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Purpose: At our institute, in vivo patient dose distributions are reconstructed for all treatments delivered using conventional linacs from electronic portal imaging device (EPID) transit images acquired during treatment using a simple back‐projection model. Currently, the clinical implementation of MRI‐guided radiotherapy systems, which aims for online and real‐time adaptation of the treatment plan, is progressing. In our department, the MR‐linac (Unity, Elekta AB, Stockholm, Sweden) is now in clinical use. The aim of this work is to demonstrate the feasibility of two‐dimensional (2D) EPID dosimetric verification for the magnetic resonance (MR)‐linac by comparing back‐projected EPID doses to ionization chamber (IC) array dose distributions. Materials and methods: Our conventional back‐projection algorithm was adapted for the MR‐linac. The most important changes involve modeling of the attenuation by and scatter from the cryostat. The commissioning process involved the acquisition of square field EPID measurements using various phantom setups (varying SSD, phantom thickness, and field size). Commissioning models were created for gantry 0°, 90°, and 180° and verified by comparing EPID‐reconstructed 2D dose distributions to measurements made with the OCTAVIUS 1500 IC array (PTW, Freiburg, Germany) for two prostate and one rectum IMRT plans (25 beams total). The average of the γ parameters (y‐mean and y‐pass rate) and the dose difference at a reference point were reported. Due to their construction, the attenuation of couch, bridge, and cryostat shows a much stronger dependence on gantry angle in the MR‐linac compared to conventional linacs. We present a method to correct for these effects. This method is validated by dose reconstruction of the 25 intensity‐modulated radiation therapy beams recorded at a certain gantry angle using the model of another gantry angle, combined with the correction method. Results: For dose verification performed at a gantry angle identical to the commissioned model, the average y‐mean and y‐pass rate values (3% global dose, 2 mm, 10% isodose) were 0.37 ± 0.07 and 98.1, 95% CI [98.1 ± 2.4], respectively. The average dose difference at the reference point was −0.5% ± 1.8%. Verification at gantry angles different from the commissioned model (i.e., using the gantry angle dependent correction) reported 0.39 ± 0.08 and 97.6, 95% CI [96.9, 98.3] average y‐mean and y‐pass rate values. The average dose difference at the reference point was −0.1% ± 1.8%. Conclusion: The EPID dosimetry back‐projection model was successfully adapted for the MR‐linac at gantry 0°, 90°, and 180°, accounting for the presence of the MRI housing between phantom (or patient) and the EPID. A method to account for the gantry angle dependence was also tested reporting similar results. [ABSTRACT FROM AUTHOR]

Aims: The main objective of this research work is to compare the dosimertic effect on lower and upper oesophagus cancer treatment using 3D conformal radiotherapy as well as to evaluate the doses administered to the organs at risk. Materials and methods: In this study, a cohort of 30 oesophageal cancer patients between the ages of 45 and 67 years registered during March 2017 to February 2018 was considered. These patients were treated through 3D conformal radiotherapy using four-field technique. Beam energy of 15 MV from Varian DHX linear accelerator was used. The given 30 patients were divided into two groups. The 1st group of 15 patients with upper oesophagus cancer was prescribed 5000 cGy doses, and the 2nd group of remaining 15 patients with lower oesophagus cancer was prescribed 4500 cGy. Computed tomography scans of every patient were obtained and then transmitted to Eclipse TPS for generating treatment plans. All radiotherapy plans were evaluated through various dosimetric indices. Statistical analysis software SPSS was utilised to get the values of means standard error and standard deviation of these indices for the treatment plan evaluation. Results: Uniformity index (UI) calculated for first group of patients showed difference of 7·4% from ideal value. A difference of 7% between ideal and calculated UI value was observed in 2nd group of patients. The values of other dosimetric indices like coverage, homogeneity, moderate dose homogeneity index (mDHI) and radical dose homogeneity index (rDHI) were found in limits specified by the Radiation Therapy and Oncology Group. The maximum difference of 6% was observed between the coverage mean values of 1st and 2nd group treatment plans. Conclusion: For oesophageal cancer, 3D conformal radiotherapy using four-field treatment plans shows homogeneous distribution of dose around the target and limits the dose to organ at risk. [ABSTRACT FROM AUTHOR]

