High Dose Rate Brachytherapy - Research Paper Example

? Health sciences and Medicine, Research Paper   Topic:  High Dose Rate (HDR) Brachytherapy Introduction Brachytherapy is a type of internalradiation treatment in which radioactive source is placed into cancerous tissues. Brachytherapy is also referred as curietherapy or enducurie therapy (Suntharalingam et al., n.d, ¶451). The sources are small, encapsulated radionuclide which may either be temporarily (for short periods) or permanent (lifetime to a complete decay of the source). Encapsulation ensures the radioactivity is contained, provides rigidity to the source and finally absorbs ? radiation and in the case of photon emitting sources, the ? radiation produced during decay. The brachytherapy sources usually comprises of ? rays which are the majority of the components of radiation released in brachytherapy. Electron capture or in some internal conversion which may occur at the source may result to the emission of characteristics X-rays. Finally the source capsule may also emit other characteristics X-rays and bremsstrahlung radiations. Usually various factors may influence the choice of a radionuclide, the photon emitting source. The choice is dictated by physical and dosimetric features which are required such as the photon energies and beam penetration into the tissues and the shielding materials to be used. The source strength, half-life, and the shielding material half-life layer (HVL) should also be put into consideration. Several millimeters (mm) of lead may be required as shielding material. This treatment allows clinicians to deliver high dose of radioactive treatment with very low negative effect to the surrounding tissues. Brachytherapy involves prescribing a radiation dose to an isodose encircling a small target volume as opposed to external beam radiation therapy where the volume treated is large. Two forms of this treatment exist, low dose rate (LDR) and high dose rate (HDR). The LDR is usually temporary and is applied to prostate cancer whereas HDR is usually permanent and is applied in many forms of cancer such as breast, lung, and sarcoma among other types of cancers. In LDR, a source with a low strength is used accompanied by longer treatment times. For instance, in the treatment of prostate cancer, tiny radioactive seeds are placed permanently in the prostate. However, in the case of HDRs, a source with a high radioactivity is contained within an afterloader device. This device delivers the radioactive source in short periods of time to gadgets such as needles, catheters which may be placed in the tumor site. These delivery devices are doubly shielded to ensure that the radioactive material does not leak and also to provide adequate shielding from ? and ? radiation from the source. In comparison to LDR, HDR takes a shorter treatment time ranging to a few minutes to days and does not necessary require multiple treatments (Varian Medical Systems, 2012, ¶1). Pulse dose rate and image guided brachytherapy are also techniques in brachytherapy. Brachytherapy treatments may be classified under different categories one of them being, the classification based on dose rate, namely; low dose rate (LDR), medium dose rate (MDR) and high dose rate (HDR). Table 1: Classification of brachytherapy based on dose rate Dose rate Numerical value of the dose rate at the dose specification point (s) Low dose rate 0.4 – Gy/h Medium dose rate 2 – 12 Gy/h High dose rate >12 Gy/h High Dose Rate (HDR) Brachytherapy In this technique the ultimate goal is to use a dose that targets the size of the cancerous tissue. A single, tiny highly radioactive source approximately 1 mm x 3 mm in size is used as the radioactive source of Iridium -192 which is welded at the end of a thin, flexible stainless steel cable. The radioactive source is placed in an afterloader which is the device housing the radioactive source. This afterloader is computer-guided and it is the one that directs the radioactive source into the catheters. Catheters are placed beforehand in the patients by the physician into the patient. In the catheter, the source travels in 5 mm steps otherwise referred as “dwell” positions. Radiation distribution from the source is determined by the dwell positions which the source steps and the length of time it stays (dwells) there (Washington and Leaver, 2009, ¶426). Dose control is enabled in HDR by varying the dwell times of the radioactive source in the catheter otherwise called applicator. HDR offers various advantages over LDR systems in that there is dose distribution, staff exposure to radiation is eliminated and outpatients’ treatments are possible. However, it should be noted that HDR has limitations such as high staff commitment and in some instances it may result in serious errors or high/lethal exposure doses. Figure 1: Nucleotron Corporation's microSelectron HDR afterloader (Varian medical systems, 2012, ¶1) Typical procedures in HDRs HDR procedures involve implant placement, simulation, dosimetry, treatment, implant removal and follow-up. The implant depends on the location, extent of the tumor among other factors. Three types of implants exist namely; intracavitary implant, intraluminal implant and interstitial implant. The intracavitary implant is where the catheter is placed in the body cavity so as to reach the tumor location. Local anesthesia is enough in this procedure which can be performed in out-patient setting. In the intraluminal implant process, the catheters are placed in a tube-like structure for example the bile duct and treatment can be done