Aim of this study was to compare the dosimetric aspects of whole breast radiotherapy (WBRT) between an irregular surface compensator (ISC) and a conventional tangential field technique using physical wedges. Treatment plans were produced for 20 patients. The Eclipse treatment planning system (Varian Medical Systems) was used for the dose calculation: For the physical wedge technique, the wedge angle was selected to provide the best dose homogeneity; for the ISC technique, the fluence editor application was used to extend the optimal fluence. These two treatment plans were compared in terms of doses in the planning target volume, the dose homogeneity index, the maximum dose, ipsilateral lung and heart doses for left breast irradiation, and the monitor unit counts required for treatment. Compared with the physical wedge technique, the ISC technique significantly reduced the dose homogeneity index, the maximum dose, the volumes received at 105% of the prescription dose, as well as reducing both the ipsilateral lung and heart doses (P < 0.01 for all comparisons). However, the monitor unit counts were not significantly different between the techniques (P > 0.05). Thus, the ISC technique for WBRT enables significantly better dose distribution in the planning target volume.
Dose distribution; irregular surface compensator technique; physical wedge technique; whole breast radiotherapy
Trigeminal neuralgia (TN) is treated in CyberKnife (Accuray Inc, Sunnyvale, USA) with the 5 mm collimator whose dosimetric inaccuracy is higher than the other available collimators. The 7.5 mm collimator which is having less dosimetric uncertainty can be an alternative for 5 mm collimator provided the dose distribution with 7.5 mm collimator is acceptable. Aim of this study is to analyze the role of 7.5 mm collimator in CyberKnife treatment plans of TN. The treatment plans with 5 mm collimators were re-optimized with 7.5 mm collimator and a bi-collimator system (5 mm and 7.5 mm). The treatment plans were compared for target coverage, brainstem doses, and the dose to normal tissues. The target and brainstem doses were comparable. However, the conformity indices were 2.31 ± 0.52, 2.40 ± 0.87 and 2.82 ± 0.51 for 5 mm, bi-collimator (5mm and 7.5 mm), 7.5 mm collimator plans respectively. This shows the level of dose spillage in 7.5 mm collimator plans. The 6 Gy dose volumes in 7.5 mm plans were 1.53 and 1.34 times higher than the 5 mm plan and the bi-collimator plans respectively. The treatment time parameters were lesser for 7.5 mm collimators. Since, the normal tissue dose is pretty high in 7.5 mm collimator plans, the use of it in TN plans can be ruled out though the treatment time is lesser for these 7.5 mm collimator plans.
Collimators; CyberKnife; stereotactic radiosurgery; trigeminal neuralgia
This analysis evaluates the feasibility and dosimetric results of a simplified intensity-modulated radiotherapy (IMRT) treatment using a cobalt-therapy unit for post-operative breast cancer. Fourteen patients were included. Three plans per patient were produced by a cobalt-60 source: A standard plan with two wedged tangential beams, a standard tangential plan optimized without the use of wedges and a plan based on the forward-planned “field-in-field” IMRT technique (Co-FinF) where the dose on each of the two tangential beams was split into two different segments and the two segments weight was determined with an iterative process. For comparison purposes, a 6-MV photon standard wedged tangential treatment plan was generated. Dmean, D98%, D2%, V95%, V107%, homogeneity, and conformity indices were chosen as parameters for comparison. Co-FinF technique improved the planning target volume dose homogeneity compared to other cobalt-based techniques and reduced maximum doses (D2%) and high-dose volume (V110%). Moreover, it showed a better lung and heart dose sparing with respect to the standard approach. The higher dose homogeneity may encourage the adoption of accelerated-hypofractionated treatments also with the cobalt sources. This approach can promote the spread of breast conservative treatment in developing countries.
