Dosimetric impact of MLC positional errors on dose distribution in IMRT.

Optimizing the positional accuracy of multileaf collimators (MLC) for radiotherapy is important for dose accuracy and for reducing doses delivered to normal tissues. This study investigates dose sensitivity variations and complexity metrics of MLC positional error in volumetric modulated arc therapy and determines the acceptable ranges of MLC positional accuracy in several clinical situations. Treatment plans were generated for four treatment sites (prostate cancer, lung cancer, spinal, and brain metastases) using different treatment planning systems (TPSs) and fraction sizes. Each treatment plan introduced 0.25-2.0 mm systematic or random MLC leaf bank errors. The generalized equivalent uniform dose (gEUD) sensitivity and complexity metrics (MU/Gy and plan irregularity) were calculated, and the correlation coefficients were assessed. Furthermore, the required tolerances for MLC positional accuracy control were calculated. The gEUD sensitivity showed the highest dependence of systematic positional error on the treatment site, followed by TPS and fraction size. The gEUD sensitivities were 6.7, 4.5, 2.5, and 1.7%/mm for Monaco and 8.9, 6.2, 3.4, and 2.3%/mm (spinal metastasis, lung cancer, prostate cancer, and brain metastasis, respectively) for RayStation. The gEUD sensitivity was strongly correlated with the complexity metrics (r = 0.88-0.93). The minimum allowable positional error for MLC was 0.63, 0.34, 1.02, and 0.28 mm (prostate, lung, brain, and spinal metastasis, respectively). The acceptable range of MLC positional accuracy depends on the treatment site, and an appropriate tolerance should be set for each treatment site with reference to the complexity metric. It is expected to enable easier and more detailed MLC positional accuracy control than before by reducing dose errors to patients at the treatment planning stage and by controlling MLC quality based on complexity metrics, such as MU/Gy.

Factors associated with quality of life in patients receiving palliative radiotherapy for bone metastases: a secondary cross-sectional analysis of data from a prospective multicenter observational study.

OBJECTIVE: To identify factors significantly associated with quality of life (QOL) and determine if these associations are strong enough to predict certain aspects of QOL without measuring them. METHODS: We conducted an exploratory secondary analysis of baseline data of 224 patients (enrolled between December 2020 and March 2021) from a previously published prospective observational study on radiotherapy for bone metastases at 26 centres. Using univariable linear regression, we assessed the association between patient/treatment factors and QOL scale scores as measured by the European Organization for Research and Treatment of Cancer (EORTC) QOL Questionnaire Core 15-Palliative (QLQ-C15-PAL) and the EORTC QOL Questionnaire Bone Metastases module (QLQ-BM22). RESULTS: Age and sex were not significantly associated with QOL. Worse performance status, higher pain scores, and opioid and single-fraction use were significantly associated with most QOL scales; these four factors were associated with worse global QOL, worse functioning status, and more severe symptoms. The coefficients of determination for most QOL scales were less than 0.2, indicating that most of the variability in QOL scores was not explained by any of the explanatory variables. CONCLUSION: Performance status, pain intensity, and opioid and single-fraction use were significantly associated with most QOL scales. However, the associations were not strong enough to estimate QOL. ADVANCES IN KNOWLEDGE: To date, the association between treatment factors and QOL in patients with bone metastases has not been fully studied. We identified the factors that were significantly associated with QOL and found that these associations were not strong enough to predict QOL.

Who should receive single-fraction palliative radiotherapy for gastric cancer bleeding?: An exploratory analysis of a multicenter prospective observational study (JROSG 17-3).

Purpose: Although the Palliative Prognostic Index (PPI) has been used to predict survival in various cancers, to our knowledge, no study has examined its applicability in gastric cancer. This study aimed to determine the baseline PPI cutoff value for recommending single-fraction radiotherapy in patients with bleeding gastric cancer. Materials and methods: This was a secondary analysis of the Japanese Radiation Oncology Study Group (JROSG) 17-3, a multicenter prospective study of palliative radiotherapy for bleeding gastric cancer. Discrimination was evaluated using a time-dependent receiver operating characteristic curve, and the optimal cutoff value was determined using the Youden index. A calibration plot was used to assess the agreement between predicted and observed survival. Results: We enrolled 55 patients in JROSG 17-3. The respective median survival times were 6.7, 2.8, and 1.0 months (p = 0.021) for patients with baseline PPI scores of ≤ 2, 2 < PPI ≤ 4, and PPI > 4. The areas under the curve for predicting death within 2, 3, 4, and 5 months were 0.813, 0.787, 0.775, and 0.721, respectively. The negative predictive value was highest when survival < 2 months was predicted and the Youden index was highest when the cutoff PPI value was 2. The calibration curve showed a reasonable agreement between the predicted and observed survival. Conclusion: Baseline PPI is useful for estimating short-term prognosis in patients treated with palliative radiotherapy for gastric cancer bleeding. A cutoff PPI value of 2 for estimating survival ≤ 2 months should be used to recommend single-fraction radiotherapy.