Purpose: In vivo range verification in proton therapy is a critical step to help minimize range and dose uncertainty. We propose to employ a time reversal (TR)‐based approach using proton‐induced acoustics (protoacoustics) to reconstruct pressure/dose distribution in heterogeneous tissues. Methods: The dose distribution of mono‐energetic proton pencil beam in a CT‐based patient phantom was calculated by Monte Carlo simulation. K‐wave toolbox was used to investigate protoacoustic pressurization, propagation and reconstruction in 2D. To address the tissue heterogeneity effect, a number of physical parameters, including mass density (ρ), speed of sound (c), volumetric thermal expansion coefficient (αV), isobaric specific heat capacity (Cp) and attenuation power law prefactor (α0), were empirically converted from CT number. The performance was evaluated using two figures of merit: mean square error (MSE) of pressure profiles and Bragg peak localization error (ΔBP). The impact of six parameters of the TR inversion was examined, including number of sensors, sampling duration, sampling timestep, spill time, noise level and number of iterations. Results: The quantitative accuracy of TR reconstruction and its dependency on the selected parameters is presented. Under optimum conditions, the positioning accuracy of the Bragg peak can be controlled below 1 mm. For instance, MSE is 0.0123 and ΔBP is 0.59 mm under the following conditions (32 sensors, sampling duration: 600 µs, sampling timestep: 40 ns, spill time: 1 µs, no noise). Conclusions: The feasibility of TR‐based protoacoustic reconstruction in 2D for proton range verification was first demonstrated. The approach is not only applicable to pencil beam, but also has potential to be extended to passive scattering systems. [ABSTRACT FROM AUTHOR]

The eye lens is recognized as one of the most radiosensitive structures in the human body. The widespread use of intensity-modulated radiotherapy (IMRT) complicates dose verification and necessitates high standards of dose computation. The purpose of this work was to assess the computed dose accuracy of eye lens through measurements using a metal–oxide–semiconductor field-effect transistor (MOSFET) dosimetry system. Sixteen clinical IMRT plans of head and neck patients were copied to an anthropomorphic head phantom. Measurements were performed using the MOSFET dosimetry system based on the head phantom. Two MOSFET detectors were imbedded in the eyes of the head phantom as the left and the right lens, covered by approximately 5-mm-thick paraffin wax. The measurement results were compared with the calculated values with a dose grid size of 1 mm. Sixteen IMRT plans were delivered, and 32 measured lens doses were obtained for analysis. The MOSFET dosimetry system can be used to verify the lens dose, and our measurements showed that the treatment planning system used in our clinic can provide adequate dose assessment in eye lenses. The average discrepancy between measurement and calculation was 6.7 ± 3.4%, and the largest discrepancy was 14.3%, which met the acceptability criterion set by the American Association of Physicists in Medicine Task Group 53 for external beam calculation for multileaf collimator-shaped fields in buildup regions. [ABSTRACT FROM AUTHOR]

The Mobius3D (M3D) system (Mobius Medical Systems) is a second-check dosimetry system. We investigated the dose calculation accuracy of this system using heterogeneous phantoms with reference beam data provided by the manufacturer using simple and patient plans. We compared the dose distributions between M3D and the treatment planning system, as well as the measurements in solid water phantoms, heterogeneous phantoms, and patient plans for Varian and Elekta accelerators. The M3D results agreed well with the measurements in the solid water phantoms for the simple plans. However, the accuracy of M3D appeared to depend on the type of accelerator, as indicated by the slight differences in the dose measurements. Furthermore, the M3D dose measurements differed by 5-10% in the lung and bone regions. Regarding the patient plans, we confirmed that M3D is reasonably accurate as a second-check system, despite the slight accelerator type-dependent dose difference. [ABSTRACT FROM AUTHOR]

