High Energy X-Ray Dosimetry Using(ZnO)_(0.2)(TeO_(2))_(0.8)Thin Film-based Real-time X-Ray Sensor

This study reports the dosimetric response of a(ZnO)_(0.2)(TeO_(2))_(0.8)thin film sensor irradiated with high-energy X-ray radiation at various doses.The spray pyrolysis method was used for the film deposition on soda-lime glass substrate using zinc acetate dehydrate and tellurium dioxide powder as the starting precursors.The structural and morphological properties of the film were determined.The I-V characteristics measurements were performed during irradiation with a 6 MV X-ray beam from a Linac.The results revealed that the XRD pattern of the AS-deposited thin film is non-crystalline(amorphous)in nature.The FESEM image shows the non-uniform shape of nanoparticles agglomerated separately,and the EDX spectrum shows the presence of Te,Zn,and O in the film.The I-V characteristics measurements indicate that the current density increases linearly with X-ray doses(0-250 cGy)for all applied voltages(1-6 V).The sensitivity of the thin film sensor has been found to be in the range of 0.37-0.94 mA/cm^(2)/Gy.The current-voltage measurement test for fading normalised in percentage to day 0 was found in the order of day 0>day 15>day 30>day 1>day 2.These results are expected to be beneficial for fabricating cheap and practical X-ray sensors.

Evaluation of the accuracy and efficiency of the in-vivo dosimetry systems for routine cancer patient dose verification

Objective： This study aimed to evaluate of the accuracy and efficiency of the in-vivo dosimetry systems for routine cancer patient dose verification. Methods： In vivo dosimetry, using diodes and thermoluminescent dosimeters （TLD） is performed in many radiotherapy departments to verify the dose delivered during treatment. A total of 40 TLD divided into two batches （one of 20 and other of 20 TLD） were used. Different doses of Co6~ beam were delivered to the TLD chips at different depths. Diodes were irradiated at different depths in a （30 x 30 x 30） cm3 water slab phantom with various conditions of Field sizes, monitor units and SSDs. Results： The limitation of the in-vivo dosimetry technique is that dose can only be in system readout difficulty and type of readout （TLD system and diode） as the patient dose is directly measured. Several authors have investigated the measurements was 1.3%, with a standard deviation of 2.6%. Results were normally distributed around a mean as -0.39 and 0.34 respectively. After the evaluation of in vivo dosimetry brain case as an example, the mean doses for both eyes were 1.8%, with a standard deviation of 2.7%. These results are similar to studies conducted with diodes and TLD＇s. Conclusion： The diode is superior to TLD, since the diode measurements can be obtained on line and allows an immediate check. Other advantages of diodes include high sensitivity, good spatial resolution, and small size, simplicity of used.

瓦里安VitalBeam直线加速器Portal Dosimetry验证通过率低故障维修

目的分析了瓦里安直线加速器得基本工作原理及故障现象,结合实际工作经验,设计合理得检修步骤,帮助医院临床工程师更快、更准确解决故障根源.方法从直线加速器结构和原理出发,结合实际工作阐述Portal Posimetry验证通过率较低故障排除方法.结果通过科学的循序渐进排查,直线加速器的突发故障现象最终得以解决.结论总结瓦里安直线加其VitalBeam中日常QA软件Portal Posimetry的作用和故障现象,为医院临床工程师和相关大型医疗设备使用维护提供参考.

Improving patient care and accuracy of given doses in radiation therapy using in vivo dosimetry verification

Objective This work aims to verify and improve the dose given for cancer patients in radiation therapy by using diodes to enhance patient in vivo dosimetry on a routine basis. Some characteristics of two available semi-conductor diode dosimetry systems were evaluated. Methods The diodes had been calibrated to read the dose at Dmax below the surface. Correction factors of clinical relevance were quantified to convert the diode readings into patient dose. The diode was irradiated at various gantry angles （increments of 45~）, various Field Sizes and various Source to Surface Distances （SSDs）. Results The maximal response variation in the angular response with respect to an arbitrary angle of 0~ was 1.9%, and the minimum variation was 0.5%. The response of the diode with respect to various field siz- es showed the minimum and the maximum variations in the measured dose from the diode; the calculated doses were -1.6% （for 5 cm x 5 cm field size） and 6.6% （for 40 cm x 40 cm field size）. The diode exhibited a significant perturbation in the response, which decreased with increasing SSD. No discrepancies larger than 5% were detected between the expected dose and the measured dose. Conclusion The results indicate that the diodes exhibit excellent linearity, dose reproducibility and minimal anisotropy; that they can be used with confidence for patient dose verification. Furthermore, diodes render real time verification of the dose delivered to patients.