Income and Employment of Patients at the Start of and During Follow-up After Palliative Radiation Therapy for Bone Metastasis.

Purpose: The aim of this study was to understand the income and employment status of patients at the start of and during follow-up after palliative radiation therapy for bone metastasis. Methods and Materials: From December 2020 to March 2021, a prospective multi-institutional observational study was conducted to investigate income and employment of patients at the start of administration of radiation therapy for bone metastasis and at 2 and 6 months after treatment. Of 333 patients referred to radiation therapy for bone metastasis, 101 were not registered, mainly because of their poor general condition, and another 8 were excluded from the follow-up analysis owing to ineligibility. Results: In 224 patients analyzed, 108 had retired for reasons unrelated to cancer, 43 had retired for reasons related to cancer, 31 were taking leave, and 2 had lost their jobs at the time of registration. The number of patients who were in the working group was 40 (30 with no change in income and 10 with decreased income) at registration, 35 at 2 months, and 24 at 6 months. Younger patients (P = 0), patients with better performance status (P = 0), patients who were ambulatory (P = .008), and patients with lower scores on a numerical rating scale of pain (P = 0) were significantly more likely to be in the working group at registration. There were 9 patients who experienced improvements in their working status or income at least once in the follow-up after radiation therapy. Conclusions: The majority of patients with bone metastasis were not working at the start of or after radiation therapy, but the number of patients who were working was not negligible. Radiation oncologists should be aware of the working status of patients and provide appropriate support for each patient. The benefit of radiation therapy to support patients continuing their work and returning to work should be investigated further in prospective studies.

Incidence of and risk factors for non-hematologic toxicity with combined radiotherapy and CDK4/6 inhibitors in metastatic breast cancer using dose-volume parameters analysis: a multicenter cohort study.

BACKGROUND: There is a lack of data on combined radiotherapy (RT) and cyclin-dependent kinase 4 and 6 inhibitor (CDK4/6i) risk factors and toxicity. This study aimed to assess the incidence of and risk factors for non-hematologic toxicities in patients treated with combined RT and CDK4/6i using dose-volume parameter analysis. METHODS: We conducted a retrospective multicenter cohort study of patients with metastatic breast cancer receiving RT within 14 days of CDK4/6i use. The endpoint was non-hematologic toxicities. Patient characteristics and RT treatment planning data were compared between the moderate or higher toxicities (≥ grade 2) group and the non-moderate toxicities group. RESULTS: Sixty patients were included in the study. CDK4/6i was provided at a median daily dose of 125 mg and 200 mg for palbociclib and abemaciclib, respectively. In patients who received concurrent RT and CDK4/6i (N = 29), the median concurrent prescribed duration of CDK4/6i was 14 days. The median delivered RT dose was 30 Gy and 10 fractions. The rate of grade 2 and 3 non-hematologic toxicities was 30% and 2%, respectively. There was no difference in toxicity between concurrent and sequential use of CDK4/6i. The moderate pneumonitis group had a larger lung V20 equivalent dose of 2 Gy per fraction and planning target volume than the non-moderate pneumonitis group. CONCLUSIONS: Moderate toxicities are frequent with combined RT and CDK4/6i. Caution is necessary concerning the combined RT and CDK4/6i. Particularly, reducing the dose to normal organs is necessary for combined RT and CDK4/6i.

Treatment response after palliative radiotherapy for bleeding gastric cancer: a multicenter prospective observational study (JROSG 17-3).

