A beam generation algorithm for linear accelerators with independent collimators

Thomas, S.; Thomas, R. L.

doi:10.1088/0031-9155/35/3/002

Cited by 23 publications

(19 citation statements)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This was applied using a bilateral, equally weighted, isocentric, parallel opposed beam configuration, in some cases brass wedges were used to maximize tumor dosage and spare surrounding normal tissues. A custom written computerized planning system b , 32,33 was used to produce an isodose plot of predicted radiation distribution on a transverse section of the cats head. The planning target volume (PTV) was the tumor mass as defined on transverse MRI scan of the skull at the maximum tumor diameter, plus a 1‐cm margin in all directions.…”

Section: Methodsmentioning

confidence: 99%

Exogenous Insulin Treatment after Hypofractionated Radiotherapy in Cats with Diabetes Mellitus and Acromegaly

Dunning

Lowrie²,

Bexfield

et al. 2009

Veterinary Internal Medicne

View full text Add to dashboard Cite

Background: The optimal treatment for feline acromegaly has yet to be established. Surgical and medical therapies are minimally effective although radiotherapy might have greater efficacy. The purpose of this study was to review the response and outcome of cats with acromegaly and insulin-resistant diabetes mellitus (DM) to radiotherapy.Hypotheses: That radiotherapy improves glycemic control in cats with acromegaly and that improved glycemic control is due to remission of clinical acromegaly; demonstrated by a fall in serum insulin-like growth factor-1 (IGF-1) concentrations.Animals: Fourteen cats with naturally occurring acromegaly. Methods: Retrospective case review; records of all cats treated for acromegaly with radiotherapy were reviewed from 1997 to 2008. Cats were selected on the basis of compatible clinical signs, laboratory features, and diagnostic imaging findings. Fourteen cats received radiotherapy, delivered in 10 fractions, 3 times a week to a total dose of 3,700 cGy.Results: Thirteen of 14 cats had improved diabetic control after radiotherapy. These improvements were sustained for up to 60 months. DM progressed in 2 cats and 1 did not respond. Seven cats responded before the final treatment. Ten cats were euthanized, 1 as a consequence of radiotherapy. In 8 cats in which IGF-1 was measured after treatment, changes in its concentration did not reflect the clinical improvement in glycemic control.Conclusions and Clinical Importance: Radiotherapy represents an effective treatment for cats with insulin-resistant DM resulting from acromegaly. IGF-1 concentration after treatment does not provide a suitable method by which remission from either acromegaly or insulin-resistant DM may be assessed.

show abstract

Section: Methodsmentioning

confidence: 99%

Exogenous Insulin Treatment after Hypofractionated Radiotherapy in Cats with Diabetes Mellitus and Acromegaly

Dunning

Lowrie²,

Bexfield

et al. 2009

Veterinary Internal Medicne

View full text Add to dashboard Cite

show abstract

“…1,2 They demonstrated that photon beam energy for medical linear accelerators varies with off-axis position, and incorporated changes in beam quality with position into dose calculations. Khan et al 3 showed that for megavoltage photon beams, changes in the attenuation coefficient in water could reach 16% when the off-axis distance increased from 0 to 18 cm, and they and other groups [4][5][6] also discussed the effect of these changes on dose calculations. Mohan and Chui, 7 as well as Lovelock et al, 8 used the Monte Carlo method to calculate changes in half-value layer ͑HVL͒ and average photon energy with off-axis distance.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, Bjärngard and Shackford 9 analyzed transmission factors in terms of an attenuation coefficient and a beam-hardening coefficient, and investigated the variation of attenuation coefficient with radius for high-energy photon beams. Many groups 1,3,5,7,9 have mentioned the effect of nonuniform attenuation by the flattening filter on the variation of beam quality with off-axis distance, however a detailed experimental investigation of this effect has not been reported.…”

