Occupational and ambient radiation exposures from Lu-177 DOTATATE during targeted therapy.

Lutetium-177 (DOTATATE) (177Lu; T1/2 6.7 days), a labelled ß- and Auger-electron emitter, is widely used in treatment of neuroendocrine tumours. During performance of the procedure, staff and other patients can potentially receive significant doses in interception of the gamma emissions [113 keV (6.4%) and 208 keV (11%)] that are associated with the particle decays. While radiation protection and safety assessment are required in seeking to ensure practices comply with international guidelines, only limited published studies are available. The objectives of present study are to evaluate patient and occupational exposures, measuring ambient doses and estimating the radiation risk. The results, obtained from studies carried out in Riyadh over an 11 month period, at King Faisal Specialist Hospital and Research Center, concerned a total of 33 177Lu therapy patients. Patient exposures were estimated using a calibrated Victoreen 451P survey meter (Fluke Biomedical), for separations of 30 cm, 100 cm and 300 cm, also behind a bed shield that was used during hospitalization of the therapy patients. Occupational and ambient doses were also measured through use of calibrated thermoluminescent dosimeters and an automatic TLD reader (Harshaw 6600). The mean and range of administered activity (in MBq)) was 7115.2 ± 917.2 (4329-7955). The ambient dose at corridors outside of therapy isolation rooms was 1.2 mSv over the 11 month period, that at the nursing station was below the limit of detection and annual occupational doses were below the annual dose limit of 20 mSv. Special concern needs to be paid to comforters (carers) and family members during the early stage of radioisotope administration.

Calibration of MTT assay in proton beams using radiochromic films.

PURPOSE: This study provides methodology of calibrating as well as controlling the output for an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) colorimetric assay irradiated in a low energy proton beam using EBT3-model GAFCHROMICTM film, without correcting for quenching effect. METHODS: A calibrated Markus ionization chamber was used to measure the depth dose and beam output for 26.5 MeV protons produced by a CS30 cyclotron. A time-controlled aluminum cylinder was added in front of the horizontal beam-exit serving as a radiation shutter. Following the TRS-398 reference dosimetry protocol for proton beams, the output was calibrated in water at a reference depth of 3 mm. EBT3 film was calibrated for doses up to 8 Gy at the same depth. To verify the dose distribution for each 96-well MTT assay plate, EBT3 film was placed at the reference depth during irradiation and cell doses were scaled by measured percent depth dose (PDD) data. RESULTS: The radiochromic film dosimetry system in this study provides dose measurements with an uncertainty better than 3.3% for doses higher than 1 Gy. From a single exposure and utilizing the Gaussian shape of the beam, multiple dose points can be obtained within different wells of the same plate ranging from 6.9 Gy (sigma ∼4%) in the central well, and 2 Gy (sigma ∼8%) for wells positioned closer to the periphery. CONCLUSIONS: We described a methodology for radiochromic film-based dose monitoring system, using low-energy protons, which can be used for the MTT assay in any proton beam, except within Bragg peak region.

Evaluations of N-(Isobutoxymethyl) acrylamide gel dosimeter by NMR technique for radiotherapy and uncertainty in dose measurements.

N-(Isobutoxymethyl) acrylamide (NIBMA) monomer in gelatin, named NIBMAGAT gel dosimeter, was prepared and investigated by nuclear magnetic imaging (NMR) for radiotherapy in the dose range of 0-30 Gy. NIBMA monomer polymerizes upon irradiation, increasing spin-spin relaxation rate R2. The addition of glycerol as a co-solvent in the gel matrix improved its radiation sensitivity better than the co-solvents of acetone and methanol. The increase of glycerol content by 1% wt/wt enhanced the sensitivity by ˜ 3.1%. This gel has better radiation sensitivity as compared to the polyacrylamide gel (PAG) dosimeter; the sensitivities of NIBMAGAT gel and normoxic polyacrylamide gel (nPAG) are ≈0.13 and ≈0.1 s-1.Gy-1, respectively. By comparing NIBMAGAT gel dosimeter with PAG, nMAG and nPAG gel dosimeters, NIBMAGAT gel dosimeter is less influenced by scanning temperature than the last three dosimeters. The gel is water equivalent and has an energy-independent response from 80 keV to 20 MeV. The overall uncertainty of dose measurement using NIBMAGAT gel is 5.46% at 2σ. Our findings suggest the applicability of using NIBMAGAT gel dosimeter by NMR technique for dose verification/planning in the practice of clinical radiotherapy.

Helical Tomotherapy versus Conventional Technique for Post Mastectomy Left Sided Breast Cancer; Dosimetric Study.