BACKGROUND: Palliative radiotherapy seems to be rarely performed for incurable gastric cancer. In this first multicenter study, we examined the effectiveness of palliative radiotherapy and investigated whether biologically effective dose (BED) is associated with survival, response, or re-bleeding. METHODS: Eligibility criteria included blood transfusion or hemoglobin levels < 8.0 g/dL. The primary endpoint was the intention-to-treat (ITT) bleeding response rate at 4 weeks. Response entailed all of the following criteria: (i) hemoglobin levels ≥ 8.0 g/dL; (ii) 7 consecutive days without blood transfusion anytime between enrollment and blood sampling; and (iii) no salvage treatment (surgery, endoscopic treatment, transcatheter embolization, or re-irradiation) for bleeding gastric cancer. Re-bleeding was defined as the need for blood transfusion or salvage treatment. RESULTS: We enrolled 55 patients from 15 institutions. The ITT response rates were 47%, 53%, and 49% at 2, 4, and 8 weeks, respectively. The per-protocol response rates were 56%, 78%, and 90% at 2, 4, and 8 weeks, respectively. Neither response nor BED (α/ß = 10) predicted overall survival. Multivariable Fine-Gray model showed that BED was not a significant predictor of response. Univariable Cox model showed that BED was not significantly associated with re-bleeding. Grades 1, 2, 3, and, ≥ 4 radiation-related adverse events were reported in 11, 9, 1, and 0 patients, respectively. CONCLUSIONS: The per-protocol response rate increased to 90% during the 8-week follow-up. The frequent occurrence of death starting shortly after enrollment lowered the ITT response rate. BED was not associated with survival, bleeding response, or re-bleeding.

Site-specific risk factors for local recurrence after rectal cancer surgery.

BACKGROUND: Quite few studies examined risk factors for local recurrence after rectal cancer surgery with respect to local recurrence sites. METHODS: Local recurrence sites were categorized into axial, anterior, posterior, and lateral (pelvic sidewall), and axial, anterior, and posterior type were combined as the "other" type of local recurrence. Among 76 patients enrolled into our prospective randomized controlled trial to determine the indication for pelvic autonomic nerve preservation (PANP) in patients with advanced lower rectal cancer (UMIN000021353), multivariate analyses were conducted to elucidate risk factors for either lateral or the "other" type of local recurrence. RESULTS: Univariate analyses showed that tumor distance from the anal verge was significantly (p = 0.017), and type of operation (sphincter preserving operation (SPO) vs. abdominoperineal resection (APR)) was marginally (p = 0.065) associated with pelvic sidewall recurrence. Multivariate analysis using these two parameters showed that tumor distance from the anal verge was significantly and independently correlated with pelvic sidewall recurrence (p = 0.017). As for the "other" type of local recurrence, univariate analyses showed that depth of tumor invasion (p = 0.011), radial margin status (p < 0.001), and adjuvant chemotherapy (p = 0.037) were significantly associated, and multivariate analysis using these three parameters revealed that depth of tumor invasion (p = 0.004) and radial margin status (p < 0.001) were significantly and independently correlated with the "other" type of local recurrence. CONCLUSION: Risk factors for local recurrence after rectal cancer surgery were totally different with respect to the intra-pelvic recurrent sites. Site-specific probability of local recurrence can be inferred using these risk factors. TRIAL REGISTRATION NUMBER: UMIN000021353.

Palliative brachytherapy and external beam radiotherapy for dysphagia from esophageal cancer: a nationwide survey in Japan.

BACKGROUND: International guidelines recommend brachytherapy for patients with dysphagia from esophageal cancer, whereas brachytherapy is infrequently used to palliate dysphagia in some countries. To clarify the availability of palliative treatment for dysphagia from esophageal cancer and explain why brachytherapy is not routinely performed are unknown, this study investigated the use of brachytherapy and external beam radiotherapy for dysphagia from esophageal cancer. METHODS: Japanese Radiation Oncology Study Group members completed a survey and selected the treatment that they would recommend for hypothetical cases of dysphagia from esophageal cancer. RESULTS: Of the 136 invited facilities, 61 completed the survey (44.9%). Four (6.6%) facilities performed brachytherapy of the esophagus, whereas brachytherapy represented the first-line treatment at three (4.9%) facilities. Conversely, external beam radiotherapy alone and chemoradiotherapy were first-line treatments at 61 and 58 (95.1%) facilities, respectively. In facilities that performed brachytherapy, the main reason why brachytherapy of the esophagus was not performed was high invasiveness (30.2%). Definitive-dose chemoradiotherapy with (≥50 Gy) tended to be used in patients with expected long-term survival. CONCLUSIONS: Few facilities routinely considered brachytherapy for the treatment of dysphagia from esophageal cancer in Japan. Conversely, most facilities routinely considered external beam radiotherapy. In the future, it will be necessary to optimize external beam radiotherapy.

