Combined Electron Beams Research Articles

Relevance of Combined Electron and Photon Beams in Radiotherapy of Head and Neck Cancers in the Era of Intensity-Modulated Radiotherapy

Introduction External beam radiotherapy (EBRT) for head and neck (H&N) cancers continues to be delivered using varied technologies, ranging from the old two-dimensional conventional radiotherapy (2DRT) techniques to the modern three-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT), and volumetric modulated arc therapy (VMAT) in different centers in India. Due to limitations of spinal cord tolerance, electron and photon beams are combined in 2DRT and 3DCRT techniques for treating nodal volume of the H&N cases. However, many centers having modern technology practice IMRT/VMAT in place of electron beams. The purpose of this study is to analyze the role of combined electron and photon beams in radiotherapy of H&N cancers and its relevance in the modern era of IMRT/VMAT.Materials and Methods Data were collected through a survey conducted on cancer centers in India where radiotherapy is being given by 2DRT, 3DCRT, and IMR/VMAT for the treatment of head and neck cancers.Results The mean percentage of H&N (H&N) cases among all cases were 39.2% (standard deviation [SD]: 14.22), out of which 16.63% (SD: 20.83) were treated with a combination of photon and electron beams and 49.73% (SD: 37.41) were treated with IMRT/VMAT. The average percentage of H&N cases of government institutes was 38.39% (SD: 14.11) and that of private institutes was 40.14% (SD: 14.11). Patients treated with photon and electron combination and IMRT/VMAT were 22.19% (SD: 11.24) and 24.05% (SD: 23.99), respectively, in government institutes, and 10.29% (SD: 11.24) and 79.09% (SD: 26.75) in private institutes.Conclusion As per this study, we conclude that despite the availability of IMRT/VMAT, a combination of electron and photon beams is still relevant in India. Since a large proportion of the patients are still treated with the electron and photon combination, it is imperative that further studies on field–junction dosimetry should be conducted to ensure accurate dose delivery.

Clinical implementation of combined modulated electron and photon beams with conventional MLC for accelerated partial breast irradiation

PurposeTo report the clinical implementation of a novel external beam radiotherapy technique for accelerated partial breast irradiation treatments based on combined electron and photon modulated beams radiotherapy (MERT+IMRT) with conventional MLC. Materials and methodsA group of patients was selected to test the viability of the technique. The prescribed dose was 38.5Gy, following a hypofractionated schema, and the structures were defined following the NSABP-B39/RTOG-0413 protocol. The plans were calculated with an in-house Monte Carlo based planning system to consider explicitly the particle interactions with the MLC. An ad-hoc breast phantom was designed for a specific QA protocol. A reduced SSD was used for electron beams. Toxicity and cosmetic effects were assessed at every follow-up visit. ResultsAll the plans achieved the dosimetric objectives and fulfilled the specific quality assurance protocol. Treatment delivery did not entail additional drawbacks for the clinical routine. Moderate or severe grade of toxicity was not reported, and the cosmetic results were comparable to those obtained with other APBI techniques. ConclusionsResults showed that MERT+IMRT with the MLC is a feasible and secure technique, and easy to be extended to other centers with the implementation of the adequate software for planning.

SU‐E‐T‐593: Outcomes and Toxicities From a Clinical Trial of APBI Using MERT+IMRT with the Same XMLC

Purpose:We present the results from a clinical trial of accelerated partial breast irradiation (APBI), using mixed modulated photon and electron beams (MERT+IMRT) with the same photon multileaf collimator (xMLC).Methods:Seven patients were enrolled in the first year of the APBI clinical trial. Patients were selected following the conditions included in the NSABP B‐39/RTOG 0413 protocol. The targets and clinically relevant normal structures were contoured on the CT images following this protocol for APBI‐EBRT. All treatments were delivered using combined modulated electron and photon beams by means of the same xMLC installed in a SIEMENS Primus linac, with a reduced SSD equal to 60 cm for electron beams. The plans were performed with a treatment planning system based on full Monte Carlo simulations, called CARMEN, developed by our group. Simultaneously, an alternative IMRT plan was calculated with the commercial TPS PINNACLE v8.0m (Philips), and both plans were compared. An ad‐hoc breast phantom with semi‐spherical geometry called NAOMI was designed for a specific QA protocol. Patients received a total dose of 38.5 Gy, delivered in 10 fractions over 5 consecutive days, with a twice‐a‐day hypofractionated schema.Follow‐up visits during 2.5 years on average were repeated at 1 month post‐treatment, every 3 months for the first year, and every 6 months for the second year. Toxicity was scored according to National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE version 3.0).Results:This APBI technique achieved high loco‐regional control rates and showed low acute toxicity (grade 1 of CTCAE) and no toxicities from first month onwards. Photographic assessment of cosmesis showed skin excellent results.Conclusion:The clinical results achieved with MERT+IMRT by using the same xMLC are comparable or even better than those obtained with other APBI techniques, thanks to a software solution without any additional equipment or specific device.

