determined. RESULTS: The systematic (and random errors) in the superior-inferior, left-right and anterior-posterior directions were: for prostate, 2.5(3.0), 2.6(3.9) and 2.9(3.9)mm; for prostate bed, 1.7(2.0), 2.2(3.6) and 2.6(3.1)mm; for cervix, 2.8(3.4), 2.3(4.6) and 3.2(3.9)mm; for rectum, 1.6(3.1), 2.1(2.9) and 2.5(3.8)mm; for anal, 1.7(3.7), 2.1(5.1) and 2.5(4.8)mm; for head and neck, 1.9(2.3), 1.4(2.0) and 1.7(2.2)mm; for brain, 1.0(1.5), 1.1(1.4) and 1.0(1.1)mm; and for mediastinum, 3.3(4.6), 2.6(3.7) and 3.5(4.0)mm. The CTV-to-PTV margins had the smallest value for brain (3.6, 3.7 and 3.3mm) and the largest for mediastinum (11.5, 9.1 and 11.6mm). For pelvic treatments the means (and standard deviations) were 7.3 (1.6), 8.5 (0.8) and 9.6 (0.8)mm. CONCLUSIONS: Systematic and random setup-errors were smaller than 5mm. The largest errors were found for organs with higher motion probability. The suggested safety margins were comparable to published values in previous but often smaller studies.

Setup errors in cone-beam computed tomography and their effects on acute radiation toxicity in cervical cancer radiotherapy.

This study aimed to evaluate cone-beam computed tomography setup errors during cervical cancer treatment and the effects of these errors on acute radiation toxicity and treatment efficacy. A total of 170 cervical cancer patients were randomly divided into image-guided radiation therapy (IGRT; 86 patients) and intensity-modulated radiation therapy (IMRT; 84 patients) groups to receive IGRT and IMRT, respectively. After correcting setup errors for the 86 patients in the IGRT group, the X-, Y- and Z-axis errors were smaller than the corresponding errors before correction (P < 0.01, P < 0.05, and P < 0.05, respectively). The setup errors unevenly influenced the affected organs and dosage distributions in the targeted regions. The frequencies of patients with grade 0 or I urinary toxicity were 86.0% (74/86) and 44.0% (37/84) in the IGRT and IMRT groups, respectively (P < 0.01), whereas the frequencies of patients with grade 0 or I gastrointestinal toxicity were 83.7% (72/86) and 53.6% (45/84) in the IGRT and IMRT groups, respectively (P < 0.01). The two groups had similar response rates (P > 0.05). IGRT significantly corrected and reduced setup errors during cervical cancer treatment and enhanced the dosage distribution accuracy within the affected organs and targeted regions. IGRT can reduce the adverse effect of radiotherapy, thereby achieving improved efficacy during cervical cancer treatment.

Unanticipated frequency and consequences of regimen-related diarrhea in patients being treated with radiation or chemoradiation regimens for cancers of the head and neck or lung.

PURPOSE: To better understand the indirect effects of standard courses of radiation therapy (RT) on distant tissue toxicity, we evaluated the frequency, course, and health and economic burden of regimen-related diarrhea in a large, multinational group of patients who were being treated for cancers of the head and neck (HNC) or lung (NSCLC). METHODS: In this exploratory, prospective study, 284 patients being treated for HNC and 60 being treated for NSCLC were stratified into four cohorts to evaluate the effect of radiation alone and radiation plus concomitant chemotherapy (CRT) on radiation-induced diarrhea (RID). RID was assessed daily throughout RT using a patient-reported five-point categorical scale. Health and resource use outcomes were evaluated at least weekly during radiation. RESULTS: Moderate to severe RID was reported in all groups and was worse among patient being treated with concomitant chemoradiation (CRT). Whereas 29 % of patients treated with radiation only developed RID, the incidence was 42 % among CRT-treated patients. Tumor site did not impact the rate of RID, but did impact the rate of development and was more acute in patients being treated for NSCLC than for HNC. Patients with significant RID had worse health and resource use outcomes than did patients without RID regardless of the form of treatment. G-tube placement, weight loss, unplanned office visits, and in-patient days were adversely affected by RID. Not surprisingly, patients treated with CRT had poorer health and resource outcomes than RT only patients, even in the absence of RID. CONCLUSION: In addition to local tissue toxicities, our results suggest that focal radiation may also be associated with significant distant tissue-centric injury here represented by RID. While these changes were seen with radiation alone, the addition of chemotherapy increased the incidence and burden of illness. RID adversely impacted resource use. This unanticipated finding supports the hypothesis that focal radiation therapy results in pathobiological changes that extend beyond the radiation field and which can produce distant changes.

