A multiwell applicator for conformal brachytherapy of superficial skin tumors: A simulation study

The effect of geometrical parameters of skin brachytherapy patch source on depth dose distribution using Monte Carlo simulation

Brachytherapy of superficial skin tumors using beta-emitting sources is a method that has been investigated by some researchers in both simulation and experimental studies with promising results. In the current study, the effect of geometrical parameters of some relevant radionuclides including Y-90, Re-188, P-32, and Ho-166 on the depth dose distribution in skin tissue has been investigated through Monte Carlo simulation. MCNPX Monte Carlo code was employed to model the above-mentioned patch sources in cylindrical format and then the effect of patch geometrical parameters including the source-to-skin distance (SSD), patch thickness, and patch diameter on depth dose distribution was assessed through modeling and calculation of the dose inside a cubic phantom mimicking the skin tissue. The obtained results demonstrated that increasing the SSD, patch thickness, and patch diameter (with the same activity) will reduce the depth dose distribution. Changing the SSD has a more significant effect on the dose gradient within the depth than other geometrical parameters. It was also observed that the effect of patch diameter on the skin-delivered dose gets less sensible as the patch size goes beyond the range of beta radiation inside tissue. Finally, it can be concluded that the patch source geometrical parameters can affect the depth dose distribution inside the skin tissue. This fact may be of concern regarding the delivery of a high radiation dose in a single treatment session. Therefore, variations of patch source geometrical parameters should be considered during the skin dose calculation plan.

Emerging technologies in brachytherapy

Brachytherapy is a mature treatment modality. The literature is abundant in terms of review articles and comprehensive books on the latest established as well as evolving clinical practices. The intent of this article is to part ways and look beyond the current state-of-the-art and review emerging technologies that are noteworthy and perhaps may drive the future innovations in the field. There are plenty of candidate topics that deserve a deeper look, of course, but with practical limits in this communicative platform, we explore four topics that perhaps is worthwhile to review in detail at this time. First, intensity modulated brachytherapy (IMBT) is reviewed. The IMBT takes advantage ofanisotropicradiation profile generated through intelligent high-density shielding designs incorporated onto sources and applicators such to achieve high quality plans. Second, emerging applications of 3D printing (i.e. additive manufacturing) in brachytherapy are reviewed. With the advent of 3D printing, interest in this technology in brachytherapy has been immense and translation swift due to their potential to tailor applicators and treatments customizable to each individual patient. This is followed by, in third, innovations in treatment planning concerning catheter placement and dwell times where new modelling approaches, solution algorithms, and technological advances are reviewed. And, fourth and lastly, applications of a new machine learning technique, called deep learning, which has the potential to improve and automate all aspects of brachytherapy workflow, are reviewed. We do not expect that all ideas and innovations reviewed in this article will ultimately reach clinic but, nonetheless, this review provides a decent glimpse of what is to come. It would be exciting to monitor as IMBT, 3D printing, novel optimization algorithms, and deep learning technologies evolve over time and translate into pilot testing and sensibly phased clinical trials, and ultimately make a difference for cancer patients. Today's fancy is tomorrow's reality. The future is bright for brachytherapy.

Additive manufacturing (3D printing) in superficial brachytherapy

The aim of this work is to provide an overview of the current state of additive manufacturing (AM), commonly known as 3D printing, within superficial brachytherapy (BT). Several comprehensive database searches were performed to find publications linked to AM in superficial BT. Twenty-eight core publications were found, which can be grouped under general categories of clinical cases, physical and dosimetric evaluations, proof-of-concept cases, design process assessments, and economic feasibility studies. Each study demonstrated a success regarding AM implementation and collectively, they provided benefits over traditional applicator fabrication techniques. Publications of AM in superficial BT have increased significantly in the last 5 years. This is likely due to associated efficiency and consistency benefits; though, more evidences are needed to determine the true extent of these benefits.

Evaluation of bone dose arising from skin cancer brachytherapy: A comparison between 192Ir and 60Co sources through Monte Carlo simulations

PURPOSE

This study aimed to calculate and compare absorbed dose to bone following exposure to ¹⁹²Ir and ⁶⁰Co sources in high dose rate (HDR) skin brachytherapy. Moreover, effects of the bone thickness and soft tissue thickness before the bone on absorbed dose to the bone are evaluated .

MATERIALS AND METHODS

¹⁹²Ir and ⁶⁰Co sources inserted in Leipzig applicators with internal diameters of 1, 2 and 3 cm with/without their optimal flattening filters were simulated by MCNPX Monte Carlo code. Then, heterogeneous phantoms (including skin, soft tissue before and after the bone, cortical bone and bone marrow) were defined. Finally, relative depth dose values for the bone and other tissues in the heterogeneous phantoms were obtained and compared.

RESULTS

The average relative depth dose values of the skin, soft tissue before and after bone and bone marrow were almost similar for both ¹⁹²Ir and ⁶⁰Co sources, with a maximum difference less than 2%. However, a 0.1-6.8% difference was observed between average relative depth dose values of these two sources for the cortical bone. The results showed that with increasing the bone thickness and bone distance from the skin surface, the average relative depth dose values of the bone marrow and cortical bone decreased for both ¹⁹²Ir and ⁶⁰Co sources inserted in the applicators without/with their optimal flattening filters. For most of evaluated the applicators without/with their flattening filters, the average relative depth dose values of the bone marrow arisen from the ⁶⁰Co source were higher than those obtained from the ¹⁹²Ir source, while an opposite trend was observed for the cortical bone .

CONCLUSION

The obtained findings showed that the average relative depth dose values of ¹⁹²Ir and ⁶⁰Co sources at the corresponding depths of the designed heterogeneous phantoms were almost similar (expect for the cortical bone). Hence, it is concluded that ⁶⁰Co source can be used instead of ¹⁹²Ir source in HDR skin brachytherapy, particularly in developing countries.