**1. Introduction**

Therapeutic management of prostate cancer has become complex, multidisciplinary and stage-specific. (Heidenereich et al., 2011) Based on PSA level, histopathological grading and clinical staging, prostate cancer is classified as low-, intermediate- and high risk for disease recurrence. The risk status often plays a major role in deciding further therapy. (Kirby & Madhavan, 2010) It is usually impossible to state that one therapy is superior to another because of the lack of randomized controlled trials. However some recommendations can be made. (Heidenereich et al., 2011, Aus et al. 2001) Based on European Association of Urology recommendations in 2010, patients with low-risk (PSA ≤10 ng/ml, Gleason score <6 and cT1c-cT2a) or intermediate risk prostate cancer (PSA 10.1-20 ng/ml, Gleason score 7 or cT2b-c) are to be treated interdisciplinary with an urologist and a radiation oncologist. Treatment options for these patients vary from watchful waiting and active surveillance to radical prostatectomy or definitive radiotherapy. Multidisciplinary tumor board is needed when discussing neoadjuvant and adjuvant treatment options in high-risk prostate cancer patients (PSA>20ng/ml, Gleason score 8-10 or ≥cT3a) (Heidenereich et al., 2011, Choe & Liauw, 2010).

Radiotherapy is widely used as curative treatment modality for prostate cancer. There is a diverse array of radiotherapeutic strategies that can be effectively used to treat both organconfined and locally advanced disease, alone or in combination with androgen-deprivation therapy. Furthermore, it has also a significant role in post-prostatectomy setting, as adjuvant or salvage radiotherapy.

In recent decades, radiotherapy in prostate cancer has undergone significant clinical and technological advances that aim to optimize cancer control outcomes while minimizing treatment morbidity. (Choe & Liauw, 2010, Hayden et al., 2010)

#### **2. External-beam radiotherapy in prostate cancer**

External-beam radiotherapy has a very long history in the curative treatment of prostate cancer. It is proven and most extensively used radiation modality. As a flexible, noninvasive, outpatient therapy, external-beam radiotherapy can be used in all stages of prostate cancer. (Hayden et al., 2010) It is based on daily delivery of radiation to a target volume using high-energy radiation beams from linear accelerators (or cobalt machines) over a course of 7 to 9 weeks.

The initial lateral fields included a volume similar to that treated with AP/PA portals. The anterior margin was 1.5 cm posterior to the projection of the anterior cortex of the pubic symphisis. Posteriorly, the fields included the pelvic and presacral lymph nodes above the

Large treated volume was obtained since the average variation of prostate position relative to bony markers was approximately 8 mm in the superior and posterior positions, 7 mm in the inferior, 5 mm in the lateral and 4 mm in anterior position. The seminal vesicles are located high in the pelvis, and posterior to the bladder, which was very critical when

When indicated, the periaortic lymph nodes could be treated through extended AP/PA portals or separate periaortic fields placed above the pelvic fields. The superior margin of the periaortic field was at the Th12-L1 vertebral interspace with the width usually above 10 cm (determined by lymphangiogram or CT scan). (Chao et al., 2002, Dobbs et al., 1999) Conventional external-beam radiotherapy required daily radiation delivery to target volume using high-energy beams (more than 10MV). In most institutions a standard fractionation was used with 1.8 to 2Gy per day. In radical approach, initially a dose of 45- 50Gy was applied to the whole pelvis or to the prostate through two parallel opposed fields (AP/PA). Than addition of a boost dose was delivered, up to a total dose of 65-66Gy through lateral opposed fields, two anterior or two posterior oblique fields. (Chao et al.,

Once a decision is being made to treat prostate cancer with external-beam radiotherapy, the radiotherapy plan is defined either to limit treatment to the gland or to extend treatment field to include the periprostatic tissues, seminal vesicles and pelvic lymph nodes. (Hayden et al. 2010) CT or MRI of the abdomen and pelvis is used to assess the involvement of surrounding structures. MRI is particularly useful for distinguishing capsular invasion, seminal vesicle involvement and periapical extension. CT scanning for treatment planning is performed to every patient, which means that two-dimensional (2D) radiotherapy is a step

The patient is immobilized in supine position with skin tattoos over the pubic symphisis and laterally over the iliac crests to prevent lateral rotation. CT scans of pelvis are obtained with slice thickness of 4-5 mm. No oral, rectal or intravenous contrast is used. The CT section at the centre of the volume is used as the main planning slice to outline patient contour, target volume, rectum, and bladder. The margins of the target volume are determined by the tumor extent. The gross tumor volume contains entire prostate gland, but if there is a risk of seminal vesicles involvement, they must be included in target volume too. The gross tumor volume is outlined on the central slice only. To allow position variation, an additional margin is added to gross tumor volume (1-1.5 cm in all directions) defining planning target volume (PTV). For two-dimensional planning, PTV is outlined on multiple sections to ensure that the entire tumor is encompassed. The rectal outline must be transposed on to the central section so that the dose can be adequately calculated. Shaping the target volume by shielding blocks or multileaf collimators reduces

Treatment technique depends on the target volume size and shape. Three-field technique using an anterior and two posterior oblique or opposed lateral fields give a high dose to the

S3 segment, which allowed some sparing of posterior rectal wall distal to this level.

reducing treated volume in T3 patients.

**2.2 Two-dimensional radiotherapy (2D-RT)** 

forward comparing to conventional radiotherapy.

2002, Dobbs et al., 1999)

the dose to normal tissues.

In the last 30 years it has undergone a long, improving path from conventional, twodimensional radiotherapy to intensity-modulated and image-guided radiotherapy and onwards. In low-risk prostate cancer its efficacy appears to be comparable to that of radical prostatectomy but with different toxicities (Choe & Liauw, 2010). For patients not suitable for surgery, external-beam radiotherapy will be the treatment of choice in most cases, alone or combined with androgen-deprivation therapy.
