Is grid therapy useful for all tumors and every grid block design?

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

Grid block design based on monte carlo simulated dosimetry, the linear quadratic and Hug–Kellerer radiobiological models

“…These findings correlate well with previous studies. [ 13 15 ] The Grid therapy response for different types of tumor cells with considering different values of α/β ratios was introduced elsewhere. [ 15 ] It is worth to note that considering different values of radiobiological parameters (i.e., α, β for LQ model and k1 , k2 , k3 for H-K model) may lead to different values for TRs, but this effect does not change the results of this study because a relative comparison was performed between 25 Grid block designs to introduce an optimal Grid block.…”

“…The impact of the geometrical design of the Grid blocks was evident during these experiments. [ 15 ] In the present study, we have developed a novel method to investigate the design of an optimal Grid block with maximum TR, minimum geometric sparing factor (GSF), and optimum ratio of the open to blocked area (ROTBA). These investigations were performed by calculating the TRs of different Grid blocks with different hole diameters and hole spacing using Monte Carlo (MC) simulation techniques.…”

Spatially fractionated radiation therapy: History, present and the future

“…GRID design has major impact on radio-resistant tumors (SF2 > 0.4), thus appropriate design of the hole diameter and hole spacing may lead to 40% higher clinical responses (i.e. hole size change from0.5 to 1.1 cm) [8].…”

“…Outcomes from tumors with different histological characteristics and treatment sites from historical clinical outcomes from GRID therapy have been summarized by Meigooni et al [8]. The clinical total response rates with grid therapy were as following: Osteosarcoma (100%), Liposarcoma (50%), Leiomyosarcoma (100%), Colorectal (100%) (4); Sarcoma (94%), SCC (92%), Melanoma (83%), Adenocarcinoma (69%) [4]; Sarcoma (83%), SCC (94%), melanoma (50%) [5]; SCC of H&N (93%) [6]; Parotid (0%), Base of tongue (30%) Maxillary sinus (50%), Nasopharynx, Retromolar trigone, and Larynx (100%) Tonsil (25%) [7].…”

“…Their results showed that TR of radioresistant tumor is known to increase with prescribed dose in grid therapy, but the TR of radio sensitive tumor does not change significantly with dose. Hence, grid therapy is expected to be biologically be more effective for radioresistant tumors [8].…”