The use of diode dosimetry in quality improvement of patient care in radiation therapy

The purpose of this work is to improve the quality of patient care in radiation therapy by implementing a comprehensive quality assurance (QA) program aiming to enhance patient in vivo dosimetry on a routine basis. The characteristics of two commercially available semi-conductor diode dosimetry systems were evaluated. The diodes were calibrated relative to an ionization chamber-electrometer system with calibrations traceable to the National Institute of Standards and Technology (NIST). Correction factors of clinical relevance were quantified to convert the diode readings into patient dose. The results of dose measurements on 6 patients undergoing external beam radiation therapy for carcinoma of the prostate on three different therapy units are presented. Field shaping during treatments was accomplished either by multileaf collimation or by cerrobend blocking. A deviation of less than ±4% between the measured and prescribed patient doses was observed. The results indicate that the diodes exhibit excellent linearity, dose reproducibility, minimal anisotropy, and can be used with confidence for patient dose verification. Furthermore, diodes render real time verification of dose delivered to patients.     

Dose-response study on thyrotoxic patients undergoing positron emission tomography and radioiodine therapy

With the acknowledged problems associated with assessment of functioning thyroid mass and hence radiation dose, our policy had been to give 75 MBq iodine-131 at 6-monthly intervals to patients with Graves' disease until they became euthyroid. Since positron emission tomography (PET) has been available at this hospital, the radiation dose to the thyroid has been calculated with an accuracy of 20%, the thyroid mass being determined from an iodine-124 PET scan. A dose-response study has been carried out on 65 patients who have received single or cumulative radiation doses of <80 Gy. The results show that patients who receive a low radiation dose (<20 Gy) at their first treatment have a high probability of remaining toxic at 12 months. In contrast, patients who receive higher radiation doses (>40 Gy) at their first treatment have a high probability of control. The probability of becoming euthyroid increases more rapidly with increasing radiation dose than the probability of becoming hypothyroid. Following this dose-response study, a new treatment protocol has been introduced. A ¹²⁴I PET tracer study prior to ¹³¹I therapy will be performed to enable a prescribed thyroid dose of 50 Gy to be delivered to patients with Graves' disease. Further ¹³¹I therapy will only be considered if patients are still toxic at 12 months.     

A method to obtain the same levels of CT image noise for patients of various sizes, to minimize radiation dose

The aim of this study was to develop a method of obtaining the same levels of CT image noise for patients of various sizes to minimize radiation dose. Two CT systems were evaluated regarding noise characteristics using phantoms and dosimetric measurements. Both CT systems performed well at dose levels used in normal clinical imaging, but only one was found to be suitable for low radiation dose applications. The CT system with the lowest noise level was used for further detailed studies. A simple strategy for manual selection of patient-specific scan parameters, considering patient size and required image quality, was implemented and verified on 11 volunteers. Images were obtained with at least the prescribed image quality at significantly reduced radiation dose levels compared with standard scan parameters. Depending on the diameter of the tomographic section, i.e. size of the subject, the dose levels could be reduced to 1-45% of the radiation dose with standard scan parameters (120 kV, 250 mAs, 10 mm). The results indicate a general potential for dose reduction in CT for slim patients. For tissue volume determination, large dose reductions can be achieved by adjusting the scan parameters for each individual. The concept of patient-specific scan parameters could be fully automated in the CT system design, but would require the scan to be specified in terms of image quality rather than X-ray tube load.     

A generic computer program for checking photon beam dose calculations

A computer program for checking photon external beam dose calculations is described. It provides a check of the treatment planning calculation by the use of machine data that are independent of that used in the initial calculation. Data required to specify any radiation beam are easily and rapidly set up and the program works for all the major manufacturers' machines. The user interface uses an interactive screen for machine data input and also for dose checking, where dose calculation is performed in real time as data are entered. The dose resulting from the planned field parameters is calculated and compared with the prescribed dose with a warning provided if the agreement is outside a set range (+/-5%). Its purpose is to act as a final quality assurance check to ensure that no significant errors occur in the monitor unit calculation.     

