IORT uses a high single dose of radiation delivered during surgery to treat cancer remnants after tumor removal. It has two objectives: increase local tumor control and increase the ratio of tumor control to damage of nearby healthy tissues. IORT can be delivered via two methods - IOERT uses electron beams from a LINAC and IOHDR uses radioactive sources. Treatment planning requires a multidisciplinary team to determine applicator positioning and appropriate dose to maximize tumor coverage while minimizing radiation to other organs. IORT provides local tumor control comparable to conventional fractionated radiotherapy but with faster treatment time and less damage to surrounding tissues.
2. INTRODUCTION
There are 3 major methods of treating cancer:
• Radiotherapy
• Surgery
• Chemotherapy
IORT
IORT uses a high single-fraction radiation dose (10-30 Gy) is
delivered during surgery to a surgically-exposed tumour bed,
immediately after a chunk of the tumour has been surgically
excised.
3. OBJECTIVES
IORT has two (2) objectives:
• increase the probability of local control of the tumour.
• increase the therapeutic ratio between local control of the
tumour and tolerance of the adjacent healthy tissues and
organs.
IORT is used for tumours difficult to be controlled by surgery or
external radiotherapy alone.
It has been used for all types of cancers – rectal cancers,
sarcomas, gynaecological cancers, breast cancers,
gastroesophageal cancers, pancreatic cancers, etc.
4. OBJECTIVES (contd.)
The surgery attempts to shrink the tumour. Possibly to
decrease the Oxygen Enhancement Ratio, and improve the
radiosensitivity of the tumour volume.
Typically, when surgical resection of a tumour mass is
performed, not all the tumour can be removed without
significant morbidity. Therefore, a bulk of the tumour is
removed surgically, and the remnant is treated with RT.
5. TECHNIQUES
The radiation may be delivered either of 2 methods:
• IOERT (uses megavoltage electron superficial
beams) - Intraoperative Electron Radiation Therapy
• IOHDR
Intraoperative High Dose Rate Brachytherapy
(>12Gy/hr)
In the early days, orthovoltage X-ray beams were also
used, but no longer in regular use, due to low tissue
penetration.
6. IOERT IOHDR
Machine LINAC
Standard (electron)
applications for all treatment
HDR Brachytherapy
Custom made applicators for
different anatomical locations
Source 3-12MeV Electrons Iridium-192 or miniature X-ray
sources
Homogeneity Better dose homogeneity More variation across tissue
Treatment
Time
Faster (2-4 mins).
Total procedure (30 - 45
mins)
Slower (5-30 mins).
Total procedure (45 - 120 mins)
Cost Costlier Lower cost
Sites Only superficial and
accessible sites
Unsuitable for pelvic
locations, narrow cavities.
Any site.
Can treat any site, including large
and convoluted surfaces.
7. TECHNIQUES
Miniature X-ray sources is a new
technological development, as a form
of IOHDR.
It is used in treatment of early stage
breast cancer as a form of
accelerated partial breast irradiation
(APBI) with Breast Conserving
Surgery (BCS).
Fig: Miniature X-ray Applicator
by Xoft Axxent
8. Miniature X-ray / IORT Machine
Head and Neck Cancer
Gastroesophageal Cancer
9. I. Determine position of tumour
II.
Open a small
incision for surgery
III
Surgically,
remove
tumour
IV.
Position applicator
in tumour bed
V. Irradiate for about 30
mins
VI. Remove
applicator,
Close incision
Fig: IOHDR for Breast
Cancer
(Image Source: Zeiss)
TREATMENT PLANNING
11. Fig: Patient undergoing IOERT using LINAC
(Image Courtesy: Gregorio Maranon University Hospital HGUGM, Spain)
12. ELIGIBILITY FOR IORT (APBI)
*following ASTRO guidelines for APBI
FACTORS SUITABLE PATIENT
GROUP
CAUTIONARY
PATIENT GROUP
UNSUITABLE
PATIENT GROUP
Age ≥ 50 years 40 – 49 years < 40 years
Tumour Size ≤ 2 cm 2.1 – 3.0cm > 3.0cm
DCIS Status
(Ductal Carcinoma
in-situ)
Patients with low-risk
DCIS (abnormal cells
in the milk ducts) –
STAGE cT1cN0M0
Intermediate-risk
(spreading from milk
ducts to
surrounding breast
tissue)
High-risk
Lesion location Localised breast
tumour suitable for
breast conservation
- -
BRCA 1/2 Mutation
(Breast Cancer
Gene Carrier)
Negative or Not
Known
Undergoing current
genetic testing
Present
13. TREATMENT PLANNING
The IORT team consists of a surgeon, radiation oncologist,
medical physicist, anaesthesiologist, nurse, pathologist and
radiation therapist.
