Practice Problems Week 3 2019

Week 3 – Electrons A linear accelerator is calibrated to deliver 1cGy = 1MU at 100cm SSD at a depth of dmax for a 15cm cone and standard open cutout. Use the data tables at the end of this problem set to calculate the MU needed to deliver the following prescriptions for each electron setup. Round to the nearest whole MU. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

14. 15. 16. 17. 18. 19. 20.

200cGy to dmax at the 90% isodose line, 6e, 10 cone, 10 standard cutout, 100cm SSD. 200cGy to dmax at the 85% isodose line, 9e, 15 cone, 11x15 cutout, 100cm SSD. 200cGy to dmax at the 90% isodose line, 6e, 6 cone, 3x5 cutout, 100cm SSD. 200cGy to dmax at the 90% isodose line, 9e, 20 cone, 10x20 cutout, 100cm SSD. 200cGy to dmax at the 80% isodose line, 12e, 10 cone, 10 standard cutout, 105cm SSD. 200cGy to dmax at the 80% isodose line, 16e, 10 cone, 8x10 cutout, 100cm SSD. 200cGy to dmax at the 90% isodose line, 6e, 6 cone, 6 standard cutout, 110cm SSD. 200cGy to dmax at the 90% isodose line, 9e, 15 cone, 4.5x13 cutout, 100cm SSD. 200cGy to 1cm depth at the 100% isodose line, 9e, 10 cone, 8x10 cutout, 100cm SSD. 200cGy to 2cm depth at the 100% isodose line, 12e, 10 cone, 5x10 cutout, 105cm SSD. 200cGy to dmax at the 90% isodose line, 9e, 20 cone, 20 standard cutout, 1cm bolus, 100cm source to bolus distance, 101cm source to skin distance. 200cGy to dmax at the 95% isodose line, 12e, 10 cone, 10 standard cutout, 0.5cm bolus, 105cm source to bolus distance, 105.5cm source to skin distance. A patient was planned for 200cGy to dmax at the 90% isodose line, 6e, 6 cone, 6 standard cutout, 100cm SSD. The therapists couldn’t get 100cm SSD, but they could get 110cm. They call you and ask what new MU need to be used for the treatment plan? 200cGy to dmax at the 80% isodose line, 16e, 20 cone, 9x18 cutout, 108cm SSD. 200cGy to dmax at the 90% isodose line, 12e, 10 cone, 8x10 cutout, 110cm SSD. 200cGy to dmax at the 85% isodose line, 9e, 6 cone, 6 circle cutout, 1cm bolus, 105cm source to bolus distance, 106cm source to skin distance. 200cGy to dmax at the 95% isodose line, 20e, 10 cone, 4.5x6 cutout, 100cm SSD. 200cGy to 5cm depth at the 100% isodose line, 20e, 20 cone, 10x20 cutout, 105cm SSD. 200cGy to dmax at the 90% isodose line, 6e, 0.5cm bolus, 6 cone, 2 circle cutout, 100cm source to bolus distance, 100.5cm source to skin distance. A patient comes in for a weekend treatment, the physicians prescribes 400cGy to the 90% isodose line, 9e, 10 cone, 10 standard cutout at 100cm SSD; what are the MU? The physician comes on Monday and wants to change the prescription to 200cGy per day, what are the new MU?