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1.

Purpose

The aim of our study was to perform the final analysis of acute toxicity and quality of life data obtained from 221 consecutive patients who suffered from intermediate-to-high risk prostate cancer.

Methods

In this trial, 221 patients were randomized to receive either hypofractionated (63?Gy in 20 fractions, 4 fractions/week) or conventionally fractionated (76?Gy in 38 fractions, 5 fractions/week) radiotherapy to the prostate and seminal vesicles. Elective pelvic lymph node irradiation with 46?Gy in 23 fractions sequentially and 44?Gy in 20 fractions simultaneously was also applied.

Results

There was no statistically significant difference in acute GU and GI toxicity in men treated with hypofractionated (SIB) (Arm 2) in comparison with patients who had conventional fractionation (Arm 1) radiation therapy. Multivariate analysis using logistic regression showed statistical significant association between acute GU?≥?1 and PTV(LN) (p?=?0.008) only. We found out that clinically relevant decrease (CRD) was significantly higher only in the urinary domain of Arm 1 at month 3 (p?=?0.02).

Conclusion

Our study demonstrated that hypofractionated radiotherapy was associated with a small but insignificant increase of acute toxicity. The reduction of overall treatment time has no significant influence on patients’ QOL in any domain.  相似文献   

2.

Aim

To develop a tool in order to guide pre-irradiation dental care (PIDC) for patients with oropharyngeal cancers.

Background

Osteoradionecrosis of the jaws is a potential complication of radiotherapy (RT) for head and neck cancers. To prevent this complication, PIDC can involve multiple dental extractions as a preventative measure to avoid post-RT complications. However, there is no standardized tool to guide PIDC.

Materials and methods

From January 2005 to October 2015, 120 head and neck cancer patients were prospectively included in a study investigating dysgeusia after RT. From this cohort, patients were enrolled according to the following inclusion criteria: histopathological confirmation of oropharyngeal squamous cell carcinoma; stage T1-4 N1-3 M0; ≤10 missing teeth. Individual teeth were retrospectively delineated on planning computed tomography and doses to dentition were assessed to generate templates.

Results

Thirty-three patients were included. Molars received highest doses with a mean dose of 50?Gy (range; 19–75?Gy). Ipsi-lateral and contralateral wisdom teeth received RT dose superior to 50?Gy in 92% and 56% of cases, respectively. Patients with advanced disease (T4 or N2c-3) received higher mean doses on inferior and ipsi-lateral dental arches compared to other patients (T1-3 N0-2b): 42?Gy vs. 39?Gy and 44?Gy vs. 39?Gy (p?<?0.05), respectively.

Conclusion

Pre-RT dose distribution templates are an objective way to prepare PIDC. Further studies with a larger cohort are needed to validate these templates.  相似文献   

3.

Aim

The present retrospective study was to compare toxicity and survival outcomes in a group of low-risk PCa patients treated with either the preoperative planning technique (145?Gy) or the real-time IoP technique (160?Gy).

Background

The two most common permanent seed implantation techniques are preoperative planning (PP) with 145?Gy and real-time intraoperative planning (IoP) with 160?Gy. Although IoP has largely replaced PP at many centres in recent years, few studies have directly compared these two techniques.

Materials and methods

Retrospective study of 408 patients with low-risk PCa treated with permanent seed implant brachytherapy at our institution between October 2003 and December 2014. Of these, 187 patients were treated with PP at a dose of 145?Gy while 221 received real-time IoP with 160?Gy.

Results

At a median follow up of 90 months, 5- and 8-year rates of biochemical relapse-free survival (BRFS) were 94.8% and 86% with the IoP technique versus 90.8% and 83.9%, respectively, with PP. The maximum dose to the urethra was <217?Gy with both techniques. Despite the higher dose, IoP did not cause any significant increase in toxicity (p?=?0.11).

