Abstract

Biplab Sarkar¹, Subhra Singhdha Biswal², Tanweer Shahid³, Mahasin Gazi¹, Jibak Bhattacharya³, Tanmay Ghosh⁴, Sandipan Roy Chowdhury ⁵, Arundhuti De³, Soumyadip Mitra⁵, Aditi Mishra⁶, Sourav Mandal⁷, Kirubha George ⁵, Prasanjit Soren⁸, Mukti Mukherjee⁵, Litan Naha Biswas³, Jawed Akhtar⁹, Prasenjit Chatterjee¹⁰, Gunturu Indira⁵, Pusarla Ch. Sekhar⁵, Asesh Samanta⁵, Rishav Raj⁵, Suchanda Goswami⁵, Ayushi Paul ⁵, Sinjini Sengupta⁵, Rajagopalan Bhaskar¹¹, Anirudh Pradhan¹², Arjunan Manikandan¹³, Karthik Appunu⁵

¹Apollo Hospitals , Radiation Oncology, KOLKATA, India; ²Apollo Hospitals, , Radiation Oncology, KOLKATA, India; ³Apollo Hospitals , Radiation Oncology, Kolkata, India; ⁴Apollo Hospitals, Radiation Oncology , KOLKATA, India; ⁵Apollo Hospitals, Radiation Oncology, Kolkata, India; ⁶Apollo Hospitals, radiation Oncology, Kolkata, India; ⁷Apollo Hospitals, Radiation Oncology, KOLKATA, India; ⁸Apollo Hospitals , radiation oncology, Kolkata, India; ⁹Apollo Hospitals, Radiation Onoclogy, Kolkata, India; ¹⁰Apollo JHospitals, radiation Oncology, Kolkata, India; ¹¹Apollo Hospitals, Radiation oncology, Kolkata, India; ¹²GLA University, Mathematics, Mathura, India; ¹³Apollo proton Cancer Centre, medical Physics, Chennai, India

This study aim to compare the dosimetric characteristics of the Craniospinal irradiation (CSI) between ring gantry Halcyon [E] (HA) and C-Arm Novalis Tx (NT) linear accelerators (LA).

CT data set of 10 low/intermediate-risk Medulloblastoma / PNET patients (age 13.1 ±6.5 years)  who previously received the VMAT based CSI treatment (23.4 Gy in 13 fractions) in  Novalis was planned in the newly commissioned Halcyon ring gantry linear accelerator in Eclipse v15.6 TPS. Multiple isocenters (2 or 3) were placed  by equally dividing the (brain+spine) PTV length, with 1st Iso at 1st, 2nd Iso at -3rd and 3rd Iso at 5th period. For Novalis, and Halcyon 2 and 3 arcs were used per isocentre. For Brain, PTV 360֯ was used while at spine iso the arc span was 260֯-180֯-100֯ for both the plans. For a fair comparison, all plans were normalized to 97% dose to cover 97% of the target volume.  With equal PTV coverage, OAR doses, MU, Volume receiving 20% and 50% doses were compared. Statistical comparison is done by Student t-test with significance level p<0.05. 

Average MU for HA and NT plans were  1795±148 and 1524 ±213 and the difference was statistically significant (P=0.048). With equal coverage of PTV, 29 OAR’s were compared (HA-NT)  for maximum and (or) mean dose as. Central organs viz. Pharynx, Larynx, Heart, Bladder, Bowel, Rectum shows a mean dose difference between 0%-4.1%. lateralised organs viz. bilateral eye, lens (max dose), parotid, submandibular gland, femur head, stomach, liver, shows a dose variation between 1.1 to 7.9%.  Esophagus, Rt and Lt kidney max dose difference (HA-NT) was -13.9%± 6.3%,  -12.4%±5.3%, and -8.5%±5.3%; first two were statistically significant p<0.04. The difference of mean volume receiving 50% and 20% dose for HA-NT were - 650±157 cc and -361.3±215;  and both were statistically significant p=0.03.  

Conclusion: Ring gantry (HA) based CSI plans are dosimetrically comparable with NT standard LA  plans in terms of PTV dose coverage; for most of the OAR’s

the doses are comparable and slightly favored the HA plans, esophagus and Lt Kidney shows a statistically significant difference. Although HA plans require a

larger MU; it reduces the lower isodoses like 50% and 20%. Figure-1 shows the visual difference in 50% isodose lines. This is because of the difference in MLC

speed between both LA, HA = 6 cm/sec and NT= 3 cm/sec. Higher MLC Speed produces a larger modulation demands larger MU but reduces the dose spade.  

 Low-risk Medulloblastoma/PNET patients have long survival. Halcyon and Novalis plans were comparable in terms of PTV/OAR dose parameters. Halcyon

produces a significantly lower low dose spillage – which may be helpful for patients in terms of quality of life and induction of radiation-induced second cancer.

Figure-1: Volume receiving 50% of the prescription dose - A visual change is observable between Halcyon and Novalis dose distribution, with Novalis showing

high low dose spillage than Halcyon linear accelerator.