Abstract
The use of rectal balloon in radiotherapy of prostate cancer is shown to be effective in reducing prostate motion and minimizing rectal volume, thus reducing rectal toxicity. Air‐filled rectal balloon has been used most commonly, but creates dose perturbation at the air‐tissue interface. In this study, we evaluate the effects of rectal balloon‐filling materials on the dose distribution to the target and organs at risk. The dosimetric impact of rectal balloon filling was studied in detail for a typical prostate patient, and the general effect of the balloon filling was investigated from a study of ten prostate patients covering a wide range of anterior–posterior and left–right separations, as well as rectal and bladder volumes. Hounsfield units (HU) of the rectal balloon filling was changed from −1000 HU to 1000 HU at an interval of 250 HU, and the corresponding changes in the relative electron density (RED) was calculated. For each of the HU of the rectal balloon filling, a seven‐field IMRT plan was generated with 6 MV and 15 MV photon beams, respectively. Dosimetric evaluation was performed with the AAA algorithm for inhomogeneity corrections. A detailed study of the rectal balloon filling shows that the GTV, PTV, rectal, and bladder mean dose decreased with increasing values of RED in the rectal balloon. There is significant underdosage in the target volume at the rectum–prostate interface with an air‐filled balloon as compared to that with a water‐filled balloon for both 6 MV and 15 MV beams. While the dosimetric effect of the rectal balloon filling is reduced when averaged over ten patients, generally an air‐filled balloon results in lower minimum dose and lower mean dose in the overlap region (and possibly the PTV) compared to those produced by water‐filled or contrast‐filled balloons. Dose inhomogeneity in the target volume is increased with an air‐filled rectal balloon. Thus a water‐filled or contrast‐filled rectal balloon is preferred to an air‐filled rectal balloon in EBRT of prostate treatment.PACS numbers: 87.55.D‐, 87.55.de, 87.55.dk, 87.55.Gh, 87.55.kd
Highlights
82 Srivastava et al.: Impact of rectal balloon filling materials in photon beam therapy androgen deprivation
In prostate intensity-modulated radiation therapy (IMRT), the varying state of rectal filling is a main factor in prostate gland motion and contributes to the majority of the organ motion.[1-8]. In addition to this interfractional motion, it has been reported that intrafractional motion of the prostate may occur, and patients with large volume of rectal gas showed significant amount of rectal displacement (> 3 mm) in the superior–anterioposterior direction.[9-15] organ motion can be minimized by using a rectal balloon and this is one of the reasons it is used routinely in particle beam therapy
The use of rectal balloon has been found to be well-tolerated and effective in reducing the intrafraction motion and improving the sparing of rectal wall by reducing the rectal volume in the high-dose region, resulting in significant reduction in rectal toxicity.[16-20]. Air-filled rectal balloons with volume varying from 40–100 cm3 have been used most commonly for external beam prostate radiotherapy.[21-25]. Use of a water-filled rectal balloon for prostate irradiation has been reported in proton therapy to reduce the rectal wall dose.[26]. While dosimetric effects of an air-filled rectal balloon have been published in terms of dose-volume studies on rectum and bladder, its effects on the coverage of prostate and PTV have not been sufficiently studied
Summary
82 Srivastava et al.: Impact of rectal balloon filling materials in photon beam therapy androgen deprivation. In prostate IMRT, the varying state of rectal filling is a main factor in prostate gland motion and contributes to the majority of the organ motion.[1-8]. In addition to this interfractional motion, it has been reported that intrafractional motion of the prostate may occur, and patients with large volume of rectal gas showed significant amount of rectal displacement (> 3 mm) in the superior–anterioposterior direction.[9-15]. The use of rectal balloon has been found to be well-tolerated and effective in reducing the intrafraction motion and improving the sparing of rectal wall by reducing the rectal volume in the high-dose region, resulting in significant reduction in rectal toxicity.[16-20]. Air-filled rectal balloons with volume varying from 40–100 cm have been used most commonly for external beam prostate radiotherapy.[21-25]. The aim of this study is to evaluate the effects of rectal balloon filling-media on the dose distribution to GTV, PTV, rectum, bladder, and overlap of PTV to rectum
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