Radiation Therapy Medical Physics Review – Delivery, Interactions, Safety, Feasibility, and Head to Head Comparisons of the Leading Radiation Therapy Techniques

Radiation therapy uses high energy radiation to kill cancer cells. Radiation therapy for cancer treatment can take the form of photon therapy (using x-rays and gamma rays), or charged particle therapy including proton therapy and electron therapy. Within these categories, numerous methods of delivery have been developed. For example, a certain type of radiation can be administered by a machine outside of the body, called external-beam radiation therapy, or by a “seed” placed inside of the body near cancer cells, called internal radiation therapy or brachytherapy. Approximately half of all cancer patients receive radiation therapy, and the form of radiation treatment depends on the type of tumor, location of the tumor, available resources, and characteristics of the individual receiving treatment. In the current paper, we discuss and review the various forms of radiation therapy, the physics behind these treatments, the effectiveness of each treatment type compared with the others, the latest research on radiation therapy treatment, and future research directions. We found that proton therapy is the most promising and effective form of radiation therapy, with photon methods such as intensity modulated radiation therapy, 3D-conformal radiation therapy, image guided radiation therapy, and volumetric modulated radiation therapy also showing very good comparative performance

Radiation therapy for primary carcinoma of the extrahepatic biliary system. An analysis of 63 cases.

From 1976 to 1988, 63 patients received radiation therapy for primary cancers of the extrahepatic biliary system (eight gallbladder and 55 extrahepatic biliary duct). Twelve patients underwent orthotopic liver transplantation. Chemotherapy was administered to 13 patients. Three patients underwent intraluminal brachytherapy alone (range, 28 to 55 Gy). Sixty patients received megavoltage external-beam radiation therapy (range, 5.4 to 61.6 Gy; median, 45 Gy), of whom nine received additional intraluminal brachytherapy (range, 14 to 45 Gy; median, 30 Gy). The median survival of all patients was 7 months. Sixty patients died, all within 39 months of radiation therapy. One patient is alive 11 months after irradiation without surgical resection, and two are alive 50 months after liver transplantation and irradiation. Symptomatic duodenal ulcers developed after radiation therapy in seven patients but were not significantly related to any clinical variable tested. Extrahepatic biliary duct cancers, the absence of metastases, increasing calendar year of treatment, and liver transplantation with postoperative radiation therapy were factors significantly associated with improved survival

Expanding the use of real-time electromagnetic tracking in radiation oncology.

In the past 10 years, techniques to improve radiotherapy delivery, such as intensity-modulated radiation therapy (IMRT), image-guided radiation therapy (IGRT) for both inter- and intrafraction tumor localization, and hypofractionated delivery techniques such as stereotactic body radiation therapy (SBRT), have evolved tremendously. This review article focuses on only one part of that evolution, electromagnetic tracking in radiation therapy. Electromagnetic tracking is still a growing technology in radiation oncology and, as such, the clinical applications are limited, the expense is high, and the reimbursement is insufficient to cover these costs. At the same time, current experience with electromagnetic tracking applied to various clinical tumor sites indicates that the potential benefits of electromagnetic tracking could be significant for patients receiving radiation therapy. Daily use of these tracking systems is minimally invasive and delivers no additional ionizing radiation to the patient, and these systems can provide explicit tumor motion data. Although there are a number of technical and fiscal issues that need to be addressed, electromagnetic tracking systems are expected to play a continued role in improving the precision of radiation delivery

Radiation induced lichen planus - an uncommon side effect

Cutaneous lichen planus is classically characterized by violaceous, pruritic, planar papules and plaques, most commonly affecting the extremities. Lichen planus following radiation therapy is extremely rare and lichen planus following radiation therapy for prostate carcinoma has not been previously reported in the literature. We report a 66-year-old man who presented to the dermatology clinic with a symmetric pruritic eruption affecting the pelvic and gluteal region within two months of radiation therapy targeting the prostate and pelvic lymph nodes for prostate adenocarcinoma. The patient did not have a prior history of lichen planus. Physical examination demonstrated well demarcated, violaceous papules and plaques in a circumferential band-like distribution on the bilateral gluteal, lumbosacral, and pelvic region. In addition, he had a few discrete lesions on the calves and dorsal feet. Punch biopsy revealed an acanthotic epidermis with "saw-tooth" rete ridges and a lichenoid inflammatory infiltrate. A diagnosis of hypertrophic lichen planus was made, reinforcing the importance for clinicians to recognize radiation therapy as a risk factor for developing lichen planus despite no prior history of lichen planus

