MV Photon Beams Research Articles

Case study: Dosimetric comparison of VMAT, IMRT and 3DCRT techniques for left-sided breast cancer treated in deep inspiration breath-hold

The aim of this case study was to compare 3D conformal radiotherapy (3DCRT) plans for patients treated for left-sided breast cancer (whole breast without positive lymph nodes in deep inspiration breath-hold (DIBH)) to volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) plans. The original clinical plans used tangential field-in-field 3DCRT technique with a combination of 6 MV and 18 MV photon beams. VMAT and IMRT plans were based on several previously published techniques and used 6 MV beams. Two patients were included in this case study and 4 plans were created and compared for each one. All plans were compared in terms of tumour coverage, gradient measure and conformity index, doses to organs at risk (OARs), the volume of body receiving 5 Gy and also the number of Monitor Units (MUs). While better tumour coverage and conformity was achieved with IMRT and VMAT plans, OARs were better spared with the 3DCRT technique, which also resulted in the lowest dose bath and number of MUs.

Technical note: Angular dependence in Fiber Optic Dosimetry using YVO4 :Eu3.

Fiberoptic dosimetry (FOD) has emerged as a useful technique that can be used in those cases when intracavitary, real time, high spatial resolution dose assessment is required. Among the several factors characterizing a dosimeter, angular response of FOD probes has to be assessed in order to consider possible clinical application. The objective of this study was to characterize the angular response of a FOD probe based on a cylindrical shaped YVO4 :Eu3+ scintillator under irradiation with a 6 MV photon beam generated by a linear accelerator (LINAC). A FOD probe was irradiated inside a plastic phantom using a 6 MV LINAC photon beam at different azimuthal angles (0° to 360°, 15° steps). Scintillation output was measured with a photomultiplier tube. Similar measurements were performed with a second FOD probe having an optical filter interposed between the scintillator and the fiber. Monte Carlo simulations using PENELOPE were carried out in order to interpret the observed results. The FOD output was symmetrical with respect to the scintillator axis. For the unfiltered probe, the signal was maximum at rear incidence (0°) and steadily decreased down to its minimum value at frontal incidence (180°) having a signal ratio of 37%. The output of the filtered probe showed a plateau from 15° up to 115°. The signal was maximum at 60° and minimum at 180° having a signal ratio of 16%. Monte Carlo simulations predicted symmetry of the deposited dose about 0° and 90°, which contrasts with experimental findings. Photoluminescence of the scintillator induced by the Cherenkov light increases the angular dependence. Radiation attenuation inside the scintillator and partial light collection of the scintillation yield by the optical fiber are responsible for asymmetrical response. Results from this study should be considered in order to minimize angular dependence in FOD. This article is protected by copyright. All rights reserved.

Development and application of absorbed dose primary standard for 60Co and high-energy photon beams using water calorimetry

Several new glass vessels, thermistor probes, and water phantoms have been designed and built at the National Institute of Metrology (China) to upgrade and develop the existing water calorimeter. The increased plane-parallel vessels have shorter thermal stability times and shallower positioning depths (∼1.3 cm) than the previous cylindrical vessels, which makes them suitable for electron beams. The sensitivity of the new probes is 10% greater than the previous ones. In this study, detailed experimental and theoretical investigations of various factors affecting the new water calorimeter are performed. The system uncertainty of the water calorimeter is reduced and the robustness of the determination of the absorbed-dose-to-water D w is improved using a variety of geometric detector vessels and two kinds of high-purity water systems saturated with high-purity gases. This new calorimeter is employed as a primary standard for determining the D w, has achieved a combined standard uncertainty of 0.24% for a 60Co beam, 0.27% for 6 MV and 10 MV photon beams and 0.30% for a 25 MV photon beam. The beam quality conversion factors kQ of ten cylindrical and three plane-parallel ionization chambers are measured using the new calorimeter to improve the reference dosimetry accuracy of high-energy clinical photon beams.