Breast neoplasms; cobalt machine; intensity-modulated radiotherapy; radiotherapy
The objective of this study is to check the feasibility of in vivo rectal dose measurement in intensity-modulated radiotherapy (IMRT) and CyberKnife treatments for carcinoma prostate. An in-house pelvis phantom made with bee's wax was used in this study. Two cylindrical bone equivalent materials were used to simulate the femur. Target and other critical structures associated with carcinoma prostate were delineated on the treatment planning images by the radiation oncologist. IMRT treatment plan was generated in Oncentra Master Plan treatment planning system and CyberKnife treatment plan was generated in Multiplan treatment planning system. Dose measurements were carried out in phantom and in patient using Gafchromic EBT3 films. RIT software was used to analyze the dose measured by EBT3 films. The measured doses using EBT3 films were compared with the TPS-calculated dose along the anterior rectal wall at multiple points. From the in-phantom measurements, it is observed that the difference between calculated and measured dose was mostly within 5%, except for a few measurement points. The difference between calculated and measured dose in the in-patient measurements was higher than 5% in regions which were away from the target. Gafchromic EBT3 film is a suitable detector for in vivo rectal dose measurements as it offers the possibility of analyzing the dose at multiple points. In addition, the method of extending this in vivo rectal dose measurement technique as a tool for patient-specific quality assurance check is also analyzed.
Gafchromic EBT3; in vivo dosimetry; rectal dose measurement
The objective of this work was to investigate and quantify the effect of sharp edges of the phantom on the point dose measurement during patient-specific dosimetry with Rapid Arc (RA). Ten patients with carcinoma of prostate were randomly selected for this dosimetric study. Rapid Arc plans were generated with 6 MV X-rays in the Eclipse (v 8.6.14) with single arc (clockwise). Dosimetry verification plans were generated for two phantoms (cylindrical and rectangular). The cylindrical phantom was solid water (diameter 34 cm) and the rectangular phantom was a water phantom (25 cm × 25 cm × 10 cm). These phantoms were pre-scanned in computed tomography (CT) machine with cylindrical ionization chamber (FC65) in place. The plans were delivered with Novalis Tx linear accelerator with 6 MV X-rays for both the phantoms separately. The measured dose was compared with the planned dose for both the phantoms. Mean percentage deviation between measured and planned doses was found to be 4.19 (SD 0.82) and 3.63 (SD 0.89) for cylindrical and rectangular phantoms, respectively. No significant dosimetric variation was found due to the geometry (sharp edges) of the phantom. The sharp edges of the phantom do not perturb the patient specific Rapid Arc dosimetry significantly.
Phantoms; point dose measurements; Rapid Arc
Four dimensional (4D) target localization system (Calypso System) was installed at our hospital, which is equipped with Beacon Transponders, Console, Electromagnetic Array, Optical System, Tracking Station, Treatment table overlay, and Calypso kVue Couch top. The objective of this presentation is to describe the results of commissioning measurements carried out on the Calypso System to verify the manufacturer specifications and also to evolve a quality assurance (QA) procedure which can be used to test its performance routinely. The QA program consists of a series of tests (QA for checking the calibration or system accuracy, Camera Calibration with L-frame fixture, Camera Calibration with T-frame fixture, System calibration Fixture targets test, Localization, and Tracking). These tests were found to be useful to assess the performance of the Calypso System.
Calypso system; electromagnetic array; target localization; tracking
In high dose rate (HDR) brachytherapy, the source dwell times and dwell positions are vital parameters in achieving a desirable implant dose distribution. Inverse treatment planning requires an optimal choice of these parameters to achieve the desired target coverage with the lowest achievable dose to the organs at risk (OAR). This study was designed to evaluate the optimum source step size and maximum source dwell time for prostate brachytherapy implants using an Ir-192 source. In total, one hundred inverse treatment plans were generated for the four patients included in this study. Twenty-five treatment plans were created for each patient by varying the step size and maximum source dwell time during anatomy-based, inverse-planned optimization. Other relevant treatment planning parameters were kept constant, including the dose constraints and source dwell positions. Each plan was evaluated for target coverage, urethral and rectal dose sparing, treatment time, relative target dose homogeneity, and nonuniformity ratio. The plans with 0.5 cm step size were seen to have clinically acceptable tumor coverage, minimal normal structure doses, and minimum treatment time as compared with the other step sizes. The target coverage for this step size is 87% of the prescription dose, while the urethral and maximum rectal doses were 107.3 and 68.7%, respectively. No appreciable difference in plan quality was observed with variation in maximum source dwell time. The step size plays a significant role in plan optimization for prostate implants. Our study supports use of a 0.5 cm step size for prostate implants.
