Accelerated Partial Breast Irradiation: Treating Less is Better

Medically reviewed by Dr Johann Tang, Senior Consultant Radiation Oncologist

View the original article here.

In patients with early stage breast cancer and post breast conserving surgery cases, adjuvant radiotherapy remains as the standard of care resulting in local control as well as overall survival benefit .

A New Paradigm Shift for Early Stage Breast Cancer Treatment

The use of mammographic screening has enabled identification of patients with early stage breast cancer earlier, thus increasing the breast conservation rates in this group of patients. However, the use of conventional fractionation radiotherapy which was usually given over 5 to 6 weeks may pose a barrier to patients who are receiving adjuvant radiotherapy, which later may lead to some patients opting for total mastectomy instead .To avoid unnecessary total mastectomies, Accelerated Partial Breast Irradiation (APBI) presents a viable alternative radiotherapy modality to patients with early stage, node negative breast cancer,  considering its shorter overall treatment duration.


Table 1. Pros and cons of multi-catheter APBI if being compared with a standard external beam radiotherapy

Type of APBI Modality

Multi-catheter APBI

The pros :

• Recent clinical phase 3 data shows that multi-catheter APBI is equivalent to a standard EBRT treatment.
• Most versatile of all the APBI modalities.
• Suitable for patients of all cup sizes.
• Can be used in patients with augmented breast implants.

The cons :

• Invasive.
• Operator dependent procedure.

MammoSite

The pros :

• Phase 2 registry data shows no inferiority to standard EBRT treatment.
•  Simple to insert and can be done in the surgical rooms.

The cons :

• Higher toxicity rates compared to multi-catheter interstitial.
• Restricted to breasts with cup C size and above as the smallest diameter of the balloon catheter is 5cm. Thus, it is not suitable for majority of the Asian patients.

Intra-operative radiotherapy with electrons (ELIOT)

The pros :

• Treatment is done at the time of breast conserving surgery.

The cons :

• Phase 3 clinical data shows higher recurrence rates compared with standard EBRT treatment.
• IORT ELIOT has fallen out of favour

Targeted intra-operative radiotherapy (TARGIT)

The pros :

• Treatment is done at the time of breast conserving surgery.

The cons :

• Phase 3 clinical data shows higher recurrence rates compared with standard EBRT treatment.
• IORT TARGIT has fallen out of favour.
• In addition, 1 in 4 post TARGIT patients will require standard EBRT due to poor pathological features.
• Not suitable for Asians due to the large electron sphere that needs to be inserted into the breasts, similar to MammoSite

APBI – External Beam

The pros :

• Non invasive
• Suitable for any breast size.

The cons :

• Clinical studies have shown APBI External Beam to have higher long-term toxicity rates.

This would reduce the logistic barriers, especially for those who are active in the workforce and find it difficult to take time off from work or need to travel long distances for their radiotherapy treatments. Thus, APBI serves as a viable alternative breast conservation treatment for patients who would otherwise have opted for total mastectomies. Furthermore, where acute and late toxicities such as radiation dermatitis, acute pneumonitis and skin fibrosis are common with conventional external beam treatment, APBI offers better toxicity outcome leading to favourable cosmesis with lesser acute and late toxicity. Table 1 summarises the pros and cons of APBI versus a standard 6-week external beam treatment.

Types of APBI modalities

There are many different APBI modalities, e.g., intraoperative, MammoSite, multi-catheter, and external beam. Each of these different APBI modalities has its pros and cons. Given the recent published data for various APBI techniques, it has emerged that multi-catheter APBI offers the best clinical evidence for efficacy with better toxicity profile if being compared with a standard conventional external beam radiotherapy treatment. Table 2 summarises the various types of APBI modalities available.

What is multi-catheter APBI?

