Clinical Investigation
Rectal Dose–Volume Differences Using Proton Radiotherapy and a Rectal Balloon or Water Alone for the Treatment of Prostate Cancer

https://doi.org/10.1016/j.ijrobp.2007.04.075Get rights and content

Purpose

To describe dose–volume values with the use of water alone vs. a rectal balloon (RB) for the treatment of prostate cancer with proton therapy.

Materials and Methods

We analyzed 30 proton plans for 15 patients who underwent CT and MRI scans with an RB or water alone. Simulation was performed with a modified MRI endorectal coil and an RB with 100 mL of water or water alone. Doses of 78–82 gray equivalents were prescribed to the planning target volume. The two groups were compared for three structures: rectum, rectal wall (RW), and rectal wall 7 cm (RW7) at the level of the planning target volume.

Results

Rectum and RW volumes radiated to low, intermediate, and high doses were small: rectum V10, 33.7%; V50, 17.3%; and V70, 10.2%; RW V10, 32.4%; V50, 20.4%; and V70, 14.6%. The RB effectively increased the rectal volume for all cases (139.8 ± 44.9 mL vs. 217.7 ± 32.2 mL (p < 0.001). The RB also decreased the volume of the rectum radiated to doses V10–V65 (p ≤ 0.05); RW for V10–V50; and RW7 for V10–V35. An absolute rectum V50 improvement >5% was seen for the RB in 5 of 15 cases, for a benefit of 9.2% ± 2.3% compared with 2.4% ± 1.3% for the remaining 10 cases (p < 0.001). Similar benefit was seen for the rectal wall. No benefit was seen for doses ≥70 gray equivalents for the rectum, RW, or RW7. No benefit of ≤1% was seen with an RB in 46% for the rectum V70 and in 40% for the rectal wall V70.

Conclusions

Rectum and rectal wall doses with proton radiation were low whether using water or an RB. Selected patients will have a small but significant advantage with an RB; however, water alone was well tolerated and will be an alternative for most patients.

Introduction

Chronic rectal toxicity remains one of the most important dose-limiting factors for the treatment of prostate cancer. Rectal toxicity has been related to the volume of the rectum and rectal wall radiated 1, 2, 3, 4, 5, 6, 7, 8, 9. Furthermore, limiting rectal dose on the basis of normal tissue constraints has been found to decrease this toxicity. As such, chronic rectal toxicity will be determined by the rectum dose–volume curve and not the dose prescribed to the target 3, 4.

A rectal balloon (RB) has the theoretical advantage of distending the rectal wall and moving it away from the high-dose area anteriorly 7, 10, 11, 12, 13. Thus it decreases the relative volume of rectum or rectal wall radiated to intermediate and high doses. For photon therapy, it also has the relative advantage of increasing rectal air volume, thereby decreasing the dose at the inner rectal wall (13).

Although an RB may likewise decrease the relative volume of the rectum or rectal wall radiated in proton therapy, it may provide only a small absolute advantage because of the low rectal doses being delivered. Furthermore, for proton therapy water is used in the RB to better control the proton dose distribution and decrease inhomogeneities due to the air–tissue interface. Thus proton therapy will not necessarily have the potential advantage of decreasing the inner rectal wall dose seen with photons. Water alone, however, may distend the rectum adequately during the course of proton therapy, obviating the need for an RB.

We analyzed 30 proton plans for 15 patients who underwent CT and MRI scans with RB or water alone. We analyzed the volumes of the rectum, rectal wall, and rectal wall at the level of the planning target volume (PTV) for this analysis.

Section snippets

Methods and Materials

Thirty plans on 15 consecutive patients treated between August 2006 and October 2006 on one of our three institutional review board–approved prostate proton protocols (UFPTI 0001, UFPTI 0002, and UFPTI 0003) were selected for the present analysis. All patients had American Joint Committee on Cancer Stage II (T1–T2N0M0) clinically confined disease to the prostate.

