Intensity modulated radiotherapy: advantages, limitations and future development

Abstract

Intensity modulated radiotherapy (IMRT) is widely used in clinical applications in developed countries, for the treatment of malignant and non-malignant diseases. This technique uses multiple radiation beams of non-uniform intensities. The beams are modulated to the required intensity maps for delivering highly conformal doses of radiation to the treatment targets, while sparing the adjacent normal tissue structures. This treatment technique has superior dosimetric advantages over 2-dimensional (2D) and conventional 3-dimensional conformal radiotherapy (3DCRT) treatments. It can potentially benefit the patient in three ways. First, by improving conformity with target dose it can reduce the probability of in-field recurrence. Second, by reducing irradiation of normal tissue it can minimise the degree of morbidity associated with treatment. Third, by facilitating escalation of dose it can improve local control. Early clinical results are promising, particularly in the treatment of nasopharyngeal carcinoma (NPC). However, as the IMRT is a sophisticated treatment involving high conformity and high precision, it has specific requirements. Therefore, tight tolerance levels for random and systematic errors, compared with conventional 2D and 3D treatments, must be applied in all treatment and pre-treatment procedures. For this reason, a large-scale routine clinical implementation of the treatment modality demands major resources and, in some cases, is impractical. This paper will provide an overview of the potential advantages of the IMRT, methods of treatment delivery, and equipment currently available for facilitating the treatment modality. It will also discuss the limitations of the equipment and the ongoing development work to improve the efficiency of the equipment and the treatment techniques and procedures.

The risk of secondary cancer in nasopharyngeal carcinoma paediatric patients due to intensity modulated radiotherapy and mega‐voltage cone beam computed tomography

“…Although the IMRT technique is the method that is usually used for treating NPC patients, it possibly increases the risk of radiation‐induced secondary cancers in normal tissues and OARs surrounding the tumour compared to conventional or conformal radiotherapy . There are two reasons for that: (i) IMRT plans typically involve the irradiation of larger volumes of normal tissue to low doses because of the configuration of the used treatment fields, (ii) IMRT can increase the peripheral dose attributable to the greater number of Monitor Units (MUs) that are used for each patient undergoing IMRT and head leakage from the treatment machine …”

“…This is because it is difficult to deliver a satisfactory radiation dose distribution to the NPC target volume by conventional radiotherapy techniques without significantly irradiating the critical tissue structures. IMRT has the ability to deliver the prescribed dose to the delineated target volume with precision, while sparing the adjacent normal tissue structures . When a patient is treated with radiotherapy, the portion of radiation reaching to the normal tissues near to the tumour is expected to increase the risks of induced secondary malignancy.…”

“…This risk is larger for paediatric patients and patients who may survive for a long time after the radiation treatments. Therefore, recurrence of tumours is not the only issue of concern after radiotherapy but also the future risk of developing secondary cancer in normal tissues of patients must be evaluated …”

“…IMRT has the ability to deliver the prescribed dose to the delineated target volume with precision, while sparing the adjacent normal tissue structures. 3 When a patient is treated with radiotherapy, the portion of radiation reaching to the normal tissues near to the tumour is expected to increase the risks of induced secondary malignancy. This risk is larger for paediatric patients and patients who may survive for a long time after the radiation treatments.…”

“…Therefore, recurrence of tumours is not the only issue of concern after radiotherapy but also the future risk of developing secondary cancer in normal tissues of patients must be evaluated. [2][3][4][5][6] In IMRT, treatment accuracy is an important issue because with its steeper dose gradient, a small deviation of the treatment field can result in unnecessary irradiation of the OARs or under-dosing the target. 7,8 This problem can be solved using Image Guided Radiation Therapy (IGRT).…”