Dosimetric analysis of 3D-conformal radiotherapy and intensity modulated radiotherapy for treatment of advanced stage cervical cancer: A comparative study

Purpose: The purpose of this study is to analyze the dosimetric parameters of three dimensional conformal radiotherapy (3DCRT), intensity modulated radiotherapy (IMRT) with seven and nine fields (7F-IMRT, 9F-IMRT) in selected advanced stage cervical cancer cases.Methods: Fifteen cases of cervical cancer (IIB to IIIB) were selected for retrospective analysis. All the cases were previously treated with 3DCRT technique with prescribed dose of 50 Gy in 25 fractions.  For this study, plans with seven fields IMRT and nine fields IMRT were generated for all patients following Radiation Therapy Oncology Group (RTOG) guidelines. The plans were compared on the basis of planning target volume (PTV) coverage (dose to 1%, 5%, 95% and 99% of target), maximum dose and mean dose to organs at risk (OARs) and also doses at different volumes of OARs. Apart from this, uniformity index (UI), homogeneity index (HI), conformity index (CI) and dose spillage index (R50%) were also calculated with respect to PTV coverage.Results: The average dose value of PTV coverage for all three techniques were comparable and all the DVH indices for 7field IMRT (UI (1.04±0.01), HI (0.07 ±0.02), CI (0.75±0.03) and R50% (4.47±0.36)) were better than 3DCRT and 9F-IMRT techniques. All OAR doses were significantly reduced in 7F- IMRT compared to 3DCRT and 9F- IMRT. The target volumes ranged from 769.2 ml to 1375.6 ml with average target volume of 1071.9 ml (SD: 205.38 ml).Conclusion: This study showed that significant dose reduction to OARs could be achieved with seven field IMRT plans by maintaining the PTV coverage compared to 3DCRT or 9F- IMRT for treating cervical cancer in advanced stages particularly from IIB to IIIB

DVH Analysis of Cobalt-60 treatment plans incorporating a recently developed MLC

Purpose: The aim of this investigation was to measure the gain in DVH indices when the recently developed MLC was used for Cobalt-60 treatments.Methods: A prototype multileaf collimator (MLC) that was retrofitted to telecobalt-60 therapy machine was reported and is currently proposed for clinical trials in our institution. Ten patients’ plans that were previously planned through an ECLIPSE® treatment planning system and were treated with open beams from Cobalt-60 machine were imported into Radiation Oncology Planning System [ROPS] and the dose calculations and dose volume histogram (DVH) analysis were performed. The plans were re-planned using the Cobalt-MLC, a feature available in the ROPS planning system. The DVH analysis consisted of conformity index (CI), homogeneity index (HI) and conformation number (CN). The results of this study are presented in this paper. The analysis specifically aimed at measuring the gain in these indices when the MLC was compared with open beams.Results: DVH Comparison of ten sites using open and Cobalt MLC fields showed that the use of MLC results in reduced normal tissue dose, while maintaining the GTV dose. Lower value of CI for normal structures was observed demonstrating the sparing of critical organs when MLC was used. The index HI was studied to show the significance of hot spots outside the PTV. Hot spots were observed even with MLC beams for some cases due to less number of fields.Conclusion: It has been demonstrated through DVH analysis that the use of the recently developed MLC for Cobalt Teletherapy machine results in benefit for the treatment of patients

Evaluation of Eclipse 3D plans using an independent treatment planning system

Purpose: The goal of the current investigation was to compare complex 3D conformal plans generated on Eclipse™ treatment planning system (TPS) with independent dose calculations from radiation oncology planning system (ROPS™) TPS used as a secondary quality assurance check.Methods: Fifteen cancer patients that were treated with complex conformal treatment plans with cobalt and linac beams, using Eclipse TPS, were selected for this study. The structure sets, treatment beam data and prescription information were exported from the Eclipse TPS using DICOM-RT export. Using custom software, these data were imported into ROPS TPS. Independent dose calculation on the ROPS planning system using Clarkson summation algorithm was done. The dose volume histograms (DVH) from both planning systems were extracted and analyzed using custom software. Dose assessment was accomplished by defining criteria based on gross tumor volume (GTV) dose coverage, dose homogeneity and mean dose. For organs at risk (OAR) other than GTV, the main dose parameters were, mean dose and percentage of volume receiving 95% of prescription dose.Results: For the GTV, all 15 cases met the criteria set for the mean dose and dose homogeneity index. However, breast cases were found to have deviation in the percentage volume receiving the 95% of prescription dose.Conclusion: Using the criteria set for plan acceptance, all the 15 clinical cases were evaluated. Except for breast tangent plans, all plans passed all the criteria set. The large deviation for breast tangent plans was attributed to differences in dose calculation algorithms

