A Novel 2D Probability Density Function Integrating the Rectal Motion and Wall Thickness in Prostate IMRT.

Background And Purpose: This study investigated the variations of rectal motion and wall thickness in prostate intensity-modulated radiotherapy using a novel 2D probability density function. To evaluate the impact of the position, thickness, and deformation of the rectum on the dose distribution in prostate intensity-modulated radiotherapy plans, probability density functions (pdf) of the deformation of rectal cross-section (D), rectal dose distribution (R), and changes in rectal wall thickness (T) were used in the planning optimization.

Materials And Methods: The problem of approximating the product of a number of Gaussian mixture distributions arises in the number of parameters describing the specific mean value, standard deviation, and weight in every Gaussian.

Leakage-Penumbra effect in intensity modulated radiation therapy step-and-shoot dose delivery.

Aim: To study the leakage-penumbra (LP) effect with a proposed correction method for the step-and-shoot intensity modulated radiation therapy (IMRT).

Methods: Leakage-penumbra dose profiles from 10 randomly selected prostate IMRT plans were studied. The IMRT plans were delivered by a Varian 21 EX linear accelerator equipped with a 120-leaf multileaf collimator (MLC).

Surgical treatment of benign diseases of the gastroesophageal junction in clinic of endoscopic surgery at MMA during the period 2005-2012: pathophysiology, surgical techniques and trends of their use.

Unlabelled: Treatment of the diseases of the gastroesophageal junction is one of the serious problems faced by gastroenteorologist and surgeons. In contrast to the proton pump inhibitors (PPI) surgery achieves a long symptoms free period. Laparoscopic surgery has its advantages as an alternative to conventional surgery.

Laparoscopic vs open resection for rectal carcinoma--a prospective analysis.

Unlabelled: In the recent years, laparoscopic surgery has established itself worldwide as a method of treatment for colorectal cancer. Several prospective randomized trials comparing laparoscopic with open resection of the colon, showing the advantages of laparoscopic surgery in terms of a shorter hospital stay, faster recovery of intestinal transit and physical activity in equivalent survival and recurrence rate. However, in many of the studies the data on laparoscopic resection for rectal cancer are scarce and it is still controversial.

Poster - Thur Eve - 22: Bone heterogeneity in kV x-ray radiotherapy.

This study evaluated the dosimetric impact of bone heterogeneity on the surface dose and dose prescription, when dose is assumed to be prescribed on a homogeneous medium in kV x-ray radiotherapy. A heterogeneous phantom containing a thin water layer (thickness = 1-5 mm) over a bone (thickness =1 cm) was used to mimic treatment sites of forehead, knee and chest wall. The phantom was irradiated by a 220 kVp photon beam with field size of 5 cm diameter.

SU-E-T-571: Prostate IMRT QA: Prediction of the Range of Rectal NTCP Using a 2D Field Approach Based on Variations of the Rectal Wall Motion and Thickness.

Purpose: The aims of this study is to (1) introduce a 2D field of possible rectal normal tissue complication probability (NTCP) in prostate intensity modulated radiotherapy (IMRT) plan, so that based on a given prescribed dose the rectal NTCP is merely a function of the rectal wall thickness and rectal motion; and (2) separate the 2D field of rectal NTCP into area of low risk and area of high risk for rectal toxicity < Grade II, based on the threshold rectal NTCP.

Methods: The 2D field of NTCP model was developed using ten randomly selected prostate IMRT plans. The clinical rectal geometry was initially represented by the cylindrical contour in the treatment planning system.

Effect of the bone heterogeneity on the dose prescription in orthovoltage radiotherapy: A Monte Carlo study.

Background: In orthovoltage radiotherapy, since the dose prescription at the patient's surface is based on the absolute dose calibration using water phantom, deviation of delivered dose is found as the heterogeneity such as bone present under the patient's surface.

Aim: This study investigated the dosimetric impact due to the bone heterogeneity on the surface dose in orthovoltage radiotherapy.

Materials And Methods: A 220 kVp photon beam with field size of 5 cm diameter, produced by a Gulmay D3225 orthovoltage X-ray machine was modeled by the BEAMnrc.

[Rupture of splenic artery aneurysm--life-threatening condition for women during pregnancy and after birth (with report of one case)].

