Damage assessment in gastric cancer treatment with adjuvant radiochemotherapy: calculation of the NTCP's from the differential HDV of the organs at risk.

OBJECTIVE: To calculate the Normal Tissue Complication Probabilities (NTCP) for the liver, right kidney, left kidney and spinal cord, as well as the global Uncomplicated Tumour Control Probability (UTCP) in gastric cancer patients who underwent a treatment with radiotherapy after radical surgery in our environment. MATERIAL AND
METHOD: In April 2000, a postoperative chemotherapy (QT-RT) protocol started in the province of Malaga for Gastric Adenocarcinomas with postsurgical stage II or higher (pT3-4 and/or pN+). This clinical protocol served as a base for our NTCP and UTCP retrospective theorical study. A virtual simulation and a 3D planning were made in all cases. The differential HDV, selected for each patient were obtained for the 4 organs at risk (OR). Hystograms reduction was made by the Kutcher and Burman's Effective Volume method. NTCP calculations by Lyman's models. The following variables were calculated: maximal dose for each organ (Dmax), Effective Volume (Veff), TD50 (Veff/Vref); NTCP for each organ of the patient; global UTCP for each patient. Differences between the 2 treatment techniques were analysed (2-field versus 4-field technique). For the NTCP calculations the computer application Albireo 1.0(R) was used.
RESULTS: 29 patients to assess with an average age of 54 +/- 10 years (range: 38-71); 65.5% men/34.5% women. The technique used was the field technique AP-PA in the 51.7% (15) and with 4 fields in 48.3% (14) of the cases. The global damage is estimated in 16% with a range between 0 and 37%. This goes up to 25% with the 2-field technique, with a wide range between 2 and 48% and it remains reduced to 4%, within a range between 0 and 12% when 4 fields are used. There were significant differences concerning the estimated damage probability (NTCP) on liver, spinal cord and left kidney, depending on the use of two or four fields.
CONCLUSION: NTCP and the global UTCP values of the organs at risk allow to compare a technique net benefit from another in each particular case, although in our theoretical study the comparison was done among the patients. It is important to stress that the calculations of the TCP and NTCP have a limited quantitative signification but they are useful and beneficial in order to decide between treatment plans when they are supported by the clinical knowledge.