SBRT Liver

1. SBRT Liver When & How ?
Dr Rushi Panchal
HOD - Radiation Oncology
Shree Krishna Hospital
Karamsad, Anand Gujarat

2. • Anatomy of liver and its segment.
• Brief about what is SBRT and clinical outcome in liver SBRT.
• Case selection criteria in both scenario
Hepatocellular carcinoma (HCC) &
Liver metastases
• Simulation to execution : Simulation  contouring  Dose Prescription 
planning  image guidance
OUTLINE
Points Not covered :
(a) Detail of Motion management (b) Follow up after SBRT

3. ANATOMY
• Blood supply : portal vein supplying 70-80% and the hepatic artery 20-
30%. There are three hepatic veins (right, middle, left) drains blood from
liver in to IVC.
• The Couinaud classification of liver anatomy : divides the liver into eight
functionally independent segments.
• The numbering of the segments is in a clockwise manner. Segment I (the
caudate lobe) is located posteriorly. It is not visible on a frontal view.
The liver is divided in three vertical planes:
• The plane of the right hepatic vein divides the right lobe into anterior
(V/VIII) vs posterior segment (VI/VII)
• The plane of the middle hepatic vein divides the liver into right and left
lobes. This plane runs from IVC to the GB Fossa.
• The umbilic plane runs from the falciform ligament to the inferior vena
cava and separates the left lateral and medial segments (II & III from IV).
• Portal vein The portal vein divides the liver into upper and lower
segments. The left and right portal veins branch superiorly and inferiorly
to project into the center of each segment.

4. Couinaud classification :
• The right border of the liver is formed by
segment V and VIII
• On a normal frontal view the segments VI and VII
because they are located more posteriorly.
• Although segment IV is part of the left hemi
more to the right.
ANATOMY

5. How to separate liver segments on cross sectional
imaging
• Left vs Right liver: IVA/B vs V/VIII Extrapolate a line from the
gallbladder fossa superiorly along the middle hepatic vein to the
IVC (red line).
• Left liver: lateral(II/III) vs medial segment (IVA/B)Extrapolate a
line along the falciform ligament superiorly to the confluence of
the left and middle hepatic veins at the IVC (blue line).
• Right liver: anterior (V/VIII) vs posterior segment
(VI/VII)Extrapolate a line along the right hepatic vein from the IVC
inferiorly to the lateral liver margin (green line).
ANATOMY
Upper segments
Lowerr segments

6. Safe delivery/Accuracy is of utmost
importance due to high fractional
dose and small number of fractions
Custom immobilization
Respiratory management
Image guidance
PTV PTV
• A critical issue in RT for HCC is the control of respiratory movement, as Liver motion is complex owing to organ deformation and rotation with respiration.
• For SBRT, control of respiratory motion should be considered more strictly than for conventional RT to ensure it receives the intended dose (to improve the
accuracy of treatment delivery without geographical miss ) while reducing the dose to surrounding normal tissue.
SBRT : Overview
Stereotactic body radiation therapy (SBRT) is the term applied in the United States by the
American Society of Therapeutic Radiology and Oncology (ASTRO) for the management and
delivery of image-guided high-dose radiation therapy with tumor-ablative intent within a course
of treatment that does notmexceed 5 fractions.

7. Unlike intracranial radiosurgery, where the PTV
is immobile within the skull and therefore
relatively easy to fix in relation to the radiation
source, at extra-cranial sites there are the
problems of internal organ motion and external
patient movement
Development of RT mainly focuses on improving two
factors: accuracy and precision. Accuracy of RT implies
that radiation can be delivered to the correct location
each time, despite various uncertainties between the
time of radiation treatment planning and the time of
actual treatment. Precision of RT means the ability to
control distribution of radiation to make sure that
prescribed dose is administered exactly to tumor site,
and that radiation is not delivered to surrounding
normal tissues.

8. • Radiotherapy for liver tumor in past, has met with
less enthusiasm than most other sites due to
inadequate knowledge about partial liver
tolerances, poor delivery techniques, inability to
control uncertainties associated with breathing
motion and risk of RILD (Radiation induced liver
damage).
• More recent experiences have demonstrated that
high-dose partial liver RT may be safer and more
effective.
• In recent years, technological advances in target
definition, treatment planning, and setup
verification have allowed radiation oncologists to
implement hypofractionated stereotactic body
radiation therapy (SBRT) for liver tumors.
SBRT : Overview

9. Internal fiducial markers can be residual
radio- opaque lipiodol after TACE or a
commercial fiducial marker which is
inserted under sono-guidance.
There are several methods accounting for target motion to
reduce errors from respiratory motion and improve the
accuracy of treatment planning or delivery and can be broadly
categorized as motion compensating (active breathing control
and tumor tracking) or motion restricting (abdominal
compression).

