Applicators

Question 1

what is colpostate

Answer 1

capsule applicator inserted into vagina and placed near cervix. e.g., ovoids. Typically has internal shielding to shape the dose distribution. There usually two lateral capsules

Question 2

what is inserted into uterus

Answer 2

tandem

Question 3

describe Fletcher-type applicator

Answer 3

2 ovoid (~cylindrical) colpostats plus a tandem

Question 4

Why has the ring replaced colpostats recently?

Answer 4

the ring allows for more than lateral source placement (lateral source design was used originally to spare the bladder anteriorly and the rectum posteriorly, back when remote afterloaders didn’t exist and the source could not be automatically stepped through an applicator). Sometimes, there is rectal involvement and ovoids cannot treat posteriorly – ring is obviously favourable choice in this situation; more freedom to tailor dose distribution to particular patient’s needs.

Question 5

describe Henschke-type applicator

Answer 5

tandem with colp[ostats that are half spheres

Question 6

describe Manchester-type applicator

Answer 6

tandem with spherical colpostats

Question 7

describe ring and tandem

Answer 7

ring-shaped applicator goes around cervix

Question 8

describe Vienna or Venezia system

Answer 8

ring and tandem but with needles coming out of the ring, used as a template for inserting interstitial needles (instead of intracavitary treatment which is more common for gyne)

Question 9

Miami-type applicator

Answer 9

vaginal cylinder plus tandem. The vaginal cylinder has six channels in this case, allowing for asymmetric dose distributions within the vagina.

Question 10

describe Heyman treatment

Answer 10

pack many capsules into uterus. Endometrium is difficult to treat as the uterine wall is of variable thickness and is often considerably distorted.

Question 11

is tandem available in different angles?

Answer 11

Yes

Question 12

how to treat endometrium?

Answer 12

use three tandems

use Heyman treatment

Question 13

describe MUPIT

Answer 13

Martinez universal perinieal interestitial template

-interstitial gyne

Question 14

describe Valencia or Leipzig applicator

Answer 14

Single source surrounded by cone shape structure- opens up to wide edge of cone on the skim

Valencia applicators have flattening filter to help achieve flatter distribution of dose (i.e., isodose curves are parallel to skin surface). The FF closes off the end at the skin. Leipzig has a forward peaked dose distribution and is open on skin end.

Leipzig f-factor is greater than 1 due to additional contribution to patient dose from scatter from applicator.
o Valencia f-factor is less than 1 (~0.7) due to reduced patient dose due to attenuation in the closed-end (i.e., reduced patient dose compared to if applicator was water)
o These f-factors help correct the TPS TG-43 based dose distribution to make it agree with the Monte Carlo simulation results.
o The Monte Carlo results are available in an Excel spreadsheet, normalized to 100% at 3 mm depth, with dose at the surface ~140%. The RO consults these spreadsheet to help with deciding on prescription. Must use Monte Carlo results to plan in this case due to non-negligible effect of metal applicators, which TG-43 does not take into account. RO may also take into account the fact that part of tumour may fall off partway through treatment.
o Only a single dwell position is used.

Question 15

describe freiburg flap applicator

Answer 15

consists of a flexible mesh style surface mold formed by 0.5 cm radius silicon spheres. The spheres are tunneled through the center with flexible catheters for the positioning of Ir-192 sources. The design of the Freiburg flap applicator keeps the distance from source to skin constant

o Useful for skin cancer on curved surface (since it molds to the shape of the surface) but has since been replaced by VMAT in this clinic since VMAT is better at limiting dose to underlying structures such as the brain in a scalp skin cancer treatment (uses a series of grazing tangents).
o It is ideal if 150% isodose can be kept off of the skin in general.

Question 16

describe Mammosite balloon applicator

Answer 16

central tandem only, is inserted into breast cancer lumpectomy cavity.
o Mammosite applicator may be inserted during lumpectomy surgery or in a separate procedure.
o Treatment can be completed in as little as five days.
o Only used if post-lumpectomy margins are clear. Easier to implant in large breasted women.
o Single and multi-lumen catheters are available.
o Balloon is filled with contrast fluid; PTV surrounds the balloon by usually ~1 cm
o Lung, skin and heart (if left-sided treatment) are main OARs of concern. Proximity of these to lumpectomy site determines whether or not patient is a suitable candidate. Generally more of an issue with smaller breast.
-seed sent into balloon

• cosmesis may be better than with EBRT
• one large insertion may be preferred over many needles

-balloon hits more surface area in the breast compared to a single needle point

Question 17

describe SAVI applicator

Answer 17

• strut adjusted volume implant
• typically 6 peripheral catherers and a central tandem
• inserted into lumpectomy cavity
• inserted via a small incision, then catheters expand to conform to the shape of the cavity
• catheters start together, expand out, then come back together

Question 18

advantage of SAVI over mammosite

Answer 18

more freedom to adjust shape of dose distribution depending on proximity of OARs (skin, lung, heart) compared to mammosite

Question 19

dwell positions for SAVI

Answer 19

 Dwell 1 for central catheter is 5 mm back from tip
 Dwell 1 for peripheral catheter is 4.6 mm back from tip
 Tips of peripheral catheters are 8 mm back from tip of central catheter
 The different struts have markers to identify which is which.

Question 20

what is a Smit sleeve

Answer 20

accessory that is inserted into the cervical internal os to allow easier localization of the external cervical os (which is used to identify point A for the Manchester system) in CT or MR images. It also helps reduce mucosal dose and keeps the cervix dilated. It is sutured in place for the duration of the treatment (i.e., even in between fractions).

Question 21

how deep do you put catheter for bronchus and esophagus?

Answer 21

deeper than you need, for safety margin (e.g., for esophagus, treat 2 cm on either side of lesion, but push catheter 5 cm beyond deepest extent of lesion).

Question 22

describe applicator QA

Answer 22

o Annual: check integrity by eye (cracks, rust, bending), check patency, level of friction when source position check ruler is used, length of indexer.
o At time of use: visual inspection, assess friction when x-ray markers are inserted.
o Dwell positions may be QA’d using autoradiographs, although we use fluoroscopy in this clinic for the purposes of acceptance testing. Autoradiograph may include double exposure whereby the applicator is irradiated with e.g., MV electrons to get an image of the applicator structure combined with images of source dwell positions.

Question 23

how to QA the position of the dwell in the applicator

Answer 23

can use fluoro- see end of tube and source location

-can use film or EPID- mark end of tube and see where dose distribution is centered

Question 24

describe applicator modelling

Answer 24

TPS has dwell position offset specific to each ring size and tandem angle