Acute toxicity in patients with high-risk prostate cancer treated with stereotactic body radiation, with irradiation to the prostate and pelvic nodes.

PURPOSE: Stereotactic body radiation therapy has been used for prostate cancer. However, the bulk of published studies on stereotactic body radiation therapy for prostate cancer has involved the irradiation of the prostate alone, without irradiation of the pelvic lymph nodes. We report our preliminary experience with this approach. MATERIAL AND METHODS: The files of patients with biopsy-proven prostate cancer treated with stereotactic body radiation therapy in our institution were reviewed. Stereotactic body radiation was delivered with intensity modulated-volumetric arctherapy with daily image-guidance. The prostate planning target volume included the prostate plus a margin of 5mm in all directions. The pelvic planning target volume included pelvic nodes plus an expansion of 6 to 7mm in all directions. The prostate planning target volume received a total dose of 36.25Gy delivered in five fractions on alternate days. The nodal planning target volume received a dose of 25Gy in the same five fractions. Patients were followed during treatment, after 1, and 3 months and every 6 months thereafter. Gastrointestinal and genitourinary toxicity was prospectively graded according to Common Terminology Criteria for Adverse Events. RESULTS: Among the 188 patients, 80 received stereotactic body radiation to the prostate and the pelvic nodes, while 108 received stereotactic body radiation to the prostate target only. Grade 2 acute gastrointestinal toxicity was 4% in both groups, and grade 2 acute genitourinary toxicity was 27% and 20% (P=0.9) for prostate only versus prostate and pelvis respectively. There was no grade 3 or higher acute gastrointestinal or genitourinary toxicity. CONCLUSION: Stereotactic body radiation therapy in five fractions including the prostate and pelvic nodes, in patients with high-risk prostate cancer, has been feasible and safe in terms of acute toxicity.

Characterisation and source identification of the total airborne particulate matter collected in an urban area of Aracaju, Northeast, Brazil.

In this work, studies using samples collected in an urban area of Aracaju city, Sergipe State, Northeast, Brazil revealed that soil dust in suspension was the main source of total airborne particulate matter (TAPM), followed by vehicular pollution. The concentration profiles for Cu, Fe, Mn, Ni, V and Ti were established for the collected TAPM samples. The concentrations of SO2 and smoke were also measured all along the 42 sampling days. Through multivariate data analysis of the results a correlation between Fe, Mn, Ni and Ti in the mineral composition of the particles was established, indicating soil dust in suspension as the main source of TAPM. The concentrations of Cu and smoke were found to be related to vehicular traffic, and the second largest source of TAPM. Enrichment factors (EF) were calculated for the studied elements, and only Cu was found to be enriched. The concentrations of the elements in TAPM were evaluated using the geoaccumulation index (Igeo), and Fe, Mn, Ni, V and Ti were found to derive from natural sources, in TAPM. However, approximately 55% of the samples did not presented Cu contamination (Igeo≤0), and the remaining 45% presented Cu concentrations levels that indicated between low to moderate (0

Determination of Zn in Dry Feeds for Cats and Dogs by Energy-Dispersive X-Ray Fluorescence Spectrometry.

This work describes an analytical method for Zn determination in dry feeds for cats and dogs by energy-dispersive X-ray fluorescence (EDXRF). Samples of dry feed were powdered and prepared in the form of pellets for direct analysis by EDXRF. The LOQ (10σ) was 0.4 mg/kg. The samples were also analyzed by inductively coupled plasma-optical emission spectrometry (ICP-OES) as an independent comparative method. Application of a paired t-test showed no significant differences between Zn concentrations obtained by EDXRF and ICP-OES (at a 95% confidence level). Analysis of variance was also applied to the results and revealed no significant differences between the two techniques (at a 95% confidence level). The precision, expressed as the RSD (n = 3), was RSD < 4.55%. This analytical method provides a simple, rapid, accurate, and precise determination of Zn in dry feeds for cats and dogs by EDXRF as direct, solid-sample analysis.

Sci-Thur AM: Planning - 08: Validation of a commercial Monte Carlo code used for stereotactic radiosurgery and stereotactic body radiation therapy.