The Estimation of Radiation Dose to Out-of-Field Points of Organs at Risk in Block and MLC Shielded Fields in Lung Cancer Radiation Therapy

Purpose: Photon-field shaping in radiation therapy with cerrobend block or Multi-Leaf Collimator (MLC) leads to an increase in the scattered dose to the out-of-field Organ At Risk (OAR). This study aimed to measure and compare the healthy organs absorbed dose outside the cerrobend block and MLC shielded field.
 Materials and Methods: Computed Tomography (CT) images were taken of a heterogeneous Thorax phantom while the target volume and organ at risk, including the spinal cord, contralateral lung, and heart were contoured. Conformal Treatment planning was performed (POP fields, total dose 40 Gy, 5 fx/week, and 2 Gy/fx) on the Prowess Panter Treatment Planning System (TPS). Irradiation was performed with 6 and 18 Mv X-ray of Siemens Oncor medical linear accelerator, once for the block-shielded field and again for the MLC-shielded field. At each energy, the radiation dose to the contoured out-of-field organs was measured by an ionization chamber and compared.
 Results: At both 6 and 18 MV energies, the out-of-field dose in the MLC-shielded fields was significantly lower than in the block-shielded ones (P < 0.001). The out-of-filed dose for contoured organ at risk was not significantly different at 18 MV compared with 6 MV. The dose calculated by the treatment planning system showed that the healthy organs absorbed doses in all conditions were significantly lower than the dosimetry results.
 Conclusion: The use of MLC to shield the lung cancer treatment filed reduces the out-of-field OARs dose compared to cerrobend block. This reduction is greater at 18 MV photon beam but this difference is not statistically significant.

Dosimetric response of Gafchromic™ EBT-XD film to therapeutic protons.

EBT-XD model of Gafchromic™ films has a broader optimal dynamic dose range, up to 40 Gy, compared to its predecessor models. This characteristic has made EBT-XD films suitable for high-dose applications such as stereotactic body radiotherapy and stereotactic radiosurgery, as well as ultra-high dose rate FLASH radiotherapy. The purpose of the current study was to characterize the dependence of EBT-XD film response on linear energy transfer (LET) and dose rate of therapeutic protons from a synchrotron. A clinical spot-scanning proton beam was used to study LET dependence at three dose-averaged LET (LETd) values of 1.0 keV/µm, 3.6 keV/µm, and 7.6 keV/µm. A research proton beamline was used to study dose rate dependence at 150 Gy/second in the FLASH mode and 0.3 Gy/second in the non-FLASH mode. Film response data from LETd values of 0.9 keV/µm and 9.0 keV/µm of the proton FLASH beam were also compared. Film response data from a clinical 6 MV photon beam were used as a reference. Both gray value method and optical density (OD) method were used in film calibration. Calibration results using a specific OD calculation method and a generic OD calculation method were compared. The four-parameter NIH Rodbard function and three-parameter rational function were compared in fitting the calibration curves. Experimental results showed that the response of EBT-XD film is proton LET dependent but independent of dose rate. Goodness-of-fit analysis showed that using the NIH Rodbard function is superior for both protons and photons. Using the "specific OD + NIH Rodbard function" method for EBT-XD film calibration is recommended.

Investigation of variance reduction techniques on photon fluence and dose calculation efficiency for Elekta Agility head using EGSnrc MC code

The aim of this study is to investigate the effects of these Variance reduction techniques on photon fluence and dose calculation efficiency. Different VRTs available in the BEAMnrc code were used to investigate the simulation efficiency for a 6 MV photon beam from an Elekta Agility head. The optimum combination of directional bremsstrahlung splitting (DBS) and bremsstrahlung cross-section enhancement (BCSE) techniques was investigated for photon fluence and dose calculation efficiency. Further combinations with other VRTs were performed. As a result, the combination of DBS and BCSE was most efficient combination for both efficiencies. Furthermore, the combination of DBS and BCSE with photon splitting VRT in DOSXYZnrc further maximized the efficiency. The setting for combining different VRTs that maximize the photon fluence efficiency at the surface of the phantom can be different to those that maximize the dose efficiency inside the phantom. Different VRT combinations, as presented in this study, can improve the simulation efficiency.

Technical note: Energy dependence of the Gafchromic EBT4 film: Dose-response curves for 70kV, 6MV, 6MV FFF, 10MV FFF, and 15MV x-ray beams.

