Predictive modeling of dose-volume parameters of carcinoma tongue cases using machine learning models.

The aim of this study is to create a single institution-based machine learning model for a dose prediction generation tool for post-operative carcinoma of the tongue cases prospectively. Intensity-modulated radiotherapy (IMRT) plans for 20 patients with carcinoma of the tongue were generated using the Eclipse treatment planning system. A machine learning model was generated using a Python 3.10 computer language in a Jupyter notebook using Anaconda software. The PTVs and OARs doses obtained from the clinical treatment plans were used as a primary dataset. Machine learning models are built with two different datasets (10 and 20) for each selected volume. Volumes from 10 new sets of patients were fed into the software for predicting the corresponding dose values. Through the input given, the plan generated dose values of 10 patients were compared with the predicted outcomes of the 10 and 20 dataset models. The model created using the PTVs volume data predicted the dose values with increased accuracy. By verifying the model prediction with the TPS generated value, both the 10 and 20 dataset models predict all the 10 PTVs data within an error bound of 3% and most of the OARs data within an error bound of 5%. The dosimetric features implemented in the machine learning models reasonably predict both the PTVs dose parameter and OARs constraints and give confidence in decision-making during the clinical planning process.

IMRT as an Alternative Technique for Intracavitary Brachytherapy in Patients with Carcinoma of the Cervix: A Feasibility Study Using Unified Dosimetric Index.

OBJECTIVE: Intracavitary brachytherapy (ICBT) plays an important role in the management of carcinoma of the cervix. This study attempts to find the feasibility of intensity-modulated radiation therapy (IMRT) as a boost for patients who are not suitable for ICBT in order to improve their disease-free and overall survival. METHODS: Twenty patients with carcinoma of the cervix were included in this study. Nine fields of IMRT and ICBT plans were generated for PTVBoost. Various dosimetric indices like coverage, conformity, homogeneity, and gradient index were calculated, and the corresponding unified dosimetric index (UDI) values were generated. Plans were classified based on combined UDI, and the UDI values were compared with those of ICBT. In addition, rectum and bladder doses were compared. RESULTS: All the dosimetric indices were within acceptable limits except for the gradient index. The gradient index of the IMRT and ICBT plans were 8.77 ± 0.26 and 1.33 ± 0.06 respectively (p < 0.0001). The mean of combined UDI with standard deviation was 32.557 ± 8.940 and plan quality was calculated from these values. Rectum and bladder doses for ICBT were lesser than IMRT (p < 0.0001). CONCLUSION: ICBT is the gold standard for boost RT in carcinoma of the cervix patients. IMRT boost is feasible for patients who are unsuitable on medical grounds for brachytherapy.

Integrated scoring approach to assess radiotherapy plan quality for breast cancer treatment.

Background: Proposal of an integrated scoring approach assessing the quality of different treatment techniques in a radiotherapy planning comparison. This scoring method incorporates all dosimetric indices of planning target volumes (PTVs) as well as organs at risk (OARs) and provides a single quantitative measure to select an ideal plan. Materials and methods: The radiotherapy planning techniques compared were field-in-field (FinF), intensity modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT), hybrid IMRT (H-IMRT), and hybrid VMAT (H-VMAT). These plans were generated for twenty-five locally advanced left-sided breast cancer patients. The PTVs were prescribed a hypofractionation dose of 40.5 Gy in 15 fractions. The integrated score for each planning technique was calculated using the proposed formula. Results: An integrated score value that is close to zero indicates a superior plan. The integrated score that incorporates all dosimetric indices (PTVs and OARs) were 1.37, 1.64, 1.72, 1.18, and 1.24 for FinF, IMRT, VMAT, H-IMRT, and H-VMAT plans, respectively. Conclusion: The proposed integrated scoring approach is scientific to select a better plan and flexible to incorporate the patient-specific clinical demands. This simple tool is useful to quantify the treatment techniques and able to differentiate the acceptable and unacceptable plans.

Hypofractionated Hybrid Radiotherapy Techniques for Synchronous Bilateral Breast Cancer.

