Radiation Fractionation

Rodrigo Arrangoiz MS, MD, FACS, FSSO
  • Three important areas form the foundation for the evolving use of altered fractionation:
    • Tissue response
    • Duration of treatment
    • Fraction size and number
  • Acutely responding tissues:
    • Are rather active in ongoing cellular proliferation
    • Most tumors (except perhaps prostate cancer, breast cancers, and melanoma) and some normal tissues such as skin, mucous membranes, and gastrointestinal epithelium:
      • Share this characteristic:
        • These tissues are most affected by the overall treatment duration rather than by the size or number of fractions used
  • Late-responding tissues:
    • Have a low proliferative rate and include the spinal cord, brain, bone, and cartilage
    • These tissues are most affected by the:
      • Size and number of fractions rather than by treatment duration:
        • Therefore are spared by decreasing the dose per fraction of radiation delivered
  • Because most tumors consist of rapidly dividing cells:
    • Local tumor control is strongly dependent on the overall treatment duration rather than on the size or number of fractions
  • When squamous cell carcinoma of the head and neck is exposed to radiation:
    • The less radiosensitive cells within the lesion:
      • Can undergo rapid proliferation:
        • Approximately 3 to 5 weeks after treatment commences
        • This accelerated repopulation can overwhelm the ongoing treatment effects of radiation:
          • Which ultimately can lead to local failure
        • The clinical significance of this phenomenon is that even with significant regression of the primary tumor mass:
          • Local failure still ultimately could result from proliferation of these resistant clones
        • Therefore it is essential to complete treatment in as short a time as possible so that accelerated repopulation is minimized:
          • Increasing the chance for local control
      • For this reason, split-course radiation:
        • Which incorporates a treatment break during the course of radiotherapy is not recommended
  • Based on the aforementioned principles:
    • The goal of altered fractionation schemes:
      • Is to improve the therapeutic ratio by maximizing the tumoricidal effect and minimizing acute and late toxicities while using readily available low-LET radiation
  • Two major categories of altered fractionation schemes exist:
    • Hyperfractionation
    • Accelerated fractionation
  • They share basic radiobiological principles yet have their own particular features (Table)
  • Accelerated fractionation:
    • Is the strategy of choice for rapidly proliferative tumors
    • Accelerated fractionation is based on the concept that the shortened overall treatment time:
      • Would reduce the opportunity for accelerated repopulation effectively
  • Hyperfractionation:
    • Is preferred for slowly proliferating tumors
    • Hyperfractionation improves the therapeutic ratio primarily through:
      • Redistribution of tumor cells into more radiosensitive phases as a result of multiple fractions
      • Differential sparing of late-responding normal tissues because of a decrease in the size of the dose per fraction
Unknown's avatar

Published by Rodrigo Arrangoiz MS, MD, FACS, FSSO

My name is Rodrigo Arrangoiz I am a breast surgeon/ thyroid surgeon / parathyroid surgeon / head and neck surgeon / surgical oncologist that works at Center for Advanced Surgical Oncology in Miami, Florida. I was trained as a surgeon at Michigan State University from (2005 to 2010) where I was a chief resident in 2010. My surgical oncology and head and neck training was performed at the Fox Chase Cancer Center in Philadelphia from 2010 to 2012. At the same time I underwent a masters in science (Clinical research for health professionals) at the University of Drexel. Through the International Federation of Head and Neck Societies / Memorial Sloan Kettering Cancer Center I performed a two year head and neck surgery and oncology / endocrine fellowship that ended in 2016. Mi nombre es Rodrigo Arrangoiz, soy cirujano oncólogo / cirujano de tumores de cabeza y cuello / cirujano endocrino que trabaja Center for Advanced Surgical Oncology en Miami, Florida. Fui entrenado como cirujano en Michigan State University (2005 a 2010 ) donde fui jefe de residentes en 2010. Mi formación en oncología quirúrgica y e n tumores de cabeza y cuello se realizó en el Fox Chase Cancer Center en Filadelfia de 2010 a 2012. Al mismo tiempo, me sometí a una maestría en ciencias (investigación clínica para profesionales de la salud) en la Universidad de Drexel. A través de la Federación Internacional de Sociedades de Cabeza y Cuello / Memorial Sloan Kettering Cancer Center realicé una sub especialidad en cirugía de cabeza y cuello / cirugia endocrina de dos años que terminó en 2016.

Leave a comment