10. A.J. Cole et al. /
Clinical Oncology
26 (2014) 67e80

11. BALL ET AL. J Appl Clin Med Phys. 2022;23:e13810.

12. https://doi.org/10.1016/j.clon.2022.02.010

13. AAPM Task group 101

14. To considered Dmax if the constraint volume was
≤0.1 cc.
Practical Radiation Oncology! (2021) 11, e355−e365
AAPM Task group 101

15. SBRT : Indication and clinical outcome
• Liver cancer : HCC & Cholangiocarcinoma
• Liver metastasis

16. Y. Hu, C. Zhao, R. Ji et al.
Journal of the National Cancer Center 2 (2022) 171–182
SBRT : Outcome in HCC

17. • Most patients had invasion of their cancer into the hepatic vasculature (a poor
prognostic factor), and a small number had metastases outside of the liver. The
median age was 66 years (range 27-84).
• Overall survival was longer for patients who received a combination of
SBRT and sorafenib, compared to those on sorafenib alone (15.8 vs. 12.3
months; one-sided p = 0.055).
• Progression-free survival was improved with the addition of SBRT, from 5.5
months with sorafenib alone to 9.2 months with the combination therapy (HR
= 0.92, p<0.001).
• Patients in the combination arm also had longer intervals before their cancers
progressed (18.5 vs. 9.5 months; HR = 0.69, p=0.034).
• Treatment-related side effects were not significantly different between the
treatment groups. 42% of patients on the sorafenib arm and 47% of patients
on the SBRT/sorafenib arm experienced severe (i.e., grade 3 or higher) side
effects, and there was one treatment-related death, on the sorafenib-only arm.

18. Y. Hu, C. Zhao, R. Ji et al.
Journal of the National Cancer Center 2 (2022) 171–182

20. However, the possibility to deliver very high RT dose
on this site is limited by the low radiation tolerance
of both liver and GI tract.
• Nine studies were retrospectiveand
• one was a prospective Phase I study.
• No randomized controlled trial was found.
SBRT : Cholangiocarcinoma

21. • While significant heterogeneity exists in
the current OMD definitions in the
literature, consensus was reached on
multiple key questions.
• Based on available data, OMD can to
date be defined as 1–5 metastatic
lesions, a controlled primary tumor
being optional, but where all
metastatic sites must be safely
treatable.
Y. Lievens et al. / Radiotherapy and Oncology 148 (2020) 157–166
ESTRO-ASTRO OMD consensus document
Progression of selected metastatic deposit whilst other remain controlled by systemic therapy.
SBRT Liver metastasis

23. SBRT Liver metastasis
https://doi.org/10.1016/j.semradonc.2022.11.008

24. Ohri et al. Int J Radiation Oncol Biol Phys, Vol. 110, No. 1, pp. 188e195, 2021
• Thirteen articles
• Stereotactic body radiation therapy for primary
liver tumors provides high rates of durable local
control, with no clear evidence for a dose response
relationship among commonly utilized schedules
(33-60 Gy, 3-5 fractions, BED 60-180 Gy ). The 1-,
2-, and 3-year actuarial local control rates
after SBRT for primary liver tumors (n = 431)
were 93%, 89%, and 86%, respectively.
• Excellent local control rates are also seen after SBRT
for liver metastases when BEDs of >100 Gy are
utilized. Lower 1- (90%), 2- (79%), and 3-year
(76%) actuarial local control rates were
observed for liver metastases. with BEDs
exceeding 100 Gy10 (3-year local control 93%)
than for those treated with BEDs of ≤100 Gy10 (3-
year local control 65%, P < .001).
• The most common histology for patients
with liver metastases was colorectal
cancer, which accounted for 32% to 100% of the
treated lesions in the articles we analyzed (overall
56% of liver metastases).
• We therefore believe that it is reasonable to use relatively conservative SBRT schedules, such as 8 to
10 Gy 5 fractions, in this patient population of primary liver cancer. More aggressive schedules should be
used with caution, especially in patients with underlying liver disease.
• Tumor control probability modeling revealed that the 2-year local control is expected to increase progressively
with BED, reaching 76% for a BED of 100 Gy and 90% for a BED of 180 Gy. Hence, relatively aggressive
SBRT schedules delivering a BED ! 100 Gy10 should be considered for patients with liver
metastases.
SBRT Liver metastasis Vs HCC