Practice patterns for postoperative radiation therapy in patients with metastases to the long bones: a survey of the Japanese Radiation Oncology Study Group.

Evidence regarding postoperative radiation therapy (PORT) for metastases to the long bones is lacking. Characterizing the current practice patterns and identifying factors that influence dose-fractionation schedules are essential for future clinical trials. An internet-based survey of the palliative RT subgroup of the Japanese Radiation Oncology Study Group was performed in 2017 to collect data regarding PORT prescription practices and dose-fractionation schedules. Responders were also asked to recommend dose-fractionation schedules for four hypothetical cases that involved a patient with impending pathological fractures and one of four clinical features (poor prognosis, solitary metastasis, radio-resistant primary tumor or expected long-term survival). Responders were asked to indicate their preferred irradiation fields and the reasons for the dose fractionation schedule they chose. Responses were obtained from 89 radiation oncologists (67 institutions and 151 RT plans) who used 22 dose-fractionation schedules, with the most commonly used and recommended schedule being 30 Gy in 10 fractions. Local control was the most common reason for preferring longer-course RT. High-dose fractionated schedules were preferred for oligometastasis, and low-dose regimens were preferred for patients with a poor prognosis; however, single-fraction RT was not preferred. Most respondents recommended targeting the entire orthopedic prosthesis. These results indicated that PORT using 30 Gy in 10 fractions to the entire orthopedic prosthesis is preferred in current Japanese practice and that single-fraction RT was not preferred. Oligometastasis and poor prognosis influenced the selection of high- or low-dose regimens.

Changing Patterns of Distant Metastasis in Patients With Lower Rectal Cancer Undergoing Intraoperative Radiotherapy.

BACKGROUND/AIM: Local radiotherapy for primary tumors may increase the incidence of distant metastasis. However, the patterns of target organs have not been clarified yet. PATIENTS AND METHODS: In our randomized controlled trial examining the oncological efficacy of intraoperative radiotherapy (IORT) for advanced lower rectal cancer, the details of the metastatic organs were evaluated. RESULTS: In the IORT group (38 patients), 2 patients had metastasis in the liver and lung simultaneously, 9 in the liver, and 4 in the lung. In the control group (38 patients), 3 had metastasis in the lung, and 2 in the liver. The IORT group tended to have liver metastases more frequently (p=0.058). Among patients with liver metastases, distant metastasis-free intervals were significantly shorter in the IORT group, however, no significant difference was observed among patients with lung metastases. CONCLUSION: After curative rectal cancer surgery with IORT, liver metastasis may be increased and accelerated.

Intraoperative radiotherapy for resectable advanced lower rectal cancer-final results of a randomized controlled trial (UMIN000021353).

AIM: Pelvic autonomic nerve preservation (PANP) is useful to preserve voiding and sexual function after rectal cancer surgery. The aim of this study was to investigate the benefit of intraoperative radiotherapy (IORT) to have complete PANP without affecting oncological outcomes. METHODS: Patients undergoing potentially curative resection of the rectum were included. They were randomized to intraoperative radiotherapy of the completely preserved bilateral pelvic nerve plexuses (IORT group) or the control group without IORT, but with limited nerve preservation. The primary endpoint was pelvic sidewall recurrence. Moreover, patients' clinicopathologic parameters, postoperative complications, voiding function, and other oncologic outcomes were compared. RESULTS: From 79 patients, three were excluded from analysis, resulting in 38 patients in each group. Patients' demographic and pathological parameters were well balanced between the two groups. The trial was terminated prematurely in July 2017, because distant metastasis-free survivals were found to be significantly worse in the IORT group compared to the control group (odds ratio 2.554; 95% CI, 1.041 ~ 6.269; p = 0.041). Neither overall survival nor pelvic sidewall recurrence did differ between the two groups (overall survival: odds ratio 1.264; 95% CI, 0.523~3.051; p = 0.603/pelvic sidewall recurrence; odds ratio 1.350; 95% CI, 0.302~6.034; p = 0.694). Postoperative complications did not differ between the groups; however, the urinary function was significantly better in the IORT group in the short and long term. CONCLUSION: With the aid of IORT, complete PANP can be done without increase of pelvic sidewall recurrence; however, IORT may increase the incidence of distant metastases. Therefore, IORT cannot be recommended as a standard therapy to compensate less radical resection for advanced lower rectal cancer.

