Radiation therapy techniques for newly diagnosed, non-metastatic breast cancer

INTRODUCTION — Radiation therapy (RT) is a critical component of therapy for women with newly diagnosed, non-metastatic breast cancer. RT techniques for women with newly diagnosed, non-metastatic invasive breast cancer will be reviewed here. An overview of RT techniques in cancer treatment is discussed separately. (See "Radiation therapy techniques in cancer treatment".)

The approach to adjuvant RT for women with newly diagnosed, non-metastatic breast cancer and the long-term complications of breast RT are covered separately. (See "Adjuvant radiation therapy for women with newly diagnosed, non-metastatic breast cancer" and "Overview of long-term complications of therapy in breast cancer survivors and patterns of relapse".)

CHOICE OF PARTICLES FOR RT — Therapeutic radiation consists of the delivery of radiation beams comprised of electrons or photons. Photons completely pass through tissues, so when used, they must be angled to traverse the target tissue only so as to avoid critical normal tissue (eg, the heart). By contrast, electrons traverse only to a specific depth (determined by the energy needed) and hence can be tailored to target the tissue of interest while sparing critical tissue. Therefore, they can be delivered directly over critical tissues. (See "Radiation therapy techniques in cancer treatment", section on 'Photons versus electrons'.)

TREATMENT PLANNING — Three anatomic regions must be considered in defining the target volume (figure 1) (see "Adjuvant radiation therapy for women with newly diagnosed, non-metastatic breast cancer"):

●The breast or chest wall (depending on the surgical approach used), which constitute the primary RT field. (See 'Primary field' below.)

●The axilla, which may be encompassed as a regional RT field. (See 'Regional field' below.)

●Other areas of draining lymphatics (including the supraclavicular, infraclavicular, and internal mammary regions), which may be included in the regional RT field. In some situations when there is heavy involvement of the axillary lymph nodes, or the presence of a supraclavicular lymph nodes, the deep cervical nodes could also be treated.

Primary field — The target area will depend on the surgical approach:

●For women who undergo breast-conserving surgery, the target volume for whole-breast RT extends medially to the middle of the sternum and generally laterally to the mid-axillary line. The field usually extends 1 cm beyond the palpable border of breast tissue. The inferior edge of the field is approximately 1 to 1.5 cm below the inframammary fold in the intact breast. Superiorly, the field typically ends at the base of the head of the clavicle.

●For women who have undergone a mastectomy, the lateral field edge should extend to the mid-axillary line with the inferior edge extending to the contralateral inframammary fold. As with RT to the intact breast, the superior field typically extends to the base of the head of the clavicle. The area to be treated should encompass the full length of the mastectomy scar.

●The primary field may consist of high tangential fields that extend to just below the humeral head. This ensures coverage of the level I and in the majority of patients, a portion of level II of the axilla in a patient who will not receive dedicated regional RT fields (figure 2). (See 'Regional field' below.)

Regional field — The indications for treatment of the regional node basins depend on the number and location of the involved nodes as well as the degree of the aggressiveness of the tumor. Depending on extent of disease, RT may be indicated to the axillary, supraclavicular/infraclavicular, and/or the internal mammary nodes. (See "Adjuvant radiation therapy for women with newly diagnosed, non-metastatic breast cancer".)

The field of RT depends on the area to be covered:

●The axillary nodes receive 85 percent of the lymphatic drainage from all quadrants of the breast. The axillary field is matched to the breast or chest fields caudally during planning. If the supraclavicular fossa is to be included in the treatment field, the target field extends medially to the pedicles of the cervical spine, superiorly to the thyroid cartilage, and inferiorly to the superior aspect of the breast/chest wall field. The lateral extension of this field depends on whether or not the full axillary region is treated.

•If only the supraclavicular and infraclavicular nodes are to be treated, the lateral field extends to the coracoid process.

•If the full axilla is to be treated, the lateral field generally extends to the mid-humeral head or lateral to the humeral head.