25. Grimm et al.
Int J Radiation Oncol Biol Phys, Vol. 110, No. 1, pp. 1e10, 2021
HCC appears to be a relatively
radiosensitive tumor, such that,
above a certain threshold dose,
there may be little benefit in
further dose escalation, and
potential for increased toxicity.
SBRT Liver metastasis Vs HCC
• 50% of patients with colorectal adenocarcinoma will
develop metastatic disease to the liver, and it is often
the first site of metastatic progression.
• Liver metastases can cause significant pain from hepatic
capsular involvement, thus negatively affecting health-
related quality of life for patients with metastatic disease.
In addition, more extensive liver disease can cause liver
dysfunction that can limit the administration of systemic
chemo- therapy and ultimately lead to death.
• The potentially curative treatment of liver metastasis with
surgical resection has been reported for many years, with
5-year survival rates now of 50%-60%.Moreover, if
patients are well selected, up to 20% can achieve long-
term disease-free survival after hepatectomy.
• Unfortunately, only 10%-20% of liver metastases are
amenable to resection. For unresectable tumors,
advances in combination chemotherapy and targeted
agents have resulted in a doubling of median survival
from 10 to 20 months in patients with metastatic
colorectal cancer over the past 2 decades.
• Alter- natives to surgery, such as radiofrequency ablation,
cryoablation, and alcohol injection, have been attempted
and have shown some benefit. However, these
techniques suffer from many limitations due to lesion
location, adjacent structures, and high recurrence rates.

26. SBRT LIVER WHEN & HOW

27. • Decompensation of liver disease (jaundice, ascites, encephalopathy) reflects non-preserved liver
function irrespective of the CP Score / (MELD) score.
• TSM : specific patient profile may induce shift of recommendation to the option that would be considered a
priority for more advanced stage.
• Untreatable progression : It represents failure of selected treatment strategy and emerges when patient
present treatment failure or progression but still fit in to their initial BCLC Stage thus warranting the
consideration of therapy corresponding to more advanced stage.
• CSPH : Hepatic venous pressure gradient >10 mmhg.

28. • CP A-B7, PS 0–2, BLCL : B,C(PVT),A (inoperable), 700 cc functional liver reserve, no Ext hep disease,
Patients with active viral hepatitis (transaminases> 2.5 times the upper normal limit) should be started on
anti-viral therapy at least 2 weeks before SBRT , no signs of hepatic decompensation ( jaundice,
Intractable ascites, encephalopathy, Varices ), > 5 mm away from GI Structure.
• SBRT is a treatment option for patients with unresectable disease ( unsuitable for resection / transplant ),
or for those who are medically inoperable due to comorbidity, can be considered as an alternative to
ablation (RFA) /embolization (TACE) techniques or when these therapies have failed/Refractory or they
are contraindicated.
• SIZE/NUMBER OF LESIONS :
patients with 1 to 3 tumors. SBRT could be considered for larger lesions or more extensive disease,
if there is sufficient uninvolved liver and liver radiation tolerance can be respected.
Indication for HCC SBRT :
• Unsuitable for resection or transplant or
radiofrequency ablation (RFA)
• Unsuitable for TACE or refractory to TACE
• Barcelona Clinic Liver Cancer Stage (BCLC)
Intermediate (B) or Advanced (C)
• Often used in 1-3 lesions, could be
considered for larger lesions or more
extensive disease if there is sufficient
uninvolved liver and liver radiation tolerance
can be respected.
• Child Pugh A/ Early Child Pugh B.
Contraindication for HCC SBRT
• Any one hepatocellular carcinoma > 15 cm / Total maximal sum of hepatocellular
carcinoma > 20 cm/ More than 5 discrete intrahepatic parenchymal foci of HCC
• Direct tumor extension into the stomach, duodenum, small bowel or large bowel/ Measureable
common or main branch biliary duct involvement with HCC
• Extrahepatic metastases or malignant nodes (that enhance with typical features of HCC) > 2.0
cm, in sum of maximal diameters (e.g. presence of one 2.4 cm metastatic lymph node or two 1.2 cm
lung lesions). Note that benign non-enhancing periportal lymphadenopathy is not unusual in the
presence of hepatitis and is permitted, even if the sum of enlarged nodes is > 2.0 cm
• Hepatic insufficiency resulting in clinical jaundice, encephalopathy and/or variceal bleed.
indications for radiotherapy include definitive treatment in Barcelona Clinic Liver Cancer (BCLC) A or B,
bridging to transplant, recurrent or large unresectable tumours, combination with TACE for large BCLC B,
BCLC C with portal vein thrombosis and palliative treatment.
Case selection for HCC SBRT