Results

Characteristics of the variables included for this analysis can be seen in Table 1. Rectum volumes were larger with the RB for all cases, resulting in a 35% relative difference. Absolute and relative differences were also seen for the rectal wall and modified rectal wall 7-cm volumes when using an RB. The rectal wall volume defined by a 3-mm-thick rim represents a volume–surface area approximation of the rectal contents excluding nonrectal tissue in the cavity. Thus, the rectal wall defines the

Discussion

Multiple randomized and prospective trials have shown an advantage for high-dose radiation 15, 16, 17, 18, 19, 20, 21. Chronic rectal toxicity, however, continues to be one of the dose-limitating factors in prostate cancer therapy 2, 3, 4, 5, 6, 8, 22, 23, 24 A clear dose–volume relationship has been demonstrated for rectal toxicity in radiotherapy for prostate cancer, which calls for new ways to decrease the rectal dose using proton therapy and rectal distention, either with an RB or with

Conclusions

We observed good compliance and low rectal doses regardless of whether water alone or an RB was used. An RB provides selected patients with a small but significant dosimetric advantage in proton prostate radiotherapy. However, most patients will derive no benefit, and some may actually be at risk for increased toxicity with an RB. Water alone was well tolerated and will benefit most patients. Careful selection has the potential to improve the therapeutic ratio of proton treatment for either an

References (29)

Cited by (25)

  • Preliminary Analysis of a Phase II Trial of Stereotactic Body Radiation Therapy for Prostate Cancer With High-Risk Features After Radical Prostatectomy

    2023, Advances in Radiation Oncology
    Citation Excerpt :

    One of the theoretical advantages of using SBRT in this scenario is based on the proposed α/β of 1.5 for prostate cancer, for which 30 Gy in 6 Gy fractions and 32 Gy in 6.4 Gy fractions (5 treatments) would be a dose equivalent in 2 Gy fractions of 64 and 72 Gy, respectively. Considering an estimated α/β of 3.5 for normal tissue, a dose equivalent in 2 Gy fractions of only 52 and 58 Gy would be delivered to the portions of the rectum or bladder receiving total prescription doses.15-17,27-34 Beyond radiobiologic advantages, a much shorter treatment schedule offers patients convenience beyond being more cost-effective compared with other RT modalities.35

  • The technological basis for adaptive ion beam therapy at MedAustron: Status and outlook

    2018, Zeitschrift fur Medizinische Physik
    Citation Excerpt :

    Prostate patients treated at MedAustron receive four very thin markers (GoldAnchor, Stockholm, Sweden) that are implanted under ultrasound guidance. Furthermore, the rectum is filled with 100 ml of saline solution [18]. In addition, patients have to follow a specific drinking protocol, i.e. the bladder is emptied half an hour before treatment and then the patients have to drink 500 ml of water to establish a comfortably filled bladder during treatment.

  • A significant decrease in rectal volume and diameter during prostate IMRT

    2011, Radiotherapy and Oncology
    Citation Excerpt :

    Prostate motion as well as its relationship with RV variability during the course of radiotherapy is not a new concern. Many institutions have implemented various rectal fixation strategies to improve reproducibility, including rectal balloon [38,41–45], ultrasound [32,46], radio-opaque markers [27,28,47], and on board imaging [26,39,48–53]. The feasibility of some of these modalities is limited by the fact that they can be invasive and some require additional costs.

  • Is there a role for endorectal balloons in prostate radiotherapy? A systematic review

    2010, Radiotherapy and Oncology
    Citation Excerpt :

    It was originally designed as an endorectal coil in magnetic resonance imaging (MRI) and the balloon has a concave shape for optimal conformation to the prostatic-rectal interface. In prostate RT 60, 80, and 100 cc of inflated air have been reported [24,30,31], resulting in balloon diameters of 4.0–4.5 cm. The second ERB (ERB2) is a 5-cm-long silkolatex balloon, fixed on a 30-cm-long two-way rectal tube, made of soft rubber with a silkolatex coating, used for barium enema procedures (Nordmann, Rüsch AG, Kernen, Germany).

View all citing articles on Scopus

Conflict of interest: none.

View full text