●The internal mammary lymph nodes follow the course of the internal mammary artery and vein, which are located superior to the pleura and lateral to the sternum (figure 1). They receive the remainder of the lymphatic drainage of the breast. In the absence of clinically and/or radiographically enlarged internal mammary nodes, the nodes located in the first three interspaces are more likely to be pathologically involved than those in the lower interspaces. Therefore, this area is typically included in the treatment field [1]. This allows the RT field to end above the level of the majority of the cardiac silhouette, minimizing the risk of long-term cardiac morbidity [2].

VIRTUAL (CT-BASED) SIMULATION — For patients undergoing breast RT, a planning session is required prior to treatment, which is called simulation. During simulation, the area to be treated is precisely mapped out to ensure that the targeted tumor volume is precisely defined with respect to the surrounding anatomical structures [3]. Simulation can be performed virtually. Virtual simulation utilizes computed tomography to reconstruct high resolution digital radiographs that can be used for planning purposes. For both clinical and computed tomography (CT)-based planning, the patient should be immobilized to allow a reproducible daily set-up.

At most centers, virtual stimulation is performed because it minimizes time expenditure for patients and permits better visualization of important structures including the chest wall, outer breast contour, central lung distance, and the cardiac border. In addition, virtual simulation can result in improved target coverage with better sparing normal tissues compared with clinical simulation [4]. Therefore, it is particularly recommended for left-sided breast cancers so that the heart can be fully visualized and spared in the planning process. Quality control of simulation methods is important to ensure that patients are treated accurately.

Technique — To perform virtual simulation, the patient is immobilized to ensure movements are minimized. Radiopaque catheters are applied to the patient to delineate the borders of the treatment field, any scars, and match line junctions. The patient is then imaged using a CT scanner with 3 mm slice spacing through the desired treatment volume. With a modern helical scanner, the entire procedure generally takes less than 15 minutes. (See "Radiation therapy techniques in cancer treatment", section on 'Treatment planning'.)

The images are used to form a virtual patient for purposes of treatment planning using a specifically designed console, which the radiation oncologist uses to design the treatment fields. Once simulation is complete, a dosimetry plan with dose calculations is generated after which patients are filmed on the treatment machine to ensure field accuracy. Once fields are approved, treatment can proceed.

Clinical issues — Simulation techniques for the chest wall are similar to those for the intact breast. However, some issues should be considered in the process of simulation:

●Large breasts − Patients with large breasts represent an important challenge in simulation because the calculated radiation dose (ie, dosimetry) of breast treatment can be quite inhomogeneous as breast size increases [5]. It is important to take into account the planned position of the patient in simulation, which can be done supine or prone. If prone position is used, the target volumes must be carefully defined to avoid missing critical tissue, especially if the tumor bed is close to the chest wall.

●Internal mammary nodes − When the internal mammary lymph nodes are targeted for treatment, CT-based simulation should be used because of the variation in body size and shape, and the thickness of the chest wall.

WHOLE-BREAST RT — Treatment of the intact breast requires two tangential fields, which are angled a few degrees beyond 180 degrees opposed, so that the deep divergent edges of the field are coplanar. This allows divergence to be directed into the air above the breast, rather than deeper into the lung. Minimizing toxicity to the underlying heart and lung must be carefully considered in the treatment plan.

●The amount of lung projected on the tangential field at the central axis correlates reasonably well with the volume of ipsilateral lung that is irradiated [6,7]. If this width is kept ≤2 cm, the risk of radiation pneumonitis is less than 1 percent. Using virtual planning, calculation of dose volume parameters such as the V20 (the volume of the lung that receives more than 20 Gy) can help to predict risk of radiation pneumonitis and thus guide radiation planning. (See "Radiation-induced lung injury".)