Challenges and choices in prostate cancer irradiation: from the three dimensional conformal radiotherapy to the era of intensity modulated, image-guided and adaptive radiation treatment.

In the last decades the status of radiotherapy was tremendously increased in terms of conformity to the target as well as image-guided techniques in conjunction with intensity-modulated radiotherapy (IMRT). The technological improvement had a significant clinical outcome for better response and lower toxicity to the surrounding normal tissues. Nowadays the incidence of rectal toxicity has been significantly decreased, especially with image guided radiation therapy (IGRT), whereas the dose escalation to the prostate has driven the clinical practice to the fact that radical radiotherapy for low or intermediate risk prostate cancer is definitely equivalent to surgery. The treatment volume can be reduced by reducing the size of the necessary margins to count for inaccuracies in target position and patient setup. This can be achieved either by improving the daily localization of the target before treatment or by adapting the treatment in response to feedback. This is the goal of image-guided and adaptive radiotherapy, respectively. These techniques improve the accuracy of dose delivery with a significant impact on clinical outcome and toxicity. 

Dose uncertainties in IMPT for oropharyngeal cancer in the presence of anatomical, range, and setup errors.

PURPOSE: Setup, range, and anatomical uncertainties influence the dose delivered with intensity modulated proton therapy (IMPT), but clinical quantification of these errors for oropharyngeal cancer is lacking. We quantified these factors and investigated treatment fidelity, that is, robustness, as influenced by adaptive planning and by applying more beam directions. METHODS AND MATERIALS: We used an in-house treatment planning system with multicriteria optimization of pencil beam energies, directions, and weights to create treatment plans for 3-, 5-, and 7-beam directions for 10 oropharyngeal cancer patients. The dose prescription was a simultaneously integrated boost scheme, prescribing 66 Gy to primary tumor and positive neck levels (clinical target volume-66 Gy; CTV-66 Gy) and 54 Gy to elective neck levels (CTV-54 Gy). Doses were recalculated in 3700 simulations of setup, range, and anatomical uncertainties. Repeat computed tomography (CT) scans were used to evaluate an adaptive planning strategy using nonrigid registration for dose accumulation. RESULTS: For the recalculated 3-beam plans including all treatment uncertainty sources, only 69% (CTV-66 Gy) and 88% (CTV-54 Gy) of the simulations had a dose received by 98% of the target volume (D98%) >95% of the prescription dose. Doses to organs at risk (OARs) showed considerable spread around planned values. Causes for major deviations were mixed. Adaptive planning based on repeat imaging positively affected dose delivery accuracy: in the presence of the other errors, percentages of treatments with D98% >95% increased to 96% (CTV-66 Gy) and 100% (CTV-54 Gy). Plans with more beam directions were not more robust. CONCLUSIONS: For oropharyngeal cancer patients, treatment uncertainties can result in significant differences between planned and delivered IMPT doses. Given the mixed causes for major deviations, we advise repeat diagnostic CT scans during treatment, recalculation of the dose, and if required, adaptive planning to improve adequate IMPT dose delivery.

Adaptive off-line protocol for prostate external radiotherapy with cone beam computer tomography.