Monte Carlo simulation of a multi-leaf collimator design for telecobalt machine using BEAMnrc code

This investigation aims to design a practical multi-leaf collimator (MLC) system for the cobalt teletherapy machine and check its radiation properties using the Monte Carlo (MC) method. The cobalt machine was modeled using the BEAMnrc Omega-Beam MC system, which could be freely downloaded from the website of the National Research Council (NRC), Canada. Comparison with standard depth dose data tables and the theoretically modeled beam showed good agreement within 2%. An MLC design with low melting point alloy (LMPA) was tested for leakage properties of leaves. The LMPA leaves with a width of 7 mm and height of 6 cm, with tongue and groove of size 2 mm wide by 4 cm height, produced only 4% extra leakage compared to 10 cm height tungsten leaves. With finite ⁶⁰ Co source size, the interleaf leakage was insignificant. This analysis helped to design a prototype MLC as an accessory mount on a cobalt machine. The complete details of the simulation process and analysis of results are discussed

Monte Carlo study of MLC fields for cobalt therapy machine

An automated Multi-Leaf Collimator (MLC) system has been developed as add-on for the cobalt-60 teletherapy machines available in India. The goal of the present computational study is to validate the MLC design using Monte Carlo (MC) modeling. The study was based on the Kirloskar-supplied Phoenix model machines that closely match the Atomic Energy of Canada Limited (AECL) theratron-80 machine. The MLC is a retrofit attachment to the collimator assembly, with 14 non-divergent leaf pairs of 40 mm thick, 7 mm wide, and 150 mm long tungsten alloy plates with rounded edges and 20 mm tongue and 2 mm groove in each leaf. In the present work, the source and collimator geometry has been investigated in detail to arrive at a model that best represents the measured dosimetric data. The authors have studied in detail the proto-I MLC built for cobalt-60. The MLC field sizes were MC simulated for 2 × 2 cm 2 to 14 × 14 cm 2 square fields as well as irregular fields, and the percent depth dose (PDD) and profile data were compared with ROPS† treatment planning system (TPS). In addition, measured profiles using the IMATRIXX system‡ were also compared with the MC simulations. The proto-I MLC can define radiation fields up to 14 × 14 cm΂ within 3 mm accuracy. The maximum measured leakage through the leaf ends in closed condition was 3.4% and interleaf leakage observed was 7.3%. Good agreement between MC results, ROPS and IMATRIXX results has been observed. The investigation also supports the hypothesis that optical and radiation field coincidence exists for the square fields studied with the MLC. Plots of the percent depth dose (PDD) data and profile data for clinically significant irregular fields have also been presented. The MC model was also investigated to speed up the calculations to allow calculations of clinically relevant conformal beams

Monte Carlo simulation of a multi-leaf collimator design for telecobalt machine using BEAMnrc code

This investigation aims to design a practical multi-leaf collimator (MLC) system for the cobalt teletherapy machine and check its radiation properties using the Monte Carlo (MC) method. The cobalt machine was modeled using the BEAMnrc Omega-Beam MC system, which could be freely downloaded from the website of the National Research Council (NRC), Canada. Comparison with standard depth dose data tables and the theoretically modeled beam showed good agreement within 2%. An MLC design with low melting point alloy (LMPA) was tested for leakage properties of leaves. The LMPA leaves with a width of 7 mm and height of 6 cm, with tongue and groove of size 2 mm wide by 4 cm height, produced only 4% extra leakage compared to 10 cm height tungsten leaves. With finite 60Co source size, the interleaf leakage was insignificant. This analysis helped to design a prototype MLC as an accessory mount on a cobalt machine. The complete details of the simulation process and analysis of results are discussed