High dose rate brachytherapy; inverse optimization; adoptive volume optimization; step size; dwell time
Online adaptive radiotherapy for bladder cancer is a novel radiotherapy technique that was found feasible in a pilot study at a single academic institution. In September 2010 this technique was opened as a multicenter study through the Trans-Tasman Radiation Oncology Group (TROG 10.01 bladder online adaptive radiotherapy treatment). Twelve centers across Australia and New-Zealand registered interest into the trial. A multidisciplinary team of radiation oncologists, radiation therapists and medical physicists represented the trial credentialing and technical support team. To provide timely activation and proper implementation of the adaptive technique the following key areas were addressed at each site: Staff education/training; Practical image guided radiotherapy assessment; provision of help desk and feedback. The trial credentialing process involved face-to-face training and technical problem solving via full day site visits. A dedicated “help-desk” team was developed to provide support for the clinical trial. 26% of the workload occurred at the credentialing period while the remaining 74% came post-center activation. The workload was made up of the following key areas; protocol clarification (36%), technical problems (46%) while staff training was less than 10%. Clinical trial credentialing is important to minimizing trial deviations. It should not only focus on site activation quality assurance but also provide ongoing education and technical support.
Adaptive radiotherapy; clinical trial; credentialing; image-guided radiotherapy
The aim of present study was to evaluate the intensity-modulated radiation therapy (IMRT) plans using different homogeneity and conformity indices in gynecological cancers, as well as to compare and find out the most reliable and accurate measure of the dose homogeneity among the available indices. In this study, a cohort of 12 patients were registered for evaluation, those receiving dynamic IMRT treatment on Clinac-2300C/D linear accelerator with 15-Mega Voltage (MV) photon beam. Dynamic IMRT plans were created on Eclipse treatment planning system with Helios dose volume optimization software. Homogeneity indices (HI) such as H index, modified H index, HI index, modified HI index, and S-index (sigma-index) proposed by M Yoon et al. (2007) were calculated and compared. The values of S-index vary from 1.63 to 2.99. The results indicate that the H and HI indices and their modified versions may not provide the correct dose homogeneity information, but the S-index provides accurate information about the dose homogeneity in the Planning Target Volume (PTV). Each plan was compared with 6-MV photon energy on the basis of S-index and conformity index (CI). Organs at risk (OAR) doses with 6-MV and 15-MV beams were also reported.
Intensity-modulated radiation therapy; homogeneity; Conformity index; gynecological cancer; dose; organ at risk
Dose calculation algorithm is one of the main sources of uncertainty in the radiotherapy sequences. The aim of this study was to compare the accuracy of different inhomogeneity correction algorithms for external photon beam dose calculations. The methodology was based on International Atomic Energy Agency TEC-DOC 1583. The phantom was scanned in every center, using computed tomography and seven tests were planned on three-dimensional treatment planning systems (TPSs). The doses were measured with ion chambers and the deviation between measured and TPS calculated dose was reported. This methodology was tested in five different hospitals which were using six different algorithms/inhomogeneity correction methods implemented in different TPSs. The algorithms in this study were divided into two groups: Measurement-based algorithms (type (a)) and model-based algorithms (type (b)). In type (a) algorithms, we saw 7.6% and 11.3% deviations out of agreement criteria for low- and high-energy photons, respectively. While in type (b) algorithms, these values were 4.3% and 5.1%, respectively. As a general trend, the numbers of measurements with results outside the agreement criteria increase with the beam energy and decrease with advancement of TPS algorithms. More advanced algorithm would be preferable and therefore should be implanted in clinical practice, especially for calculation in inhomogeneous medias like lung and bone and for high-energy beams calculation at low depth points.
