Reducing scatter radiation to the contralateral breast with a mobile, conformal shield during breast cancer radiotherapy

Characterization of a novel scale maille contralateral breast shield: SMART Armor

During breast radiotherapy treatment, the contralateral breast receives radiation doses to the skin and subcutaneous tissue caused mainly from incident electron contamination and low energy photon scatter radiation. Measurements have shown that for a typical hybrid tangential treatment, these dose levels can be up to 17% of maximum applied prescription dose if no shielding is used during the treatment process. This work examined the use of different shielding metals, aluminum, copper, and lead to reduce peripheral radiation dose to evaluate the optimal metal to form the basis of a contralateral breast radiation shield. This work also shows a simple but novel method to substantially reduce this unwanted radiation dose with the use of a copper scale maille sheet which can be easily and accurately draped over a patient's contralateral breast during treatment. The copper scale maille is flexible and can thus conform around typical breast shapes. It can also form irregular shaped edges to match those outlined by typical tangential treatment fields. As the shield is made from copper, it is nontoxic and can potentially be used directly on patients for treatment. The designed copper scale maille has shown to reduce contralateral breast skin and subcutaneous dose by up to 80% for typical radiation fields used in breast radiotherapy.

Microsatellite instability analysis of bilateral breast tumors suggests treatment-related origin of some contralateral malignancies

PURPOSE

High-frequency microsatellite instability (MSI-H) occurs frequently in colorectal cancers and some other tumor types, but is very uncommon in breast cancer. In the earlier study devoted to microsatellite analysis of allelic imbalances, the authors accidentally detected several MSI-H tumors in patients with the bilateral form of breast cancer (biBC). The present study was designed to examine this unexpected phenomenon in more detail.

METHODS

All DNA samples were tested by the standard panel of MSI-specific markers BAT25, BAT26, BAT40, D5S346, and D17S250. If the tumor was unstable for at least one marker, or PCR amplification was not successful for any of the listed above loci, the analysis of additional five dinucleotide markers (D1S225, D11S4167, D22S272, D22S1166, and D3S3527) was performed. Tumors showing instability in > or = 30% loci were classified as MSI-H.

RESULTS

In biBC group, MSI-H status was detected in 6/60 (10%) contralateral tumors, but in 0/50 (0%) first malignancies (P = 0.021) and only in 1/22 (5%) synchronous biBC (P = 0.434). None of 52 unilateral breast cancers showed MSI-H status. Shifts of mononucleotide markers were revealed in four second carcinomas from biBC patients but in none of the breast tumors from other categories.

CONCLUSIONS

MSI-H is detected with a noticeable frequency in bilateral but not in unilateral breast cancers. Preferable occurrence of MSI-H in second metachronous tumors from biBC patients allows to hypothesize that the development of some contralateral breast neoplasms is casually related to the adjuvant treatment of the initial malignancy.

Shielding of the Contralateral Breast During Tangential Irradiation

The purpose of this study was to investigate both optimal and practical contralateral breast shielding during tangential irradiation in young patients. A shaped sheet of variable thickness of lead was tested on a phantom with rubber breasts, and an optimized shield was created. Testing on 18 consecutive patients 50 years or younger showed shielding consistently reduced contralateral breast dose to at least half, with small additional reduction after removal of the medial wedge. For younger patients in whom radiation exposure is of considerable concern, a simple shield of 2 mm lead thickness proved practical and effective.

Multilayer Gafchromic film detectors for breast skin dose determination in vivo

Assessment of skin dose delivered to patients from radiotherapy x-ray beams should be performed both inside and outside the prescribed treatment fields. A multilayer Gafchromic film detector which has high sensitivity for detection of radiation can be used to measure skin dose in a two-dimensional map over the skin surface if required. This is an advantage over other detectors, which only provide point dose estimates. A study of 25 patients undergoing breast irradiation was performed to analyse the ability of the multilayer detector to analyse skin dose and to assess both in-field and out-of-field radiation doses delivered during tangent field breast irradiation. Results show that the main contributor to total skin dose within the treatment field was delivered by exit dose. However, outside the field, most dose was delivered by entry beams. Patients with smaller breast separations where found, in general, to receive a higher total skin dose from entry and exiting beams at the central axis. Results also showed that a significant skin dose was delivered outside the treatment field and the main cause of this dose was from electron contamination from entry beams. The multilayer Gafchromic film detector provided adequate skin dose assessment within one fraction of treatment for in vivo results.

