Localisation of the Prostate - Coursework Example

Localisation of the Pro Radiotherapy is one of the treatments of choice in managing pro cancer, often used in combination with other modalities in more aggressive cases. Localisation efforts are initiated to isolate the radiation dose to the target prostate so that it will minimize unnecessary damage to other surrounding structures. This paper will discuss the relevant anatomy and physiology of the prostate and surrounding structures, the pathophysiology and management of prostate cancer, the use of radiotherapy for prostate cancer, and the localisation modalities to be employed for radiotherapy in prostate cancer. Prostate and Prostate Cancer The prostate is one of the organs in the male reproductive system responsible in releasing a fluid to alkalinise the semen (Hugging, Scott & Heinen, 1942) in order for the sperms to survive in the acidic environment of the female vagina. It is divided into four zones, namely the peripheral, central, transition and anterior fibromuscular zones (Meyers, 2000), while it can also be divided more commonly into four lobes, namely the anterior, posterior, lateral and middle lobes. The prostate is located superior to the anus, anal sphincter, bulbourethral gland, testes, penis and the urogenital diaphragm. It is inferior to the urinary bladder and the seminal vesicle. It is anterior to the rectum, coccyx, common ejaculatory duct and also the seminal vesicles. It is posterior to the symphysis pubis. On the medial part of the prostate lies the prostatic urethra. Its proximity to the rectum allows the prostate to be palpable in rectal examinations. Among those structures commonly harmed by ineffective localisation of prostate radiotherapy is the rectum, bones (symphysis pubis, pubic bones, and the coccyx) and the seminal vesicles. The veins where the blood flows away from the prostate are the prostatic venous plexus, pudcordal plexus, vesicle plexus and the internal iliac vein. Lymph nodes around the prostate are the external iliac lymph nodes, internal iliac lymph nodes and the sacral lymph nodes. These venous and lymphatic structures are responsible for the possible metastasis of malignant prostate cells to the surrounding structures beyond the prostate. Radiotherapy beyond the prostate, especially to the lymph nodes is necessary as the cancer reaches beyond stage 2, while the venous system will allow the predictability of metastasis to other organs. The cancer of the prostate begins with genetic changes within the prostate cells triggered by different possible risk factors such as genes, aging, race, environmental, increased saturated fat intake, decreased fruit and vegetable intake and vitamin D, and some sexually-transmitted disease, though the exact cause of prostate cancer is currently unknown (Black & Hawks, 2005). The genetically-modified cell will replicate and will become an enlarged tissue of malignant cells, occupying space and competes with normal cells, disrupting normal body functions such as compressing the urethra within the prostate. The rich venous and lymphatic link from the prostate will facilitate the movement of the malignant cells to other parts of the body and will further extend the disruption of the bodily functions leading to death. Signs and symptoms are often absent until urinary and other system dysfunction manifests. Diagnosis of prostate cancer can be staged using the tumour-node-metastasis (TNM) and Jewett stages, while the cancer’s aggressiveness through Gleason system. Measurement of prostate-specific antigen (PSA), digital rectal examination, transrectal / transurethral ultrasound, prostatic tissue biopsy, computerized tomography scans (CT scan), and magnetic resonance imaging (MRI) will confirm the presence of prostate cancer and possible metastasis. Treatment of prostate cancer can be radiotherapy, hormone therapy, or both (Black & Hawks, 2005). Two most common radiation therapy procedures are external-beam radiation therapy and brachytherapy. Since brachytherapy already confines its treatment to the prostate which does not require imaging modalities when placed correctly, the paper will focus on external beam radiotherapy which requires various imaging modalities to accurately locate and target the prostate during radiation treatment. External Beam Radiotherapy External beam radiotherapy is the most common radiation treatment modality for prostate cancer, which delivers radiation to the prostate using a machine called the linear particle accelerator which accelerates photons at high speed targeting the prostate, producing a megavoltage x-ray which destroys prostate cancer cells. It is known to be one of the newer technologies which improve the outcomes of prostate cancer management (Peschel & Colberg, 2003). Reoccurrences of prostate cancer following external beam radiotherapy is not uncommon (Pollack & Zagars, 1997). If not effectively localised, the radiation will damage normal tissues surrounding the prostate as well. Among the side effects of external beam radiotherapy is the radiation-induced proctitis. Dearnaley et al (1999) noted fewer incidences of proctitis when lower radiation was delivered to the rectum and bladder while maximizing the dose for the target prostate. Several imaging modalities in the localisation of the prostate is necessary to limit the radiation dose to the target prostate while leaving the surrounding structures