The treatment plan depends on the organ/tumour treated, and is
usually agreed upon between the radiation oncologist and
medical physicist.
IORT requires an Operating Room (OR) for the surgical procedure
and a treatment room for delivery of the radiation dose.
14. TREATMENT PLANNING (contd.)
The transition between the OR and RT treatment
rooms must be carefully planned and all steps
involved properly worked out and practised, esp. as
the patient may still be under anaesthesia, and the
surgical area upon.
The RT treatment room must be adequately sterilized
to OR standards.
Where possible, the OR and RT rooms should be
merged into one location.
15. IORT Applicators are important for three reasons:
● To define the target area;
● To shield tissues outside the target area from
radiation;
● To keep sensitive tissues from falling into the target
area during irradiation. In breast cancer treatment, it
protects against irradiating the heart and the lungs.
TREATMENT PLANNING (contd.)
16. TREATMENT PLANNING (contd.)
AAPM TG-48 recommends that:
• 90% isodose curve should cover the target volume,
• Dose should be prescribed at dmax
Beam energy is usually selected to place the 90%
isodose line of the dose distribution of the chosen
applicator at the distal depth of the target.
18. QA/QC IN IORT
Quality Assurance in IORT procedure consists of
three components:
• Basic quality assurance dealing with the IORT equipment.
• Pre-treatment quality assurance dealing with equipment
preparation and verification prior to IORT treatment.
• Treatment quality assurance during the IORT procedure.
19. ADVANTAGES
• Reduces the chance of residual tumour at the site of surgery
(eliminates microscopic tumour foci), thus maximizing local control
(LC) of tumours, and reducing probability of local recurrence (LR).
• Maximizes the radiobiological effect of a single high dose of
radiation.
• Faster treatment time (reduces it from weeks to 1 day).
• Minimal exposure of surrounding tissues (esp. OARs) to radiation,
thus reducing normal tissue toxicity.
20. DISADVANTAGES
• Since IORT is almost always given in a single session, it
becomes more difficult to correct misadministration of dose.
• Requires dedicated equipment (HDR machine).
• In IOERT, transporting the patient from the OR to the
LINAC is tasking. Though this is being solved by mobile
LINACs like the CyberKnife.
21. DISADVANTAGES (contd.)
• Higher risk of long-term deterministic effects, such as fibrosis, in
late responding tissues.
• The dose is usually high and close to the tolerance levels of the
normal tissue. Thus, a second full-dose course of radiotherapy may
not usually possible, even after months.
22. CONCLUSION
IORT provides a convenient time-saving advanced
radiotherapy option requiring a multi-disciplinary medical
team working closely together.
There are certain eligibility criteria for patients to receive
IORT, which depends on patient’s age, general health,
spread of tumour, stage of tumour, etc.
However, when used, it has been shown to have good
LC and LR results, comparable to conventional fractional
radiotherapy.
23. REFERENCES
E. B. Podgorsak. Radiation Oncology Physics: A Handbook For Teachers And
Students. IAEA: 2005.
G. Tosi, M. Ciocca. Radiation Protection in the Commissioning and in the Use of a
IORT-dedicated Mobile LINAC. Italy: European Institute of Oncology. 2003.
IORT: An Emerging Technology. Imaging Technology News.
www.itnonline.com/article/iort-emerging-technology . Accessed: March 30, 2017.
Intraoperative radiotherapy with electrons: Fundamentals, Results and Innovation.
www.ecancer.org/journal/7/full/339... Accessed: April 2, 2017.
G. N. Cohen, M. Zaider. AAPM Monograph No. 31, Brachytherapy Physics, (2nd
Edition) Intraoperative Radiation Therapy (IORT). New York. Memorial Sloan-
Kettering Cancer Center. 2005.