Correction-based algorithm; external radiotherapy; inhomogeneity correction algorithms; model-based algorithm; photon dose calculation; treatment planning system
Equivalent field for electron beams is considered by using pencil beam theory. According to the Fermi-Eyges model the dose distribution of an electron pencil beam has a Gaussian profile. For this function determination of mean square radial displacement scattering of electrons is important. In this study the contribution of back scatter electron has been taken into account by using the multiple scattering theories for calculating mean square radial displacement scattering. The dimension of standard equivalent field depends on depth and shape of treatment field. Here the depth under study is the depth that mean square radial displacement scattering is extremum and the shape of treatment field is rectangular. In this study four energies were used 6, 9,12 and 15 MeV electron beams of 2100C/D Varian Linac. Findings of this study are based on analytical calculations, which are in good agreement with other experimental data. The findings of this study that were resulted from formula, shows, for all circular fields of radius ≥LSE (lateral scattering equilibrium) were considered broad field and equivalent. For validating the findings, Percentage Depth Dose (PDD) and Output factors were measured in 15 MeV electron beams for 7 × 3-cm, 6 × 4-cm and 4 × 2-cm and their equivalent squares and equivalent circular fields and compared.
Dosimetry; electron therapy; field equivalence; mass angular scattering power; pencil beam theory
The radioprotective potential of bioflavonoid, rutin (RUT) and quercetin (QRT) was investigated in Swiss albino mice exposed to gamma radiation. The radioprotective potential of RUT and QRT was assessed in pre-treatment group of mice followed on radiation-induced changes in glutathione (GSH), glutathione-S-transferase (GST), superoxide dismutase (SOD), catalase (CAT), and lipid peroxidation (LPO) levels were also analyzed. Elevation in the GSH, GST, SOD, CAT, and decreased LPO levels were observed in RUT and QRT pretreated group when compared to the irradiated animals. Furthermore, it was observed that RUT and QRT treatment was found to inhibit various free radicals generated in vitro, viz., 2,2-diphenyl-1-picrylhydrazyl(DPPH), O2, 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS)+, and OH in a concentration-dependent manner. This study clearly demonstrates the free radical scavenging action of RUT and QRT, indicating that it may have its potential as a radioprotective agent. Furthermore, the presence of a phenolic group in RUT and QRT is known to contribute to scavenging the radiation-induced free radicals and inhibition of oxidative stress. Present findings demonstrate the potential of RUT and QRT in mitigating radiation-induced oxidative stress, which may be attributed to the inhibition of radiation-induced decline in the endogenous antioxidant levels and scavenging of radiation-induced free radicals.
Antioxidant; free radicals; rutin; quercetin
Building materials, collected from different sites in Ramsar, a northern coastal city in Iran, were analyzed for their natural radionuclide contents. The measurements were carried out using a high resolution high purity Germanium (HPGe) gamma-ray spectrometer system. The activity concentration of 226Ra, 232Th, and 40K content varied from below the minimum detection limit up to 86,400 Bqkg-1, 187 Bqkg-1, and 1350 Bqkg-1, respectively. The radiological hazards incurred from the use of these building materials were estimated through various radiation hazard indices. The result of this survey shows that values obtained for some samples are more than the internationally accepted maximum limits and as such, the use of them as a building material pose significant radiation hazard to individuals.
Ramsar; building materials; gamma spectrometry; hazard indices
For the head-and-neck cancer bilateral irradiation, intensity-modulated radiation therapy (IMRT) is the most reported technique as it enables both target dose coverage and organ-at-risk (OAR) sparing. However, during the last 20 years, three-dimensional conformal radiotherapy (3DCRT) techniques have been introduced, which are tailored to improve the classic shrinking field technique, as regards both planning target volume (PTV) dose conformality and sparing of OAR’s, such as parotid glands and spinal cord. In this study, we tested experimentally in a sample of 13 patients, four of these advanced 3DCRT techniques, all using photon beams only and a unique isocentre, namely Bellinzona, Forward-Planned Multisegments (FPMS), ConPas, and field-in-field (FIF) techniques. Statistical analysis of the main dosimetric parameters of PTV and OAR’s DVH’s as well as of homogeneity and conformity indexes was carried out in order to compare the performance of each technique. The results show that the PTV dose coverage is adequate for all the techniques, with the FPMS techniques providing the highest value for D95%; on the other hand, the best sparing of parotid glands is achieved using the FIF and ConPas techniques, with a mean dose of 26 Gy to parotid glands for a PTV prescription dose of 54 Gy. After taking into account both PTV coverage and parotid sparing, the best global performance was achieved by the FIF technique with results comparable to that of IMRT plans. This technique can be proposed as a valid alternative when IMRT equipment is not available or patient is not suitable for IMRT treatment.
