The influence of patient geometry on the selection of chest wall irradiation techniques in post-mastectomy breast cancer patients

Electron arc therapy for bilateral chest wall irradiation: treatment planning and dosimetric study

AIMS

The treatment of patients with synchronous bilateral breast cancer is a challenge. We present a report of dosimetric data of patients with bilateral chest walls as the target treated with electron arc therapy.

MATERIALS AND METHODS

Ten consecutive patients who had undergone electron arc therapy to the bilateral chest wall for breast cancer were analysed. After positioning and immobilisation, patients underwent computed tomography scans from the neck to the upper abdomen. Electron arc plans were generated using the PLATO RTS (V1.8.2 Nucletron) treatment planning system. Electron energy was chosen depending upon the depth and thickness of the planning target volume (PTV). For all patients, the arc angle ranged between 80 and 280° (start angle 80°, stop angle 280°). The homogeneity index, coverage index and doses to organs at risk were evaluated. The patient-specific output factor and thermoluminescence dosimetry (TLD) measurements were carried out for all patients. The total planned dose to the PTV was 50Gy/25 fractions/5 weeks.

RESULTS

The mean PTV (± standard deviation) was 568.9 (±116)cm(3). The mean PTV coverage was 89 (±5.8)% of the prescribed dose. For the right lung, the mean values of D(1) and D(10) were 46 (±7.6) and 30 (±9)Gy, respectively. For the left lung, the mean values of D(1) and D(10) were 45 (±7) and 27 (±8)Gy, respectively. For the heart, the mean values of D(1), D(5) and D(10) were 21 (±15), 13.5 (±12) and 9 (±9)Gy, respectively. The mean values of TLD at various pre-specified locations on the chest wall surface were 1.84, 1.82, 1.82, 1.89 and 1.78Gy, respectively

CONCLUSION

The electron arc technique for treating the bilateral chest wall is a feasible and pragmatic technique. This technique has the twin advantages of adequate coverage of the target volume and sparing of adjacent normal structures. However, compared with other techniques, it needs a firm quality assurance protocol for dosimetry and treatment delivery.

Feasibility of breast conservation after neoadjuvant taxene based chemotherapy in locally advanced breast cancer: a Prospective Phase I trial

BACKGROUND

Neoadjuvant chemotherapy is the standard care for locally advanced breast cancer. Our study aimed at evaluating the feasibility of breast conversation surgery (BCS) after neoadjuvant chemotherapy.

PATIENTS AND METHODS

Forty five patients had stage IIB (except those with T2N1 disease) and stage IIIA were selected to 3 cycles taxane-based neoadjuvant chemotherapy. Patient who had tumours ≤5 cm underwent a tentative BCS while patients who had tumour size >5 cm underwent radical surgery. Negative margin is essential for BCS. Adjuvant chemotherapy and 3-D radiotherapy ± hormonal treatment were given to all patients.

RESULTS

Thirty four patients had BCS. Response to chemotherapy was the only statistically significant factor which influences the BCS. Incidence of local recurrence was 5.9% for patients who had BCS at a median follow up 24 months.

CONCLUSION

Breast conservation is feasible in selected cases of locally advanced, non metastatic cancer breast. We recommend that patients who have tumour size ≤4 cm after chemotherapy are the best candidates for BCS.

Recommendations for clinical electron beam dosimetry: supplement to the recommendations of Task Group 25

The goal of Task Group 25 (TG-25) of the Radiation Therapy Committee of the American Association of.Physicists in Medicine (AAPM) was to provide a methodology and set of procedures for a medical physicist performing clinical electron beam dosimetry in the nominal energy range of 5-25 MeV. Specifically, the task group recommended procedures for acquiring basic information required for acceptance testing and treatment planning of new accelerators with therapeutic electron beams. Since the publication of the TG-25 report, significant advances have taken place in the field of electron beam dosimetry, the most significant being that primary standards laboratories around the world have shifted from calibration standards based on exposure or air kerma to standards based on absorbed dose to water. The AAPM has published a new calibration protocol, TG-51, for the calibration of high-energy photon and electron beams. The formalism and dosimetry procedures recommended in this protocol are based on the absorbed dose to water calibration coefficient of an ionization chamber at 60Co energy, N60Co(D,w), together with the theoretical beam quality conversion coefficient k(Q) for the determination of absorbed dose to water in high-energy photon and electron beams. Task Group 70 was charged to reassess and update the recommendations in TG-25 to bring them into alignment with report TG-51 and to recommend new methodologies and procedures that would allow the practicing medical physicist to initiate and continue a high quality program in clinical electron beam dosimetry. This TG-70 report is a supplement to the TG-25 report and enhances the TG-25 report by including new topics and topics that were not covered in depth in the TG-25 report. These topics include procedures for obtaining data to commission a treatment planning computer, determining dose in irregularly shaped electron fields, and commissioning of sophisticated special procedures using high-energy electron beams. The use of radiochromic film for electrons is addressed, and radiographic film that is no longer available has been replaced by film that is available. Realistic stopping-power data are incorporated when appropriate along with enhanced tables of electron fluence data. A larger list of clinical applications of electron beams is included in the full TG-70 report available at http://www.aapm.org/pubs/reports. Descriptions of the techniques in the clinical sections are not exhaustive but do describe key elements of the procedures and how to initiate these programs in the clinic. There have been no major changes since the TG-25 report relating to flatness and symmetry, surface dose, use of thermoluminescent dosimeters or diodes, virtual source position designation, air gap corrections, oblique incidence, or corrections for inhomogeneities. Thus these topics are not addressed in the TG-70 report.