Design and development of an add-on automated multi-leaf collimator for telecobalt therapy machine and study of its characteristics

Purpose: The purpose of the paper is to present the design, development and dosimetric characteristics of an automated Multi-leaf collimator (MLC) integrated along with an inexpensive Treatment Planning System (ROPS), developed for existing telecobalt units as an add-on without making any modifications to the treatment machine.Method: The prototype MLC design consists of 28 tungsten alloy leaves (14 leaf pairs) having a mass density of 18 g cm-3. Each of the leaves projects 10 mm width at the isocenter, which is at 80 cm from the source. The automation has been achieved with a dedicated linear actuator for each leaf. Radiochromic films and IC PROFILER™ (Sun Nuclear Corporation, Melbourne, FL) were used for the measurement of beam profiles and the profiles were analyzed to arrive at radiation field width, beam flatness, symmetry and beam penumbra.Results: The prototype MLC can define radiation fields of up to 14 × 14 cm² within the prescribed tolerance values of 2 mm. The flatness and symmetry were found to be within the prescribed tolerance value of 3%. The penumbra for a 10 × 10 cm² field size is 9.5 mm which is less than the generally acceptable value of 12 mm for a telecobalt machine. The maximum leakage through the leaf ends in closed condition was observed to be 7.3% which is less than the values reported for other MLCs designed for medical linear accelerators.Conclusion: It is concluded that dosimetric parameters and the leakage radiation of the prototype MLC are well below their recommended tolerance values. The MLC can be used for carrying out conformal radiotherapy with existing telecobalt machines

DVH Analysis of Cobalt-60 treatment plans incorporating a recently developed MLC

Purpose: The aim of this investigation was to measure the gain in DVH indices when the recently developed MLC was used for Cobalt-60 treatments.Methods: A prototype multileaf collimator (MLC) that was retrofitted to telecobalt-60 therapy machine was reported and is currently proposed for clinical trials in our institution. Ten patients’ plans that were previously planned through an ECLIPSE® treatment planning system and were treated with open beams from Cobalt-60 machine were imported into Radiation Oncology Planning System [ROPS] and the dose calculations and dose volume histogram (DVH) analysis were performed. The plans were re-planned using the Cobalt-MLC, a feature available in the ROPS planning system. The DVH analysis consisted of conformity index (CI), homogeneity index (HI) and conformation number (CN). The results of this study are presented in this paper. The analysis specifically aimed at measuring the gain in these indices when the MLC was compared with open beams.Results: DVH Comparison of ten sites using open and Cobalt MLC fields showed that the use of MLC results in reduced normal tissue dose, while maintaining the GTV dose. Lower value of CI for normal structures was observed demonstrating the sparing of critical organs when MLC was used. The index HI was studied to show the significance of hot spots outside the PTV. Hot spots were observed even with MLC beams for some cases due to less number of fields.Conclusion: It has been demonstrated through DVH analysis that the use of the recently developed MLC for Cobalt Teletherapy machine results in benefit for the treatment of patients.</p

Evaluation of gafchromic EBT film for intensity modulated radiation therapy dose distribution verification

This work was undertaken with the intention of investigating the possibility of clinical use of commercially available self-developing radiochromic film – Gafchromic EBT film – for IMRT dose verification. The dose response curves were generated for the films using VXR-16 film scanner. The results obtained with EBT films were compared with the results of Kodak EDR2 films. It was found that the EBT film has a linear response between the dose ranges of 0 and 600 cGy. The dose-related characteristics of the EBT film, like post-irradiation color growth with time, film uniformity and effect of scanning orientation, were studied. There is up to 8.6% increase in the color density between 2 and 40 h after irradiation. There was a considerable variation, up to 8.5%, in the film uniformity over its sensitive region. The quantitative difference between calculated and measured dose distributions was analyzed using Gamma index with the tolerance of 3% dose difference and 3 mm distance agreement. EDR2 films showed good and consistent results with the calculated dose distribution, whereas the results obtained using EBT were inconsistent. The variation in the film uniformity limits the use of EBT film for conventional large field IMRT verification. For IMRT of smaller field size (4.5 × 4.5 cm), the results obtained with EBT were comparable with results of EDR2 films