Head and neck; 3DCRT techniques; dosimetric comparison
Electron dose distributions calculated using the currently available analytical methods can be associated with large uncertainties. The Monte Carlo method is the most accurate method for dose calculation in electron beams. Most of the clinical electron beam simulation studies have been performed using non- MCNP [Monte Carlo N Particle] codes. Given the differences between Monte Carlo codes, this work aims to evaluate the accuracy of MCNP4C-simulated electron dose distributions in a homogenous phantom and around inhomogeneities. Different types of phantoms ranging in complexity were used; namely, a homogeneous water phantom and phantoms made of polymethyl methacrylate slabs containing different-sized, low- and high-density inserts of heterogeneous materials. Electron beams with 8 and 15 MeV nominal energy generated by an Elekta Synergy linear accelerator were investigated. Measurements were performed for a 10 cm × 10 cm applicator at a source-to-surface distance of 100 cm. Individual parts of the beam-defining system were introduced into the simulation one at a time in order to show their effect on depth doses. In contrast to the first scattering foil, the secondary scattering foil, X and Y jaws and applicator provide up to 5% of the dose. A 2%/2 mm agreement between MCNP and measurements was found in the homogenous phantom, and in the presence of heterogeneities in the range of 1-3%, being generally within 2% of the measurements for both energies in a "complex" phantom. A full-component simulation is necessary in order to obtain a realistic model of the beam. The MCNP4C results agree well with the measured electron dose distributions.
Dose distribution; dosimetry; electron therapy; heterogeneous phantom; Monte Carlo N Particle
The present study is aimed at comparing the planning and delivery efficiency between three-dimensional conformal radiotherapy (3D-CRT), field-in-field, forward planned, intensity modulated radiotherapy (FIF-FP-IMRT), and inverse planned intensity modulated radiotherapy (IP-IMRT). Treatment plans of 20 patients with left-sided breast cancer, 10 post-mastectomy treated to a prescribed dose of 45 Gy to the chest wall in 20 fractions, and 10 post-breast-conserving surgery to a prescribed dose of 50 Gy to the whole breast in 25 fractions, with 3D-CRT were selected. The FiF-FP-IMRT plans were created by combining two open fields with three to four segments in two tangential beam directions. Eight different beam directions were chosen to create IP-IMRT plans and were inversely optimized. The homogeneity of dose to planning target volume (PTV) and the dose delivered to heart and contralateral breast were compared among the techniques in all the 20 patients. All the three radiotherapy techniques achieved comparable radiation dose delivery to PTV-95% of the prescribed dose covering > 95% of the breast PTV. The mean volume of PTV receiving 105% (V105) of the prescribed dose was 1.7% (range 0-6.8%) for IP-IMRT, 1.9% for FP-IMRT, and 3.7% for 3D-CRT. The homogeneity and conformity indices (HI and CI) were similar for 3D-CRT and FP-IMRT, whereas the IP-IMRT plans had better conformity index at the cost of less homogeneity. The 3D-CRT and FiF-FP-IMRT plans achieved similar sparing of critical organs. The low-dose volumes (V5Gy) in the heart and lungs were larger in IP-IMRT than in the other techniques. The value of the mean dose to the ipsilateral lung was higher for IP-IMRT than the values for with FiF-FP-IMRT and 3D-CRT. In the current study, the relative volume of contralateral breast receiving low doses (0.01, 0.6, 1, and 2Gy) was significantly lower for the FiF-FP-IMRT and 3D-CRT plans than for the IP-IMRT plan. Compared with 3D-CRT and IP-IMRT, FiF-FP-IMRT proved to be a simple and efficient planning technique for breast irradiation. It provided dosimetric advantages, significantly reducing the size of the hot spot and minimally improving the coverage of the target volume. In addition, it was felt that FiF-FP-IMRT required less planning time and easy field placements.