Our project consisted of validating the BrainLab iPlan Monte Carlo algorithm, used in conjunction with the stereotactic radiosurgery (SRS) mode of the Varian Novalis TX linear accelerator, for clinical use. Our approach was to "benchmark" the iPlan algorithm by comparing dose distributions with those obtained using a BEAMnrc model of the Novalis SRS mode. The BEAMnrc model was obtained by modifying an existing accelerator model to include the SRS flattening filter and source characteristics of the Novalis TX, and by reprogramming a component module to model the high definition 120-leaf multi-leaf collimator. The free parameters of interleaf air gap and leaf density were adjusted by matching to interleaf leakage profiles measured with EBT2 film. The BEAMnrc model was used to perform comparisons of depth dose curves and planar distributions for fields in homogeneous and heterogeneous slab phantoms between both MC codes and film. The source parameters of electron beam energy, size and angular spread were determined to be 6.6 MeV, 0.7 mm and 0.8 mm (cross and in-plane), and 1.27°, respectively. Comparisons between iPlan and EGSnrc MC codes show agreement within 2% for PDD curves, and a high pass rate (>98%) on gamma analysis (3%/3mm) for planar distributions, when the scored quantity is dose to medium. Discrepancies between both MC codes and film measurements were seen near bone inhomogeneities, where the film trend agrees somewhat with iPlan MC reporting dose-to-water. Further work is being performed to understand these differences and how film is used to measure dose near bone.

MO-F-BRB-05: Monte Carlo Modeling of the Novalis TX Stereotactic Radiosurgery Mode.

PURPOSE: To model the stereotactic mode of the Varian-Brainlab Novalis TX linear accelerator using the BEAMnrc Monte Carlo user code Methods: The EGSnrc Monte Carlo user codes BEAMnrc and DOSXYZnrc were used for photon simulations and dose calculations, respectively. A Monte Carlo model of a Varian Clinac 21 EX was modified to model the stereotactic radiosurgery (SRS) mode of the Novalis, taking into account the smaller dimensions of the SRS flattening filter and limited field sizes. The parameters of source such as energy, size and angular spread, were readjusted following a new procedure outlined by Almberg et al, 2012. A component module, DYNVMLC, previously used to model the Varian Millennium 120 multi-leaf collimator (MLC), was reprogrammed to include the four leaf types of the Varian high definition 120 leaf MLC. Interleaf air-gap and leaf density were adjusted to match interleaf leakage profiles measured with EBT2 film. Subsequent validation included profiles, percent depth dose curves and output factors measured with ion chambers, and other film measurements. RESULTS: From PDD measurements, the energy of the incident electron beam was determined to be 6.6 MeV. From penumbra measurements, the electron radial intensity distribution, given as the full width at half maximum of a Gaussian distribution, was found to be 0.7 mm (cross-plane) and 0.8 mm (in-plane). From profiles in water, the mean angular spread had to be adjusted to 1.27° to achieve an acceptable match. The interleaf air-gap and the density of the leaves of the HDMLC were determined to be 0.0047 cm and 18.5 g/cm3 , respectively. CONCLUSIONS: The Almberg procedure was successfully implemented in determining the electron beam parameters to model the Novalis Tx's SRS mode. Dose profiles simulated with the new HDMLC component module agreed with measurements within 2%.

Searching for optimal dose-volume constraints to reduce rectal toxicity after hypofractionated radiotherapy for prostate cancer.

