Abstract
Grid therapy is a treatment technique that has been introduced for patients with advanced bulky tumors. The purpose of this study is to investigate the effect of the radiation sensitivity of the tumors and the design of the grid blocks on the clinical response of grid therapy. The Monte Carlo simulation technique is used to determine the dose distribution through a grid block that was used for a Varian 2100C linear accelerator. From the simulated dose profiles, the therapeutic ratio (TR) and the equivalent uniform dose (EUD) for different types of tumors with respect to their radiation sensitivities were calculated. These calculations were performed using the linear quadratic (LQ) and the Hug‐Kellerer (H‐K) models. The results of these calculations have been validated by comparison with the clinical responses of 232 patients from different publications, who were treated with grid therapy. These published results for different tumor types were used to examine the correlation between tumor radiosensitivity and the clinical response of grid therapy. Moreover, the influence of grid design on their clinical responses was investigated by using Monte Carlo simulations of grid blocks with different hole diameters and different center‐to‐center spacing. The results of the theoretical models and clinical data indicated higher clinical responses for the grid therapy on the patients with more radioresistant tumors. The differences between TR values for radioresistant cells and radiosensitive cells at 20 Gy and 10 Gy doses were up to 50% and 30%, respectively. Interestingly, the differences between the TR values with LQ model and H‐K model were less than 4%. Moreover, the results from the Monte Carlo studies showed that grid blocks with a hole diameters of 1.0 cm and 1.25 cm may lead to about 19% higher TR relative to the grids with hole diameters smaller than 1.0 cm or larger than 1.25 cm (with 95% confidence interval). In summary, the results of this study indicate that grid therapy is more effective for tumors with radioresistant characteristics than radiosensitive tumors.PACS number(s): 87.55.‐x
Highlights
Introduction207 Gholami et al.: Is grid therapy useful for all tumors?advanced bulky tumors.[2]. In this technique, an open X-ray field is being converted to a set of pencil beam type radiation fields using an external block.[3]
207 Gholami et al.: Is grid therapy useful for all tumors?advanced bulky tumors.[2]
Advanced bulky tumors.[2]. In this technique, an open X-ray field is being converted to a set of pencil beam type radiation fields using an external block.[3]. This block is normally made of lead or Cerrobend, and it could be created using an multileaf collimator (MLC) system in the linear accelerators.[3]. Several investigators have reported that this technique has the advantage of a higher potential to repair normal tissues.[4,5,6] Different kinds of tumors have been treated using this technique and significant tumor responses have been observed without serious toxicities.[7]
Summary
207 Gholami et al.: Is grid therapy useful for all tumors?advanced bulky tumors.[2]. In this technique, an open X-ray field is being converted to a set of pencil beam type radiation fields using an external block.[3]. Some radiotherapy centers have begun the routine use of spatially fractionated radiotherapy in the management of malignant disease for tumors larger than 6 cm Despite these promising clinical outcomes, there is a lack of a protocol in the clinical references on selection of appropriate patient or disease for this type of treatment technique. There is a missing recommendation for the geometrical design of a grid block with appropriate hole size (i.e., diameter) and hole center-to-center distances, which could provide an optimum therapeutic result. In this project, the effectiveness of the grid therapy is being evaluated for tumors with different radiation sensitivities. The integrity of these evaluations has been validated by comparison of the model-based data with the clinically published values
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