Abstract The characteristic depth-dose profile of protons traveling through material is the main advantage of proton therapy over conventional radiotherapy with photons or electrons. However, uncertainties regarding the range of the protons in human tissue prevent to exploit the full potential of proton therapy. Therefore, a non-invasive in-vivo dose monitoring is desired. At the ion beam center MedAustron in Wiener Neustadt/Austria, patient treatment with proton beams started in December 2016. A PET/CT is available in close vicinity of the treatment rooms, exclusively dedicated to offline PET monitoring directly after the therapeutic irradiation. Preparations for a patient study include workflow tests under realistic clinical conditions using two different phantoms, irradiated with protons prior to the scan in the PET/CT. GATE simulations of the C-11 production are used as basis for the prediction of the PET measurement. We present results from the workflow tests in comparison with simulation results, and by this, we demonstrate the applicability of the PET monitoring at the MedAustron facility. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of the present study was to evaluate the practicability of liquid ionization chamber (LIC) for pretreatment dose verification of the advanced radiotherapy techniques such as volumetric modulated arc therapy (VMAT). Materials and Methods: The dosimetric characteristics of LIC such as repeatability, sensitivity, monitor unit linearity, dose rate dependence, angular dependence, voltage-current response, and output factors were investigated in 6 MV therapeutic X-ray beams. The LIC was cross-calibrated against 0.125-cc air-filled thimble ionization chamber. A dedicated dosimetry insert made up of Perspex to incorporate the LIC at proper location in the intensity-modulated radiation therapy thorax phantom was locally fabricated. The collection efficiency and ion recombination correction factor was determined using the two-dose rate method. Pretreatment dose verification measurement of VMAT treatment plans were carried out using the liquid ionization chamber as well as small volume (0.125 cc) air-filled thimble ionization chamber. The measured dose values by the two dosimeters and TPS calculated dose at a given point were compared. Results: The relative percentage differences between the TPS calculated and measured doses were within ± 1.57% for LIC and ± 2.21% for 0.125 cc ionization chamber, respectively. Conclusions: The measured dose values by the two dosimeters and TPS calculated dose at a given point were found comparable suggesting that the LIC could be a good choice of dosimeter for pretreatment dose verification in VMAT. [ABSTRACT FROM AUTHOR]

Background: Independent verification of the dose delivered by complex radiotherapy can be performed by electronic portal imaging device (EPID) dosimetry. This paper presents 5‐yr EPID in vivo dosimetry (IVD) data obtained using the Dosimetry Check (DC) software on a large cohort including breast, lung, prostate, and head and neck (H&N) cancer patients. Material and Methods: The difference between in vivo dose measurements obtained by DC and point doses calculated by the Eclipse treatment planning system was obtained on 3795 radiotherapy patients treated with volumetric modulated arc therapy (VMAT) (n = 842) and three‐dimensional conformal radiotherapy (3DCRT) (n = 2953) at 6, 10, and 15 MV. In cases where the dose difference exceeded ±10% further inspection and additional phantom measurements were performed. Results: The mean and standard deviation (μ±σ) of the percentage difference in dose obtained by DC and calculated by Eclipse in VMAT was: 0.19±3.89% in brain, 1.54±4.87% in H&N, and 1.23±4.61% in prostate cancer. In 3DCRT, this was 1.79±3.51% in brain, −2.95±5.67% in breast, −1.43±4.38% in bladder, 1.66±4.77% in H&N, 2.60 ± 5.35% in lung and −3.62±4.00% in prostate cancer. A total of 153 plans exceeded the ±10% alert criteria, which included: 88 breast plans accounting for 7.9% of all breast treatments; 28 H&N plans accounting for 4.4% of all H&N treatments; and 12 prostate plans accounting for 3.5% of all prostate treatments. All deviations were found to be as a result of patient‐related anatomical deviations and not from procedural errors. Conclusions: This preliminary data shows that EPID‐based IVD with DC may not only be useful in detecting errors but has the potential to be used to establish site‐specific dose action levels. The approach is straightforward and has been implemented as a radiographer‐led service with no disruption to the patient and no impact on treatment time. [ABSTRACT FROM AUTHOR]

Objective: Intensity‐modulated radiation therapy (IMRT) plays an increasingly important role in clinical applications, and dose verification is particularly crucial for each patient. In the present study, we retrospectively analyzed the results of dose verification in 924 actual IMRT plans, including the relationship between gamma pass rates and the location of lesions, and the total number of monitor units, and the maximum area of the collected dose. Methods: All the 924 IMRT plans implemented in a Varian Trilogy accelerator between 1 January 2014 and 31 March 2016 at Shandong Cancer Hospital were acquired. The Varian Eclipse planning system was used for all treatment planning and verification. Then, actual implemented plans were transplanted into a water phantom. Subsequently, the derived fluence was compared with the actual measured fluence by gamma analysis with the gamma criteria (3%/3 mm). Results: A total of 924 IMRT plans were categorized into six groups, including the brain, head and neck, chest, abdomen, pelvis, and breast. The gamma pass rate average was >98% for 902 IMRT plans, whereas 22 plans did not pass the first time. A correlation was observed between the treatment site and gamma pass rate (P = 0.017). Meanwhile, a negative correlation was observed between the gamma pass rate and the total number of monitor units (P < 0.001), and the largest area of the acquisition dose (P < 0.001), respectively. Varian Trilogy accelerator IMRT QA data has a stable pass rate with a 100 confidence limit (CL) value of 95.19. Conclusion: There was a correlation between the pass rate and the treatment site, the total number of monitor units, and the maximum area of collected dose. When using Mapcheck for patient plan dose verification, the gamma pass rate is very high, and only a few of them need to be analyzed. [ABSTRACT FROM AUTHOR]