PURPOSE: To evaluate the feasibility of using Helical Tomotherapy (HT) for post mastectomy left-sided breast cancer. METHODS AND MATERIALS: Treatment plans were generated for 5 post mastectomy left sided breast cancer patients treated at king Faisal Specialist Hospital & Research Center, Riyadh, Saudi Arabia, comparing three-dimensional technique with the HT planning. The prescribed dose was 50 Gy in 25 fractions; the planning target volume (chest wall and nodal volumes) was contoured according to RTOG atlas and the heart, lungs, spinal cord and contralateral breast were contoured as Organs at Risks (OARs). RESULTS: Both plans achieved the planning criteria, however the HT plan increased the minimal dose to the PTV (78% vs. 45.4%, p=0.043), improving the dose conformity (0.76 vs. 0.38, p=0.034) and dose homogeneity (1.05 vs. 1.2, p=0.08), while a three-dimensional technique has better V20 of lung (15.8% vs. 22.6%, p=0.04), Mean Lung Dose (7.6Gy vs. 13.8Gy, p=0.043), contralateral breast dose (0.1 vs. 12.7, p=0.043) and comparable Mean Heart Dose (4.4Gy vs. 5.3Gy, p=0.136). CONCLUSION: Both plans achieved comparable target coverage and OARs sparing, however HT plans provided better dose conformity and homogeneity than did the three-dimensional plans at the cost of less sparing of the heart, left lung and contralateral breast for treatment of left-sided post mastectomy breast cancer.

Radiotherapy dose escalation with concurrent chemotherapy in locally advanced cervix cancer is feasible

Background. To test the feasibility of radiotherapy dose escalation using volumetric arc therapy (VMAT) and image-guided radiotherapy (IGRT) with concurrent chemotherapy in locally advanced cervix cancer (LACC) and compare this with whole-pelvis three-dimensional conformal radiation therapy (CRT) in terms of clinical toxicity. Methods. Database was reviewed for all LACC patients treated during 2011 and 2012. Twenty patients who were treated with escalated dose of radiotherapy using VMAT were selected for analysis. A matched cohort of 40 patients who had 3DCRT between 2005 and 2008 was selected as control. Mean basal hemoglobin, average weekly hemoglobin, and maximal drop in hemoglobin were measured for both 3DCRT and VMAT groups and treatment toxicity scored according to RTOG criteria. Charts were also reviewed for other acute and late toxicities including the rate of compliance with prescribed treatment. Results. Mean age was 46 (30-63) and 47 years (33-67), mean tumor size was 5.5 and 5 cm and blood transfusion rate was 55 and 45 % in CRT and VMAT groups, respectively. Hemoglobin toxicity (Grade I-II) was encountered in 97.5 and 90 % (p 0.0.3) while Grade I-III Leukopenia was 90 and 70 % (p 0.02), respectively. There was no Grade 3 or 4 GI or GU toxicity. Conclusion. VMAT/IGRT with dose escalation is feasible in LACC without excessive toxicity as compared to CRT "Box". We propose a randomized control trial of this novel approach of higher radiation dose and volume against the standard prescription based on CRT (AU)

No disponible

Radiotherapy dose escalation with concurrent chemotherapy in locally advanced cervix cancer is feasible.

BACKGROUND: To test the feasibility of radiotherapy dose escalation using volumetric arc therapy (VMAT) and image-guided radiotherapy (IGRT) with concurrent chemotherapy in locally advanced cervix cancer (LACC) and compare this with whole-pelvis three-dimensional conformal radiation therapy (CRT) in terms of clinical toxicity. METHODS: Database was reviewed for all LACC patients treated during 2011 and 2012. Twenty patients who were treated with escalated dose of radiotherapy using VMAT were selected for analysis. A matched cohort of 40 patients who had 3DCRT between 2005 and 2008 was selected as control. Mean basal hemoglobin, average weekly hemoglobin, and maximal drop in hemoglobin were measured for both 3DCRT and VMAT groups and treatment toxicity scored according to RTOG criteria. Charts were also reviewed for other acute and late toxicities including the rate of compliance with prescribed treatment. RESULTS: Mean age was 46 (30-63) and 47 years (33-67), mean tumor size was 5.5 and 5 cm and blood transfusion rate was 55 and 45 % in CRT and VMAT groups, respectively. Hemoglobin toxicity (Grade I-II) was encountered in 97.5 and 90 % (p 0.0.3) while Grade I-III Leukopenia was 90 and 70 % (p 0.02), respectively. There was no Grade 3 or 4 GI or GU toxicity. CONCLUSION: VMAT/IGRT with dose escalation is feasible in LACC without excessive toxicity as compared to CRT "Box". We propose a randomized control trial of this novel approach of higher radiation dose and volume against the standard prescription based on CRT.

Effective spatially fractionated GRID radiation treatment planning for a passive grid block.