Conclusions

The present study shows that real-time intraoperative brachytherapy at a dose of 160?Gy yield better biochemical control than preoperative planning at 145?Gy. In addition, urinary toxicity did not increase, despite the dose escalation, probably because the dose constraints to the urethra were met despite the increased dose escalation. These findings support the use of real-time IoP.  相似文献   

4.

Introduction

The incidence of breast carcinoma (BC) has increased in the last years. Between 2 and 12% of patients diagnosed with BC will develop bilateral breast carcinoma (BBC). The treatment of these carcinomas is more aggressive than unilateral BC.

Purpose

To perform a retrospective qualitative analysis of BBC patients whose treatment has included brachytherapy (BT) and to present a revised literature on this issue.

Material and methods

The cases of BBC whose treatment included brachytherapy were revised. The literature on this issue was refreshed.

Results

Five women, aged between 54 and 78 at the time of the diagnosis, submitted to conservative surgery followed by external radiotherapy (RT) with boost of BT or exclusive BT (APBI), in the IPO-P BT Service between 2003 and 2016.

Discussion

The patients with BBC have slightly higher rates of local recurrences, mostly in the tumor bed, where there is a higher risk of local recurrence. Patients treated with BT had lower rates of recurrences than those treated with photons and electrons.

Conclusions

BBC represents a complex challenge for doctors, because in some cases there is a tendency to use more aggressive treatments and, at the same time, it is not easy to achieve the timing for the correct treatment.  相似文献   

5.

Background

Posaconazole is used for the prophylaxis of invasive fungal disease (IFD). Previous studies have shown it to be cost-effective compared to fluconazole/itraconazole. However, posaconazole has never been economically evaluated in developing countries.

Aims

The aim of the present study was to perform a cost-effectiveness analysis of posaconazole compared to fluconazole in public (SUS) and private hospitals (PHS) in Brazil.

Methods

A cost-effectiveness simulation was conducted on the basis of a pivotal study on the use of posaconazole in acute myeloid leukemia (AML) patients, adjusting the costs to Brazilian data.

Results

A pharmacoeconomic analysis was performed on a hypothetical sample of 100 patients in each drug group. The total cost of posaconazole use alone was USD$ 220,656.31, whereas that for fluconazole was USD$ 83,875.00. Our results showed that patients with IFD remain hospitalized for an additional 12 days, at an average cost of USD$ 850.85 per patient per day. The total money spent by PHS for 100 patients for 100 days was USD$ 342,318.00 for the posaconazole group and USD$ 302,039.00 for the fluconazole group. An analysis of sensitivity (10%) revealed no intergroup difference.

Conclusions

In Brazil posaconazole is cost-effective, and should be considered for the prophylaxis of patients with AMD/myelodysplasia (AML/MDS) undergoing chemotherapy.  相似文献   

6.

Aim

This study evaluated the frequency and long-term dynamics of early and late post irradiation damage after proton–photon or photon therapy for locally advanced prostate cancer.

Background

The results of a randomized study of proton–photon or photon therapy using several fractionation regimes were analyzed in 272 patients with high and intermediate risk of progression.

Materials and methods

Three variants of proton boost fractionation were studied sequentially: 3.0 (8 daily fractions), 4.0 (5 fractions, 3 or 5 fractions/week), and 5.5 (3 fractions, 3 fractions/week) Gy(RBE).

Results

A significant decrease in the severity of both acute and late gastrointestinal injuries is achievable with a proton beam. The dynamics of late gastrointestinal and genitourinary toxicity over a 10-year period were generally characterized by a decrease in severity of morbidity by 30% and 15%, respectively.

Conclusions

Local irradiation with a fractional dose of 3.0–5.5 Gy(RBE) and a cumulative dose of 28.0–28.8 Gy(RBE) for protons significantly reduces the early and late rectitis severity, but does not reduce the risk of lower urinary tract injuries. Fractionation regimens do not significantly differ in toxicity levels.  相似文献   

7.

