Radiotherapy pt.3 Flashcards
What are different tumor volumes involved in radiotherapy planning?
GTV: Gross tumor volume (clinical)
CTV: Clinical tumor volume (clinical)
PTV: Planning target volume (geometric
Dosimetric volumes (Treated volume and irradiated volume)
What does CTV represent?
Represents the microscopic tumor cells, the volume where we are supposed to find the microscopic cells (depends on anatomy, pathology, and site of local recurrences) which can be found
- around the macroscopic tumor–> after surgical removal and pathology examination
- Draining lymph nodes–> Requires knowledge of anatomy and physiology
- Sites of local recurrence –> Follow up
Rectal cancer treatment
Preoperative RT+CT followed by surgery which includes total mesorectal excision
Microscopic cancer foci in lung cancer
- In lung adenocarcinomas 35% of the miscroscopic foci is found in the area of 0.8 cm around the main disease (95% of microscopic tumoral cells)
- In squamous lung tumors they are found in a range of 0.6cm, thus influencing the
radiotherapy approach: - Squamous → 0.6 cm margin
- Adenocarcinoma → ≥6 mm margin
Microscopic cancer foci in rectal cancer
Microscopic cancer foci are found in the mesorectum round 40% of cases and in the outter region of the mesorectom in 25% of cases
Distal tumor deposits in the mesorectal fat 3 cm from the cancer: 6.5%
80% of nodes at the level of the tumor
Where does the rectum drain its lymph?
70% Superior lymph Nodes (along the SRA to the inferior mesenteric nodes)
30% Lateral Lymph Nodes (internal Iliac, obturator)
What is planning target volume?
The volume that takes into account target movements:
- Patient Set up. positioning
- Tumor and Organ motion (e.g. breathing, bladder filling)
What is image guided radiotherapy?
Imaging devices mounted on the treatment machines to visualize:
- The Patient poisition (set-up)
- The TARGET/organ at risk position
What is portal imaging?
Displays the position of the fields in relation to the bone
What do the CTV-PTV margins depend on?
The CTV-PTV margins DEPENDS on:
- IGRT SYSTEM used and the
- FREQUENCY of imaging acquisition during treatment
- implemented CORRECTIONS
What is the treated volume?
Treated Volume (TV):
- Is volume of normal tissue surrounded by the prescribed (iso)dose
- TV > PTV
What do the dimensions of treated volume depend on?
The dimension of the TV depends on the RT technique used. The more the dose is shaped around the target the smaller the TV is
What is the irradiated volume?
- The Volume surrounded by the 50% (iso)dose
- Represents the normal tissue at risk of second tumor
What imaging is used for rectal cancer staging?
MRI for tumor and local nodes
What is considered curable and non curable for rectal cancer?
- Stage 1-3 are curable (M0, no nodal involvement until stage 3)
- Stage 4 is uncurable (Any T, Any N, M1a-b)
What is the treatment for different stages of rectal cancer?
Stage 1:: local excision
Stage 2: Surgery
Stage 3: neo RT- Surgery + CT (if high risk factors)
Stage 4: Chemo + Radiotherapy
What is total mesorectal excision?
en bloc removal of the rectum together with the mesorectal fat column
Radiotherapy modality for rectal cancer
Short course ((downstaging not needed)) of 25 GY (5Gy per day for 5 days) followed by immediate (2-3 days) surgery
or
Long course (downstaging needed) of 45-50 Gy (1.8-2Gy per day for 5 weeks) then delayed (6-8 weeks) surgery
Locally advanced treatment for rectal cancer
Neoadjuvant radiotherapy followed by surgery followed by chemo(if risk factors are present)
What is the mesorectum?
Fibrovascular fatty tissue containing lymphatic drainage and nodes surrounding posterior and lateral rectum enveloped by the mesorectal fascia
Totality of total mesorectal excision in rectal cancer
Residual distal mesorectal fat in 50% of patients who underwent TME
Where is local recurrence found in rectal cancer patients?
The majority of RL in the posterior lower 2/3 of the pelvis
Arteries supplying rectum
Superior, middle, and inferior rectal arteries
When should inguinal nodes be removed in rectal cancer?
- Are not in the drainage of rectal cancer
- Must be included in case of anal canal and anal sphincter infiltration or anterior organs infiltration (vagina, prostate)
- Positive inguinal nodes
- Massive invasion of external anal sphincter
- cT4 with infiltration of the lower third of the vagina
Damage to pudendal nerve symptoms
Pain, sexual dysfunction, urinary dysfunction
Risk of recurrence of rectal cancer in ischiorectal fossa
LOW risk of recurrence in TME era:
Risk of LR 1%
Involved in 10% of patients with LR
Recurrences in IRF due to tumor spillage during inadequate dissection
Need for guidelines for radiation oncologists
The use of guidelines and atlas for delineation Increases consistency between radiation oncologists
What is the anterior wall of the ischiorectal fossa represented by?
The anterior wall is represented by the inferior fascia of urogenital diaphragm (dàiafram) and by the superficial transverse perineal muscle
What is the posterior wall of the ischiorectal fascia represented by?
The posterior wall is represented mainly by the gluteus maximus and by sacrotuberous ligament
what is the ischio-rectal fossa and its borders
Fatty triangular area bounded by the levator ani and the external anal sphincter medially
By the obturator internus muscle and the ischial tuberosity laterally
and the skin inferiorly
Where are ingiunal nodes found?
In an area bounded posteriorly by triangle formed by ilio-psoas, pectineus, sartorius and abductor longus muscles
What is the 5 year survival when N+ extra mesorectal
Around 40%
What is the presacral space and its inclusion in surgery?
Virtual space which is included in the delineation of the mesorectum and the lateral lymph node subsite
The neuroforamina should not be included, unless there is direct infiltration or close proximity of the tumor
What are lateral lymph nodes in rectum divided into?
POSTERIOR Lateral Nodes: Internal Iliac Nodes
ANTERIOR Lateral Nodes: Obturator Nodes
When are posterior lateral nodes included?
Include always in the CTV
When are anterior lateral nodes included in resection?
Include in case of:
Positive internal iliac nodes
cT4
N2
When should external iliac nodes be included in resection?
Include in case of:
cT4
Positive anterior lateral lymph nodes (obturator nodes)