EBT4 was newly released for radiotherapy quality assurance to improve the signal-to-noise ratio in radiochromic film dosimetry. It is important to know its dose-response characteristics before its use in the clinic. This study aims to investigate and compare the dose-response curves of the Gafchromic EBT4 film for megavoltage and kilovoltage x-ray beams with different dose levels, scanning spatial resolutions, and sizes of region of interest (ROI). EBT4 film (Lot#07052201) calibration strips (3.5×20cm2 ) were exposed to a 10×10cm2 open field at doses of 0, 63, 125, 500, 750, 1000cGy using 6MV photon beam. EBT4 film strips from the same lot were then exposed to each x-ray beam (6MV, 6MV FFF, 10MV FFF, 15MV, and 70kV) at six dose values (50, 100, 300, 600, 800, 1000cGy). A full sheet (25×20cm2 ) of EBT4 film was irradiated at each energy with 300cGy for profile comparison with the treatment planning calculation. At two different spatial resolutions of 72 and 300dpi, each film piece was scanned three consecutive times in the center of an Epson 10000XL flatbed scanner in 48-bit color. The scanned images were analyzed using FilmQA Pro. For each scanned image, an ROI of 2×2cm2 at the field center was selected to obtain the average pixel value with its standard deviation in the ROI. An additional ROI of 1cm diameter circle was also used to evaluate the impact of ROI shape and size, especially for FFF beams. The dose value, average dose-response value, and associated uncertainty were determined for each energy and relative responses were analyzed. The Student's t-test was performed to evaluate the statistical significance of the dose-response values with different color channels, ROI shapes, and spatial resolutions. The dose-response curves for the five x-ray energies were compared in three color channels. Weak energy dependence was found among the megavoltage beams. No significant differences (average ∼1.1%) were observed for all doses in this study among 6 MV, 6 MV FFF, 10 MV FFF, and 15 MV beams, regardless of spatial resolution and color channel. However, a statistically significant difference in dose-response was observed up to 12% between 70kV and 6MV beams. The dose-response curves for Gafchromic EBT4 films were nearly independent of the energy of the photon beams among 6MV, 6MV FFF, 10MV FFF, and 15MV. For very low-energy photons (e.g., 70kV), a separate calibration from the same low-energy x-ray is necessary.

Collapsed Cone Superposition Algorithm Validation for Chest Wall Tangential Fields using Virtual Wedge Filters.

Virtual wedge (VW) is used in radiotherapy to compensate for missing tissues and create a uniform dose distribution in tissues. According to TECDOC-1583 and technical reports series no. 430, evaluating the dose calculation accuracy is essential for the quality assurance of treatment planning systems (TPSs). In this study, the dose calculation accuracy of the collapsed cone superposition (CCS) algorithm in the postmastectomy radiotherapy of the chest wall for breast cancer was evaluated by comparing the calculated and measured dose in VW fields. Two tangential fields with the typical VW angles were planned using ISOgray TPS in a thorax phantom. The CCS algorithm was used for dose calculation at 6 and 15 MV photon beams. The obtained dose distributions from EBT3 film spaces and TPS were evaluated using the gamma index. The measured and calculated dose values using VW in a heterogeneous medium with different beam energies were in a good agreement with each other (acceptance rate: 88.0%-93.4%). The calculated and measured data did not differ significantly with an increase/decrease in wedge angle. In addition, the results demonstrated that ISOgray overestimated and underestimated the dose of the soft tissue and lung in the planned volume, respectively. According to the results of gamma index analysis, the calculated dose distribution using VW model with the CCS algorithm in a heterogeneous environment was within acceptable limits.

Cylindrical ionization chamber response in static and dynamic 6 and 15 MV photon beams