Esophageal cancer as second primary tumor after breast cancer radiotherapy

BACKGROUND

An increased risk of esophageal cancer has been reported in survivors of breast cancer treated with radiotherapy. This study further characterizes this association.

METHODS

Through hospital databases, 118 patients (109 men, 9 women) treated for esophageal cancer between 1985 and 1993 were identified, of whom 37 had 60 synchronous or metachronous cancers. 5 women had primary esophageal cancer after having breast cancer, and are the subjects of this case-control study.

RESULTS

All 5 women had been treated with radical mastectomy and adjuvant radiotherapy; none received chemotherapy. Their ages at the time of breast cancer ranged from 36 to 82 years; at esophageal cancer, 61 to 95 years. Time between radiotherapy and esophageal cancer varied from 13 to 31 years. All esophageal cancers were squamous cell carcinomas. Mean survival after esophageal cancer was 14.2 months.

CONCLUSIONS

Radio-induced esophageal cancer can occur as a second primary cancer in women who survive at least 1 decade after mastectomy and adjuvant radiotherapy.

Contralateral breast cancer risk

The use of breast-conserving treatment approaches for breast cancer has now become a standard option for early stage disease. Numerous randomized studies have shown medical equivalence when mastectomy is compared to lumpectomy followed by radiotherapy for the local management of this common problem. With an increased emphasis on patient involvement in the therapeutic decision making process, it is important to identify and quantify any unforeseen risks of the conservation approach. One concern that has been raised is the question of radiation- related contralateral breast cancer after breast radiotherapy. Although most studies do not show statistically significant evidence that patients treated with breast radiotherapy are at increased risk of developing contralateral breast cancer when compared to control groups treated with mastectomy alone, there are clear data showing the amount of scattered radiation absorbed by the contralateral breast during a routine course of breast radiotherapy is considerable (several Gy) and is therefore within the range where one might be concerned about radiogenic contralateral tumors. While radiation related risks of contralateral breast cancer appear to be small enough to be statistically insignificant for the majority of patients, there may exist a smaller subset which, for genetic or environmental reasons, is at special risk for scatter related second tumors. If such a group could be predicted, it would seem appropriate to offer either special counseling or special prevention procedures aimed at mitigating this second tumor risk. The use of genetic testing, detailed analysis of breast cancer family history, and the identification of patients who acquired their first breast cancer at a very early age may all be candidate screening procedures useful in identifying such at- risk groups. Since some risk mitigation strategies are convenient and easy to utilize, it makes sense to follow the classic 'ALARA' (as low as reasonably achievable) principles and to minimize scattered radiation for these special risk groups and perhaps for all patients undergoing breast radiotherapy. This paper reviews the literature on the risk of radiation- related second contralateral breast cancers.

Measurement of dose to the contralateral breast during radiation therapy for breast cancer: reduction by the use of superflab

The effect of radiation in regard to breast carcinogenesis is well studied and analysed from data from atomic bomb survivors, patients treated for acute mastitis and tuberculosis patients monitored by fluoroscopy. Therefore the radiation received by the untreated breast during breast irradiation of the other breast, is of concern to clinicians. Using thermoluminescence dosimeters, we have measured the dose received by contraleteral breast of six patients during radiation therapy. Most of the dose received will be from the collimator scatter and leakage. We investigated the effect of an absorber, superflab, in reducing the skin dose to contralateral breast. With the overlaying of a cm superflab on the breast, the skin (surface) dose could be reduced by 40-75% of its original value. This is an effective and practical method of reducing significantly the dose to contralateral breast during breast conservation therapy. Superflab can be made conveniently at low cost.