Spinal cord dose is higher than expected in head and neck radiation.

Myelopathy is a feared consequence of radiation therapy. Risk factors are multifocal; therefore, total dose calculation is crucial. We evaluated the contribution of scatter radiation to obtain an accurate cumulative spinal cord dose. Twenty patients undergoing three field head and neck radiation by Cobalt or 6 MV Linac had a total cord dose calculated from direct and scatter radiation. The cord was removed from the radiation field at tumor doses no higher than 4,400 cGy. Total tumor dose ranged from 5,400-7,400 cGy (mean 6060). All patients achieved the prescribed dose and none were lost to follow up (mean 36 months). It was found that scatter radiation can contribute as much as 20% extra dose to the spinal cord. Mean extra dose was 9% (range 1%-20%). This additional dose ranged from 52-810 cGy (mean 339 cGy). No apparent difference was seen with Cobalt or Linac source. Our conclusion was that significant additional dose is delivered to the spinal cord by scatter radiation and that scatter may contribute more to the development of myelopathy than previously believed.     

The equivalent dose contribution from high-dose-rate brachytherapy to positive pelvic lymph nodes in locally advanced cervical cancer

PurposeDefinitive radiation therapy for locally advanced cervical cancer involves external beam radiation therapy (EBRT) and high-dose-rate (HDR) brachytherapy. There remains controversy and practice pattern variation regarding the optimal radiation dose to metastatic pelvic lymph nodes (LNs). This study investigates the contribution of the pelvic LN dose from HDR brachytherapy.Methods and MaterialsFor 17 patients with 36 positive pelvic LNs, each LN was contoured on a computed tomography (CT) plan for EBRT and on brachytherapy planning CTs using positron emission tomographic images obtained before chemoradiation. The mean delivered dose from each plan was recorded, and an equivalent dose in 2-Gy fractions (EQD2) was calculated. A Student's t test was performed to determine if the mean delivered dose is significantly different from the mean prescribed dose and EQD2.ResultsThe average prescribed dose from the total EBRT was 54.09 Gy. The average prescribed HDR dose to International Commission on Radiation Units point A was 26.81 Gy. The average doses delivered to the involved LNs from EBRT and brachytherapy were 54.25 and 4.31 Gy, respectively, with the corresponding EQD2 of 53.45 and 4.00 Gy. There was no statistically significant difference (p < 0.05) between the mean delivered and the prescribed doses for EBRT and between the delivered dose and the EQD2 for EBRT and brachytherapy.ConclusionsOur study shows that the HDR contribution is 7% (4.00 Gy) of the total EQD2 (57.45 Gy). The HDR contribution should be accounted for when prescribing the EBRT boost dose to pelvic LNs for the optimal therapeutic dose.     

'Boomerang' technique: an improved method for conformal treatment of locally advanced nasopharyngeal cancer

The primary aim of the present study was to assess radiation dosimetry and subsequent clinical outcomes in patients with locally advanced nasopharyngeal cancer using a novel radiation technique termed the 'Boomerang'. Dosimetric comparisons were made with both conventional and intensity modulated radiation therapy (IMRT) techniques. This is a study of 22 patients treated with this technique from June 1995 to October 1998. The technique used entailed delivery of 36 Gy in 18 fractions via parallel opposed fields, then 24 Gy in 12 fractions via asymmetric rotating arc fields for a total of 60 Gy in 30 fractions. Patients also received induction and concurrent chemotherapy. The radiation dosimetry was excellent. Dose-volume histograms showed that with the arc fields, 90% of the planning target volume received 94% of the prescribed dose. Relative to other conventional radiation therapy off-cord techniques, the Boomerang technique results in a 27% greater proportion of the prescribed dose being received by 90% of the planning target volume. This translates into an overall 10% greater dose received for the same prescribed dose. At 3 years, the actuarial loco-regional control rate, the failure-free survival rate and the overall survival rate were 91, 75 and 91%, respectively. At 5 years, the actuarial loco-regional control rate, the failure-free survival rate and the overall survival rate were 74, 62 and 71%, respectively. The Boomerang technique provided excellent radiation dosimetry with correspondingly good loco-regional control rates (in conjunction with chemotherapy) and very acceptable acute and late toxicity profiles. Because treatment can be delivered with conventional standard treatment planning and delivery systems, it is a validated treatment option for centres that do not have the capability or capacity for IMRT. A derivative of the Boomerang technique, excluding the parallel opposed component, is now our standard for patients with locally advanced nasopharyngeal cancer when IMRT is not available.     

