Brachytherapy RTT Review Course Laura Doyle, MS

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1 Brachytherapy RTT Review Course Laura Doyle, MS

2 Applica;on of lecture to the exam Applicable sec;on of ARRT Examina;on Content to Brachytherapy A.I.a.1. Sources of Radia;on, radioac;ve material A.I.e. Measurement of Radia;on Units of measurement, Instrumenta;on A.II.a. Fundamental principles of radia;on protec;on A.IV.b. Quality Control Procedures B.IV.c.2. Treatment Op;ons C.II.a. Treatment prescrip;on D.III.a,b,e. Monitoring Treatment Delivery D.IV. Documenta;on E.V. Medical Emergencies

3 Brachytherapy - Defini;on Refers to the treatment of cancer with radia;on at close distances Uses small, sealed sources of radia;on

4 Brachytherapy Applica;ons Intracavitary- sources placed into body cavity close to target volume Vaginal cylinder Inters;;al- sources implanted within ;ssue/tumor Head and Neck Surface- sources placed on top/over the ;ssue Eye plaque, skin Intraluminal- sources placed inside a lumen Lung Intraopera;ve- sources implanted during a surgery Lung mesh Intravascular Beta- Cath

5 Brachytherapy Classifica;ons Temporary Dose delivered over a short ;me and sources are removed once prescribed dose has been fulfilled Permanent Dose is delivered over the radioac;ve life of the source un;l complete decayed

6 Brachytherapy Classifica;ons Low Dose Rate Gy/hr High Dose Rate- >12 Gy/hr Defini;ons from ICRU report 38

7 Brachytherapy Isotopes Selec;ng the most appropriate isotope depends on a number of factors: Energy Half life Shielding considera;ons Source strength Dose rate Economic considera;ons

8 Brachytherapy Isotopes Ra- 226* Cs- 137* Ir- 192 I- 125 Ra- 223 Pd- 103 Au- 198 Sr- 90/Y- 90 Cs- 131

9 Types of Radia;on Gamma Characteris;c x- rays Alpha Beta

10 Review of decay equa;on A = 0 A e λt λ = T 12 where: A 0 = Ini;al ac;vity; A= ac;vity afer ;me t; t = ;me; λ= decay constant

11 Half life Half Life (T1/2): The ;me required to reduce its ac;vity to half of its original value.

12 Example of half life 10 Ci Ir- 192 Source on 1/1/15 What is the ac;vity of the source on 4/14/15? Where do we start We know half life = 74 days We need to calculate the ;me from original ac;vity 74 days STOP! Think before you calculate

13 Example of half life 10 Ci Ir- 192 Source on 1/1/15 What is the ac;vity of the source on 4/14/15? 0.693*74days A = 10e 74days

14 Approxima;on of source decay Isotope Half Life Approximate ;me for 1% decay Co yr 1 month Cs yr 5 months Ir day 1 day I day 1 day Ra yr 23 years

15 Example of Source Decay What is the ac;vity of a 0.5 mci I- 125 seed afer 2 months? What is the ac;vity of a 9 Ci Ir- 192 source afer 3 months?

16 Units of ac;vity/source strength Apparent ac;vity: mci, Ci, Bq Ac5vity (A): Number of disintegra;ons per second(dps) 1 Ci = 3.7 x dps 1 dps = 1 Becquerel (Bq) Equivalent mass of Radium: mgraeq Air Kerma Strength: U = cgycm 2 h - 1

17 Remote aferloading systems Most commonly Ir- 192 Usually single source, maximum 12 Ci Used for intracavitary, inters;;al, surface, intraluminal applica;ons

18 Ir day half life Usually replaced quarterly in remote aferloading units Mean energy- 380 kev

23 Aoenua;on Ir- 192 Half value layer Lead: 6mm; Concrete: 43mm Tenth value layer Lead: 16mm; Concrete: 152mm Remember that you can t TURN OFF a radioac;ve source, so you must rely on sufficient shielding IAEA Report 47 p 109

24 Dwell ;me/dwell posi;on Dwell posi*on- loca;on where the source stops Dwell *me- ;me the source spends at each loca;on Step size- distance between dwell posi;ons As the source decays, dwell ;me must increase to achieve the same dose distribu;on

25 Dwell ;me/source ac;vity Dwell ;me Source ac;vity

26 Treatment with Remote Aferloader Pa;ent is posi;oned on table/bed/stretcher Aferloader is secured close to the pa;ent Applicator or needles are connected to HDR aferloader through specified channels Personnel exit the room and the treatment is delivered Pa;ent is monitored via audio and visual means The pa;ent and room are surveyed afer the conclusion of the treatment

27 Advantages of remote aferloading brachytherapy Decreased radia;on exposure to personnel Shorter treatment ;mes Outpa;ent procedure Decreased size of applicators

28 Brachytherapy Wrioen Direc;ve Must Specify: Applicator Isotope Total Dose Dose/Frac;on Point/Volume

29 HDR Documenta;on Wrioen Direc;ve Source Ac;vity Total Dwell ;me Dwell posi;ons Number of channels/catheters Room/Pa;ent survey

30 Emergency Personnel/Equipment Must have on hand: Lead pig Wire cuoers Large Forceps Syringe (for mammosite/balloon applicators) Most states require at least an AMP and AU present throughout the en;re treatment. Know your state regula;ons!!!