Purpose. To investigate the response of the CC13 ionization chamber under non-reference photon beam conditions, focusing on penumbra and build-up regions of static fields and on dynamic intensity-modulated beams. Methods. Measurements were performed in 6 MV 100 × 100, 20 × 100, and 20 × 20 mm2 static fields. Monte Carlo calculations were performed for the static fields and for 6 and 15 MV dynamic beam sequences using a Varian multi-leaf collimator. The chamber was modelled using EGSnrc egs_chamber software. Conversion factors were calculated by relating the absorbed dose to air in the chamber air cavity to the absorbed dose to water. Correction and point-dose correction factors were calculated to quantify the conversion factor variations. Results. The correction factors for positions on the beam central axis and at the penumbra centre were 0.98–1.02 for all static fields and depths investigated. The largest corrections were obtained for chamber positions beyond penumbra centre in the off-axis direction. Point-dose correction factors were 0.54–0.71 at 100 mm depth and their magnitude increased with decreasing field size and measurement depth. Factors of 0.99–1.03 were obtained inside and near the integrated penumbra of the dynamic field at 100 mm depth, and of 0.92–0.94 beyond the integrated penumbra centre. The variations in the ionization chamber response across the integrated dynamic penumbra qualitatively followed the behaviour across penumbra of static fields. Conclusions. Without corrections, the CC13 chamber was of limited usefulness for profile measurements in 20-mm-wide fields. However, measurements in dynamic small irregular beam openings resembling the conditions of pre-treatment patient quality assurance were feasible. Uncorrected ionization chamber response could be applied for dose verification at 100 mm depth inside and close to large gradients of dynamically accumulating high- and low-dose regions assuming 3% tolerance between measured and calculated doses.

BEAM MATCHING EVALUATION OF TWO SIMILAR LINEAR ACCELERATORS.

To evaluate the beam-matching of two Siemens Primus medical linear accelerators (Linacs), the output factor (Sc,p), wedge factor, quality index (TPR20/10), percentage depth dose (PDD) and beam profiles were compared for 6 and 15MV photon beams. The output factor, the PDD and the beam profile for electron beam compared for 5, 7, 8, 10 and 12MeV electron beams. The gamma (γ) analysis of 2mm/2% and 3mm/3% was performed. According to the measurements, it can be said that 6MV photon beams in all field sizes (except 4×4cm2) are beam matched. For 15MV, although the PDDs were matched in all field sizes (except 4×4cm2) for both 2mm/2% and 3mm/3% γ criteria, beam profiles in field sizes larger than 10×10cm2 for 3mm/3% and in field sizes larger than 8×8cm2 for 2mm/2% were not matched. The electron beams in all applicator sizes (except 5×5cm2 applicator) pass the acceptance γ criteria of 3mm/3% (γ<1). Electron beams do not fulfill beam matched in case of the acceptance γ criteria of 2mm/2%.

Evaluation of Radiation Treatment Planning Algorithms in IMRT and VMAT: A Comparative Dosimetric Study in Lung Equivalent Heterogeneous Medium.

In Radiotherapy, computation of dose is important since in a small field with heterogeneity, dose is usually computed with discrepancies. The present study was aimed to evaluate the dosimetry of treatment planning algorithms in lung equivalent heterogeneous medium for Volumetric Modulated Arc Therapy (VMAT) with step and shoot Intensity-Modulated Radiation Therapy (ss-IMRT), and dynamic Intensity-Modulated Radiation Therapy (d-IMRT). In this experimental study, Computerized Imaging Reference System (CIRS) phantom was used with an inhomogeneous Racemosa wood cylinder for two types of tumors, namely, Left Lung Central Tumor (LCT) and Left Lung Peripheral Tumor (LPT) in the CIRS left lung cavity. The computed tomography (CT) datasets were employed with the generation of VMAT, d-IMRT and ss-IMRT plans for the LCT and LPT irradiated with 6 MV photon beams. In this study, the accuracy and efficacy of two algorithms: Monte Carlo (MC) and the Pencil Beam (PB), from the Monaco treatment planning system (TPS), were tested by using Gafchromic EBT3 films and CIRS thorax phantom. Regardless of treatment techniques, both algorithms exhibited higher divergence in LPT than LCT. In both LCT and LPT, the highest deviation was near the tumor-lung junction. However, the deviation was higher in the PB algorithm than MC algorithm, with a minimally acceptable variation of -0.8%. The MC algorithm shows more consistency for EBT3 measured dose in lung equivalent heterogeneous medium. However, accurate dose predictions are complicated due to electronic disequilibrium within and at the interface of inhomogeneity. These constraints may cause variations from the anticipated outcomes of the treatments.

