AOCNP Radiation Therapy Principles and Side Effects 1 — Questions and Answers
Question 1: What is the primary mechanism by which ionizing radiation kills cancer cells?
- Directly disrupting cell membrane integrity
- Inducing DNA double-strand breaks leading to apoptosis or mitotic catastrophe (Correct answer)
- Activating natural killer cells to attack tumor cells
- Inhibiting angiogenesis within the tumor microenvironment
Correct answer: Inducing DNA double-strand breaks leading to apoptosis or mitotic catastrophe
Radiation kills cells primarily through direct and indirect (free radical-mediated) DNA double-strand breaks. Cells unable to repair this damage undergo apoptosis, necrosis, or mitotic catastrophe. Rapidly dividing cells are most sensitive due to less time for DNA repair between divisions.
Question 2: Stereotactic body radiation therapy (SBRT) differs from conventional radiation in that SBRT delivers:
- Lower doses over many fractions (25–35 treatments)
- Ablative doses in 1–5 fractions with high precision (Correct answer)
- Proton beams exclusively
- Whole-body radiation prior to bone marrow transplant
Correct answer: Ablative doses in 1–5 fractions with high precision
SBRT (also called SABR) delivers ablative doses (typically 25–60 Gy) in 1–5 fractions using highly conformal techniques (IMRT/VMAT with image guidance). It is used for early-stage lung cancer, liver metastases, spinal metastases, and other oligometastatic disease.
Question 3: Radiation recall is an acute dermatitis reaction triggered by certain chemotherapy agents administered after prior radiation. Which agent is most classically associated with radiation recall?
- Carboplatin
- Doxorubicin (Adriamycin) (Correct answer)
- Vincristine
- Cyclophosphamide
Correct answer: Doxorubicin (Adriamycin)
Radiation recall is an inflammatory skin reaction in a previously irradiated field triggered by certain drugs, most classically anthracyclines (doxorubicin), gemcitabine, taxanes, and capecitabine. It can occur weeks to years after radiation and may also affect internal organs.
Question 4: Which grading system is used by oncology nurses to assess and document radiation-induced side effects including mucositis and dermatitis?
- Karnofsky Performance Scale
- CTCAE (Common Terminology Criteria for Adverse Events) (Correct answer)
- ECOG Performance Status Scale
- NCI-ODWG grading
Correct answer: CTCAE (Common Terminology Criteria for Adverse Events)
The CTCAE (published by NCI) is the standardized system for grading adverse events in oncology, grading toxicities from 1 (mild) to 5 (death). Radiation-induced dermatitis, mucositis, esophagitis, and other toxicities are all graded using CTCAE criteria.
Question 5: Total body irradiation (TBI) is most commonly used in what context?
- Palliative pain control for bone metastases
- Myeloablative conditioning prior to hematopoietic stem cell transplantation (Correct answer)
- Prophylactic cranial irradiation in small cell lung cancer
- Definitive treatment of localized prostate cancer
Correct answer: Myeloablative conditioning prior to hematopoietic stem cell transplantation
TBI is a component of myeloablative conditioning regimens before allogeneic HSCT for hematologic malignancies. It destroys residual leukemic/lymphomatous cells, suppresses the immune system to prevent graft rejection, and ablates the bone marrow to create space for engraftment.
Question 6: Late radiation toxicity in the pelvis most commonly manifests as which of the following?
- Acute radiation dermatitis
- Radiation proctitis, cystitis, or small bowel injury (Correct answer)
- Immediate hair loss in the field
- Acute nausea and vomiting
Correct answer: Radiation proctitis, cystitis, or small bowel injury
Late pelvic radiation effects (occurring >3–6 months post-treatment) include radiation proctitis (rectal bleeding, tenesmus), hemorrhagic cystitis, small bowel obstruction, fistula formation, and sexual dysfunction. These differ from acute effects and may be permanent or progressive.
