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Comparing CTVs for permanent prostate brachytherapy
1Department of Radiation Oncology, University of La Laguna Tenerife, Santa Cruz de Tenerife, Spain, caoton@gmail.com.
Summary
The risk of prostate cancer spreading outside the prostate gland (extraprostatic extension) is high, necessitating a 3 mm clinical target volume (CTV) margin. Planning for this expanded CTV in low dose rate brachytherapy is feasible and dosimetrically sound.
Area of Science:
- Oncology
- Radiation Oncology
- Medical Physics
Background:
- Current guidelines for clinical target volume (CTV) delineation in prostate cancer low dose rate (LDR) brachytherapy vary, with the American Brachytherapy Society (ABS) recommending CTV = prostate and the European Society for Radiotherapy and Oncology (ESTRO) advocating for CTV = prostate + 3 mm excluding the rectum.
- Significant debate exists among authors regarding the optimal CTV definition for LDR brachytherapy.
Purpose of the Study:
- To evaluate the appropriateness of existing CTV recommendations for prostate cancer LDR brachytherapy.
- To assess the feasibility and dosimetric impact of applying seed distributions to different CTV definitions, specifically an expanded CTV with a 3 mm margin.
Main Methods:
- A retrospective analysis of 98 patients treated with Iodine-125 (125I) seeds (145 Gy) with an initial CTV = prostate was performed.
- The risk of extraprostatic extension (EPE) was assessed for each patient. The adequacy of the original treatment plan for an expanded CTV (prostate + 3 mm) was evaluated, and new plans with seed distributions were generated for this expanded CTV.
- Dosimetric comparisons were conducted between the original and newly generated plans.
Main Results:
- The mean risk of EPE was found to be 28.46%, indicating a substantial likelihood of tumor extension beyond the prostate.
- Applying the original treatment plan to the expanded CTV (prostate + 3 mm) resulted in unsatisfactory dosimetry.
- New treatment plans with optimized seed distributions were successfully generated for all 98 patients, meeting all dosimetric specifications for the expanded CTV.
Conclusions:
- The high observed risk of EPE supports the necessity of incorporating a 3 mm margin around the prostate for the CTV in all cases.
- The ESTRO-recommended CTV (prostate + 3 mm excluding the rectum) is feasible for LDR brachytherapy and allows for planning that better accounts for the probable extent of prostate cancer.
- This approach optimizes treatment planning to encompass the most likely spread of the tumor, potentially improving treatment outcomes.