31 Cervical Endometrial Vaginal Breast Endobronchial Intravascular Prostate Surface/skin HDR applica;ons

32 Intracavitary GYN Brachytherapy Cervix Tandem and ovoids Tandem and ring LDR or HDR techniques Source distribu;on or dwell ;mes based on dose to Point A

33 Tandem, ovoids, and ring Nucletron product catalog

34 Ring and Tandem/ovoids dose distribu;on Pear distribu;on Normalized to point A

35 Dose Specifica;on Point A Uterine vessels cross ureters 2 cm superior to external os 2 cm lateral to cervical canal Rela;ve to tandem posi;on

36 Dose specifica;on- Point B Point B parametrium/nodes 2 cm superior to os and 5 cm lateral from mid- pelvis Does not move with shif of tandem or uterus Typically 25% of prescrip;on dose

37 Points A & B B A

38 ICRU points Bladder and Rectum Maximum dose approximately 80% of Point A or prescrip;on dose Can be shielded by ovoid shields or cap on ring

39 Vaginal cylinder

40 Surface dose and cylinder r r+0.5 Dose prescribed to surface or 0.5 cm from the surface Treatment length Vaginal cancers Vaginal cuff/apex for endometrial cancer

41 Dose Specifica;on Cylinder Diameter As cylinder diameter increases Treatment ;me to achieve same dose increases Mucosal dose compared to dose at 5 mm depth decreases

42 Dose Specifica;on Cylinder WHY?? Remember ISL Choose the largest cylinder Diameter Dose (cgy) Inverse Square Law Distance from source (cm)

43 Bladder/Rectum points Rectum- 5mm from posterior vaginal wall Prescrip;on point generally 5mm from cylinder surface Bladder- iden;fied with Foley balloon and contrast

44 Inters;;al GYN SYED implant Either LDR or HDR Involves overnight stay in hospital and surgical placement of device

45 Accelerated Par;al Breast Irradia;on 3.4 Gy/fx to 1 cm from surface of balloon/ applicator 10 frac;ons, 2 frac;ons per day Variable fill volume based on cavity size Single or mul;ple lumens, mul;ple dwells

46 Mul;- lumen Breast Applicators Mammosite Training Guide

47 Mul;- lumen Breast Applicators Image from: &

48 Prostate Monotherapy or combined with EBRT TJU protocol: 15 Gy followed by external beam boost Plas;c needles, similar procedure to permanent LDR implant

49 HDR for Skin Malignancies Leipzig/Valencia Applicators Tungsten shielded Superficial skin, intra- oral and vaginal cuff Alterna;ve to orthovoltage or electrons

50 HDR for Skin Malignancies Flap Applicators Adapts to any shape or loca;on on body (great for extremi;es and curved surfaces Ensures fixed skin to catheter distance of 5 mm

Intravascular brachytherapy Beta- Cath system Sr- 90 20, 40, 60 mm source train Prescrip;on based on

51 Intravascular brachytherapy Beta- Cath system Sr , 40, 60 mm source train Prescrip;on based on vessel diameter and injury length (between Gy) Treatment indica;on: preven;on of in- stent restenosis

52 Advances in HDR Brachytherapy Imaging CT planning has allowed for beoer assessment of OAR doses as well as target coverage (points vs DVH) Useful when combining with external beam or in situa;ons of retreatment Fusion capability allows for more accurate assessment of applicator placement in subsequent frac;ons and delinea;on of target and cri;cal structures Dosimetry Op;miza;on Isodose manipula;on Dwell ;me and posi;on flexibility

53 Low Dose Rate Brachytherapy

54 LDR Applica;ons Prostate Cervix Vaginal Breast Head and neck Surface

55 Prostate Seed Implant Most common indica;on early stage prostate cancer Permanent placement of radioac;ve sources Total dose (I 125 :145 Gy; Pd 103 : 110Gy) Varies based on technique Pre- planning Real- ;me planning Inverse op;miza;on

56 Prostate Seed Implant - Procedure Volume Study TRUS or CT Pre- plan/nomogram Seed order Implant date US Needle placement Seed inser;on Imaging Post- implant dosimetry

57 Common LDR Sources I- 125 Half life- 60 days Mean Energy- 28 kev HVL mm Pb Pd- 103 Half life- 17 days Mean Energy- 21 kev HVL mm Pb Cs- 131 Half life- 9.7 days Mean Energy- 30 kev HVL mm Pb

58 LDR Source Composi;on Physical length Ac;ve length Contain radio- opaque markers

59 SIRT SIR and Thera Spheres Selec;ve Internal Radia;on Therapy Y- 90 microspheres inserted into hepa;c artery become lodged in tumor/normal liver vasculature (β emioer) Goal To deliver a high dose to liver tumor while sparing normal liver (achievable due to preferen;al blood flow and spheres uptake in tumors)

60 Radioemboliza;on Y- 90 Beta emioer Average beta emission energy = 0.93 MeV Average penetra;on range in ;ssue ~ 2.5mm Physical half life = 64.1 hr Sir- spheres (resin) for hepa;c metastases Theraspheres (glass) for unresectable hepatocellular carcinoma (HCC) µm Courtesy of Sirtex

61 Radia;on Safety and QA

62 HDR Brachytherapy Quality Assurance Daily checks Quarterly Source Exchanges Annual checks

63 LDR Brachytherapy Quality Assurance Per pa;ent source assay Inventory Storage and decay Annual checks

64 Brachytherapy vs. External Beam Distance from source of radia;on to treatment site Dura;on of treatment Total dose and frac;ona;on schemes Heterogeneity correc;ons*

65 Inverse Square Law Main component of dose reduc;on for higher energy brachytherapy sources Remember the equa;on: I 2 I 1 = D 1 2 D 2 2

66 Handling of Radioac;ve Sealed Sources Remember the basics of Radia;on Safety: Time Distance Shielding Always prac;ce ALARA

67 Radia;on Detectors Ioniza;on Chamber GM Meter Scin;lla;on Detector

69 Thank you! Good Luck!

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