Response to “Radiation Therapeutic Gain and Asian Botanicals,” by Stephen Sagar

Numerous botanical agents, many of which are used in whole medical system practices (i.e. traditional Chinese medicine, Ayurvedic medicine, etc.), have been shown to exhibit radiomodifying effects on tumors and normal tissues in-vitro and invivo studies. Some of these agents can enhance the therapeutic gain of radiation therapy by either acting as a radiosensitizer to tumor cells and/or as a radioprotector to normal cells. Botanical agents are comprised of multiple phytochemical compounds that may work individually or synergistically to not only improve radiation therapy outcomes, but may also exhibit a variety of anti-cancer effects as well. It will be important to evaluate these botanicals for efficacy, tumor specificity, and safety profiles before they can be recommended during radiation therapy

Eccrine poromatosis following chemotherapy and radiation therapy

Eccrine poroma presents as a single, symptomless erythematous papule in areas with a high density of eccrine sweat glands. Although rare, eccrine poromas can present as multiple lesions, otherwise known as eccrine poromatosis. The etiology of eccrine poromatosis is unclear. We present two cases of eccrine poromatosis in patients who had undergone chemotherapy, radiation therapy, and stem cell transplant. This case report serves to raise awareness of this condition and highlight its association with malignancies and their treatment

Effect of variations in atelectasis on tumor displacement during radiation therapy for locally advanced lung cancer

Purpose Atelectasis (AT), or collapsed lung, is frequently associated with central lung tumors. We investigated the variation of atelectasis volumes during radiation therapy and analyzed the effect of AT volume changes on the reproducibility of the primary tumor (PT) position. Methods and materials Twelve patients with lung cancer who had AT and 10 patients without AT underwent repeated 4-dimensional fan beam computed tomography (CT) scans during radiation therapy per protocols that were approved by the institutional review board. Interfraction volume changes of AT and PT were correlated with PT displacements relative to bony anatomy using both a bounding box (BB) method and change in center of mass (COM). Linear regression modeling was used to determine whether PT and AT volume changes were independently associated with PT displacement. PT displacement was compared between patients with and without AT. Results The mean initial AT volume on the planning CT was 189 cm3 (37-513 cm3), and the mean PT volume was 93 cm3 (12-176 cm3). During radiation therapy, AT and PT volumes decreased on average 136.7 cm3 (20-369 cm3) for AT and 40 cm3 (−7 to 131 cm3) for PT. Eighty-three percent of patients with AT had at least one unidirectional PT shift that was greater than 0.5 cm outside of the initial BB during treatment. In patients with AT, the maximum PT COM shift was ≥0.5 cm in all patients and \u3e1 cm in 58% of patients (0.5-2.4 cm). Changes in PT and AT volumes were independently associated with PT displacement (P \u3c .01), and the correlation was smaller with COM (R2 = 0.58) compared with the BB method (R2 = 0.80). The median root mean squared PT displacement with the BB method was significantly less for patients without AT (0.45 cm) compared with those with AT (0.8cm, P = .002). Conclusions Changes in AT and PT volumes during radiation treatment were significantly associated with PT displacements that often exceeded standard setup margins. Repeated 3-dimensional imaging is recommended in patients with AT to evaluate for PT displacements during treatment. Summary This study analyzed 12 patients with atelectasis and 10 patients without atelectasis who underwent repeat 4-dimensional fan beam computed tomography during radiation therapy. Patients with atelectasis had significantly greater tumor displacements than patients without atelectasis, and these tumor displacements often exceeded standard setup margins. Patients with atelectasis may benefit from repeated 3-dimensional imaging during radiation therapy and possible replanning for large tumor displacements

Computationally Modeling Compton Scattering to Understand Radiation Therapy

Radiation therapy is becoming a popular method of cancer treatment due to its effectiveness and precision. Improvements in radiation therapy treatments rise from an increased understanding of the interactions between radiation and matter, where Compton scattering is the primary interaction. The main objective of this research project is to model Compton scattering using the program MATLAB to better understand the energetic and special distribution of scattering events. Monte Carlo Methods and the Klein Nishina formula were used to simulate the interactions within a material. It was found that a simulation with higher number of events more realistically reflects the probabilistic nature of this interaction and the range of possible scattering outcomes and shows the way in which energy would be deposited when a patient is irradiated with a large number of photons. The effect of the initial photon energy and cut-off interaction energy in the simulation are also explored. This work forms a foundation for future simulations, which would incorporate different types of interactions to simulate treatment