29. Prerequisite
For all patients, the following criteria calculated from baseline CT or MR scans should be
met:
Liver volume minus intrahepatic GTV > 700 cc.
Intrahepatic tumor GTV/liver volume ratio <80%. (The effective liver volume irradiated (Veff)
had to be less than 0.8, where 1.0 represents whole organ irradiation)
Minimal distance from GTV to stomach, duodenum, small or large bowel > 1 cm.
• Varying approaches to dose selection have been adopted and include a
biological individualized strategy based on the effective volume of irradiated
liver and Lyman normal tissue complication probability (NTCP) estimation of
classic radiation-induced liver disease or a critical volume approach, which
limits the dose received by a specified volume of normal liver often 700 mL.
• As well as liver doses, luminal doses are also important. One trial, with one of
the highest high-grade GI toxicity rates, did not specify luminal constraints, which
may have contributed to the high toxicity, although pre-existing GI ulceration may
have had an impact. Another study observed that all patients with high-grade
GI toxicity had lesions 0.5 cm from luminal structures. Thus, luminal
constraints or specification of minimal distances between targets and lumen,
or both, are necessary.

30. • Age is not considered in selection criteria, as even elderly
and fragile patients can safely undergo SBRT. This non-invasive
and well-tolerated therapy is a good option for patients
unsuitable for surgery.
• Intrinsic radio-sensitivity of tumours is not an issue ,as
SBRT can be used regardless of histopathology thanks to
the use of ablative doses, with similar local control rates in
radioresistant and radiosensitive primary tumour.
Indication & Contraindication in Liver mets
Safety :
• >700 cc residual liver
• Focal tumor distribution
• >5 mm from luminal GI tissue
Efficacy :
• Size : <3cm vs 3-6cm vs >6cm
• Number of tumors : < 3 v.s
3-5 vs >5
• Tools to select patients :
1) Imaging :
PET to rule out extrahepatic disease
Primovist MR to rule out diffuse hepatic metastases
2) Natural history :
should have expected survival of > 6 months from
the their primary lesion.
Patients presenting with synchronous metastasis
should also have adequate systemic and local
treatment before proceeding with liver directed
treatment.

31. Lowest risk : central, away from luminal GI, ribs, biliary tract
Liver SBRT: Lowest Risk to Higher Risk locations

32. Low risk : sup/lateral liver
Liver SBRT: Lowest Risk to Higher Risk locations

33. Potential risk : central lesions, biliary
Liver SBRT: Lowest Risk to Higher Risk locations

34. Higher risk : Adjacent to stomach and bowel
Liver SBRT: Lowest Risk to Higher Risk locations

35. Simulation
Supine & arms up
Custom immobilization is recommended (e.g. With vacuum immobilization, patient positioning
boards, knee cushions, and/or breath hold immobilization with active breathing control).

36. BALL ET AL. J Appl Clin Med Phys. 2022;23:e13810.
Simulation

37. • Intravenous contrast-enhanced, multiphasic CT is required for
GTV delineation. Needs 2 – 2.5 mm slice thickness for Scan.
If fixed oral contrast/ water intake is given then repeat at time of
treatment.
• For HCC : Tumor enhances on the arterial phase before washing
out during venous and delayed phases, obtained during breath
hold.
• For liver mets : PV Phase is used to delineate hypo vascular
mets and Arterial phase for Hyper vascular mets.
• 4D-CT can aid in estimation of motion & generation of i-GTV/ITV.
• MRI sequences &/ PET-CT can further assist with GTV definition.
• CTV margins are typically not employed except prior TACE (t)
sites (CTVt), or adjacent RFA (r) (or MW ablation) cavity (CTVr) are
permitted.
• PTV margins are usually individualized and are ideally 5 mm but
up to 10 mm may be required, depending on the motion
management strategy.
Aorta and branches IVC,PV,Solid organ
Parenchyma
Renal collecting, ureter,
U_bladder
NON CONTRAST
ARTERIAL
ENHANCMENNT
VENOUS PHASE_
WASHOUT
DELAYED PHASEMORE
WASHOUT
CAPSULE/PSE
UDO CAPSULE
Simulation & Target Volume Contouring Aspects HCC