●When the myocardium is within the treatment field despite optimal treatment planning, one can shape the fields using custom blocks [8]. However, this must be done carefully to ensure that relevant breast tissue is not also shielded. Newer methods of radiation planning and delivery (ie, conformal or intensity-modulated therapy and/or active breathing control) may permit maximal sparing of normal tissues. (See 'Novel RT planning and delivery techniques' below and "Cardiotoxicity of radiation therapy for breast cancer and other malignancies".)

An alternative technique for whole-breast RT uses linear accelerators and asymmetric collimator jaws to set the isocenter of the breast field at the deep edge and to half-beam block the field using the asymmetric collimator. Half-beam blocking with a so-called "beam splitter" is discouraged, since these external blocks still transmit 3 to 5 percent of the incident radiation, contributing unnecessary dose to the contralateral breast [9,10].

Dose and fractionation — Standard whole-breast RT delivers 1.8 to 2.0 Gy daily fractions over 5 to 5.5 weeks (total dose, 45 to 50 Gy). An alternative schedule may be used in which either 40 Gy or 42.5 Gy is delivered in 15 or 16 fractions, with whole-breast treatment completed in approximately three weeks [11]. The evidence and indications for both of these schedules is discussed separately. (See "Adjuvant radiation therapy for women with newly diagnosed, non-metastatic breast cancer".)

Approach to the patient with large breasts — For women with large breasts, it is important to minimize skin folds to decrease the risk of radiation-related skin toxicities, including the long-term risk of telangiectasias or fibrosis.

Others recommend treating women with large breast volumes in a prone position [12]. In a randomized clinical trial in 378 patients with large breast size treated with adjuvant breast radiotherapy, treatment in the prone position was associated with lower rates of moist desquamation compared with treatment in the standard supine position (27 versus 40 percent) [13]. Homogeneity can also be improved using this technique, and some have suggested that RT exposure to other tissues is reduced [14]. (See "Overview of long-term complications of therapy in breast cancer survivors and patterns of relapse" and "Radiation dermatitis".)

However, prone positioning may not be well tolerated by all and is not appropriate if regional nodal irradiation is also required.

ACCELERATED PARTIAL BREAST IRRADIATION — Accelerated partial breast irradiation (APBI) refers to the use of focused RT to a limited portion of the breast. Options for the delivery of APBI include brachytherapy, intraoperative RT, or external beam radiation. Conformal external beam radiation is the most commonly used delivery system in the United States. The indications and results following APBI are discussed separately. (See "Adjuvant radiation therapy for women with newly diagnosed, non-metastatic breast cancer", section on 'Accelerated partial-breast irradiation'.)

External beam RT — APBI using external beam RT is delivered postoperatively, which allows final review of the pathology, including an assessment of surgical margins. In addition, the treatment is noninvasive, and standard dosimetry and treatment equipment are employed.

Conformal external beam RT — Three-dimensional conformal external beam RT requires virtual simulation and combines multiple RT fields to deliver a specific dose of RT to the tumor bed region while sparing the majority of normal surrounding tissue and solid organs [15,16]. The dose typically delivered ranges from 35 to 38.5 Gy in 10 fractions. Treatment is usually administered twice a day (BID), over one week, or possibly once a day (QD) over two weeks [17]. (See "Radiation therapy techniques in cancer treatment", section on 'Conformal therapy'.)

While the large APBI randomized trials used 38.5 Gy in 10 treatments BID in one week, it seems that BID is less frequently used in routine clinical practice, possibly due to increase in late toxicity and poor cosmesis in the RAPID trial [18]. A QD fractionation seems to be preferable for patients and clinicians. The Florence trial used a dose of 30 Gy in five nonconsecutive once-daily fractions [19]. Other authors have suggested the fractionation used in the FAST FORWARD trial (26 Gy in five consecutive fractions). (See "Adjuvant radiation therapy for women with newly diagnosed, non-metastatic breast cancer", section on 'Accelerated partial-breast irradiation'.)

