International Journal of Cancer Therapy and Oncology
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Impact of jaw position on sparing organs at risk in 3-dimensional conformal radiation therapy of pancreatic cancer
Get PDFPurpose: The objective of this work is to investigate the impact of collimator jaw position on dose to organs at risk (OARs) during a 3-dimensional conformal radiotherapy (3DCRT) of pancreatic cancer and postulate a method to minimize OAR dose by proper positioning of the jaws.Methods: Clinically delivered 3DCRT treatment plans for 10 patients optimized with multiple static beams using multileaf collimator (MLC) leaves conformed to a block margin around target, and collimator jaws aligned with outer extent of the block margin were selected. Subsequent plans were generated by displacing the collimator jaws outward in lateral, superior-inferior or both directions by 1 and 2 cm without altering the MLC position. Computed dose to OARs and target with unaltered dose normalization were compared against the corresponding dose obtained from the original plans.Results: Outward displacement of the collimator jaws by 1 cm in lateral and/or superior-inferior direction resulted in a significant increase in mean dose to the studied OARs. The increase was found to be proportional to the outward displacement of the jaws. The increase in maximum dose to spinal cord was significant in a few patients while it was insignificant for all other OARs.Conclusion: Collimator jaws aligned with outer extent of a block margin minimize dose to OARs. Any gap between the block margin and the collimator jaws can lead to an inadvertent delivery of higher dose to the OARs. Hence, the use of an optimal jaw position during treatment planning becomes important to all patient plans
Quantitative evaluation of the impact of heterogeneity correction on left breast cancer radiotherapy performed with respiratory gating
Get PDFPurpose: Our objective was to assess the impact of a heterogeneity correction to the calculated dose for left breast cancer gated radiotherapy.Methods: Ten patients with left breast cancer were studied. For each patient 2 treatment plans were generated. In plan 1 the dose was calculated using a Pencil Beam Convolution (PBC) algorithm. In plan 2 the dose was calculated using the Modified Batho's (MB) density correction method. To compare the two plans a dosimetric analysis was carried out including monitor units (MU), isodose curves, cumulative and differential dose volume histograms (cDVH, dDVH), coverage index, conformity index for target volume and the two dimensional (2D) gamma index (γ). Wilcoxon signed rank and Spearmen's tests were used to calculate p-values and correlation coefficients (r), respectively.Results: MB method reduced the MU by on average 1.12 ± 5.33%. The analysis of cDVH showed that the MB method calculated significantly higher doses for target volumes, lung and heart, p < 0.05. The data demonstrated a strong correlation between the dosimetric parameters derived from plan 1 and plan 2 with r > 0.9. The 2D γ analysis showed that the difference between plan 1 and plan 2 could reach ± 10%. The γ evaluation showed a high impact of density correction for left breast cancer with gating technique.Conclusion: This study confirms that using the MB method integrated with a PBC algorithm, the calculated dose will be increased to target volumes, lung and heart. Even more so since gating usually tends to decrease average lung density by about 39% by treating during an arrested inspiration phase. Thus, attention should be paid when changing from PBC to newer algorithms with gating techniques, since the probability of cardiac mortality and lung toxicity are correlated to absorbed dose
A phantom study for in-vivo dosimetry of high dose rate brachytherapy applicators
Get PDFPurpose: The aim of the current investigation was to calibrate the diode in-vivo dosimetry (IVD) system for high-dose-rate (HDR) brachytherapy and to design a phantom study for in-vivo dosimetry of HDR brachytherapy applicators.Methods: Gamma Med Plus with Abacus 3.1 treatment planning system (TPS), and diode dosimetry system has been used in this study. Calibration and different correction factors of diode have been measured in water phantom. Treatment simulation, planning of different applicators for esophagus, rectum/vagina and cervix (fletcher & ring), dose delivery and finally in-vivo verification at prescription point using diode in water phantom has been performed.Results: The mean calibration factor for diode for Ir-192 HDR source is 1.256 (N=15) with σ ± 0.0015. The overall average percentage difference between TPS dose and diode dose was 1.87% (σ ± 2.64) for all measurements, 1.86% (σ ± 2.73) for esophagus, 1.86% (σ± 2.94) for rectum/vagina and 1.67% (σ ±2.81) for fletcher and 2.07% (σ ± 2.26) for ring applicators, respectively. These results advocate that the dose calculated by TPS and dose measured using diode for the various clinical situations deliberated here are in good agreement (~2%) at the points of clinical importance.Conclusion: The in-vivo phantom dosimetry study gives both a confidence that the treatments are being delivered as prescribed and enhance the reliability of the HDR brachytherapy treatment. This may be used for acceptance testing/commissioning of new treatment planning system and to validate the new brachytherapy techniques in the clinics.