Dosimetric Properties of Brass Mesh Bolus for High-energy Photon Beam

To investigate fundamental dosimetric properties of surface dose, exit dose, and beam profile of the brass mesh bolus for 4, 6, and 10 MV high-energy photon beams in radiation therapy. Surface dose and exit dose in the water-equivalent phantom were measured, and percent depth doses (PDDs) were calculated with no bolus, one layer of brass mesh, two layers of brass mesh bolus, three layers of brass mesh bolus, and 0.5 cm tissue-equivalent (TE) bolus. Exit dose was measured at a phantom thickness of 10 cm. Beam profiles were measured at phantom depths of 0 cm and 10 cm. All dosimetry was performed for 4, 6, and 10 MV photon beams using a linear accelerator. The surface dose at a phantom depth of 0 cm increased to 37.3%, 36.3%, and 31.0% for 4, 6, and 10 MV, respectively, with the brass mesh bolus compared to the case of no bolus. The surface dose decreased with one layer of brass mesh bolus compared to that with the 0.5 cm TE bolus. On the other hand, the exit dose increased to 22.0%, 23.1%, and 22.8% for 4, 6, and 10 MV, respectively, with the brass mesh bolus compared to the case of no bolus. The beam profile at the depth of 0 cm showed oscillations, and the difference between the maximum and minimum doses was up to 13.1% with one layer of brass mesh bolus. It was suggested that the brass mesh bolus not only increases the surface dose but also has different properties from the conventional TE bolus.

Evaluation of the RadCalc collapsed cone dose calculation algorithm against measured data.

This work describes the experimental validation of the RadCalc (Lifeline software Inc, Tyler) collapsed cone dose calculation algorithm against measured data for a range of scenarios. 6 MV photon beam data were measured in a large water tank on a Varian TrueBeam linear accelerator. These were input into the RadCalc software, in conjunction with head geometry and output calibration information, then used to create a collapsed cone beam model. The model performance was assessed by comparison against measurement, using a selection of homogeneous and inhomogeneous geometries not incorporated into the original beam model. Dose calculations generated using the collapsed cone algorithm are generally in good agreement with measurement. However, the primary collimating of the linac is not accounted for in the RadCalc model and hence dose in the corners of large fields is significantly overestimated. Percentage depth doses were within 0.5% beyond a depth of 2 cm. The dose in the build-up region was underestimated by RadCalc Version 7.1.4.1, with (Distance To Agreement) discrepancies of up to 3 mm which were corrected in Version 7.2.2.0. Beam profiles for homogeneous phantom comparisons were within 2% in the central 80% of the field with out of field dose underestimated by no more than 3%. Dose comparisons in heterogeneous geometries were acceptable and generally within 3.5%. The largest observed differences were found at density interfaces and a result of the RadCalc dose resolution of 2 mm against 1 mm measured. Absolute dose comparisons demonstrated that RadCalc agreed with measurement to within 1.2% under homogeneous media irradiation geometries. For static beam IMRT deliveries agreement was within 2% or 2 mm of measured data, and for complex VMAT deliveries within 3% or 2 mm. The implementation of the (model-based) photon collapsed cone algorithm in RadCalc shows generally good agreement with measured data over a range of simple and complex scenarios considered.

Monitoring Linear Accelerator Output Constancy and Overall Performance Using the PTW Quickcheckwebline

Daily morning quality assurance (QA) for all available beams using conventional phantom measures only output and beam quality. PTW QUICKCHECKwebline (PTW QCw) is a compact movable light-weight dosimetry equipment used for daily QA, capable of measuring flatness, symmetry, beam quality and output constancy of a given beam in a single exposure. The purpose of this study was to analyze and monitor the output constancy of a medical linear accelerator using PTW QCw and assess the overall performance of the PTW QCw. The output parameters of 4, 6 and 15 MV photon beams and 4, 6, 8, 10, 12 and 15 MeV electron beams of the Elekta Synergy linear accelerator in Kathmandu Cancer Center were analyzed. It was found in the study that all the parameters were well within the recommended tolerance limit of ±3%. Some known modifications in the settings of the linear accelerator gantry, couch, and collimator were introduced separately during the exposures, and the percentage variations from the baseline values were noted to check the sensitivity of the PTW QCw using 6 MV photon beam. The PTW QCw was able to detect the deviations introduced to the external irradiation conditions for both photon and electron beams under daily testing conditions. The results from this study suggest that daily dosimetric consistency measurements using the PTW QCw helps to monitor the overall performance of the linear accelerator.