Intensity-modulated RT — Intensity-modulated RT (IMRT) uses a linear accelerator to deliver focused small beams of radiation that follow the exact contours of a tumor or target volume. Higher radiation doses can be used because the damage to surrounding tissue is limited, possibly resulting in more effective treatment. Computer imaging is used to evaluate the tumor throughout the course of treatment, permitting the most precise dose and treatment changes based on the changing tumor characteristics. IMRT requires special equipment that is available at most hospitals and radiation centers, but its use in breast cancer for APBI delivery has been limited [20-22]. It should be noted that IMRT is the technique used in the FLORENCE APBI trial [19]. A more general discussion of IMRT is covered separately. (See "Radiation therapy techniques in cancer treatment", section on 'Intensity-modulated radiation therapy'.)

Brachytherapy — Brachytherapy for breast cancer involves the temporary placement of radioactive material into body tissues for local radiation treatment. Brachytherapy can be delivered with interstitial, intracavitary, or intraoperative delivery systems. (See "Radiation therapy techniques in cancer treatment", section on 'Brachytherapy'.)

Interstitial brachytherapy — For interstitial brachytherapy, several small hollow catheters are placed into the breast surrounding the partial mastectomy site (figure 3) [23]. Potential disadvantages of this approach include the risk of infection and poor cosmesis with scarring due to the multiple catheters, although these complications have largely been seen in older studies. (See 'RT boost' below.)

●Catheter placement − The number of catheters used is dependent upon the size and shape of the target. The placement of the catheters is determined using RT planning software along with stereotactic mammography, ultrasound, or computed tomography guidance.

●Radioactive seed insertion – High- or low-dose-rate radioactive seeds are inserted into the catheters as described above. The catheters are removed when treatment is completed. (See 'Technical considerations' below.)

Intracavitary brachytherapy — For intracavitary brachytherapy, a radiation delivery device is placed into the partial mastectomy site [24]. Single lumen and multi-lumen balloon catheter and non-balloon devices have all been used successfully (picture 1 and figure 4) [25-27]. The presumed advantage of the multi-lumen devices as compared with single lumen catheters is more precise dosimetric planning and safer treatment delivery, avoiding skin and other organ damage.

●Placement of the device – Consideration of intracavitary brachytherapy requires a surgical cavity large enough to accommodate the device (figure 5) [28,29].

The device can be placed at the time of lumpectomy ("open technique") or several days later under ultrasound guidance ("closed technique"). The closed technique is preferable because, if the device is placed during surgery, final pathology results may require the device to be removed due to involved margins or positive lymph nodes [24]. The device can usually be placed percutaneously in the office setting after final pathology results are available. In addition, infection rates are lower with the closed technique [30].

A cavity evaluation device may be placed initially in the operating room and then exchanged for the treatment device (figure 6). The cavity evaluation device is used to assess the partial mastectomy cavity, evaluate skin spacing, and assist in the selection of the correct balloon size applicator for delivery of intracavitary RT. This technique typically delivers a total dose of 34 Gy to the target site at a dose of 3.4 Gy twice daily over one week.

Intraoperative radiation therapy — Intraoperative RT condenses the entire therapeutic dose into a single fraction, permitting surgery and radiation to be completed in one day. Potential advantages include accurate delivery of RT directly to the surgical margins and a decreased dose of radiation to skin and subcutaneous tissue since these can be retracted during treatment. Drawbacks to the use of intraoperative radiation include the extended time in the operating room, the inability to verify the radiation dosimetry, and the lack of final pathology information at the time of radiation.

Several devices have been used for intraoperative radiation:

●A portable, spherical, radiation-generating device is placed into the partial mastectomy cavity just after specimen resection, and purse string sutures are placed within the breast to ensure that the breast tissue is in contact with the applicator surface. Treatment is then delivered with low energy x-rays, for a dose of approximately 20 Gy at the applicator surface and 5 Gy at a depth of 1 cm over 20 to 45 minutes, depending upon the size of the cavity and the device [31,32].