Breast cancer; contralateral breast; field in field breast plan; intensity-modulated radiation therapy
The effective radiation dose of human from natural sources is about 2.4 mSv/y and the dose limit for radiation workers is 20 mSv/y. Ramsar, a city in Iran, has been the subject of concern in the last forty years for a high level of radiation measured in some spots as high as 260 mSv/y. Carcinogenesis is one of the most studied effects of radiation especially in high doses. Recent studies showed that the high level of natural radiation received by inhabitants of this area, paradoxically don’t have significant health effect. Natural killer (NK) cells and cytotoxic T cells are the most important cells in tumor immune surveillance and CD107a is a widely expressed intracellular protein located in the lysosomal/endosomal membrane. CD107a transiently located on the cell membrane can be used as a marker of CD8 + T cell degranulation following stimulation. It is also expressed, to a lower extent, on activated NK cells. In this study, 60 healthy people were selected randomly and their consent obtained and confounding factors such as sex, age, life-styles was matched then the count of activated NK and CD8 + cells was compared in high and normal background radiation areas inhabitants of Ramsar. After filling the questionnaire and measurement of background radiation, blood samples of 30 healthy people from each region were analyzed immediately by means of flowcytometry. The leukocytes and their subsets were not significantly different between two groups and the count of active cells was higher in control group. The result shows that the changes in immune system occur due to radiation and maybe it is as a result of higher radiosensitivity of activated cells.
CD107a; cytotoxic T cell; high background radiation area; natural killer cell; Ramsar
In order to evaluate the long-term viability, the iron content stability, and the labeling efficiency of mammalian cells using magnetic cell labeling; dextran-coated ultrasmall superparamagnetic iron oxide (USPIOs) nanoparticles with plain surfaces having a hydrodynamic size of 25 nm were used for this study. Tests were carried out in four groups each containing 5 flasks of 5.5 × 106 AD-293 embryonic kidney cells. The cell lines were incubated for 24 h using four different iron concentrations with and without protamine sulfate (Pro), washed with phosphate-buffered saline (PBS) and centrifuged three times to remove the unbounded USPIOs. Cell viability was also verified using USPIOs. There were no significant differences in the cell viability between the control group of cells and those groups with iron uptake at the specified iron concentrations. The average iron uptake ratio compared to that of the control group was (114 ± 1). The magnetic resonance images (MRI) at post-labeling day 1 and day 21 showed (75 ± 4)% and (22 ± 5)% signal decrements compared to that of the control, respectively. The Perl's Prussian blue test showed that 98% of the cells were labeled, and the iron concentration within the media did not affect the cell iron uptake. Magnetic cellular labeling with the USPIO-Pro complex had no short or medium term (3 weeks) toxic effects on AD-293 embryonic kidney cells.
Cell labeling; cell viability; magnetic resonance images; protamine sulfate; ultrasmall superparamagnetic iron oxide
The objective of this paper was to measure the peripheral dose (PD) with diode and thermoluminescence dosimeter (TLD) for intensity modulated radiotherapy (IMRT) with linear accelerator (conventional LINAC), and tomotherapy (novel LINAC). Ten patients each were selected from Trilogy dual-energy and from Hi-Art II tomotherapy. Two diodes were kept at 20 and 25 cm from treatment field edge. TLDs (LiF:MgTi) were also kept at same distance. TLDs were also kept at 5, 10, and 15 cm from field edge. The TLDs were read with REXON reader. The readings at the respective distance were recorded for both diode and TLD. The PD was estimated by taking the ratio of measured dose at the particular distance to the prescription dose. PD was then compared with diode and TLD for LINAC and tomotherapy. Mean PD for LINAC with TLD and diode was 2.52 cGy (SD 0.69), 2.07 cGy (SD 0.88) at 20 cm, respectively, while at 25 cm, it was 1.94 cGy (SD 0.58) and 1.5 cGy (SD 0.75), respectively. Mean PD for tomotherapy with TLD and diode was 1.681 cGy SD 0.53) and 1.58 (SD 0.44) at 20 cm, respectively. The PD was 1.24 cGy (SD 0.42) and 1.088 cGy (SD 0.35) at 25 cm, respectively, for tomotherapy. Overall, PD from tomotherapy was found lower than LINAC by the factor of 1.2-1.5. PD measurement is essential to find out the potential of secondary cancer. PD for both (conventional LINAC) and novel LINACs (tomotherapy) were measured and compared with each other. The comparison of the values for PD presented in this work and those published in the literature is difficult because of the different experimental conditions. The diode and TLD readings were reproducible and both the detector readings were comparable.
