Technical Note: On maximizing Cherenkov emissions from medical linear accelerators.

PURPOSE: Cherenkov light during MV radiotherapy has recently found imaging and therapeutic applications but is challenged by relatively low fluence. Our purpose is to investigate the feasibility of increasing Cherenkov light production during MV radiotherapy by increasing photon energy and applying specialized beam-hardening filtration. METHODS: GAMOS 5.0.0, a GEANT4-based framework for Monte Carlo simulations, was used to model standard clinical linear accelerator primary photon beams. The photon source was incident upon a 17.8 cm3 cubic water phantom with a 94 cm source to surface distance. Dose and Cherenkov production was determined at depths of 3-9 cm. Filtration was simulated 15 cm below the photon beam source. Filter materials included aluminum, iron, and copper with thicknesses of 2-20 cm. Histories used depended on the level of attenuation from the filter, ranging from 100 million to 2 billion. Comparing average dose per history also allowed for evaluation of dose-rate reduction for different filters. RESULTS: Overall, increasing photon beam energy is more effective at improving Cherenkov production per unit dose than is filtration, with a standard 18 MV beam yielding 3.3-4.0× more photons than 6 MV. Introducing an aluminum filter into an unfiltered 2400 cGy/min 10 MV beam increases the Cherenkov production by 1.6-1.7×, while maintaining a clinical dose rate of 300 cGy/min, compared to increases of ~1.5× for iron and copper. Aluminum was also more effective than the standard flattening filter, with the increase over the unfiltered beam being 1.4-1.5× (maintaining 600 cGy/min dose rate) vs 1.3-1.4× for the standard flattening filter. Applying a 10 cm aluminum filter to a standard 18 MV, photon beam increased the Cherenkov production per unit dose to 3.9-4.3× beyond that of 6 MV (vs 3.3-4.0× for 18 MV with no aluminum filter). CONCLUSIONS: Through a combination of increasing photon energy and applying specialized beam-hardening filtration, the amount of Cherenkov photons per unit radiotherapy dose can be increased substantially.

Infrastructure and equipment for radiation oncology in the Spanish National Health System: analysis of external beam radiotherapy 2015-2020.

PURPOSE: Planning for radiation oncology requires reliable estimates of both demand for radiotherapy and availability of technological resources. This study compares radiotherapy resources in the 17 regions of the decentralised Spanish National Health System (SNHS). MATERIALS AND METHODS: The Sociedad Española de Oncología Radioterápica (SEOR) performed a cross-sectional survey of all Spanish radiation oncology services (ROS) in 2015. We collected data on SNHS radiotherapy units, recording the year of installation, specific features of linear accelerators (LINACs) and other treatment units, and radiotherapeutic techniques implemented by region. Any machine over 10 years old or lacking a multileaf collimator or portal imaging system was considered obsolete. We performed a k-means clustering analysis using the Hartigan-Wong method to test associations between the gross domestic regional product (GDRP), the number of LINACs per million population and the percentage of LINACs over 10 years old. RESULTS: The SNHS controls 72 (61%) of the 118 Spanish ROS and has 180 LINACs, or 72.5% of the total public and private resources. The mean rate of LINACs per million population is 3.9 for public ROS, and 42% (n = 75) of the public accelerators were obsolete in 2015: 61 due to age and 14 due to technological capability. There was considerable regional variation in terms of the number and technological capacity of radiotherapy units; correlation between GRDP and resource availability was moderate. CONCLUSION: Despite improvements, new investments are still needed to replace obsolete units and increase access to modern radiotherapy. Regular analysis of ROS in each Spanish region is the only strategy for monitoring progress in radiotherapy capacity.

Thermal limits on MV x-ray production by bremsstrahlung targets in the context of novel linear accelerators.