Aim

To assess the feasibility of transferring to the University of Tsukuba Hospital for proton beam therapy (PBT) during intensive chemotherapy in children with Ewing sarcoma family of tumors (ESFT) who had been diagnosed and started their first-line treatment at prefectural or regional centers for pediatric oncology.

Background

The treatment of ESFT relies on a multidisciplinary approach using intensive neoadjuvant and adjuvant chemotherapies with surgery and radiotherapy. Multi-agent chemotherapy comprising vincristine, doxorubicin, cyclophosphamide, ifosfamide, and etoposide (VDC-IE) is widely used for ESFT, and the interval between each course is very important for maintaining the intensity and effect of chemotherapy.

Materials and methods

Clinical information of patients who received PBT and VDC-IE between April 2009 and May 2016 was collected retrospectively. The intervals between each course of VDC-IE and adverse events were assessed.

Results

Fifteen patients were evaluated. No delays in the intervals of chemotherapy due to transfer were observed. There were no adverse events caused during/just after transfer and no increases in adverse events. The estimated 4-year overall and event-free survival rates were 94.6% and 84.8%, respectively.

Discussion

Although the results of efficacy are preliminary, survival rates were comparable with past studies. More experience and follow-up are required to further assess the efficacy of PBT for patients with ESFT.

Conclusion

Multidisciplinary therapy for children with ESFT involving transfer to our hospital for PBT during VDC-IE was feasible without treatment delay or an increase in adverse events.  相似文献   

8.

Aim

To evaluate whether hypofractionation with integrated boost to the tumour bed using intensity-modulated radiation therapy is an acceptable option and to determine whether this treatment compromises local control, toxicity and cosmesis.

Background

Retrospective studies have demonstrated that patients who are treated with HF and integrated boost experience adequate local control, a dosimetric benefit, decreased toxicity and acceptable cosmesis compared with conventional fractionation.

Materials and methods

A retrospective, observational and longitudinal study was conducted from January 2008 to June 2015 and included 34 patients with breast cancer (stage 0–II) who were undergoing conservative surgery.The prescribed doses were 45?Gy in 20 fractions (2.25?Gy/fraction) to the breast and 56?Gy in 20 fractions (2.8?Gy/fraction) to the tumour bed.

Results

Thirty-four patients were included. The mean follow-up was 49.29 months, and the mean age was 52 years. The mean percentage of PTV from the mammary region that received 100% of the prescribed dose was 97.89% (range 95–100), and the mean PTV percentage of the tumour bed that received 100% of the dose was 98% (95–100).The local control and the overall survival were 100%, and the cosmesis was good in 82% of the patients. Grade 1 acute toxicity was present in 16 patients (47%), and grade 1 chronic toxicity occurred in 6 cases (18%).

Conclusion

The results of the present study demonstrate that hypofractionation with integrated boost using intensity-modulated radiation therapy is an acceptable option that provides excellent local control and low toxicity.  相似文献   

9.

Aim

To identify factors influencing toxicity in patients affected by localized prostate cancer treated with conformal image-guided radiotherapy.

Background

Image guidance in combination with conformal techniques is the standard of care in localized prostate cancer, but factors affecting toxicity are still under investigation.

Materials and methods

294 patients were analyzed. Median age at diagnosis was 71?year. 76?Gy (38?×?2?Gy) were delivered to the target volume. We used the χ2 test to analyse associations between toxicity and dosimetric and clinical parameters. Multivariate analysis was performed using binary logistic regression. Kaplan–Meier method was used for survival analysis.

