Dependence of the safe rectum dose on the CTV-PTV margin size and treatment technique - Abstract

BACKGROUND: Late rectal injury is a common side effect of external beam radiotherapy for prostate cancer.

AIM: The aim of this study was to evaluate what total dose may be safely delivered for prostate patients for 3DCRT and IMRT techniques and the CTV-PTV margin.

MATERIALS AND METHODS: 3DCRT and IMRT plans were prepared for 12 patients. For each patient PTV was defined with CTV-PTV margins of 0.4, 0.6, …, 1.0 cm, and total doses of 70, 72, …, 80 Gy, with 2 Gy dose fraction. NTCP values for the rectum were calculated using the Lyman model. Both techniques were compared in terms of population mean DVH.

RESULTS: Significantly smaller NTCPs for IMRT were obtained. For both techniques diminishing the margin CTV-PTV of 2 mm leads to decreasing the NTCP of about 0.03. For total dose of 80 Gy the NTCP was smaller than 10% for the 4 mm margin only. The QUANTEC dose volume constraints were more frequently fulfilled for the IMRT technique than for the 3DCRT technique.

CONCLUSIONS: The IMRT technique is safer for prostate patients than the 3DCRT. If very high total doses are applied the CTV-PTV margin of 0.4 cm and the IMRT technique should be used. If the CTV-PTV margin of 0.6 cm is applied, the NTCP is smaller than 10% for the 3DCRT and IMRT techniques for the total doses smaller than 74 Gy and 78 Gy, respectively.

Written by:
Kukołowicz P, Kukołowicz H, Tyburska I.   Are you the author?
The Maria Skłodowska - Curie Memorial Cancer Center and Institute of Oncology, Medical Physics Department, Warsaw, Poland.

Reference: Rep Pract Oncol Radiother. 2015 May-Jun;20(3):198-203.
doi: 10.1016/j.rpor.2014.12.004

PubMed Abstract
PMID: 25949223 Prostate Cancer Section