Use Of Wedge Filters Research Articles

Experimental evaluation of a radiation dose management system-integrated 3D skin dose map by comparison with XR-RV3 Gafchromic® films

ObjectiveTo assess the interactive Skin Dose Map® tool (SDMTool) integrated to the radiation dose management system (RDMS) DoseWatch® with Gafchromic® films for implementation in routine practice. MethodsA retrospective dose estimation software SDMTool was used to calculate Peak Skin Dose (PSD) and display the patient skin dose distribution. PSD was calculated with a triangle mesh of 0.055 cm2 resolution on ICRP 110 male anthropomorphic phantom and with a square ROI of 1 cm2 on flat phantom. The tool uses Radiation Dose Structured Reports (RDSR) data to model exposure events and calculate the PSD per event. The PSD and the skin dose distribution estimated with SDMTool were evaluated in comparison with Gafchromic® films positioned under the PMMA phantom (20 cm) for 13 configurations. Measurements were performed on a Philips system. Statistical analysis were carried out to compare PSDFilm and PSDSDM. ResultsAverage differences between PSDFilm and PSDSDM were 6% ± 6% (range from −3% to 22%) for flat phantom and 5% ± 7% (range from −3% to 25%) for ICRP phantom. Concordance was good between the measured PSDFilm and the estimated PSDSDM with Lin’s coefficient estimation and 95% Confidence Interval of 0.979 [0.875; 0.984] for flat phantom and 0.977 [0.877; 0.985] for ICRP phantom. Dose map representations are concordant for 11 of the 13 tests on PMMA phantom. Disparities arose from the limitations of the RSDR format: table displacement during fluoroscopy events and the use of wedge filter. ConclusionThe results found in this experimental evaluation show that the SDMTool is a suitable alternative to Gafchromic® film to calculate PSD.

Characterization of GaN dosimetry for 6 MV photon beam in clinical conditions

We characterized a recently proposed implantable GaN-based dosimeter in clinical conditions, for its application in external radiotherapy according to ESTRO (European Society for Radiotherapy & Oncology) practical guidelines. Our studies were carried out using a 6 MV photon beam with the dosimeter under test in a water tank or a PMMA phantom. They were focused on evaluating short term and long term reproducibility of measurements, and assessing the effects of parameters such as field size, source-skin distance, use of wedge filter, beam incidence, dose rate, accumulated dose, GaN-induced dose perturbation, air cavities and temperature. The estimated repeatability and reproducibility are better than 0.5% and 2% at 1σ respectively. There are no significant effects of the parameters under our studies, apart from field size and temperature. The field-size dependence is due to over-compensation of the GaN response method of the dosimeter, the resulting errors remain lower than 5% for field sizes up to 10 × 10 cm2. The temperature dependence mainly results from the GaN luminescence properties, and causes the GaN response to decrease steadily when increasing temperature, with a sensitivity of −1.4%/°C. The observed quasi-linear temperature dependence may facilitate the correction to improve the accuracy of measurements.

Radiation Therapy for Early Glottic Carcinoma: Factors Influencing the Outcome.

To evaluate the influence of mid treatment hemoglobin level with the other prognostic factors on the outcome in patients with TisT1N0 glottic carcinoma treated with radiotherapy (RT). Between October 1995 and December 2008, a total of 84 patients diagnosed with Tis-T1N0 glottic carcinoma were treated with definitive RT. The influence of tumor, treatment, and patient-related factors on local control (LC) and overall survival (OS) were analyzed. The median follow up time was 30 months (ranges, 4-180 months). Local and/or locoregional relapse was observed in 11 patients (13%) (3 locoregional and 8 local). The estimated 5- and 10-year LC and OS rates were 87%, 85%, and 87%, 70% for the entire study group, respectively. Multivariate analyses revealed that older age (≥50 years) and the use of wedge-filter were found to be favorably influencing the LC (p= 0.025 and p= 0.030, respectively). Mid treatment hemoglobin level more than 13 g/dl was determined statistically significant for improving both LC and OS (p= 0.011 and p= 0.021). Older age and use of wedge filter were found to be independent prognostic factors for LC. Mid treatment hemoglobin level of more than 13 g/dl was correlated to superior LC and OS rates. Monitoring the changes of hemoglobin levels during therapy has to be considered to improve the outcome.