Evaluation of skin dose associated with different frequencies of bolus applications in post-mastectomy three-dimensional conformal radiotherapy

Background

The study aimed to calculate chest-wall skin dose associated with different frequencies of bolus applications in post-mastectomy three-dimensional conformal radiotherapy (3D-CRT) and to provide detailed information in the selection of an appropriate bolus regimen in this clinical setting.

Methods

CT-Simulation scans of 22 post-mastectomy patients were used. Chest wall for clinical target volume (CTV) and a volume including 2-mm surface thickness of the chest wall for skin structures were delineated. Precise PLAN 2.11 treatment planning system (TPS) was used for 3D-CRT planning. 50 Gy in 25 fractions were prescribed using tangential fields and 6-MV photons. Six different frequencies of bolus applications (0, 5, 10, 15, 20, and 25) were administered. Cumulative dose-volume histograms were generated for each bolus regimen. The minimum, maximum and mean skin doses associated with the bolus regimens were compared. To test the accuracy of TPS dose calculations, experimental measurements were performed using EBT gafchromic films.

Results

The mean, minimum and maximum skin doses were significantly increased with increasing days of bolus applications (p < 0.001). The minimum skin doses for 0, 5, 10, 15, 20, and 25 days of bolus applications were 73.0% ± 2.0%, 78.2% ± 2.0%, 83.3% ± 1.7%, 88.3% ± 1.6%, 92.2% ± 1.7%, and 93.8% ± 1.8%, respectively. The minimum skin dose increments between 20 and 25 (1.6% ± 1.0%), and 15 and 20 (4.0% ± 1.0%) days of bolus applications were significantly lower than the dose increments between 0 and 5 (5.2% ± 0.6%), 5 and 10 (5.1% ± 0.8%), and 10 and 15 (4.9% ± 0.8%) days of bolus applications (p < 0.001). The maximum skin doses for 0, 5, 10, 15, 20, and 25 days of bolus applications were 110.1% ± 1.1%, 110.3% ± 1.1%, 110.5% ± 1.2%, 110.8% ± 1.3%, 111.2% ± 1.5%, and 112.2% ± 1.7%, respectively. The maximum skin dose increments between 20 and 25 (1.0% ± 0.6%), and 15 and 20 (0.4% ± 0.3%) days of bolus applications were significantly higher than the dose increments between 0 and 5 (0.2% ± 0.2%), 5 and 10 (0.2% ± 0.2%), and 10 and 15 (0.2% ± 0.2%) days of bolus applications (p ≤ 0.003). The TPS overestimated the near-surface dose 10.8% at 2-mm below the skin surface.

Conclusion

In post-mastectomy 3D-CRT, using a 1-cm thick bolus in up to 15 of the total 25 fractions increased minimum skin doses with a tolerable increase in maximum doses.

CT planning for breast cancer

Radiotherapy to the affected breast or chest wall is well established as an integral part of postoperative management of breast cancer. However, it is known to be associated with increased cardiac and pulmonary morbidities and mortalities. Modern technologies, such as CT planning, have shown to improve treatment planning by accurately delivering optimal doses to the target volumes, while minimizing doses to sensitive structures, thus reducing potential treatment-related adverse effects. The purpose of this study is to report on our experiences with CT planning of adjuvant radiotherapy for breast cancer.

Critical appraisal of treatment techniques based on conventional photon beams, intensity modulated photon beams and proton beams for therapy of intact breast

PURPOSE

To analyse different treatment techniques with conventional photon beams, intensity modulated photon beams, and proton beams for intact breast irradiation for patients in whom conventional irradiation would cause potentially dangerous lung irradiation.

MATERIALS AND METHODS

Five breast cancer patients with highly concave breast tissue volume around the lung were considered at planning level in order to assess the suitability of different irradiation techniques. Three-dimensional dose distributions for conventional two-field tangential photon treatment, two-field intensity modulated radiotherapy (IMRT), three-field non-IMRT, three-field IMRT, and single-field proton treatment were investigated, aiming at assessing the possibility to reduce lung irradiation below risk levels. Analysis of dose-volume histograms and related physical and biological parameters (significant minimum, maximum and mean doses, conformity indexes and equivalent uniform dose (EUD)) for planned target volume (PTV) and lung was carried out. Dose plans were compared with the conventional two-field tangential photon technique.

RESULTS

PTV coverage was comparable for non-IMRT and IMRT techniques (EUD from 47.1 to 49.4 Gy), and improved with single-field proton treatment (EUD=49.8 Gy). Lung irradiation was reduced, in terms of mean dose, with three-field (9.5 Gy) and proton technique (3.5 Gy), with respect to the conventional two-field treatment (12.9 Gy); also a reduction of the lung volume irradiated at high doses was observed. Better results could be achieved with protons. In addition, cardiac irradiation was also reduced with those techniques.

CONCLUSIONS

Geometrically difficult breast cancer patients could be irradiated with a three-field non-IMRT technique thus reducing the dose to the lung which is proposed as standard for this category of patients. Intensity modulated techniques were only marginally more successful than the corresponding non-IMRT treatments, while protons offer excellent results.