Modern Radiotherapy Techniques for Breast Cancer Treatment

Abstract

There are many radiotherapy techniques used to treat breast cancer. Each techniques have their own limitations. The treatment techniques are valid depending on the facilities available to the department. The patient could be treated any technique as the expert knowledge to the center. This chapter will explain about the techniques used in current practice of breast cancer treatment. It will be explained why one technique procedure is better than others. The dose prescription and protocol will be not discussed. It depends on the department policy and facilities. The chapter will be the practical purpose that readers can use straight.

1. Introduction

Breast cancer is the second common type of cancer worldwide after lung cancer and it is the most frequent cancer in the women [1, 2]. As the report, lung cancer is the first common cancer. Breast cancer alone accounts for 29% of all new cancers among women in 2014 [3] and it is the second cause of cancer death in women both in Europe and in the USA [2, 3].

Therapeutic application of radiation has developed significantly over the past century. The development is momentous. It began with brachytherapy and even now continuing in parallel to the external beam radiation techniques. Gradually the use of fascinating advanced external beam radiation techniques is getting a base standard.

There are several therapeutic methods for breast cancer treatment, such as, surgery, systemic therapy, hormonotherapy, and radiation therapy (RT). Radiation therapy is utilized supplementarily to surgery and/or systematic therapy. It is also used as a single treatment procedure. Breast cancer radiation therapy utilizes high-energy X-rays, protons, electrons, or other particles to kill tumor cells. Radiation therapy for breast cancer can be delivered in two techniques i.e., Brachytherapy and External radiation.

2. Brachytherapy

The primary stage localized tumors are treated by brachytherapy. Brachytherapy is a form of internal radiation therapy for cancer treatment where a potted radioactive source is positioned in or near a tumor to demolish tumor cells. The early stage localized tumors are used to treat by brachytherapy. The tumors have not spread (metastasized) to other parts of the body.

Brachytherapy has been in use for most of the twentieth century. In the 1920s, Keynes used interstitial radium needles to implant the entire breast to treat breast cancer [3]. With the advent of megavoltage radiation, external-beam radiation therapy (EBRT) was used to treat the whole breast, with brachytherapy being utilized as a boost for unresected tumors. The high total doses resulted in poor cosmetic results, and therefore, the trend was to perform lumpectomy followed by EBRT and lower doses of brachytherapy [4, 5].

3. External radiation

External radiation therapy is used for lung, breast, head and neck, abdomen etc. cancer treatment. It is an external device provides high energy X-ray radiation from outside body to the localized tumors. It is reliable, comfortable, and minimum side effects depend on which parts of body is being exposed to radiation.

Besides technological hardware and software advances in delivery and planning systems, the fractionation schemes have changed a lot the last decades with recent hypo-fractionated radiotherapy schemes or emerging partial-breast irradiation protocols. The technical evolution allowed us a successive reduction in the treatment-related complications such as fibrosis and long-term cardiac toxicity. It has shown that the locoregional control rates increased concentrating more on heart and coronary sparing with four-dimensional (4D) breath-hold techniques. Advanced radiotherapy procedures need to be applied in routine clinical care with maximum safety and efficacy. It increases the benefit of locoregional treatment and to decrease the risks of late complications.

3.1 New techniques in external radiation

The treatment of breast cancer by external radiotherapy varies in organization to organization depending on the conveniences and applying treatment protocol. The radiation dose delivery stays complicated to the thoracic wall after complete mastectomy or to the breast conservation surgery. Radiation fields are mostly tangential to include the breast or thoracic wall. The fields are matched to a supraclavicular field in some cases.

3.2 Three-dimensional conformal radiotherapy (3D-CRT)

Three-dimensional conformal radiation therapy (3D CRT) is an advanced technique that includes the use of new imaging technologies computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET) CT etc.). It generates three-dimensional images of a tumor. 3D CRT permits for a high level of accuracy and the accuracy in the delivery of radiation treatment. The planning target volume (PTV) and organ at risk for three-dimensional conformal radiotherapy (3DCRT) have been defined according to international commission on radiation units & measurements (ICRU) reports 50 and 62 [5, 6]. 3D CRT can use high-energy X-ray beams to be delivered to breast, pelvis head and neck etc. tumors to minimize the dose to the organ at risk.