SU-DD-A1-06: Improving Patient Safety through a Simple Independent On-Line Beam Monitoring System

Purpose: To investigate the effectiveness of an independent on-line monitor for validation of beam delivery. Method and Materials: An on-line beam monitoring system consisting of a spatially sensitive large area ionization chamber mounted below the MLC, has been tested to validate treatment beams. The accuracy of a beam delivery is ensured by comparing the measured ion chamber signals with the pre calculated expected values. The system performance has been evaluated by phantom treatments of 20 patients' IMRT plans for various anatomic sites, delivered in multiple fractions over a period of six months. The performance of the system has been analyzed in terms of reproducibility, dosimetry and sensitivity. The sensitivity of the system has been evaluated by introducing a number of probable errors, including errors in MLC leaves and jaw positions. The uniqueness of signals per field, in terms of a temporal signature has been investigated by calculating a statistical index between IMRT fields taken from plans of same anatomic site. Results: The system response was reproducible to within 0.4%. The agreement between the calculation and measured signals for prostate IMRT field segments were within 1% on average, with a maximum deviation of 5%. The system response for a small geometrical segment changed by 2% for a leaf bank calibration error of 1 mm or a single leaf positioning error of 3 mm. Incorrect fields and incorrect use of wedge filters were easily identified. To date all the fields have been found to have unique temporal signature. Conclusion: An independent simple on-line beam monitoring system has been tested for validation of beam delivery. The results of a clinical simulation study demonstrated that the system is capable of validating daily beam delivery and capturing probable errors. The system could potentially improve quality and patient safety in radiation therapy

Measurement of Photoneutron Dose Produced by Wedge Filters of a High Energy Linac Using Polycarbonate Films

Radiotherapy represents the most widely spread technique to control and treat cancer. To increase the treatment efficiency, high energy linacs are used. However, applying high energy photon beams leads to a non-negligible dose of neutrons contaminating therapeutic beams. In addition, using conventional linacs necessitates applying wedge filters in some clinical conditions. However, there is not enough information on the effect of these filters on the photoneutrons produced. The aim of this study was to investigate the change of photoneutron dose equivalent due to the use of linac wedge filters. A high energy (18 MV) linear accelerator (Elekta SL 75/25) was studied. Polycarbonate films were used to measure the dose equivalent of photoneutrons. After electrochemical etching of the films, the neutron dose equivalent was calculated using Hp(10) factor, and its variation on the patient plane at 0, 5, 10, 50 and 100 cm from the center of the X-ray beam was determined. By increasing the distance from the center of the X-ray beam towards the periphery, the photoneutron dose equivalent decreased rapidly for the open and wedged fields. Increasing of the field size increased the photoneutron dose equivalent. The use of wedge filter increased the proportion of the neutron dose equivalent. The increase can be accounted for by the selective absorption of the high energy photons by the wedge filter.

Dynamic conical conformal radiotherapy using a C-arm–mounted accelerator: dose distribution and clinical application

Purpose The aim of this study was to solve anisotropy in the dose distributions from rotational conformal radiotherapy (RCRT) by using a C-arm–mounted accelerator. Methods and materials The linac head was designed to move along the C-arm with a maximum angle of 60° (from a vertical position toward the gantry). Simultaneous rotation of the gantry creates a dynamic conical irradiation technique. Dynamic conical conformal radiation therapy (Dyconic CRT) was developed by combining the technique with continuous motion of a multileaf collimator. Dose distributions were measured in phantoms using film densitometry and compared with conventional RCRT. Dose distributions in actual radiation therapy patients are also presented. Results Dyconic CRT enabled the precise delivery of noncoplanar beams without rotating the table. The measurements showed that three-dimensionally isotropic dose falloff was achieved with Dyconic CRT. Dose inhomogeneity in the sagittal direction with Dyconic CRT was compensated for by use of wedge filters. Conclusions The drawbacks of the dose distributions produced by RCRT were overcome with the use of Dyconic CRT.

Evaluation of the peripheral dose to uterus in breast carcinoma radiotherapy.