Machine Performance Check束流均匀性改变对Portal Dosimetry计划剂量验证的影响

目的:探究Machine Performance Check(MPC)系统束流均匀性变化对Portal Dosimetry(PD)计划验证的影响,为临床MPC均匀性的阈值设定和电子影像系统(EPID)的校准频率提供参考。方法:选取本中心EDGE加速器上首次治疗患者26例和10 cm×10 cm方野1例,制定治疗计划和验证计划。在MPC束流均匀性偏差增大的情况下,分别在EPID校准前和校准后执行验证计划,并在计划系统PD模块中分析,统计对比图像剂量和γ通过率。本研究还列出EDGE加速器一年间MPC束流均匀性的结果。结果:MPC 1年的统计结果显示束流均匀性偏差的升高趋势明显并且速度加快,表明EPID存在设备老化现象。EPID校准前后验证计划的图像剂量和γ通过率的对比结果表明不同能量方野计划在影像板中心附近的剂量差异为1%~2%,临床射野计划由于复杂性提高,剂量差异最大可以达到10%。EPID校准后的γ通过率高于校准前。结论:EPID探测器的一致性改变对PD计划剂量验证有一定影响,提示临床MPC均匀性阈值为2%时能够对PD计划剂量验证起到预警作用,EPID应在MPC重新采集基线之前校准,以保证验证计划的质量,保证患者放疗的安全性。

Dosimetry Comparison between Volumetric Modulated Arc Therapy with RapidArc and Fixed Field Dynamic IMRT for Local-Regionally Advanced Nasopharyngeal Carcinoma

Objective: A dosimetric study was performed to evaluate the performance of volumetric modulated arc radiotherapy with RapidArc on locally advanced nasopharyngeal carcinoma (NPC). Methods: The CT scan data sets of 20 patients of locally advanced NPC were selected randomly. The plans were managed using volumetric modulated arc with RapidArc and fixed nine-field coplanar dynamic intensity-modulated radiotherapy (IMRT) for these patients. The dosimetry of the planning target volumes (PTV), the organs at risk (OARs) and the healthy tissue were evaluated. The dose prescription was set to 70 Gy to the primary tumor and 60 Gy to the clinical target volumes (CTV) in 33 fractions. Each fraction applied daily, five fractions per week. The monitor unit (MU) values and the delivery time were scored to evaluate the expected treatment efficiency. Results: Both techniques had reached clinical treatment’s requirement. The mean dose (Dmean), maximum dose (Dmax) and minimum dose (Dmin) in RapidArc and fixed field IMRT for PTV were 68.4±0.6 Gy, 74.8±0.9 Gy and 56.8±1.1 Gy; and 67.6±0.6 Gy, 73.8±0.4 Gy and 57.5±0.6 Gy (P<0.05), respectively. Homogeneity index was 78.85±1.29 in RapidArc and 80.34±0.54 (P<0.05) in IMRT. The conformity index (CI: 95%) was 0.78±0.01 for both techniques (P>0.05). Compared to IMRT, RapidArc allowed a reduction of Dmean to the brain stem, mandible and optic nerves of 14.1% (P<0.05), 5.6% (P<0.05) and 12.2% (P<0.05), respectively. For the healthy tissue and the whole absorbed dose, Dmean of RapidArc was reduced by 3.6% (P<0.05), and 3.7% (P<0.05), respectively. The Dmean to the parotids, the spinal cord and the lens had no statistical difference among them. The mean MU values of RapidArc and IMRT were 550 and 1,379. The mean treatment time of RapidArc and IMRT was 165 s and 447 s. Compared to IMRT, the delivery time and the MU values of RapidArc were reduced by 63% and 60%, respectively. Conclusion: For locally advanced NPC, both RapidArc and IMRT reached the clinic requirement. The target volume coverage was similar for the different techniques. The RapidArc technique showed some improvements in OARs and other tissue sparing while using reduced MUs and delivery time.