●Electronic brachytherapy using a portable linear accelerator has been used to deliver 21 Gy in one fraction intraoperatively, with a lead shield placed on the pectoralis fascia to protect the lung [31,33,34].

Technical considerations

Dosing — Brachytherapy can be delivered with either low or high dose rates. In addition, radioactive seeds are inserted into the catheters as described above. The catheters are removed after approximately five days, when treatment is completed.

●Low-dose-rate RT – Low-dose-rate RT consists of approximately 45 to 50 Gy delivered to the target site at a rate of 30 to 70 cGy/hour. This is an inpatient procedure that requires patients to be hospitalized in a private room while treatment is being administered. This technique is now used very rarely.

●High-dose-rate RT – High-dose-rate RT is completed as an outpatient procedure over a five-day period. This technique typically delivers a total dose of 34 Gy to the target site at a dose of 3.4 Gy twice daily.

Verification of conformance — When the appropriate radiation delivery device is in place, a CT scan is performed to evaluate tissue conformance, skin spacing, symmetry of the balloon in relation to the central catheter, and the device catheter to determine if treatment can be delivered. Verification of the conformance and integrity of the device are necessary to ensure that the correct dose of RT is provided to the partial mastectomy cavity and surrounding breast tissue.

Adequate conformance generally requires that less than 10 percent of the planning target volume is composed of air or fluid [35]. Large air or fluid pockets between the device and tissue may require device removal [25]. In addition, the device-to-skin distance should be greater than or equal to 7 mm to avoid skin damage, which precludes use of this technique for superficial lesions.

POSTMASTECTOMY RT — For women who undergo a mastectomy, the chest wall can be treated with tangential photon fields, similar to the intact breast. The field borders are the same, as are the considerations regarding the underlying volume of heart and lung.

Delivery of an adequate dose to the chest wall skin is important, and the skin-sparing effect of photons must be taken into consideration. When the photon beam strikes the absorbing surface, there is an initial build-up of dose that reaches a maximum, the depth of which increases with increasing energy and then attenuates. This skin-sparing effect is desirable when treating a deep lesion but not superficial tissues such as the chest wall skin. In these cases, a bolus (a material with similar density to tissue that is placed directly on the skin surface) must be used (mostly every other day) to ensure that the skin receives a therapeutic radiation dose. The beam strikes the absorbing surface at the bolus, whose thickness is calculated so that the maximum dose to the target volume occurs closer to the skin surface.

If a bolus is used, patients should be informed that skin erythema is an expected effect. The reaction peaks toward the end of therapy and then quickly heals. If skin erythema occurs too early in the patient course or is more than desired, the bolus can be discontinued.

Satisfactory treatment of the chest wall can also be accomplished with electrons [36-38]. However, electrons deposit a high dose to the superficial skin, which cannot be modified from day to day, unlike the placement of a bolus during photon beam therapy. Patients with sensitive skin can develop a brisk skin reaction before the treatment is concluded, making the last few days of treatment uncomfortable. Use of electrons can also increase dose to the underlying lung depending on electron energy. Careful planning not only of field arrangements but also electron energies is needed if electrons are used to treat the chest wall.

REGIONAL NODE RT — With virtually every treatment technique, the axilla and supraclavicular fossa are treated with an anterior photon field. When treatment is limited to the supraclavicular fossa and axillary apex, the field is typically 7 to 8 cm wide. We angle this field 10 degrees off the spine so that divergence does not enter the cervical cord. When the full axilla requires treatment, the field is extended laterally to include a part of the humeral head, and a posterior axillary boost is generally added to compensate for the underdosing of the deeper tissues in the axilla by the anterior fields depending upon the depth to the mid-plane of the axilla.