The absorbed dose outside of the direct fields of radiotherapy treatment (or peripheral dose, PD) is responsible for radiation exposure of the fetus in pregnant women. Because the radiological protection of the unborn child is of particular concern in the early period of the pregnancy, the aim of this study is to estimate the PD in order to assess the absorbed dose in the uterus in a pregnant patient irradiated for breast carcinoma therapy. The treatment was simulated on an Alderson-Rando anthropomorphic phantom, and the radiation dose to the fetus was measured using an ionisation chamber and thermoluminescence dosemeters. Two similar treatments plans with and without wedges were delivered, using a 6 MV photon beam with two isocentric opposite tangential fields with a total dose of 50 Gy, in accordance with common established procedures. Average field parameters for more than 300 patients were studied. Measurements showed the fetal dose to be slightly lower than 50 mGy, a level at which the risk to the fetus is uncertain, although several authors consider this value as the dose threshold for deterministic effects. The planning system (PS) underestimated PD values and no significant influence was found with the use of wedge filters.

A patient dose verification program using diode detectors

In this work, we present a comprehensive patient dose verification program using a commercial dual diode detector system for external photon beam radiotherapy. To achieve acceptable accuracy, factors potentially affecting diode sensitivity need to be carefully considered in dose determination. Several authors have shown that diode sensitivity depends on temperature, saturation, linearity, radiation damage, and beam incidence angle. In addition, we found that the use of wedge filters, block trays at a close distance to the detectors, variation in radiation field size, as well as measurement SSDs may affect diode sensitivity significantly. In practice, we use a 5% dose deviation of measured dose from expected patient dose to prompt reevaluation of patient dosimetry. This yields a 90% acceptance rate in clinical patient cases.

Use of a CT simulator in radiotherapy treatment planning for breast conserving therapy

A CT simulator (CT-S) is a real-time, CT-linked, 3-D treatment planning system, which consists of a CT scanner, a multi-image display, a treatment planning device with real-time visual optimization, and a laser beam projector. This system was clinically evaluated in 339 Stage 0,I and II breast cancers in 337 patients who received breast conserving therapy. Following quadrantectomy or wide excision with complete axillary dissection, a total of 50 Gy was delivered to the ipsilateral breast using 60Co γ-rays. In patients with involved surgical margins, boost electron irradiation was also given. Treatment planning could be accomplished within 40–50 min using the CT-S. The parameters for the tangential portals could be optimized for each patient, and the wedge filters and the electron energy for boost irradiation could be appropriately selected. The incidence of moist desquamation and depigmentation at the areola was slightly decreased with the use of wedge filters. During the follow-up for 2–71 months (median, 22 months), local recurrence and symptomatic radiation pneumonitis occurred in one patient each. The CT-S appears to be useful for the individualized optimization of tangential irradiation fields in breast conserving therapy.

Quality assurance of the EORTC trial 22881/10882: “assessment of the role of the booster dose in breast conserving therapy”: the Dummy Run

The EORTC trial 22881/10882 is a randomised trial with the aim to assess the role of the boost dose in breast conserving therapy in stage I and II breast cancer. In order to detect potential protocol deviations concerning irradiation technique and in the dose specification procedure of participating institutions before actual patient accrual, a Dummy Run was performed. Three transverse sections of a patient were sent to 16 participating institutions with a request to make a three-plane treatment plan according to the protocol prescriptions. A treatment chart and beam data were also requested for recalculation of the dose. Additional information was asked in a questionnaire. On evaluation, the techniques differed considerably with respect to photon beam energy, varying between 60Co gamma-rays and 8 MV X-rays, and the use of wedge filters. Two institutions did not apply wedges, whereas wedge angles in the other institutions varied between 6° and 45°. Twelve institutions used collimator rotation and/or a table wedge to diminish the amount of irradiated lung volume. The dose was specified in a point according to the protocol prescription in 11 institutions and to the 90, 95 or 100% isodose curve in four. Twelve institutions applied lung density corrections during treatment planning, while nine reported problems with their planning system in off axis dose distribution calculation and/or the simulation of collimator rotation. Recalculation of the dose at the isocentre showed agreement within 2% compared with the stated dose. The dose reported in the tumour excision area varied between 93 and 100%. It can be concluded that good accordance and high quality breast irradiation can be achieved by all institutions participating in the trial, provided a few recommendations are followed. The results of this analysis show the necessity and usefulness of a quality assurance programme at the initial phase of a clinical trial.