PO-0697: Clinical implementation of APBI using combined modulated electron and photon beams by means of the same MLC device

PO-0697: Clinical implementation of APBI using combined modulated electron and photon beams by means of the same MLC device

Electron Intensity Modulation with Multileaf Collimation for Mixed-beam Partial Breast Irradiation

Currently, patients undergoing partial breast irradiation are typically treated with 3-5 non-coplanar high energy photon beams. The addition of electron beams has the potential of improving target coverage and sparing of critical structures due to rapid dose falloff with depth and reduced exit dose. The purpose of this work was to explore the use of mixed-beam therapy (MBT), with combined intensity-modulated electron and photon beams in the treatment of partial breast targets. Electron fields used in MBT were modulated using the X-ray MLC without an electron applicator.

Prophylactic inguinal-femoral irradiation as an alternative to primary lymphadenectomy in treatment of vulvar carcinoma

In a complete geographic series of 294 cases of primary vulvar carcinomas prophylactic inguinal-femoral irradiation was used as a standard postoperative therapy. Inguinal lymph node dissection was performed in only 27 cases (9%) and was not part of the standard surgery. The histology was squamous cell carcinoma in 269 cases (92%). The primary surgery was total vulvectomy, partial vulvectomy, or local resection of the tumor. The main type of radiotherapy was adjuvant inguinal irradiation. Two separate, symmetrical and rectangular inguinal fields were irradiated with combined photon and electron beams. In the complete series 127 recurrences (43%) were recorded. Local (24%) and regional recurrences (19%) were most frequent. Type of surgery was not associated with the risk of tumor recurrence. The 5-year overall survival rate was 53% and the relapse-free survival (RFS) rate was 55%. Tumor grade was significantly (P=0.007) associated with the RFS. The inguinal RFS rate was 75% both for patients treated with adjuvant inguinal irradiation without lymphadenectomy and patients treated with primary lymph adenectomy +/- inguinal irradiation. Postoperative complications were recorded in 22%. Postoperative complications occurred most frequently in the subgroup undergoing inguinal lymphadenectomy. Chronic lymph edemas were the most serious late tissue reactions.

Optimization of combined electron and photon beams for breast cancer

Recently, intensity-modulated radiation therapy and modulated electron radiotherapy have gathered a growing interest for the treatment of breast and head and neck tumours. In this work, we carried out a study to combine electron and photon beams to achieve differential dose distributions for multiple target volumes simultaneously. A Monte Carlo based treatment planning system was investigated, which consists of a set of software tools to perform accurate dose calculation, treatment optimization, leaf sequencing and plan analysis. We compared breast treatment plans generated using this home-grown optimization and dose calculation software for different treatment techniques. Five different planning techniques have been developed for this study based on a standard photon beam whole breast treatment and an electron beam tumour bed cone down. Technique 1 includes two 6 MV tangential wedged photon beams followed by an anterior boost electron field. Technique 2 includes two 6 MV tangential intensity-modulated photon beams and the same boost electron field. Technique 3 optimizes two intensity-modulated photon beams based on a boost electron field. Technique 4 optimizes two intensity-modulated photon beams and the weight of the boost electron field. Technique 5 combines two intensity-modulated photon beams with an intensity-modulated electron field. Our results show that technique 2 can reduce hot spots both in the breast and the tumour bed compared to technique 1 (dose inhomogeneity is reduced from 34% to 28% for the target). Techniques 3, 4 and 5 can deliver a more homogeneous dose distribution to the target (with dose inhomogeneities for the target of 22%, 20% and 9%, respectively). In many cases techniques 3, 4 and 5 can reduce the dose to the lung and heart. It is concluded that combined photon and electron beam therapy may be advantageous for treating breast cancer compared to conventional treatment techniques using tangential wedged photon beams followed by a boost electron field.

Electron Wedges for Radiation Therapy

Purpose: Brain tumors can be advantageously treated with electron over photon radiation, by exploiting the rapid fall-off in dose with depth. This advantage could be further enhanced by utilizing multiple electron beams. However, in some beam configurations, wedged dose profiles would be necessary for the dose uniformity. Unlike photons, shaped pieces of material placed in electron beam severely degrade the energy, give additional scattering and, therefore, are suboptimal. The purpose of this study was to create wedged electron fields, using intensity modulation. The combination of electron wedges enables a more uniform coverage of brain tumors with a reduced dose to normal tissue. Methods and Materials: Intensity modulation was performed for 10 to 50 MeV electrons using a narrow scanning elementary beam of a racetrack Microtron accelerator, delivering radiation pulses with coordinates and intensities prescribed by a custom scan matrix. Dispensing more pulses (or longer pulses) within the field to increase the local dose, one can sharpen the penumbra at depth and generate wedged dose distributions of arbitrary angle as well as many other desired profiles. We modulated the electron beams, measured dose distributions using film in an anthropomorphic phantom, and compared the results with conventional techniques. Results: Intensity modulation of electron beams decreases the 50–90% penumbra at depth by 40% and increases the flatness by 80%. Wedged profiles at depth can be created for any angle up to about 70°, depending on the beam energy. Multiple modulated electron beams give smaller 20–70% but larger 70–100% isodose regions than photon beams. Conclusions: Electron beams can improve dose distributions in brain compared to the same number of photon beams, reducing the 20–70% isodoses region in normal tissue by 30%. Intensity modulation significantly improves the dose distribution from combined electron beams providing a sharper penumbra, better conformity, and reduced margin.