Amongst all the APBI modalities, multicatheter interstitial APBI is the oldest method, hence has the longest clinical follow-up and experience. Given that the area of highest risk of local recurrence involves the tumour cavity plus a 1.5 to 2-cm margin, targeting and delivering high doses of radiation to this high risk volume decreases the chance of a local recurrence. Radiation delivery is achieved by placing plastic catheters surrounding the tumour cavity. This allows the dose delivery to be highly conformal to the high risk volume, concentrating the high dose to this region, whilst sparing the surrounding organs at risk such as the normal breast tissue, ribs, lungs, and heart. This would lead to lower long-term toxicity on these organs at risk. Contrast to EBRT treatment where the dose enters the breast externally and penetrates all tissues in its path before exiting on the opposite side, all the normal tissues irradiated would be subjected to long-term toxicity. These EBRT side effects include radiation dermatitis, cardiac toxicity and pulmonary fibrosis, whereas these side effects are seldom seen in patients who have undergone multicatheter APBI.

Table 3. Summary of the study results published by the American Society for Therapeutic Radiation Oncology (ASTRO), American Brachytherapy Society (ABS), and European Society for Therapeutic Radiation Oncology (ESTRO)

Who are the eligible patients?

Whilst older studies using multicatheter interstitial APBI did not achieve good results which might be due to poor patient selection, recent studies have demonstrated that with careful patient selection, good clinical results and local control can be achieved with this technique. The results of the recent studies form the basis of consensus guidelines published by the American Society for Therapeutic Radiation Oncology (ASTRO), American Brachytherapy Society (ABS), and European Society for Therapeutic Radiation Oncology (ESTRO), indicating which patients are suitable for multicatheter APBI, which group of the patients shall be offered with caution, and which ones of them are not suitable for the procedure. In general, the suitable and cautionary patients can be offered this procedure. At the National University Cancer Institute Singapore (NCIS), these two groups of patients make up about 80% of the total cases seen. Our experience at NCIS have shown that post breast conserving surgery patients who are above 40 years old and diagnosed with early stage breast cancer have shown to be suitable candidates for APBI.

Multi-catheter APBI treatment schedule

Under local anaesthesia, implantation of the catheters usually takes place on a Friday morning and lasts for one hour. Immediately post implantation, the patient will undergo a planning CT scan and then be discharged. The treatment commences from Monday to Friday on the following week, 2 sessions a day (i.e. morning and afternoon). After the Friday treatment session, the catheters are removed.


Table 4. Sample of APBI planning & treatment schedule

Multi-catheter APBI technique

Target localisation

Ultrasound guided localisation of the target is essential to a successful implant. Under ultrasound guidance, about 0.5-1 cc of omnipaque is injected into the tumour cavity. This is to allow the tumour cavity to be easily identifiable on the pre-procedure CT scan. In addition, instead of using a skin surface marker pen, the outline of the cavity is marked by imprinting the straw on the breast skin surface as the marker pen can be accidentally washed off easily when the area is cleaned with chlorhexidine solution before the procedure. By imprinting the straw marks on the skin, the impression of the cavity outline remains even after the cleaning of the ipsilateral breast preprocedure.

By placing contrast into the seroma cavity, it is easier to see on the pre-procedure CT scan. Pre procedure CT scan is then acquired to gain information on the location of the tumour in respect to the nipple and the depth of the normal breast tissue so as to avoid the risk of a pneumothorax by puncturing the underlying ipsilateral lung. Before the procedure, it is advisable to mark out the outline of medial borders of the brassiere against the bra. This is to ensure that no catheters are placed medially to this line such that it may be seen when the patient wears a low cut revealing dress. By doing this, it also ensures that patients are more confident of continuing their activities of daily living by having the freedom of what to wear and yet able to continue treatment.

Anaesthesia

Moderate sedation is usually the mode of anaesthesia.

Procedure

The template approach is most suitable for patients with B to D cup size breast due to the use of Kuske Template size.