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Abstract The use of intensity-modulated radiation therapy (IMRT) is developing rapidly in clinical routines. Because of the high complexity and uniqueness of IMRT treatment plans, patient-specific pretreatment quality assurance is generally considered a necessary prerequisite for patient treatment. In this work, we proposed a modified methodology of electronic portal imaging device (EPID)–based dose validation for pretreatment verification of IMRT fields by applying artificial neural networks (ANNs). The ANN must be trained and validated before use for pretreatment dose verification. For this purpose, 20 EPID fluence maps of IMRT prostate anterior-posterior fields were used as an input for ANN (feed forward type) and a dose map of those fluence maps that were predicted by treatment planning system as an output for ANN. After the training and validation of the neural network, the analysis of 10 IMRT prostate anterior-posterior fields showed excellent agreement between ANN output and dose map predicted by the treatment planning system. The average overall fields pass rate was 96.0% ± 0.1% with 3 mm/3% criteria. The results indicated that the ANN can be used as a low-cost, fast, and powerful tool for pretreatment dose verification, based on an EPID fluence map. Résumé L'utilisation de la radiothérapie avec modulation d'intensité (RTMI) se développe rapidement dans la routine clinique. En raison de la grande complexité et du caractère unique des plans de traitement en RTMI, l'assurance de qualité préalable au traitement et spécifique au patient est généralement considérée comme un prérequis nécessaire au traitement. Dans cette étude, nous proposons une méthodologie modifiée de validation de dose basée sur appareil d'imagerie à portail électronique (EPID) pour la vérification avant traitement par l'application de réseaux neuronaux artificiels (RNN). Le RNN doit être entraîné et validé avant son utilisation pour la vérification de la dose avant le traitement. À cette fin, 20 cartes de fluence EPID de champ antéropostérieur (AP) de la prostate en RCMI ont été utilisés comme intrants pour le RNN (de type chargement en avant) et une carte de doses de ces cartes de fluence ayant été prédites par le système de planification de traitement (SPT) a été utilisée comme sortie pour le RNN. Après l'entraînement et la validation du réseau neural, l'analyse de dix champs AP de la prostate en RCMI a montré un excellent accord entre la sortie du RNN et la carte de doses prédite par le SPT. Le taux de réussite moyen global des champs était de 96,0% ± 0,1% avec un critère de 3 mm/3%. Les résultats indiquent que le RNN peut être utilisé comme outil rapide, puissant et peu coûteux pour la vérification de la dose avant le traitement, à partir d'une carte de fluence EPID. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the optimum density scaling factors of phantom materials for a commercially available three‐dimensional (3D) dose verification system (Delta4) were investigated in order to improve the accuracy of the calculated dose distributions in the phantom materials. At field sizes of 10 × 10 and 5 × 5 cm2 with the same geometry, tissue‐phantom ratios (TPRs) in water, polymethyl methacrylate (PMMA), and Plastic Water Diagnostic Therapy (PWDT) were measured, and TPRs in various density scaling factors of water were calculated by Monte Carlo simulation, Adaptive Convolve (AdC, Pinnacle3), Collapsed Cone Convolution (CCC, RayStation), and AcurosXB (AXB, Eclipse). Effective linear attenuation coefficients (μeff) were obtained from the TPRs. The ratios of μeff in phantom and water ((μeff)pl,water) were compared between the measurements and calculations. For each phantom material, the density scaling factor proposed in this study (DSF) was set to be the value providing a match between the calculated and measured (μeff)pl,water. The optimum density scaling factor was verified through the comparison of the dose distributions measured by Delta4 and calculated with three different density scaling factors: the nominal physical density (PD), nominal relative electron density (ED), and DSF. Three plans were used for the verifications: a static field of 10 × 10 cm2 and two intensity modulated radiation therapy (IMRT) treatment plans. DSF were determined to be 1.13 for PMMA and 0.98 for PWDT. DSF for PMMA showed good agreement for AdC and CCC with 6 MV x ray, and AdC for 10 MV x ray. DSF for PWDT showed good agreement regardless of the dose calculation algorithms and x‐ray energy. DSF can be considered one of the references for the density scaling factor of Delta4 phantom materials and may help improve the accuracy of the IMRT dose verification using Delta4. [ABSTRACT FROM AUTHOR]