Spontaneous rupture of a splenic artery aneurysm is an uncommon and usually catastrophic event during pregnancy and puerperium. The mortality rate among pregnant women is very high at 75% with a fetus mortality rate of 95%. This report describes the clinical course of a 25-year-old woman with hemorrhagic shock four hours after elective Cesarean Section.

Dosimetry of a small air cavity for clinical electron beams: A Monte Carlo study.

This study investigated dosimetric changes in a water phantom when a small air cavity was presented at the central axis of a clinical electron beam. We used 6-, 9-, and 16-MeV electron beams with a 10 x 10 cm(2) applicator and cutout produced by a Varian 21 EX linear accelerator. Percentage depth doses (PDDs) for different depths (0.

Dosimetric dependence of the dimensional characteristics on a lead shield in electron radiotherapy: a Monte Carlo study.

This study investigates the dosimetric dependence of the dimension of a lead (Pb) layer for shielding using clinical electron beams with different energies. Monte Carlo simulations were used to generate phase space files of the 4, 9 and 16 MeV electron beams produced by a Varian 21 EX linear accelerator using the EGSnrc-based BEAMnrc code, and validated by measurements using films. Pb layers with different thicknesses (2, 4, 6 and 8 mm) and diameters (2.

Sci-Thurs PM: Delivery-01: Sliding Window IMRT: Uncertainties of the leading edge and plateau of the beam profile.

The aim of this work is to analyze the dependence of the dose profile uncertainties for the sliding window IMRT (SW-IMRT) beams under the condition of an extreme dose rate (DR) and leaf velocity (LV). The deviations of the edges and plateau for the beam profiles of small number of MUs delivered using the dynamic MLC were studied. Field sizes with lengths of 5 and 10 cm were irradiated by photon beams of 2-8 MU/beam, DR = 100-600 MU/min and LS = 1-5 cm/s.

Poster - Thurs Eve-24: Dosimetry study on the penumbra region for the irregular MLC fields with stepping patterns.

The aim of this study is to investigate the dosimetric effect in the penumbra region for the multi-leaf collimator (MLC) fields with stepping patterns. Various irregular MLC fields with different stepping patterns were designed. Radiographic films were used to measure the beam profiles (cross-plane (X1-X2 jaw) and in-plane (Y1-Y2 jaw)) for different MLC field configurations of varying lengths of protruded leaves adjacent (on one or both sides) to the beam profile axis.

Monte Carlo simulation of backscatter from lead for clinical electron beams using EGSnrc.

In electron radiotherapy of superficial lesions in the eyelid, lip, buccal mucosa, ear, and nose, backscattered electrons are produced from the lead shield used to protect the critical tissue underneath the tumor. In this study, the backscattered electrons, produced by clinical electron beams using a Varian 21 EX linear accelerator, were studied using Monte Carlo simulations. The electron backscatter factor (EBF), defined as the ratio of dose at the tissue-lead interface to the dose at the same point without the presence of backscatter, was calculated using the Monte Carlo EGSnrc-based code.

Surface dosimetry for oblique tangential photon beams: a Monte Carlo simulation study.

The effect of beam obliquity on the surface relative dose profiles for the tangential photon beams was studied. The 6 and 15 MV photon beams with 4 x 4 and 10 x 10 cm2 field sizes produced by a Varian 21 EX linear accelerator were used. Phase-space models of the photon beams were created using Monte Carlo simulations based on the EGSnrc code, and were verified using film measurements.

Effect of electron beam obliquity on lateral buildup ratio: a Monte Carlo dosimetry evaluation.

The impact of the oblique electron beam on the lateral buildup ratio (LBR), used in the electron pencil beam model to predict the per cent depth dose (PDD) and dose per monitor unit (MU) for an irregular electron field, was examined using Monte Carlo simulation. The EGSnrc-based Monte Carlo code was used to model electron beams produced by a Varian 21 EX linear accelerator for different beam energies, angles of obliquity and field sizes. The Monte Carlo phase space model was verified by measurements using electron diode and radiographic film.

SWIMRT: a graphical user interface using sliding window algorithm to construct a fluence map machine file.

A custom-made computer program, SWIMRT, to construct "multileaf collimator (MLC) machine" file for intensity-modulated radiotherapy (IMRT) fluence maps was developed using MATLAB and the sliding window algorithm. The user can either import a fluence map with a graphical file format created by an external treatment-planning system such as Pinnacle3 or create his or her own fluence map using the matrix editor in the program. Through comprehensive calibrations of the dose and the dimension of the imported fluence field, the user can use associated image-processing tools such as field resizing and edge trimming to modify the imported map.