Results

Median follow-up was 62.9 months. Acute grade ≥2 gastro-intestinal toxicity (GI) was 12.1%. Acute genito-urinary (GU) toxicity of grade ≥2 was 33.9%. Actuarial 4 and 5 years late grade ≥2 GI was 3% and 4%, respectively. Four and 5-year late grade ≥2 GU toxicity was 6% and 10%. At multivariate analysis for acute toxicity rectal V70 was correlated with GI toxicity (p?=?0.01, HR 2.73 CI 1.19–6.26), and smoking habit with GU toxicity (p?<?0.01, HR 2.50 CI 1.51–4.14). For late toxicity, rectal V70 was correlated with gastro-intestinal toxicity (p?=?0.04, HR 4.76 CI 1.07–21.13), and pre-radiotherapy urinary symptoms with genito-urinary toxicity (p?=?0.01, HR 2.84 CI 1.29–6.22).

Discussion

Conformal image-guided radiotherapy shows low rates of toxicity. Smoking should be avoided during radiotherapy. Besides the evaluation of high doses received by the organs at risk, individual factors, such as co-morbidities and lifestyle choices, have an impact on normal-tissue complication risk.  相似文献   

10.

Aim

To evaluate the association between dose–volume histogram (DVH) values in organs at risk (OAR) and patient-reported HRQoL outcomes.

Background

Data on the association between DVHs and health-related quality of life (HRQoL) in prostate cancer (PCa) patients are limited.

Materials and methods

Five-year follow-up study of 154 patients with organ-confined (stage T1/T2) PCa treated with EBRT between January 2003 and November 2005. HRQoL was evaluated with the Expanded Prostate Cancer Index (EPIC). DVH for OARs (penile bulb, rectum and bladder) were created for all patients for whom data were available (119/154; 77%). The functional data analysis (FDA) statistical method was used. HRQoL data was collected prospectively and data analysis was performed retrospectively.

Results

Worsening of urinary incontinence and obstructive symptoms correlated with higher DVH dose distributions at 24 months. Increased rectal bleeding at months 24 and 60 correlated with higher DVH dose distributions in the 40–70?Gy range. Patients with deterioration in rectal incontinence presented a higher DVH distribution range than patients without rectal incontinence. Penile bulb DVH values and erectile dysfunction were not significantly associated.

Conclusions

DVH parameters and post-radiotherapy HRQoL appear to be closely correlated, underscoring the importance of assessing DVH values prior to initiating EBRT to determine the risk of developing HRQoL related adverse effects. Advanced treatment modalities may be appropriate in high risk cases to minimize treatment-related toxicity and to improve treatment outcomes and HRQoL. Future studies are needed to better elucidate the association between pre-treatment DVH parameters in organs at risk and subsequent HRQoL.  相似文献   

11.

Background

T2 magnetic resonance imaging (T2MR) is a new method for the diagnosis of invasive candidiasis, although most studies have analyzed its role in patients with candidemia or not infection.

Case report

We present the case of a patient with arteritis and thrombosis of the hepatic graft resulted from an undocumented fungal infection in the explanted liver.T2MR in serum was a suitable diagnostic tool for the diagnosis of the deep-seated invasive candidiasis in the absence of candidemia or the isolation of the yeast in culture.

Conclusions

T2MR allowed the diagnosis of deep-seated invasive candidiasis in an immunodepressed patient without candidemia, even before the onset of symptoms.  相似文献   

12.

Aim

The present study evaluated the increment of cardiac risk (CR) and absorbed dose in radiotherapy of the internal mammary chain (IMC), in particular with photon portals of 4 6?MV, and cobalt therapy (Co60); and, electron portals of 8, 12 and 16?MeV applied in the left breast, considering the adoption of a combined photon (16?Gy) and electron (30?Gy) protocols.

Materials and methods

The modified ICRP-reference female model of 60?kg, 163?cm and 43 years of age, coil RCP-AF, was modelled. The MCNP6/SICODES codes were employed, where the spatial dose distributions and dose-volume histograms were generated. Toxicity limits and a CR model were considered.

Results

CR associated with the 6?MV, 4?MV and Co60 portals increased 41.1; 40.6 and 34.5%, respectively; while, in 8, 12 and 16?MeV portals, they were 5.0, 32.5 and 49.2%, respectively. High anomalous scatter radiation from electron portals was found in the left lung providing an average dose of 3.3–5.0?Gy.