unharmed by the radiation. Intensity-Modulated Radiation Therapy (IMRT) IMRT is one of the advanced localisation technique in external beam radiotherapy wherein the intensity of each beams from the linear particle accelerator can be controlled by the practitioner, allowing a more intense beam to be delivered to the target tissue while minimal or no radiation to healthy tissues. This allows a higher radiation dose to the prostate as well as to the lymph nodes near to it (Cahlon, Hunt & Zelefsky, 2008). IMRT outstand the three-dimensional conformal radiation therapy in terms of radiation dose distribution (Verhey, 1999). This technology uses multiple fields and angles wherein each beam is of varying intensity (Goffman & Glatstein, 2002). As the intensity of beams is modulated to deliver minimal radiation dose to healthy tissues, this procedure will also reduce the side effects of radiation therapy (Nuttling et al, 2000). The intensity of the beam to be administered varies depending on site (Pugachev et al, 2001), though the safest limits of radiation dose administration needs further large-scale cohort research (Teh et al, 1999). De Meerleer et al (2007) noted the decreased morbidity of patients undergoing this treatment. Cahlon, Hunt & Zelefsky (2008) believed that it is the most effective, widely used, and safest for prostate cancer, though clinical concerns are still to be considered (Goffman & Glatstein, 2002). However, there are still risks in IMRT common to other radiotherapy procedures. Kry et al (2005) identified the occurrences of secondary malignancies after treatment, though minimal compared to conventional radiation therapy. Hall (2006) described the reasons of potential induction of these secondary malignancies arising from “leakage radiation” and when some of the multiple fields still deliver low radiation doses. Zelefsky et al (2002) also reported the present yet reduced acute and late toxicities from IMRT treatment. The benefits from IMRT outweigh the risks involved (Zelefsky et al, 2001). One of the latest improvement in IMRT is the simultaneous modulated accelerated radiation therapy wherein the duration of the treatment will be shortened (Teh, Woo & Butler, 1999), allowing more minimal time of exposure from radiation. Other modalities to be used in better localisation include the use of “Vac-Lok bag-and-box system” and rectal balloon (Teh et al, 2002). Another approach, the “Cu-ATSM-guided IMRT” was feasible yet further investigation about its use is needed (Chao et al, 2001). Image-Guided Radiotherapy (IGRT) A more advanced and sophisticated imaging modality is the IGRT, wherein an online image of the target prostate tissues and other affected adjacent structures will serve as a guide in localising the prostate during radiotherapy. Through the use of an image guide, the shape and the location of the target prostate will be determined, wherein the focus of radiation dose will be delivered. The image is three-dimensional, generated by fluoroscope or radio-opaque contrast medium, which was taken prior or during the radiation therapy through the use of cone-beam computerized tomography (Dawson and Sharpe, ; Oelfke, 2009; Smitsmans et al, 2004). Being certain with the geometric features of the prostate and other affected structures will allow maximisation of focus to the malignant tissues while reducing the delivered radiation dose to normal tissues (De Crevoisier et al, 2007). The main problem of IGRT is the prostate being a non-stationary organ. The images taken prior to the radiation therapy might have some deviations during the actual treatment. According to Wong et al (2005), the prostate might move for 2 centimetres. How the organ moves depend from patient to patient (Kupelian et al, 2008). An intra-fractional uncertainty margin of 6 millimetres was evaluated by Polat et al (2008). This margin of uncertainty can be removed using the application of an “offline dose compensation technique” (Wu, Liang & Yan, 2006). Combination of Localisation Modalities Due to the uncertainties in accurately locating the prostate during external beam radiotherapy, a combination of all possible modalities should be taken into consideration. Smitsmans et al (2004) employed the use of cone-beam CT scan with online and offline image-guide used with the linear particle accelerator. Teh et al (2002) combined the use of a rectal baloon and a “bag-and-box system” to stabilize the protate while undergoing IMRT. Ghilezan et al (2001) combined the use of IMRT and IGRT using cone-beam computerized tomography. Conclusion Several localisation modalities are now available for radiation therapy of the prostate in effort to prevent unnecessary dose to healthy tissues which might develop into secondary malignancies. The most common of these includes the intensity-modulated radiotherapy and the image-guided radiotherapy, though the risks are still present on both modalities. Rectal balloon, “bag-and-box system” and offline imaging gives further aid in localizing the prostate. Further studies are needed to identify a standard treatment modality for prostate cancer management which can accurately deliver the radiation dose to target structures while excluding the surrounding healthy tissues. References Black J & Hawks JH 2005, Medical-surgical nursing: clinical management for positive outcomes 7th edition, Singapore: Elsevier. 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