also in an outpatient setting. The third and final implant is the interstitial implant which is a bit complex than the former two. Anesthesia local, general or spinal is required for these implants which are done mostly in the operating room. These implants encompass the tumor as they are inserted through the body tissue. Simulation is the second step in HDR and it involves taking CT or using x-ray films to determine the precise location of implant in the body. Images from CT/x-ray films are used in dosimetry to plan for the appropriate treatment in the computer. Calculations are done to match the radiation dose with the target volume while ensuring the surrounding normal tissues do not receive lethal radiations. In the treatment stage, ends of the catheter opening to the outside are connected to transfers tubes which are in turn connected to the afterloader. Programmed instructions guide the afterloader onto where to direct the radiation source and the duration in which the source will stay at each dwell position. At this instance the patient is alone in the brachytherapy room whereas the medical team monitors the procedure through an intercom and closed circuit TV monitors. HDR ensure no radiation is left in the patient. Once the treatment is done, the source is retracted back into the HDR afterloader. Usually treatment last between 60 min to 90 minutes depending on the source of implant and the radiation source activity (California Endocurietherapy Medical Corp, 2009, ¶1). Implant removal follows treatment. For the intracavitary and intraluminal catheters remove is simple, however with interstitial catheters, sutures holding the template and catheters in place are clipped followed by gentle removal of the implants. It advisable for a follow-up to be done to monitor the patient recovery after high dose rate brachytherapy is done. High dose rate effect in brachytherapy High dose rate brachytherapy differs from fractionated external beam radiation therapy in the volume effect though both may have the same rate of dose rate delivery (Mazeron et al., 2002, ¶103). The outcome associated with this process may involve repair, repopulation and reoxygenation of target tissues. The biological effects of the dose will depend on the dose rate. HDR brachytherapy may be delivered as a monotherapy or as an intermediate dose of external beam radiotherapy (Koukourakis et al., 2009, ¶327945). For instance in the treatment of prostate cancer, the HDR brachytherapy is applied where the source is placed temporarily. Usually a high-activity iridium 192 (192 Ir) is used and it delivers a high radiation dose for a short period. Conventional brachytherapy employs manual afterloading systems which is not employed in modern brachytherapy such as implement in high dose brachytherapy (HDR). The components of afterloading systems in an HDR include a safe house enclosing the radioactive source, the radioactive source and a remote operating console, source control and drive mechanism, source transfer guide tubes and treatment catheters and a treatment planning computer. Other than 192Ir, 60Co and 137Cs are also common radioactive sources use in HDR. However 192Ir is a common source use since it has medium average ? (gamma) ray energy of about 400 keV and is also highly specific. Whereas LDR may use multiple sources the HDR uses a single source mostly 192Ir which can deliver dose rates greater than 2 Gy/min against multiple source doses used in LDR devices which delivers doses in the range of 0.4 – 2 Gy/min (Suntharalingam et al., n.d, ¶464). It is worth noting that, because of the high dose activity delivery in HDR, only automatic afterloading is used and there is no case where manual afterloading is implemented. Application in Disease: Case Example Prostate Cancer Brachytherapy has been combined with external beam radiation to provide good result in treatment of prostate cancer. According to Stock et al (1998, ¶101), brachytherapy (HDR) alone is not sufficient in treating the disease. External beam radiotherapy is used first to target the prostate and pelvic organs and then HDR therapy is performed to deliver a high dose of radiation to improve tumor control in these organs. Therefore, the external beam radiation helps in removing the microscopic deposits of cancer in these organs whereas the HDR therapy ensures a further high dose of radiation is delivered to these tissues without due harm to adjacent normal tissues. This counter strategy therefore ensures the tumor is removed from the tissues with minimal damage to the patients’ health. HDR is especially recommended for patients with a localized prostate cancer with a guarantee for minimal interference to adjacent tissues. However, it should be noted that most of the issues regarding HDR brachytherapy may not be fully established such as the appropriate radiation dose and the number of fractions. Further studies therefore are recommended to clear these ambiguities. However some research reports that further investigation towards developing a one treatment for prostate cancer combined with external brachytherapy are in progress. Advantages of HDR brachytherapy In comparison to LDR seed brachytherapy, HDR brachytherapy has several advantages. These benefits may be identified in several lines such as being practical, physical or biological. The practical benefit of HDR is in regard to it being temporary; thus no radioprotection is required after the treatment. A physical advantage of the procedure is the ability to place the afterloading catheters even in extraprostatic tissues of the prostate