If the internal mammary (IM) nodes are to be treated (see "Adjuvant radiation therapy for women with newly diagnosed, non-metastatic breast cancer", section on 'RT of internal mammary nodes'), we use computed tomography for virtual simulation to achieve adequate coverage of the target area while minimizing toxicity to normal tissues. The IM nodal region can be treated with partially wide tangents [2] or electrons [39] technique. The approach must be individually tailored with the final field arrangement taking into account body habitus. When treating the IM nodes, two methods should be avoided. The use of "deep tangents", defined as tangents brought across the midline to include the IM nodes inside a high-dose volume [40], if it exposes a prohibitive volume of lung in the treatment field. In addition, "en face" photon treatment [41] is not recommended because a "cold triangle" of tissue that does not receive radiation therapy cannot be avoided. In addition, a substantial dose to the heart is delivered, predisposing the patient to later cardiac events.

RT BOOST — For appropriately selected patients, additional doses of RT to the tumor bed (RT boost) are indicated following breast RT to further reduce the risk of a local recurrence. Although the RT boost can be supplied with electrons, photons, or an interstitial implant, with equivalent outcomes [42], electrons have become the method of choice at most institutions [43]. Our typical electron boost dose is 10 to 14 Gy, which, when added to the 46 to 50 Gy delivered to the whole breast, gives a final tumor bed dose of 60 Gy. (See "Adjuvant radiation therapy for women with newly diagnosed, non-metastatic breast cancer", section on 'RT boost to the tumor bed'.)

Modifications to the boost dose include the following situations:

●For women treated with breast-conserving surgery who have a focally positive margin (in the absence of an extensive intraductal component) on final pathology, a higher boost dose is often used to ensure a total 64 to 66 Gy dose to the tumor bed.

●For women previously treated with mastectomy who have an unresectable chest wall recurrence, a total dose of 70 Gy or higher may be required for optimal tumor control.

Since the surgical scar following breast-conserving surgery does not always correspond to the area of tumor removal, the tumor bed should ideally be identified with surgical clips at the time of lumpectomy [44,45]. Others have used ultrasound or computed tomography to help define the tumor bed [46,47]. CT-based planning assists in defining the shape of the field and the depth of the tumor bed for proper electron dosimetry. The indications for an RT boost are discussed separately. (See "Adjuvant radiation therapy for women with newly diagnosed, non-metastatic breast cancer".)

Although a boost is typically administered sequential to whole breast radiation, trials are evaluating simultaneous integrated boost as a way to decrease treatment duration and reduce toxicity, including breast hardness. In a randomized open label trial (IMPORT HIGH), 2617 patients who had received breast conserving surgery for pT1-3, pN0-3 nonmetastatic breast cancer were randomly assigned to one of three groups: control (40 Gy in 15 fractions to the whole breast and 16 Gy in 8 fractions sequential photon tumor-bed boost), test group 1 (36 Gy in 15 fractions to the whole breast, 40 Gy in 15 fractions to the partial breast, and 48 Gy in 15 fractions concomitant photon boost to the tumor-bed volume), and test group 2 (36 Gy in 15 fractions to the whole breast, 40 Gy in 15 fractions to the partial breast, and 53 Gy in 15 fractions concomitant photon boost to the tumor-bed volume) [48]. Image-guided radiotherapy was used in all groups, including the control group.

Results showed that the risk for local recurrence was similar in all groups; there was no advantage for escalating to 53 Gy simultaneous integrated boost, which was associated with increased breast induration. At a median follow-up of 74 months, five-year in breast tumor recurrence was 1.9 percent for the control group, 2.0 percent for test group 1, and 3.2 percent for test group 2. Five-year incidence of clinician-reported breast induration was 11.5 percent for the control group, 10.6 percent for test group 1, and 15.5 percent for test group 2. Although these are promising data, we await long term data prior to incorporating concurrent boost into routine practice.

NOVEL RT PLANNING AND DELIVERY TECHNIQUES — Conformal and intensity-modulated radiation therapy (IMRT) techniques are evolving as a means of improving the planning and delivery of RT. In contrast to standard RT delivery, which uses fixed fields that are shaped using individualized lead alloy blocks, conformal and intensity-modulated therapy permits the delivery of a high-dose volume that conforms in three dimensions to the shape of the defined target, while minimizing the dose to normal tissue [39].