Quality assurance of pelvic autonomic nerve-preserving surgery for advanced lower rectal cancer--preliminary results of a randomized controlled trial.

BACKGROUND: Pelvic autonomic nerve-preserving (PANP) lateral node dissection (LLND) has been introduced in rectal cancer surgery in Japan, but quality assurance of this approach has not been tested by randomized controlled trials. METHODS: Patients with advanced lower rectal cancer were randomized either to complete PANP + LLND surgery combined with intraoperative radiotherapy (preserved group; n = 28) or to pelvic autonomic nerve resection + LLND surgery (resected group; n = 27). Operation-related parameters were compared statistically. RESULTS: Patient and tumor characteristics were well comparable. The incidence of anastomotic breakdown, intrapelvic abscess, and small bowel obstruction was not different between the two groups. In the preserved group, no patients had ureteral stenosis, pelvic bone fractures, or peripheral neuropathy due to intraoperative radiotherapy. Sphincter-preserving operation was possible with similar ratio in both groups. Adjuvant chemotherapy was given with similar ratio in both groups. The average operation time was 513 minutes in the preserved group and 409 minutes in the resected group, with a significant difference between the two groups. The average amount of hemorrhage was not different significantly between the preserved group (996 ml) and the resected group (970 ml). Circumferential resection margin status and operative curability were similar between the two groups. The average number of harvested and metastatic nodes in the mesentery and pelvic sidewall was not different significantly between the two groups. CONCLUSIONS: This study revealed, for the first time, that the surgical quality of PANP + LLND is the same as pelvic autonomic nerve resection + LLND.

Radiosurgery for cerebral arteriovenous malformation during pregnancy: A case report focusing on fetal exposure to radiation.

INTRODUCTION: We present the case of a pregnant woman who underwent linear accelerator (LINAC)-based stereotactic radiosurgery (SRS) and we discuss the fetal exposure to radiation. CLINICAL PRESENTATION: A 20-year-old woman at 18 weeks of gestation presented with right cerebral hemorrhage and underwent urgent evacuation of the hematoma. She recovered well after surgery, but cerebral angiography after the surgery revealed a small deeply seated arteriovenous malformation (AVM) in the right frontal lobe extending to the right basal ganglia. METHODS AND RESULTS: We examined the diffuse AVM and treated it with LINAC-based SRS at 24 weeks of gestation. Before SRS, the fetus was exposed to a radiation dose of 8.26 mGy, which was estimated by conducting an experiment using an adult RANDO phantom, and a radiophotoluminescent (RPL) glass rod dosimeter (GRD) system. The patient underwent Caesarean delivery at 36 weeks of gestation and gave birth to a healthy baby. CONCLUSION: The exposure of fetus to radiation during SRS was exceedingly low. SRS can be used as an alternative treatment to microsurgery for resolving small deeply seated AVMs even in pregnant patients.

Impact of intra-operative radiotherapy on evacuatory function following ultra-low anterior resection. A preliminary result of prospective randomized trial.

BACKGROUND/AIMS: Preoperative radiotherapy and/or chemotherapy have been reported as effective treatment for locally advanced low rectal carcinoma. However, recent follow-up studies represented severe postoperative evacuatory disorder, which annoys patients' quality of life. METHODOLOGY: The present study was a part of a randomized trial protocol comparing between intraoperative radiotherapy with pelvic autonomic nerve preservation and control group without radiation. Of these, 24 patients having sphincter preservation were followed in terms of their bowel function with questionnaire and anorectal manometry. RESULTS: In terms of background, patients' age, gender, depth of the tumor invasion and lymph node metastasis showed no significant difference between the groups. After stoma closure, frequency of bowel movement was increased and incontinence scores worsened in both groups. However, no significant difference was noted between the groups, postoperatively. Regarding anorectal manometry, postoperative anal sphincter tones were stable compared even to pre-operative findings and no difference was noted between the groups postoperatively. Anal canal length and sensory factor were stable and no difference between the groups. Volumetric factors such as rectal capacity and maximum tolerable volume were also stable even after ultra-low anterior resection. CONCLUSIONS: Intraoperative radiotherapy did not affect adversely on evacuatory function following ultra-low anterior resection in the early postoperative period. Long-term follow-up is warranted.

