Urinary Toxicity After Radiotherapy For Prostate Cancer: Dose Maps To Identify Dose-effect Relationships

Main Category: Radiology / Nuclear Medicine
Also Included In: Prostate / Prostate Cancer;  Urology / Nephrology;  Cancer / Oncology
Article Date: 22 Sep 2008 - 4:00 PDT

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After external radiotherapy for prostate cancer, patients can suffer from long-term urinary problems, including incontinence and obstruction. Many studies have investigated the relationship between urinary problems and the radiation dose the bladder was exposed to, as estimated during the planning of the treatment. Clear dose-effect relationships are, however, seldom reported. This could be due to the variable filling and position of the bladder during treatment, making the predicted position of the bladder more difficult and inconsistent. Furthermore, usually only the dose to the total bladder is analysed and local structures are not evaluated separately.

We studied whether dose maps of the bladder area adjacent to the prostate, could identify local dose-effect relationships for urinary problems. In a dose map, the dose in a defined anatomical region is mapped for each patient. By calculating the mean dose map of patients without a complaint, and subtracting this map from the mean dose map of patients with a complaint, we obtained dose difference maps. These maps visualised the local areas where patients with a complaint, received more dose than patients without that complaint.

From these dose difference maps we learned that patients suffering from obstruction received on average a much higher dose to the region where the ureters enter the bladder. Patients who reported cramps and/or pain requiring medication), received on average more dose to the bladder area close to the pubic bone.

This study provides very useful information on the development of urinary problems after radiothe¬rapy, not previously reported. In the near future, we will extend our analyses by evaluating other side effects of radiotherapy.

Heemsbergen Wilma et al. Netherlands Cancer Institute / Antoni van Leeuwenhoek Hospital, Amsterdam, Netherlands

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