Physical aspects of external beam radiotherapy for the treatment of malignant pleural mesothelioma

The optimization of radiotherapy for the treatment of malignant mesothelioma highlights many of the currently outstanding problems in clinical radiation physics. The experimental investigation of an intuitively attractive irradiation technique with combined photon and electron beams using a specially constructed phantom has established that, due to the penetration in low density material of both primary electrons and those secondary to photon irradiation, the normal lung tissue is not spared to any significant degree by such a technique. Furthermore, great care needs to be exercised in the treatment planning calculations for this approach if absolute dosimetry errors as large as 50% are to be avoided.

Results of irradiation in the squamous cell carcinomas of the anterior faucial pillar-retromolar trigone.

Between January 1966 and August 1981, 159 patients with previously untreated squamous cell carcinomas of the anterior faucial pillar or retromolar trigone received definitive radiation therapy at The University of Texas M. D. Anderson Hospital and Tumor Institute. All except 11 patients were treated by external radiation including combination of electron beams with high-energy photons or 60Co to doses ranging from 60 Gy to 75 Gy. In the N0 patients, as a rule, only the ipsilateral subdigastric nodes were treated electively to a dose of 50 Gy. The 5-year determinate survival rate for the overall group was 83%. The cumulative recurrence rate showed that 92% of the patients had recurrence by 2 years. Therefore, all patients except those who died with no evidence of local disease less than 2 years after treatment were evaluated for local control. The failure rate for the evaluable patients was 29% for T1 lesions, 30% for T2 lesions, 24% for T3 lesions, and 40% for T4 lesions. After salvage surgery, which consisted of intraoral resection in one-third of the patients and of a composite operation in the other two-thirds, the ultimate failure rate was 0% for T1 lesions, 6% for T2 lesions, 8% for T3 lesions, and 20% for T4 lesions. Whereas stage was a poor indicator for treatment outcome, there was a significantly higher failure rate for infiltrative and/or ulcerated lesions (35%) than for exophytic or superficial lesions (15%). Histologic grade was of no prognostic significance, nor was there any significant difference in the failure rate for lesions originating on the anterior faucial pillar versus that for lesions on the retromolar trigone. Following radiotherapy, 30% of the patients developed some degree of bone exposure but only 5.6% (9 patients) required a segmental mandibular resection. The probability of bone exposure was not dose related and more likely reflected tumor location on the mucoperiosteum. Of the whole group, 16 patients (10%) experienced a neck failure with 8 ultimate failures after salvage surgery. Among the 16 patients who had neck failures, 13 were originally staged N0; 6 of these patients had failures that occurred in the electively treated ipsilateral subdigastric area, but the field was too small to cover the nodes adequately. Aspects of the radiotherapy techniques with combined electron and photon beams that may influence the treatment outcome are discussed.

Proposal for a magnetic-film memory accessed by combined photon and electron beams

A magnetic-film memory accessed by combined photon and electron beams is proposed. The electron beam is used to heat a selected bit, which results in lowering the switching threshold so that information can be written selectively into that bit by means of an external magnetic field. Reading is accomplished by simultaneously illuminating a bit with an electron and a photon beam. Then a thermally modulated magnetic-optical signal is generated by intensity modulation of the electron beam. This arrangement is advantageous since a high-resolution photon beam and photon deflector are not required. The frequency response for thermally modulating a 1-μm bit is calculated to be ∼500 MHz; the necessary temperature dependence of the magneto-optical coefficient and the coercive force can be obtained by using composite films made from layers having different Curie points. Various magneto-optical configurations are readily devised which yield the value of a bit (one or zero) in terms of the phase (0 or π) between the magneto-optical signal and the electron-beam intensity modulation. The shot noise limited signal-to-noise ratio (SNR) is determined by heating of a bit from the photon beam. It is calculated that for a low-loss magnetooptical material such as EuO a 1-μm bit can be read in 1 μs when illuminated with a 1000-μm photon beam. The base-line temperature rise due to heating from the photon beam can be kept small by using narrow pulses of light (width \sim10^{-11} second), as, for example, from a mode-locked laser.