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Dose measurement and dose calculation
Digital Poster
Physics
Dosimetric comparison: VMAT based CSI in Ring gantry Halcyon and Cantilever linear accelerator
Biplab Sarkar, India
PO-1626

Abstract

Dosimetric comparison: VMAT based CSI in Ring gantry Halcyon and Cantilever linear accelerator
Authors:

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

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Purpose or Objective

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).

Material and Methods

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. 

Results

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

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.