SRS MapCHECK、ArcCHECK及Portal Dosimetry在立体定向治疗计划剂量验证对比

目的探究SRS MapCHECK(SRS)、ArcCHECK(Arc)及Portal Dosimetry(PD)3种剂量验证系统在立体定向治疗计划验证中的应用情况。方法随机选取在我院行立体定向放疗的肿瘤患者45例,依据治疗计划分别设计SRS、Arc及PD的验证计划,并在Varian VitalBeam直线加速器上执行。在10%剂量阈值下,记录3%/2 mm、3%/1 mm、2%/2 mm、2%/1 mm和1%/1 mm的γ评价标准下3种剂量验证系统治疗计划的通过率情况。结果3种剂量验证系统在不同的评价标准下得到的治疗计划的γ通过率存在差异,但在3%/2 mm和2%/2 mm评价标准下,SRS和PD验证得到的γ通过率无显著差异(P值均>0.05);在3%/1 mm、2%/1 mm和1%/1 mm评价标准下,Arc和PD验证得到的γ通过率无显著差异(P值均>0.05);在确定治疗计划是否可行上,SRS优于Arc和PD,PD略优于Arc。结论3种剂量验证系统都可用于立体定向治疗计划的剂量验证,其中SRS因具有较高的空间分辨率,在立体定向治疗计划验证上优势明显,临床应用时可优先考虑,此外,SRS剂量验证较严格的γ评价标准可采用2%/1 mm,Arc和PD剂量验证较严格的γ评价标准可采用2%/2 mm或3%/1 mm。

Proton therapy dosimetry using positron emission tomography

Protons deposit most of their kinetic energy at the end of their path with no energy deposition beyond the range, making proton therapy a valuable option for treating tumors while sparing surrounding tissues. It is imperative to know the location of the dose deposition to ensure the tumor, and not healthy tissue, is being irradiated. To be able to extract this information in a clinical situation, an accurate dosimetry measurement system is required. There are currently two in vivo methods that are being used for proton therapy dosimetry: (1) online or in-beam monitoring and (2) offline monitoring, both using positron emission tomography (PET) systems. The theory behind using PET is that protons experience inelastic collisions with atoms in tissues resulting in nuclear reactions creating positron emitters. By acquiring a PET image following treatment, the location of the positron emitters in the patient, and therefore the path of the proton beam, can be determined. Coupling the information from the PET image with the patient's anatomy, it is possible to monitor the location of the tumor and the location of the dose deposition. This review summarizes current research investigating both of these methods with promising results and reviews the limitations along with the advantages of each method.

Ionization Chamber Dosimetry for Conventional and Laser-Driven Clinical Hadron Beams

The practice of using the direct ionization radiation (electrons, protons, antiprotons, pions, ions, etc) or of the indirect ionization radiation (photons, neutrons, etc) in economy and social life has led to the introduction of the absorbed dose magnitude (ICRU 1953) defined as the energy absorbed per mass unit of the irradiated substance. This is a fundamental magnitude valid for any type of ionizing radiation, any irradiated material and any radiation energy. In case of clinical hadron beams generated by conventional accelerators or those controlled by lasers, IAEA TRS 398 recommends the absorbed dose to water. This may be determined employing the calorimeter method with water or graphite, chemical method, fluence based measurements as Faraday cups or activation measurements, and the ionization chamber method. In this paper the selected method was the thimble air filled ionization chamber method for determination of absorbed dose to water.

Applicability of Lung Equivalent Phantom Using the Cork with Absorbed Water in Radiotherapeutic Dosimetry

The radiation dosimetry in medical practice requires special phantom to simulate the organs and tissues of a human body. To achieve the same elemental composition as that of the human lung by weight percent, we constructed lung equivalent phantom (LEP) using cork with absorbed water in order for it to uniformly absorb the water. Then, we presented the physical properties and dosimetric characteristics of other commercial phantoms and the LEP. We found that the physical properties and dosimetric characteristics of the LEP were approximately the same as those of human lung tissue. LEP constitutes a new dosimetry tool because it can provide the dose distributions and point doses similar to those for the body with respiratory motion of lung.

