ADENOCARCINOMA STAGE 2b - 1289805

Hello! My dad was diagnosed with lung adenocarcinoma ( a 3 cm single nodule on the left lobe) on November. A week later he had a VATS lobectomy. The doctors were very optimistic saying it was stage 1a. The biopsy, however, showed it was a poorly differentiated adenocarcinoma which invades the visceral pleura and extends to parietal pleura- no lymph nodes involved (16 resected),resection margins free ( T3N0 M0 tumor, stage 2b?). The surgreon said he did a great job and he insisted that it was stage I, with no need for adjuvant chemotherapy. However, the oncologist said that my father had to do a three cycle cabo- alimta chemo and 20 radiations to try to prevent local recurrence. My father has already had the first chemo with no side effects. I would like your opinion about radiations. What are the chances of recurrence- local or distant failure? Let me say that my father is 70 years old ex smoker with no other health problems cardiologist said that his heart function is excellent, taking into consideration his age). I'm anxiously waiting for your answer. Thank you in advance