AIMS: Late rectal toxicity is a major concern for prostate cancer patients treated with radiotherapy. Rectal dose-volume constraints, set as guidelines to reduce its incidence, vary among institutions. From a group of patients uniformly treated with hypofractionated radiotherapy, we correlated the incidence of late rectal toxicity with rectal dose-volume rectal constraints as described in three randomised trials for prostate cancer. MATERIALS AND METHODS: Favourable-risk prostate cancer patients received a dose of 66 Gy in 22 fractions without hormonal therapy. Toxicity was prospectively assessed using Common Toxicity Criteria v3. The whole or part of the rectum and rectal wall were contoured as an organ at risk for all patients. The rectal constraints of the RTOG 0126, RTOG 0415 and the PROFIT trials were used to correlate with late rectal toxicity. RESULTS: The median follow-up time was 58 months. Late rectal toxicity was 62, 20 and 18% for grades 0, 1 and 2/3, respectively. No statistically significant correlation was found between late rectal toxicity and the rectal constraints used in the three trials. The number of patients violating the recommended constraints was similar for the group with grade 2/3 toxicity and the group without any toxicity. Analysis derived from the actual dose-volume histogram dose parameters of this group of patients did not show a relationship between dose to volume of the rectum and late rectal toxicity that could generate a guideline of dose constraints. CONCLUSION: For this group of patients, despite the use of recognised dose-volume constraint guidelines of three trials, we were unable to establish a relationship between these constraints and the late rectal toxicity registered. Further studies on the correlation of dosimetric parameters with rectal toxicity, particularly for hypofractionated regimens, are required. Non-dosimetric factors may also be involved in the risk of late rectal toxicity.

Fractionated stereotactic radiotherapy in the treatment of pituitary macroadenomas.

BACKGROUND: The use of fractionated stereotactic radiotherapy (FSRT) has evolved with technical advances in noninvasive immobilization, radiation delivery, and image guidance. The application of FSRT to pituitary tumours is aimed at reducing toxicity through improved dose conformality and reduced treatment margins. The aim of the present paper is to report our own experience and to review the published data on FSRT for pituitary macroadenomas. METHODS: Between September 2000 and October 2005, 13 patients with pituitary macroadenoma underwent FSRT at our institution. In 12 patients, radiotherapy treatment followed surgical resection (transsphenoidal resection in 8, frontal craniotomy in 3, and multiple transsphenoidal resections followed by craniotomy in 1). In 4 patients, the tumours were functional (2 adrenocorticotropic hormone-secreting, 1 prolactinoma, and 1 growth hormone-secreting); the tumours in the remaining patients were clinically non-secretory. Before radiation, 3 patients had panhypopituitarism, and 6 patients had visual field defects. All patients were treated with FSRT using non-coplanar micro-multileaf collimation portals. A median dose of 50.4 Gy (range: 45-60 Gy) was prescribed to the 76.9%-95.2% isodose surface and delivered in 1.8-Gy fractions. The median planning target volume (gross tumour plus 3 mm) was 33.5 cm3 (range: 3.2-75 cm3). RESULTS: After a median follow-up of 24 months (range: 6-60 months), local control was 100%. One patient achieved clinical complete response. Treatment was well tolerated acutely for all patients. Neither radiation-induced optic neuropathy nor any radiation-related endocrine dysfunction was observed in our patients. CONCLUSIONS: In accordance with published series, we found FSRT to be safe and effective in the management of large pituitary macroadenomas.

Poster - Thurs Eve-19: IGRT QA for helical tomotherapy.

Helical tomotherapy (HT) with daily imaging using mega-voltage computed tomography for 3D image guided radiotherapy (IGRT). We present two techniques developed in our department to verify the integrity of the HT IGRT process. A phantom was constructed of two equally sized (5×10×10cm3 ) polystyrene blocks stacked on top of each other, each piece having a hole capable of receiving a small volume ionization chamber. A piece of Radiochromic film fits neatly in between the blocks. The phantom was CT scanned and the CT slices were transferred to the HT treatment planning system (TPS). The first procedure is used daily to test the image registration aspects of the IGRT process, and involves setting the phantom on the tomotherapy treatment unit table in an arbitrary position, imaging it, and performing image registration to determine what displacements are necessary to return the phantom to the planned position. A variation of this test is to place the phantom at a position incurring known displacements and ensuring the registration recognizes the shifts. The second procedure verifies the entire IGRT procedure, and includes the first procedure and the delivery of a treatment plan. An inverse plan is created to deliver simultaneously 2 and 3 Gy to 2 pre-defined targets. The treatment plan can be setup as a QA plan in the TPS software, allowing for a detailed comparison of ion chamber measurements and film dosimetry to the planned dose distribution. We have found that these QA procedures adequately test the IGRT capabilities of our HT unit.

Impact of geometric uncertainties on dose distribution during intensity modulated radiotherapy of head-and-neck cancer: the need for a planning target volume and a planning organ-at-risk volume.