Purpose Full integration of EPID-based dosimetry in a global quality control workflow is still complicated. All the actual solutions are based on a relation between image gray-level signal and total linac-delivered dose. In this study, we propose a simple algorithm relying pixel gray-level of EPID image with average linac delivered dose per acquisition frame. Methods Calibration models are constructed for Varian and Elekta linacs including scattering conditions and EPID-arm backscatter-specific corrections. Only simple homogeneous fields are required to establish the EPID dose conversion model for each x-ray beam. Then, the model was evaluated by comparing calculated and converted dose distributions for homogeneous and modulated beams using gamma maps. Results To fit average dose per frame (Dfnorm) vs pixel gray value (Ngnorm) of each EPID image, a logarithmic curve [ABSTRACT FROM AUTHOR]

SBRT for lung cancer is being rapidly adopted as a treatment option in modern radiotherapy centres. This treatment is one of the most complex in common clinical use, requiring significant expertise and resources. It delivers a high dose per fraction (typically ∼6–30 Gy/fraction) over few fractions. The complexity and high dose delivered in only a few fractions make powerful arguments for the application of in vivo dosimetry methods for these treatments to enhance patient safety. In vivo dosimetry is a group of techniques with a common objective – to estimate the dose delivered to the patient through a direct measurement of the treatment beam(s). In particular, methods employing an electronic portal imaging device have been intensely investigated over the past two decades. Treatment verification using in vivo dosimetry approaches has been shown to identify errors that would have been missed with other common quality assurance methods. With the addition of in vivo dosimetry to verify treatments, medical physicists and clinicians have a higher degree of confidence that the dose has been delivered to the patient as intended. In this review, the technical aspects and challenges of in vivo dosimetry for lung SBRT will be presented, focusing on transit dosimetry applications using electronic portal imaging devices (EPIDs). Currently available solutions will be discussed and published clinical experiences, which are very limited to date, will be highlighted. [ABSTRACT FROM AUTHOR]

Radiation dose verification in radiotherapy is essential to determine the dose delivered to irradiated tissue while minimizing normal tissue toxicity. However, the challenge remains in determining topographic radiation dose profiles due to limitations in conventional dosimeters. Herein, we report a robust technique for visualizing and verifying clinical doses based on reusable, flexible scintillating films comprising lanthanide-doped persistent luminescent nanoparticles. These nanoparticle-based films outperform commercially available radiochromic films in terms of linear response to irradiation doses between 0 and 25 Gy. We demonstrate topographic persistent luminescence dosimetry for radiotherapy of mice and rabbits with malignant tumors. Our data show a higher signal-to-background ratio, especially at lower (<0.1 Gy) and higher (>10 Gy) X-ray doses. We also demonstrate that topographic persistent luminescence dosimetry can record complex clinical dose distributions for dose verification and radiotherapy planning. [Display omitted] ● A new dose verification method based on a stable, reusable, sensitive, and flexible X-ray dosimeter is first reported for clinical radiotherapy. ● This nanoparticle film shows better liner response to irradiation dose compared to commercially available Gafchromic films in the range of 0–25 Gy. ● The film enables accurate X-ray dose measurements for radiotherapy of small tumors in mice and large tumors in rabbits and shows higher signal-to-background ratios. ● The scintillation film can be used to record clinical complex topographic dose patterns and accurately measure the X-ray dose according to patient radiotherapy planning. [ABSTRACT FROM AUTHOR]

External beam radiotherapy (EBRT) for carcinoma of uterine cervix is a basic line of treatment with three dimensional conformal radiotherapy (3DCRT) in large number of patients. There is need for an established method for verification dosimetry. We tried to document absorbed doses in a group of carcinoma cervix patients by inserting a 0.6 cc Farmer type ion chamber in the vaginal cavity. A special long perspex sleeve cap is designed to cover the chamber for using in the patient′s body. Response of ionization chamber is checked earlier in water phantom with and without cap. Treatment planning was carried out with X-ray computed tomography (CT) scan and with the chamber along with cap in inserted position, and with the images Xio treatment planning system. Three measurements on 3 days at 5-6 fraction intervals were recorded in 12 patients. Electrometer measured charges are converted to absorbed dose at the chamber center, in vivo. Our results show good agreement with planned dose within 3% against prescribed dose. This study, is a refinement over our previous studies with transmission dosimetry and chemicals in ampules. This preliminary work shows promise that this can be followed as a routine dose check with special relevance to new protocols in the treatment of carcinoma cervix with EBRT.