Body mass index versus bladder and rectal doses using 2D planning for patients with carcinoma of the cervix undergoing HDR brachytherapy
Get PDFPurpose: To assess bladder and rectum doses in relation to body mass index of patients undergoing high dose rate brachytherapy for the treatment of carcinoma of the cervix.Methods: The cohort consists of fifty subjects with carcinoma of the uterine cervix presented with grade II and III. Patient’s height and weight was measured before the insertion of applicator in situ. Body mass index (BMI) of the patient was calculated in accordance to World Health Organization definition (weight in Kg/ height in m2). Adequacy of position and orientation of the applicator was confirmed with the help of orthogonal X-ray images and the same were transferred to the treatment planning system (TPS) to generate treatment plan. Prescription doses were optimized to Point A and to reference lines placed at 0.5 cm apart from the surface of ovoids. The following dose reference points were identified on orthogonal x-ray images for analysis using the rectal marker and Foleys bulb inflated with radio opaque dye Rectal points at the level of femoral heads (RL) and pubis symphysis (RLP), Anorectum Junction (AR Jn) point and Rectosigmoid (RS) point and Bladder point (BL). Pearson regression analysis was used to analyze data from TPS.Results: The mean BMI was 22.7 kg/m2 and average age was 49.9 years. Analysis showed that RL point dose and BMI were inversely correlated with a coefficient -0.45 (p = 0.001). The trend continued along the rectal tube in cranio-caudal direction, as RLP and AR Jn points showed inversion co-efficiency with increase in BMI,-0.48 (p < 0.01) and -0.51 (p < 0.01) respectively. Bladder point showed weak positive correlation to BMI, 0.12 (p = 0.38).Conclusion: Significant rectal dose reduction is observed with increase in BMI. Bladder dose did not show statistically significant correlation with BMI. Based on the findings, BMI constitutes a confounding factor in the treatment of carcinoma of cervix
Role of Interleukin-18 in Thyroid tumorigenesis
Get PDFPurpose: Although the significance of Interleukin-18 (IL-18) has been studied in pathogenesis of different cancers including, ovarian, gastric, breast, lung carcinoma and melanoma, its role in thyroid cancer- the most common endocrine malignancy has not yet been looked at extensively. Hence, this study intended to examine the role of IL-18 in thyroid tumorigenesis.Methods: Sixty seven patients with benign thyroid diseases and 106 thyroid cancer patients (including 83 papillary, 6 follicular, 9 medullary and 8 anaplastic thyroid carcinoma patients) were enrolled in the study. To accomplish the aim, the circulating levels of IL-18 were estimated by enzyme linked immunosorbent assay (ELISA) from all patients and compared with controls. Further, protein expression of IL-18 was determined from the primary tumors of the patients using immunohistochemistry.Results: It was observed that the circulating levels of IL-18 were significantly higher in all patients: benign thyroid diseases (p = 0.006), papillary (p < 0.001), follicular (p = 0.023), medullary (p = 0.002) and anaplastic thyroid cancer (p < 0.001) than the controls. In addition to this, IL-18 could well discriminate papillary (AUC = 0.627, p =0.008) and anaplastic thyroid carcinoma patients (AUC = 0.777, p = 0.011) from patients with benign thyroid diseases. However, the difference between tumoral protein expression of IL-18 in patients with benign thyroid diseases and thyroid carcinoma was not significant. The Kaplan - Meier survival analysis revealed that neither the circulating nor the tumoral protein expression of IL-18 was the significant predictor of disease free survival (DFS) or overall survival (OS) in papillary thyroid cancer patients.Conclusion: Though not a significant prognosticator, circulating IL-18 may be useful as a differentiating factor in thyroid tumorigenesis and the increase in serum IL-18 levels may be provoked in response to the tumor. Thus, including IL-18 along with the current treatment practice may have a significant role in better management of the disease. However, further exploration of this interleukin is required in a larger series of patients with longer follow up period