A Novel Technique to Validate Dosimetry for Single-Isocenter Multiple-Target VMAT Stereotactic Radiosurgery

Each year, 170,000 cancer patients in the United States develop brain metastases. Many of them present with multiple small lesions. Historically, Linac-based stereotactic radiosurgery (SRS) was used to treat single solitary brain metastasis with a diameter of less than 3.0 cm, while whole brain radiation therapy (WBRT) was used to treat multiple brain metastases mainly as palliative therapy. Evidence-based practices reveal that WBRT results in poor treatment outcomes, with high local recurrence rates, decreased cognitive function, and even the onset of dementia. Recently, volumetric modulated arc therapy (VMAT) SRS has been tested as an alternative treatment to WBRT. Owing to its inherent complexity and high risk, it is imperative to perform rigorous testing prior to its clinical implementation. In this paper, we present a novel technique for dosimetry validation of VMAT SRS.

Risk Management of Clinical Reference Dosimetry of a Large Hospital Network Using Statistical Process Control

Managing TG-51 reference dosimetry in a large hospital network can be a challenging task. The objectives of this study are to investigate the effectiveness of using Statistical Process Control (SPC) to manage TG-51 workflow in such a network. All the sites in the network performed the annual reference dosimetry in water according to TG-51. These data were used to cross-calibrate the same ion chambers in plastic phantoms for monthly QA output measurements. An energy-specific dimensionless beam quality cross-calibration factor, , was derived to monitor the process across multiple sites. The SPC analysis was then performed to obtain the mean, , standard deviation, σk, the Upper Control Limit (UCL) and Lower Control Limit (LCL) in each beam. This process was first applied to 15 years of historical data at the main campus to assess the effectiveness of the process. A two-year prospective study including all 30 linear accelerators spread over the main campus and seven satellites in the network followed. The ranges of the control limits (±3σ) were found to be in the range of 1.7% - 2.6% and 3.3% - 4.2% for the main campus and the satellite sites respectively. The wider range in the satellite sites was attributed to variations in the workflow. Standardization of workflow was also found to be effective in narrowing the control limits. The SPC is effective in identifying variations in the workflow and was shown to be an effective tool in managing large network reference dosimetry.

Variation in patient dose due to differences in calibration and dosimetry protocols

For precise and accurate patient dose delivery,the dosimetry system must be calibrated properly according to the recommendations of standard dosimetry protocols such as TG-51 and TRS-398. However, the dosimetry protocol followed by a calibration laboratory is usually different from the protocols that are followed by different clinics, which may result in variations in the patient dose.Our prime objective in this study was to investigate the effect of the two protocols on dosimetry measurements.Dose measurements were performed for a Co-60 teletherapy unit and a high-energy Varian linear accelerator with 6 and 15 MV photon and 6, 9, 12, and 15 MeV electron beams, following the recommendations and procedures of the AAPM TG-51 and IAEA TRS-398 dosimetry protocols. The dosimetry systems used for this study were calibrated in a Co-60 radiation beam at the Secondary Standard Dosimetry Laboratory(SSDL) PINSTECH,Pakistan, following the IAEA TRS-398 protocol. The ratio of the measured absorbed doses to water in clinical setting,D_w(TG-51/TRS-398), was 0.999 and 0.997 for 6 and15 MV photon beams,whereas these ratios were 1.013,1.009, 1.003, and 1.000 for 6, 9, 12, and 15 MeV electron beams, respectively. This difference in the absorbed dosesto-water D_w ratio may be attributed mainly due to beam quality(K_Q) and ion recombination correction factor.