IMRT uses a computer-defined variable intensity pattern to modulate the intensity of the delivered beam over the treated field so that a uniform and standardized dose is delivered over the entire breast. Data using IMRT delivery to the breast and/or chest wall in patients with breast cancer suggest that dose distribution is more homogeneous [49,50]. However, the impact of computer-controlled treatment delivery on oncologic outcomes and long-term toxicity must be assessed before IMRT can be routinely recommended over more contemporary non-IMRT techniques. The technical aspects of intensity-modulated radiation therapy are discussed separately. (See "Radiation therapy techniques in cancer treatment", section on 'Intensity-modulated radiation therapy'.)

In specialized centers, an alternative treatment involves the use of protons, which allows for more precise targeting of the tumor with little impact on normal tissue, in particular the cardiac exposure [51]. However, this remains highly investigative in breast cancer and is mostly available on clinical trials. (See "Radiation therapy techniques in cancer treatment", section on 'Proton beam'.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Breast cancer".)

SUMMARY

●Introduction – Radiation therapy (RT) is a critical component of therapy for women with newly diagnosed, non-metastatic breast cancer. (See 'Introduction' above.)

●Primary field – For women who are candidates for RT after breast surgery, the primary field for treatment depends on the surgical approach used (see 'Primary field' above):

•For women treated with breast-conserving surgery, the target volume for whole-breast RT extends medially to the middle of the sternum and laterally, generally to the mid-axillary line. The field usually extends 1 cm beyond the palpable border of breast tissue. The inferior edge of the field is approximately 1 to 1.5 cm below the inframammary fold in the intact breast. Superiorly, the field typically ends at the base of the head of the clavicle.

•For women treated with a mastectomy, the lateral field edge should extend to the mid-axillary line with the inferior edge extending to the contralateral inframammary fold. As with RT to the intact breast, the superior field typically extends to the base of the head of the clavicle. The area to be treated should encompass the full length of the mastectomy scar.

●Regional field – The indications for treatment of the regional node basins depend on the number and location of the involved nodes. Depending on extent of disease, RT may be indicated to the axillary, supraclavicular/infraclavicular, and/or the internal mammary nodes. (See 'Regional field' above.)

●Virtual simulation – Virtual simulation utilizes computed tomography to reconstruct high resolution digital radiographs, which can be used for treatment planning purposes. Compared with clinical simulation, it permits better visualization of important structures including the chest wall, outer breast contour, central lung distance, and the cardiac border. (See 'Virtual (CT-based) simulation' above.)

●Whole-breast RT – For women who undergo whole-breast RT, treatment of the intact breast requires two tangential fields, which are angled a few degrees beyond 180 degrees opposed, so that the deep divergent edges of the field are coplanar. This allows divergence to be directed into the air above the breast, rather than deeper into the lung. (See 'Whole-breast RT' above.)

●Postmastectomy radiation – For women who undergo a mastectomy with or without immediate reconstruction followed by postmastectomy radiation, the chest wall can be treated with tangential photon fields, similar to the intact breast. The field borders are the same, as are the considerations regarding the underlying volume of heart and lung. Delivery of an adequate dose to the chest wall skin is important, and the skin-sparing effect of photons must be taken into consideration. (See 'Postmastectomy RT' above.)

●Regional node radiation – When regional nodes are to be treated, with virtually every treatment technique, the axilla and supraclavicular fossa are treated with an anterior photon field. When treatment is limited to the supraclavicular fossa and axillary apex, the field is typically 7 to 8 cm wide. We angle this field 10 degrees off the spine so that divergence does not enter the cervical spine/cord. (See 'Regional node RT' above.)

●Radiation boost – Our approach to an RT boost to the tumor bed takes into account the surgical treatment and pathologic results. (See 'RT boost' above.)