Treatment plans are independently calculated for each patient. There is various combination such as gantry angles, beam weightage, multi leaf collimator (MLC) positioning, number of fields including field in field (FiF). These are the effective ways to reduce heart dose with 3DCRT in the treatment of breast cancer (Figure 1).

Figure 1.

The figure displays the dose distribution on transversal, coronal, sagittal plane and beams eye view (BEV) for a right-side breast cancer planning using FiF technique. The breast PTV is shown as a blue contour and the colourwash represents 95% of the prescription dose.

3.3 Monoisocentric techniques

The mono isocentric technique reduces the dose in organs at risk such as lung and heart. It also allows the avoidance of the cold and the hot spots. A single isocenter is placed in the junction of tangential and supraclavicular fields. The superior half of the tangential fields and the lower half of the anterior field are half-blocked. The field matching accepted using asymmetric jaws to beam-split along the central axis plane. The treatment delivery needs one time to do set up inside the treatment room to treat tangential and supraclavicular fields. The total treatment delivery time is effectively reduced (Figure 2).

Figure 2.

The figure illustrates the dose distribution on transversal, coronal, sagittal plane and beams eye view (BEV) for left-side breast cancer planning in mono-isocentric technique for irradiation of tangential breast fields and supraclavicular field.

3.4 Intensity modulated radiotherapy (IMRT)

Intensity modulated radiation therapy (IMRT) is a modern treatment technique entrenched on delivery of non-uniform fluence. IMRT treatment delivers radiation beams at several different gantry, collimator angles and strengths to provide precise doses to PTV of breast cancer while sparing the dose to organ at risk such as heart, lungs, contra lateral breast and normal tissue. The treatment delivery can be either with fixed field or dynamic MLC technique. Dosimetric studies have well recognized advantage of tangent IMRT compared to 2D conventional planning or 3DCRT in providing better PTV coverage and organ at risk (OAR) sparing. Intrafraction motion lowers treatment plans predominantly for treatment of left breast. This motion can be restricted by breath-hold or respiratory gated techniques [7]. The importance of breast IMRT is well recognized. However, the routine clinical application of breast IMRT must be prudently considered (Figure 3).

Figure 3.

The figure shows the dose distribution on transversal, coronal, sagittal plane and beams eye view (BEV) for a right-side breast cancer planning using dose dynamic IMRT. The breast PTV is shown as a blue contour and the colourwash represents 95% of the prescription dose.

3.5 Volumatic modulated radiotherapy (VMAT)

Traditionally 2-dimensional or 3D conformal radiation techniques often result in large dose inhomogeneity throughout the treatment volumes, inadequate target coverage, or excessive normal tissue doses especially when coverage to the internal mammary nodes is required. Volumetric modulated arc therapy (VMAT) is a novel procedure extension of intensity-modulated radiotherapy (IMRT). An optimized three-dimensional dose distribution may be delivered in rotation of gantry and collimator simultaneously. Breast planning with volumetric modulated arc therapy has been explored mainly for left-sided breast treatments, with the primary committed of decreasing the heart dose and developing target dose homogeneity. VMAT planning technique that produced acceptable target volume coverage, excellent homogeneity throughout the PTV, and tolerable doses to the normal structures (Figure 4).

Figure 4.

The dose distribution on transversal, coronal, sagittal plane and beams eye view (BEV) for a left breast cancer planning using VMAT. The breast PTV is shown as a red contour and the colourwash represents 95% of the prescription dose.

3.6 Stereotactic body radiotherapy (SBRT)

Stereotactic radiation therapy is most frequently used to treat cranial tumor. The radiation therapy in other parts of the body, such as the lung, spine and liver called stereotactic body radiation therapy (SBRT). It delivers a high dose per fraction in a single or multiple fractions. The radiation dose delivers directly to the tumor, sparing nearby healthy tissue. The data of breast SBRT are not established sufficient. It has not validated in a significant prospective study with long term follow up in terms of long-term disease control. Stereotactic body radiation therapy for breast cancer may replace surgery in patients who wish to avoid surgery.

3.7 Deep inspiration breath hold technique

Deep inspiration breath hold (DIBH) is a radiation therapy treatment technique. Patients hold a deep breath throughout while radiation is given. By holding a deep breath in, lungs fill with air and heart will move away from chest wall. The TPS planned and expected delivery doses could be different due to respiratory motion during the treatment delivery. Several research showed that PTV dose heterogeneity increases as respiratory motion grows. The lung and heart doses also change due to respiratory motion. So that a larger margin is suggested from CTV to PTV margin [7]. DIBH technique could help to reduce the dose to heart and lung arising from respiratory motion. Breath-hold technique’s dosimetric advantages have been clearly in the literature [8], although the technique is not yet in widespread use.