Once the cavity is localised, the ipsilateral breast area is surgically prepped under sterile conditions. To avoid injury of the underlying chest wall structures or causing a pneumothorax, the overlying breast is pinched and gently lifted off the chest wall before applying the template and securing it. Also to note is that the C12 grid position ideally should be in the centre of the tumour cavity to ensure that adequate grid space is available on either side of the template for catheter insertion. Usually, four anchoring needles are then placed in an asymmetric pattern at C8, 12, 14 and A13. The purpose of the asymmetric pattern is to aid easy orientation of the template in reference to the patient’s anatomy as well as to secure and prevent slipping of the template from the breast.

A CT scan is then obtained with the anchoring catheters in-situ. These images are then reconstructed on the Oncentra planning system (Nucletron Elekta, Netherlands).

The images are then reoriented in Oncentra to depict the “template view”. This template view is crucial in determining where the rest of the catheters should be placed. Next, an overlying photocopy of the template on a transparency is placed on the top of the screen and the “template view” template magnification is matched 1:1 to the overlaid template transparency.

The corresponding anchoring needle positions are then marked on the overlaid transparency. Similar to the previous step, PTV-Eval contour and the chest wall contour are also outlined to the transparency. Once done, the rest of the catheter placement can be easily determined.

Once the catheters are placed, they are then replaced with plastic catheters to ensure patient’s comfort. The blind end is flushed to the skin while the other end is trimmed to size. A numbered button is then heat-sealed to secure the other end of the catheter.

In general, any catheter within the PTV-Eval needs to be inserted. For the catheters out of the PTV-Eval, if they are within 1 cm of the PTVEval contour, they would need to be inserted as well. By using this method, one can easily determine the exact number of catheters required to cover the PTV-Eval volume and avoid under or over insertion of catheters. For cosmetic reason, it is worthwhile to avoid placing catheters outside of the patient’s low cut dress neckline so that the catheters cannot be seen when a low cut dress is worn. If the catheters protrude out into the neckline area, the best recommended measure is to manually reside the entry point of the catheter to below the neckline without compromising the dosimetric coverage. Treatment delivery of the radioactive 192-Iridium source is via an after-loader machine which is remotely controlled. On the day of the treatment, the patient’s catheters are connected to the after-loader using special tubes. This is a safety mechanism to ensure that there is no chance that the radioactive source may be left in the patient. Contrary to popular belief, as the radioactive source is never in the patient, the patient is not radioactive and is free to carry babies or be around pregnant women.

Multi-catheter APBI offers favourable longterm cosmetic results with little residual evidence of catheter implantation. Unlike EBRT treatment where there is about 5% chance of long-term skin pigmentation and fibrosis from radiation skin fibrosis, patients with multi-catheter APBI do not experience this, which may result in higher patient satisfaction.

Special advantages of multi-catheter APBI

Augmented breast implant patients For patients with augmented breast implants and are diagnosed with early stage breast cancer, mastectomy is currently the only option. Having mastectomy would defeat their purpose of undergoing augmentation in the first place as majority of the patients would want to retain their breasts for various reasons. Multi-catheter APBI now offers this group of patients the chance of breast conserving treatment, allowing them to undergo adjuvant radiotherapy, conserving their breast, and avoiding a mastectomy. Done under image guidance, the chance of puncturing the breast implants using the multi-catheter APBI template technique will be low. In contrast, EBRT cannot achieve such conformal dose distribution, leading to contracture of the silicone capsule and skin fibrosis from the radiation dermatitis.

Conclusion

There is a new paradigm shift for a shorter yet effective radiotherapy treatment for early stage breast cancer. In selected patients, multi-catheter APBI is an effective alternative to conventional EBRT treatment, offering shorter overall treatment duration of five days, equivalent efficacy, and yet offering better toxicity profile. Increasing both physicians’ and patients’ awareness of such treatment options would thus lead to more informed decisions and better patient overall satisfaction about their treatment choice without compromising on treatment outcomes.

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