Radiation Therapy Principles and Side Effects Flashcards

What is the primary advantage of proton beam therapy over conventional photon (X-ray) radiation?

Answer: Bragg peak allows dose concentration at the tumor with minimal exit dose

Protons deposit maximum energy at the Bragg peak, a sharp dose drop-off at a specific depth, with minimal dose beyond the target. This physical property significantly reduces radiation dose to normal tissues beyond the tumor, decreasing toxicity particularly for pediatric tumors and tumors near critical structures.

Radiation-induced xerostomia (dry mouth) is most effectively prevented by which technique when treating head and neck cancers?

Answer: Intensity-modulated radiation therapy (IMRT) with parotid gland sparing

IMRT allows dose sculpting that significantly spares the parotid glands (mean dose <26 Gy), substantially reducing the incidence and severity of permanent xerostomia compared to conventional 3D-conformal techniques. Amifostine has modest benefit and significant toxicity.

A patient who received thoracic radiation develops new onset cough, low-grade fever, and dyspnea 4–6 weeks after completing treatment. Which diagnosis should be suspected first?

Answer: Radiation pneumonitis

Radiation pneumonitis typically develops 4–12 weeks after thoracic radiation, presenting with low-grade fever, dry cough, and dyspnea. CT shows ground-glass opacities or consolidation within the radiation field. Treatment is high-dose corticosteroids; differentiation from infection is critical.

Which nursing intervention is most important for patients receiving pelvic radiation to prevent vaginal stenosis?

Answer: Use of vaginal dilators beginning 2–4 weeks after radiation completion

Vaginal dilators are recommended beginning 2–4 weeks after pelvic radiation completion (or sooner as tolerated) to prevent fibrosis and stenosis. Regular sexual activity or dilator use maintains vaginal patency and reduces scar tissue formation, preserving quality of life and facilitating follow-up gynecologic exams.

The linear-quadratic model is used in radiation oncology to calculate which of the following?

Answer: Biologically effective dose (BED) when comparing different fractionation schedules

The linear-quadratic (LQ) model calculates the BED to compare the biological equivalence of different fractionation schedules. The α/β ratio characterizes tissue sensitivity — late-reacting tissues (α/β ~3 Gy) are more sensitive to large fractions, while tumors and early-responding tissues (α/β ~10 Gy) are less so.

During external beam radiation for prostate cancer, which intervention helps ensure reproducibility and reduces rectal dose?

Answer: Filling the bladder and emptying the rectum (rectal preparation) before each fraction

For prostate EBRT, patients are instructed to have a comfortably full bladder (to push bowel away) and an empty rectum before each treatment session. This setup reproducibility reduces rectal dose, prostate displacement, and acute/late rectal toxicity including proctitis.