Real-time dosimetry in external beam radiation therapy

With growing complexity in radiotherapy treatment delivery,it has become mandatory to check each and every treatment plan before implementing clinically.This process is currently administered by an independent secondary check of all treatment parameters and as a pre-treatment quality assurance (QA) check for intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy treatment plans.Although pre-treatment IMRT QA is aimed to ensure the correct dose is delivered to the patient,it does not necessarily predict the clinically relevant patient dose errors.During radiotherapy,treatment uncertainties can affect tumor control and may increase complications to surrounding normal tissues.To combat this,image guided radiotherapy is employed to help ensure the plan conditions are mimicked on the treatment machine.However,it does not provide information on actual delivered dose to the tumor volume.Knowledge of actual dose delivered during treatment aid in confirming the prescribed dose and also to replan/reassess the treatment in situations where the planned dose is not delivered as expected by the treating physician.Major accidents in radiotherapy would have been averted if real time dosimetry is incorporated as part of the routine radiotherapy procedure.Of late real-time dosimetry is becoming popular with complex treatments in radiotherapy.Realtime dosimetry can be either in the form of point doses or planar doses or projected on to a 3D image dataset to obtain volumetric dose.They either provide entrance dose or exit dose or dose inside the natural cavities of a patient.In external beam radiotherapy,there are four different established platforms whereby the delivered dose information can be obtained:(1)Collimator;(2)Patient;(3)Couch;and(4)Electronic Portal Imaging Device.Current real-time dosimetric techniques available in radiotherapy have their own advantages and disadvantages and a combination of one or more of these methods provide vital information about the actual dose delivered to radiotherapy patients.

A SIMPLIFIED IN VIVO DOSIMETRY FOR TOTAL BODY IRRADIATION PRIOR TO BONE MARROW TRANSPLANTATION

For TBI (total body irradiation) prior to BMT(bone marrow transplantation )and in order to guarantee exact treatment,it is necessary to perfect in vivo dosimetry to detect any deviation of the treatment and to verify the dose dis-tribution. A simplified and convenient transmission type in vivo dosimetry and problems are introduced and discussed.

A Clinical Dosimetry Analysis of Total Body Irradiation for Leukemia Patients

Background and Purpose: To perform a retrospective in vivo dosimetry study of 129 total body irradiation (TBI) on leukemia and bone marrow transplant patients treated in our clinic from 2008 to 2011 and to find out if there is any indication of the necessity of developing a new efficient TBI approach. Materials and Methods: The in vivo dosimetry data of 129 patients treated with TBI between 2008 and 2011 were retrieved from the database and analyzed. These patients were mostly treated with the regime of a single fraction or 6 fractions with some exceptions of 8-fraction or 2-fraction treatments depending on the protocols that were applied. For every fraction of treatment, 10 pairs of diode dosimeters were used to monitor the doses to the midline of head, neck, arms, mediastinum, left lung, right lung, umbilicus, thigh, knee, and ankle for both AP and PA fields. The doses to the midline of the above body parts were considered to be the average of the AP and PA readings of each diode pair. Dose deviation from the prescribed value for each body part was studied by plotting the histogram of the frequency versus deviation and comparing this with the dose delivered to the midline of the umbilicus to where the dose was prescribed. The correlation of dose deviation to body part thickness was also studied. By studying the dose deviations, we can find the uniformity of general dose distributions for conventional TBI treatments. Results: The retrospective dosimetry study of the 129 TBI patient treatments indicates that for most of the patients treated in our clinic, the doses received by different body parts monitored with in vivo dosimetry were within the window of 10% difference from the prescribed dose. The inhomogeneity of dose on different body parts could be manually improved by using compensators, but the method is cumbersome and time consuming. The dose deviation in many histograms ranging from about ?10% to 10% indicates some incongruity of dose distribution. This could be due to the method of using lead compensators for a manual dose adjustment which could not ideally compensate for different body thicknesses everywhere. Conclusions: The conventional TBI could give uniform dose to the major body parts under the online in vivo dosimetry monitoring at the level of 10%, but the treatment procedure is cumbersome and time consuming. This implies the importance of developing a new and efficient TBI method by adopting modern radiation therapy technique.