Concurrent definitive chemoradiation incorporating intensity-modulated radiotherapy followed by adjuvant chemotherapy in high risk locally advanced cervical squamous cancer: a phase II study

BackgroundAlthough the prognosis of locally advanced cervical cancer has improved dramatically, survival for those with stage IIIB-IVA disease or lymph nodes metastasis remains poor. It is believed that the incorporation of intensity-modulated radiotherapy into the treatment of cervical cancer might yield an improved loco-regional control, whereas more cycles of more potent chemotherapy after the completion of concurrent chemotherapy was associated with a diminished distant metastasis. We therefore initiated a non-randomized prospective phaseII study to evaluate the feasibility of incorporating both these two treatment modality into the treatment of high risk locally advanced cervical cancer.ObjectivesTo determine whether the incorporation of intensity-modulated radiotherapy and the addition of adjuvant paclitaxel plus cisplatin regimen into the treatment policy for patients with high risk locally advanced cervical cancer might improve their oncologic outcomes.Study designPatients were enrolled if they had biopsy proven stage IIIA-IVA squamous cervical cancer or stage IIB disease with metastatic regional nodes. Intensity-modulated radiotherapy was delivered with dynamic multi-leaf collimators using 6MV photon beams. Prescription for PTV ranged from 45.0 ~ 50.0 Gy at 1.8 Gy ~ 2.0 Gy/fraction in 25 fractions. Enlarged nodes were contoured separately and PTV-nodes were boosted simultaneously to a total dose of 50.0–65 Gy at 2.0- 2.6 Gy/fraction in 25 fractions. A total dose of 28 ~ 35 Gy high-dose- rate brachytherapy was prescribed to point A in 4 ~ 5 weekly fractions using an iridium- 192 source. Concurrent weekly intravenous cisplatin at 30 mg/m2 was initiated on the first day of radiotherapy for over 1-h during external-beam radiotherapy. Adjuvant chemotherapy was scheduled within 4 weeks after the completion of concurrent chemo-radiotherapy and repeated 3 weeks later. Paclitaxel 150 mg/m2 was given as a 3-h infusion on day1, followed by cisplatin 35 mg/m2 with 1-h infusion on day1-2 (70 mg/m2 in total).ResultsFifty patients achieved complete response 4 weeks after the completion of the treatment protocol, whereas 2 patients had persistent disease. After a median follow-up period of 66 months, loco-regional (including 2 persistent disease), distant, and synchronous treatment failure occurred in 4,5, and 1, respectively. The 5-year disease-free survival, loco-regional recurrence-free survival, distant-metastasis recurrence-free survival was 80.5%, 90.3%, and 88.0%, respectively. Four of the patients died of the disease, and the 5-year overall survival was 92.1%. Most of the toxicities reported during concurrent chemo-radiotherapy were mild and transient. The occurrence of hematological toxicities elevated mildly during adjuvant chemotherapy, as 32% (16/50) and 4% (2/50) patients experienced grade 3–4 leukopenia and thrombocytopenia, respectively. Grade 3–4 late toxicities were reported in 3 patients.ConclusionsThe incorporation of intensity-modulated radiotherapy and adjuvant paclitaxel plus cisplatin chemotherapy were highly effective and well-tolerated in the treatment of high-risk locally advanced cervical cancer. The former yields an improved loco-regional control, whereas distant metastases could be effectively eradicated with mild toxicities when adjuvant regimen was prescribed.

A dosimetric comparison for SBRT plans of localized prostate cancer between Cyberknife and Varian Truebeam STX device