PURPOSE: To study the impact of target geometrical and linac operational parameters, such as target material and thickness, electron beam size, repetition rate, and mean current on the ability of the radiotherapy treatment head to deliver high-dose-rate x-ray irradiation in the context of novel linear accelerators capable of higher repetition rates/duty cycle than conventional clinical linacs. METHODS: The depth dose in a water phantom without a flattening filter and heat deposition in an x-ray target by 10 MeV pulsed electron beams were calculated using the Monte-Carlo code MCNPX, and the transient temperature behavior of the target was simulated by ANSYS. Several parameters that affect both the dose distribution and temperature behavior were investigated. The target was tungsten with a thickness ranging from 0 to 3 mm and a copper heat remover layer. An electron beam with full width at half maximum (FWHM) between 0 and3 mm and mean current of 0.05-2 mA was used as the primary beam at repetition rates of 100, 200, 400, and 800 Hz. RESULTS: For a 10 MeV electron beam with FWHM of 1 mm, pulse length of 5 µs, by using a thin tungsten target with thickness of 0.2 mm instead of 1 mm, and by employing a high repetition rate of 800 Hz instead of 100 Hz, the maximum dose rate delivered can increase two times from 0.57 to 1.16 Gy/s. In this simple model, the limiting factor on dose rate is the copper heat remover's softening temperature, which was considered to be 500°C in our study. CONCLUSIONS: A high dose rate can be obtained by employing thin targets together with high repetition rate electron beams enabled by novel linac designs, whereas the benefit of thin targets is marginal at conventional repetition rates. Next generation linacs used to increase dose rate need different target designs compared to conventional linacs.

A feasibility study of 2-mm bolus for postmastectomy radiation therapy.

PURPOSE: The purpose of this study was to prospectively evaluate the use of daily 2-mm bolus in patients undergoing postmastectomy radiation without reconstruction using optically stimulated luminescence dosimetry and weekly assessment of skin toxicity. METHODS AND MATERIALS: We prospectively collected data from the first 49 women treated with a daily 2-mm Superflab bolus during their postmastectomy radiation therapy from 2013 to 2016 at The University of Chicago Comprehensive Cancer Center at Silver Cross. Within the first 3 days of starting radiation therapy, we measured the surface dose in vivo at 5 anatomical locations under the 2-mm bolus on the chest wall. We assessed weekly the acute skin toxicity during radiation using the National Cancer Institute Common Toxicity Criteria. Patients with reconstruction before radiation therapy were excluded. RESULTS: Forty-nine women with a mean age of 54.3 years were treated with daily 2-mm bolus to the chest wall following mastectomy. Median follow-up was 32.7 weeks. The mean percentages of prescribed dose (standard deviation) for the median, central, lateral, superior, and inferior optically stimulated luminescence dosimeters were 100.1% (5.6%), 108.1% (6.7%), 98.1% (6.5%), 102.6% (8.9%), and 106.3% (6.6%), respectively. The majority (71.4%) of women experienced a maximum acute National Cancer Institute Common Toxicity Criteria skin toxicity score of 2, with only 12.2% experiencing a score of 3. There were no grade 4 toxicities. There were no local recurrences during our follow-up period. CONCLUSIONS: A daily 2-mm bolus is a feasible regimen for chest wall bolus during postmastectomy radiation therapy with acceptable dose buildup and skin toxicity.

Experimental determination of field factors ([Formula: see text]) for small radiotherapy beams using the daisy chain correction method.

Recently, Alfonso et al proposed a new formalism for the dosimetry of small and non-standard fields. The proposed new formalism is strongly based on the calculation of detector-specific beam correction factors by Monte Carlo simulation methods, which accounts for the difference in the response of the detector between the small and the machine specific reference field. The correct calculation of the detector-specific beam correction factors demands an accurate knowledge of the linear accelerator, detector geometry and composition materials. The present work shows that the field factors in water may be determined experimentally using the daisy chain correction method down to a field size of 1 cm × 1 cm for a specific set of detectors. The detectors studied were: three mini-ionization chambers (PTW-31014, PTW-31006, IBA-CC01), three silicon-based diodes (PTW-60018, IBA-SFD and IBA-PFD) and one synthetic diamond detector (PTW-60019). Monte Carlo simulations and experimental measurements were performed for a 6 MV photon beam at 10 cm depth in water with a source-to-axis distance of 100 cm. The results show that the differences between the experimental and Monte Carlo calculated field factors are less than 0.5%-with the exception of the IBA-PFD-for field sizes between 1.5 cm × 1.5 cm and 5 cm × 5 cm. For the 1 cm × 1 cm field size, the differences are within 2%. By using the daisy chain correction method, it is possible to determine measured field factors in water. The results suggest that the daisy chain correction method is not suitable for measurements performed with the IBA-PFD detector. The latter is due to the presence of tungsten powder in the detector encapsulation material. The use of Monte Carlo calculated [Formula: see text] is encouraged for field sizes less than or equal to 1 cm × 1 cm for the dosimeters used in this work.

