External Beam Radiation Therapy (EBRT)
The most common method of radiation therapy is EBRT. Ionising radiation is delivered either using a radioactive source or using an electromagnetic energy from a machine. This is placed at some distance from the tissue to be treated (see Figure 2). It is differentiated from brachytherapy where radioactive sources are implanted or placed internally (i.e. administered internally) (Moore-Higgs, 2007). EBRT equipment is classified according to energy produced and depth of penetration within the intended area (Moore-Higgs, 2007).
In EBRT, the first step is the planning or simulation session. In this session, marks are placed on the body and measurements are taken to direct the radiation beam in the correct position for each treatment. This is followed by a schedule of daily treatment. The patient is placed on a treatment couch and then radiation doses are applied from multiple directions to the pelvis. This allows EBRT to be done on an outpatient basis. Usually, the treatment is delivered five days a week for 4 to 6 weeks. Small amounts of radiation are administered daily rather than using fewer large doses. This enables reduction of tissue damage surrounding the tumour. Normal cells can recover during weekend rests.
Figure 2: EBRT of the pelvis
(“External beam radiotherapy”, 2014; Health Sciences North, 2013) Intensity-modulated Radiation Therapy (IMRT)
IMRT is a newer EBRT technique which uses numerous intensity levels via intensity- modulated beams (D’Souza et al., 2012). In these intensity-modulated beams, the direction off any single beam or placement of any single source can be varied (D’Souza et al., 2012). This enables achievement of narrow margins of both dose distributions and dose gradients. This is difficult with conventional and 3-D modes (D’Souza et al., 2012, Light, 2007). Flexibility in dose administration is achievable with IMRT and is seen as a major advance in radiation therapy since it permits higher doses to be given whilst sparing normal tissues (Light, 2007). Intensity of beams is equal irrespective of tumour thickness in conventional therapy. In IMRT, the intensity of the beam can be varied along the treatment field based on the tumour thickness. The beam is stronger where the tumour is thicker and lighter where the tumour is thinner. Thus unnecessary radiation is eliminated (Life Bridge Health, 2014).
The course of treatment in IMRT lasts five to eight weeks at the frequency of five days a week. The patient is in the treatment room for 15-30 minutes for each radiation session. Both EBRT and IMRT are painless (UCFS Medical Centre, 2014).
Further studies are evaluating IMRT for treating gynaecological cancers (D’Souza et al., 2012). IMRT is also used to treat rectal (Ng et al., 2012; Brooks et al., 2013) and anal cancers (Menkarios et al., 2007; Bazan et al., 2011).
Vaginal Brachytherapy (Internal Radiation Therapy)
Brachytherapy (brachy=Greek for short distance), also referred to as internal radiation or implant therapy, refers to the temporary or permanent placing of a radioactive source very close to or in contact with the targeted tissue (Moore-Higgs, 2007). Brachytherapy works by providing a high dose of radiation to a specific tumour volume with a quick decline in dose to bordering normal tissues (Moore- Higgs, 2007).
Brachytherapy can be combined with EBRT, surgery, or chemotherapy if required. It is used for enhancing control of local disease, and to treat high risk tumour recurrence areas, improve comfort with recurrent disease, safeguard vital organ function, and save normal surrounding tissue from damage (Moore-Higgs, 2007).
Either a High Dose Rate (HDR) or a Low Dose Rate (HDR) is possible in Brachytherapy/internal radiation. The radiation can be delivered with a vaginal cylinder applicator (see Figure 3 below and Figures 5, 6 and 7) or an applicator that treats the cervix and the uterus independently (Oncolink, 2006).
Figure 3: Vaginal cylinder applicator (Oncolink, 2006)
For the vaginal brachytherapy, women are treated in a lead-lined room. After positioning the cylinder properly, the radiation technician takes x-ray images or CT scans to verify the placement of the cylinder (Oncolink, 2006) (see figure 4). On calculation of the radiation dose by the physicist and radiation therapy technician the treatment machine directs the radioactive sources to the applicators for the required duration. During the process, women may feel vaginal pressure and experience marginal discomfort. If tandems and ovoids (see figures 4, 5 and 6) are used gauze packing is inserted in the vaginal vault to prevent movement of the applicators. In
some cases, contrast (barium) may be inserted in the rectum using a small tube. The use of a Foley catheter and the rectal contrast facilitates x-ray examination so that the absorbed radiation dose by the bladder and rectum can be established.
Radiation exposure to others is averted by not allowing anyone into the treatment room. During this time, video cameras and two-way microphones assist monitoring the treatment. The duration of treatment time can vary from 5 to 20 minutes. After achievement of the treatment dose, the source is extracted into the HDR machine. A physicist then checks to ensure that no radioactivity exists in the woman’s body or outside the machine. Then the applicator is removed by the physician (Oncolink, 2006).
Figure 4: Side view of tandem and ovoids placed in a patient (Nucletron B.V., 2014)
If HDR is not appropriate, low dose rate (LDR) brachytherapy may be recommended. In LDR brachytherapy, the patient is anesthetised before the insertion of the radioactive material as in the case of HDR. However, this procedure is done under in-patient conditions varying from 2 to 3 days. During the time the radioactive source is placed vaginally, friends and family are not allowed to visit, to avoid their radiation exposure. The duty times of the nurses are also controlled for the same reason (Oncolink, 2006).
Figure 5: Radiation applicators (Varian Medical Systems, 2014)
Figure 6: Radiation applicators (Mayo Clinic Health Library, 2014)
Figure 7: X-ray of inserted radiation application rods (UC San Diego Moores Cancer Center, 2014)