Balancing patient dose and image quality

The formation of images in diagnostic radiology involves a complex interdependence of many factors. The ideal balance is to obtain an image which is adequate for the clinical purpose with the minimum radiation dose. Factors which affect radiation dose and image quality can be grouped under three headings; radiation quality, photon fluence and removal of scattered radiation. If optimal performance is to be achieved, it is necessary to understand how these factors influence image formation and affect radiation dose, and apply methodology for image quality and dose analysis at each stage in the development and use of X-ray equipment.     

A planning study of simultaneous integrated boost with forward IMRT for multiple brain metastases

The objective of this study was to evaluate the dose conformity and feasibility of whole-brain radiotherapy with a simultaneous integrated boost by forward intensity-modulated radiation therapy in patients with 1 to 3 brain metastases. Forward intensity-modulated radiation therapy plans were generated for 10 patients with 1 to 3 brain metastases on Pinnacle 6.2 Treatment Planning System. The prescribed dose was 30 Gy to the whole brain (planning target volume [PTV]_wbrt) and 40 Gy to individual brain metastases (PTV_boost) simultaneously, and both doses were given in 10 fractions. The maximum diameters of individual brain metastases ranged from 1.6 to 6 cm, and the summated PTVs per patient ranged from 1.62 to 69.81 cm³. Conformity and feasibility were evaluated regarding conformation number and treatment delivery time. One hundred percent volume of the PTV_boost received at least 95% of the prescribed dose in all cases. The maximum doses were less than 110% of the prescribed dose to the PTV_boost, and all of the hot spots were within the PTV_boost. The volume of the PTV_wbrt that received at least 95% of the prescribed dose ranged from 99.2% to 100%. The mean values of conformation number were 0.682. The mean treatment delivery time was 2.79 minutes. Ten beams were used on an average in these plans. Whole-brain radiotherapy with a simultaneous integrated boost by forward intensity-modulated radiation therapy in 1 to 3 brain metastases is feasible, and treatment delivery time is short.     

The effect of constipation on rectal dosimetry following prostate brachytherapy

The purpose of this study is to report the effect of dilatation of the anorectum on rectal dosimetry following an ¹²⁵I prostate implant. Three months following prostate brachytherapy, 2 computed tomography (CT) scans of the prostate gland were obtained within 90 minutes of each other. The first CT scan revealed a dilated anorectum secondary to constipation. The second CT was obtained following the administration of an enema with a successfully evacuated rectum. Differences in radiation doses to the distended and empty rectum were computed via the mean dose, the maximum dose per slice, the distance from the base, and in terms of the surface of the anterior quadrant of the rectum receiving 100%, 125%, 150%, 175%, 200%, and 250% of the prescribed dose. The dose to the rectal wall was substantially increased in the distended state for all evaluated parameters. In general, the mean dose to the rectal wall was increased by a factor of 1.5 in the distended state. In both scenarios, the dose to the rectal wall peaked near midgland. In terms of 10° rectal wall sectors receiving a given percentage of the prescribed minimal peripheral dose, S%mPD, the S₁₀₀, S₁₂₅, S₁₅₀, S₁₇₅, S₂₀₀, and S₂₅₀ were substantially greater for the distended versus the empty rectum. The magnitude of the percentage difference in dose between the distended and evacuated rectum increased with dose level while the difference in the number of sectors receiving a given dose level was greatest at 125% and 150% of the prescribed dose. We recommend detailed postimplant attention to bowel habits for at least 2 half-lives of the implanted isotope to minimize rectal distention, decrease radiation dose to the anterior rectal wall, and subsequently minimize potential constipation related rectal toxicity.     