Diode; TLD-100; intensity modulated radiotherapy; linear accelerator; peripheral dose; tomotherapy
Radiation Therapy (RT) plays a pivotal role in the curative approach for carcinoma of the cervix. Inspite of the emergence of various new conformal techniques in RT, conventional techniques still hold vital importance. Majority of the patients worldwide are treated with 2D-RT techniques. 2D-RT techniques have been proven to be non-inferior and simpler in comparison to 3D-RT in the context of carcinoma of the cervix. However, inadequate target volume coverage with improper portal design can preclude the chances of cure. We demonstrate the need for abolishing guesswork in terms of target volume determination through the example of a patient's sagittal magnetic resonance image showing a case of the retroverted uterus which would have been likely to be missed from the treatment portals if they were designed using definitions based on bony landmarks.
Carcinoma cervix; clinical-target-volume; four-field box technique; gynaecological radiation oncology; lateral portals for carcinoma cervix; uterine cervix
In vivo dosimetry was carried out for 152 patients receiving external beam radiotherapy and the treatment sites were divided into two main groups: Thorax, Abdomen, and Pelvic (120 fields) and Head and Neck (52 fields). Combined entrance and exit dose measurements were performed using LiF: Mg, Cu, P thermoluminescent dosimeters (TLDs). Water-equivalent (effective) thicknesses and target dose were evaluated using dose transmission data. The ratio of measured to expected value for each quantity was considered as an indicator for the accuracy of the parameter. The average ratio of the entrance dose was evaluated as 1.01 ± 0.07. In the diameter measurement, the mean ratio of effective depth divided by the contour depth is 1.00 ± 0.13 that shows a wide distribution which reflects the influence of contour inaccuracies as well as tissue inhomogeneities. At the target level, the mean ratio of measured to the prescribed dose is 1.00 ± 0.07. According to our findings, the difference between effective depth and patient depth has a direct relation to target dose discrepancies. There are some inevitable sources which may cause the difference. Evaluation and application of effective diameter in treatment calculations would lead to a more reliable target dose, especially for fields which involve Thorax, Abdomen, and Pelvic.
External beam radiotherapy; in vivo do simetry; target dose; thermoluminescent dosimetry
In this study, dose prediction accuracy of Acuros XB (AXB) dose calculation algorithm beyond air gap thickness (range 2, 4, and 6 cm) in simple inhomogeneous phantoms was investigated. The evaluation of AXB was performed by comparing the doses calculated by AXB with the doses calculated by Anisotropic Analytical Algorithm (AAA) and the measured data for different field sizes (3 × 3, 5 × 5, and 10 × 10 cm2) of a 6 MV photon beam. The dose computation was performed within Eclipse treatment planning system, and measurements were acquired with a cylindrical ionization chamber. Central axis depth dose comparisons were done in solid–water material region up to 5 cm distance from air/solid—water interface. The results of AXB had better agreement with measurements at all measured points than that of AAA. The discrepancies between AXB and measured data were seen from − 3.81% to + 0.9%, whereas the AAA differences with measurement from − 3.1% to − 10.9%. The combination of the smallest test field size and the largest air gap produced the highest range (1-5 cm distance from air/solid–water interface) in dose difference (AAA: −4.0% to − 10.6% and AXB: −3.8% to + 0.6%). The AAA computational time was about 8 times faster than that of AXB. In conclusion, AXB is more appropriate to use for dose predictions, especially when low-density heterogeneities are involved.
Anisotropic analytical algorithm; Acuros; air gap; dose prediction; heterogeneity correction