3.8 Prone breast irradiation

The supine (face up) position is common for most patients undergoing breast conservation radiation treatment. Prone breast irradiation technique is a special technique to treat breast cancer. The patient placed comfortably on a specially constructed treatment table with a breast board in the prone position (face down) to deliver radiation dose. This technique has become both feasible and reproducible [9] with the help of CT and MRI treatment planning system. The heart may be particularly at risk to late effects of radiation when treatment is given in the supine position for left breast [10] (Figure 5).

Figure 5.

The dose distribution on transversal beams eye view (BEV) for a left breast cancer planning using VMAT in prone position. The breast PTV is shown as a blue contour and the isodose represents as a color bar.

Recent studies [11, 12] have demonstrated good coverage of PTV and a significant reduction in dose to ipsilateral lung, thyroid, contralateral breast, contralateral lung, and esophagus when compared to supine position. However, prone breast radiation may not be appropriate for all women.

3.9 Proton beam therapy (PBT)

Proton beat therapy (PBT) is a special treatment that can precisely target to PTV and provide high radiation doses to a tumor. The clinical application of proton beam external radiotherapy has been rising in breast cancer treatment. Bragg peak of proton beam gives the advantage of excellent PTV coverage and reducing damage to neighboring tissue and organs at risk such as the heart and lungs. PBT brings carefully potential to reduce the risk of cardiac events, maintaining the mean heart dose at ≤1 Gy [13].

PBT radiobiological effect rate is higher than (1.1) photons beam. Extensive cost of equipment and maintenance are an important barrier fact to become widespread in clinical use although it has high dosimetric advantage. The current studies [14, 15] showed the great benefit of PBT for breast cancer patients compared to conventional treatment with photon beam.

3.10 Hybrid irradiation

Modern dynamic irradiation techniques by linear accelerators, such as field in Filed (FiF), intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT), at the time to generate more uniform and conformal dose distributions for the planning target volume (PTV) and less dose to OAR [16, 17]. However, dynamic radiation techniques allow the risk of increased induction of secondary tumors at compliment to larger areas of low-dose exposure and increased monitor units (MU) [18]. To equilibrium the respective benefits of static and dynamic radiation techniques, Mayo et al. [19] have established a composite method combining 3DCRT and IMRT named hybrid intensity-modulated radiation therapy (H-IMRT) (Figure 6).

Figure 6.

The figure shows the dose distribution on transversal, DVH, coronal, sagittal planes respectively for 70% 3D FiF plus 30% VMAT (hybrid plane). The green and blue line indicate 95% and 90 isodose line covering PTV (red line).

Hybrid is an advanced new technique which uses conventional 3-Dimensional Conformal Radiotherapy (3DCRT) and Intensity Modulated Radiotherapy (IMRT) or Volumetric Modulated Arc Therapy (VMAT). Normally, the ratio of 3DCRT and IMRT or VMAT needs to be determined. The different proportions of 3DCRT and VMAT were used for breast cancer patients to determine the optimal weightage for hybrid technique so that the planning target volume (PTV) coverage improve as well as the dose to the organ at risk (OAR) decline.

4. Quality assurance

Patient specific quality assurance is a method for verification of the clinical planned dose before to start the treatment. The planned dose is compared to delivered dose. The methodology contains various dosimetric tasks that have been performed prior to the treatment of individual patient. Any dose calculation or delivery errors would be revealed. Patient specific QA has benefit to target. The underdose or overdose are harm to the patient. Patient specific QA has been done by film dosimetry, Delta4 phantom [20], Octavius 4D phantom [21], EPID, MapCHECK etc. Each device has their own advantages (Figure 7).

Figure 7.

A screenshot from Octavius 4D measurement analyzed in Verisoft. Showing the result of 3 beams SBRT delivery of lung cases. Panels (a), (b), and (c) show dose map in eclipse, Octavius calculated dose matrices and γ-distribution in transversal, sagittal and coronal plans column wise respectively having 3 beams of SBRT delivery for lung case (figure is taken from [21]).