J Korean Soc Ther Radiol Oncol.  2010 Sep;28(3):166-176. 10.3857/jkstro.2010.28.3.166.

PTV Margins for Prostate Treatments with an Endorectal Balloon

• Kim HJ
• Chung JB
• Ha SW
• Kim JS
• Ye SJ

• KMID: 1460149
• DOI: http://doi.org/10.3857/jkstro.2010.28.3.166

Abstract

PURPOSE
To determine the appropriate prostate planning target volume (PTV) margins for 3-dimensitional (3D) conformal radiotherapy (CRT) and intensity-modulated radiation therapy (IMRT) patients treated with an endorectal balloon (ERB) under our institutional treatment condition.
MATERIALS AND METHODS
Patients were treated in the supine position. An ERB was inserted into the rectum with 70 cc air prior to planning a CT scan and then each treatment fraction. Electronic portal images (EPIs) and digital reconstructed radiographs (DRR) of planning CT images were used to evaluate inter-fractional patient's setup and ERB errors. To register both image sets, we developed an in-house program written in visual C++. A new method to determine prostate PTV margins with an ERB was developed by using the common method.
RESULTS
The mean value of patient setup errors was within 1 mm in all directions. The ERB inter-fractional errors in the superior-inferior (SI) and anterior-posterior (AP) directions were larger than in the left-right (LR) direction. The calculated 1D symmetric PTV margins were 3.0 mm, 8.2 mm, and 8.5 mm for 3D CRT and 4.1 mm, 7.9 mm, and 10.3 mm for IMRT in LR, SI, and AP, respectively according to the new method including ERB random errors.
CONCLUSION
The ERB random error contributes to the deformation of the prostate, which affects the original treatment planning. Thus, a new PTV margin method includes dose blurring effects of ERB. The correction of ERB systematic error is a prerequisite since the new method only accounts for ERB random error.

Keyword

Prostate; Endorectal balloon; PTV margin; Setup error

MeSH Terms

Electronics
Electrons
Humans
Prostate
Radiotherapy, Conformal
Rectum
Supine Position