Compliance of Bhabhatron-II telecobalt unit with IEC standard - Radiation safety

Implementation and Validation of Anisotropic Analytical Algorithm in Eclipse Treatment Planning System for Indigenous Telecobalt Machine (Bhabhatron II)

Background

The photon dose calculation model anisotropic analytical algorithm (AAA) available with eclipse integrated treatment planning system (TPS) (Varian) supports telecobalt dose calculation from Version 13.6 onward. Formerly, pencil beam convolution (PBC) was used for modeling telecobalt machines. Eclipse TPS no longer supports PBC dose calculation algorithm in v13.6 and above. The AAA dose calculation model is a three-dimensional PBC/superposition algorithm. Its configuration is based on Monte-Carlo-determined basic physical parameters that are tailored to measured clinical beam data.

Aim

The study investigated the feasibility of clinical implementation of AAA in Eclipse TPS for Bhabhatron II.

Materials and Methods

The indigenous telecobalt machine, Bhabhatron II, was configured as a generic machine because an inbuilt machine model for the same was not available in Varian Eclipse TPS algorithm library. In such a scenario, it was necessary to evaluate and validate dosimetric parameters of the TPS because improper tailoring would cause errors in dose calculations. Beam data measurements of the machine were carried out which were used for configuration of the algorithm.

Result

After successful configuration, a variety of plans created in TPS were executed on the machine and subsequently evaluated.

Conclusion

From this study, we concluded that AAA-based dose calculation in TPS is very well suited for accurate dose calculations for telecobalt machine and can be implemented for clinical use.

An Assessment of Dosimetric Characteristics of Inline 2.5 Mega Voltage Unflattened Imaging X-Ray Beam

Purpose:

The aim of this work is to study the dosimetric parameters of newly introduced 2.5 MV imaging x-ray beam used as inline imaging to do setup verification of the patient undergoing radiation therapy. As this x-ray beam is in megavoltage range but comprises of a lower energy spectrum. It is essential to study the pros and cons of 2.5 MV imaging x-ray beam for clinical use.

Methods:

The mean energy was calculated using the NIST XCOM table through MAC. Profile analysis was done using RFA to understand the percentage depth dose, degree of unflatteness, symmetry, penumbra and out of field dose. Dose to skin for the 2.5 MV x-ray beam was analysed for field sizes 10x10 cm², 20x20 cm², 30x30 cm². Leakage measurements for treatment head and at the patient plane were done using IEC 819/98 protocol. Finally, the spatial resolution and contrast were analyzed with and without patient scatter medium.

Results:

The MAC at 15 cm off-axis was found to be lower than that at the CAX. Similarly, there was a decrease in mean energy from 0.47 MV to 0.37 MV at 15 cm off-axis. The reduction of mean energy towards off-axis is lower than the other high energy MV x-ray beams. The tuned absolute dose of 1 cGy/MU is consistent and within < ±1 %. The relative output factors were found to be in correlation with Co-60. The beam quality of 2.5 MV x-ray beam was found to be 0.4771. The profile parameters like the degree of unflatness of the 2.5 x-ray beam were studied at 85 %, 90 %, 95 % lateral distances, and the penumbra at different depth and field sizes are higher than the 6 MV treatment beam. In addition, out of field dose also drastically increases to a maximum of up to 30 % laterally at 5cm at deeper depths. The skin dose increases from 48.51 % to 88.15 % from 6 MV to 2.5 MV x-ray beam for the field size 10x10 cm². Also, the skin dose increases from 88.15 % to 91.78 % from the field size 10x10 cm² to 30x30 cm². Although the measured leakage radiation for 2.5 MV x-ray beam at the patient plane and other than patient planes are with the tolerance limit, an increase in exposure towards gantry side compared to other areas around treatment head and the patient plane may lead to more skin dose to head and chest while imaging pelvis region. The MLC transmission of 2.5 MV x-ray beam such as inter, intra and edge effect are 0.40 %, 0.37 % and 11% respectively. The spatial resolution of 2.0, 1.25 and 0.9 LP/mm was observed for KV, 2.5MV, and 6 MV x-ray beams. The spatial resolution and contrast of 2.5 MV x-ray beam are superior to 6 MV x-ray beam and inferior to KV x-rays.

Conclusions:

The 2.5 MV x-ray imaging beam is analysed in view of beam characteristics and radiation safety to understand the above-studied concepts while using this imaging beam in a clinical situation. In future, if 2.5MV x-ray beam is used for treatment purpose with increased dose rate, the above-studied notions can be incorporated prior to implementation.

Radiation Oncology in India: Challenges and Opportunities

Rising cancer incidence and mortality in India emphasize the need to address the increasing burden of this disease and the stark inequities in access to radiotherapy and other essential medical treatments. State-of-the-art technology is available within the private sector and a few hospitals in the public sector, but 75% of patients in the public sector in India do not have access to timely radiotherapy. This inequity in access to radiotherapy in the public sector is amplified in rural areas, where most of India׳s population lives. A long-term government commitment to machine purchase and human resource development in the public sector is needed to improve access. A number of innovative initiatives to improve cancer treatment and access have emerged that could support such an investment. These include local production of equipment, twinning programs between institutions in high- and low-income countries to exchange knowledge and expertise, and nongovernmental and state-sponsored schemes to sponsor and support patients in their cancer journey. Strengthening of cancer registries and regulatory bodies with authority to enforce minimum standards is also required to improve care. The more uniform and frequent availability of high-quality radiotherapy can improve cancer outcomes and may be regarded as a marker of a comprehensive and equitable system of health care delivery.

Development, physical properties and clinical applicability of a mechanical Multileaf Collimator for the use in Cobalt-60 radiotherapy

According to the Directory of Radiotherapy Centres (DIRAC) there are 2348 Cobalt-60 (Co-60) teletherapy units worldwide, most of them in low and middle income countries, compared to 11046 clinical accelerators. To improve teletherapy with Co-60, a mechanical Multi-Leaf Collimator (MLC) was developed, working with pneumatic pressure and thus independent of electricity supply. Instead of tungsten, brass was used as leaf material to make the mechanical MLC more affordable. The physical properties and clinical applicability of this mechanical MLC are presented here. The leakage strongly depends on the fieldsize of the therapy unit due to scatter effects. The maximum transmission through the leaves measured 2.5 cm from the end-to-end gap, within a field size of 20 cm × 30 cm defined by jaws of the therapy unit at 80 cm SAD, amounts 4.2%, normalized to an open 10 cm × 10 cm field, created by the mechanical MLC. Within a precollimated field size of 12.5 cm × 12.5 cm, the end-to-end leakage is 6.5% normalized to an open 10 cm × 10 cm field as well. This characteristic is clinically acceptable considering the criteria for non-IMRT MLCs of the International Electrotechnical Commission (IEC 60601-2-1). The penumbra for a 10 cm × 10 cm field was measured to be 9.14 mm in plane and 8.38 mm cross plane. The clinical applicability of the designed mechanical MLC was affirmed by measurements relating to all relevant clinical properties such as penumbra, leakage, output factors and field widths. Hence this novel device presents an apt way forward to make radiotherapy with conformal fields possible in low-infrastructure environments, using gantry based Co-60 therapy units.