Rationale and design of the worldwide prospective multicenter registry on radiation dose estimates of cardiac CT angiography in daily practice in 2017 (PROTECTION VI)

BackgroundCardiac computed tomography angiography (cardiac CTA) is an increasingly used versatile imaging method to evaluate coronary and cardiac morphology. Owing to improvements in technology, image quality has continuously improved over the last 10–20 years. At the same time, numerous non-randomized and randomized studies have been performed to reduce the associated radiation exposure. Currently, it is unclear if the advances in technology and knowledge about radiation reduction translated into reduced levels of cardiac CTA radiation dose in daily clinical practice as well as a wide utilization of dose-saving strategies.MethodsThe PROTECTION VI study is a multicenter, prospective, worldwide registry designed to evaluate radiation dose exposure, utilization of dose-saving strategies and diagnostic image quality during cardiac CTA in current daily practice. Assessment of image quality will be addressed by the evaluation of diagnostic image quality at the local study site and the calculation of quantitative image quality parameters in an imaging core laboratory. Above 4000 patients will be enrolled from approximately 70 sites in Europe, North America, South America, Asia and Australia. The study will analyze median radiation dose levels, image quality, frequency of use and efficacy of algorithms for dose reduction, and patient and study-related predictors associated with radiation dose.ConclusionsThe PROTECTION VI study is designed to provide a reliable estimate of current radiation dose for cardiac CTA and to assess the potential for additional dose reductions.     

Evaluation of post-plan dosimetry using TRUS and CT after transperineal prostate seed implant

The purpose of this study was to evaluate the variability in dosimetry due to the change in prostate volume for permanent transperineal brachytherapy seed implant. This research is the beginning of an in-house quality assessment program. Nineteen cases were retrospectively evaluated. A single physician defined prostate volumes in all cases. Group A consisted of 3 cases that were treated with external-beam radiation therapy (EBRT) to 4500 cGy, followed by a brachytherapy implant boost of 10,800 cGy. Group B included 16 cases that were implant only, prescribed to 14,400 cGy. Prostate images were acquired before seed implant using transrectal ultrasound (TRUS), immediately following seed implant using TRUS, and by computed tomography (CT) acquired several weeks postimplant. The prostate images were digitized into a commercial treatment planning system for planning purposes and dosimetric evaluation for the 3 procedures. Prostate volumes were calculated by the treatment planning system. Additional data collected included the percentage of prostate receiving the prescribed dose and dose to 90% and 80% of the prostate. The dose delivered to V₁₅₀ was also recorded. Overall, the postimplant ultrasound plan showed similar coverage to the ultrasound preplan, while the CT postplan revealed less than expected dosimetric coverage. The postplan CT results prompted us to evaluate our scheduling process, as well as prostate definition using TRUS and CT.     

New organ-based tube current modulation method to reduce the radiation dose during computed tomography of the head: evaluation of image quality and radiation dose to the eyes in the phantom study

A new organ-based tube current modulation (NOB-TCM) method was designed with the intent to decrease tube current by 30% over a prescribed 90° radial arc across the anterior aspect of the radiosensitive organ, without increasing tube current in the remaining radial arc. We compared a reference scan and five other dose-reducing methods with regard to effects on dose, practicality, and image quality to determine the most effective method for the reduction of the radiation dose to the eyes during CT examinations of the head. We compared the radiation doses to the eyes and physical image quality in different regions of interest for TCM and shielding scans. Three types of TCM scans were performed: longitudinal TCM, angular TCM, and NOB-TCM. A bismuth sheet and lead goggles were each applied for the shielding scan. Relative to the reference scan, the dose to the eye was reduced to 25.88% with NOB-TCM, 44.53% with lead goggles, and 36.91% with a bismuth shield. Relative to the reference scan, the mean signal-to-noise ratio (SNR) was decreased to 8.02% with NOB-TCM, 28.36% with lead goggles, and 32.95% with the bismuth shield. The SNR of the anterior region of interest was decreased to 11.89% with NOB-TCM and 87.89% with the bismuth shield. The average figure of merit was increased by 11.7% with longitudinal TCM and 13.39% with NOB-TCM, compared with the reference scan. NOB-TCM is a superior solution for head CT, including the orbital area, due to the reduction in radiation exposure without significant loss in image quality.     