OBJECTIVE: This study intends at a dosimetric comparison of four different hybrid plans which is a combination of different radiation therapy techniques, for synchronous bilateral breast cancer (SBBC) irradiation using a hypofractionated dose regimen. METHODS: Four different hybrid techniques: 3DCRT+IMRT, 3DCRT+VMAT, IMRT+VMAT, and VMAT+IMRT were planned using computed tomography (CT) images of fifteen SBBC patients.  All hybrid plans were generated using a hypofractionated dose prescription of 40.5 Gy in 15 fractions. 70% of the dose was planned with a base-dose component and the remaining 30% of the dose was planned with a hybrid component. The plans were evaluated based on the PTV and organs at risk (OARs) dosimetric parameter results and computed a plan quality score for each plan. RESULTS: The results for PTV parameters have shown that the 3DCRT+VMAT and 3DCRT+IMRT plans were better than other plans. The 3DCRT±IMRT plan was provided better results for OARs, while IMRT±VMAT and VMAT+IMRT plans were increased the low dose volumes to the heart and lungs. The 3DCRT+VMAT plan was required less monitor units and treatment time compared to other plans. CONCLUSION: The overall plan quality score that integrated the dosimetric parameters of PTV and OARs indicated that the 3DCRT+VMAT hybrid plan is superior for SBBC treatment.

Surface dose and build-up region depth dose measurements in non-standard beams of Cyberknife and tomotherapy systems.

The purpose of this study was to measure the surface dose and build-up region depth dose characteristics of 6 MV photon beams in Cyberknife and helical tomotherapy (HT) systems for non-standard small fields using parallel plate chambers (Roos and Markus), Gafchromic EBT3 films, and nanoDot optically stimulated luminescence dosimeters (OSLDs), as well as to investigate the effect of oblique incidence on the surface dose of the beam. All measurements were conducted in a virtual water phantom under machine-specific reference conditions. The Roos and OSLDs overestimated the surface dose when compared with the Markus chamber and EBT3 films by 20%. We applied water equivalent thickness (WET) correction to account for the intrinsic build-up thickness of the detectors from their effective point of measurement (EPOM). With WET correction, a reasonably close surface dose estimate was obtained for all detectors, within 1.9% agreement for the 60 mm collimator of Cyberknife and 3.1% agreement for the HT system, with a 5 × 10 cm2 field size. The surface dose increased from the normally incident Cyberknife and HT fields with increasing angle of incidence. The surface dose increased to twice its value at normal incidence for highly oblique angles of incidence above 55°. For the tested fields, a reasonable surface dose estimate could be measured with the detectors if the correction for intrinsic buildup thickness was applied. Nevertheless, the use of Roos chambers with large dimensions and nanoDot OSLDs is not recommended for estimating the surface dose for small fields.

Hybrid planning techniques for hypofractionated whole-breast irradiation using flattening filter-free beams.

OBJECTIVE: The aim of this study was to assess the feasibility of flattening filter-free (FFF) photon beams in hybrid intensity-modulated radiation therapy (H-IMRT) and hybrid volumetric modulated arc therapy (H-VMAT) for left-sided whole-breast radiation therapy with a boost volume (RT) using a hypofractionated dose regimen. PATIENTS AND METHODS: RT plans of 25 patients with left-sided early-stage breast cancer were created with H­IMRT and H­VMAT techniques under breath-hold conditions using 6­MV FFF beams. In hybrid techniques, three-dimensional conformal radiotherapy (3DCRT) plans were kept as base-dose plans for the VMAT and IMRT plans. In addition, H­IMRT in step-and-shoot mode was also calculated to assess its achievability with FFF beams. RESULTS: All hybrid plans achieved the expected target coverage. H­VMAT showed better coverage and homogeneity index results for the boost target (p < 0.002), while H­IMRT presented better results for the whole-breast target (p < 0.001). Mean doses to normal tissues were comparable between both plans, while H­IMRT reduced the low-dose levels to heart and ipsilateral lung (p < 0.05). H­VMAT revealed significantly better results with regard to monitor units (MU) and treatment time (p < 0.001). CONCLUSION: The 6­MV FFF beam technique is feasible for large-field 3DCRT-based hybrid planning in whole-breast and boost planning target volume irradiation. For breath-hold patients, the H­VMAT plan is superior to H­IMRT for hypofractionated dose regimens, with reduced MU and treatment delivery time.

Hybrid volumetric modulated arc therapy for whole breast irradiation: a dosimetric comparison of different arc designs.