Delivery validation of an automated modulated electron radiotherapy plan.

PURPOSE: Modulated electron radiation therapy (MERT) represents an active area of interest that offers the potential to improve healthy tissue sparing in treatment of certain cancer cases. Challenges remain however in accurate beamlet dose calculation, plan optimization, collimation method, and delivery accuracy. In this work, the authors investigate the accuracy and efficiency of an end-to-end MERT plan and automated delivery method. METHODS: Treatment planning was initiated on a previously treated whole breast irradiation case including an electron boost. All dose calculations were performed using Monte Carlo methods and beam weights were determined using a research-based treatment planning system capable of inverse optimization. The plan was delivered to radiochromic film placed in a water equivalent phantom for verification, using an automated motorized tertiary collimator. RESULTS: The automated delivery, which covered four electron energies, 196 subfields, and 6183 total MU was completed in 25.8 min, including 6.2 min of beam-on time. The remainder of the delivery time was spent on collimator leaf motion and the automated interfacing with the accelerator in service mode. Comparison of the planned and delivered film dose gave 3%/3mm gamma pass rates of 62.1%, 99.8%, 97.8%, 98.3%, and 98.7% for the 9, 12, 16, and 20 MeV, and combined energy deliveries, respectively. Delivery was also performed with a MapCHECK device and resulted in 3%/3 mm gamma pass rates of 88.8%, 86.1%, 89.4%, and 94.8% for the 9, 12, 16, and 20 MeV energies, respectively. CONCLUSIONS: Results of the authors' study showed that an accurate delivery utilizing an add-on tertiary electron collimator is possible using Monte Carlo calculated plans and inverse optimization, which brings MERT closer to becoming a viable option for physicians in treating superficial malignancies.

Optically stimulated luminescence in vivo dosimetry for radiotherapy: physical characterization and clinical measurements in (60)Co beams.

A commercial optically stimulated luminescence (OSL) dosimetry system was investigated for in vivo dosimetry in radiation therapy. Dosimetric characteristics of InLight dot dosimeters and a microStar reader (Landauer Inc.) were tested in (60)Co beams. The reading uncertainty of a single dosimeter was 0.6%. The reproducibility of a set of dosimeters after a single irradiation was 1.6%, while in repeated irradiations of the same dosimeters it was found to be 3.5%. When OSL dosimeters were optically bleached between exposures, the reproducibility of repeated measurements improved to 1.0%. Dosimeters were calibrated for the entrance dose measurements and a full set of correction factors was determined. A pilot patient study that followed phantom validation testing included more than 100 measured fields with a mean relative difference of the measured entrance dose from the expected dose of 0.8% and the standard deviation of 2.5%. In conclusion, these results demonstrate that OSL dot dosimeters represent a valid alternative to already established in vivo dosimetry systems.

Monte Carlo commissioning of clinical electron beams using large field measurements.

Monte Carlo simulation can accurately calculate electron fluence at the patient surface and the resultant dose deposition if the initial source electron beam and linear accelerator treatment head geometry parameters are well characterized. A recent approach used large electron fields to extract these simulation parameters. This method took advantage of the absence of lower energy, widely scattered electrons from the applicator resulting in more accurate data. It is important to validate these simulation parameters for clinically relevant fields. In the current study, these simulation parameters are applied to fields collimated by applicators and inserts to perform a comprehensive validation. Measurements were performed on a Siemens Oncor linear accelerator for 6 MeV, 9 MeV, 12 MeV, 15 MeV, 18 MeV and 21 MeV electron beams and collimators ranging from an open 25 x 25 cm(2) applicator to a 10 x 10 cm(2) applicator with a 1 cm diameter cerrobend insert. Data were collected for inserts placed in four square applicators. Monte Carlo simulations were performed using EGSnrc/BEAMnrc. Source and geometry parameters were obtained from previous measurements and simulations with the maximum field size (40 x 40 cm(2)). The applicators were modelled using manufacturer specifications, confirmed by direct measurements. Cerrobend inserts were modelled based on calliper measurements. Monte Carlo-calculated percentage depth dose and off-axis profiles agreed with measurements to within the least restrictive of 2%/1 mm in most cases. For the largest applicator (25 x 25 cm(2)), and 18 MeV and 21 MeV beams, differences in dose profiles of 3% were observed. Calculated relative output factors were within 2% of those measured with an electron diode for fields 1.5 cm in diameter or larger. The disagreement for 1 cm diameter fields was up to 5%. For open applicators, simulations agreed with parallel plate chamber-measured relative output factors to 1%. This work has validated a recent methodology used to extract data on the electron source and treatment head from large electron fields, resulting in a reduction in the number of unknown parameters in treatment head simulation. Applicator and insert collimated electron fields were accurately simulated without adjusting these parameters. Results demonstrate that commissioning of electron beams based on large electron field measurements is a viable option.