Section: Introductionmentioning

confidence: 99%

Linear accelerator photon beam quality at off‐axis points

Yu¹,

Sloboda²,

Murray³

1997

Medical Physics

View full text Add to dashboard Cite

Transmitted intensity through water was measured in a narrow-beam geometry for different energy x-ray beams from commercial accelerators. In order to accurately obtain the attenuation coefficient of the incident beam using transmission data, a novel formula was developed based on consideration of beam hardening in phantom. The value of the attenuation coefficient obtained by fitting transmission data to this formula was found to be independent of the absorber thickness used in experiments, whereas the attenuation coefficient obtained from the traditional formula, I(x) = I0 exp(-mux), changed by up to 7% with absorber thickness for a given beam. The beam hardening coefficient obtained from our formula indicates that the attenuation coefficient in water changes by about 0.33% per cm near the surface for the high-energy photon beams studied. Variations in beam quality with off-axis distance were subsequently investigated using the new formula. Results show that the attenuation coefficient at the water surface increased by about 15% for 15 and 18 MV beams, and by 11%-13% for 6 MV beams, when the off-axis distance at 100 cm from the source was changed from 0 to 18 cm. Consideration of the physics of bremsstrahlung production suggests that these variations should be mainly determined by the shape of the flattening filter, i.e., by the path length of rays traversing the filter in different directions. This expectation was confirmed by observing that the attenuation coefficient at the phantom surface can be related to the ray path of the beam in the flattening filter using the new transmission formula.

show abstract

Section: Introductionmentioning

confidence: 99%

“…In the 1990s, some studies have addressed asymmetric and wedged asymmetric fields using symmetric field data (8–11) . The method based on work by Thomas and Thomas (10) generates asymmetric field profiles by computing the off‐center ratio (OCR) of the asymmetric field while using output factors and PDDs of the equivalent symmetric field. A second method, proposed by Kwa et al, (12) applies to the situation where only one of the independent jaws is closed down to form an asymmetric field of smaller width or length than the original symmetric field.…”

Section: Introductionmentioning

confidence: 99%

Analytical approach for determining beam profiles in water phantom of symmetric and asymmetric fields of wedged, blocked, and open photon beams

Birgani

Chegeni

Arvandi

et al. 2013

J Applied Clin Med Phys

View full text Add to dashboard Cite

Nowadays, in most radiotherapy departments, the commercial treatment planning systems (TPS) used to calculate dose distributions needs to be verified; therefore, quick, easy‐to‐use, and low‐cost dose distribution algorithms are desirable to test and verify the performance of the TPS. In this paper, we put forth an analytical method to calculate the phantom scatter contribution and depth dose on the central axis based on the equivalent square concept. Then, this method was generalized to calculate the profiles at any depth and for several field shapes — regular or irregular fields—under symmetry and asymmetry photon beam conditions. Varian 2100 C/D and Siemens Primus Plus linacs with 6 and 18 MV photon beam were used for irradiations. Percentage depth doses (PDDs) were measured for a large number of square fields for both energies and for 45° wedge, which were employed to obtain the profiles in any depth. To assess the accuracy of the calculated profiles, several profile measurements were carried out for some treatment fields. The calculated and measured profiles were compared by gamma‐index calculation. All γ–index calculations were based on a 3% dose criterion and a 3 mm dose‐to‐agreement (DTA) acceptance criterion. The γ values were less than 1 at most points. However, the maximum γ observed was about 1.10 in the penumbra region in most fields and in the central area for the asymmetric fields. This analytical approach provides a generally quick and fairly accurate algorithm to calculate dose distribution for some treatment fields in conventional radiotherapy.PACS number: 87.10.Ca

show abstract

A beam generation algorithm for linear accelerators with independent collimators

Cited by 23 publications

References 5 publications

Exogenous Insulin Treatment after Hypofractionated Radiotherapy in Cats with Diabetes Mellitus and Acromegaly

Exogenous Insulin Treatment after Hypofractionated Radiotherapy in Cats with Diabetes Mellitus and Acromegaly

Linear accelerator photon beam quality at off‐axis points

Analytical approach for determining beam profiles in water phantom of symmetric and asymmetric fields of wedged, blocked, and open photon beams

Contact Info

Product

Resources

About