PURPOSE: To find an optimal arc design for hybrid volumetric modulated arc therapy (H-VMAT), a combination of conventional 3DCRT and VMAT plans for left-sided whole breast radiation therapy. METHODS AND MATERIALS: A total of 26 left-sided early-stage breast cancer patients were selected for this study. To find the superior plan, H-VMAT with three different arc designs including, two partial arcs (2A), four partial arcs (4A) and four tangential arcs (TA) were created for each study case by combining 3DCRT and VMAT with 75% 3DCRT/25% VMAT dose proportion of prescription dose. RESULTS: All H-VMAT plans achieved the expected target coverage. A higher conformity index and homogeneity index were achieved for 2A and 4A H-VMAT plans and significantly differ from TA H-VMAT (p < 0.003). The heart and ipsilateral lung dose parameters were comparable among all plans except heart V40Gy which was significantly less in 4A H-VMAT plan (p < 0.05). The contralateral lung, contralateral breast, spinal cord, normal tissue doses and MU were significantly less in TA H-VMAT (p < 0.03). The beam-on time was significantly less in 2A H-VMAT (p < 0.0001). CONCLUSION: 2A and 4A H-VMAT techniques are effective in improving the PTV dosimetric parameters as well as reducing the OAR doses. Further, 2A H-VMAT delivers less MU and beam-on time compared to 4A H-VMAT.

Evaluation of beam matching accuracy among six linacs from the same vendor.

The purpose of this study was to evaluate the dosimetric variation among six non-beam-matched Varian linacs using different techniques for the same plans. Six non-beam-matched Varian machines, comprising two Clinac iX, two 600 C/D (Unique), and two True Beam Tx photon 6 MV X-ray devices were acquired. Sixty patients with of head and neck (H&N; 30) and pelvic (30) treatment sites were chosen. For all 60 patients, three-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT), and volumetric-modulated radiotherapy (VMAT) plans were generated for the Clinac iX-1 device; all plans were migrated to the remaining machines, using the eclipse treatment planning system without any modification. The dosimetric variation among the six machines for each target volume and organ at risk was recorded and analyzed. In H&N cases, the maximum variation among the six machines with 3DCRT, IMRT, and VMAT was 2.57%, 2.6%, and 2.6%, respectively. In pelvic cases, the maximum variation among the six machines with 3DCRT, IMRT, and VMAT was 2.2%, 1.95%, and 2.05%, respectively. Our overall results show that dosimetric variation, while interchanging the plans among the six machines at phantom and patient levels, remains within the limits of clinical acceptability. The noted variation was not correlated with any of these treatment techniques: 3DCRT, IMRT, or VMAT.

Hybrid volumetric modulated arc therapy for chest wall irradiation: For a good plan, get the right mixture.

PURPOSE: To find the optimal dose weighting for hybrid volumetric modulated arc therapy (H-VMAT), a combination of conventional 3DCRT and VMAT plans for left sided chest wall and supraclavicular radiation therapy. METHODS & MATERIALS: 20 left-sided breast cancer patients who received adjuvant radiotherapy were considered for this study. To find the optimal weighting, 5 H-VMAT plans were generated for each study case by combining different dose proportions of 3DCRT and VMAT plans including: 90% 3DCRT/10% VMAT, 80% 3DCRT/20% VMAT, 70% 3DCRT/30% VMAT, 60% 3DCRT/40% VMAT, 50% 3DCRT/50% VMAT. Further field-in-field, optimal H-VMAT and VMAT alone plans were compared. RESULTS: All H-VMAT plans achieved the expected target coverage. A higher conformity index was achieved for 50% 3DCRT/50% VMAT plan, while better homogeneity index was achieved for 80% 3DCRT/20% VMAT plan. Mean and low doses were less in 90% 3DCRT/10% VMAT plan. Compared with other proportions, 80% 3DCRT/20% VMAT and 70% 3DCRT/30% VMAT weighted H-VMAT plans achieved balanced results for PTVs and OARs. CONCLUSION: The optimal dose mixture for H-VMAT technique is 70% to 80% for 3DCRT and 20% to 30% for VMAT. The optimal H-VMAT achieved balanced results for the PTVs and OARs compared with field-in-field and VMAT alone plans.

Magnetic resonance image guidance in external beam radiation therapy planning and delivery.

The use of magnetic resonance (MR) imaging in radiation oncology is improving dramatically. This review article discusses the necessity of image guidance and how MR finds a significant place in radiotherapy planning and delivery. The challenges to and current solutions for an in-house MR simulation, dedicated MR simulator, estimation of electron density using MR image sets and development of MR-compatible treatment planning systems are presented. This article also reviews the feasibility, advantages and limitations of MR image-guided radiation therapy (MR-IGRT) and its drive toward the integration of radiation beams with MR technology. Specifications of Co-60 MR technology and three other MR-linac projects worldwide are presented. Online and real-time MR guidance is also discussed.

Radiation therapy for breast cancer: Literature review.