PURPOSE: The goal of this work was to prepare and to evaluate an off-line adaptive protocol for prostate teleradiotherapy with kilovoltage cone beam computer tomography (CBCT). PATIENTS AND METHODS: Ten patients with localized prostate carcinoma treated with external beams underwent image-guided radiotherapy. In total, 162 CBCT images were collected. Position of prostate and pubis symphysis (PS) with respect to the isocenter were measured off-line. Using the CBCT scans obtained in the first three fractions the average position of prostate in relation (AvPosPr) to PB was calculated. On each CBCT scan, the position of prostate with respect to AvPosPr was calculated and cumulative histogram of prostate displacement with respect to AvPosPr was prepared. Using this data, the adaptive protocol was prepared in which (1) based on the CBCT made in the first three fractions the AvPosPr to PS is obtained, (2) in all other fractions two orthogonal images are acquired and if for any direction set-up error exceeds 0.2 cm the patient's position is corrected, and (3) additionally, the patient's position is corrected if the AvPosPr exceeds 0.2 cm in any direction. To evaluate the adaptive protocol for 30 consecutive patients, the CBCT was also made in 10th and 21st fraction. RESULTS: For the first 10 patients, the results revealed that the prostate was displaced in relation to AvPosPr >0.7 cm in the vertical and longitudinal directions only on 4 and 5 images of 162 CBCT images, respectively. For the lateral direction, this displacement was >0.3 cm in one case. For the group of 30 patients, displacement was never >0.7, and 0.3 cm for the vertical and lateral directions. In two cases, displacements were >0.7 cm for the longitudinal direction. CONCLUSION: Implementation of the proposed adaptive procedure based on the on-line set-up error elimination followed by a reduction of systematic internal error enables reducing the CTV-PTV margin to 0.7, 0.7, and 0.4 cm for the vertical, longitudinal, and lateral directions, respectively.

Accident prevention in day-to-day clinical radiation therapy practice.

Nearly 50-60% of cancer patients will undergo radiotherapy at some point in their treatment. Around 85% of the world's population live in developing countries served by approximately 30% of the world's radiotherapy facilities. It has been suggested that 1 megavoltage unit is required for every 500 new treatment courses per year, while others estimate that 1 megavoltage unit is needed for every 300 new treatments. However, these numbers do not necessarily take into account the development of new technologies and treatment modalities, which are more time- and resource-intensive. The International Commission on Radiological Protection has emphasised that 'purchasing new equipment without a concomitant effort on education and training and on a programme of quality assurance is dangerous', and 'the decision to implement a new technology for radiation therapy should be based on a thorough evaluation of the expected benefits, rather than being driven by the technology itself'. It is estimated that the rate of serious mistakes could be as high as 0.2%, which is several orders of magnitude higher than the rate reported for commercial aviation. So, how safe is safe? It can be stated that the development of a culture of safety is critical and requires efforts in education and training, which could prove difficult in overloaded departments.

Three-dimensional patient setup errors at different treatment sites measured by the Tomotherapy megavoltage CT.

BACKGROUND AND PURPOSE: Reduction of interfraction setup uncertainty is vital for assuring the accuracy of conformal radiotherapy. We report a systematic study of setup error to assess patients' three-dimensional (3D) localization at various treatment sites. PATIENTS AND METHODS: Tomotherapy megavoltage CT (MVCT) images were scanned daily in 259 patients from 2005-2008. We analyzed 6,465 MVCT images to measure setup error for head and neck (H&N), chest/thorax, abdomen, prostate, legs, and total marrow irradiation (TMI). Statistical comparisons of the absolute displacements across sites and time were performed in rotation (R), lateral (x), craniocaudal (y), and vertical (z) directions. RESULTS: The global systematic errors were measured to be less than 3 mm in each direction with increasing order of errors for different sites: H&N, prostate, chest, pelvis, spine, legs, and TMI. The differences in displacements in the x, y, and z directions, and 3D average displacement between treatment sites were significant (p < 0.01). Overall improvement in patient localization with time (after 3-4 treatment fractions) was observed. Large displacement (> 5 mm) was observed in the 75(th) percentile of the patient groups for chest, pelvis, legs, and spine in the x and y direction in the second week of the treatment. CONCLUSION: MVCT imaging is essential for determining 3D setup error and to reduce uncertainty in localization at all anatomical locations. Setup error evaluation should be performed daily for all treatment regions, preferably for all treatment fractions.