CT‐based analysis of dose homogeneity in total body irradiation using lateral beam

Susanta K Hui,Bruce Thomadsen,R.K Das,Douglas Henderson

doi:10.1120/jacmp.v5i4.1980

Abstract

A computed tomography (CT) based treatment planning system for total body irradiation (TBI) is presented and compared with the commonly practiced lateral treatment delivery. The TBI regimen has been proved to be an essential conditional regimen for patients undergoing bone marrow transplantation. The advantage of the TBI regimen with bone marrow transplantation (BMT) in hematological malignancies can be offset by toxicities arising from TBI in posttransplant complications. With the increasing survival rates, the evaluation of long‐term side effects and quality of life has become an important area of research interest. There have been several treatment techniques developed over the decades designed to achieve accurate dose delivery and dose homogeneity. This paper reports on the verification of the dose delivery for a basic lateral technique using thermoluminescent dosimeters (TLDs) placed in an anthropomorphic phantom and its correlation with CT‐based treatment planning. CT‐based treatment plans on several patients were used to evaluate the doses delivered to the whole body and critical organs. A large variation in doses delivered to the whole body was demonstrated, with some parts of the bone marrow failing to receive the prescribed dose and some critical organs, such as the lungs, receiving excessive doses. Placing the arms at the sides only partially compensates for the increased transmission of the lungs because the arms only shadow part of the lung. This study shows that CT‐based treatment planning for TBI provides precise and accurate dose calculations and allows for the correlation of clinical outcomes with the doses actually delivered to various organs.PACS numbers: 87.53.Dq, 87.66.Xa, 87.66.Sq

Highlights

The total body irradiation (TBI) treatment has been accepted as an important radiotherapy treatment for hematological malignancies and is used in conjunction with chemotherapy as a conditioning regimen for bone marrow transplantation (BMT) or peripheral blood stem cell transplantation.[1,2] Total body irradiation serves two purposes: first, it provides immunosuppression, allowing subsequent engraftment of the transplanted stem cells; second, it contributes to eradicating a modest number of radiosensitive tumor cells, clearing the host marrow to allow repopulation with donor marrow cells
The thermoluminescent dosimeters (TLDs) were placed inside the Rando phantom at organ sites of interest, such as manubrium, lungs, xyphoid, iliac crest, and hip, for dose verification during a TBI treatment
TLD measurement in phantom TLD-based dose verification for the Rando phantom shows significant dose variation compared with the intended dose delivery

Summary

Introduction

The total body irradiation (TBI) treatment has been accepted as an important radiotherapy treatment for hematological malignancies and is used in conjunction with chemotherapy as a conditioning regimen for bone marrow transplantation (BMT) or peripheral blood stem cell transplantation.[1,2] Total body irradiation serves two purposes: first, it provides immunosuppression, allowing subsequent engraftment of the transplanted stem cells; second, it contributes to eradicating a modest number of radiosensitive tumor cells, clearing the host marrow to allow repopulation with donor marrow cells. Pulmonary complications, renal toxicities, cataracts, and reduced pituitary function are the main long-term affects of TBI. Lethal pulmonary complication was observed to be only 3.8% for a patient who received inhomogeneity corrected lung dosage of up to 9.4 Gy, whereas a 19.2% LPC risk (p = 0.05) was observed beyond 9.4 Gy. Morgan et al[9] have reported a 20% LPC rate for allogeneic transplanted patients using higher dose rates (>0.1 Gy/min). Morgan et al[9] have reported a 20% LPC rate for allogeneic transplanted patients using higher dose rates (>0.1 Gy/min) This is consistent with the expected protective effect of lung toxicities by lowering the dose rate, based on a short component for the repair of sublethal cellular damage

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Discussion

Conclusion