Dosimetric Evaluation ofPlanning Techniques in Lung SBRT

Authored by:Toby Shutters, B.S. RT(R) (T)

Indiana University School of MedicineMedical Dosimetry Graduate Certificate Program

Indianapolis, Indiana

 Co-Authored by:

Jeannie Jimerson, M.S. RT (T), CMDRichard Roudebush VA Medical Center

SBRT

Hypofractionation

High Conformality

Steep Dose Gradients

Stereotactic Body Frame

http://www.erasmusmc.nl/radiotherapie/patientenzorg/behandelmethoden/uitwendigebestraling/128828/314368/

Non-small Cell Lung Cancers (NSCLC)

Surgical Options

Lobectomy

Wedge resection or segmentectomy

Comorbidities

RadiationConventional External

BeamSBRT

Small Daily Fractions

Total Fractions 27 to 33

5 year survival rate of 10 to 30%

Large Daily Fractions

Total Fractions 1 to 5

3 year local control rates of up to 98%

Increases in late toxicities

LocationDosimetrically challenging

Tumors adjacent to the chest wall areaDeliver high conformal dosesMinimize critical structure doses

Late toxicitiesChest wall painRib fractures

ToxicitiesNatonal Institute Common Terminology

Criteria for Adverse EventsGrade 1

Mild painGrade 2

Moderate painGrade 3

Severe painGrade 4

Disabling pain

Doses

Andolino et al

10% risk of grade 1 or greater at 30 Gy with 15cc’s

30% risk at 30 Gy with 40 cc’s

50 Gy greater incidence of rib fracture or chest wall pain

Dunlap et al

30 Gy in 3-5 fractions should be less than 30cc’s

50 Gy greater incidence of rib fracture or chest wall pain

Dosimetric EvaluationThis study retrospectively analyzed three

planning techniques to determine if a there was a dosimetric advantage utilizing noncoplanar geometry. All five patients had adjacent or invasive chest wall lesions. The plans were evaluated using the Conformality Index from RTOG 0813 and 0915. Chest wall and rib volumes were examined at V30Gy, V45Gy, and V50Gy.

Methods and Materials5 patients with adjacent chest wall tumors

Eclipse Version 8.0

Elekta Bodyframe

GTV’s and PTV’s

OAR’s through RTOG protocols

Evaluation of dose

Methods and Materials, continuedTwo sets of blocks

Modifications to blocks and weighting of PTV

95% of the PTV volume covered by prescription

Most common isodose 80%

Three Planning TechniquesCoplanar (COP)

No couch rotations

Mixed Planar (MP)Some couch rotations, some not

Non-coplanar (NCP)All couch rotations

Three Planning Techniques: COPField Label Gantry Angle Couch Rotation

AP 0 0

RAO 333 333 0

RAO 305 305 0

RAO 278 278 0

RPO 250 250 0

RPO 223 223 0

RPO 195 195 0

LPO 168 168 0

LPO 140 140 0

LPO 113 113 0

LAO 85 85 0

LAO 58 58 0

LAO 30 30 0

000

Three Planning Techniques: MP

Field Label Gantry Angle Couch Rotation

RPO 210 0

RT LAT 270 0

RAO 315 0

AIO 340 90

ASO 30 90

LAO 50 0

LSO 90 20

LIO 90 340

LPIO 160 340

PA 180 0

Three Planning Techniques: NCPField Label Gantry Angle Couch

Rotation

LPSO 2 160 50LPSO 1 122 18LAIO 2 101 345LASO 1 79 15LAIO 1 58 342LASO 1 37 16LAIO 1 19 306RASO 2 350 306RAIO 2 323 26RASO 1 302 342RAIO 1 281 10RPSO 2 259 345RPIO 1 238 15RPSO 1 217 345

Plan Evaluations

4 fractions of 12 Gy for total of 48 Gy95 % coverage of PTVRTOG 0915 for OAR verificationChest wall/rib volume at 2cm contourDVH at V10 Gy, V30 Gy, V45 Gy, and V50 GyConformality Index

ResultsConformality Index (CI)RTOG 0813 and 0915Optimum CI less than 1.2Minor Deviations between 1.2 and less than

1.5All three techniques

Optimal or minor deviations40% or 6 out of 15 optimalMP: met 1.2 for all but one patientCOP and NCP: met 1.2 one patient each

Results

1 2 3 4 51

1.1

1.2

1.3

1.4

1.5

Conformality Index

Mixed

COP

NCP

Patient #

Con

form

ali

ty I

ndex

P1 P2 P3 P4 P50

5

10

15

20

25

30

Chestwall Volume 30 Gy

MixedCOPNCP

Patient#

Volu

me

(cc)

P1 P2 P3 P4 P50

1

2

3

4

5

6

7

8

Chestwall Volume 45 Gy

MixedCOPNCP

Patient #

Volu

me

(cc)

P1 P2 P3 P4 P50

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Chestwall Volume 50 Gy

MixedCOPNCP

Patient #

Volu

me

(cc)

P1 P2 P3 P4 P50

1

2

3

4

5

6

7

Rib Volume 30 Gy

MixedCOPNCP

Patient #

Volu

me

(cc)

P1 P2 P3 P4 P50

0.5

1

1.5

2

2.5

3

3.5

4

Rib Volume 45 Gy

MixedCOPNCP

Patient #

Volu

me

(cc)

P1 P2 P3 P4 P50

0.5

1

1.5

2

2.5

3

3.5

Rib Volume 50 Gy

MixedCOPNCP

Patient #

Volu

me

(cc)

SynopsisDose/Volume relationship

Analysis of three different planning techniques for dose conformality

V30 Gy, V45 Gy, and V50 Gy similar for NCP and MP

CI was met more often for MP than NCP

P1 P2 P3 P4 P50

20

40

60

80

100

120

140

160

180

200

Chestwall Volume 10 Gy

MixedCOPNCP

Patient #

Volu

me

(cc)

P1 P2 P3 P4 P50

5

10

15

20

25

30

35

Rib Volume 10 Gy

MixedCOPNCP

Patient #

Volu

me

(cc)

ConclusionCure for early stage NSCLC is surgicalAging population has comorbiditiesMedically inoperable offered SBRTSBRT has late toxicitiesImproved survival decrease toxicitiesAnalyzed 3 planning techniques for volumes

and conformalityNCP offers no dosimetric advantage

increases treatment timeMP is best option