3D CRT

Question 1

Define 3D CRT

Answer 1

Based on 3D anatomic information
Uses 3D dose distribution
Designs and delivers conformal treatment plan to target volume, adequate dose to tumor, minimum dose to normal tissue

Question 2

3 categories of dose calculation algorithm in 3D CRT

Answer 2

Correction based algorithm
Model based algorithm
Monte Carlo algorithm

Question 3

Correction based algorithm are based on?

Answer 3

Measured data obtained in cubic water phantom
PDD(Percentage Depth Dose)
Cross beam profile

Question 4

Examples of Correction based algorithm

Answer 4

Clarkson integration using scatter-air ratio, delta volume, dose spread array

Question 5

Limitations of correction based algorithm

Answer 5

Unable to calculate dose accurately in

1. Treatment where electronic equilibrium may not exist such as those involving initial buildup region
2. Lung irradiation with high energy beams
3. very small fields as in SRT

N.B. Model based algorithm is capable of all 3

Question 6

Examples of model based algorithm

Answer 6

Pencil beam convolution
Convolution/superposition of dose kernels
Monte Carlo

Question 7

Which algorithm is sufficiently accurate at tissue interface?

Answer 7

Monte Carlo

Question 8

7 Steps for treatment planning process for 3D CRT

Answer 8

1. Imaging data acquisition
2. Image registration
3. Image segmentation
4. Beam aperture design
5. Field multiplicity
6. Plan optimization
7. Plan evaluation
8. Delivery of 3D CRT
9. Verification

Question 9

Criteria for optimal plan evaluation

Answer 9

1.Biologic criteria
     TCP Tumor Control Probability
     NTCP Normal Tissue Complication Probability
2.Physical criteria
    Isodose curves and surfaces
    DVH

Question 10

Forms of DVH

Answer 10

Cumulative(Integral) DVH : most common

Differential DVH

Question 11

What is reference point?

Answer 11

Normalized 100% dose prescription at a point located at the center of PTV

ICRU 50/62