38. Analyze the tumor in all phases of triple
phase CT And See the greatest resolution
Simulation & Target Volume Contouring Aspects HCC

39. Simulation & Target Volume Contouring Aspects HCC
• The primary tumor(s) and any tumor vascular thrombi must be
treated
• The Gross Tumor Volume (GTV) is defined as all parenchymal
and vascular HCC visualized on contrast enhanced CT and/or
MRI, most often best seen on arterial phase (as hyperintensity)
and/or venous or delayed phase (as hypointensity relative to
liver). Vascular HCC thrombi (GTVv) most often are best seen
on venous phase imaging as hypointensity relative to the
contrast in the vessel, Vascular HCC may be combined with
parenchymal HCC (labeled as GTVp or GTVpv) if they are to be
treated to the same dose.
• Treatment of non-tumor extrahepatic vascular thrombi, RFA
cavities and prior TACE sites is not recommended. no
prophylactic nodal irradiation is allowed.
• It is expected that there will be no expansion from GTV to CTV
for the majority of cases. However, CTV expansions to include
regions at high risk for microscopic disease, including non-
tumor vascular (v) thrombi (CTVv), prior TACE (t) sites (CTVt), or
adjacent RFA (r) (or other ablation) sites (CTVr) are permitted.
• PTV will provide a margin around each CTV to compensate for
set-up and internal organ motion
• minimum PTV margin of 4 mm around each CTV is required in
all directions (for example if active breathing control is used
with excellent reproducibility). The maximum permitted PTV
margin is 20 mm, expected to be used uncommonly. PTV
margins ≤ 10 mm are a goal.

40. 4D CT Scan Simulation

41. 4D Simulation

42. 4D Simulation

43. BALL ET AL. J Appl Clin Med Phys. 2022;23:e13810.
Simulation & Target Volume Contouring Aspects HCC

44. OAR Contouring for HCC
• At minimum, these structures are required to be contoured at the level of the PTV and over any region received >
10 Gy. It requires : Normal Liver ( Liver – GTV), Stomach, Duodenum, Small bowel, large bowel, Sp_Cord, Heart,
Ribs, Lungs, Kidney, CBD, Gall bladder, Great vessel.
• An upper abdominal/liver atlas, posted at the ITC website, may be used as a guide for contouring.

45. • Individualized dose prescription (27.5- 50Gy in 5#) to isodose covering 95% of PTV based on tumor size, the
volume of normal tissues irradiated (correlated with mean liver dose), as proximity of GI luminal structures to PTV,
normal tissue constraints must be maintained, CP Score (severity of liver Disease). Treatment on alternate day.
• When using SBRT for HCC as a bridging therapy, as the final objective is not complete ablation, doses no higher than 45
Gy in five fractions are recommended, and consideration should be given to reduce the doses in central lesions or in other
locations in which fibrosis may lead to a potential increased risk of toxicity.
• The dose to multiple PTVs may be different. Vascular tumor thrombosis (e.g., portal vein thrombosis) dose should be the
same as the HCC prescription dose. However, lower doses are acceptable if required to maintain normal tissue limits. RFA
cavities can be treated to differential doses to optimize normal liver sparing .
• The goal is to use the highest allowable prescription dose to the PTV, while respecting normal tissue constraints. In the
absence of adjacent GI luminal structures that may limit dose, the PTV dose prescription should be as high as possible
based on mean liver dose (MLD, defined as the mean dose to the liver minus all GTVs).
Dose prescription for HCC
For small tumors away from luminal GI tissues, a fixed dose may be used (eg, 40 Gy in 5 fractions), but for
larger tumors, where doses must be limited because of normal liver tolerance, an individualized strategy, based
on escalating dose based on liver constraints, is most appropriate.