We assessed the effect of geometric uncertainties on target coverage and on dose to the organs at risk (OARS) during intensity-modulated radiotherapy (IMRT) for head-and-neck cancer, and we estimated the required margins for the planning target volume (PTV) and the planning organ-at-risk volume (PRV). For eight head-and-neck cancer patients, we generated IMRT plans with localization uncertainty margins of 0 mm, 2.5 mm, and 5.0 mm. The beam intensities were then applied on repeat computed tomography (CT) scans obtained weekly during treatment, and dose distributions were recalculated.The dose-volume histogram analysis for the repeat ct scans showed that target coverage was adequate (V(100) >/= 95%) for only 12.5% of the gross tumour volumes, 54.3% of the upper-neck clinical target volumes (CTVS), and 27.4% of the lower-neck CTVS when no margins were added for PTV. The use of 2.5-mm and 5.0-mm margins significantly improved target coverage, but the mean dose to the contralateral parotid increased from 25.9 Gy to 29.2 Gy. Maximum dose to the spinal cord was above limit in 57.7%, 34.6%, and 15.4% of cases when 0-mm, 2.5-mm, and 5.0-mm margins (respectively) were used for prv.Significant deviations from the prescribed dose can occur during IMRT treatment delivery for head-and-neck cancer. The use of 2.5-mm to 5.0-mm margins for PTV and PRV greatly reduces the risk of underdosing targets and of overdosing the spinal cord.

Stereotactic radiosurgery in the management of angiographically occult vascular malformations.

PURPOSE: To evaluate the role of stereotactic radiosurgery in the treatment of angiographically occult vascular malformations (AOVMs). METHODS AND MATERIALS: From 1987 to 1996, 21 patients, 10 males and 11 females, median age of 41 years (range: 7-75 years), with an intracerebral AOVM underwent stereotactic radiosurgery at our institution. All were considered at high risk for surgical intervention. The vascular lesions were located in the brainstem (17 patients), basal ganglia (2), occipital lobe (1), and cerebellum (1). Diagnosis was based on high-resolution magnetic resonance imaging (MRI). Clinical presentation at onset included previous intracerebral hemorrhage (20 patients) and epilepsy (1). All patients were treated with a linac-based radiosurgical technique. The median dose delivered was 25 Gy (range 13-50 Gy), typically prescribed to the 80-90% isodose surface (range 50-90%), which corresponded to the periphery of the vascular malformation. Patients were followed by clinical neurologic assessment and by MRI on a regular interval basis. RESULTS: Follow-up was obtained in 20 patients; clinical or MRI information was not available for 1 patient, and this patient was excluded from our analysis. At a median follow-up of 77 months (range: 4-141 months), follow-up MRIs postradiosurgery do not demonstrate any changes in the appearance of the AOVM. Four patients developed an intracranial bleed at 4, 8, 35, and 57 months postradiosurgery. Annual hemorrhage rates were considerably higher in the observation period preradiosurgery than postradiosurgery (30% vs. 3.2%, p < 0.001). Complications postradiosurgery were observed in 4 patients. Three patients developed mild to moderate edema surrounding the radiosurgical target, expressed at 5, 8, and 24 months, respectively. In all cases, the edema was transient and resolved completely on subsequent MRIs. One of the 4 patients developed radiation necrosis 8 months after radiosurgery. CONCLUSION: The use of stereotactic radiosurgery in the treatment of AOVM continues to be controversial. Our results appear to show a reduction in the risk of symptomatic hemorrhage post treatment. Patients with previous history of hemorrhage or progressive neurologic deficit and small, well circumscribed lesions may benefit from a trial of stereotactic radiosurgery.

An alternative mantle irradiation technique using 3D CT- based treatment planning for female patients with Hodgkin's disease.

