Radiation Oncology: Indications & Adverse Effects

How does radiation therapy kill cells?

• 1/3rd of time the radiation directly hits the DNA

• 2/3rd of time the radiation creates ROS and causes indirect damage

What type of cell death does radiation therapy cause?

Mostly causes mitotic cell death, but some tumor types (lymphoma, MCT, thymoma) have apoptotic death

What is stereotactic body radiation therapy (SBRT)?

High dose per fraction delivered over a short (<5 fractions) period of time = hypofraction

How does SBRT spare normal tissue?

Avoidance through collimation

SBRT qualifications

gross disease, intact, healthy skin

SBRT disqualifications

pathologic fracture, oronasal fistula, inability to adequately avoid normal tissues

SBRT requirements

o CT scan

o Immobilization

o Target localization

OSA biggest risk factors with SBRT

Pathologic fracture and skin changes

SBRT vs conventional RT

How can radiation be used for palliative care?

• Improve function

• Improve hygiene

• Unobstruct urethra/ureter

• Stop bleeding

What is IMRT?

• Conformal radiation therapy based on CT scan

• Fractionated OR hypofractionated

Advantages of IMRT

treats complex tumor shapes and minimizes dose to normal tissues

What are some neoplastic conditions treated with RT?

• Osteosarcoma

• Nasal tumors

• Brain tumors

• Soft tissue sarcomas

• MCT

• Oral malignant melanoma

• TCC

• Cardiac hemangiosarcoma

• Chemodectoma

• Adrenal tumors

• Liver tumors

• Lung tumors

• Thyroid carcinoma

What are some non-neoplastic conditions that can be treated with radiation therapy?

• Sialocele

• OA

• MUO

• Pulmonic stenosis

• Feline idiopathic cystitis

Acute adverse effects

o Within first three months

o Cells with rapid turnover: skin, GI tract, hematopoietic system

Early delayed adverse effects

2 weeks to 4 months to neuro tissue due to demyelination or edema

Late adverse effects

o 3 months to years

o Slow dividing tissues: lung, kidney, heart, bone, liver

Where do radiation effects occur?

within the radiation field and are related to the tissues that have been exposed to radiation

What are some examples of adverse effects?

• Nausea hours after irridiating abdomen from release of 5HT

• Fatigue from ROS

• Pneumositis from destruction of type I pneumocytes

• Mast cell degranuation minutes to weeks

Mast cell degranulation signs

erythema, edema, hypotension, vomiting, hyporexia, melena, coagulation abnormalities

Acute CNS adverse effects management

pretreat with prednisone, mannitol or hypertonic saline for herniation

Skin fibrosis management

pentoxifylline and vitamin E make RBCs and WBCs more flexible so that they can penetrate through smaller vessels and get to fibrosed tissue

Esophageal stricture management

dilations and semi-solid diet, feeding tubes, hydrocortisone injection at stricture site

Ostenecrosis management

surgical debridement, antibiotics, hyperbaric oxygen

Drug interactions

• Use of some chemotherapeutics can exacerbate radiation side effects: dacarbazine, iomustine, doxorubicin, cisplatin, gemcitabine, paclitaxel, toceranib (GI)

• Concurrent use of antioxidants may interfere with radiation cell killing due to interference with damage from ROS