Conclusions

To RCP-AF, the Co60 portal for IMC-RT presented more attractive dose distribution, whose 16?Gy for photon-component produced less CR increase, 5% lower than the other photon portals. Considering electron portals, the smallest CR increase was produced by 8?MeV portal while 12–16?MeV made the risk higher. There is a call for a less hardened energetic spectrum in order to reduce CR; however, holding suitable IMC penetration. A combined Co60/8–12?MeV may bring benefits, reducing CR. The lowest risk was found to 46?Gy electron portals exclusively.  相似文献   

13.

Aim

To identify clinical and dosimetric factors associated with the development of hematologic toxicity (HT) for cervical cancer (CC) treated with chemotherapy and 3D conformal radiotherapy.

Background

Chemoradiotherapy is the standard of care management for CC patients with IB2-IVA clinical stages (CS). This treatment carries toxicities, standing out the one that occurs at the hematologic level.

Subjects and methods

CC patients with IB2-IVA CS treated with chemotherapy and 3D conformal radiotherapy (50?Gy) plus Brachyterapy (7?Gy x3 or 9?Gy x2) at our institution between March 2016 and March 2017. Clinical and dosimetric factors were studied as was their probable association with the development of HT.

Results

59 patients were analyzed. 89.8% of the subjects developed some grade of HT and 50.2% developed ≥grade 2 toxicity. No statistical relationship was found for the dosimetric factors: V10?>?90% (p?=?0.47) and V20?>?80% (p?=?0.17). Regarding clinical factors: neither age >50 years (p?=?0.88) nor diabetes mellitus (DM) showed statistical relationship with development of ≥grade 2 HT (p?=?0.88 and p?=?0.61, respectively). On the contrary, obesity showed a significant association (p?=?0.02). For other factors analyzed, we found statistical correlation for epidermoid histology and ≥III A CS (p?=?0.01 and p?=?0.02, respectively).

Conclusions

We did not find statistical relationship between HT and the clinical factors of age >50 years and DM. Statistical relationship for the dosimetric factors V10?>?90% and V20?>?80% was not found as well. On the contrary, obesity, epidermoid histology and ≥IIIA CS, showed statistical significance for development of HT ≥grade 2.  相似文献   

14.

Aim

To evaluate the dose distribution to the left anterior descending (LAD) coronary artery in patients treated with postoperative three-dimensional conformal radiotherapy (3DCRT).

Background

Postoperative radiotherapy may increase the risk of heart disease, particularly in patients with left-sided breast cancer. Clinical data on doses to the LAD are limited.

Materials and methods

Retrospective study of 14 patients who underwent postoperative 3DCRT for left breast cancer in 2014. All data were retrieved from medical records. Means, medians, ranges, and percentages were calculated.

Results

The mean dose to the LAD in patients with V25 < 1% was 0.12 cGy. Dmean, Dmax and V25 to the heart were, respectively, 3.7 Gy (range, 0.9–4.18), 40.3 Gy (9.28–62.9), and 1.59 cGy. The mean Dmean and Dmax values in the sample were 9.71 Gy and 33.2 Gy, respectively. The maximum dose to the LAD (D2%) ranged from 3.66 to 53.01 Gy. Due to the spacing of the CT slices (5 mm), it was not possible to completely contour the entire artery. The mean dose to the heart (3.3 Gy) was considered acceptable.

Conclusions

The maximum dose to the LAD was as high as 53 Gy, suggesting an increased risk of cardiac morbidity. This study underscores the value of contouring the LAD and the value of the breath hold technique to reduce maximum cardiac doses. Smaller CT cuts (2.5 mm) can improve contouring. Larger studies with long-term follow up are needed to determine the radiation tolerance dose for the LAD.  相似文献   

15.