Concave shape with variable size target volume makes treatment planning for the breast/chest wall a challenge. Conventional techniques used for the breast/chest wall cancer treatment provided better sparing of organs at risk (OARs), with poor conformity and uniformity to the target volume. Advanced technologies such as intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) improve the target coverage at the cost of higher low dose volumes to OARs. Novel hybrid techniques present promising results in breast/chest wall irradiation in terms of target coverage as well as OARs sparing. Several published data compared these technologies for the benefit of the breast/chest wall with or without nodal volumes. The aim of this article is to review relevant data and identify the scope for further research in developing optimal treatment plan for breast/chest wall cancer treatment.

Commissioning and Acceptance Testing of the existing linear accelerator upgraded to volumetric modulated arc therapy.

AIM: The RapidArc commissioning and Acceptance Testing program will test and ensure accuracy in DMLC position, precise dose-rate control during gantry rotation and accurate control of gantry speed. BACKGROUND: Recently, we have upgraded our linear accelerator capable of performing IMRT which was functional from 2007 with image guided RapidArc facility. The installation of VMAT in the existing linear accelerator is a tedious process which requires many quality assurance procedures before the proper commissioning of the facility and these procedures are discussed in this study. MATERIALS AND METHODS: Output of the machine at different dose rates was measured to verify its consistency at different dose rates. Monitor and chamber linearity at different dose rates were checked. DMLC QA comprising of MLC transmission factor measurement and dosimetric leaf gap measurements were performed using 0.13 cm(3) and 0.65 cm(3) Farmer type ionization chamber, dose 1 dosimeter, and IAEA 30 cm × 30 cm × 30 cm water phantom. Picket fence test, garden fence test, tests to check leaf positioning accuracy due to carriage movement, calibration of the leaves, leaf speed stability effects due to the acceleration and deceleration of leaves, accuracy and calibration of leaves in producing complex fields, effects of interleaf friction, etc. were verified using EDR2 therapy films, Vidar scanner, Omnipro accept software, amorphous silicon based electronic portal imaging device and EPIQA software.(1-8.) RESULTS: All the DMLC related quality assurance tests were performed and evaluated by film dosimetry, portal dosimetry and EPIQA.(7.) CONCLUSION: Results confirmed that the linear accelerator is capable of performing accurate VMAT.

Dosimetric evaluation of a three-dimensional treatment planning system.

The computerized treatment planning system plays a major role in radiation therapy in delivering correct radiation dose to the patients within ±5% as recommended by the ICRU. To evaluate the dosimetric performance of the Treatment Planning system (TPS) with three-dimensional dose calculation algorithm using the basic beam data measured for 6 MV X-rays. Eleven numbers of test cases were created according to the Technical Report Series-430 (TRS 430) and are used to evaluate the TPS in a homogeneous water phantom. These cases involve simple field arrangements as well as the presence of a low-density material in the beam to resemble an air in-homogeneity. Absolute dose measurements were performed for the each case with the MU calculation given by the TPS, and the measured dose is compared with the corresponding TPS calculated dose values. The result yields a percentage difference maximum of 2.38% for all simple test cases. For complex test cases in the presence of in-homogeneity, beam modifiers or beam modifiers with asymmetric fields a maximum percentage difference of 5.94% was observed. This study ensures that the dosimetric calculations performed by the TPS are within the accuracy of ±5% which is very much warranted in patient dose delivery. The test procedures are simple, not only during the installation of TPS, but also repeated at periodic intervals.

Feasibility study on effect and stability of adaptive radiotherapy on kilovoltage cone beam CT.

BACKGROUND: We have analyzed the stability of CT to density curve of kilovoltage cone-beam computerized tomography (kV CBCT) imaging modality over the period of six months. We also, investigated the viability of using image value to density table (IVDT) generated at different time, for adaptive radiotherapy treatment planning. The consequences of target volume change and the efficacy of kV CBCT for adaptive planning issues is investigated. MATERIALS AND METHODS.: Standard electron density phantom was used to establish CT to electron density calibrations curve. The CT to density curve for the CBCT images were observed for the period of six months. The kV CBCT scans used for adaptive planning was acquired with an on-board imager system mounted on a "Trilogy" linear accelerator. kV CBCT images were acquired for daily setup registration. The effect of variations in CT to density curve was studied on two clinical cases: prostate and lung. RESULTS: The soft tissue contouring is superior in kV CBCT scans in comparison to mega voltage CT (MVCT) scans. The CT to density curve for the CBCT images was found steady over six months. Due to difficulty in attaining the reproducibility in daily setup for the prostate treatment, there is a day-to-day difference in dose to the rectum and bladder. CONCLUSIONS: There is no need for generating a new CT to density curve for the adaptive planning on the kV CBCT images. Also, it is viable to perform the adaptive planning to check the dose to target and organ at risk (OAR) without performing a new kV CT scan, which will reduce the dose to the patient.