radiation therapy Flashcards
What is the dosage unit for treating with ionizing radiation?
Gy or Gray
how may Gy of radiation are given to treat non melanoma skin cancer
30-66 Gy (or Grays)
How many Gy are used to treat MF
20-40 Gy (Grays)
How many Gy are used to treat Merkel Cell carcingom
50-66
since cure rates and local control are the same for for one dose or fractionation of radiation why fractionate?
To decrease chronic radiation toxicity.
How many fractions a week of radiation is normally given?
Five.
Radiation works by damaging what cellular structure?
DNA double strand breaks cause mitotic catastrophe.
What areas are not ideal for radiation therapy in scc.
areas that are edematous or at risk for poor healing such as lower leg, foot, dorsum of hand.
what is the measurement of one gray of ionizing radiation.
absorption of one joule of radiation energy per kilogram of matter. Gy= J/Kg
what age range for treatment of non melanoma skin cancer.
> 60 years
What are the four general principles of radiation Tx?
- > 60 yo
- Fractionation
- Contraindicated in Genetic disease predisposing to skin cancer and connective tissue disease.
- Don’t re irradiate a previous radiation site.
When might you use radiation in a melanoma?
- In Situ Lentigo Maligna non surgical candidate,
2. Adjunctive or palliative treatment
What is radiation recall?
Inflammatory rxn in a former radiation field following chemotherapy.
When would someone consider Radiation Therapy RT in merkel cell carcinoma.
It should always be considered even after resection.
List the radiosensitivity of skin cancers from most to least
SCC BCC Merkel cell carcinoma Kaposi's Angiosarcoma Lentigo Maligna Melanoma
What radiation margins are recommended for MCC Merkel cell carcinoma?
5cm
When might you not do adjuvant radiation tx for MCC Merkel cell carcinoma?
if tumor is less than 1cm and there is no immunosuppression or angiolymphatic invasion.
What is the difference between definitive and adjuvant radiation TX
Definitive treatment means radiation is the sole treatment. Adjuvant means combined with another TX to reduce risk of recurrence.
When do you give radiation tx following keloid surgery
within 24 hours one dose
what percent of keloids don’t return following excision plus radiation (the long term success rate)
75%
In advanced SCC adjuvent RT improved survival in which group. Entire cohort, those with perineural invasion, those with regional disease
Entire cohort
What is the standard number of grays delivered with radiation treatments for each fraction.
1.8-2.0 Gy