Monte Carlo simulations of dose near a nonradioactive gold seed.

The relative doses and hot/cold spot positions around a non-radioactive gold seed, irradiated by a 6 or 18 MV photon beam in water, were calculated using Monte Carlo simulation. Phase space files of 6 and 18 MV photon beams with a field size of 1 x 1 cm2 were generated by a Varian 21 EX linear accelerator using the EGSnrc and BEAMnrc code. The seed (1.

Intensity modulated radiation therapy with irregular multileaf collimated field: a dosimetric study on the penumbra region with different leaf stepping patterns.

Using a Varian 21 EX linear accelerator with a multileaf collimator (MLC) of 120 leaves, the penumbra regions of beam profiles within an irregular multileaf collimated fields were studied. MLC fields with different leaf stepping angles from 21.8 degrees to 68.

Electron radiotherapy: a study on dosimetric uncertainty using small cutouts.

This note investigated the dosimetric uncertainties due to the positional error when centring a small cutout to the machine central beam axis (CAX) in electron radiotherapy. A group of six circular cutouts with 4 cm diameter were made with their centres shifting 0, 2, 4, 6, 8 and 10 mm from the machine CAX for the 6 x 6 cm(2) applicator. The per cent depth doses, beam profiles and output factors were measured using the 4, 9 and 16 MeV clinical electron beams produced by a Varian 21 EX linear accelerator.

Study on surface dose generated in prostate intensity-modulated radiation therapy treatment.

The surface doses of 6- and 15-MV prostate intensity-modulated radiation therapy (IMRT) irradiations were measured and compared to those from a 15-MV prostate 4-beam box (FBB). IMRT plans (step-and-shoot technique) using 5, 7, and 9 beams with 6- and 15-MV photon beams were generated from a Pinnacle treatment planning system (version 6) using computed tomography (CT) scans from a Rando Phantom (ICRU Report 48). Metal oxide semiconductor field effect transistor detectors were used and placed on a transverse contour line along the Phantom surface at the central beam axis in the measurement.

Measurement for the MLC leaf velocity profile by considering the leaf leakage using a radiographic film.

A method to measure the velocity profile of a multi-leaf collimator (MLC) leaf along its travel range using a radiographic film is reported by considering the intra-leaf leakage. A specific dynamic MLC field with leaves travelling from the field edge to the isocentre line was designed. The field was used to expose a radiographic film, which was then scanned, and the dose profile along the horizontal leaf axis was measured.

A comparison of prostate IMRT and helical tomotherapy class solutions.

The purpose of this study was to assess a variety of potential IMRT class solutions as compared to a helical tomotherapy (HT) class solution for localized prostate cancer. Target and critical structures were contoured on 10 prostate cancer patient CT datasets. HT treatment plans were compared to four different IMRT approaches by paired t-tests.

Peripheral dose outside applicators in electron beams.

The peripheral dose outside the applicators in electron beams was studied using a Varian 21 EX linear accelerator. To measure the peripheral dose profiles and point doses for the applicator, a solid water phantom was used with calibrated Kodak TL films. Peak dose spot was observed in the 4 MeV beam outside the applicator.

IMRT: improvement in treatment planning efficiency using NTCP calculation independent of the dose-volume-histogram.

The normal tissue complication probability (NTCP) is a predictor of radiobiological effect for organs at risk (OAR). The calculation of the NTCP is based on the dose-volume-histogram (DVH) which is generated by the treatment planning system after calculation of the 3D dose distribution. Including the NTCP in the objective function for intensity modulated radiation therapy (IMRT) plan optimization would make the planning more effective in reducing the postradiation effects.

A graphical user interface for an electron monitor unit calculator using a sector-integration algorithm and exponential curve-fitting method.

A new electron monitor unit (MU) calculator program called "eMUc" was developed to provide a convenient electron MU calculation platform for the physics and radiotherapy staff in electron radiotherapy. The program was written using the Microsoft Visual Basic.net framework and has a user-friendly front-end window with the following features: (1) Apart from using the well-known polynomial curvefitting method for the interpolation and extrapolation of relative output factors (ROFs), an exponential curve-fitting method was used to obtain better results.