Measurement of environmental radiation in X-ray room with passive integrating dosimeter

Radiation dose limits in the controlled area of an X-ray room have been prescribed at 1.3 mSv/3 months by the Enforcement Regulations of the Medical Service Law. Leakage effective dose must be measured once within a period that does not exceed six months. Scattered radiation and leakage effective dose were measured in 4 X-ray rooms (chest X-ray room, general-purpose X-ray room, skull and neck X-ray room, and X-ray CT room) with the optically stimulated luminescence dosimeter (OSLD), which is a passive integrating dosimeter. The availability of the measurement method for radiation control with OSLD was evaluated. Scattered radiation in the inside wall surface of the skull and neck X-ray room was less than 1.3 mSv/3 months of the dose limits. There was more scattered radiation in the X-ray CT room than in other X-ray rooms, and the maximum dose was 428 mSv/3 months, measured on the floor. All measurements of leakage effective dose in the 4 X-ray rooms were less than the radiation dose limit, and most measurements of leakage effective dose were less than the detection limits of the dosimeter. Leakage effective dose as calculated by Law 188 (Law 188-Dose) was less than the radiation dose limits in three X-ray rooms, the exception being the X-ray CT room. The Law 188-Dose of the X-ray CT room exceeded 1.3 mSv/3 months at the walls where primary X-rays were directed. The measurement method of leakage effective dose with an ionization survey meter was not able to guarantee the workload of each X-ray apparatus. Therefore, we were not able to confirm the security of X-ray rooms by measurement with an ionization survey meter. Scattered radiation in X-ray rooms was generated intermittently and showed a low dose rate. Consequently, it was established that dose leakage from X-ray rooms must be measured with an integrating dosimeter. It was suggested that the measurement method of environmental dose with OSLD was useful to measurement for radiation control.     

Relative electron dosimetry using the Scanditronix-Wellhöfer beam imaging system-2G

The Beam Imaging System 2G (BIS-2G) from Scanditronix-Wellhöfer is a two-dimensional (2D) charge-coupled device (CCD)-camera that measures the scintillation light produced by incident radiation. We examined the performance of the BIS-2G as a tool in quality control of patient boluses. In an attempt to simplify the production of the patient boluses, bolus edges were built as staircases and the dose distributions were measured and compared to the dose profiles below corresponding sloped bolus edges. Perspex plates covering half the irradiated field were used as generalized bolus edges. All BIS-2G measurements were performed using buildup of solid water while a diode measured corresponding dose profiles in a water phantom. Below the patient boluses, regions with doses < 95% and > 107% of the prescribed dose were defined. Below the edge, the relative doses measured by the BIS-2G were generally within 3% in dose and 3 mm in position compared to the diode measurements. Close to the field edge below the bolus, the BIS-2G measurements were in some cases as much as 7% lower in dose than the diode measurements. The BIS-2G measurements revealed hotspots below the patient boluses covering 1–16% of the total irradiated area. The highest point dose measured below the patient boluses ranged from 105% to 125% of the prescribed dose. For all bolus thicknesses, each edge in the staircase bolus caused a fluctuation in dose and increased the maximum dose compared to the sloped edge. For several cases, the maximum dose increased with 13% in relative dose, e.g., from 103% to 116%. The BIS-2G was found to be a useful tool in quality control of patient boluses, revealing large hot spots in the treatment volume for several patients. Bolus edges built as staircases cause considerable dose fluctuations and increase the maximum dose, and can therefore not be recommended.     

An overview of methods in stereotactic radiosurgery.

