Plan Dose Evaluation of Three Dimensional Conformal Radiotherapy Planning (3D-CRT) of Nasopharyngeal Carcinoma (NPC): Experience of a Tertiary Care University Hospital in Pakistan

Background: Radiation therapy is the mainstay of treatment for nasopharyngeal carcinoma. Importanceof tumor coverage and challenges posed by its unique and critical location are well evident. Therefore weaimed to evaluate our radiation treatment plan through dose volume histograms (DVHs) to find planningtarget volume (PTV) dose coverage and factors affecting it. Materials and
Methods: This retrospective studycovered 45 histologically proven nasopharyngeal cancer patients who were treated with definitive 3D-CRT andchemotherapy between Feb 2006 to March 2013 at the Department of Oncology, Section Radiation Oncology ,AgaKhan University Hospital, Karachi, Pakistan. DVH was evaluated to find numbers of shrinking field (phases),PTV volume in different phases and its coverage by the 95% isodose lines, along with influencing factors.
Results: There were 36 males (80%) and 9 females (20%) in the age range of 12-84 years. Stage IVA (46.7%)was the most common stage followed by stage III (31.1). Eighty six point six-percent received induction, 95.5%received concurrent and 22.2% received adjuvant chemotherapy. The prescribed median radiation dose was70Gy to primary, 60Gy to clinically positive neck nodes and 50Gy to clinically negative neck regions. Mean doseto spinal cord was 44.2Gy and to optic chiasma was 52Gy. Thirty seven point eight-percent patients completedtheir treatment in three phases while 62.2% required four to five phases. Mean volume for PTV3 was 247.8 cm3(50-644.3), PTV4 173.8 cm3 (26.5-345.1) and PTV5 119.6 cm3 (18.9-246.1) and PTV volume coverage by 95%isodose lines were 74.4%, 85.7% and 100% respectively. Advanced T stage, intracranial extension and tumorvolume >200 cm3 were found to be important factors associated with decreased PTV coverage by 95% isodose line.
Conclusions: 3D CRT results in adequate PTV dose coverage by 95% isodose line. However advanced T stage,intracranial extension and large target volume require more advanced techniques like IMRT for appropriatePTV coverage.