[Quality assurance in radiotherapy]. / Assurance de la qualité en radiothérapie.

Quality assurance in radiotherapy affects the radiotherapy department organization, management, patient follow-up, distribution of responsibilities, training and equipment management. The development of innovative techniques for radiotherapy and associated radiotherapy equipment requires an adaptation of the concepts of quality assurance and quality control as practiced last 30 years. A new paradigm and new methods adapted from industry, including patient safety and quality care in a more holistic approach to quality assurance and quality control.

Report of AAPM Therapy Physics Committee Task Group 74: in-air output ratio, Sc, for megavoltage photon beams.

The concept of in-air output ratio (Sc) was introduced to characterize how the incident photon fluence per monitor unit (or unit time for a Co-60 unit) varies with collimator settings. However, there has been much confusion regarding the measurement technique to be used that has prevented the accurate and consistent determination of Sc. The main thrust of the report is to devise a theoretical and measurement formalism that ensures interinstitutional consistency of Sc. The in-air output ratio, Sc, is defined as the ratio of primary collision water kerma in free-space, Kp, per monitor unit between an arbitrary collimator setting and the reference collimator setting at the same location. Miniphantoms with sufficient lateral and longitudinal thicknesses to eliminate electron contamination and maintain transient electron equilibrium are recommended for the measurement of Sc. The authors present a correction formalism to extrapolate the correct Sc from the measured values using high-Z miniphantom. Miniphantoms made of high-Z material are used to measure Sc for small fields (e.g., IMRT or stereotactic radiosurgery). This report presents a review of the components of Sc, including headscatter, source-obscuring, and monitor-backscattering effects. A review of calculation methods (Monte Carlo and empirical) used to calculate Sc for arbitrary shaped fields is presented. The authors discussed the use of Sc in photon dose calculation algorithms, in particular, monitor unit calculation. Finally, a summary of Sc data (from RPC and other institutions) is included for QA purposes.

An experimental attenuation plate to improve the dose distribution in intraoperative electron beam radiotherapy for breast cancer.

Intraoperative electron beam radiotherapy (IOERT) is a technique in which a single-fraction high dose is intraoperatively delivered to subclinical tumour cells using an electron beam after breast-conserving surgery. In IOERT, an attenuation plate consisting of a pair of metal disks is commonly used to protect the normal tissues posterior to the breast. However, the dose in front of the plate is affected by backscatter, resulting in an unpredictable delivered dose to the tumour cells. In this study, an experimental attenuation plate, termed a shielding plate, was designed using Monte Carlo simulation, which significantly diminished the electron beam without introducing any backscatter radiation. The plate's performance was verified by measurements. It was made of two layers, a first layer (source side) of polymethyl methacrylate (PMMA) and a second layer of copper, which was selected from among other metals (aluminium, copper and lead) after testing for shielding capability and the range and magnitude of backscatter. The optimal thicknesses of the PMMA (0.71 cm) and copper (0.3 cm) layers were determined by changing their thicknesses during simulations. On the basis of these results, a shielding plate was prototyped and depth doses with and without the plate were measured by radiophotoluminescence glass dosimeters using a conventional stationary linear accelerator and a mobile linear accelerator dedicated for IOERT. The trial shielding plate functioned as intended, indicating its applicability in clinical practice.

Calculation of energy-deposition distributions and microdosimetric estimation of the biological effect of a 9C beam.