Evaluation of Mid-Plane Dose by Flat Panel Transit Dosimetry Method and by EBT2 Film Incident Dosimetry

Purpose: The aim of this study is to validate an easily applicable flat panel dosimetry method based on the back projection approach and to compare this method with the incident dosimetry by EBT2 film method for mid-plane dose calculations. Methods: The dosimetric characteristics of the flat panel were determined for 6 MV photon energy. Then, the methodology to calculate the dose on the central axis of the photon beam was described. While, the flat panel dosimetry method was validated with phantom measurements using an ionization chamber. Once the method was validated, in vivo measurements of ten prostate patients treated with 6 MV photon energy 3D conformal plans were also performed both with the flat panel and the EBT2 films. Results: The phantom measurements revealed a mean dispersion of 1.7% between flat panel and ionization chamber doses and 2.2% between flat panel and EBT2 film doses. While, the in vivo measurements in prostate patients revealed a mean dispersion of 0.8% between flat panel doses and treatment planning calculated doses and 1% between flat panel and EBT2 film doses. Conclusions: The presented flat panel dosimetry method is accurate, easily applicable to all types of flat panels without the use of any sophisticated software and is not time consuming.

Position Verification of the RADPOS 4-D <i>In-Vivo</i>Dosimetry System

The accuracy of the position measurements obtained by the radiation positioning system (RADPOS) was evaluated under static and dynamic conditions. In the static verifications, the RADPOS was fixed to the treatment couch in a photon treatment room and a proton treatment room, and was translocated with the treatment couch in x, y and z directions. Because the presence of magnetic and/or electrically conductive materials can cause a systematic shift in the measured position by distorting the RADPOS transmitted field, the effect of metals on the performance of the positioning system was also investigated. Dynamic verification was performed using the couch drive and a dynamic anthropomorphic thorax phantom. We thus confirmed the utility of RADPOS as a position sensor to perform in vivo dosimetry.

Thermal Equilibration in the Cavity Volume of a Farmer Ion Chamber for Routine Dosimetry

A Farmer ion chamber with an air cavity volume is the most widely used dosimeter for accurate dose determinations in radiotherapy. The quantity of ionization in the cavity volume occurred a given radiation dose has to be corrected to the cavity air temperature according to a dosimetry protocol because the mass of air in the cavity volume is subject to atmospheric variations. In the present study, we aim to measure the thermal equilibration time in the cavity volume of a Farmer ion chamber for the routine dosimetry. The Farmer ion chamber’s electrode was replaced by a thin thermocouple and coated by the PMMA for a waterproofing so that the measurement of the temperature in the cavity performed in water. As a result of the measurement, A Farmer ion chamber in thermal equilibrium with waterproofing equilibrates rapidly, followed by an exponential fall-off. In water, equilibration to less than 10% of the initial temperature difference required only a few minutes. Thermal equilibrium time is hardly affected by the room temperature change.

<i>In-Vivo</i>Dosimetry Method for Measuring Peak Surface Dose Using Radiochromic Films during Computed Tomography Scanning of the Sinus

Purpose: During computed tomography (CT) helical scanning mode the patient surface dose distribution is assumed to be non-uniform, therefore point dose measurement methods may lead to imprecise estimation of the radiation dose received by the patient skin in particular. We have used XRQA2 films as in-vivo dosimeters to measure the entrance skin dose during sinus exams. Methods: The films were placed under the patient head rest in order to sample the entrance surface dose in-vivo. We have performed in-vivo film irradiation on 23 patients in this study to verify the clinical suitability of the method and were found adequate. Results: The measured average ESD in the sinus exam was 11.7 ± 1.0 mGy, the PSD was 15.7 ± 1.7 mGy and the CTDI(vol) was 13.3 ± 0.1 mGy. The ratio of ESD/CTDI(vol) and PSD/CTDI(vol) was 0.88 and 1.18 respectively. The results indicate that the scanner registered CTDI(vol) underestimates the PSD and in the same time it overestimates the ESD by 18% and 13.6% respectively. Conclusion: The observed differences between the ESD, PSD and CTDI(vol) although seem small for the radiation dose range measured during CT of the sinus [13.2 - 13.4] mGy, but important for the medical physicist to know, since monitoring of patients’ doses from CT examinations is becoming more mandatory. The use of radiochromic film as in-vivo dosimeter does not interfere with the clinical radiological exam and does not produce any image artifacts. The method can be used to study other CT examinations specially the ones with large beam width, high pitch factor and high dose exams. The method allows measurement of the peak skin dose, examination of the CT dose profile and the 2D dose distribution in the XZ plan.