Aim

The aim of the study is to evaluate the differences in dosimetry between tandem-ovoid and tandem-ring gynaecologic brachytherapy applicators in image based brachytherapy.

Background

Traditionally, tandem ovoid applicators were used to deliver dose to tumor in intracavitary brachytherapy. Tandem-ring, tandem-cylinder and hybrid intracavitary, interstitial applicators are also used nowadays in cervical cancer brachytherapy.

Methods and materials

100 CT datasets of cervical cancer patients (stage IB2 – IIIB) receiving HDR application (50 tandem-ovoid and 50 tandem-ring) were studied. Brachytherapy was delivered using a CT-MRI compatible tandem-ovoid (50 patients) and a tandem-ring applicator (50 patients). DVHs were calculated and D2cc was recorded for the bladder and rectum and compared with the corresponding ICRU point doses. The point B dose, the treated volume, high dose volume and the treatment time were recorded and compared for the two applicators.

Results

The mean D2cc of the bladder with TR applicator was 6.746 Gy. TO applicator delivered a mean D2cc of 7.160 Gy to the bladder. The mean ICRU bladder points were 5.60 and 5.63 Gy for TR and TO applicator, respectively. The mean D2cc of the rectum was 4.04 Gy and 4.79 Gy for TR and TO applicators, respectively. The corresponding ICRU point doses were 5.10 Gy and 5.66 Gy, respectively.

Conclusions

The results indicate that the OAR doses assessed by DVH criteria were higher than ICRU point doses for the bladder with both tandem-ovoid and tandem-ring applicators whereas DVH based dose was lower than ICRU dose for the rectum. The point B dose, the treated volume and high dose volume was found to be slightly higher with the tandem-ovoid applicator. The mean D2cc dose for the bladder and rectum was lower with tandem-ring applicators. The clinical implication of the above dosimetric differences needs to be evaluated further.  相似文献   

16.

Aim

In this study, we intend to compare two different setup procedures for female breast cancer patients.

Background

Imaging in radiotherapy provides a precise localization of the tumour, increasing the accuracy of the treatment delivery in breast cancer.

Materials and methods

Twenty breast cancer patients who underwent whole breast radiotherapy (WBRT) were selected for this study. Patients were divided into two groups of ten. Group one (G1) was positioned by tattoos and then the patient positioning was adjusted with the aid of AlignRT (Vision RT, London, UK). In group two (G2), patients were positioned only by tattoos. For both groups, the first 15 fractions were analyzed, a daily kilovoltage (kV) cone beam computed tomography (CBCT) image was made and then the rotational and translational displacements and, posteriorly, the systematic (Σ) and random (σ) errors were analyzed.

Results

The comparison of CBCT displacements for the two groups showed a statistically significant difference in the translational left–right (LR) direction (ρ = 0.03), considering that the procedure with AlignRT system has smaller lateral displacements. The results of systematic (Σ) and random (σ) errors showed that for translational displacements the group positioned only by tattoos (G2) demonstrated higher values of errors when compared with the group positioned with the aid of AlignRT (G1).

Conclusions

AlignRT could help the positioning of breast cancer patients; however, it should be used with another imaging method.  相似文献   

17.

Objective

A new method was presented to prepare clinical-grade human adipose-derived stromal stem cells (ASCs) and its safety in vitro, such as biological characteristics and genetic features alteration were investigated.

Methods

The morphology of the ASCs which were cultured in vitro using serum-free medium was observed. Cell cycle and CD markers profile were tested by flow cytometry, while karyotype was analyzed by the chromosome G-banding technology. Growth factors expression was tested by ELISA and tumor-related genes were analyzed by the real-time PCR, respectively.

Results

ASCs were adult stem cells with spindle shape. The proliferation ratio of ASCs began to slow down after 10 passages, and was significant after 15 passages. Cell cycle analysis revealed that the percentage of G2 phase and S phase cells was stable. There was no obvious missing, translocation or dislocation in terms of karyotype. Expression level of tumor relevant genes and cytokines at different passages had no significant difference.

