Mouth Cancer Treatment | Head and Neck Cancer | Mouth Cancer Treatment
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Introduction
The head and neck is a complex anatomical region in which many different cancer types may arise with varying behaviour according to site of origin. Mostly head and neck cancer spreads locally and only give rise to distant metastases late in the course of the disease if at all. The treatment of head and neck cancer is technically challenging because tumours typically arise from the mucosal linings of the upper airways or digestive system. These tumours in the head, neck, throat and mouth may compromise the basic functions of breathing, eating and drinking at an early stage. Surgery and radiotherapy are both highly active treatment modalities, and the cure rate ranges from 30-90% depending on stage and site of disease at presentation. The natural history of dominant local disease, and the radiosensitivity of the majority of head and neck cancers make radiotherapy an attractive and important curative modality of treatment. Radiotherapy is an important part of treatment for all types of cancers such as mouth cancer, head, neck and throat cancer as it has the advantage of organ preservation, and therefore the functional outcome is often better than with surgical approaches. The side effects of radiotherapy are frequent, and may compromise the quality of life of patients after treatment. The proximity of head and neck tumours to radiosensitive organs often limits the dose of radiation that can be delivered, and this may contribute to local treatment failure. IMRT in head and neck cancer
Intensity-modulated radiotherapy (IMRT) is a new conformal radiotherapy technique that uses computer-generated beams to produce high-dose radiotherapy volumes that can avoid irradiation of normal tissues in the head and neck region in case of head and neck cancer. The aims of the current research programme in IMRT in head and neck cancer are to evaluate the potential benefits of inverse planned IMRT compared to current radiotherapy techniques, to maximise efficiency of IMRT delivery, and to implement clinical trials of IMRT for appropriate tumour sites. The first phase of the programme of this head and neck cancer treatment was to perform planning studies on groups of patients who had been treated with conventional radiotherapy techniques. Patients with head and neck tumours underwent treatment planning for conventional radiotherapy (RT), 3-dimensional conformal RT (3DCRT) and inverse-planned IMRT. Dose distributions were compared using dose-volume histograms for tumour and normal tissues, and normal tissue complication probabilities were calculated. Methods were developed to optimise beam number and direction to determine the most efficient delivery techniques. Equispaced coplanar, non-equispaced, and non-coplanar techniques were assessed. This research programme in conjunction with the Royal Marsden Hospital is unique in the UK. The close working relationship between the ICR physics group headed by Professor Steve Webb, and Clinicians at the ICR/RMH have led to a rapid translation of the physical principles of IMRT into the clinic. IMRT allows delivery of higher
radiation doses
For thyroid carcinoma, a conventional two-phase RT technique is used with the aim of homogeneous irradiation of the thyroid bed to 60 Gy and adjacent lymph nodes to 45-50 Gy. These aims frequently had to be compromised because the maximum dose to the spinal cord risked radiation damage (myelopathy). 3DCRT was found to significantly reduce the irradiated volume of normal tissue, but did not improve target coverage, and had no effect on the spinal cord maximum dose. IMRT (Figure 1) reduced the dose to the spinal cord by 12% and achieved the goal PTV dose in all patients tested. Benefits of similar magnitude were achieved using nine, seven and five equispaced IMRT fields, but the use of fewer fields resulted in a significantly worse dose distribution. The first clinical protocol for head and neck IMRT treated the first patient in January 2002, and will explore the role of IMRT in the treatment of thyroid tumours, and other head and neck cancers when the planning target volume surrounds the spinal cord. In patients with tumours of the throat (larynx and pharynx) the protocol will investigate the role of higher doses of radiation delivered with IMRT. It is hoped that dose-escalation will improve local cancer control and reduce the need for laryngectomy, a treatment to remove the voice-box, which causes loss of natural speech and leaves patients with a tracheostomy. This ICR/RMH protocol will be the first head and neck IMRT trial in the UK, and the first dose-escalation protocol of head and neck cancer IMRT in Europe. Data collected from these studies will provide a source of material for modelling the effects of radiation on normal tissues and tumours, which may be used to predict cure and complication rates in the future. Figure 1. An IMRT dose distribution for thyroid cancer showing spinal cord sparing  IMRT may allow reduction
of normal tissue radiation damage
Radiotherapy has an important role in the management of parotid gland tumours and helps in mouth cancer and head and neck cancer treatment. Current techniques lead to irradiation of the mouth, eyes
and the middle and inner ear. The potential of IMRT to reduce the
irradiation of these organs was investigated, with a view to reducing
side effects of treatment. IMRT reduced the doses to the oral cavity,
and the structures within the ear. IMRT is usually delivered using
multiple equispaced beams around the patient, but this was not the
optimal arrangement for head and neck tumours because of unacceptable
doses delivered to the healthy salivary glands and eyes. A computerised
optimisation algorithm was therefore designed by Dr Carl Rowbotton
(IMRT physics group) to avoid, when possible, beam-orientations that
passed through such low radiation tolerance organs. A fast IMRT algorithm
based on the Bortfeld method determined the profile of the intensity-modulation
and a fast simulated-annealing algorithm found the “optimal”
beam-arrangement. The optimisation process took 1-3 hours of computation
time, and the algorithm produced plans that maintained the advantages
of multiple equispaced fields IMRT using only three or four fields
(Figure 2). The algorithm also produced non-coplanar beam arrangements,
but no significant improvement in the dose distributions were seen.
This should reduce the time required for IMRT delivery, and verification.
Figure 2. A 3-field IMRT dose distribution showing parotid gland sparing 
Parotid gland sparing radiotherapy techniques are the next major
area of clinical study. Many patients with head and neck cancer
develop radiation damage to salivary gland tissue which frequently
leads to distressing complications such as dryness in the mouth,
accelerated dental decay and damage to bones in the jaw. These side
effects are currently considered an acceptable cost of curative
treatment. IMRT has the capability to reduce the dose to the salivary
glands, and this hypothesis will be tested in a Multi-centre International
Phase III clinical trial led by the ICR/RMH. The overall aim of this trial is to improve the quality of life after radiotherapy for all the patients who are suffering from head and neck cancer by reducing these complications. Conclusions
IMRT represents a significant advance in conformal radiotherapy. IMRT plans for tumours with a concave shape show the greatest improvements compared to conventional and 3DCRT. The benefits of this head and neck cancer treatment are greatest for tumours where normal tissue structures within the concavity can be spared. For non-concave tumours, dose homogeneity is improved compared to current techniques, and for all tumour sites studied to date some normal tissue sparing was observed. Treatment delivery is possible with 3-5 optimised beam directions, and clinical assessment of this technique is underway. Hot topics and future work
The next five to ten years will see a continued expansion of the use of high-technology radiotherapy solutions mouth and head and neck cancer treatment.The key to the appropriate use of these technologies is a scientific assessment of the benefits of new treatments in clinical trials. IMRT theoretically will allow higher doses of radiation to be delivered and safely. This should have real benefits for patients. The role of academic institutions such as ours is to lead with well designed clinical trials addressing important questions, and producing technical solutions which are both beneficial to patients and are able to be implemented in other radiotherapy centres Nationally and Internationally. Head and neck cancer is an ideal tumour site for assessing these technologies. In the future the use of IMRT may be to direct highly localised radiation doses to activate vectors containing potent cytotoxic genes expressed from radio-inducible promoters, activating pro-drugs or used in conjunction with radio-sensitisers where the IMRT will provide the geographic specificity to avoid unnecessary sensitisation of normal tissues. |
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