Stereotactic radiosurgery delivers a single high dose of ionizing radiation to a radiographically well-defined, small intracranial target without delivering a significant proportion of the prescribed dose to the surrounding brain tissue. Three methods of delivering the radiosurgical technique include the gamma knife, heavy charged particle beams and external high-energy photon beams from linear accelerators.     

A Figure of Merit Comparison between Bremsstrahlung and Monoenergetic X-Ray Sources for Angiography

A figure of merit (FOM) has been developed which embodies parameters related to image quality in the numerator and radiation integral dose to the patient in the denominator. In this manner, maximizing image quality and minimizing radiation dose amounts to maximizing the FOM. Furthermore, the FOM is designed to be independent of x-ray exposure (number of photons used), and this eliminates one important parameter in an optimization scenario. Monoenergetic x-ray beams (0% bandwidth) are compared with conventional Bremsstrahlung x-ray sources from a tungsten target, for angiographic imaging systems using 144 mg/cm2 Csl image intensifiers as the detector. Thus the results are applicable to both digital subtraction angiography (DSA) and digital fluoroscopic procedures involving iodine-based contrast (e.g., roadmapping). The results demonstrate improvement factors (the ratio of the best FOM of the monoenergetic beam over the best FOM of the polyenergetic beam) ranging from 2.3 to 1.4. The improvement factors averaged over four iodine contrast thicknesses (50, 100, 500, and 1000 mg/cm2) were 1.61 (σ = 0.159) for the 10 cm thick patient, 1.68 (σ= 0.172) for the 20 cm thick patient, and 1.82 (σ= 0.186) for the 30 cm thick patient. The conclusions are that monoenergetic x-ray beams are capable of delivering the same image quality at about half the radiation dose to the patient compared to conventional X-ray tubes.     

Dose calculations for local irradiation of endometrial carcinoma

A program for a personal computer has been developed to calculate and optimize dose distributions around a high dose intracavitary afterloading applicator having a single source. The problems of the local irradiation of the endometrium-carcinoma are emphasized in connection with the optimization criteria for an adequate irradiation planing. Exemplarily, the anisotropic proportions of absorption around a special type of applicator are calculated. In addition, an algorithm for optimization of dwell times of three-dimensional arranged source positions according to a prescribed dose distribution is theoretically presented. Further, an easy way of finding isodosis by given source positions and dwell times is introduced by taking into consideration the need to superimpose the dose distribution with external radiation fields. All calculations are tested in a water phantom.     

Communicating risk information in medical practice.

The public's preceptions about the risks of radiation are adversely influenced by the many negative reports by the media on the hazards of all radiation. As a result, patients express concern about the risks of radiation from radiologic examinations. Radiologists are well positioned to dispel these fears because of their training and their access to and ability to interpret information from scientific organizations specifically concerned with the determination of radiation risk. To do this, radiologists must be willing to communicate with patients and be accessible. Pamphlets and handouts can be given to anxious patients before examinations. In direct interaction with patients, the radiologist must listen to them and be prepared to address their concerns, especially those about repeat examinations, exposure during pregnancy, inadvertent exposure of the fetus, exposure of children, use of radiation in research, and misadministration of radionuclides. In addition, radiologists can help patients by educating referring physicians, other medical staff, and nurses. They can also reach the public by being a spokesperson at meetings of local organizations or by accepting opportunities to speak to the media. All these efforts help counteract negative perceptions aroused by the media.     

Recent trends in radiation therapy for pediatric cancer

A recent strategy in the treatment of pediatric cancer is the "total cell kill", in which the main part of therapy depends on intensive, aggressive chemotherapy with or without bone marrow transplantation. Radiotherapy, like surgery, plays a role in local treatment. Recent progress in therapy has permitted cures even of patients with advanced cancer. Disease-free patients should have the same quality of life as that of healthy children of the same sex and age. Therefore, both saving the patient's life and providing him or her with a good quality of life are important in treatment policy. To obtain these goals, radiation therapy has been included in combined multi-modality therapy for the management of pediatric cancer. Other important concerns are to reduce the radiation dose and determine the timing of radiation therapy.