46. Dose prescription for HCC

47. 3 × 15–25 Gy : for patients with tumors <3 cm in
size and adequate liver reserve (CP-A5)
5 × 10–12 Gy : for patients with tumors between 3
and 5 cm or inadequate liver reserve (CP-A 6)
10 × 5–5.5 Gy : for patients with tumors >5 cm in
size or CP-B scores.
S. Apisarnthanarax et al Practical Radiation Oncology! (2022) 12, 28−51

48. Plan evaluation for HCC :
• The prescription isodose should encompass 95% of PTV. A goal is that 100% of the CTV is encompassed by the
prescription dose. Maximum dose within PTV = 150%. Maximum dose outside PTV = 120% of the maximal PTV
prescription. Differential prescription to GTV/HOT-CORE : 20-30% higher.
• Efforts should be made to keep the 30Gy isodose as conformal as possible.
• If multiple PTVs, the MLD should be evaluated with the prescription dose corresponding to the highest dose level
that any PTV is treated.
• Reducing the maximal dose to all luminal gastrointestinal normal tissues should be a planning priority to reduce
the risk of gastrointestinal toxicity.
• Target coverage :
Rx isodose should encompass 95% PTV / 100% CTV coverage
• Normal tissue avoidance :
– Prescription dose based on volume of normal liver irradiated (correlated with mean liver dose)
– In absence of adjacent luminal structures to limit dose, PTV dose may be the highest allowable
• Conformality :
Prescription isodose
30 Gy isodose
• Most simple solution meeting acceptability criteria :
VMAT – 1 arc vs. 2 arcs

49. Constraints for HCC
• Mean liver dose & Dose to 700cc should be given priority over Veff to minimize
NTCP.
• Liver being parallel organ can receive high doses of radiation as long as a sufficient
volume of healthy liver tissue is spared. Kavanagh et al. used a similar SBRT
dosimetric constraint by requiring that 700 mL of the normal liver receive no more
than a total of 15 Gy in a three- fraction regimen for liver SBRT. This critical
volume- type restriction for the normal liver is comparable to liver surgeons requiring
a certain predicted minimal volume of liver to remain in order to ensure that a patient
has adequate and reasonable liver functional reserve after surgical resection.
• The effective liver volume (Veff) irradiated is a model based on the normal liver
volume and the volume irradiated. The Veff is defined as the normal liver volume
minus all GTVs, which if homogenously irradiated to the maximum dose would
be associated with the same estimated risk of RILD as the delivered
heterogeneous treatment plan. A lower Veff correlated with significantly lower risks
of RILD, demonstrating in the setting of dose escalation, high doses can be delivered
as long as the mean dose to the liver is taken into account.
Non-liver
OARs

50. Mean dose to liver should be restricted to
18Gy in CP A5-6 for 5-6 # and < 6Gy in CP
B7
S. Apisarnthanarax et al Practical Radiation Oncology! (2022) 12, 28−51

51. SBRT Liver metastasis

53. Pre & post SBRT considerations
• Pre SBRT :
– Ensure recovery from chemo (> 2 weeks gap )
• Caution with anti-VEGF therapy
– Fiducial markers – in needed for IGRT
– Antiemetics - if stomach irradiated
– Steroid - if high risk for biliary edema or massive vascular invasion
– Antiviral therapy if untreated Hepatitis B : start Antiviral 2 weeks before
• Post SBRT :
– Consider proton pump inhibitors – if stomach irradiated

54. Image Guidance
• Daily image guidance is necessary.
• Orthogonal x-rays and cone beam CT (CBCT) are most
commonly employed. CBCT matching has been suggested
to be superior to orthogonal x- rays.
• The use of peritumoral fiducials ( Gold seeds ), with both
x-rays and CBCT, can further enhance setup.
• The presence of lipiodol following TACE, or surgical clips,
has also been used as surrogates for tumor position if not
then liver contour can be taken in to the account.
• Depending on the method of respiratory motion
compensation, CBCT acquired in breath hold or as a 4D-
CBCT to assist in matching.
Lipiodol / fiducial useful
in IGRT
LIVER
DUODENUM
LARGE BOWEL
STOMACH

55. A. Burton et al. Physics and Imaging in Radiation Oncology 24 (2022) 21–29

56. BALL ET AL. J Appl Clin Med Phys. 2022;23:e13810.

57. Future implementation : MR Guided radiotherapy
• The implementation of daily online image guidance using MRI in the context of the MR-linac will
provide enhanced soft tissue information compared to CBCT, thus improving setup accuracy, without
the need for fiducials.
• The system may also allow intrafraction motion monitoring. Adaptive radiotherapy would allow
creation of “plans of the day,” based on each day's anatomy, which could further improve accuracy.
• These measures may reduce uncertainties, PTV margins, and normal tissue irradiation, hopefully
reducing toxicities and improving the therapeutic ratio for HCC SBRT.