Positional reproducibility and effects of a rectal balloon in prostate cancer radiotherapy

Abstract

Despite the increasing use of the rectal balloon in prostate cancer radiotherapy, many issues still remain to be verified objectively including its positional reproducibility and relevance to treatment morbidity. We have developed a custom rectal balloon that has a scale indicating the depth of insertion and dilates symmetrically ensuring positional reproducibility. Fifty patients with prostate cancer treated by definitive 3D-conformal radiotherapy (3D-CRT) or intensity-modulated radiotherapy (IMRT) with rectal balloon were analyzed. Each of first five patients undergone computed tomography (CT) three times with a rectal balloon. The positional reproducibility was tested by Intraclass Correlation Coefficient (ICC) from the CT-to-CT fusion images. Planning variables and clinical acute toxicities were compared between when or not applying balloon. An ICC of greater than 0.9 in all directions revealed an excellent reproducibility of the balloon. Rectal balloon improved considerably the mean dose and V(45Gy)-V(65Gy) in plan comparison, and especially in 3D-CRT the rectal volume exposed to more than 60 Gy dropped from 41.3% to 19.5%. Clinically, the balloon lowered acute toxicity, which was lowest when both the balloon and IMRT were applied simultaneously. The rectal balloon carries excellent reproducibility and reduces acute toxicity in 3D-CRT and IMRT for prostate cancer.

Keywords: 3D Conformal Radiotherapy; Acute Toxicity; Prostatic Neoplasms; Radiotherapy, Intensity-Modulated; Rectal Balloon.

Fig. 1

The rectal balloon and its application to the patient. (A) Constituents of the rectal balloon. (B) Measurement of the insertion depth of the rectal balloon using a marked scale on the rectal tube (black arrow). (C) Pre-treatment supine position. (D) Inflated rectal balloon.

Fig. 2

Positional reproducibility test for the rectal balloon. (A) Three levels of balloon displacement measurements on the fused sagittal image between the first (gray) and second CT (thermal). (B) Displacement measurement of the mid-rectangles between the first, second, and third CT. (C, D) Displacement of the balloon on the third CT compared to the first CT. (E, F) Displacement of the balloon on the first CT compared to the second CT. (G, H) Displacement of the balloon on the first CT compared to the third CT.

Fig. 3

Identification of the rectal balloon (blackarrow) on: (A) the verification film (RIT 113®) and (B) the EPID image on a lateral beam port. d1 represents the sagittal diameter of the balloon, d2 represents the distance between the anterior surface of the balloon and the top of the couch table.

Fig. 4

Change in dose distribution and dose volume histogram (DVH) according to the balloon in prostate cancer radiotherapy. (A) 3D-CRT without balloon. (B) 3D-CRT with balloon. (C) IMRT without balloon. (D) IMRT with balloon. (E) Rectal DVH.

Fig. 5

Balloon displacement by rectal gas identified on the megavoltage CT (MVCT) scan of helical tomotherapy. (A) Rectal gas and balloon on MVCT image (yellow). (B) Balloon on the initial CT image (gray). (C) Unmatched balloon surface between the MVCT and initial CT image.