As the Stereotactic Body Radiotherapy (SBRT) approach began to increase in treating patients with localized prostate cancer, it became necessary to investigate which methods used in practice were better. The aim of this study is to perform a dosimetric comparison of the advantages and disadvantages of SBRT treatments for localized prostate cancer delivered by CyberKnife (CK) and Varian Truebeam STX (FF and FFF). Seventeen intermediate and high-risk patients with localized prostate cancer were included in the study. SBRT plans for the CK system and Varian Truebeam STX systems with and without Flattening Filters (Tru-FF and Tru-FFF) were prepared for each patient. Plans prepared for each patient were planned at a fraction dose of 6.7 Gy at 6 MV energy and a target dose of 33.5 Gy in 5 fractions. For all plans, cumulative dose-volume histograms (DVHs) were generated for target volumes and organs at risk (OAR). The maximum doses of PTV (41 Gy) in CK plans are higher than the maximum doses (35 Gy) in VMAT plans prepared with Tru-FF or Tru-FFF beams. The mean dose of the rectal wall (10.06 ± 2.40Gy for CK) is still relatively low compared to other plans (13.46 ± 2.16 Gy for Tru-FF and 13.61 ± 2.32 Gy for Tru-FFF). The bladder wall (14 Gy for CK, 26 Gy for Tru-FF and Tru-FFF) and femoral head (6.8 Gy for CK, 9 Gy for Tru-FF and 9.4 Gy Tru-FFF) doses were also lower for CK plans. The CK plans provide better tumour control due to low doses in critical organs and high target doses than the Tru-FF or Tru-FFF plans. It was observed that CK and VMAT plans for SBRT with 6 MV photon beams provided acceptable results in term of treatment planning criteria such as Conformity Index and Homogeneity Index. It is recommended to use a target tracking system to provide an accurate and reliable SBRT treatment with VMAT and CK techniques.

Protocol determination for OSL in vivo measurements of absorbed dose in the oral mucosa in oral cancer patients: A pilot study

Radiation-induced oral mucositis (RIOM) is one of the major oral complications caused by radiotherapy (RT), and can lead a negative impact on patients’ quality of life. Considering that there is no specific radiation therapy dose constraint for oral mucosa, the need to study the correlation between absorbed dose and effect in this area is crucial. This pilot study aims to report in vivo OSL dosimetry protocol to investigate the dose distribution in the oral mucosa in patients with oral cancer using Intraoral customised Stent (IOS). For measurements, aluminium oxide nanoDot dosimeters and a microStar ii OSL reader from Landauer Inc. were used. The OSL dosimetry system was calibrated with a 6 MV photon beam using an Elekta Synergy linear accelerator and solid water phantoms following the recommendations of the AAPM TG 191 protocol. The dose distribution in the oral mucosa using seven OSL dosimeters fixed on the intraoral stent was evaluated and compared with the dose distribution available from the RT planning for the patient. Our experimental results showed the expected linearity response of the nanoDot dosimeters from 20 to 200 cGy. The repeatability of readings was better than 1.0% in all commissioning measurements. The uncertainty budget of the commissioning analysis resulted in an overall type An uncertainty of ∼3.4% at the 1-sigma level for dose calculation, compatible with the TG 191 protocol. The dose distribution in the oral mucosa was assessed and dose deviations up to 35% can be found in high dose gradient regions of the treatment planning. This type of deviation may impact on the development and progression of RIOM, as analysed in this protocol. It is feasible to establish this procedure in vivo dosimetry for a patient undergoing RT using a multidisciplinary approach. Additionally, intraoral customised stents can decrease radiation doses in the oral mucosa, and the understanding of the dose distribution in the oral mucosa may help to minimise damages from radiation.

Doses delivered to small and large breasts and adjacent organs in left breast cancer patients utilizing 3D and IM radiotherapy

BackgroundRadiotherapy is still the most facilitated modality for treatment of malignant tumors, including breast cancer, with or without chemotherapy and after surgery or when surgery is impossible. AimThe present article concerns a number of parameters used in radiation therapy techniques, involving the minimum, maximum, mean dose, volume covered with 95% of dose, and global maximum dose delivered to planning target volume (PTV), and the organs at risk, including left lung, heart, thyroid gland, spinal cord, humerus, super clavicle lymph node, and the right breast using the constraints of Radiation Therapy Oncology Group (RTOG). Patients and MethodsTwenty patients with breast tumors, females only, were enrolled in the study. A LINAC with a 6 MV photon beam was used to deliver the prescribed dose. The whole breast irradiation was applied to each patient using two planning techniques: 3D conformal and intensity modulated radiotherapy, and the planning was constructed within 95%–107% of the prescribed dose to the planning target volume as recommended by the RTOG. ResultsThe results showed a significant difference (at the level of P < 0.05) between the two planning techniques based on the doses received by PTV and the OARs. The results were discussed. ConclusionWe concluded that inverse intensity modulation radiation therapy (IMRT) for breast cancer does not improve late toxicity or oncologic outcomes. So, inverse IMRT is not yet the norm, and health insurance usually doesn't pay for treatment unless it's absolutely necessary, like to stop a heart attack. .