which is past the prostate capsule and other sections such as the seminal vesicles and bladder base. This in turn is helpful in prostate cancer as more advanced forms of this cancer can be treated since the source is able to cover the extracapsular and seminal vesicle. Another advantage of HDR is its ability to ensure shorter procedures which may be implemented in outpatient setting thereby reducing the expensive hospital stays. Since the applicators are immobilized, HDR ensures that there is a stable and consistence localization of the source which translates into better treatment. It should be noted that HDR have smaller catheters (applicators) as compared to LDRs thereby reducing pain to the patients which may occur during insertion. For instance, the HDR gynecological tandem is 3 mm in diameter compared with a 7 mm diameter for an LDR catheter. Dose optimization is possible with HDR as it allow a better optimization of isodose distribution according to the shape and size of the treatment volume. These together with the prominent advantage of HDR which ensures health workers are not subjected to the radiation are some of the benefits of HDR brachytherapy. The tumor dose and dose to target organs can be relied upon in HDR since there is an accurate dosimetric calculation. In the light of proven literature sources evidence, radiobiological impact of a high dose radiation is advantages in delivery of an efficient biological effect due to a high dose per fraction delivery as compared to low dose brachytherapy or even external beam radiation. However the process has some setbacks as to any technique. Due to the complexity of the HDR systems, it therefore translates to more resources being availed to training of physicians, dosimetrists and radiation therapists on their operation. In radiobiology, several factors contribute to recovery of the body after radiation exposure. This is as a result of changes in chemistry of the target volume cells. It therefore worth noting that in terms of radiobiology effect of HDR, it may lead to more toxicity to normal cells as a result of its high dose rate in normal tissues adjacent to target volume (Kubo et al., 1998, ¶377). This is in contrast to LDR are much safer. Therefore, the high dose in HDR leaves a smaller window as compared to LDR, which may compromise the health of the patients if any error is made in the anatomical or even geometrical information (Kubo et al., 1998, ¶377). In some unique cases the HDR retraction system may fail leading t overexposure of the patients to source radiation. This may have catastrophic outcomes on the patient well being. Conclusion In respect to all forms of brachytherapy, two important aspects which have been observed to exist include the use of an appropriate dosimetric model for the treatment and proper dose calculation as well as the use of well calibrated sources. The calibration is important vital since treatment in brachytherapy observes a target area as opposed to external beam emission. This therefore requires stringent practices in calibration to ensure the treatment reaches its target. In conclusion, given the importance and amenability of high dose brachytherapy to deliver high to affected organs, this treatment remains a vital tool in radiotherapy room to assure removal of tumors with minimal negative impact to patient’s health. The method involves use of implants and also reduces the medical team interaction with the patients in the course of treatment. This has in turn reduced radioactive exposure to these professional. The method engages an automated system in planning treatment and various treatment stages thereby ensuring accurate delivery of radiation to the affected tissues. Manual calculation and treatment planning are by passed in high dose brachytherapy. The cost of treatment may also be reduced. However it should be noted that the method is complex as it engages various medical workers who should be well trained to guarantee delivery of the procedure with minimal errors. Due to automation of the procedures, an error in calculation may expose the patient to very high dose, lethal sometimes, and therefore extra caution should be exercised. References California Endocurietherapy Medical Corp (2009). Understanding High Dose Rate Brachytherapy. Available at http://www.cetmc.com Koukourakis, G., Kelekis, N., Armonis, V. and Kouloulias, V. (2009). Brachytherapy for prostate cancer: a systematic review. Adv Urol.2009, 327945 Kubo, H.D., Glasgow, G.P., Pethel, T.D., Thomadsen, B.R. and Williamson, J.F. (1998). HDR Brachytherapy treatment delivery: Report of the AAPM radiation therapy committee task Group No. 59. Am. Assoc.Phys. Med. 376-403. Available at http://www.aapm.org/pubs/reports/rpt_61.pdf Mazeron, J.J.,Scalliet, P., Van Limbergen, E.and Lartigau, E. (2002). Radiobiology of Brachytherapy and the Dose-Rate Effect. Available at http://www.estro-education.org/publications/documents/e%204%20%2023072002%20radiobiology%20print_proc.pdf Stock, R.G., Stone, N.N., Tabert, A., et al (1998). A dose-response study for I-125 prostate implants. International Journal of Radiation Oncology Biology Physics, 41(1):101-108. Suntharalingam, N., Podgorsak, E.B. and Tolli, H. (n.d). Chapter 13: Brachytherapy: Physical and clinical aspects. Available at http://www-naweb.iaea.org/NAHU/DMRP/documents/Chapter13.pdf Varian Medical Systems (2012). Brachytherapy, available at http://www.varian.com/BrachytherapySeed Implant&Afterloader.htm Washington, C.M. and Leaver, D. (2009). Principles and Practice of Radiation Therapy, (Mosby) 3rd Edition Read More