Among the alternative beams being recently considered for external cancer radiotherapy, (9)C has received some attention because it is expected that its biological effectiveness could be boosted by the beta-delayed emission of two alpha particles and a proton that takes place at the ion-stopping site. Experiments have been performed to characterise this exotic beam physically and models have been developed to estimate quantitatively its biological effect. Here, the particle and heavy-ion transport code system ( PHITS ) is used to calculate energy-deposition and linear energy transfer distributions for a (9)C beam in water and the results are compared with published data. Although PHITS fails to reproduce some of the features of the distributions, it suggests that the decay of (9)C contributes negligibly to the energy-deposition distributions, thus contradicting the previous interpretation of the measured data. We have also performed a microdosimetric calculation to estimate the biological effect of the decay, which was found to be negligible; previous microdosimetric Monte-Carlo calculations were found to be incorrect. An analytical argument, of geometrical nature, confirms this conclusion and gives a theoretical upper bound on the additional biological effectiveness of the decay. However, no explanation can be offered at present for the observed difference in the biological effectiveness between (9)C and (12)C; the reproducibility of this surprising result will be verified in coming experiments.

The use of photostimulable phosphor systems for periodic quality assurance in radiotherapy.

The fusion of radiological and optical images can be achieved through charging a photostimulable phosphor plate (PSP) with an exposure to a field of X- or gamma-rays, followed by exposure to an optical image which discharges the plate in relation to the amount of incident light. According to this PSP characteristic, we developed a simple method for periodic quality assurance (QA) of light/radiation field coincidence, distance indicator, field size indicators, crosshair centering, coincidence of radiation and mechanical isocenter for linear accelerators. The geometrical accuracy of radiological units can be subjected to the same QA method. Further, the source position accuracy for an HDR remote afterloader can be checked by taking an autoradiography of the radioactive source and simultaneously an optical image of a reference geometrical system.

[Evaluation of the accuracy of a compensating filter based on compact NC-Mill for radiation therapy].

The present report describes the fabrication technique and dosimetry aspects of a desktop numerically controlled milling machine (NC-Mill) based a compensator system that uses lead clay (Shield cray, Reactor Experiments, Inc., U.S.A.). Effective path lengths of patients were determined for CT image sets using the ray-tracing technique and converted to compensator thickness with the equivalent TMR method. Rigid urethane foam was processed with the NC-Mill to produce a mold for filters, and the lead clay was adopted as the compensating material. The dose distribution was measured on the compensating plane of an anthropomorphic phantom and a stair-step PMMA phantom. It was found that the radiation field with inhomogeneous dose was as high as 30%+/-3% with the compensating filters. In addition, when the absorbed dose at the central axis of 52 compensating filters that were used clinically was measured, 75.0% showed an error of less than +/-3%, and 3.8% showed the maximum dose error: >+/-5%. Overall, the present system was capable of producing dose uniformity to within +/-5% for a stair-step phantom, an anthropomorphic phantom, and clinical situations.

Optically stimulated luminescence (OSL) of carbon-doped aluminum oxide (Al2O3:C) for film dosimetry in radiotherapy.

INTRODUCTION AND PURPOSE: Conventional x-ray films and radiochromic films have inherent challenges for high precision radiotherapy dosimetry. Here we have investigated basic characteristics of optically stimulated luminescence (OSL) of irradiated films containing carbon-doped aluminum oxide (Al2O3:C) for dosimetry in therapeutic photon and electron beams. MATERIALS AND METHODS: The OSL films consist of a polystyrene sheet, with a top layer of a mixture of single crystals of Al2O3:C, ground into a powder, and a polyester base. The total thickness of the films is 0.3 mm. Measurements have been performed in a water equivalent phantom, using 4, 6, 10, and 18 MV photon beams, and 6-22 MeV electron beams. The studies include assessment of the film response (acquired OSL signal/delivered dose) on delivered dose (linearity), dose rate (1-6 Gy/min), beam quality, field size and depth (6 MV, ranges 4 x 4-30 x 30 cm2, dmax-35 cm). Doses have been derived from ionization chamber measurements. OSL films have also been compared with conventional x-ray and GafChromic films for dosimetry outside the high dose area, with a high proportion of low dose scattered photons. In total, 787 OSL films have been irradiated. RESULTS: Overall, the OSL response for electron beams was 3.6% lower than for photon beams. Differences between the various electron beam energies were not significant. The 6 and 18 MV photon beams differed in response by 4%. No response dependencies on dose rate were observed. For the 6 MV beam, the field size and depth dependencies of the OSL response were within +/-2.5%. The observed inter-film response variation for films irradiated with the same dose varied from 1% to 3.2% (1 SD), depending on the measurement day. At a depth of 20 cm, 5 cm outside the 20 x 20 cm2 6 and 18 MV beams, an over response of 17% was observed. In contrast to GafChromic and conventional x-ray films, the response of the Al2O3:C films is linear in the clinically relevant dose range 0-200 cGy. CONCLUSIONS: Measurement of the OSL signal of irradiated films containing Al2O3:C is a promising technique for film dosimetry in radiotherapy with no or small response variations with dose rate, beam quality, field size and depth, and a linear response from 0 to 200 cGy.