OBJECTIVE: To commission a grid block for spatially fractionated grid radiation therapy (SFGRT) treatments and describe its clinical implementation and verification through the record and verify (R&V) system. METHODS: SFGRT was developed as a treatment modality for bulky tumours that cannot be easily controlled with conventionally fractionated radiation. Treatment is delivered in the form of open-closed areas. Currently, SFGRT is performed by either using a commercially available grid block or a multileaf collimator (MLC) of a linear accelerator. In this work, 6-MV photon beam was used to study dosimetric characteristics of the grid block. We inserted the grid block into a commercially available treatment planning system (TPS), and the feasibility of delivering such treatment plans on a linear accelerator using a R&V system was verified. Dose measurements were performed using a miniature PinPoint(TM) ion chamber (PTW, Freiburg, Germany) in a water phantom and radiochromic film within solid water slabs. PinPoint ion chamber was used to measure the output factors, percentage depth dose (PDD) curves and beam profiles at two depths, depth of maximum dose (zmax) and 10 cm. Film sheets were used to measure dose profiles at zmax and 10-cm depth. RESULTS: The largest observed percentage difference between output factors for the grid block technique calculated by the TPS and measured with the PinPoint ion chamber was 3.6% for the 5 × 5-cm(2) field size. Relatively significant discrepancies between measured and calculated PDD values appear only in the build-up region, which was found to amount to <4%, while a good agreement (differences <2%) at depths beyond zmax was observed. Dose verification comparisons performed between calculated and measured dose distributions were in clinically acceptable agreements. When comparing the MLC-based with the grid block technique, the advantage of treating large tumours with a single field reduces treatment time by at least 3-5 times, having significant impact on patient throughput. CONCLUSION: The proposed method supports and helps to standardize the clinical implementation of the grid block in a safer and more accurate way. ADVANCES IN KNOWLEDGE: This work describes the method to implement treatment planning for the grid block technique in radiotherapy departments.

Dosimetry of biological irradiations using radiochromic films.

Delivering accurate radiation dose to blood specimens during biological irradiations is essential in quantifying damage of ionizing radiation. To estimate dose to blood samples as accurately as possible, pieces of EBT2 model GAFCHROMIC™ film were placed within an approximately 10 mm finely ground rice layer that was used to simulate test specimens inside 40 mL plastic flasks. Irradiations of flasks were carried out using an X-RAD 320 irradiator with a beam quality of 320 kVp and a measured half value layer of 1.12 mm Cu, in air and in a full scattering setup which consisted of either rice or Solid Water™ (SW) surrounding flasks, filled to the same level at top of the flasks, together with a 5 cm thick SW slab beneath them. Outputs, per cent depth doses and beam profiles at different depths were measured and compared between setups. For the same setting, the dose delivered to the middle flask under the full scattering setup is 22% larger than with the in-air setup at the depth of the specimen and 9.2% more homogeneous across the specimen thickness of 10 mm (2.3% variation in comparison to the surface). Rice showed a fairly similar performance to SW within 1% at the same depth of 10 mm. Experimental setup based on full scattering conditions was shown to provide faster, more homogenous and fairly uniform dose delivery to biological specimens in comparison to conventionally used in-air setups.

SU-E-T-237: Leading 25 in 25: A Bibliometric Analysis of Classics Articles in IMRT.

PURPOSE: Scientific publication in IMRT has experienced significant development since its introduction. Bibliometric analyses allow an understanding of how this publication trend is organized at an aggregated level. Citation analysis is one of the most widely used bibliometric tools of scientometrics. Analysis of classics, defined as an articles with 100 or more citations, is common in the biomedical sciences as it reflects an article's influence and the recognition it receives in its professional and scientific community. Our objective was to identify the 25 most frequently cited classic articles in IMRT in the past 25 years. METHODS: The 25 most-cited IMRT articles were identified by searching ISI's Web of Knowledge and Pubmed databases for all related publications from 1986 through 2011. Articles were evaluated for several characteristics such as author(s), institution, country of origin, publication year, type, and number of citations. An unadjusted categorical analysis was performed to compare all articles published in the search period. RESULTS: Our search yielded a cumulative total of 37,197 entries for the publication period. Original research and clinical trial articles accounted for 25,827 and 312, respectively, for a total of 25,719 entries. The 25 most-cited articles were identified from the latter sum and selected out of 123 classics. The number of citations per article ranged from 203 to 504. IMRT classics appeared in one general and five core journals. CONCLUSIONS: This study analyzed publication patterns focused on IMRT, its most influential classic articles, journals that published them, their authors and other salient characteristics. Such information is of importance to researchers and those who wish to study the history and development of the field.

Detecting electron beam energy shifts with a commercially available energy monitor.

Routine electron beam quality assurance requires an accurate, yet practical, method of energy characterization. Subtle shifts in beam energy may be produced by the linac bending magnet assembly, and the sensitivity of a commercially available electron beam energy-monitoring device for monitoring these small energy drifts has been evaluated. The device shows an 11% change in signal for a 2 mm change in the I50 energy parameter for low energy electron beams (in the vicinity of 6 MeV) and a 2.5% change in signal for a 2 mm change in the I50 energy parameter for high energy electron beams (in the vicinity of 22 MeV). Thus the device is capable of detecting small energy shifts resulting from bending magnet drift for all clinically relevant electron beams.