Men's Health, General, Women's Health | October 20, 2014 | Author: The Super Pharmacist
Conventional radiotherapy is often in the form of waves of atomic particles or energy that possess certain physical properties (e.g. gamma-ray) that can destroy cancer cells and thus prevent tumour growth and disease progression. However, their properties or delivery methods may result in exposure of nearby normal healthy tissue to the same radiation. This may cause severe adverse effects which may even include the growth of other tumour types due to cellular DNA damage. Other side-effects of radiotherapy may include nausea, fatigue, inflammatory tissue damage and nerve damage (which may lead to chronic pain).
These problems are particularly relevant in cases of tumours located in areas in which many other complex and important structures are found. These include the head and neck. Here, radiation therapy is associated with both short- and long-term adverse effects. These distressing symptoms may be avoided by 'focusing' the radiation used to a narrower point, targeting cancer cells with greater specificity while sparing normal tissues. Therefore, the ideal radiotherapy lends itself to the formation of these 'thinner' waves, or beams, which may be delivered to a tumour with increased accuracy and decreased side-effects.
Radiation in the form of a proton beam is a prime example of this. Proton beam radiation is a form of ionising radiation that can destroy tumour cells through extensive DNA damage. The particle size and certain other unique properties of proton beam radiation are associated with an accurate 'aim', which means that it more accurately targets tumour cells while sparing the surrounding healthy tissues. The upper limit, or 'Bragg's peak', of its 'dose' regulates how much radiation the patient is exposed to per radiotherapy session. These factors are, in theory at least, linked to more effective tumour destruction and reduced side-effects.
Proton beam therapy was invented in the 1950s, but has recently experienced a renaissance in popularity due to investigations into its efficacy in radiotherapies in anatomically difficult and important locations in which tissue loss may significantly affect survival and life quality in the event of survival, such as the eye.
Ocular tumours are extremely challenging to remove, and almost inevitably result in large-scale tissue destruction which may lead to the loss of vision. However, proton therapy has demonstrated positive results in tumour treatment, and even the retention of the eye.
Ocular cancers against which proton beam therapies are often applied are uveal melanomas, or melanoma of the iris, but may include other, rarer forms of tumour arising in the eye. Proton beam therapy is also used in the treatment of other surgically challenging or treatment-resistant cancers such as those of the lung or prostate.
A review of 36 patients with melanoma of the eye (the iris) found that 0% of the patients experienced metastasis, return of cancer cells or required procedures such as enucleation (eyeball removal) after proton beam therapy at a follow-up point of approximately 50 months. However, 22 patients developed cataract and 3 developed new-onset or aggravated glaucoma. (It may be an indicator of how severe eye cancer can be when these are referred to as 'acceptable complications' in clinical literature.)
Another interventional trial tested the efficacy of proton beam therapy in 18 patients with retinal haemangioma (a cancer of small blood vessels). Eight patients exhibited complete resolution of exudation (a symptom of this cancer related to retinal detachment) after an average of 84 months' follow-up after treatment. However, there was no significant change in visual acuity as a result of proton beam therapy, and some patients still required surgery to address retinal detachment.
A small-scale study investigated adverse effects on the eyelid tissue of ten patients with conjunctival melanoma undergoing proton beam therapy. 60% of these were found to have developed abnormal growths in conjunctival cells. This may indicate that proton beam therapy may still cause inadvertent tissue damage despite its increased accuracy, depending on the location of the tumour in question.
Radiotherapy is regarded as a risky strategy in the treatment of lung cancer, as the exposure of the rest of the chest wall is associated with adverse effects, most notably nerve damage.
However, a one-way trial of 10 patients who had reported chronic pain as a result of prior radiotherapy found that proton beam therapy significantly reduced inadvertent chest wall exposure while maintaining the same coverage in comparison with conventional treatment.
A phase 2 clinical trial investigated combined proton beam treatment and chemotherapy in 15 stage III non-small cell lung carcinoma patients.
Eleven of the patients exhibited disease progression, and 6 had a recurrence of primary tumours. Average survival was 26.7 months, and severe adverse effects were observed in the majority of patients (although many of these were side-effects also associated with chemotherapy).
Proton beam therapy is often viewed as a preferred option in the treatment of cancers located in the skull, or in the vicinity of the joints between the head and neck, as it may spare important nervous tissue in this region; damage to which may affect normal movement, function and life quality.
A one-way trial of proton beam therapy in 33 patients with tumours of the base of the skull (chordomas) found that response to treatment was achieved in 86% of patients, and there was a 92% survival rate at 2 years. However, 18% exhibited adverse effects in the form of hearing loss in one ear, although no other severe side-effects were observed.
A retrospective study of 62 head/neck melanoma patients treated with proton beam therapy or conventional radiotherapy found that 1- and 2-year survival and response rates were high for both groups, but there was no significant difference between them. The rates of relapse, new tumour development and serious adverse effects for each group were also comparable.
Proton beam therapy is increasingly applied to cases of prostate cancer. A trial randomising 93 patients to conventional radiotherapy and 96 to proton beam therapy appeared to show no difference in response between these two groups. However, when patients with a specific type of tumour ('poorly differentiated' prostate tumours) were analysed separately, patients in the proton beam group showed significant reductions in tumour size at 5 and 8 years post-treatment.
In patients eligible for biopsy during the follow-up, proton beam therapy elicited (not significantly) reduced positive results. However, the proton therapy group (all tumour types) experienced significantly less rectal bleeding (indicating a lesser degree of tissue damage) in comparison with the (combined) conventional therapy group.
A review of proton beam therapy in prostate cancer, including 211 patients, found that the 5-year rates of disease freedom (as measured by clinical or biochemical markers) ranged from 99% for patients at a low risk of relapse to 76% for those at high risk. There were no significant changes in bladder or bowel function following treatment, indicating minimal adverse effects.
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