重粒子放射治療用於淋巴轉移陽性攝護腺癌的進展:

骨盆腔照射策略及劑量分佈

藍天立、胡育文、林慧嘉、林芳薏、謝東昇、劉裕明

台北榮民總醫院 重粒子及放射腫瘤部 放射腫瘤科

Carbon Ion Radiotherapy for Lymph Node Positive Prostate Cancer: Advancements in Pelvic Irradiation Strategies and Dose Distribution Performance

Tien-Li Lan, Yu-Wen Hu, Hui-Chia Lin, Fang-Yi Lin, Tung-Sheng Hsieh, Yu-Ming Liu

Department of Heavy Particles and Radiation Oncology, Taipei Veterans General Hospital, Taipei, Taiwan

Purpose:

In Japan, carbon ion radiotherapy (CIRT) has been covered by the National Health Insurance since April 2018, leading to its widespread adoption in the treatment of prostate cancer. Annually, over 2000 prostate cancer patients undergo treatment with CIRT in Japan. The efficacy of CIRT in managing prostate cancer has been well-documented, demonstrating a lower incidence of late toxicities such as rectal bleeding and hematuria compared to conventional treatments.

However, a significant proportion of patients are deemed unsuitable candidates for CIRT, primarily due to the presence of positive lymphadenopathies (LAPs) in the pelvic region or a high risk of lymph node metastasis necessitating whole pelvic irradiation. Consequently, the presence of these limitations has prompted the exploration of alternative strategies to facilitate pelvic irradiation in such cases.

Materials and Methods:

Since May 2023, the Taipei Veterans General Hospital Department of Heavy Particles and Radiation Oncology has administered carbon ion radiotherapy to more than 160 patients, with over one-third of cases targeting primary prostate cancer. In conventional radiotherapy, the upper border of irradiation typically extends to L5/S1 for N0 patients at high risk, and to L4/5 for patients presenting with pelvic lymphadenopathy.

Two primary strategies for pelvic irradiation have been employed. The first involves utilizing conventional photon therapy as a foundational treatment to encompass the entire pelvic region, supplemented by carbon ion therapy as a targeted boost to the entire prostate and gross lymphadenopathies. Presently, no standardized models exist to reliably convert clinical doses between particle beams and photons, potentially leading to uncertainties and dose calculation errors.

The second strategy involves exclusive employment of carbon ion therapy for pelvic irradiation. Building upon previous experiences in cervical cancer carbon ion radiotherapy, which have established the safety and efficacy of this approach, carbon ion therapy serves as the sole modality for the entire irradiation schedule. Despite a maximum irradiation field size of 20 cm, a "patch field technique" is employed to adequately cover the entire target volume.

Utilizing the VQA treatment planning system, we generated a carbon ion treatment plan for a patient diagnosed with prostate cancer accompanied by pelvic lymphadenopathies spanning bilateral iliac and obturator regions. The photon treatment plan was developed using the Eclipse system. To assess the conformity of each treatment plan, we employed the modified conformity index, calculated as the area treated by the 95% isodose level divided by the area of the planning target volume.

In this ongoing study, our objective is to validate the suitability of carbon ion treatment for prostate cancer patients requiring pelvic irradiation. The treatment regimen consists of 12 fractions administered via simultaneous integrated boost technique, delivering 54 Gy to the prostate and bilateral seminal vesicles, 51.6 Gy to pelvic lymphadenopathies, and 36 Gy to the entire pelvic region. The determination of the upper border of pelvic irradiation hinges upon the presence or absence of gross pelvic lymphadenopathy.

Results:

Focusing on the primary target encompassing the whole prostate and bilateral seminal vesicles, the conformity index for carbon ion treatment was 1.01, while for photon radiotherapy, it measured 1.53. Regarding the low dose administered to the whole pelvic area, the conformity index for carbon ion treatment was 0.96, whereas for photon radiotherapy, it was 1.63.

Furthermore, to evaluate both coverage and selectivity, we employed the modified Paddick conformity index using the 95% dose coverage. For the high dose region encompassing the whole prostate and bilateral seminal vesicles, the modified Paddick index was 0.76 for carbon ion treatment and 0.64 for photon irradiation. Similarly, for the low dose irradiation of the whole pelvic region, the index was 0.78 for carbon ion therapy and 0.60 for photon irradiation.

Based on these results, we can confidently assert that carbon ion therapy is a safe and effective modality for pelvic irradiation, demonstrating superior dose distribution performance compared to conventional photon radiotherapy.

Conclusions:

Carbon ion radiotherapy emerges as a viable option for prostate cancer patients necessitating whole pelvic irradiation. In our study, we have substantiated both the safety and the superiority of dose coverage afforded by carbon ion therapy when contrasted with conventional photon irradiation.