PURPOSE: For female patients, radiotherapy treatment for Hodgkin's disease invariably results in the irradiation of breast tissue that may lead to radiation induced secondary cancers. The risk for secondary breast cancer is correlated with dose. We have developed a technique in an attempt to increase breast sparing during mantle field irradiation for female patients. MATERIAL AND METHODS: To minimize the irradiated breast volume, a virtual simulation technique making use of a Styrofoam breast immobilization board has been developed whereby the patient lies prone with the breasts positioned in grooves within the board. The breast position is adjusted using Styrofoam wedges, and breast placement is verified using an AP CT-pilot view. A CT scan of the neck and thoracic regions is taken, and the lymph nodes, breast volume and critical structures are outlined. Virtual simulation of the mantle fields (typically AP/PA isocentric beams) is performed, and beam blocks are drawn on the digitally reconstructed radiographs (DRR) generated by the virtual simulation package. The shielding is designed to allow adequate margins around the lymph nodes while maximizing shielding of the lung and breast tissues. The para-aortic fields are also easily determined through virtual simulation, where multi-planar reconstructions (MPR) and 3D renderings of the patient's CT data are used to determine the field limits and beam gaps. In addition to allowing for the geometric optimization of the positioning of the breasts under the lung shields, the virtual simulation technique provides the necessary information for a 3D dosimetric analysis, including dose-volume histograms (DVHs) of the irradiated breast volume. RESULTS: The 3D breast sparing technique was qualitatively and quantitatively compared to non-CT-based techniques and other 3D techniques currently available to assess the protection of the breasts. In a preliminary analysis, virtual simulation images (DRRs, 3D rendering and multi-planar reconstruction) demonstrated the advantage of using the breast sparing technique. A further analysis of DVHs showed a reduction of at least 50% in the volume of breast tissue irradiated when using the breast positioning board and virtual simulation as compared to the conventional simulation techniques where a breast immobilization board was not used. CONCLUSIONS: The use of a breast immobilization board and of a virtual simulation technique is recommended for the planning and treatment of female patients with Hodgkin's disease. DVH analysis has shown that this leads to a decrease in the volume of breast irradiated. It is hoped that this approach will reduce the risk of secondary breast malignancies in female patients with Hodgkin's disease.

Dosimetry of hip irradiation for the prevention of heterotopic bone formation after arthroplasty.

PURPOSE: The dosimetry of hip irradiation for the prevention of heterotopic bone formation following arthroplasty is complicated by the use of custom shielding in the treatment portal, and the fact that irradiation is usually required during a 48 hour period following surgery. Both the machine output and depth dose factors of the resulting fields are modified by the presence of the shielding blocks. A simplified dosimetric approach, based on correction factors for both the output and depth dose as a function of field geometry is presented for various megavoltage energy beams. MATERIALS AND METHODS: Measurements of relative dose factors (RDF) and percentage depth dose (PDD) were carried out for different combinations of field size, block size and separation between adjacent blocks. Both RDF and PDD measurements were made in a water phantom. Ratios of RDF and PDD were obtained by dividing individual measurements or curves by the corresponding values for the open field (i.e., without blocks). The average values of these ratios constitute the correction factors to be applied for a given MU or treatment time calculation. RESULTS: Extensive RDF and PDD measurements reveal that for the field and block dimensions of interest the correction factors for RDF can be parameterized as a function of separation between two adjacent blocks and beam energy alone and the depth correction factors are additionally only a function of depth. The correction factors for depth dose are equally valid for fixed source-skin distance techniques (that use PDD) and fixed source-axis distance techniques (that use TMR). CONCLUSION: A simple model for the calculation of output in hip irradiation is presented for the situation where the use of computer-based algorithms may not be practical. The model accurately predicts the RDF of the treatment portal to within 2% and the PDD to within 2% for the range of field sizes, block sizes, block gaps and beam energies of interest ignoring other variables.

Limiting values of backscatter factors for low-energy x-ray beams.

Models for the calculation of upper and lower limiting values to the backscatter factor (BSF) are presented. The upper limit is obtained from Monte Carlo simulations of infinite parallel beams incident on semi-infinite phantoms with the dose contributions from all orders of photon scatter considered. The lower limits are calculated using an analytical photon transport model which considers only the primary dose and the scatter dose from photons that have undergone single scattering interactions in the phantom. The limiting values can be used to evaluate measured and modelled BSF values for x-ray beams with photons of < or = 150 keV. A parametrization of the limiting values in terms of photon energy and irradiation field size is presented so that results determined for monoenergetic beams can be extended to polyenergetic spectra. The utility of the limits is illustrated by comparisons made with BSFs from the literature.