A comparative study on the risk of second primary cancers in out-of-field organs associated with radiotherapy of localized prostate carcinoma using Monte Carlo-based accelerator and patient models.
OBJECTIVE
A physician's decision regarding an ideal treatment approach (i.e., radiation, surgery, and/or hormonal) for prostate carcinoma is traditionally based on a variety of metrics. One of these metrics is the risk of radiation-induced second primary cancer following radiation treatments. The aim of this study was to investigate the significance of second cancer risks in out-of-field organs from 3D-CRT and IMRT treatments of prostate carcinoma compared to baseline cancer risks in these organs.


METHODS
Monte Carlo simulations were performed using a detailed medical linear accelerator model and an anatomically realistic adult male whole-body phantom. A four-field box treatment, a four-field box treatment plus a six-field boost, and a seven-field IMRT treatment were simulated. Using BEIR VII risk models, the age-dependent lifetime attributable risks to various organs outside the primary beam with a known predilection for cancer were calculated using organ-averaged equivalent doses.


RESULTS
The four-field box treatment had the lowest treatment-related second primary cancer risks to organs outside the primary beam ranging from 7.3 x 10(-9) to 2.54 x 10(-5)%/MU depending on the patients age at exposure and second primary cancer site. The risks to organs outside the primary beam from the four-field box and six-field boost and the seven-field IMRT were nearly equivalent. The risks from the four-field box and six-field boost ranged from 1.39 x 10(-8) to 1.80 x 10(-5)%/MU, and from the seven-field IMRT ranged from 1.60 x 10(-9) to 1.35 x 10(-5)%/MU. The second cancer risks in all organs considered from each plan were below the baseline risks.


CONCLUSIONS
The treatment-related second cancer risks in organs outside the primary beam due to 3D-CRT and IMRT is small. New risk assessment techniques need to be investigated to address the concern of radiation-induced second cancers from prostate treatments, particularly focusing on risks to organs inside the primary beam.
Bednarz
Bryan
B
Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02108, USA. bbednarz@partners.org
Athar
Basit
B
Xu
X George
XG
D000328:Adult; D006801:Humans; D008297:Male; D008954:Models, Biological; D009010:Monte Carlo Method; D009381:Neoplasms, Radiation-Induced / Q000209:etiology*; D016609:Neoplasms, Second Primary / Q000209:etiology*; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011829:Radiation Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects; D012306:Risk