Skin-sparing effect occurs during photon irradiation of materials.
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Scientific literature and reference entries confirm that high-energy photon and megavoltage radiation exhibit a skin-sparing effect due to charged particle equilibrium build-up at air-tissue interfaces.
Introduction: Radiation-induced dermatitis (RID) is a common adverse effect of radiation therapy, in spite of skin-sparing effect of megavoltage. Approximately 90% of the patients who received radiation therapy may develop skin reaction of any grade during therapy, leading to therapy delays, diminution of patients' health state, and quality of life. It has been noticed by many authors that there are several topical agents available which may be used for the prevention of RID. In this study, we used topical Aloe vera gel for the treatment of high-grade radiation dermatitis. Materials and Methods: This prospective study was conducted on 85 patients of head and neck, breast, and cervical cancer during 2015–2016. All the patients have received external beam radiotherapy by cobalt-60, at least 46 Gy (dose completed with high-dose rate brachytherapy in cancer cervix). According to the Radiation Therapy Oncology Group skin reaction grading, patients with Grade III and Grade IV skin reaction were advised to use A. vera gel on irradiated area thrice daily with routine skin and nursing care. Results: In this study, head and neck cancer patients were 42%, breast 23%, and cervical 35%. Sixty-seven percent were female and 33% were male patients. The median age of the patients was 43.3 years (range, 25–70 years). The prescribed radiation doses were 46–70 Gy, 2 Gy per fraction, for treatment duration of 32–52 days, using a field size of 80–380 cm2 according to the treatment site. Of 85 patients, 65 were treated with concurrent weekly chemotherapy. Grade III (65.8%) and Grade IV (34.1%) dermatitis occurred in the 5th week of radiotherapy, which causes treatment delay, ranging 2–10 days, according to the severity and patient-related factors. It has been noticed that after application of A. vera gel, dermatitis completely recovered within 3–7 days. The recovery time was prolonged in operated versus nonoperated patients of head and neck cancer. Conclusion: Rapid cell division in the skin leads to RID. 35%–40% of dose is received by the skin despite skin-sparing effect of megavoltage, and it increases in parallel opposing field. Till date, no treatment is available which can prevent RID. In our observational study, it was noticed that A. vera gel was effective in fast recovery of high-grade RID without any adverse reaction. This single-institution study is not large enough to justify its standardized use; further studies are required to establish A. vera gel as a treatment measure for RID.
Purpose Most of the breast treatments uses a megavoltage photon beams. This kind of energy exhibits a skin-sparing effect that is a concern in some stages of both breast conservative and post-mastectomy irradiation. To overwhelm this effect a bolus material is placed on the skin. However, when using commercial non-customized bolus, small air gaps can occur in certain regions of the treatment area where the bolus cannot establish the perfect match with the irregular skin of the patient, altering locally the expected skin dose. The objective of this study is to verify the improvement in the breast radiotherapy treatment using a customized bolus produced by 3D rapid manufacturing (3D-RM) techniques, and compare it with the commercial ones. Measurement of the surface dose and comparisons with the doses calculated by the Treatment Planning System (TPS) were also performed. Methods The customized 3D rapid manufactured bolus was prepared for an anthropomorphic female phantom breast area. 3D-CRT treatment plans for right breast were performed on CT scans of the phantom both with the customized and commercial bolus. The skin dose was measured in 5 points on the phantom breast surface using a MOSFET-based system. Results A better fitting to the surface of the phantom was observed for the customized bolus, reducing the air gaps and improving the daily positioning on the irregular breast surfaces. The average differences between calculated and measured doses in the customized and commercial bolus ranged from 2 to 10%. However, the highest dose difference (approximately 10%) was observed for the commercial bolus. Conclusions The 3D rapid manufactured bolus can reduce the uncertainty in the daily positioning and help to overcome the dose discrepancy due to unwanted air gaps affecting breast cancer radiation therapy. With the commercial bolus a higher dose difference relatively to TPS was observed. The skin dose increase is observed in the same proportion for both boluses.
desirable to maximize "skin-sparing" (since the relative dose to the skin is lower for such high-energy beams). Medically useful photon beams can also be derived
External beam radiation therapy (EBRT) is a form of radiotherapy that utilizes a high-energy collimated beam of ionizing radiation, from a source outside the body, to target and kill cancer cells. The radiotherapy beam is composed of particles, which are focussed in a particular direction of travel using collimators. Each radiotherapy beam consists of one type of particle intended for use in treat
Very low-energy superficial X-rays – 35 to 60 keV (mammography, which prioritizes soft-tissue contrast, uses very low-energy kV X-rays)
Superficial radiotherapy X-rays – 60 to 150 keV
Diagnostic X-rays – 20 to 150 keV (mammography to CT); this is the range of photon energies at which the photoelectric effect, which gives maximal soft-tissue contrast, predominates.
Orthovoltage X-rays – 200 to 500 keV
Supervoltage X-rays – 500 to 1000 keV
Megavoltage X-rays – 1 to 25 MeV (in practice, nominal energies above 15 MeV are unusual in clinical practice).
Megavoltage X-rays are by far most common in radiotherapy for the treatment of a wide range of cancers. Superficial and orthovoltage X-rays have application for the treatment of cancers at or close to the skin surface. Typically, higher-energy megavoltage X-rays are chosen when it is desirable to maximize "skin-sparing" (since the relative dose to the skin is lower for such high-energy beams).
Medically useful photon beams can also be derived from a radioactive source such as iridium-192, caesium-137, or cobalt-60. (Radium-226 has also been used as such a source in the past, though has been replaced in this capacity by less harmful radioisotopes.) Such photon beams, derived…
Perturbations of charged particle equilibrium (CPE) at interfaces of materials of different atomic composition can lead to considerable differences in the energy deposition by photons and neutrons. Specific examples of these interface perturbations are encountered during irradiation of body cavities and soft tissue adjacent to bone or metallic implants and irradiation of cells in monolayer on the bottom of culture dishes. Another example is the build-up of CPE at air-tissue interfaces, referred to in radiotherapy as the skin sparing effect. For photon irradiation excess production of secondary electrons in high-Z materials, such as glass, bone or gold, will induce appreciably higher doses and decreased cell survival compared to the equilibrium situation. The energy dissipation of fast neutrons in biological materials occurs through recoil protons, heavy recoil nuclei and products of nuclear reactions. Owing to the large contribution from recoil protons to the neutron kerma, the hydrogen content of the biological material mainly determines the energy deposition. For neutron irradiation of cells in monolayer, CPE can be established or deliberately avoided by mounting tissue-equivalent plastic or carbon discs in front of the cells, respectively. This approach makes it possible to distinguish the biological effects of the low- and high-LET radiation components.
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