The use of wedge filters to improve dose distribution with the partial rotation technique.

Rotational arcs covering less than 360 degrees are frequently used in order to spare critical structures in radiation therapy; however, this results in a lack of dose uniformity in the target volume. Wedge filters can be used to restore dose uniformity in the treatment volume when limited arcs are employed. The authors emphasize the use of small rotational arcs (less than 90 degrees) in treating eccentrically located tumors such as those of the spinal cord and describe a simple model which can be used to calculate the wedge angle as a function of the arc angle.

Conventions for wedge filter specifications.

The use of wedge filters in radiation therapy is well established. With the recent increase in the use of megavoltage radiation equipment, there has been a corresponding increase in the use of wedge filters, particularly in the U.S.A. Agreed conventions for specification of wedge field size, wedge angle, wedge isodose normalization, wedge factor and wedge isodose display therefore become increasingly important to both user and manufacturer. The intent of this letter is to suggest that such conventions be adopted.

An Indicator and Recorder for Checking Diaphragm Settings on a Cobalt 60 Unit

An applicator on a conventional X-ray set is used both to limit the field size and to assist in setting up to the patient. Since the applicator is a detachable and therefore more obvious component, there is little chance of error and use of the wrong field size. With high-energy units, however, it is usual to adjust the field size by variable diaphragms at a distance from the patient and hidden within the cover of the machine. The field size set is not obvious, and it is possible for the operator to forget to adjust the diaphragms or adjust them wrongly (particularly, for example, to set 8 × 10 cm instead of 10 × 8 cm). These errors are less likely where the field size is shown on the patient by an area of light from a built-in light source. This facility is not available on the unit at Oxford (constructed by Messrs. Husband & Co., Sheffield), and even if it were the frequent use of wedge filters or metal compensators (Ellis, Lewis, Oliver and Hall, 1959) would mean that such a light beam would not be visible on the skin, at any rate in the final stages of the set up. However, some check on the setting of the diaphragms appeared to be desirable. In multifield systems the same field settings may be used for several consecutive treatments, and it would therefore be inconvenient to reset the diaphragms each time.

Simultaneous lateral placentography.

In an attempt to localize the placenta radiographically in the third trimester, notably in patients who have histories of bleeding or are proposed for cesarean section, we have tried a variety of technics. In our hands, these have met with varied success, and numerous advantages and disadvantages have been noted. We were perplexed by our results with direct placentography by the so-called “soft-tissue technic,” particularly the lateral view. Exposure sufficient to demonstrate the posterior uterine wall is usually too penetrating to delineate the anterior abdominal and uterine walls and the converse is also true. The necessity for two sets of films thus arises. The vagaries of sight development technic become pronounced except in experienced hands, which are not always available in all institutions. To overcome some of these handicaps, a number of authors have made use of wedge filters or differential intensifying screens. The former, however, are not readily available commercially and the latter require a...

Wedge filters for use with a 100-curie cobalt 60 teletherapy unit.

Wedge filters have proved to be of considerable help to the radiotherapist in planning X-ray treatments of tumours accessible to irradiation by two angled fields (Ellis and Miller, 1944). By their use it is possible to deliver a reasonably homogeneous dose to lesions whose satisfactory irradiation would be impracticable with conventional field layouts. The 100-curie cobalt 60 beam unit at the General Infirmary at Leeds operates at a source-skin distance of 20 cm and produces a γ-ray output and percentage depth doses similar to those from a 200–250 kV X-ray machine at 50 cm F.S.D. (Spiers and Morrison, 1955). In these circumstances a need for wedge filters has arisen, for reasons similar to those which hold in X-ray work. The use of wedge filters with γ radiation was mentioned by Johns (1954) in connection with the kilo-curie unit at Saskatoon. This note describes the construction and measurement of wedge filters for the 100-curie unit and discusses some general principles of their design. In the clinical use of this unit, field localisation and satisfactory beam direction are achieved by setting up the applicator against the aluminium sheet facing of a wax jig specially made to fit the appropriate part of the patient. Such an individual jig obviously offers a suitable place for devices peculiar to the treatment of that patient.

Device for the control of radiation distribution in moving beam therapy.