Stereotactic body radiation therapy (SBRT) to treat spinal metastases has shown excellent clinical outcomes for local control. High dose gradients wrapping around spinal cord make this treatment technically challenging. In this work, we present a spine SBRT case where a dosimetric error was identified during pre-treatment dosimetric quality assurance (QA). A patient with metastasis in T7 vertebral body consented to undergo SBRT. A dual arc volumetric modulated arc therapy plan was generated on the Pinnacle treatment planning system (TPS) with a 6 MV Elekta machine using gantry control point spacing of 4°. Standard pre-treatment QA measurements were performed, including ArcCHECK, ion chamber in CTV and spinal cord (SC) region and film measurements in multiple planes. While the dose measured at CTV region showed good agreement with TPS, the dose measured to the SC was significantly higher than reported by TPS in the original and repeat plans. Acceptable agreement was only achieved when the gantry control point spacing was reduced to 3°. A potentially harmful dose error was identified by pre-treatment QA. TPS parameter settings used safely in conventional treatments should be re-assessed for complex treatments. [ABSTRACT FROM AUTHOR]

Advanced radiotherapy technology enables the dose to more accurately conform to the tumor target area of the patient, providing accurate treatment for the patient, but the gradient of the patient's radiation dose at the tumor edge is getting larger, which putting forward higher requirements for radiotherapy dose verification. The dose verification system software KylinRay-Dose4D can verify the patient's pre-treatment plan and the in vivo /on-line dose during the patient's treatment, providing important reference for the physicist to modify the radiotherapy plan and ensuring that the patient receives accurate treatment. This study introduces the overall design and key technologies of KylinRay-Dose4D, and tests the pre-treatment plan dose checking calculation and 2D/3D dose verification through clinical cases. The test results showed that the 2D/3D gamma pass rate (3 mm/3%) of KylinRay-Dose4D reconstructed dose compared with TPS plan dose and measured dose is larger than 95%, which indicating that the reconstructed dose of KylinRay-Dose4D meets the requirement of clinical application.

The study was aimed to compare accuracy of monitor unit verification in intensity modulated radiation therapy (IMRT) using 6 MV photons by three different methodologies with different detector phantom combinations. Sixty patients were randomly chosen. Zero degree couch and gantry angle plans were generated in a plastic universal IMRT verification phantom and 30Χ30Χ30 cc water phantom and measured using 0.125 cc and 0.6 cc chambers, respectively. Actual gantry and couch angle plans were also measured in water phantom using 0.6 cc chamber. A suitable point of measurement was chosen from the beam profile for each field. When the zero-degree gantry, couch angle plans and actual gantry, couch angle plans were measured by 0.6 cc chamber in water phantom, the percentage mean difference (MD) was 1.35%, 2.94 % and Standard Deviation (SD) was 2.99%, 5.22%, respectively. The plastic phantom measurements with 0.125 cc chamber Semiflex ionisation chamber (SIC) showed an MD=4.21% and SD=2.73 %, but when corrected for chamber-medium response, they showed an improvement, with MD=3.38 % and SD=2.59 %. It was found that measurements with water phantom and 0.6cc chamber at gantry angle zero degree showed better conformity than other measurements of medium-detector combinations. Correction in plastic phantom measurement improved the result only marginally, and actual gantry angle measurement in a flat- water phantom showed higher deviation.

This paper describes the initial experience of quality assurance (QA) tests performed on the millennium multi-leaf collimator (mMLC) for clinical implementation of intensity-modulated radiotherapy (IMRT) using sliding window technique. The various QA tests verified the mechanical and dosimetric stability of the mMLC of linear accelerator when operated in dynamic mode (dMLC). The mechanical QA tests also verified the positional accuracy and kinetic properties of the dMLC. The stability of dMLC was analyzed qualitatively and quantitatively using radiographic film and Omnipro IMRT software. The output stability, variation in output for different sweeping gap widths, and dosimetric leaf separation were measured. Dose delivery with IMRT was verified against the dose computed by the treatment planning system (TPS). Monitor units (MUs) calculated by the planning system for the IMRT were cross-checked with independent commercial dose management software. Visual inspection and qualitative analysis showed that the leaf positioning accuracy was well within the acceptable limits. Dosimetric QA tests confirmed the dosimetric stability of the mMLC in dynamic mode. The verification of MUs using commercial software confirmed the reliability of the IMRT planning system for dose computation. The dosimetric measurements validated the fractional dose delivery.