Intraoperative radiotherapy for oncological and function-preserving surgery in patients with advanced lower rectal cancer.

BACKGROUND: Pelvic autonomic nerve preservation (PANP) with lateral lymph node dissection (LLND) has been introduced in rectal cancer surgery in Japan; however, its indication has not been standardized yet. MATERIALS AND METHODS: Forty-four patients with advanced lower rectal cancer were randomized to either the standard treatment group (control group) or the intraoperative radiotherapy (IORT) group. All patients underwent potentially curative resection of the rectum with total mesorectal excision. The control group underwent bilateral LLND and limited PANP. The IORT group underwent bilateral LLND, complete PANP, and IORT. Patients allocated to the IORT group received IORT to the bilateral preserved pelvic nerve plexuses. Patients' clinicopathologic parameters, postoperative complications, voiding function, and prognosis were compared between the two groups. RESULTS: Among 44 patients enrolled, three patients were excluded from the analysis, resulting in 19 patients in the IORT group and 22 patients in the control group. Patients' demographic and pathological parameters and postoperative complications were well balanced between the two groups. Oncological outcomes including overall and disease-free survival were also similar. Local recurrence was observed in one patient in each group. Among the 34 patients not complicated with intrapelvic abscess, the mean duration of urinary catheter indwelling was 8 days in the IORT group and 13 days in the control group (p = 0.055). In the long term, medication for urination was necessitated in four patients in the control group, whereas in none in the IORT group (p = 0.059). DISCUSSIONS: Oncological outcomes in the IORT group are equal to those in the control group, and voiding functions in the IORT group are superior to those in the control group. These results suggest that IORT may be useful to expand the indication of complete PANP with LLND for advanced lower rectal cancer.

Radiation-induced apoptosis of oligodendrocytes in the adult rat optic chiasm.

OBJECTIVES: The present study characterized glial cell injury provoked in adult rat chiasm within 24 hours after a single, high-dose irradiation of 20 Gy. METHODS: All chiasmal glial cells in a section were counted, and the percentage of TUNEL-positive glial cells exhibiting apoptotic morphology was defined as the apoptotic rate. RESULTS: Numbers of apoptotic cells increased significantly (p<0.0001) from 3 to 8 hours after exposure, but returned to baseline levels by 24 hours. Little evidence of apoptosis was observed in non-irradiated chiasms. Similar patterns of increase in apoptotic rate were observed in the genu of the corpus callosum, but the extent was significantly lower (p=0.047) in the optic chiasm, with a maximal rate of 1.9%. Immunohistochemically, apoptotic cells were positive for CNP, a marker for oligodendrocytes. DISCUSSION: These data indicate that chiasmal irradiation induces limited, but significant apoptotic depletion of the oligodendroglial population, and may participate in the development of radiation-induced optic neuropathy.

Dose evaluation and effective dose estimation from multi detector CT.

Computed tomography (CT) has evolved remarkably through device improvement and advancement of peripherals, including computers. In 1999, multi detector-row CT (MDCT) appeared and rapid high-speed scanning became possible. However, usefulness of MDCT in actual clinical application cannot be assessed until the exposure doses are assessed appropriately. Since CT examinations need a comparatively high dose, it is necessary to evaluate patient exposure for introduction of MDCT. Patient doses by three types of MDCTs were evaluated for cases of scanning of the chest and abdomen-pelvis. The examination conditions were the same as those in actual clinical examinations. The obtained effective doses were 9.4-28 mSv for the chest examination and 13-28 mSv for the abdomen-pelvis. The average surface doses varied between 16-43 mGy for the chest examination and 20-37 mGy for the abdomen-pelvis. The highest surface dose was 57 mGy for the abdomen-pelvis examination. The exposed doses differed according to scanning method and imaging conditions such as tube current, slice thickness and so on. It seemed that there is room for dose reduction by proper adjustment of scan conditions in MDCT examinations.