Use of an electron spoiler for radiation treatment of surface skin diseases

Evaluation of Therapeutic Properties of a Low Energy Electron Beam Plus Spoiler for Local Treatment of Mycosis Fungoides: A Monte Carlo Study

Background:

When using low-energy electron beams for the treatment of skin lesions, such as Mycosis Fungoides (MF), a beam spoiler is used to decrease electron therapeutic depth (R₉₀) while increasing the surface dose.

Objective:

The aim of this study was to evaluate the characteristics of a 5 MeV electron beam when using a spoiler for the local treatment of MF skin lesions by Monte Carlo (MC) simulation.

Material and Methods:

In this experimental study, a Siemens Primus treatment head and an acrylic spoiler, positioned at the end of applicator, were simulated using BEAMnrc, an EGSnrc user code. The modelled beam was validated by measurement using MP3-M water tank, Roos parallel plate chamber and Semi flex Chamber-31013 (all from PTW, Freiburg, Germany). For different spoiler thicknesses, dose distributions in water were calculated for 2 field sizes and were compared to those for the corresponding open fields.

Results:

For a 1.3 cm spoiler, therapeutic range changed from 1.5 cm (open field) to 0.5 cm and 0.4 cm for 10 × 10 cm² and 20 × 20 cm² field sizes, respectively. Maximum increase in penumbra width was 2.8 and 3.8 cm for 10 × 10 cm² and 20 × 20 cm² field sizes, respectively. Maximum increase in bremsstrahlung contamination was %2 in both field sizes.

Conclusion:

R₉₀ decreased exponentially with increase in spoiler thickness. The effect of field size on penumbra was much larger for spoiled beam compared to the open beam. The results of this research can be applied to optimize the radiation treatment of MF patients in our hospital.

Design and Implementation of a Monte Carlo Framework for Assessment of Spoiler Applications in Abutting Electron Fields

Background:

Field matching problems in abutting electron fields can be managed by using spoilers.

Objective:

The aim of this study was to design a Monte Carlo framework for the assessment of spoiler application in abutting electron fields.

Material and Methods:

In this experimental study, a Siemens Primus treatment head was simulated for a 5 MeV electron beam using BEAMnrc, DOSXYZnrc and EGSnrc user codes. Validation of beam model was done by measurement using a MP3-M water tank and a Semi-flex Chamber-31010 (PTW, Freiburg, Germany). An in-house routine was developed to calculate the combined isodose curves resulting from simulated adjacent fields. The developed framework was analyzed using PMMA and chromium spoilers.

Results:

The penumbra width increased from 27.5 mm for open fields to 42 mm for PMMA and 40 mm for chromium. The maximum junction dose reduced from 115% for open fields to 107% for PMMA and 108% for chromium. R₉₀ reduced about 6 mm for PMMA and 3 mm for chromium. Uniformity index reduced from 93% to 77% for both spoilers. Surface dose increased from 79% to 89% for PMMA and 88% for chromium.

Conclusion:

Using spoilers, penumbra width at the surface was increased, size and depth of hot spots as well as the therapeutic range were reduced and dose homogeneity at the junction of abutting electron fields was improved. For both spoilers, the uniformity index reduced, and surface percent dose increased. The results of this research can be used to optimize dose distribution in electron beam treatment using abutting fields.

Clinical implementation of a wide-field electron arc technique with a scatterer for widespread Kaposi's sarcoma in the distal extremities

A novel wide-field electron arc technique with a scatterer is implemented for widespread Kaposi's sarcoma (KS) in the distal extremities. Monte Carlo beam modeling for electron arc beams was established to achieve <2% deviation from the measurements, and used for dose calculation. MC-based electron arc plan was performed using CT images of a foot and leg mimicking phantom and compared with in-vivo measurement data. We enrolled one patient with recurrent KS on the lower extremities who had been treated with photon radiation therapy. The 4- and 6-MeV electron arc plans were created, and then compared to two photon plans: two opposite photon beam and volumetric modulated arc with bolus. Compared to the two photon techniques, the electron arc plans resulted in superior dose saving to normal organs beneath the skin region, although it shows inferior coverage and homogeneity for PTV. The electron arc treatment technique with scatterer was successfully implemented for the treatment of widespread KS in the distal extremities with lower radiation exposure to the normal organs beyond the skin lesions, which could be a treatment option for recurrent skin cancer in the extremities.

Adjuvance in refractory keloids using electron beams with a spoiler: Recent results

AIM

To present clinical results of adjuvant irradiation of excised refractory keloid wounds using a novel bolus-free technique developed within our group to irradiate the skin surface with a linear accelerator.

BACKGROUND

The use of a bolus to increase surface dose over a newly excised keloid presents several problems. Previous solutions are unsatisfactory. Our technique is promising but needs to be evaluated in practice.

MATERIALS AND METHODS

Twenty refractory skin keloids in 19 patients were excised and irradiated in Hospital Plató (Barcelona, Spain) using a 6 MeV electron beam with a 4-mm aluminium spoiler. 15 Gy in fractions of 3 Gy were delivered to the excision site plus a safety margin. All patients were examined during the follow-up (median: 40 months, interval: 12-68 months) and toxicities were recovered.

RESULTS

At the end of the follow-up period, 76% of the cases had not recurred, while the complete response rate amounted to 53%. Residual hypertrophic scars were classified as partial responses. After therapy, itching and pain were observed in 30% of the patients, as well as one telangiectasia and two hyperchromatic scars.

CONCLUSION

Our technique avoids using a bolus while combining the benefits of electron beam therapy in keloids (fewer secondary effects, and fewer and shorter treatments) with a dose deposition adequate for skin surface treatments. Our results are in line with the most successful therapies evaluated in the literature, as secondary effects are acceptable and recurrence rates are low.