When a physician implants radium or other radioactive material in tissues in the pelvis following a cycle of roentgen therapy, he is attempting to improve the distribution pattern of radiation or energy absorbed in certain specific areas. If we ask, what, from a physical standpoint, constitutes an approach to an ideal radiation technic, one of the answers may be stated as follows. It is the production within the body of three-dimensional isodose curves at some specific optimum level of dosage whose shape will closely approximate the shape of the particular tissue mass under treatment; the dosage within the mass outlined by such isodose curves shall be relatively uniform and of a high order of magnitude relative to dosage external to the mass. Although we cannot, strictly speaking, add up in r units and equivalents the tissue or integral dose from varying sources such as x-radiation and gamma emitters, none the less it is quite generally agreed that the type of radiation is of little particular importance, provided the distribution of energy absorption is satisfactory. Howard Nielsen (1) and others (2) have plotted numerous isodose curves for rotational roentgen therapy in the medium-voltage range and have pointed out that, particularly in the pelvis, the shape of the curves and therefore the distribution from simple rotational or pendulum therapy alone is not satisfactory. Nielsen states: “Both the rotatory axis and the target axis distance are fixed.” After careful consideration of all the factors affecting the shape of isodose curves within various portions of the body, including use of wedge filters and multiple positioning of the centers of rotational cycles, it becomes apparent that, if rotational therapy in the medium-voltage range is employed, variation of both the target-skin and target-tumor distance, together with variation of milli-amperage or speed during the rotational cycle, must be accomplished in order to modify satisfactorily the distribution of the radiation. Thus, we may rotate a patient in a vertical or horizontal axis, concomitantly varying the target-skin distance, or we may keep the patient motionless while moving the radiation source through an irregular orbit about the tumor, and preferably in more than one plane. If we rotate the patient around a vertical axis, then the patient must sit up or stand erect lashed to some supporting framework. Not only is this an unpleasant and oftentimes a frightening procedure, but in many instances it may be prohibited by the physical condition of the patient. Organs, particularly in the abdomen and pelvis, assume different positions and relationships with the patient vertical than when he is prone or supine. Also, because of fatigue and relaxation, the relationship of organs may and probably will change even during the period of rotation.

A note on the use of wedge filters in transparent ended x-ray therapy applicators.

A description is given of the use of removable wedge filters at the top diaphragm of standard transparent ended X-ray therapy applicators, together with details of construction and resulting isodose curves.

The use of wedge filters in X-ray therapy

Summary To assist in obtaining uniform irradiation throughout the treated volume, techniques have been developed using wedge filters, i.e., non-uniform (metal) filters whose thickness varies in one direction across the field. Specifications are given of wedges for use with radiation of 1 mm. Cu h.v.l. and field sizes of 5 × 5 cm., 6 × 8 cm., 8 × 10 cm., and 10 × 15 cm. (the wedge directions being along the first of the two dimensions in each case) to produce isodose curves of approximately 45° slope. Measured isodose curves for these applicators are presented, together with field summations for two wedge fields at right angles, two wedge fields and a central normal field in a hemihexagonal arrangement, and two opposed wedge fields with a normal field at right angles. The use of these techniques in larynx, posterior tongue, antrum and ethmoid sinuses, nose, chest, and abdominal wall, limb, and cerebral treatments are discussed and illustrated by photographs. The use of a shallow wedge in superficial treatment of a curved surface is also briefly considered.

The Use of Wedge Filters in Deep X-ray Therapy

In the treatment of tumours by X-ray beams when the lesion is situated only a few centimetres deep to the skin, it is a matter of some difficulty to irradiate the tumour uniformly, using a cross-fire technique with the normal type of beam. This is especially so if it is desirable to avoid irradiating normal tissue deeper than the tumour. The irradiation of a tumour confined to one side of the floor of the mouth, for example, is not easy if it is desired to avoid strong irradiation of the other side of the mouth. The beams must then be confined to the affected side. The use of two or more normal fields directed at the tumour from one side of it gives an uneven dose distribution with a region of high dose near the surface. For a few years we have employed at the Sheffield Radium Centre a technique which we have called a “Wedge Technique” in an attempt to obtain uniformity of dosage in these circumstances without irradiating normal tissue more than necessary. The general principle is to introduce into the be...