High Impact Papers from January – March, 2015
Get PDFHigh impact papers from a particular Issue are selected based on the quality of the article and the number of citations. High impact papers are typically recognized once the Issue completes the publication time period of 12 months.Following articles are recognized as High Impact Papers from January-March, 2015:Jassal K, Sarkar B, Munshi A, Roy S, Paul S, Mohanti BK, Ganesh T, Chougule A, Sachdev K. Consistency analysis for the performance of planar detector systems used in advanced radiotherapy. Int J Cancer Ther Oncol. 2015; 3(1):030110. DOI: 10.14319/ijcto.0301.10Read Download Khanal SP, Ouhib Z, Benda RK, Leventouri T. Evaluation of surface dose outside the treatment area for five breast cancer irradiation modalities using thermo-luminescent dosimeters. Int J Cancer Ther Oncol 2015; 3(1):030117. DOI: 10.14319/ijcto.0301.17Read Download (High impact papers from April-June, 2015 will be recognized in the next Issue of the IJCTO
An experimental method to calculate the on-axis dose in small field for stereotactic radiotherapy
Get PDFPurpose: The use of small fields in advanced radiotherapy techniques has increased, in particular in stereotactic treatments. However, measuring on-axis dose in such fields is challenging. In this study, we developed an analytic model to accurately estimate the on-axis dose in small fields.Methods: Our study was carried out using 6 MV photon beams from four linear accelerators and with three dosimeters placed in a water tank: EBT3 Gafchromic films, a 31016 PinPoint ionization chamber and a 60017 E diode. The out-of-field leakage factor defined as the ratio of the central axis dose to the off-axis dose was modeled. On-axis doses estimated from out-of-field measurements were compared with the measured ones.Results: The experimental validation of the present method was performed for square and rectangular fields with sizes ranging from 0.5 ⨯ 0.5 cm2 to 10 ⨯ 10 cm2. We found the leakage factor exhibits an exponential decrease independent of the accelerator. This behavior can be integrated in the model to estimate the on-axis dose with an agreement better than 2% compared to EBT3 film measurements at a 10 cm depth and an 8 cm cross-plane off-axis distance.Conclusion: We have developed an analytic model to estimate the on-axis dose in small fields based on the out-of-field leakage measurement. This model can be used to validate dose and output factor measurements
A portable secondary dose monitoring system using scintillating fibers for proton therapy of prostate cancer: A Geant4 Monte Carlo simulation study
Get PDFPurpose: The main purpose of this study was to monitor the secondary dose distribution originating from a water phantom during proton therapy of prostate cancer using scintillating fibers.Methods: The Geant4 Monte Carlo toolkit version 9.6.p02 was used to simulate a proton therapy of prostate cancer. Two cases were studied. In the first case, 8 × 8 = 64 equally spaced fibers inside three 4 × 4 × 2.54 cm3 Delrin® blocks were used to monitor the emission of secondary particles in the transverse (left and right) and distal regions relative to the beam direction. In the second case, a scintillating block with a thickness of 2.54 cm and equal vertical and longitudinal dimensions as the water phantom was used. Geometrical cuts were implemented to extract the energy deposited in each fiber and inside the scintillating block.Results: The transverse dose distributions from the detected secondary particles in both cases are symmetric and agree to within <3.6%. The energy deposited gradually increases as one moves from the peripheral row of fibers towards the center of the block (aligned with the center of the prostate) by a factor of approximately 5. The energy deposited was also observed to decrease as one goes from the frontal to distal region of the block. The ratio of the energy deposited in the prostate to the energy deposited in the middle two rows of fibers showed a linear relationship with a slope of (-3.55±2.26) × 10-5 MeV per treatment Gy delivered. The distal detectors recorded a negligible amount of energy deposited due to higher attenuation of the secondary particles by the water in that direction.Conclusion: With a good calibration and with the ability to define a good correlation between the radiation flux recorded by the external fibers and the dose delivered to the prostate, such fibers can be used for real time dose verification to the target. The system was also observed to respond to the series of Bragg Peaks used to generate the Spread Out Bragg Peak inside the water phantom. Such Bragg Peaks were detected by the fibers. The energy deposited inside the lateral blocks were also observed to decrease as one goes away from the beam nozzle due to increased attenuation