Enhanced Cherenkov imaging for real-time beam visualization by applying a novel carbon quantum dot sheeting in radiotherapy.

Cherenkov imaging can be used to visualize the placement of the beam directly on the patient's surface tissue and evaluate the accuracy of treatment planning. However, Cherenkov emission intensity is lower than ambient light. At present, time gating is the only way to realize Cherenkov imaging with ambient light. This study proposes preparing a novel carbon quantum dot (cQD) sheeting to adjust the wavelength of Cherenkov emission to obtain the optimal wavelength meeting the sensitive detection region of the camera, meanwhile the total optical signal is also increased. By combining a specific filter, this approach might help in using lower-cost camera systems without intensifier-coupled to accomplish in vivo monitoring of the surface beam profile on patients with ambient light. The cQD sheetings were prepared by spin coating and UV curing with different concentrations. All experiments were performed on the Varian VitalBeam system and optical emission was captured using an electron multiplying charge-coupled device (EMCCD) camera. To quantify the optical characteristics and certify the improvement of light intensity as well as signal-to-noise ratio (SNR) of cQD sheeting, the first part of the study was carried out on solid water with 6 and 10 MV photon beams. The second part was carried out on an anthropomorphic phantom to explore the applicability of sheeting when using different radiotherapy materials and the imaging effect of sheeting with the impact of ambient light sources. Additionally, thanks to the narrow emission spectrum of the cQD, a band-pass filter was tested to reduce the effect from environmental lights. The experimental results show that the optical intensity collected with sheeting has an excellent linear relationship (R2 >0.99) with the dose for 6 and 10 MV photons. The full-width half maximum (FWHM) in x and y axis matched with the measured EBT film image, with accuracy in the range of ±1.2and ±2.7mmstandard deviation, respectively. CQD sheeting can significantly improve the light intensity and SNR of optical images. Using 0.1mg/ml sheeting as an example, the signal intensity is increased by 209%, and the SNR is increased by 147.71% at 6 MV photons. The imaging on the anthropomorphic phantom verified that cQD sheeting could be applied to different radiotherapy materials. The average optical intensity increased by about 69.25%, 63.72%, and 61.78%, respectively, after adding cQD sheeting to bolus, mask sample and the combination of bolus and mask. Corresponding SNR is improved by about 62.78%, 56.77%, and 68.80%, respectively. Through the sheeting, optical images with SNR>5 can be obtained in the presence of ambient light and it can be improved through combining with a band-pass filter. When red ambient lights are on, the SNR is increased by about 98.85% after adding a specific filter. Through a combination of cQD sheeting and corresponding filter, light intensity and SNR of optical images can be increased significantly, and it shed new light on the promotion of the clinical application of optical imaging to visualize the beam in radiotherapy.

A prospective randomized comparison of simultaneous integrated boost with sequential boost intensity-modulated radiotherapy in locally advanced head and neck cancer.

A comparison of simultaneous integrated boost (SIB) with sequential boost (SEQ) using intensity-modulated radiotherapy along with concurrent cisplatin in locally advanced head and neck cancer (HNC) was made with regard to their survival outcomes and toxicity profile. A total of 34 patients were enrolled between October 2016 and March 2019. They were randomized into two arms, SIB and SEQB. All patients were treated with 6 MV photon beam on Linear Accelerator with weekly concurrent cisplatin at 35 mg/m2. Overall survival (OS) and disease-free survival (DFS) were the primary end points and acute and late toxicities were the secondary end points. The median follow-up period was 40.6 and 37.3 months for SIB and SEQB, respectively. At the end of 5 years, the median OS was 40.6 and 37.3 months (P = 0.947) and the median DFS was 35.1 and 37.3 months in the SIB and SEQB arms, respectively (P = 0.991). Complete response at 3 months was 64.7% and 76.5% and partial response was 23.5% and 17.6%, whereas progressive disease was 11.8% and 5.9% in SIB and SEQB arms, respectively. Acute dermatitis, mucositis, dysphagia, and salivary gland toxicities were higher in the SIB arm compared to the SEQB arm. SIB and SEQ arms were comparable in terms of OS and DFS. However, the acute toxicities were higher in the SIB arm, although the difference was not significant, compared to the SEQB arm.