Ethereal fire: antecedents of radiology and radiotherapy.

OBJECTIVE: The objective is to explore the events that led to the implementation of X-radiation for medical purposes within months of its discovery. CONCLUSION: The century-long experience with electrotherapeutics and the concurrent adoption of ultraviolet light therapy, facilitated the swift inclusion of X-radiation into medical practice.

Antiepileptic therapy in patients with central nervous system malignancies.

More than 200,000 patients are diagnosed with primary or metastatic brain tumors each year in the United States. Of these patients, 20% to 40% will develop seizures at presentation, and another 20% to 40% will require treatment for seizures during their illness. Although the use of antiepileptic drugs (AEDs) in patients who have had seizures seems reasonable, the issue of prophylactic AED use for patients who have not had a seizure is an intensely debated subject. The American Academy of Neurology released a position statement in May 2000 addressing the use of anticonvulsants in newly diagnosed brain tumor patients who have never had a seizure. After a review of the literature, including all trials showing class I evidence, multivariate analysis using calculated odds ratios failed to show a prophylactic benefit of preventing a first seizure versus the risk of side effects and recommended not using prophylactic anticonvulsants in newly diagnosed patients with brain tumor. Despite this recommendation, a recent survey of the American Association of Neurologic Surgeons revealed that most neurosurgeons still use anticonvulsants prophylactically in patients with brain tumor. This review mainly includes primary brain tumors, but most of the concepts are transferable to patients with metastatic tumors.

Computational evaluation of changes in ionizing radiation dose distribution in tissues caused by EM applicators when external radiation and hyperthermia act simultaneously.

PURPOSE: The presented theoretical study investigates the influence of CFMA-like electromagnetic microstrip applicators (MAs) on ionizing radiation intensity and depth radiation dose distribution (DRDD) in irradiated tissues which are tightly covered with a MA. METHODS: It is shown that at relatively low photon energy (<200 keV) the MA does not affect noticeable the profile of the DRDD curve and does not lead to skin overdosing. Nevertheless, it significantly (up to 20-35%) decreases the low energy ionizing radiation intensity. For high energy photons (>1 MeV), on the contrary, the decrease of radiation intensity, caused by the MA, is small (3-10%), but the profile of the DRDD curve, calculated by means of the Monte-Carlo method, is significantly affected. RESULTS: The radiation dose maximum is shifted to the skin, resulting in possible skin overdosing. Radiation absorption characteristics of MA are calculated and compared with published parameters of EM horn and US applicators now in use for external simultaneous radiation and hyperthermia (ESRH) procedures. The MA provides the minor ionizing radiation absorption. Due to it and owing to their conformability with the tissue surface the MAs would not require any additional means or devices to be used for ESRH treatment procedures with any common ionizing radiation equipment. CONCLUSIONS: The necessity of development means for decreasing the time of radiation equipment occupation during ESRH procedures is pointed out.

Dosimetric properties of magnetically collimated electron beams for radiation therapy.

A method of generating magnetically collimated electron beams is developed and the dosimetric properties of magnetically collimated electrons are investigated. An in-air magnetic collimator device was designed and constructed for the study. The magnetic collimator was placed above the exit port of a 14 x 14 cm2 electron cone. Axial magnetic field of approximately 0.6 Tesla is generated inside the collimator via an array of permanent magnets. Fixed and rotational magnetically collimated electron beams were delivered and measured in phantoms. We found that magnetically collimated electron beams significantly lower the surface dose as compared with conventional electron beams. A magnetically collimated arc beam further reduces the surface dose to less than 20% of the maximum dose inside the target. The dose per monitor unit at d(max) for the magnetically collimated electron beams was significantly (approximately 40%) higher than that of the conventional electron beams. The use of magnetic collimation may lead to improved delivery techniques for breast and head and neck cancer treatments.