Abstract
External beam radiation therapy for prostate cancer can result in urinary, sexual, and rectal side effects, often impairing quality of life. A polyethylene glycol‐based product, SpaceOAR© hydrogel (SOH), implanted into the connective tissue between the prostate gland and rectum can significantly reduce the dose received by the rectum and hence risk of rectal toxicity. The optimal way to manage the hydrogel and rectal structures for plan optimization is therefore of interest. In 13 patients, computerized tomography (CT) scans were taken pre‐ and post‐SpaceOAR© implant. A prescription of 60 Gy in 20 fractions was planned on both scans. Six treatment plans were produced per anonymized dataset using either a structure of rectum plus the hydrogel, termed composite rectum wall (CRW), or rectal wall (RW) as an inverse optimization structure and intensity modulated radiotherapy (IMRT) or volumetric modulated arc therapy (VMAT) as a treatment technique. Dose‐volume histogram metrics were compared between plans to determine which optimization structure and treatment technique offered the maximum rectal dose sparing. RW structures offered a statistically significant decrease in rectal dose over CRW structures, whereas the treatment technique (IMRT vs VMAT) did not significantly affect the rectal dose. There was improvement seen in bladder and penile bulb dose when VMAT was used as a treatment technique. Overall, treatment plans using the RW optimization structure offered the lowest rectal dose while VMAT treatment technique offered the lowest bladder and penile bulb dose.
Highlights
A recent estimate by the Canadian Cancer Society predicts that about 1 in 2 Canadians will be diagnosed with cancer in their lifetime and 1 of 4 will die of the disease
Rectal dose sparing greater than 25% was achieved in most post- SpaceOAR c Hydrogel treatment plans generated in this planning study
The rectal wall optimization structure offered a statistically significant reduction in rectal dose compared to the composite rectum wall (CRW)
Summary
A recent estimate by the Canadian Cancer Society predicts that about 1 in 2 Canadians will be diagnosed with cancer in their lifetime and 1 of 4 will die of the disease. Potential toxicities of EBRT can include rectal, urinary and sexual dysfunction due to the proximity of the rectum, bladder and penile bulb/neurovascular bundles to the prostate.[19] The rectum is the dose-limiting organ in prostate cancer external beam irradiation due to its proximity to the prostate, with the anterior rectal wall often falling within the planning target volume.[17,20,54,70,71] In recent years a number of products have been developed to spare the rectum during radiotherapy One such innovation is SpaceOAR c hydrogel (SOH), a polyethylene glycol-based product, that is injected between the rectum and the prostate to displace the prostate away from the rectum. Characterizing the interactions will aid in describing radiation damage to tissue
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