Conclusions

The clinical-grade ASCs prepared with this new method, less than ten passages, was safe for clinical trials.  相似文献   

18.

Aim

The aim of this research is to establish if variation exists in the dose delivered for head and neck (HN) localisation computed tomography (CT) imaging in radiation therapy (RT); to propose a national diagnostic reference levels (DRLs) for this procedure and to make a comparison between the national DRL and a DRL of a European sample.

Background

CT has become an indispensable tool in radiotherapy (RT) treatment planning. It is a requirement of legislation in many countries that doses of ionising radiation for medical exposures be kept ‘As Low As Reasonably Achievable’. There are currently no dose guidelines for RT localisation CT of the HN.

Materials and methods

All RT departments in Ireland and a sample of European departments were surveyed. Dose data on CT dose length product (DLP); dose index volume (CTDIvol); current time product; tube voltage and scan length was acquired for ten average-sized HN patients from each department. DRLs were proposed for DLP and CTDIvol using the rounded 75th percentile of the distribution of the means.

Results

42% of Irish departments and one European department completed the survey. Significant variation was found in the mean DLP, CTDIvol and scan lengths across the Irish departments. The proposed Irish DRL is 882?mGy?cm and 21?mGy and the European department DRL is 816?mGy?cm and 21?mGy, for DLP and CTDIvol, respectively.

Conclusions

Variation exists in doses used for HN RT localisation CT. DRLs have been proposed for comparison purposes with the aim of dose optimisation.  相似文献   

19.

Objective

The current study proposes an automated machine learning approach for the quantification of cells in cell death pathways according to DNA fragmentation.

Methods

A total of 17 images of kidney histological slide samples from male Wistar rats were used. The slides were photographed using an Axio Zeiss Vert.A1 microscope with a 40x objective lens coupled with an Axio Cam MRC Zeiss camera and Zen 2012 software. The images were analyzed using CellProfiler (version 2.1.1) and CellProfiler Analyst open-source software.

Results

Out of the 10,378 objects, 4970 (47,9%) were identified as TUNEL positive, and 5408 (52,1%) were identified as TUNEL negative. On average, the sensitivity and specificity values of the machine learning approach were 0.80 and 0.77, respectively.

Conclusion

Image cytometry provides a quantitative analytical alternative to the more traditional qualitative methods more commonly used in studies.  相似文献   

20.

Aim

The aim of this study is to calculate neutron contamination at the presence of circular cones irradiating by 18 MV photons using Monte Carlo code.

Background

Small photon fields are one of the most useful methods in radiotherapy. One of the techniques for shaping small photon beams is applying circular cones made of lead. Using this method in high energy photon due to neutron contamination is a crucial issue.

Materials and methods

Initially, Varian linac producing 18 MV photons was simulated and after validating the code, various circular cones were also simulated. Then, the number of neutrons, neutron equivalent dose and absorbed dose per Gy of photon dose were calculated along the central axis.

Results

Number of neutrons per Gy of photon dose had their maximum value at depth of 2 cm and these values for 5, 10, 15, 20 and 30 mm circular cones were 9.02, 7.76, 7.61, 6.02 and 5.08 (n cm?2 Gy?1), respectively. Neutron equivalent doses per Gy of photon dose had their maximum at the surface of the phantom and these values for mentioned collimators were 1.48, 1.33, 1.31, 1.12 and 1.08 (mSv Gy?1), respectively. Neutron absorbed doses had their maximum at the surface of the phantom and these values for mentioned collimators sizes were 103.74, 99.71, 95.77, 81.46 and 78.20 (μGy/Gy), respectively.

Conclusions

As the field size gets smaller, number of neutrons, equivalent and absorbed dose per Gy of photon increase. Also, neutron equivalent dose and absorbed dose are maximum at the surface of phantom and then these values will be decreased.  相似文献   

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