Prostate image-guided radiotherapy by megavolt cone-beam CT

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Technology

Background:

• Accurate patient setup is crucial for effective prostate radiotherapy.
• Traditional methods like electronic portal imaging (EPI) have limitations in verifying soft tissue positioning.
• Megavolt cone-beam CT (MV-CBCT) offers potential for improved setup verification.

Purpose of the Study:

• To evaluate the efficacy of MV-CBCT in assessing setup errors in prostate radiotherapy.
• To compare different MV-CBCT image registration methods (bone, soft tissue, automatic) against electronic portal imaging (EPI).

Main Methods:

• Weekly setup verification using EPI and MV-CBCT in 9 patients.
• MV-CBCT registration methods: manual bone (BMR), manual soft tissue (STR), and automatic (AR).
• Evaluation of shifts along anteroposterior (AP), craniocaudal (CC), and laterolateral (LL) axes.
• Analysis of calcification mismatch in 4 additional patients to assess registration accuracy.

Main Results:

• No significant differences between EPI and BMR in any axis within a 2 mm tolerance.
• Significant differences (p < 0.001) along the AP axis comparing EPI vs AR and EPI vs STR.
• Lower calcification mismatch (p < 0.05) along AP using STR compared to BMR or AR.

Conclusions:

• Bone markers are not reliable surrogates for prostate target position.
• MV-CBCT-based soft tissue registration (STR) is superior for verifying and correcting patient setup in prostate radiotherapy.
• MV-CBCT facilitates accurate assessment of soft tissue position for improved treatment accuracy.