Analytic derivation of central axis percent depth dose calculations in transition zones with loss of electronic equilibrium
Get PDFPurpose: The study of megavoltage photon dose distribution behind and near small areas of low and high density material is best understood with Monte Carlo (MC) dose calculation or direct measurements which may not be always be possible. This is especially true for air-tissue area where the replacement of soft tissue scattering material by air results in the loss of electronic equilibrium and changes in the lateral spread of the beam as well. Monte Carlo calculations are the standards to correctly evaluate in homogeneities in transition zones. If one could develop a model with sufficient accuracy to obtain similar results, this would be very helpful clinically.Methods: To this end, we have developed an exponential model and derive an explicit expression that accounts for the under dosage. The model is an extension of a much earlier work done with electrons and photons. Our analytic model is based on the experience of the underlying physics assuming exponential attenuation of photons in matter.Results: It differs from a similar work by solving the problem correctly and introducing parameters that can be traced to direct measurements without the need of extensive statistical data analysis. It combines the generation of free electrons through ionization and their attenuation to a simple differential equation for the central axis depth dose. It involves two parameters, which can be obtained from 1) direct beam measurements, 2) primary photon attenuation coefficients from physics tables and 3) iteration techniques.Conclusion: The simplicity of the model allows us to extend our derivation to situations such as transitions zones of different densities in areas such as head and neck and lung. A clinical example is illustrated to demonstrate the problems encountered in treating cancer of the larynx
Autologous fat transfer as prostate-rectal spacer: Technique description and early results
Get PDFPurpose: Several attempts have been made to increase the distance between the prostate and the rectum through injection of different synthetic compounds, generating space between organs. To report an original technique to increase the distance between the rectum and the prostate, by autologous fat implantation into the rectoprostatic space, with the aim of providing physical dosimetry protection and rectal dose sparing.Methods: We prospectively evaluated twelve patients subjected to autologous fat implantation as recto-prostatic spacer subsequently receiving prostate either radical (n = 6), or salvage brachytherapy for local recurrence after external beam radiation therapy (EBRT) (n = 6). Standard permanent prostate brachytherapy seed implantation was performed through transperineal approach and under transrectal ultrasonography (TRUS) and template guidance. Prescribed D90 dose for Iodine - 125 monotherapy was 140 - 160 Gy, reduced by 30% for rescue cases to obtain a Rectum V100 under 1 cc.Results: Lipo-transfer was completed in all 12 patients. Control CT scan at 1 month showed average distances of: 10.7 mm (range) (2.8 - 15.9 mm), 7.6 (1.8 - 11.6 mm) and 6.8 (4.2 - 8.3) mm at prostate base, middle and apex, respectively. Shortest separation distance observed was at apex and midline, while largest was observed the sides and at seminal vesicles level. Control CT at 3 months showed average distances of 9.6 mm (1.9 - 14.6 mm), 6.3 mm (1.8 - 10.2 mm) and 5.4 mm (3.8 - 7.2 mm) at prostate base, middle and apex, respectively. Most complications were minor.Conclusion: Autologous fat transfer is a feasible and simple procedure for experienced practitioners with low complication rates, which allows dose escalation to the prostate.